Modification Research On Reactive Blending Of Poly (Î’-hydroxybutyrate-co-Î’-hydroxybutyvalerate)

PHBV/PDLLA blends, dynamic crosslinked PHBV/PDLLA blends, dynamic crosslinked PHBV/PBS blends and PHBV/ SiO₂ composites were prepared by melt processing. Mechanical properties, phase morphologies, rheological properties, crystallization behavior and thermal degradation properties of the systems were studied.PDLLA is a kind of totally biodegradable material not depending on oil products. Properties of PHBV/PDLLA blends with different content of PDLLA were investigated. The mechanical properties of PHBV, such as tensile strength, flexural strength/modulus, elongation at break and impact strength, can be improved by incorporation of PDLLA. Phase morphology was gradually changed into a two-continuous phase structure from a sea-island phase strecture with increasing the content of PDLLA in the blends. The thermal degradation of PHBV can be restriced in a certain extent by incorporation of PDLLA. The thermal stability of PHBV was enhanced and the processing window was broadened. PDLLA accelerated nucleation of PHBV but decresed the crystallinity and the growth rate of spherulite.Dynamic crosslinking of PHBV/PDLLA was initiated by dicumyl peroxide (DCP) and the infulence of DCP content on properties of PHBV/PDLLA blends was investigated. The torque of melt blends in HAAKE mixer and the gel fraction of crosslinked PHBV/PDLLA blends increased with increasing DCP content. The testing results of mechanical properties indicated that mechanical properties of PHBV/PDLLA blends with different content of PDLLA were ameliorated after dynamic crosslinking at 0.5 phr DCP. Based on rheological experiment, the storage modulus and complex viscosity of crosslinked PHBV/PDLLA are much higher that those of PHBV/PDLLA before crossslinking. A solid-like behavior was observed in the low frequency zone resulting in a crosslinking network. SEM observation showed that, the size of PDLLA phase in blends decreased remarkably and the interface between PHBV and PDLLA became nebulated after dynamic crosslinking, indicating the interfacial adhension between PHBV and PDLLA increased. Results of DSC and XRD displayed that crystallization process of PHBV/PDLLA was restricted by dynamic crossslinking while a more intergrated spherulitic morphology was obtained, observed by POM.PBS is also a semicrystalline biodegradable plastic. The mechanical properties of PHBV can be improved to some extent by incorporation of PBS, but can be improved significantly after dynamic crosslinking. The influence of DCP content on properties of PHBV/PBS was studied. Stress-strain behavior showed that elongation at break of PHBV/PBS blends increased by 80-100 times after dynamic crosslinking, from 4-5% to 400%, without sacrificing yield stress. The brittleness of material was ameliorated effectively, which may result in a wide application. SEM analysis of impact fracture surface and AFM analysis of phases indicated that the interfacial adhesion was enhanced by dynamic crosslinking, and the compatibility between these two polymers increased. Results of DSC and XRD displayed that the crystallization process of PHBV and PBS was accelerated by dynamic crosslinking with an increased onset crystallization temperature. The nucleation density of PHBV spherulite in blends at 120oC increased obviously after dynamic crosslinking.SiO₂ can be uniformly dispersed in PHBV matrix. Melting behavior, non-isothermal crystallization and isothermal crystallization kinetics were investigated by DSC. SiO₂ can accerelate the crystallization process notablely through acting as a nucleation agent. The thermal onset degradation temperatures of PHBV/silica composite were higher than that of PHBV.