Study On Modification Of Biodegradable Poly(3-hydroxybutyrate)

Bacterial Poly (3-hydroxybutyrate)(PHB) is well known as a kind of thermoplastic aliphatic polyester. Owning to many advantages such as biodegradability and biocompatibility, it has a well applicable prospect. However, its application is limited to a certain extent because it is quite brittle and is unstable in the molten state. In this paper, on the basis of studying the main properties of PHB, the disadvantages of PHB were improved through modification of PHB chain structure and aggregation state. The crystallization, rheological property, mechanical properties and degradability of PHB blends and copolymer were investigated in detail. The modification of PHB aggregation state included PHB/ nucleating agent,PHB/ cellulose acetate butyrate (CAB),PHB/CAB-g-polyethylene glycol (PEG),PHB/CAB/CAB-g-PHB blends and the modification of PHB chain structure was graft copolymerization of methyl acrylate(MA) onto PHB.The results showed that the original PHB had a rather high content of water-soluble impurity (inorganic salt) and low oil-soluble impurity (organic micromolecule). PHB was typical pseudoplastic fluid. The apparent viscosity of PHB decreased with shear rate and the temperature had a great effect on the apparent viscosity.When nucleating agent was added, the crystalline temperature and crystalline rate of PHB increased; the size of PHB spherulites decreased; the thermostability and mechanical property of PHB were improved. Polymer-nucleating agent had a greater effect than inorganic nucleating agent.When CAB was added, the crystallinity of PHB decreased; the PHB spherulites became small and imperfect. Compared with pure PHB, the flow temperature of PHB/CAB blends decreased; thermal degradation was reduced and the processability was improved. But the mechanical properties of PHB/CAB blends were not good because PHB and CAB were not miscible when PHB percent was high. The elongation at break of PHB/CAB blends was very low. Unlike PHB/CAB blends, PHB/CAB-g-PEG blends were miscible system because of the introduction of PEG long side chain. So the toughness of these blends was much better than PHB/CABblends and showed obvious characteristic of tenacity fracture. As for as PHB/CAB/CAB-g-PHB blends concerned, the miscibility of PHB and CAB was improved when CAB-g-PHB graft copolymer was added. The CAB-g-PHB took effect as compatilizer of PHB/CAB blends. So the toughness of PHB/CAB/CAB-g-P blends was much better than PHB/CAB blends.The study on PHB-g-PMA graft copolymer showed that reactive condition had a great effect on graft ratio of copolymer. The melting temperature of copolymer decreased and the spherulites became more imperfect when graft ratio increased. Because of the introduction of PMA flexible side chain, the PHB-g-PMA graft copolymer had better processability and mechanical properties than PHB.