Location: Plant Polymer ResearchTitle: Thermal and mechanical properties of compression-moulded poly(lactic acid)/gluten/clays bio(nano)composites Author
|Mohamed, Abdellatif - King Saud University|
|Alamri, Mohammed - King Saud University|
|Hussain, Shahzad - King Saud University|
|Alruqaie, I - King Saud University|
Submitted to: Polymers & Polymer Composites
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2015
Publication Date: 1/2/2016
Citation: Mohamed, A.A., Finkenstadt, V.L., Gordon, S.H., Alamri, M.S., Hussain, S., Alruqaie, I.M. 2016. Thermal and mechanical properties of compression-moulded poly(lactic acid)/gluten/clays bio(nano)composites. Polymers & Polymer Composites. 24(5):375-386.
Interpretive Summary: Bio-composites comprised of agricultural-based polymers blended with biodegradable plant-based fillers are being produced to develop green polymeric biodegradable materials that have properties comparable to those of petroleum-based plastics. Poly(lactic acid) is a biodegradable bio-polymer prepared through lactic acid fermentation followed by controlled polymerization. Gluten is a high molecular weight viscoelastic wheat protein composed of monomeric subunits that influence the formation of flour dough in baking. Nanoclays are naturally occurring mineral particles that are known to increase the tensile and other viscoelastic properties when added to bio-composite materials. In this research we prepared novel blends of poly(lactic acid), gluten and two nanoclays in a melt mixer and compression-molded them to produce hydrophobic, yet biodegradable thermoplastic bio-composites. We then tested the new poly(lactic acid)/gluten/nanoclay bio-composites for many thermal and mechanical properties using some of our state-of-the-art instruments and analytical methods. Potentially useful behavior was observed in their melting and transition temperatures, thermal degradation rate tensile strength, water sensitivity and biodegradability. These are promising results for performance of flexible and rigid packaging such as films, bottles, trays, and wire and cable coatings used for electronics. The new bio-composites could extend product shelf life and even protect and remove bacteria in fresh food.
Technical Abstract: Bio(nano)composites comprising agricultural-based polymers blended with biodegradable plant-based fillers and clays were produced to develop novel hydrophobic, yet biodegradable materials that have properties comparable to those of petroleum-based plastics. Poly (lactic acid) (PLA), wheat vital gluten (VG), and 3, 6, and 9% nanoclays (NC1 or NC2) were mixed in a Haake Rheocord torque rheometer at 170°C for 10 min. Blends were compression-moulded and tested using modulated DSC (MDSC), thermogravimetric analysis (TGA), Instron, FTIR, and HPLC. The DSC profile of neat PLA exhibited a glass transition (Tg) and exothermic (Cry) followed by endothermic (Mel) transitions. The profile showed a Tg of 0.46 J/g/°C, Cry with 29.6 J/g, whereas Mel exhibited 28.3 J/g. Vital wheat gluten displayed a single Tg (0.45 J/g/°C). Enthalpic relaxation of PLA was noted in the presence of clays, where the overall DSC profiles of PLA were different, especially during melting. The hydrophobic nature of NC1 clay created shoulders during PLA melting. The degradation kinetics of the blends followed a multistep mechanism, as shown by the TGA data. The tensile strength dropped because of processing and due to the addition of clay, whereas elongation was reduced by the presence of NC1. Higher Young’s modulus value due to NC1 or NC2 indicated stiffer bio(nano)composites. Better biodegradability was indicated after proteinase-K enzyme treatment in the presence of NC1. Due to the hydrophobic nature of NC1, the amount of the acetic acid-extractable protein was reduced. FTIR analysis showed no evidence of chemical reaction between PLA, gluten and the clays, but suggested the occurrence of significant non-covalent intermolecular interactions.