Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2008
Publication Date: 9/8/2009
Citation: Mohamed, A., Finkenstadt, V.L., Gordon, S.H., Biresaw, G., Palmquist, D.E., Rayas-Duarte, P. 2009. Thermal Properties of Extruded Injection-Molded Polycaprolactone/Gluten Bioblends Characterized by TGA, DSC, SEM and Infrared Photoacoustic Spectroscopy. Journal of Applied Polymer Science. 110(5):3256-3266.
Interpretive Summary: Despite the convenience and the practicality of petroleum-based polymers used for food and other consumer goods packing, there is evidence for ecological disturbance. The development and use of biodegradable plastics in packaging for environmental protection has been stimulated by public concerns and interest. Most polymer composites are difficult to recycle or incur substantial cost for disposal. Green composites use agricultural-based polymers and biodegradable plant-based fillers. Preparation of beneficial polymer composites is possible only when the biodegradable polymers are compatible with the bio-fillers. Compatibility can be determined by measuring the degree of intermolecular interactions between the biodegradable polymers and bio-fillers in the bio-composites. In this work, the degree of interaction in polymer bioblends containing natural biodegradable polymer and vital wheat gluten were investigated using Thermal Analysis. The study included different levels of vital gluten for up to 70% blended with a synthetic polymer (Polycaprolactone). The heat degradation mechanism of the composites was also determined. The current study will enable us to introduce these blends for consideration by the packaging industry. The blends will also reduce the cost of Polycaprolactone and increase the agriculture by-products utilization and value.
Technical Abstract: In order to determine the degree of compatibility between Polycaprolactone resin (PCL) and vital wheat gluten (VG), PCL was compounded with VG at 90:10, 80:20, 70:30, 60:40, 50:50, and 30:70. The composites were blended by extrusion followed by injection molding. Thermal, morphological, and structural properties for both extruded (EX) and injection-molded (IM) were done using, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Scanning Electron Microscope, and Fourier Transform Infrared (FTIR). Samples were heated and cooled, where neat PCL showed a glass transition (Tg) at -67.0 deg C in the heating cycle with 0.20 delta Cp, followed by a melting transition at 56.6 deg C. The cooling cycle exhibited a crystallization transition at 30.1 deg C. VG showed a Tg at 63.0 deg C and 0.45 J/g/deg C delta Cp. One degradation profile was observed in the TGA for the neat PCL and VG, while composites showed a two-step transition devoid of clear line between the two polymers. The TGA data showed that neat and PCL degradation followed a one-step mechanism, while composites showed two-steps degradation or more. The degradation activation energy (Ea) has increased at higher levels of VG due the slow degradation of VG in nitrogen environment. From the DSC and TGA data, it is apparent that some sort of interaction between PCL and VG was present. The FTIR analysis indicated the physical nature of the interaction as opposed to chemical interaction. The enzymatic activity was much higher on the extruded composites than the injection-molded as indicated by higher weight loss.