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The objective of this study is to conduct FTIR and DSC analysis on laminated paper cup coating samples to determine the composition. Excelplas undertakes forensic analysis for various coating based failure investigations and problem solving with its Laboratory situated in Melbourne, Australia. FT-IR analysis was performed according to ASTM E 573, using an Alpha Measurement Module by Bruker Optik. The thermal analysis by DSC was performed according to ASTM D 3418, using a DSC Q20 by TA instruments.

Figure 1. Sample cups with one known to LDPE and the rest unknown

FTIR Analysis

Fourier Transform Infrared (FT-IR) spectroscopy was used for ‘finger-printing’ for material identification of the polymer and filler components. The FT-IR analysis was performed according to ASTM E573 ‘Standard Practices for Internal Reflection Spectroscopy” using an Alpha Measurement Module by Bruker Optik see figure 2. Smaller samples of the core were cut from the larger sample. Spectra of the core were searched against an internal library database for identification.

Figure 2. Bruker Optik FTIR instrument (right).

DSC Analysis

Differential Scanning Calorimetry (DSC) thermal analysis was used to determine the thermal transition temperatures of the material.

Figure 3. FTIR results with all four samples overlaid (below).

The thermal analysis by DSC was performed according to ASTM D 3418,

using a DSC Q20 by TA instruments.

Figure 4. DSC chromatogram of one samples inside coating (below).

In our opinion, and based on the results of the analysis, Set 1 ‘Control’ was found to have an inside coating composed of Low Density Polyethylene (LDPE). Set 2, Set 3 and Set 4 were found to have compositionally similar inside coatings that were consistent with a type of wax coating. The melting point of the wax coating was around 90-93°C, which is much higher than paraffinic wax, and it is likely that the wax coating may be insect or plant-based. The exact source of the wax could not be positively determined.