Evaluate Polyethylene Polymer Properties Mechanical, Melt Flow, Crystallinity, Density, Molecular Weight

PKG 825 POLYMERIC PACKAGING MATERIALS LABORATORY EXERCISE V EVALUATION OF POLYETHYLENE UNKNOWNS Objective • The purpose of this lab is to summarize the results obtained from lab 1 to lab 4 for the two polyethylene resins and to analyze them in terms of the influence of structure, crystallinity, etc. on polymer properties. • In this report you are expected to integrate the four previous reports to draw conclusions about your polyethylene samples and discuss why you obtained the test results you did. • You should include such factors as the influences of crystallinity and average molecular weight, etc., to compare and contrast your results. Draw as many conclusions as you can about each sample. Required Reading 1. Laboratory reports 1 to 4 in PKG 825. 2. Review of lectures I to VII. Procedure • You should summarize, discuss, evaluate, and integrate your four previous reports. Do NOT include a discussion of test methodology. Be sure to show your reasoning. Include a discussion of any anomalous findings and possible explanations. Evaluate your degree of confidence in sample identification. Results and Discussion Your report should include, but not only limited to, the following results and discussion: 1. Summary of test data from lab 1 to lab 4* Lab 1: Mechanical properties (impact strength, tensile strength, elongation, and modulus of elasticity) Lab 2: Melt flow index (Manual and automatic) Lab 3: Density, melting temperature, and percent crystallinity (density gradient and DSC method) Lab 4: Average molecular weight (Mn, Mw, and Mz) and DI – Provided values * The testing method should be stated in the data report. A detailed discussion of the methodology is not required. PKG 825, FS22 – Polymeric Packaging Materials 2 2. Summary of properties Briefly describe the definition, importance, and application of each property measured in lab 1 to lab 4. 3. Reference values List the typical values of these properties for HDPE, LDPE, and LLDPE. You can find those values either from a reference book or website. Be sure to list your reference at the end of the report. • Impact strength • Tensile strength • Elongation • Modulus of elasticity • Melt flow index • Density • Melting temperature • Percent crystallinity • Average molecular weight 4. Identification of two unknown PE resins Based on your results obtained from lab 1 to lab 4, and the comparison to the reference values you get from step 3, identify your two unknown PE resins. Discuss your reasoning, especially when there are discrepancies in your results. 5. Discuss properties Based on the results obtained from lab 1 to lab 4, discuss the properties of the two PE resins: • Mechanical properties • Processability • Heat sealability • M.W. and M.W.D. PKG 825, FS22 – Polymeric Packaging Materials 3 - Conclusions - References - Supporting information – any additional information relevant to the lab Format of the lab report - Papers should be written using a word processor. - One-inch margins all around  Title Font: Times New Roman Bold 12, capitalize the first letter of each word (e.g., Evaluation of the Environmental Footprint of Mayonnaise Packaging Delivery Systems). Center in the middle of the page. After paragraph spacing of 6 pt.  For most projects, three levels of subheadings are adequate; occasionally a fourth level could be necessary. Indicate the level of subheads within the text by inserting the following codes just before the heading: 1. First level 1.1. Second level 1.1.1. Third level 1.1.1.1. Fourth level - First Subtitle Font: Times New Roman Italic 12, after paragraph spacing of 6 pt. - Second Subtitle Font: Times New Roman Underline 12, after paragraph spacing of 6 pts. - Text Font: Times New Roman 12, 1.5 line spacing. Indented to the left. After paragraph spacing of 6 pts. - Header: Insert the title of the laboratory in Times New Roman Bold 12 (gray color) starting from the second page. - Page numbers: bottom right of the page. Starting from the second page. - Abbreviations • Abbreviations/acronyms must be defined when they appear for the first time in the main text. Please compile a list of abbreviations at the beginning.  References Literature references must be numbered consecutively in the text and typed in PKG 825, FS22 – Polymeric Packaging Materials 4 square brackets as superscripts after any punctuation, e.g., ... as shown by Huglin [10]. Journals: [1] H. R. Kricheldorf, A. Stricker, Macromol. Chem. Phys. 1999, 200, 1726- 1733. Books: [2] G. Wegner, K. Müllen, “Electronic Materials: The Oligomer Approach”, 1st edition, Wiley- VCH, Weinheim 1998, 189pp. Compilations: [3] R. E. Bareiss, “Polymolecularity Correction Factors”, in Polymer Handbook, 3rd edition, [4]J. Brandrup, E. H. Immergut, Eds., J. Wiley & Sons, New York 1989, p. VII/149 ff. Patents: [5] Ger. 838217 (1952), Farbenfabriken Bayer AG, invs.: W. Lehmann, H. Rinke Internet Access: [46] K. Arai, S. Ohya, ‘‘Biodegradable Lactide and PolyesterCopolymers for use in Packaging and Their Film Properties’’, 2001, Dainippon Ink and Chemicals, Inc. Available at:http://www.dic.co.jp/eng/rd/tech/rev02/rep0210.html. Access date: 8/25/2020.  Footnotes must be given on the respective page and cited in the text as a b c, etc. Please note they must not be part of the reference section. Figures • The term figure includes line drawings (sketches, graphs, and flowcharts) and halftones (photographs, radiographs, and x-rays). • Number figures consecutively (Figure 1, Figure 2, Figure 3, etc.). Each figure should be cited within the text, e.g. (Figure 2). • Schemes could be used when they are needed. • The title and caption for figures should be below the figure. Tables • Tables should be enumerated in Arabic numbers. The whole format of the table should be single space, and the font should be Times New Roman. After the paragraph space should be zero. • The title and caption for tables should be above the table http://www.dic.co.jp/eng/rd/tech/rev02/rep0210.html PKG 825 POLYMERIC PACKAGING MATERIALS LABORATORY EXERCISE V EVALUATION OF POLYETHYLENE UNKNOWNS Objective Procedure Results and Discussion 1. Summary of test data from lab 1 to lab 4* 2. Summary of properties 3. Reference values 4. Identification of two unknown PE resins 5. Discuss properties Figures Determination of Molecular Weight and Molecular Weight Distribution of Polymers by Gel Permeation Chromatography PKG 825 PACKAGING PLASTICS Laboratory 4 Determination of Molecular Weight and Molecular Weight Distribution Polymers by Gel Permeation Chromatography Submitted by: Krassimir D Vladimirov Contact information: Email: vladimir@msu.edu Date:10-31-2022 Executive Summary Polymers consist of monomers chemically joined into long chains to form repeat units in the polymer chain. Knowing the length of the polymer chains is necessary to comprehend the physical characteristics of a polymer, such as mechanical strength, solubility, and brittleness. The molecular weight is a frequent unit of measurement for chain length. Plastic polymers are polydisperse. They differ in that they have polymer chains of different lengths. There is no unique molecular weight. The molecular weights and chain lengths that make up the polymer are distributed. An average molecular weight derived from the molecular weights of all the chains in the sample must be used to characterize the molecular weight of a polymer. When we talk about molecular weight and molecular weight distribution of a polymer, we also look at the number average molecular weight, Mn, weight average molecular weight, Mw, and the average molecular weight, Mz. These three parameters play a very important role when we look at molecular weight distribution and polymer dispersity. The polymer dispersity is the ratio between the weighted average molecular weight and the number average molecular weight and it is a very important factor that can affect the plastic polymer’s mechanical properties and what processes to choose for this particular polymer. When plastic polymers have a molecular weight of over 1000 Daltons, you can notice that their properties do not differ much. This lab exercise explains the frequently employed tests. This lab explains how to use molecular weight averages that can be found using size exclusion chromatography (SEC) and gel permeation chromatography,(GPC) respectively. The manner and shape of molecular weight distributions can significantly influence fundamental polymer properties that are critical for various applications. In this lab, we tested two samples of different polyethylene resins for their molecular weight, molecular distribution, and dispersity index and analyze how these factors affect the rheological and mechanical properties of the two polymers. We plotted the results from the GPCand compared the molecular weight distribution whether its narrow or broad molecular weight distribution and how they affect the polymer properties. Both molecular weight distribution (MWD) shape and dispersity can significantly impact the polymer properties including their overall performance, processability, and rheological behavior. Low dispersity polymers are preferred for their easy processability, but we can see that higher dispersity polymers with dispersity between 1.2 -1.50 and high dispersity polymers, dispersity bigger than 1.50 can be equally desirable and show very good mechanical properties and characteristics. In this lab, we were able to observe the two different polyethylene resin samples, compare the results from the GPC with the results from the other labs that we conducted, and discussed how the results translate into the different polymer properties, mechanical, rheological, optical and melt flow index. Keywords and Acronyms Gel Permeation Chromatography(GPC), Molecular Weight, Molecular Weight Distribution, Dispersity Index, Calibration Curve, Number Average Molecular Weight, Weight Average Molecular Weight, Z-Average Molecular Weight Introduction The standard testing procedure ASTM D6474-20 is a standard test method for determining the molecular weight distribution of polyolefins and molecular weight averages by high-temperature gel permeation chromatography (GPC). Polyethylene and various polyolefins and polypropylenes are tested using this method. This standard uses a polystyrene sample for calibration and is applicable to polyethylene samples. The polyethylene sample is dissolved in a solvent and injected into a chromatographic column packed with a substrate, which separates the molecules based on their size and solution in this test method. The separated molecules are detected and recorded as they elute from a column according to size using a sensitive detector and concentration. Retention times are converted to molecular weights via calibration. The calibration curve and detector response are used to calculate molecular weight averages in molecular weight distribution. In this lab, we determine the molecular weights and molecular weights distribution of two different polyethylene samples, sample A and sample B. A polymer is made up of different sizes of large molecules. Because each of these molecules has a different molecular weight, we calculate the average molecular weight, which is the average of all the different molecules present in the polymer. There are several methods for calculating this average. There is a number average molecular weight that is based on the number of molecules in the polymer and is generally sensitive to the lower molecular mass of molecules in the polymer. The molecular weight average is more sensitive to higher molecular mass and is based on the weight of the molecules in the sample. The Z average molecular weight, on the other hand, is sensitive to even higher molecular masses and is indicative of properties like melt flow and elasticity of the polymer. Then there's the viscosity average molecular weight, which is typically determined through a series of experiments. However, we can use some equations to calculate the viscosity average molecular weight and each of these different molecular weights. They are indicative of properties such as melt, boiling point, freezing point, and osmotic pressure, which are more related to when a polymer is in the form of a salute and are more related to when a polymer is in the form of salute. In cases where all of the molecules on the polymer are the same size or weight, Mw and Mn, which are the weight average and number average molecular weights, will be the same. However, in general, that is not the case. The weight average molecular weight is always greater than the number average molecular weight, which is why the dispersity index is always positive, and the dispersity index is a good indicator of the molecular weight distribution. A lower dispersity index indicates that the ratio is closer to one. A lower dispersity index indicates that the chains are more similar in size, resulting in a narrow molecular weight distribution, whereas a higher dispersity index would indicate a broader molecular weight distribution. And the greater the dispersity index, the wider the molecular weight distribution. Molecular weight distribution provides a lot of information about many other properties, such as mechanical properties. The molecular weight of the polymer also affects the sealing temperature range. The molecular weights and the dispersion index, when combined, are indicative of a variety of properties, including the glass transition temperature, melting temperature, viscosity and mechanical properties of the polymer, coefficient of friction, and a variety of other properties that we have already discussed in previous labs. They are used as a quality control tool primarily for two of the properties, such as the dispersity index. They indicate whether cracking on the surface is likely to occur and also a good indicator of the durability of the polymer. The chemical structure, molecular weight, and molecular weight distribution of a polymer are very important and fundamental properties. All thermo-physical and mechanical properties, such as cohesive forces, transition temperatures, viscosity, surface tension, solubility, miscibility, and tensile strength, are determined directly by these two properties. They also control the morphology (degree of crystallinity and packing density), molecular mobility, and various relaxation phenomena, i.e. the visco-elastic response behavior of the polymer, in a more indirect way. The majority of these properties increase with increasing molecular weight and reach a plateau at a high molecular weight. Objectives The goal of this lab is to familiarize students with Gel Permeation Chromatography (GPC). To become familiar with the test procedures for determining the molecular weight distribution of packaging materials in order to calculate the number average molecular weight, the weight average molecular weight, the Z average molecular weight, and the dispersity index. The students would be able to calculate the number average (Mn) molecular weight, weight average molecular weight (Mw), Z average molecular weight(Mz), and Dispersity index (Đ) of the polymer samples. They will comprehend the procedures used to calculate the molecular weight and molecular weight distribution and would understand the working mechanism and graphical plots associated with the GPC, as well as the difference in molecular weight and dispersity and how they are part of the polymer revision processes. Materials and Methods GPC (Gel Permeation Chromatography) Figure 1 Schematic diagram of chromatographic techniques SEC, or size exclusion chromatography, is a type of chromatography in which separation occurs by size. Solute molecules of various sizes and shapes move through a solid phase of Particles with controlled porosity Smaller molecules can get into more pores than larger molecules. As a result, the movement of molecules is slowed. As a result, larger molecules travel faster. and come out of the column first, causing GPC to generate a separation based on molecular weight and size. GPC is made up of the following parts: a. Mobile phase The solvent (mobile phase) should be chosen to best dissolve the test specimen, be compatible with the column, and permit detection by the best means. However, it should not interact either with the sample or the column packing. Some examples are: - Trichlorobenzene for polyethylene (PE) - Tetrahydrofuran (THF) for polystyrene (PS) b. Column exclusion range The column set must adequately cover the sample molecular weight range. In other words, the packing material in the column must contain a broad range of pore sizes that accommodates the test specimen molecular weight range, in which case, a normal distribution of chromatogram will be obtained. Commonly used column packing material (stationary phase) include: [1] - Hydrophilic dextran (Sephadex) beads for water-soluble polymers - Lipophilic polystyrene beads for organic-soluble polymers - Porous glass beads with pore diameters of 10-250 nm for polymers in the molecular weight range of 103 to 107 Daltons - Swollen, cross-linked polymer beads mostly PS c. Detectors [1,2] - Refractometer (refractive index (RI) detector): detects the difference in refractive index (RI) between the separating column (sample + solvent) and the reference column (solvent only) - IR (Infrared) detector: IR absorbance as a measure of concentration due to the functional groups or their ratio in a polymer - Variable wavelength UV detector Using GPC to determine average Mw and MWD Using GPC to determine average Mw and MWD consists of two stages: A. Construct a calibration curve using mono-disperse polystyrene standards (Đ <1.1) with different B. Analyze the sample and calculate the average Mw and Đ molecular weights Materials and Experimental Procedure Materials - Polystyrene standards - 2 mL glass vial, cap with PTFE septum, PTFE filter membrane 47 mm, 0.45 micron - Equipment: Water Gel Permeation Chromatography (GPC) Experimental procedure 1. Polymer was weighed at about 20 mg and transferred into a 10 mL volumetric flask. 2. A selected solvent (e.g., THF) was used to dissolve the polymer. The sample should not be shaken vigorously because it will break down the molecules. 3. The solvent containing the dissolved sample was then filtered through a PTFE filter membrane and the filtrate was then transferred into a 2 ml glass vial. 4. This vial was closed with a cap with a PTFE septum. 5. The vial was placed into a 96-position circular tray and this tray was placed onto a rotating turntable. 6. After the tray was positioned in the injector, the compartment door was closed. 7. The information (i.e., the position of the sample in the tray) and set procedure were then inserted and selected using the Water Breeze software. 8. The sample was automatically injected into the chromatographic column. Sample detection The sample was detected by a refractive index (RI) detector. The column used was HR Styragel. The specifications of the column are as follows: Column calibration This process is important to determine the relationship between retention time and molecular weight. Polystyrene standards are commonly used for calibration purposes and the molecular weights are calculated relative to polystyrene. The concentration of the standards depends on their molecular weight as recommended in Table 2. To calibrate the column, solutions of standard polystyrene of 10 different molecular weights in trichlorobenzene were made up and run through the GPC. The collected data can be entered into the data module and the data module will calculate a calibration curve by either a linear or third-order polynomial relation with the least square fit. A minimum of three points is necessary for the linear fit and five or more are necessary for the third-order fit (preferably at least 10 for a third-order curve). Data and Calculations See the attached Excel spreadsheet showing all the DATA and calculations, graphs with the plots for MW and MWD, Mn, Mz, and Mz. Discussions During our lab, we tested and recorded the test results of two different PE resins, Sample and Sample B using Gel Permeation Chromatography (GPC) and Size Exclusion Chromatography (SEC). We plotted and compared the results for the two polyethylene samples and compared their molecular weight, M, molecular weight distribution, MWD, and dispersity index (Đ). We saw from the results from the lab that Sample A has a wide molecular distribution and higher molecular weight and dispersity index =2.6 and polyethylene sample B has a narrower molecular weight distribution and dispersity index =1.9. We calculated the dispersity index based on the values of the weight average molecular weight and the number average molecular weight. The polymer sample A has a higher molecular weight and wide MWD which permits easier processing, and narrow MWD enhances the performance of the plastics polymer. The larger the dispersity index the larger the molecular weight distribution, Polymer A =2.6 > 1.9 Polymer B. The two samples are from Polyethylene resins polyethylene is made by chain polymerization and the chain polymerization usually yields a dispersity index from 1.5 to 2.0. The average molecular weight and the molecular weight distribution both have an impact on polymer flow as well as mechanical and thermal properties. These results result from the interactions between the polymer's chain strands. It's crucial to consider the molecular weight distribution while choosing the heat seal temperatures and sealing ranges. In comparison to a polymer with a wider distribution, one with a tighter molecular weight distribution melts across a smaller temperature range. To achieve excellent seals over a wider range of temperatures, a broad molecular weight distribution is therefore generally advantageous in heat sealing. Polyolefin polymers line polyethylene are usually selected to make plastic films because they provide excellent transparency, processability, and a strong seal between the films and other materials. Polyethylenes have very good and acceptable heat-sealing properties. Polymers usually have broad molecular weight distribution. When Molecular weight increases, higher adhesion, and stronger seals are observed. The high molecular chains polymer has a more effective sealing interface as compared to the low-weight chains, between the high and low molecular distribution of the same polymer samples, the sample with wider MWD, Sample A, will have a lower seal initiation temperature. The mechanical and physical bulk properties of polymers are significantly influenced by molecular weight dispersity and branching. In general, mechanical qualities, like yield at break and impact strength, are improved by a higher molecular weight. High molecular weight increases how far the material can stretch before rupturing. High molecular weight increases the impact resistance of the material and increases the chemical resistance of the material. High molecular weight also raises the temperature at which glass melts, though. Additionally, melt viscosity complicates the processing and manufacturing of polymeric materials. High molecular weight increases the viscosity of the polymer, making it harder to process, the longer the polymer chains, the harder it is to make them flow because they are more tangled. Low molecular weight polymers have lower mechanical properties because of a lack of chain entanglement and higher molecular mobility. This makes it easier for the polymer to respond to stresses and has a lower modulus of elasticity, but a higher melt flow rate, which is very good for processability. The opposite is true in the case of polymer dispersity. The yield strength is increased by the molecular weight dispersion but the tensile and impact strengths are decreased. A smaller distribution with fewer dispersion results in higher mechanical qualities. The lower molecular weight component of the distribution reduces brittleness and lowers melt viscosity, improving processability, but the high molecular weight region creates processing challenges due to its significant contribution to melting viscosity. Polymer with high molecular weight has a lower Melt Flow Index indicating lower viscosity of the polymer melt. These types of polymers are more suitable for extrusion and blow molding. Polymers with lower molecular weight show higher MFI and are suitable for injection molding. Besides the mechanical properties, the molecular weight and MWD affect the transparency, gloss, and haze of the plastic film. Broad molecular weight distribution increases haze and reduces film gloss. A broader molecular weight distribution results in increased impact strength, and on the other hand, the tear strength is reduced because of lower molecular weight fractions and the plastic material tends to decrease resistance to tear. Conclusions In conclusion, we successfully tested two samples from different resins of polyethylene by using Gel Permeation Chromatography (GPC) and Size Exclusion Chromatography. This method is a way to determine molecular weight, molecular weight distribution (MDW), and polymer dispersity. They are very important parameters to determine the mechanical, optical, thermal, and seal properties of the polymers. This method allows scientists and chemists to measure the molecular weight distribution and dispersity of a polymer and predict its properties and what type of processes can be used for the polymer. References 1. ASTM D6474-20 Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High Temperature Gel permeation Chromatography 2 . Principles of Polymer Systems, 4th edition, Ferdinand Rodriguez, Taylor & Francis, PA, 1996. 3. PKG 817 Course Pack AInstruments for Analysis of Packaging Materials@, J. R. Ciacin, S. G. Gilbert, J. Miltz, and J. K. Han, School of Packaging, Michigan State University, 2002. 3. Reprint from http://www.msu.edu/~tanprase/Teaching@, Lab 4 of PKG 825, Krittika Tanprasert, 2002. Support materials: · Sample A and Sample B Data and Calculations, Graphs with plots. 2 PKG 825 PACKAGING PLASTICS Laboratory 4 Determination of Molecular Weight and Molecular Weight Distribution Polymers by Gel Permeation Chromatography Submitted by: Krassimir D Vladimirov Contact information: Email: vladimir@msu.edu Date: 10 - 31 - 2022 PKG 825 PACKAGING PLASTICS Laboratory 4 Determination of Molecular Weight and Molecular Weight Distribution Polymers by Gel Permeation Chromatography Submitted by: Krassimir D Vladimirov Contact information: Email: vladimir@msu.edu Date:10-31-2022 PKG 825 PACKAGING PLASTICS Laboratory 3 Determination of Percent Crystallinity of Polyethylene by Density Gradient and Differential Scanning Calorimetry Submitted by: Krassimir D Vladimirov Contact information :Email:vladimir@msu.edu Date:10-16-2022 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Executive Summary Differential Scanning Calorimetry and Density Gradient Technique were used in this lab to determine the degree of crystallinity of two different samples of PE. Using the DSC we determined the heat of fusion Hf of the polymer and used it to determine the degree of crystallinity by dividing it by the heat of fusion of 100% crystalline PE polymer. We used the Density Gradient Technique to determine the density of two polymer samples and used the determined densities to calculate the percentage of crystallinity of the two PE resin samples. We calculated the percentage of crystallinity by using the density of pure crystal and pure amorphous polymers. Both methods yielded values of the percent crystallinity of PE that are very close to the percent crystallinity of comparable PE polymers. These methods are very important in the quick determination of the percent crystallinity of a polymer because a lot of the polymer properties depend on the crystallinity like melting and glass transition temperatures, and mechanical, barrier, and optical properties. They are very important parameters when choosing packaging materials and help manufacturers make informed decisions. Keywords and Acronyms Calorimetry, differential scanning, the density of polymer, percent crystallinity, heat flow, melting temperature, glass transition temperature, heat of fusion Introduction The degree of crystallinity for the polymer is important because it affects the physical properties of the polymer-like elastic modulus, density, permeability, melting, and glass transition 2 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry temperature, thermal and mechanical properties. The percentage of crystallinity also indicates the ratio of crystalline to amorphous regions of the polymer. A direct measure of crystallinity provides a fundamental property from which these other physical properties can be predicted and determined. The percentage of crystallinity has a direct effect on these polymer properties. Th thermal properties include heating, sealing temperature, specific heat capacity, and transition temperatures like Tg and Tm. To measure the crystallinity percentage of polymers, we use the Density Gradient Technique as designated in ASTM D1505-18 Standard Test Method for the Density of Plastics by the Density- Gradient Technique, the ASTM D3418-21 Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry and another method that is used is the Scattering of X-Rays. The ASTM D3418-21 Test Method covers the transition of temperatures and enthalpies of fusion and crystallization of polymers by differential scanning calorimetry. The ASTM D1505-18 Method covers the determination of the density of solid plastics and by using the determined values for the density, we can calculate the percent crystallinity of the polymers. Differential Scanning Calorimetry is a method that measures heat flow in and out of a polymer resin as a function of timer or temperatures. The polymer crystallinity can be determined by quantifying the heat associated with the melting of the polymer or the heat of fusion. The Density Gradient Technique is based on comparing specimens of known density with the test specimen. A gradient test tube is used to compare and record how the different polymer specimens will float in a tube full of known liquid with a known density. Measurements are 3 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry taken based on the level at which the test specimen sink and are used to calculate the test polymer density and the percent crystallinity. Objectives The objective of this lab exercise is to familiarize the students with the test procedures for determining the crystallinity percentage of plastic packaging materials How to use the density gradient technique to determine the density of the polymer samples and then use the density measurements to estimate the crystallinity of the polymer samples. How to use the differential scanning calorimetry to determine the melting point and percent of crystallinity of polyethylene samples. Lab 3 Part A: Density Gradient Technique Materials and Methods • Equipment: Ray ran Auto Density Gradient Column • Procedure: ASTM D1505-18 Standard Test Method for Density of Plastics by the Density- Gradient Technique • Materials: Two (2) polyethylene (PE) resins Sample A PE resin and Sample B PE resin • Density gradient and glass floats with known density Briefly stated, this technique involves four stages: 1. Prepare a density gradient tube. 2. Construct the calibration curve with glass floats of known density. 3. Test the specimen and calculate its density from the calibration curve. 4. Calculate the percent crystallinity 4 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry To prepare the density gradient tubes, two solutions A and B are picked for the density gradient because their densities fall within the relevant range (A is a denser liquid and B is a lighter liquid). They are mixed in a glass tube to create a liquid column whose density drops linearly as it rises. Glass beads with known density are inserted into the column during calibration After remaining still in the liquid, their locations are noted. The calibration curve is built as a function of sinking distance and density. The sinking places are noted, matching densities are calculated using the calibration curve, and the average density of the test specimen is reported when measuring the density of the test specimens. Once calibrated, the Ray Ran Auto Density column automatically calculates the density of the test specimen. The specimens in the column that corresponds to a location in the column can be found using the microscope that is located at the front of the column. The density then is determined from the calibration curve using that location. The % of crystallinity can be determined using the density that was calculated. Experimental procedure 1. The density gradient with isopropanol (d = 0.79 g/cc at 230C) and diethylene glycol (d = 1.11 g/cc at 230C) (see table 1 in ASTM D1505-18), using method C (see A1.3 in ASTM D1505-10), has been prepared. See Figure 1. 2. Add the calibrated glass floats to the density-gradient tube (performed by TA before the lab). 3. After the floats reach the equilibrium position, record their positions and density (data provided by TA). 4. Construct the calibration curve by plotting density as a function of position (the plot should be linear) 5. Wet 3 test specimens with the less dense liquid (isopropanol). Three samples of Sample A resin and three samples of Sample B resin 6. Submerge the prepared specimen in the top of the gradient tube with a pair of forceps, gently shake it to detach any air bubbles, and allow the specimen to sink to its equilibrium position. 5 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry 7. Note the equilibrium position only if it has remained unchanged for 10-15 minutes. 8. Compute the apparent density of the test specimen with the help of the calibration curve. 9. From the average apparent density value, determine the % crystallinity of the test specimen. Data and Calculations Table 1 6 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Figure 2 We use the data from table one to prepare the density gradient. Based on the data we construct the calibration curve with density-known glass beads. We test the specimen, plot the data and calculate the density, and using the density value we calculate the percent crystallinity. Test Specimen DATA Table 2 7 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Using the data we calculated for the density, will calculate the % of crystallinity for the two samples, A and B. Using the equation from the calibration curve we calculated the values for the density in Table 2. y=789.68x+739.9 Then we would use the following equation to calculate the 5 of crystallinity of the two samples A and B of the PE polymer: α ₘ and α = volume and mass percent crystallinity, respectivelyᵥ d, dc, d =density of the test polymer samples ₐ dc – 1.011 g/cc density of pure crystal PE polymer d - 0.862 g/cc at 23°C density of pure amorphous PE polymer ₐ d – is the value of the calculated average density for the test specimen Sample A and B To calculate the % crystallinity we need to convert the g/cm³ to g/cc. 1cm³=1 cc α= d−da dc−da ∗100=( 0.940−0.8621.011−0.862 )∗100=¿(0.078 g/cm³)/(0.149 g/cm³)*100 = 52.35% of crystallinity for Sample B PE polymer α= d−da dc−da ∗100=( 0.945−0.8621.011−0.862 )∗100=¿ (0.083 g/cm³)/(0.149 g/cm³)*100 = 55.70 % of crystallinity for Sample A PE Polymer 8 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Lab 3 Part B: Differential Scanning Calorimetry Materials and Methods • Equipment: TA Instrument DSC • Procedure: ASTM D3418-21 Standard test method for transition temperatures of polymers by differential scanning calorimetry • Materials: Two (2) polyethylene (PE) resins • DSC and its application in determining percent crystallinity 1. What is DSC? DSC is a type of thermal analysis. According to ICTA (International Congress on Thermal Analysis), DSC is defined as a technique in which the difference in energy inputs into a substance and reference material is measured as a function of temperature whilst the substance and reference material are subject to a controlled temperature program Figure 3 9 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Figure 4 3 . Determine Tg, Tm, ΔHf [1,2] Tg: Glass transition temperature designates the point at which torsional oscillations and/or rotational motions in polymer chains 20–50 carbon atoms in length either freeze in (on cooling) or unfreeze (on heating). As in the case of branching polymers, the segmental motions occur on the backbone chain bonds as well as in nearby chains. Tg is significant since it describes the polymer's condition at normal temperature. Due to the segmental movement of the backbone, the polymer is in a rubbery state above Tg, while below Tg, the polymer is in a glassy state and brittle. Tm: The polymer's structural integrity is lost when it enters the liquid phase, which is marked by the transition from the solid to the liquid phase. Because amorphous polymers lack a melting temperature, it is only relevant for crystalline or semi-crystalline polymers. Due to variations in the size and regularity of the individual crystallites, a semi-crystalline polymer melts over a temperature range. In this scenario, Tm is reported as a single value when the polymer has finished melting. Tm is significant since it stands for the lowest temperature at which the polymer can be processed. Relation between Tm and Tg: Generally speaking, the ratio of Tm and Tg (both expressed in 10 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Kelvin) ranges from 1.4 to 2.0. fr the vast majority of semi-crystalline polymers. Tm/Tg 1.6 g m ΔHf: The energy required for the creation or melting of crystalline areas in a polymer is known as the heat of fusion (Hf), and it is measured in calories per gram. The area under the melting curve is equivalent to Hf in a DSC scan. ΔH and % crystallinity: Given that we know the Hf of the test specimen in pure crystalline form (100 percent crystallinity) and that we presume that Hf is proportional to the% crystallinity of the test specimen, we may calculate the% crystallinity as follows: Where: ΔHf = heat of fusion of semi-crystalline polymer, cal/g ΔHf* = heat of fusion of 100% crystalline sample, cal/g. For PE, this value is 68.4 cal/g or 286.2 J/g Experimental procedure: 1. Prepare a sample a. Handle all samples with tweezers and gloves b. Cut your sample with a razor blade so both sides of the sample are flat and the weight is in the range of 5-10 mg 2. Put the sample in the pan and crimp the pan 3. Reference pan (empty pan) is provided 4. Load the sample 11 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry a. Remove the bell jar, cell cover, and silver lid b. Place the sample pan on the front platform and the reference pan on the rear platform, centering the pans within the grid c. Replace the silver lid, cell cover, and bell jar 5. Enter experiment information through the TA controller a. Open the TA controller program b. Click on wizard c. Choose “Conventional DSC” and click “Next” d. Choose “DSC ramp” and click “Next” e. In the experimental parameter, enter the following information • Start temp: click “use current” • Heating rate: 100C/min • Final temp: 2000C • Click “Next” f. In sample information, enter the following information • Sample name • Sample size (in mg) • Comment if needed • Data file: store the sample in an appropriate folder • Click “Next” g. In the sample information note, enter the following information • Operator name • Pan type (aluminum) • Purge gas (nitrogen) 12 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry • Flow rate (70 mL/min) • Click “Next” h. Check the checklist and click “Finish” 6. Make sure the nitrogen gas tank is on PKG 825, Fall 2020 9 7. Press “Start” 8. To analyze the data, open “TA Universal Analysis” a. Open the saved data, the path usually is TA>DATA>DSC> b. Click on the icon “Integrate peak sig horizontal”, which is located on the top menu of the screen c. Use the mouse to choose the starting and ending point for peak integration d. Right-click pick mouse, then choose to accept limits The integration will give you the ΔHf and T Data and Calculations Sample A PE Resin Figure 5 13 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Tm=112.29°C Peak Melting temperature Tm =46.62°C Onset Melting Temperature Tm= 118.32°C End Melting Temperature Tm/Tg ≈ 1.6 In Kelvin Tm=112.29 +273.15 (K) = 385.44 Tg= 385.44/1.6 ≈ 240.90 K Tg= -32.25°C Tg glass transition temperature for this PE sample is 32.25°C. Figure 6 Figure 6 shows the integration curve. The area under the curve is the Heat of Fusion Hf. Area = -113.73 W/g , need to convert to J/g W/g=J/(s-g) or cal/g 14 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry ΔHf=-113.73 W/g = - 113.73J/(s-g) = 113.73 J/g The %= (113.73 J/g)/(286.2 J/g) = 39.73% crystallinity of Polymer Resin A sample Sample B Figure 7 Melting Tm=129.6°°C Tm/Tg ≈1.6 in Kelvin 129.67 +273.15 = 402.82 Kelvin Tm onset = 55.69 Tg= 402.82/1.6 = 251.76 K = -21.39°C Tm end= 136.6 Tg glass transition temperature for PE polymer Sample B is - 15 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry 21.39°C Figure 8 ΔHf= 249.56 W/g % crystallinity = (ΔHf/ ΔHf)*100 = (249.56 J/g /286.2 j/g)*100= 87% crystallinity Discussions During our lab, we tested and recorded the test results of two different PE resins, Sample and 16 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry Sample B using the Density Gradient Technique and Differential scanning Calorimetry. We can see that the results from the Density Gradient technique methods are a lot closer for the two polymer Samples and Sample B. The percent crystallinity from sample A was 55.70% and sample B was 52.35%. The results indicate that the two samples are from a similar grade PE polymer and based on these results for the crystallinity we can say that the properties of the polymers would have similar mechanical, optical, and barrier properties. During the DSC method, the results for the percent crystallinity had a bigger difference, Sample A = 69.73%, Sample B = 87%. The glass transition temperatures of the two polymers that were determined were also similarly different, Sample A = -32.25°C and Sample B= 21.39°C. We can see more clearly from the DSC method results that the two PE polymer samples have different percentages of crystallinity, but not very big differences in glass transition temperature, but the results overall are similar to a similar rade PE polymers. The glass transition temperature is defined as the temperature at which torsional oscillations and/or rotational motions in polymer chains 20-50 carbon atoms long either freeze in (on cooling) or unfreeze (on heating). Segmental motions occur on the backbone chain bonds as well as in nearby chains, as in branching polymers. Tg is significant because it describes the polymer's state at room temperature. The polymer is in a rubbery state above Tg due to the segmental movement of the backbone, while it is glassy and brittle below Tg. These two polymer samples have very similar glass transition temperatures. The structural integrity of the polymer is lost when it enters the liquid phase, which is indicated by the transition from the solid to the liquid phase. It is only relevant for crystalline or semi- crystalline polymers because amorphous polymers lack a melting temperature. A semi- 17 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry crystalline polymer melts over a temperature range due to variations in the size and regularity of the individual crystallites. When the polymer has finished melting, Tm is reported as a single value. Tm is important because it represents the lowest temperature at which the polymer can be processed. The percent crystallinity increases the strength of the polymer, because in the crystalline phase, the intermolecular bonding is more significant, and that is why the polymer deformation can result in higher strength leading to oriented chains. With increased crystallinity, we see increased strength of the polymer, but it can be more brittle as well. The polymer with the higher crystallinity would be more opaque and decreased optical properties because of the higher crystallinity and higher density of the polymer structure. The higher crystallinity of the polymer also will contribute to a better barrier property like permeability and diffusion. When the polymer has a higher crystallinity, it would be more difficult for the permeant to diffuse through the polymer chains. Conclusions In conclusion, we successfully tested samples from different resins of polyethylene using the by using Density Gradient Technique and Differential Scanning Calorimetry. These methods are a quick and easy way to determine the percent crystallinity of PE polymers, which is very important to determine their mechanical, optical, permeability, and barrier properties. We determined the crystallinity of polymers through measurement of the heat fusion and density of the PE polymers. 18 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry References 1. ASTM D1505-18 Standard Test Method for Density of Plastics by the Densit GradientTechnique 2. ASTM D3418-21 Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry 3. Principles of Polymer Systems, 4th edition, Ferdinand Rodriguez, Taylor & Francis, PA, 1996. 4. Plastics Packaging: Properties, Processing, Applications, and Regulations, R.J. Hernandez, S. E. Selke, J. D. Culter, Hanser Gardner Publications, Inc., 2000. 4. Thermal Analysis of Foods, edited by V. R. Harwalker and C.-Y. Ma, Elsevier Applied Science, 1990. 5 . Plastics Packaging: Properties, Processing, Applications, and Regulations, S. E. Selke&J. D. Culter, 3rd ed. Hanser,2016 Support materials: - Sample A and Sample B - Lab Part A and Part B 19 Determination of Percent Crystallinity of Polyethylene by The Density Gradient and Differential Scanning Calorimetry 20 PKG 825 PACKAGING PLASTICS Laboratory 2 Determination Of Melt Flow Index By Extrusion Plastometer Submitted by: Krassimir D Vladimirov Contact information: Email:vladimir@msu.edu Date:10-02-2022 Submitted to: Dr. Rafael Auras E-mail:aurasraf@msu.edu James MacNamara E-mail:macnama2@msu.edu Determination of Melt Flow Index by Extrusion Plastometer Executive Summary Melt Flow Index (MFI) is the most popular parameter in the plastic industry for distinguishing various grades of polymers and enables manufacturers to prepare polymer resins suitable for specific fields of application. To measure the MFI we used the ASTM D1238-20 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastomer. We tested two different polyethylene resin samples using Ray-Ran Melt Flow Indexer MK II Digital Model 2 A. There were two test procedures that we used to measure the Melt Flow Index: procedure A(manual operation) and procedure B( automatically timed flow rate measurement). The Melt Flow Index is the ability of a plastic polymer to flow in a small interval of time through a die on the melt flow indexer. The polymer is heated in a small oven on the tester and a load is applied to the molten plastic and extruded over 10 minutes. The weight of the material is recorded, measured, and used to calculate the MFI of the plastic material. Melt Flow Index is the result of extruded plastic driven through a die in 10 minutes. The test was repeated and the results were compared. The results of the MFI of the two different polymers are used to provide information on the molecular weight, molecular weight distribution, viscosity, and other polymer properties. Because of the inverse proportionality between the MFI and the viscosity of the polymer, polymer grades with higher Melt Flow rates tend to have lower molecular weight. The MFI is used to distinguish different grades of polymers, quality control, and determine the extent of degradation. We can predict the Molecular Weight, Molecular Weight Distribution, and molecular architecture of the polymer. Lower MFI means higher MW, and for the same MW, 2 Determination of Melt Flow Index by Extrusion Plastometer narrower the MWD and lower MFI. For leaner polymers, the same MW and MWD indicate lower MFI. The MFI results are commonly used by manufacturers of polymers for injection molding and extrusion industries to determine the processing conditions for different grades of polymers. Knowing the plastic material’s quality by the manufacturer makes the process parameters selection much easier for this particular plastic material. Keywords and Acronyms Thermoplastics, Melt Flow Index, Polyethylene resins, Molecular Weight, Viscosity Introduction Polymeric plastic materials are used in many industries ranging from electronics, furniture, electronics, automobile, aviation, and light industries. One of the quality control indicators is determining the Melt Flow Index of the thermoplastic polymer. Quality is very important for the plastic polymer because it makes it easier to choose the process parameters for injection molding and extrusion, and reduces the time for production preparation. The Melt Flow Index is a measure of the flow of the molten thermoplastic polymer. It is defined as the weight of the polymer in grams, extruded in 10 minutes through a die with a specific diameter and length, by pressure applied by weight under a certain temperature. The method for measuring the Melt Flow Index used is the ASTM D1238-20 Standard Test Method for melt flow Rates of Thermoplastics by Extrusion Plastometer. The test specimens were two commercial polyethylene (PE) resin samples. The test conditions were according to the standard temperature of 190°C and a total load of 2.16 kg. This method is often used by the plastic industry to measure the MFI of a polymer as a simple and quick means of quality control. The equipment is used with polymer resin granules. Melt Flow Index is used to provide the measure of the flow of melted plastic polymer, in our case polyethylene, and it can be used to differentiate the grades of the polymer and the degradation of the plastic polymer. In general, plastic polymers with higher MFI are used in injection molding and lower MFI polymers are used with blow molding or extrusion processes. The MFI is a measure to assess the average molecular weight of 3 Determination of Melt Flow Index by Extrusion Plastometer a polymer and is an inverse measure of the melt viscosity, in other words, the higher the MFI, the more polymer flows under test conditions. Objectives The purpose of these lab exercises is to familiarize the students with the test methods and procedures used to determine the Melt Flow Index of plastic polymers used for packaging materials. To learn how to determine the melt flow index of a selected polymer sample using the Extrusion Palstometwr technique. How to use the results for the MFI relate to the polymer properties and characteristics like viscosity, molecular weight, and molecular weight distribution and how these results are used as means for quality control of the plastic material. Materials and Methods For this lab exercise we use the following type of equipment:  Equipment: Ray-Ran Melt Flow Indexer MK II Digital Model 2 A . See Figure 1 4 Determination of Melt Flow Index by Extrusion Plastometer Figure 1  Procedure: ASTM D1238-20 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastomer  Materials: Two commercial polyethylene (PE) resin samples  Test Conditions. Table 1 (Refer to Table 3 of the ASTM D1238-20 Standard) Table 1 Temperature=190° Total Load =2.16 kg Experimental procedure: 1. Check the equipment 2. Select test conditions 3. Insert the die and the piston into the cylinder of the plastometer 4. Wait for 15 minutes 5. Remove the piston, then add samples (see table 1 in ASTM D1238-20) and allow some time to melt. Usually 7 minutes 6. Purger samples out until the line on the plunger line up with the top of the cylinder 7. Follow the steps in procedure A or B to complete the test There are two procedures used to measure the Melt Flow Index: Procedure A (manual operation) And Procedure B (automatically timed flow rate measurements). A. Procedure A (manual operation) 5 Determination of Melt Flow Index by Extrusion Plastometer Briefly, this is the procedure in which the extrudate is weighed after the piston travels for a certain period. The MFI is expressed in g/10 min. 1. Start timer and make the initial cut-off 2. Stop timer when time interval is reached and make the final cut off 3. Weight the extrudate and do the calculation to get the MFI (g/10 min) 4. Replicate the test 3 times for both sample A and sample B B. Procedure B (Automatically Timed Flow Rate Measurement) In this procedure, the travel distance of the piston is pre-selected. In each measurement, the time needed for the piston to travel that specified distance is the measurement taken during the test. 1. Select travel distance for the piston to either 0.635 cm(0.25 in) or 2.54 cm (1 in) 2. Make the initial cut-off when the auto timer starts 3. Make the final cut-off when the auto time stops 4. Record the time required for the piston 5. Do the calculations to get MFI 6. Replicate the test 3 times for both sample A and sample B Calculation A Procedure A (Manual Operation) (See 10 and table 2 in ASTM D1238-20) MFI (gm/10 minutes)= Weight Time ∗10 Procedure B: Automatically Timed Flow Rate Measurement (See 11 and table 4 in ASTM D1238- 20) MFI(gm/10minutes) = (426*L * d )/t MFI(gm/10 minutes)= 426∗L∗dt 6 Determination of Melt Flow Index by Extrusion Plastometer Where: L = length of piston travel, cm d = density of resin at test temperature, g/cm3 t = time of piston travel for length L, sec 426 = mean value of areas of piston and cylinder x 600 (see Fig 1 and 2 in ASTM D1238-20) Method to calculate density d (g/cm3 ) d = W/Vol d= W Vol Where: d = density of resin, g/cm3 W = weight of extrudate in time t at test temperature T, g Vol = volume of extrudate in time t at test temperature, cm3 Vol = A L = ( π D24 )∗L Where: A = mean area of piston and cylinder, cm2 L = length of piston travel, cm D = mean diameter of piston and cylinder, cm DATA and calculations: Procedure A, Manual Operation, 7 Determination of Melt Flow Index by Extrusion Plastometer Two specimen samples were tested, Sample A and Sample B from commercial grade polyethylene resins in the form of granules. The test conditions were according to the ASTM D1238-20 standard temperature of 190°C and a total load of 2.16 kg. The samples were preheated for at least 7 minutes. The test was repeated three times for Sample A and Sample B polyethylene resins. Results are entered in Table 2. Table 2 The results were calculated using the formula: MFI (gm/10 minutes)= Weight Time ∗10 Sample Calculation: 8 Determination of Melt Flow Index by Extrusion Plastometer Sample A: MFI (gm/10 minutes)= 0.6833g 0.5min ∗10=13.666 g/10 min time Sample B: MFI (gm/10 minutes)= 0.1924 g 6min ∗10 = 0.320 g/10 min time Procedure B: Automatically Times Flow Rate Measurement Two specimen samples were tested, Sample A and Sample form commercial grade polyethylene resins in the form of granules. The test conditions were according to the ASTM D1238-20 standard temperature of 190°C and a total load of 2.16 kg. The samples were preheated for at least 7 minutes. In sample A, the piston travel distance was set at 2.54, and the piston travel distance for Sample B was set at 0.635 cm. The test was repeated three times for Sample A and Sample B polyethylene resins. The results are entered in Table 3 : Table 3 9 Determination of Melt Flow Index by Extrusion Plastometer MFI (gm/10 minutes)= 426cm ²∗2.54 cm∗0.6473 g/cm ³ 43 s =¿16.288 gm/10 min Where: L = length of piston travel, cm = 2.54 c d = density of resin at test temperature, g/cm3 =0.6473 g/cm³ density t = time of piston travel for length L, sec = 43 s 426 = mean value of areas of piston and cylinder x 600 (see Fig 1 and 2 in ASTM D1238-20) 426 is the means of cm² of the piston land (foot) and the cylinder where the piston travels time 600 426 cm( gc m3 ) sec =426 g sec∗cm² = ( 426600 )g cm2∗minutes 10 Determination of Melt Flow Index by Extrusion Plastometer Method to calculate density d (g/cm3 ) d = W/Vol d= W Vol= 1.1585 g 1.7897 cm ³=0.6473 g/cm³ density Where: d = density of resin, g/cm3 W = weight of extrudate in time t at test temperature T, g =1.1585 g Vol = volume of extrudate in time t at test temperature, cm3 Vol = A L = ( π D24 )∗L = ( 3.14∗(0.94742 2 cm ²) 4 )∗2.54 cm=¿1.7897 cm³ volume Where: A = mean area of piston and cylinder, cm2 L = length of piston travel, cm= 2.54 cm D = mean diameter of piston and cylinder, cm 9.4742 mm = 0.94742 cm . The diameter value is based on ASTM 1238-20 standard π=3.14 constant Sample B calculations MFI (gm/10 minutes)= MFI(gm/10 minutes)= 426 cm ²∗0.635 cm∗0.5868 g/cm ³471 s = 0.337gm/10 min Where: L = length of piston travel, cm = 2.54 cm d = density of resin at test temperature, g/cm3 =0.5868 g/cm³ density t = time of piston travel for length L, sec = 471 s 426 = mean value of areas of piston and cylinder x 600 11 Determination of Melt Flow Index by Extrusion Plastometer 426 is the means of cm² of the piston land (foot) and the cylinder where the piston travels time 600 (10 min) Method to calculate density d (g/cm3 ) d = W/Vol d= W Vol= 0.2312g 0.4474cm ³=0.5168 g/cm³ density Where: d = density of resin, g/cm3 W = weight of extrudate in time t at test temperature T, g =1.1585 g Vol = volume of extrudate in time t at test temperature, cm3 Vol = A L = ( π D24 )∗L = ( 3.14∗(0.94742 2 cm ²) 4 )∗0.635 cm=¿0.4474 cm³ volume Where: A = mean area of piston and cylinder, cm2 L = length of piston travel, cm= 0.635 cm D = mean diameter of piston and cylinder, cm 9.4742 mm = 0.94742 cm . The diameter value is based on ASTM 1238-20 standard π=3.14 constant Discussions In this lab exercise, we learned about the Melt Flow Index of plastic polymers. We tested two commercial-grade polyethylene (PE) resin samples in the form of granules; Sample A and Sample B. For the procedure, we used the ASTM D1238-20 Standard Test Method for the Melt Flow Rates of Thermoplastics by Extrusion Plastometer. We used Procedure A, Manual Operation, and Procedure B, Automatically Timed Flow Rate Measurement. The difference between Procedure A, Annual procedure, and Procedure B, Automatically Timed, is that for the 12 Determination of Melt Flow Index by Extrusion Plastometer manual procedure the time is constant and for the automatic procedure the volume is constant. We can determine based on the results that the Sample A of the polyethylene resin has a lot higher Melt Flow Index than Sample B. The test results from the Manual Procedure and the Automatically Timed Flow Rate Measurement for Sample A a little different. The average melt Flow Index for Sample A from the Manual procedure is 13.664 gm/10 min and the Automatic Procedure is 16.745 gm/10min. The different test results can be affected by different factors that can influence the outcome of the tests. The results for Sample B from both procedures are almost the same, the average MFI for the manual procedure is 0.324 gm/10 min and for the automatically timed, the average MFI is 0.312 cm/10 min. The results for Sample B are almost the same with a very small deviation. Based on the results for the MFI we can determine certain characteristics and properties of the polyethylene polymer samples. The MFI is a measure of the polymer's flow characteristics or rheological properties in the molten state under exact applied pressure. Since the polymers are made of different chain lengths .either linear or branched, they can determine the flow characteristics of the polymer. Sample A has a lower molecular weight than Sample B. Since during the polymerization process, the chains can become either long or short, which is also known as molecular weight distribution, which can affect the polymer melt flow rate. The MFI is an assessment of the molecular weight distribution and it is an opposite measure of the melt viscosity. The higher the MFI, the more polymer flows under test conditions and corresponds to lower viscosity and low molecular weight, in other words, high MFI and low molecular weight, low viscosity polymer, and low MFI .high molecular weight and high viscosity polymer. Molecular weight distribution has a very strong effect on the shear viscosity of the polymer, and the more branched the chain is, the more it can affect the viscosity of the polymer because it is related to the molecular weight distribution. For the same Molecular 13 Determination of Melt Flow Index by Extrusion Plastometer Weight Distribution and Molecular Weight, a linear polymer has a lower MFI, and the narrower the Molecular Weight Distribution, the lower the MFI. MFI is one of the most popular parameters in the plastic industry for distinguishing various grades of polymers and determining their end-use. MFI is widely used for quality control for plastic materials because it can give very good indications of how the plastic polymer can be used and for what type of manufacturing processes. MFI can be used to optimize the processing conditions of plastic polymers based on their applications. It is particularly useful during the manufacturing process to determine if there is a batch-to-batch variation of the plastic polymer. In the plastic industry polymers with a higher MFI are usually used in injection molding, and lower MFI polymers are used with blow molding and extrusion processes. MFI is very important for quality control in injection molding because the quality of mold depends on the process conditions like temperature, pressure, and rheological properties of the molding compound (Shenoy and Saini). The accuracy of the Melt Flow Test procedure depends on variations in the test technique, apparatus geometry, and test conditions which can cause discrepancies in determining the Melt Flow Rate. Different factors can affect the results of the Melt Flow test. One of them is the levelness of the instrument. The instrument needs to be vertical so that the piston to move up and down without any issues and can not slow down because the instrument is angled. This can increase the friction between the piston and the barrel and slow down the piston’s movement. The piston needs to move in an exact vertical plane indicated by the bubble level that should be placed on the top of the barrel or the piston. Another factor is the die cleanliness. The die should be cleaned completely after every test so that any residues of plastics can be removed and keep the die opening clean without any clogging. The build-up of the material can reduce the diameter 14 Determination of Melt Flow Index by Extrusion Plastometer of the die and result in erroneous results. The Melt Flow Index depends on the temperature in the barrel. The temperature in the barrel is very important to be kept even during the test. That is why the term temperature gauge must be maintained and calibrated to the temperature within the barrel. The high temperature will cause a higher rate of flow and the low temperature will cause a low rate of flow. Another factor that is also very important is the preheat time, which will allow the material to heat up and fully melt and reach even temperature throughout the barrel and achieve even flow during the test. Conclusion Melt Flow Index is the most popular and quick method to measure the flow properties of plastic polymers and is often used to assess material variations and determine material viscosity. It helps us to determine important polymer characteristics and properties. It is widely used in the plastic industry for quality control and the proper choice of materials and selection of process parameters.MFI is used to optimize and specify the end use of a particular grade of a given polymer. References 1. ASTM.‘‘D1238-20 Standard Test Methods for Melt Flow Rates of Thermoplastics by Extrusion Plastomer”, ASTM, West Conshohocken, PA 2004. 2. Adapted (section 7.2) from Handbook of Plastics Testing Technology, V. Shah, John Wiley and Sons, 1984. 3. Plastics Packaging: Properties, Processing, Applications, and Regulations, R.J. Hernandez, S. E. Selke, J. D. Culter, Hanser Gardner Publications, Inc., 2000 4. [16](PDF)Aroon Shenoy, D.R. Saini “Melt Flow Index: More Than Just a Quality 15 Determination of Melt Flow Index by Extrusion Plastometer Control Rheological Parameter. Part 1” March 1986,Advances in Polymer Technology 6(1):1-58 https://www.researchgate.net/publication/228037927_Melt_Flow_Index_More_Than_Just _a_Quality_Control_Rheological_Parameter_Part_I Supporting materials: - Lab 2 Procedure A, sample A, and B, and Procedure B, sample A and B calculation results 16 https://www.researchgate.net/publication/228037927_Melt_Flow_Index_More_Than_Just_a_Quality_Control_Rheological_Parameter_Part_I https://www.researchgate.net/publication/228037927_Melt_Flow_Index_More_Than_Just_a_Quality_Control_Rheological_Parameter_Part_I Determination of Melt Flow Index by Extrusion Plastometer 17 PKG 825 PACKAGING PLASTICS Laboratory 1 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Submitted by: Krassimir D Vladimirov Contact information :Email:vladimir@msu.edu Date:09-18-2022 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Executive Summary Tensile and impact tests are critical for understanding the mechanical properties of various plastic materials under load. For the tensile test lab, we tested two different polyethylene resins, ten samples each, using the ASTM D638-22 Standard Test Method on Instron Universal Testing Machine. For the impact, the Test uses the ASTM D256-10(2018) Standard Test Method to determine the IZOD Pendulum impact resistance of plastics. To perform this test, we used the TMI 43-I Izod Impact Tester and tested two polyethylene resins, six samples each. The data from each test was used to determine material properties of the plastics such as tensile strength, modulus of elasticity, tensile strength at yield and break, percent of elongation, and impact strength. These test results were used to compare the properties of the plastic materials and determine if they are brittle or ductile, tough, or soft. The results were used to compare the two different samples from the polyethylene polymer resins and compare the two in terms of their mechanical properties. For the tensile test, we can see that Sample A has a higher presence of elongation and then Sample B and Sample B have a higher Modulus of Elasticity than Sample A. The higher modulus of elasticity would mean that the material is stiffer and whether it is susceptible to permanent deformations. The lower modulus of elasticity shows that the plastic material is more versatile mechanically, more pliable not brittle, flexible, elastic, and ductile. From the Izod test, we can explore which sample is tougher on impact. These test results determine where and how we can these plastic materials and what type of real-world applications especially when choosing packaging material. These material properties can be used for the selection of plastic material for your packaging needs based on what the plastics structures would be used for. They have real-world implications if chosen correctly. In my industry, we use a lot of stretch wrap and shrink wrap plastics that stabilize the pallet loads and retail units and distribution bundles. The relies upon the plastic stretch and shrink wrap to keep it safe from the environment and distribution process. The impact strength of a plastic polymer is important when you choose a primary package for your products, especially if it’s the retail or distribution unit, and make sure that the package will be intact and presentable when it gets to the consumer. The Izod impact test will determine how the chosen material will react under load and impact. 2 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Keywords and Acronyms MOE-Modulus of Elasticity, Polymer, Tensile Strength Test, Impact Izod Test,stress-strain curve, elastic, plastic, strain at yield, stress at yield. crystallinity. Impact, toughness, brittle. Introduction The mechanical properties of materials are determined through laboratory experiments that simulate possible real-life scenarios and applications. Numerous factors influence how loads are applied to various materials. Mechanical properties are critical for the design process and application of different packaging materials. The purpose of these lab exercises is to determine the tensile properties and impact strength of polymers under different conditions. For the tensile properties of the polymer, we are using the ASTM D638-14 Standard test method using two samples of polyethylene resins to determine the behavior of the material under axial stretch loading. The materials are tested under determined conditions like temperature, humidity, and testing machine speed. The results of all the tests are reported in SI standard units. The data from the test is used to find the elastic limit, elongation percentage, modulus of elasticity, proportional limit, toughness, tensile strength, and yield point. The tensile elongation that occurs when materials are pulled with tension, is a measure of both elastic and plastic deformation. When performing the tensile test we measure the stress and strain values and use them to determine the mechanical properties of the polymer plastic material. For the impact test, we use the ASTM D256-10(2018) Standard test method for determining the Izod pendulum impact resistance of the plastic polymer. We used two sets of samples of polyethylene resins to measure their resistance to impact from a swinging pendulum. Based on the results we determine if the material is tough, soft, brittle, or ductile. The Izod impact represents the kinetic energy that is required to start a fracture on the specimen and keeps it going until it is broken. The Izod impact test shows the toughness of the material, which is the ability of the material to absorb energy during impact and plastic deformation. The toughness of the material takes into account both the strength of the material and ductility. 3 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Objectives The purpose of these lab exercises is to familiarize the students with the test methods used to determine the impact strength and tensile properties ( modulus of elasticity, tensile strength, percentage elongation, yield stress, strain) of unknown polyolefin polymer samples. These will help the students understand some of the material properties, such as ductility, brittleness, elasticity, and toughness. Better understand the behavior of the material under load and impact. Lab 1 Part A: Tensile Strength Materials and Methods For this lab exercise we use the following type of equipment:  Equipment: Universal Testing Machine (Instron). See Figure 1 Figure 1  Procedure: ASTM D638-22 Standard Test Method for Tensile Properties of Plastics.  Materials: Two different unknown polyethylene samples Test specimens were prepared for you from two polyethylene resins. Sample A – ten tests, Sample B -ten tests.  The resins were injection molded using a 30T2 Boy machine, and they were cut according to the ASTM D638-22 specifications.  Injection Molding Conditions.Refer to Table 1 4 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Table 1  1. Samples: See figure 2 Figure 2 W (width)= 13 mm L (length) = 57 G ( length of the testing area) = 50 mm D ( distance between grips) =115 mm WO (width overall) = 19 mm LO (length overall) 165 mm R (radius) = 76 T (thickness of the specimen) = 3.2 mm 5 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance  Conditioning procedure 23oC, 50% RH, not less than 40 hours before the test  Test conditions 23oC, 50% RH  Speed of testing. The speed of the test is 500 mm/min. Experimental procedure: 1. Turn the Instron on, followed by the computer 2. Open the Bluehill software on the desktop. 3. Click “Test”. Choose the method “PKG 825.im_tens”. Click Next. 4. Set the gauge length on the Instron to 50 mm: Press the JOG UP or JOG DOWN button on the panel of the Instron to have a jaw separation of 50 mm. Verify the jaw separation with a ruler. After the desired jaw separation is achieved, press the “RESET GL” button on the panel of the machine. 5. Enter the test’s file name on the computer and select a folder to save your file. Click “Next”. 6. Enter the specimen information on the computer. 7. Insert the specimen into the jaws. Close the jaws with the peddle on the floor. 8. Click “Balance Load” on the computer and then click “START”. 9. The specimen will be stretched, and the machine will stop when the test is completed. Remove the sample by first opening the jaws and clamping the sample (peddle on the floor). 10. Click “OK” when prompted for the gauge length to return to its initial position. PKG 825 – Lab I - Mechanical Properties 3 11. Click “Continue Test”. Follow steps 6-10 for additional specimens. 12. Record the required data. (The excel file with all the data will be uploaded on d2l after the test is completed). 13. Close the Bluehill Software and turn off Instron. 6 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 3 Based on the results of the test we calculate the Tensile strength at yield, at the break, we find the proportional limit of the material, which represents the linear portion of the stress/strain curve and stops when the graph curves. Calculate the Tensile strength at the Yield or point of Break, Modulus of Elasticity at the Proportional Limit which is Stress over Strain at the proportional limit. The yield point is the part of the curve where there is an increased strain without an increase in stress. Based on the graph from the results we can determine the area of resilience and toughness. We do the calculations using these equations: Tensile Strengh@PL(psi) = Force ( lb) Cross−sectional area (i n2 ) ¿ ¿ Strain@PL(in/in)= Entention@ PL ( ¿ ) Original length ( ¿ ) 7 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Tensile Stress (psi)= MaxForce (lb ) Cross−sectional area (i n2 ) Strain at Break (in/in) = Extentionat break (¿ ) Original length ( ¿ ) Strain at Yield(in/in)= Extentionat Yield ( ¿ )Original length (¿ ) Modulus of Elasticity(psi)= Tensile Strength@PL( psi)Strain@PL (¿ /¿ ) DATA and calculations: Sample A with 10 specimens tested. Results entered in Table 2 Table 2 Sample A MOE@PL Modulus of Elasticity at Proportional Limit Stress @PL Stress at Proportional Limit MPa Strain@ PL Strain at Proportional Limit mm/mm Percent Elongation @Yield % Tensile Strength @Yield MPa Load at Yield N Test 1 81.113 5.68784 0.07012 38.16 10.18 436.358 Test 2 72.3963 7 0.09669 38.87 11.12 462.646 Test 3 65.7544 7.89 0.119992 38 11.12 461.811 Test 4 72.9677 7.88 0.107993 34.60 11.58 481.73 Test 5 63.3500 8.13 0.128334 19.92 11.01 457.828 Test 6 63.5100 8.15 0.128327 36.83 10.86 451.969 Test 7 67.0334 8.20 0.122327 37.33 11.09 461.45 Test 8 66.29 7.18 0.108331 45.03 10.84 450.852 Test 9 72.2058 7.87 0.108994 36.43 11.51 478.792 Test 10 63.55 7.88 0.123993 40.03 11.23 467.088 Average 68.81734 7.59 0.1115101 36.52 11.05 461.052 8 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Sample B with 10 specimens tested. Results are entered in Table 3. Table 3 Sample B MOE@PL Modulus of Elasticity at Proportional Limit Stress @PL Stress at Proportional Limit MPa Strain@ PL Strain at Proportional Limit Mm/mm Percent Elongation @Yield % Tensile Strength @Yield MPa Load at Yield N Test 1 436.4326 10.35 0.023021 22.53 36.14 1503.25 Test 2 380.5866 9.81 0.025776 26.23 33.54 1395.20 Test 3 415.0449 10.13 0.024407 18.23 30.57 1233.89 Test 4 378.1574 10.27 0.027158 23.37 32.43 1288.04 Test 5 358.4357 10.10 0.028178 23.37 32.43 1348.96 Test 6 311.1894 12.02 0.038626 28.23 30.87 1284.16 Test 7 440 10.10 0.020957 16.63 31.47 1309.15 Test 8 434.80 10.61 0.024402 18.67 34.40 1403.83 Test 9 465.70 10.41 0.022353 19.70 30.59 1306.88 Test 10 385.16 10.24 0.027495 18.83 31.41 1306.74 Average 400.5507 10.40 0.026237 21.58 32.39 1338.01 Sample calculations for Sample A specimen 1 Tensile Strengh@PL(psi) = Force ( lb) Cross−sectional area (i n2 ) ¿ ¿=436.358N /¿¿ = Tensile Strength at Yield =10.17694 MPa/m2 We measure the tensile strength at the yield point because is the highest point on the graph on the stress-strain curve, the highest it can withstand without deformation 9 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Tensile Strengh@PL(psi) = Force ( lb) Cross−sectional area (i n2 ) ¿ ¿ = 249.611N /¿¿ = Tensile strength at PL = 5.68784 Mpa/m2 Tensile strength at the Proportional limit on the stress-strain curve Strain@PL(in/in)= Entention@ PL ( ¿ ) Original length ( ¿ ) = 4.18343 (mm ) 50 (mm ) = 0.07012 mm/mm Strain at Yield(in/in)= Extentionat Yield ( ¿ )Original length (¿ ) = 19.0333 (mm )50 (mm ) = 0.380668 mm/mm Strain at Break (in/in) = Extentionat break (¿ ) Original length ( ¿ ) = 43.0331 (mm ) 50 (mm ) = 0.8606612 Modulus of Elasticity(psi)= Tensile Strength@PL( psi)Strain@PL (¿ /¿ ) = 5.687840.07012 (mm ) = 81.113 MOE at the Proportional Limit is calculated by using the values of stress and strain at the proportional limit. Sample A, specimen 1 also needed a toe correction. Please see the stress-strain curves below based on the above calculations: 10 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 4 Figure 5 11 Stress-Strain Curve PL Break Point Yield Point Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 6 Discussions In this lab exercise, we learned about the tensile testing of plastic polymers. From the stress- strain curve based on the results from testing Sample A specimens and Sample B specimens, we can easily recognize the elastic regions on the curve, which is where the material can recover to its original dimensions after the load is released. After the elastic region, we can see the region where the material shows its plastic properties, where some of the changes in dimensions become permanent. We calculated the Modulus of Elasticity of the two samples best on the proportional limit of the two samples on the stress-strain curve. 12 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Based on the results we can see that the Sample B specimens have a higher Modulus of Elasticity at the proportional limit on average of 400 and Sample A specimens 68. The proportional limit is where the linear relationship between stress and strain ends. When we have a higher modulus of elasticity, it means that the material needs a bigger among of stress to produce strain. This usually means that the material is stiffer and more rigid. In our case, the Sample B material is stiffer than Sample A polymers and has bigger resistance to stretching. The higher the elastic modulus of the material, the stiffer the material is and not very susceptible to permanent deformations. When a polymer has a high MOE is usually more brittle and tough, harder, and stronger and when the polymer material has low MOE is usually softer and weaker, but more ductile and elastic. E can also see that the specimens from Sample A have a lower tensile strength at yield, 11.05 on average versus 32.39 on Sample B specimens. When the polymer has a higher tensile strength is harder, stronger, and more brittle than the polymer with lower tensile strength. Usually, polymers with higher tensile strength have a higher degree of crystallinity, and based on our calculations we can say that a sample B polymer plastic has a higher degree of crystallinity than Sample A polymer. The higher degree of crystallinity a polymer has it usually has higher its density, and the intermolecular forces are stronger and more significant, hence having increased strength. The tensile strength of polymers also changes with increasing molecular weight. The higher the molecular, the higher the tensile strength, larger chains, and the intermolecular forces are stronger. You need more energy to disrupt the polymer structure and permanent deformation. In low tensile strength polymers, the molecular weight is lower and the chains can move easily because of weaker secondary bonds. . But this is not always the case with molecular weight distribution. Sometimes broad molecular weight distribution can lower the tensile strength of a 13 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance polymer. When comparing the stress-strain curve and based on its characteristics of it, we can see a lot of differences in mechanical properties of the Sample A and Sample B polymers. Based on the elongation of a PL we can see that sample B polymer specimens are harder, tougher, and stronger than Sample A polymer, but Sample A polymer can also be softer and tougher at the same time, Higher tensile strength of Polymer B shows that it is also harder, tougher and stronger, and Sample A is weaker, and not as strong. Also, we can see that Sample B polymer is more brittle than Poplymer A sample, but sample A is tougher because can higher percentage of elongation and is more ductile, and it can experience more strain before it ruptures. We can see from the stress-strain curve that it a lot more stress to produce a strain in Polymer B than in Polymer A. From both Tensile and Izod Impact tests, we can agree that the percentage of crystallinity in the plastic polymer affects its mechanical properties. Based on the tensile test results we saw that the sample with a higher percentage of crystallinity has higher tensile strength and density, is less ductile, and needs a lot more energy to produce a stretch. But from the results of the Izod Impact test, we see that with the increase in crystallinity the plastic material decreases its toughness, becomes more brittle and has lower impact strength. Lab 1 Part B: Izod Impact Strength Materials and Methods 1. The test method used is the ASTM D256-10(2018) Standard Test Method for determining the Izod Pendulum impact resistance of plastic materials 2. Equipment: Ray-Ran Advanced Universal Pendulum Impact Tester. Figures 7 and 8 14 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 7 Figure 8 3. The resin is compression molded into sheets using a Carver Laboratory Press Model 30T2 Boy machine according to the ASTM D256-10(2018) specification 4. Injection Molding Conditions: Figure 9 Figure 9 5. Dimensions of the Izod-Type Test Specimen Figure 10 15 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 10 A = 10.16 ± 0.05; B = 31.8 ± 1.0; C = 63.5 ± 2.0; D = 0.25 R ± 0.05; E = 12.70 ± 0.02 6. Conditioning procedure 23oC, 50% RH, not less than 40 hours after notching 7. Testing conditions 23oC, 50% RH 8. Sample two different unknown polyethylene samples Sample A and Sample B 9. The capacity of the pendulum in joules, or foot-pounds-force, or inch-pounds-force 10. The width of the specimen (see Fig 6 of the ASTM D256-10(2018)) 11. Number of the test specimen for each resin 5 specimens per Sample A and B 12. Type of failure for each test specimen C – Complete Break (The specimen separates into two or more pieces) H – Hinge Break (One part of the specimen cannot support itself above the horizontal when the other part is held vertically) P – Partial Break (The specimen has fractured at least 90% of the distance between the vertex of the notch and the opposite side) NB – Non-Break (The specimen has fractured less than 90% of the distance between the vertex of the notch and the opposite side) 16 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance 13. The number of those specimens in each category of failure 14. Impact strength in joules per meter, or foot-pounds-force per inch, of the width of the specimen, and the average impact strength in each category of failure except for non- break (see 11.1.8, 11.1.10, and 5.8 of the ASTM D256-10(2018)) 15. % specimen failing in each category Experimental procedure: Notching Figure 11 Notching Equipment: TMI Notching Cutter Figure 12 17 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 12 DATA Sample A and Sample B 6 specimens each. Figure 13 18 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Figure 14 Picture showing the impact and level of failure of each of the specimens from Sample A and Sample B polymers. Figure 15 19 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance Discussions In this lab exercise, we learned about the Izod impact test of materials and study the ability of different samples to deform under impact and their ability to absorb energy before they fracture. We tested two different samples Sample A and Sample B with six specimens each. The samples were made of two polyethylene resins. We can see that there is a big difference between the fracture failures of Sample A polymer and Sample B polymer. The Sample A specimens had NB failures -Non-Break at an average thickness of 0.4017 and average Impact strength of 3.61815. The Sample B specimens had all P-Partial Break failures at 0.3904 thickness on average and 2.185 Impact strength. This exercise clearly shows that the Sample A samples are tougher and can withstand impact without failures. When the samples are notched, the notch serves as a stress concentration zone. Sample A has a higher impact strength than Sample B and based on the results we can see that Polymer B has less toughness and it is the brittle polymer of the two because it can not withstand sudden impact and has lower impact strength. Toughness usually measures the energy required to cause a fracture in material and failure. We can see that the more impact strength the polymer has, the less brittle it is. The crystallinity of the polymer can influence its toughness and whether it's hard and brittle. With the increase of crystallinity, the impact strength and the toughness of the polymer decrease. The polymer can be strong, but brittle plastic with lower impact strength. Conclusions In conclusion, we successfully tested samples from different resins of polyethylene using the Tensile and Izod Impact test. The test helped us identify the different mechanical properties of 20 Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance these plastic materials and how to use the stress-strain curve in identifying these properties. We saw that some of the samples had good tensile strength, and toughness and some are more ductile and brittle. These types of tests help us choose the right plastic materials based on the application and need to use them. References 1. ASTM.‘‘D638-22 Standard Test Method Tensile Properties of Plastics”, ASTM, West Conshohocken, PA 2004. 2. ASTM.‘‘D256-10(2018) Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics”, ASTM, West Conshohocken, PA 2022 3. Adapted from Ahttp://www.msu.edu/~tanprase/Teaching.htm, Lab 1 of PKG 825, Krittika Tanprasert, 2002. 4. Principles of Polymer Systems, 6th edition, Ferdinand Rodriguez, Cohen, Ober&Archer, CRC Press, FL, 2015. 5. Plastics Packaging: Properties, Processing, Applications, and Regulations, S. E. Selke&J. D. Culter, 3rd ed. Hanser,20163 6. https://onlinelibrary.wiley.com/doi/pdf/ 10.1002/9781118950623.app1Physical,Thermal,and Mechanical Properties of Polymers Suppoer materials: - Sample A test 1 calculations with the Stress-Strain Curve excel file attached 21 https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781118950623.app1Physical,Thermal,and https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781118950623.app1Physical,Thermal,and Mechanical Properties: Determination of Tensile Properties and Izod Impact Resistance 22