Study On The Crystallization And Viscoelastisity Of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) (PHBV)

PHBV, one of Polyhydroxyalkanoates (PHA) family, has been considered as biodegradable and biocompatible polymer that will significantly extend the range of biomaterial application suitable for tissue engineering. However, the brittleness of PHBV limits its application. In this study, based on the crystallization of PHBV, several problems are mentioned, including the viscoelasticity, the influence of annealing to crystal structure and the crystallization of electropun PHBV. Based on these study of structure and properties, the origin of brittleness was analyzed, while a method of revolve this problem was provided. Moreover, crystallization of PHBV during electrospinning was studied.Statistic tests (including creep and stress relaxation) and dynamic mechanical tests of PHBV fibers were studied. Results shows that the creep strain increases with the increase of measuring temperature at constant applied stress while creep ratio becomes. With the store time goes on, the compliance and the balance stress of PHBV fibers decrease, due to the increase of crystallinity. Obviously, fresh PHBV fibers performelasticity behavior at first, then turn to plasticity behavior and finally become brittle. In the dynamic mechanical analysis, the change of a transition with the frequency can be described by the Arrhenius Equation.The activation energy of a transition is 68.15KJ.Annealing of PHBV was also conducted. It is observed that annealing improved the physical property of PHBV. During annealing, the molecular chain rearranged and the lamellar thickness increased, which made the crystal-amorphous interface decreased. Thus the constraint to the amorphous chains is decreased, let to the improvement of strength and break elongation. In addition, the influence of anneal temperature and time to the physical property were studied. The best annealing temperature is between 110°C-120°C, annealing time is about one hour.An electrospinning method was used to fabricate biodegradable Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofibers. Samples' crystal structure and crystallinity were investigated by wide angle x-ray diffraction (WAXD) and different scanning calorimetry (DSC). Surprisingly, the same crystal structure and similar crystallinity were found in electrospun and bulk PHBV samples in this study On the other hand, electrospun PHBV crystallizes in a very short time, while normally it takes near one week to get the constant crystallinity from melt or solution. An enhanced self-seeding model was purposed to explain theabove phenomena. This model indicates that a huge amount of nuclei formed during the elctrospinning process due to the very large surface ratio to volume, while solvent evaporation only influences the crystal growth step.