Thermal Analysis and FTIR Study of Plastic Films Used for Packaging. Austin Wyles Shaker High School 445 Watervliet-Shaker Rd.

Transcription

1 Thermal Analysis and FTIR Study of Plastic Films Used for Packaging. Austin Wyles Shaker High School 445 Watervliet-Shaker Rd., Latham, NY Abstract: Polymers are used in many types of product packaging. These polymers are either amorphous or semi-crystalline. These polymers behave differently under different conditions. These differences can be attributed to their chemical structures and can be analyzed using different techniques such as FTIR and DSC. The FTIR technique show different functional groups and DSC experiments quantify the varying thermal properties of the samples. These allow further research on the properties of polymers. 1.1 Introduction The polymer films used in packaging can be divided into two main groups based on structure, semi-crystalline and amorphous. The structures of amorphous polymers are organically shaped, whereas the semi-crystalline plastics have similarities to both groups containing both an organic shape and an organized structure that a crystalline polymer would have. These differences in structure shapes affect their characteristics Hypothesis: How does the difference in structure (semi-crystalline and amorphous polymers) affect the DSC and FTIR experiment results? Figure Experiments We used FTIR and DSC techniques to analyze the sample polymers. Using the DSC we could easily see the difference between the semi-crystalline and amorphous polymers; also one can determine the differences between LDPE and HDPE by seeing the different peaks each have; differences that are harder to see using a FTIR experiment. An FTIR experiment shows the makeup of the of the polymer samples, by showing different bonds that are present in the plastic. 1

2 2.2 Samples a) b) c) d) Sample ID Types of Polymers Name of Samples DSC and FTIR Result Summary (a) PVDC (Polyvinylidene chloride) Stretch-Tite No melting transition between 50 o C to 250 o C Distinct 1700 cm -1 FTIR peak (must be from C=O containing plasticizer); C-Cl stretch occurs in cm -1 [2] (b) LLDPE HDPE like Glad with adhesive Tm (main) at 128 o C No 1700 cm -1 FTIR peak (c) LLDPE LDPE like Bag with LDPE Tm (main) at 122 o C No 1700 cm -1 FTIR peak (d) LLDPE HDPE like Bag from Sealed Air Packaging Tm (main) at o C No 1700 cm -1 FTIR peak Table 1. Summary of polymer types and characteristic DSC and FTIR results. 2.3 Differential Scanning Calorimetry (DSC) DSC is a type of thermal analysis instrument that gives us quick and precise transition temperatures, while using a minimum amount of a sample. From the DSC experiments one can observe transitions such as glass transitions, crystallization, melting curing and decomposition temperatures. We used TA Instruments DSC (Model Q2000) using aluminum sample pans and sample weight for analysis typically ranges between 2 mg and 3 mg. Samples are heated/cooled at a rate of 20 o C/min. TA Universal Analysis 2000 software has been used to further analyze the DSC data and prepare the figures in this report.[3] 2.4 Fourier Transform IR (FTIR) FTIR is a type of chemical analysis technique that collects data based on the infrared spectrum and how the polymers absorb regions of IR light. With this technique one can see the different bond vibrations. For example the C-H bond vibration occurs around 3000 cm^-1. And for HDPE the C-H bend happens cm -1 forms a linear bond which makes the polymer denser. In addition, the spectrum profile at wave numbers lower than 1500 cm-1 is sometime complex and called finger print region. [4] This region proves very helpful to name our polymer film samples. We have used Perkin-Elmer (Model Spectrum Two) for taking FTIR spectrum in the wavelength range of 4000 and 700 cm -1. FTIR samples were prepared on business cards where the polymer samples were placed in front of a 3 cm diameter whole in the card. [3] 2

3 2.5 Results and Discussion In Figure 2.1, sample d, the sealed air package, there is a clear melting and crystallization points. This polymer is linear low density polyethylene that has HDPE tendencies. The Tm is 125 C and the Tc is 118 C. Figure 2.1 Sample a, Figure 2.2, the cellophane shows no transition point from the glass state to a rubber form in the tested temperature range of -100 C to 250 C-. This is a clear indication that this sample is an amorphous polymer. 3

4 Figure 2.2 In Figure 2.1 on the left, Sample c, the bag with a LDPE label on it showed a clear melting and crystallization, but it also contains broader peaked regions that could be blamed on the branched parts of the low density poly ethylene polymer that the bag is made up o Figure 2.3 Figure 2.4, compares sample b and d which are both LLDPE, but sample b has HDPE properties. The branched structures of sample d give it a lower strength than sample b. Regarding sample b within the cm -1 range you see the brief double spike than could be the C-H bond that are either asymmetric or symmetric. HDPE like This can also be seen in Figure 2.5, a FTIR spectrum of a PEAD sample. The CH2 molecule can be found in the middle of the polymer and the CH3 can be found at the ends of the polymer. The CH3 makes the polymer more linear in form and therefore denser. LDPE like 4

5 Figure 2.5 Figure Conclusion In summary, by using different polymer sample structures and then comparing them with DSC and FTIR techniques, they showed how differing structures whether they re semicrystalline or amorphous, have varied FTIR and DSC results. Using the thermal analysis of the DSC combined with the IR results of the FTIR, we can then identify the polymer. If research is continued it should include further analysis of the differences of HDPE and LDPE by utilizing TGA and the DSC data to compare the different polymers. 3.2 Acknowledgement 5

6 I would like to thank the Research in Polymers Program at Rensselaer Polytechnic Institute and National Science Foundation (Award Number ). My teachers and instructors that helped spark my interest in the sciences. 3.3 References [1] [2] [3] Dr. Chang Y. Ryu [4] 6