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FTIR and DSC of polymer films used for packaging:LLDPE, PP and PVDCJohn PetrovichSHAPE American High SchoolAbstract:Polymers are compounds used in various materials. There are a plethora of methods usedto analyze the composition and other properties of the material; these include Fourier TransformInfrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The profiles of theDSC display varying melting peaks and glass transition regions for different samples. Thisindicates that DSC can be used to determine different qualities of polymeric materials whichinclude, but are not limited to, high density character, low density character, amorphousness, andsemi crystallinity. We found from the DSC profile that the melting point for variouspolyethylene samples range from approximately 120-130 degrees C. The DSC profile for thepolypropylene (PP) shows peaks at 163 and 156 degrees C at the main and secondary meltingpeaks respectively. The DSC profile for Stretch-Tite does not even have melting peaks. Itinstead has glass transition regions found at approximately 60 and 95 degrees C. The lack of amelting peak in the polyvinylidene chloride (PVDC) sample is indicative of an amorphouspolymer.Introduction: Polymer films are extensively used commercial packaging. Species used in packaginginclude, but are not limited to polyester (PET), polyamide, polyvinyl chloride (PVC),polystyrene (PS), polypropylene (PP) and polyethylene (PE).Polyethylene can form with different densities. These include low density (LDPE), linearlow density (LLDPE), medium density (MDPE), high density (HDPE), and ultra-highdensity (UHDPE).It is possible for samples of LLDPE to take on characteristics of either LDPE or HDPE.Polymers can exist in two different morphologies while in a solid phase:o Amorphous: Molecules are randomly oriented within the polymer. Thesepolymers can easily be altered in shape and generally exist in a rubbery state.o Semi crystalline: An arrangement of ordered molecules with some amorphousregions. These polymers are stiff and exist in a glassy state.This paper is focused on answering the following hypotheses:Hypothesis: Can we utilize DSC and FTIR data to determine why different LLDPEsamples exhibit properties similar to either LDPE or HDPE? Can one identify whether apolymer material is crystalline or amorphous based upon DSC melting temperature data?1

Samples:The pictures of the polymeric material samples that we used in this experiment are shownin figure 1. These samples are used in the physical state seen in the pictures.(a)(b)(d)(e)(c)(f)Figure 1: (a) Ziplock Sandwich Bags, (b) PE-LD bag with recycling code 4, (c) Glad wrap withadhesive side, (d) Act II popcorn bags, (e) Stretch-Tite Saran Wrap, (f) Walmart BagDifferential Scanning Calorimetry (DSC):DSC is a method of analysis that allows the user to measure glass transition, meltingtemperature, and crystallization temperature while a polymeric material sample is being heatedor cooled. Each polymer film tested had a specific melting and recrystallization point that wasreflected in the DSC as an endothermic and exothermic peak, respectively. During our research,we subjected various samples through a heating phase, a cooling phase, and another heatingphase.We used a TA Instruments DSC (Model Q2000) using low mass Aluminum sample pansand a sample weight with a mass of approximately 2-3 milligrams. The polyvinyl chloridesample was heated/cooled at a rate of 20 degrees centigrade per minute. All other samples wereheated/cooled at a rate of 10 degrees centigrade per minute. For the data analysis of the DSCprofiles, TA Universal Analysis 2000 was used.Fourier Transform Infrared Spectroscopy (FTIR):FTIR is a spectroscopic method of analysis where IR rays are absorbed by bonds in amolecule. These IR ray’s energy can be related to the vibrational energy of different bondsfound within different functional groups in a compound. To provide a few examples, one might2

be able to find a relatively large O-H peak at approximately 3500-3200 cm-1. Anotherprominent example that can be seen in a plethora of polymer samples in the carbonyl functionalgroup peak (C O) which occurs at about 1690 – 1820 cm-1. Peaks in lower energy areas on anFTIR graph are collectively known as the fingerprint region. Each region is unique for anindividual compound and are thus extremely helpful in comparisons between different FTIRgraphs.The exact model used in this research was the Perkin Elmer (Model Spectrum Two) fortaking spectrum data in the wavelength range of 4000-7000 cm-1. Samples were prepared bycutting 3 cm in diameter from each film and taping it to a Rensselaer Summer Program businesscard.Results:FTIR: The first portion of my research involved placing my samples into a FTIRspectrophotometer in hopes of revealing differences in functional groups between the variouspolymers. The following IR spectra are from those that I prepared with the assistance of variousteacher’s assistants:(a) Ziplock Bag (PE)(c) Glad Wraps with Adhesive (PE)(b) Bag PE-LD (PE)(d) Walmart Bag (PE)3

(e) Act II Popcorn Wrapper (PP)(f) Stretch-Tite Wrap (PVDC)FTIR spectra from previously published polymer chemistry literature is seen below. Dueto a lack of HDPE or LDPE specific LLDPE FTIR spectra, comparison with the samples abovewas done with regular HDPE and LDPE spectra:Low Density Polyethylene:4

High Density Polyethylene:Polypropylene:5

Polyvinylidene ChlorideComparing my LLDPE-LDPE IR spectra with the example from previous literature, onemight tell that the same functional groups are present, but their respective peaks are of slightlydifferent proportions. One must recognize that the comparison is between LLDPE-LDPE andLDPE, and a differentiation in the amount of branching in both samples accounts for some of thedifferent proportions in peaks. Another reason for this might be due to the fact that ourexperimental samples had color additives within them. This particular possible source of errorcan be seen when the peak is fatter than the established reference.Something similar occurs when comparing the experimental LLDPE-HDPE samples withthe established reference from previous literature. This is particularly evident in the WalmartBag sample. The aromatic C-H peak approximately at 2900 cm-1 is particularly thick whencompared to findings of the European Commission. This thickness is due to the grey coloradditives found in the Walmart bag.The experimentally determined IR spectrum for PP that we generated varied a great dealfrom the spectrum from the other literature. Most of the same functional groups are still present,but there are distinct curves in the profile that are not present from the spectrum generated by theEuropean Commission. These curves are due to the sample that we used being of a relativelyhigh thickness. It is also worth mentioning a strange fingerprint region not present in thereference spectrum. This could possibly be due to additives or contamination, a much less likelypossibility considering the sample had been disinfected in a Suprasil ozone/UV oven.When one compares the LLDPE-HDPE and LLDPE-LDPE spectra, they lack anynoticeable difference in structure. The only exception would be the inclusion of additionalthickness/length to peaks due to additional branching in some samples.In a similar manner, FTIR didn’t provide much information concerning levels ofcrystallinity of polypropylene and polyvinylidene chloride besides its structure. The FTIR6

spectra generated in this experiment were similar to those determined by the EuropeanCommission except for the fact that the fingerprint regions are of slightly different proportions.This could be due to color additives, additional branching, or the reflection of IR light from thesample due to its thickness.DSC: The second portion of my research involved putting my samples in a DifferentialScanning Calorimeter in order to determine melting temperature.Ziplock Bag (LDPE-like LLDPE)Tm(Main)MeltingPeak118.54DegreesC2nd MeltingPeak105.42Degrees CHeat ofFusion113.8 J/gZiplock Bag (LDPE-like LLDPE)Tm(Secondary)Melting Peak119.64Degree C2nd MeltingPeak105.01Degree CHeat ofFusion98.07 J/g7

For this LDPE-like LLDPE DSC profile, notice that both the Tm(main) andTm(secondary) peaks are found around 118-120 degrees C. Also notice that both DSC profileshave a distinct second peak. This peak exists due to differentiating densities throughout thepolymeric sample.PD-LE Bag (LDPE-like elting PeakHeat ofFusion117.27Degrees C81.21 J/gPD-LE Bag (LDPE-likeLLDPE) ltingPeak117.27Degrees CHeat ofFusion81.21J/g8

For this sample, both main and secondary temperature peaks fall around 120 degrees C.Both DSC profiles also have an additional peak due to a differentiation in density within thepolymer sample.Glad Cling Wrap (HDPE-likeLLDPE) PeakN/AHeat ofFusion149.1J/gGlad Cling Wrap (HDPE-likeLLDPE) ltingPeakN/AHeat ofFusion149.1J/g9

This HDPE-like LLDPE sample only has one noticeably melting peak in both DSCprofiles. This is a stark contrast with the two peaks experienced in the LDPE-like LLDPEsamples. It is also worth mentioning that the melting peak is found at a higher temperature( 130 Degrees C). This is higher than the value determined for the LDPE-like LLDPE samples.Walmart Bag (HDPE-like eltingPeakN/AHeat ofFusion119.2J/gWalmart Bag (HDPE-like condMeltingPeakN/AHeat ofFusion132.7J/g10

Notice that the melting peaks for this HDPE-like sample is also close to 130 degrees C.The fact that this sample along with the other HDPE-like sample above have melting peaksnearly ten degrees higher may indicate that these species are highly ordered with little branching.Act II Popcorn Wrapper tingPeak176.98Degrees CHeat ofFusion161.2J/gAct II Popcorn Wrapper ndMeltingPeakN/AHeat ofFusion84.21J/g11

In this polypropylene sample, we experienced an anomaly at the main melting peakduring the initial heating. As seen in the first DSC profile on the page, there is an additionalmelting peak not observed in the graph directly above. This is most likely due to residualreactants from its synthesis or contamination before analysis. The second peak at approx.176.98degrees C can be attributed to this residue burning away.Stretch-Tite Wrap (PVDC)Tm(Main)1st Glass Transition60.97 Degrees C2nd Glass Transition95.36 Degrees CFor this PVDC sample, it is important to note that it lacks a melting peak. The lack of adistinctive melting point indicates that the sample has a greater amorphous character than it doescrystalline. Instead of a melting peak, the polymer film has two glass transitions, the firstoccurring at approximately 61 degrees C and the other occurring at approximately 95 degrees C.Compared to the established literature, the glass transitions are extremely high for the agreedupon glass transition temperature for PVDC falls around 16 degrees C. This difference in glasstransition temperature range can be accounted for if one considers the additives that could bepresent in the Stretch-Tite wrap.12

Conclusion:In this research project, we created various samples from polymeric materials and ranthem through FTIR spectroscopy and Differential Scanning Calorimetry. I did so with the intentof discovering whether or not one could determine why LLDPE could exhibit LDPE or HDPElike characteristics. I also carried out this research with a secondary intent of being able todetermine whether or not a polymeric sample was amorphous or semi crystalline just fromreading DSC profiles.Seeing as FTIR analysis did not provide much insight as to why LLDPE exhibitsHDPE or LDPE like characteristics past structure, I put the samples through DSC. For theZiplock bag and PE-LD bag (LDPE-like LLDPE samples), their DSC profiles show two distinctmelting peaks that occur at approximately 110 degrees C and 120 degrees respectively. For theGlad adhesive wrap and the Walmart bag (HDPE-like LLDPE samples), the DSC profiles showone distinct melting peak that occurs closer to the 125-130 degree C range. The fact that theHDPE-like LLDPE samples’ melting peaks occur a temperatures ten degrees higher than LDPElike LLDPE samples agrees with the idea that HDPE samples are more highly ordered with lessbranching. This piece of evidence supports the portion of my hypothesis where DSC caneffectively be used to determine why LLDPE can exhibit HDPE and LDPE character.The DSC profile for the popcorn wrapper (PP) shows peaks at 163 and 156 degrees C atthe main and secondary melting peaks respectively. The DSC profile for Stretch-Tite does noteven have melting peaks. It instead has glass transition regions found at approximately 60 and95 degrees C. The lack of a melting peak in the PVDC sample is indicative of an amorphouspolymer, and thus confirms the hypothesis that DSC melting temperature data can be used toconfirm whether a sample is crystalline or amorphous.Further research that could conducted involves exposing the samples tothermogravimetric analysis to see the level of thermal degradation. This would be especiallyhelpful in making firmer conclusions concerning the contamination found in the PVDC sample.Acknowledgements:I would like to thank the Research in Polymers Program at Rensselaer PolytechnicInstitute as well as the National Science Foundation (Award Number 1308617). I would alsolike to thank Dr. Ryu, Dr. Ma, Sara Till, Casey Wong, Miriam Shao, Ben Stovall, my fellowhigh school research classmates, the SHAPE American High School Science Department(particularly Todd Mitchell), and my family for their generous support