Thermal Analysis and FTIR Study of Plastic Films Used for Packaging.
Austin Wyles
Shaker High School
445 Watervliet-Shaker Rd., Latham, NY 12110
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 1.1
2.1 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 Samples
a)
b)
c)
Name of
Samples
d)
Sample ID
Types of
Polymers
(a)
PVDC
(Polyvinylidene
chloride)
(b)
LLDPE –
HDPE like
Glad™ with
adhesive
Tm (main) at 128 oC
No 1700 cm-1 FTIR peak
(c)
LLDPE –
LDPE like
Bag with LDPE
Tm (main) at 122 oC
No 1700 cm-1 FTIR peak
(d)
LLDPE –
HDPE like
Bag from Sealed Tm (main) at 126.12 oC
Air Packaging No 1700 cm-1 FTIR peak
DSC and FTIR Result Summary
No melting transition between – 50 oC to 250 oC
Distinct 1700 cm-1 FTIR peak (must be from C=O
containing plasticizer); C-Cl stretch occurs in 850
– 515 cm-1 [2]
Stretch-Tite™
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 oC/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 1350-1480 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
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 125̊ C and the Tc is 118̊ 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 -100̊ C to
250̊ C-. This is a clear indication that this sample
is an amorphous polymer.
3
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 1350-1480
-1
cm range you see the brief double spike than could be the C-H bond that are either asymmetric
HDPE like This can also be seen in Figure 2.5, a FTIR spectrum of a PEAD sample. The
or symmetric.
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
Figure 2.5
Figure 2.4
3.1
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
I would like to thank the Research in Polymers Program at Rensselaer Polytechnic Institute and National
Science Foundation (Award Number 1308617). My teachers and instructors that helped spark my interest
in the sciences.
3.3 References
[1] http://www.chemguide.co.uk/analysis/ir/fingerprint.html
[2]http://www2.dupont.com/Plastics/en_US/assets/images/Product/htn_whitepaper_r8_fig01.gif
[3] Dr. Chang Y. Ryu
[4] http://www.scielo.br/img/revistas/po/2011nahead/aop_0666fig02m.jpg
6