Study On Modification And Fiber Formation Of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (phbv)

Poly(3 -hydroxybutyrate-co-3 -hydroxyvalerate)(PHBV)copolymers are microbial polymers,presenting the advantages of biodegradability, bioabsorption and biocompatibility,attracting wide attention of many scientists and researchers.However,the application of PHBV has often been limited by some disadvantages,such as slow crystallization rate, high crystallinity,poor thermal stability,low elongation at break. Modification of PHBV has received attentions in resent years.Due to the characters of PHBV,PHBV fiber shows many drawbacks in the processing of melt spinning,for example,the fiber intensity is much low,which was leaded by bad thermal stability of PHBV in the melt spinning process,and the slow crystallization rate leads that as-spun fiber of PHBV is brittle and sticky.These have limited the application of PHBV in spinning field.Therefore,this paper used the methods for increasing the molecular weight of PHBV and decreasing the decline of molecular weight in the melt processing to improve the fiber physical performance.The second part,the titanium(TiO₂)and carbon dioxide polymer(PPC)were selected to blend with PHBV,the result showed that the crystallization rate of PHBV was increased,and the fiber was not brittle and sticky again.Through the physical blending and reactive extrusion,it can accelerate the application for PHBV melt spinning.For increasing the molecular weight of PHBV,the chemical chain extension of PHBV was studied.As the chain extender,the isophorone diisocyanate(IPDI)prepolymer was synthesized,which was the polymerization production of poly(2-methyl-1,3-propylene adipate) (PMPA)and IPDI firstly.Then the chain extension of PHBV was studied using the methods of chain extension in solution state and solid state polymerization.The results indicated that it was not to improve the molecular weight of PHBV effectively,because the molecular chain was large,and the thermal degradation was easy to occur.Based on this,the method of reactive extrusion was studied in detail. The result showed that this method didn't improve the molecular weight of PHBV comparing with pure PHBV,but it could increase the molecular weight of PHBV greatly compared with melting extrusion with non-adding prepolymer.This indicated that in the process of reactive extrusion,the thermal degradation and chain extension were all existent and competitive synchronously,and the result also indicated that the crystallization rate and crystallization capability of PHBV were decreased, which was harmful for improving the fiber properties.To improve the fiber brittleness,the effect of TiO₂ on the spinnability of PHBV was researched.By studying the crystallization capability of PHBV/TiO₂ blending,the result showed that TiO₂ became the nucleating agent of PHBV and reduced the spherulite dimension,so the brittleness and stickiness of PHBV fiber was limited availably,the as-spun fiber also exhibited some soft behavior and drawing properties,and the fiber was not easy to change to brittleness.And by adjusting the processing conditions during the spinning,the PHBV blends fiber that had good properties to spinning.In conclusion,through the study of reactive extrusion of PHBV and the research of PHBV/TiO₂ blends,these would establish a theoretic foundation for the blending,reactive extrusion and direct spinning of PHBV,IPDI prepolymer and TiO₂.