Rheological characterization studies of PHB based bioplastic and its nanocomposites

Use of biodegradable plastics is considered to be one solution to the problem of disposal of undegradable plastic waste. Apart from addressing the global concern of disposal of plastic waste, bio-based biodegradable plastics can help in recycling the carbon dioxide from the environment. Polyhydroxy alkonates (PHA) are bio-degradable plastics that can be derived from biological sources and can degrade rapidly in suitable environment. Polyhydroxybutyrate (PHB) and its copolymers are members of PHA family and their properties are comparable to petroleum-based plastics like Polypropylene (PP). Certain limitations such as brittleness, sensitivity towards thermal degradation and slower crystallization limit their use in demanding applications. Further improvement in the properties of PHB based plastics is an area of active research.;Incorporation of nanofillers is one of the approaches for improvement in properties of biodegradable plastics. Layered silicate clays are found to be promising and economical nanofillers. Modification of layered silicate clays with organic surfactants results in better compatibilization with polymers. Significant improvements in properties in various base polymers have been reported by using layered silicates as nanofillers.;The present study explores the potential of improvements in properties of PHB based bioplastic by addition of layered silicate nanofillers and characterizing the resulting nanocomposites using rheological methods. The PHB based plastic supplied by Metabolix Inc. was melt blended with three organoclays, Cloisite 30B, Cloisite 93A and Cloisite 10A, obtained from Southern Clay Products. The nanocomposites were prepared by adding these clays in PHB based plastic at concentrations of 1%, 3% and 5% by weight. The compounds were tested using a parallel plate oscillatory rheometer and a capillary rheometer. Injection molded tensile specimens of these compounds were tested on Instron tensile tester.;From the rheological characterization, it was found that 93A clay exhibits reasonable level of dispersion at 5% loading levels. The tensile strength and the stiffness were also considerably increased. Rheological behavior of 10A based nanocomposites suggests excellent dispersion and possible exfoliation, however this is accompanied by drastic reduction in viscosity of the compounds and they were found unsuitable for melt processing. Rheological curves of the compounds based on 30B type clay did not show significant dispersion of the clay. Tensile strength of these compounds was found to be deteriorated.