If the soft PVC carrier and the PE film are purchased materials, analytical laboratory resources will be needed for quality control to identify the raw materials used. Often, all additives contained in all materials used must be identified in order to ascertain their compatibility with the adhesive, which of course must also undergo compositional analysis. The focus of the product quality control efforts would typically be the determination of the polymer composition and the adhesive resin content. For these and similar tasks, Pyrolysis-GC/MS has proven particularly useful. Thermal fragmentation followed by GC separation and MS determination offers a range of possibilities for qualitative and quantitative analysis as the three following examples show.
Using Pyrolysis GC/MS to determine additives in polymers
To help assess, whether an adhesive would be compatible with a PVC carrier film, the plasticizer used in the PVC was determined. A combined analysis procedure of IR spectroscopy and pyrolysis GC/MS was used; in both cases, methods were selected, which didn’t rely on solvent-based extraction. Based on the IR analysis, it was determined that there was polyurethane in the PVC, but no phthalate. The PVC film was then pyrolyzed at 800 °C and the fragments identified. In addition to the hydrochloric acid fragment, which is to be expected when pyrolyzing PVC, a high intensity peak for the hexamethylene diisocyanate (HDI or HMDI) fragment was found. This information made it clear that a polyurethane- based plasticizer, which contained HMDI as isocyanate component, was used for the PVC. Based on experience, the plasticizer was deemed compatible for use with the adhesive.
Quantifying additives with pyrolysis GC/MS
In order to quantify adhesive resin content, in this case rosin aka colophony resin, a pyrolysis GC/MS method based on matrix- matched calibration was developed. The main challenges during method development were to identify and select suitable pyrolysis fragments as markers for individual adhesive resins and to optimize sample preparation in order to achieve adequate reproducibility. Methyl abietate (m/z = 316) was selected as marker for rosin methyl ester (see figure). For hydrated rosin resins, norabietan (m/z = 262) was used as quantification marker. Both methods were developed as Single Ion Monitoring (SIM) methods in order to achieve better signal to noise ratios and higher sensitivity. The sample preparation was optimized as follows: The adhesive material sample was weighed on silicone-coated release paper, i.e. anti-adhesive paper (sample weight: 0.5-1 mg). Then the sample was sprinkled with a fine glass powder, which prevents the sample from adhering to the pyrolysis tube without interfering with the pyrolysis process and without impacting the analysis result. For all samples and calibration standards, duplicate analyses were performed and the mean values used. Calibration standards were generated by adding 5 to 40 % (w/w) rosin resin to resinfree polyacrylate adhesive material made up of n-butyl acrylate, 2-ethylhexyl acrylate and acrylic acid. The calibration standards were pyrolyzed at 800 °C resulting in a calibration curve with a correlation coefficient of 0.9916. The calibrated methods were subsequently used to determine both the rosin resin and the hydrated rosin resin contents in polyacrylate adhesives. Additional hydrated resin types were analyzed to determine whether hydrated rosin glycerol ester resin or other esterbased resins could be analyzed quantitatively. Multiple rosin methyl ester resins from different manufacturers were finally analyzed. For both methods it was found that the rosin resin content could be determined with a standard deviation below 4 %. Given the highly heterogeneous nature of such adhesive resins, the developed pyrolysis GC/MS methods for quantitative determination of resin content are considered sufficiently accurate. Using this method, the rosin resin content of polyacrylate adhesives can be determined for quality control purposes. Further investigations will determine whether the methods can be applied to other matrices such as synthetic caoutchouc materials. It should also be possible to expand the use of the method to determine other resin classes such as polyterpene resins and hydrocarbon resins.
Pyrolysis GC/MS is a versatile technique, which can be used for qualitative as well as quantitative analysis of polymers in general and, as shown in this work, also of adhesive materials. Of particular benefit to the analyst is the very limited effort required for sample preparation as well as the considerable depth of information obtained – even from just a single analysis. Editor: GDeußing
Source and further more information
 Aylin Meß, Vjaceslav Frank und Andreas Westphal, tesa SE, Quickbornstraße 24, 20253 Hamburg
 Automated Pyrolysis