Poly(3-hydroxybutyrate-co-3-hydroxyvalerate):Block Copolymerization Modification And Tensile Properties Of Electrospinning Membranes

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a polyester synthesized by microbial fermentation. It can be employed for ideal environment-friendly material owing to its renewable and biodegradability. However, PHBV has some disadvantages and its affects processing and limits to diverse application. Such as narrow processing window due to a high melting temperature and a low thermal degradation temperature, and high crystallinity which results low mechanical properties and long-term degradation. In order to overcome these performance defects, block copolymerization modification method was adopted to introduce PCL and POSS block into the PHBV molecular chain in our work. The main content and results are as follows:(1) PHBV has low reactivity because of high molecular weight and lack of hydroxy. In order to obtain reactive PHBV which would serve as material for block copolymer based on PHBV, the telechelic hydroxylated PHBV macromonomers (PHBV-diol) with low molecular weight was synthesized by alcoholysis of PHBV by dibutyltin dilaurat catalyst system and p-toluene sulfonic acid catalyst system respectively. The results showed that crystal structure of PHBV-diol had no obvious change compared with PHBV; PHBV-diol showed double melting phenomenon and melting temperature was 20? lower than that of PHBV; The thermal stability of PHBV-diol was improved.(2) POSS/PCL hybrids which would serve as material for block copolymer based on PHBV were synthesized by using hydroxylated POSS as initiator to initiate ring-opening polymerization of e-CL. Crystal structures, melting and crystallization behavior and crystal morphologies of POSS/PCL hybrids were studied. The results showed that the crystallization of PCL segment and POSS segment were hampered mutually. In high POSS-containing PCL hybrids, POSS and PCL segment could form separated crystalline phase and the crystal morphologies of PCL matrix was similar to the shape of "snowflake". Mo method was successfully described non-isothermal crystallization kinetics of POSS/PCL hybrids. Thermal degradation of POSS/PCL hybrids were studied and found that thermal stability of POSS/PCL hybrids was improved compared with PCL homopolymer and the thermal decomposition proceeded by four-step.(3) PHBV/PCL/POSS block copolymers were synthesized by using 1,6-hexamethylene diisocyanate (HDI) as coupling agent, POSS/PCL hybrids and PHBV-diol as reactants (two step method). Another PHBV/PCL/POSS block copolymers were synthesized by using 1,6-hexamethylene diisocyanate (HDI) as coupling agent, PCL, POSS and PHBV-diol as reactants (one step method). These two kind of PHBV/PCL/POSS block copolymers had different chemical structure. Crystal structures, melting and crystallization behavior and thermal stability of PHBV/PCL/POSS block copolymers were studied. The results showed that PHBV block could form crystalline phase and PCL or POSS block could form crystalline phase as the content increased. During the cooling scan, high content of POSS block hindered the crystallization of PHBV and PCL block. The crystallization temperature of the three block were lower than that of their corresponding homopolyer which indicated that crystallization of the three block was hampered mutually. During the heating scan, the cold crystallization of PHBV block was observed, the melting temperature of PHBV block was 20-30? lower than that of original PHBV. In the PHBV/PCL/POSS block copolymers prepared from POSS/PCL prepolymer, the melting temperature of PHBV block remained almost constant with increasing PCL content, while it decreased in PHBV/PCL/POSS block copolymers prepared from low molecular weight PCL and POSS. The degree of crystallinity of PHBV block was lower than that of original PHBV. The thermal degradation of PHBV/PCL/POSS block copolymers proceeded by four-step and the thermal stability was less than original PHBV.(4) The PHBV/PCL/POSS block copolymers fiber was obtained by electrospinning. The results indicated that the spinning voltage and spinning distance had big effect on morphology of the fiber. The crystallinity of PHBV/PCL/POSS block copolymers fibrous membranes was lower than that of PHBV. The tensile strength and the elongation at break of PHBV/PCL/POSS block copolymers fibrous membranes were increased and the elongation at break increased by 78 times compared to original PHBV.