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Title: Extrusion foaming of bioplastics for lightweight structure in food packaging
Authors: Duangphet, Sitthi
Advisors: Song, J
Tarverdi, K
Keywords: PHBV;Crystallization;Rheology;Thermal degradation;Tensile testing
Issue Date: 2012
Publisher: Brunel University School of Engineering and Design PhD Theses
Abstract: This thesis reports the systematic approaches to overcome the key drawbacks of the pure PHBV, namely low crystallisation rate, tensile strength, ductility, melt viscosity, thermal stability and high materials cost. The physical, mechanical, thermal, and rheological properties of the pure PHBV were studied systematically first to lay a solid foundation for formulation development. The influence of blending with other biopolymers, inclusion of filler, and chain extender additives in terms of mechanical properties, rheology, thermal decomposition and crystallization kinetics were then followed. Creating lightweight structures by foaming is considered to be one of the effective ways to reduce material consumption, hence the reduction of density and morphology of PHBV-based foams using extrusion foaming technique were studied comprehensively in terms of extrusion conditions (temperature profiles, screw speed and material feeding rate) and the blowing agent content. The material cost reduction was achieved by adding low-cost filler (e.g. CaCO3) and reduction of density by foaming. The thermal instability was enhanced by incorporation of chain extender (e.g. Joncryl) and blending with a high thermal stability biopolymer (e.g. PBAT). The polymer blend also improved the ductility. Adding nucleation agent enhanced the crystallization rate to reduce stickiness of extruded sheet. The final formulation (PHBV/PBAT/CaCO3 composite) was successfully extruded into high quality sheet and thermoformed to produce prototype trays in an industrial scale trial. The effect of the extrusion conditions (temperature profiles, screw speed and material feeding rate) and the blowing agent content are correlated to the density reduction of the foams. 61 and 47 % density reduction were achieved for the commercial PHBV and the PHBV/PBAT/CaCO3 composite respectively and there exists further scope for more expansion if multiple variable optimisation of the conditions are carried out.
Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.
Appears in Collections:Brunel University Theses
Mechanical and Aerospace Engineering
Dept of Mechanical Aerospace and Civil Engineering Theses

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