No abstract

Boron nitride (BN), talc, hydroxyapatite (HA), and zinc stearate (ZnSt) were investigated as nucleation agents (NA) for nonfossil-based poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) plastics. Nonisothermal crystallization behaviors of the P3/4HB/NA blends were examined by DSC. It revealed that BN is the most efficient nucleation agent to promote the crystallization rate, however, but not the crystallization degree. The lasting crystallization of P3/4HB was also removed. The nucleation effect was strengthened with increase of BN content up to 1% and then slackened deeply when further BN was added. Isothermal crystallization analysis revealed that the addition of nucleation agent BN does not alter the crystal growth mode of P3/ 4HB, with maintaining the Avrami parameter n value around 2.40. Talc did enhance the crystallization of P3/4HB with however milder crystal growth rate. HA and ZnSt did not promote, but depressed the crystallization of P3/4HB plastics.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) blend films were prepared by solvent-cast method. The nonisothermal crystallization results showed that PHBV and P3/4HB are miscible due to a single glass transition temperature (T g ), which is dependent on blend composition. The isothermal crystallization results demonstrate that the crystallization rate of PHBV becomes slower after adding amorphous P3/4HB with 19.2 mol% 4HB, which could be proved through depression of equilibrium melt point (T C and 84 C, respectively. FTIR analysis showed that PHBV/P3/4HB blend films would maintain the helical structure, similar to pure PHBV. Meanwhile, with increasing P3/4HB content, the inter-and intrainteractions of PHBV and P3/4HB decrease gradually. Besides, a lower elastic modulus and a higher elongation at break were obtained, which show that the addition of P3/ 4HB would make the brittle PHBV to ductile materials.

The biodegradable behaviors of monofilament suture made from bacterial biopolyester poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) was investigated both in lipase solution and by implant into rat tergal muscles. Results showed that the monofilament suture lost its tensile strength gradually accompanied by decrease of molecular weight. The suture retained approximately 65% of its original strength after lipase degradation for 12 weeks, whereas the molecular weight decreased from 4.5 x 10(5) to 3.8 x 10(5). However, the crystallinity of the suture, after lipase degradation for 12 weeks, increased from 27 to 33%. This may ascribe to improve orientation arrangement of molecular chain in the monofilament after the fragment from amorphous regions dissolved in the buffer solution. The roughness of surface morphology increased with degradation. Rat implantation showed no remarkable tissue responses during in vivo degradation. Foreign body reactions were much milder than chromic catgut, which is one of the most common commercially available sutures.

Biopolyesters poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with an 11 mol % 4HB content [P(3HB-co-11%-4HB)] and a 33 mol % 4HB content [P(3HB-co-33%-4HB)] were blended by a solvent-casting method. The thermal properties were investigated with differential scanning calorimetry. The single glass-transition temperature of the blends revealed that the two components were miscible when the content of P(3HB-co-33%-4HB) was less than 30% or more than 70 wt %. The blends, however, were immiscible when the P(3HB-co-33%-4HB) content was between 30 and 70%. The miscibility of the blends was also confirmed by scanning electron microscopy morphology observation. In the crystallite structure study, X-ray diffraction patterns demonstrated that the crystallites of the blends were mainly from poly(3-hydroxybutyrate) units. With the addition of P(3HB-co-33%-4HB), larger crystallites with lower crystallization degrees were induced. Isothermal crystallization was used to analyze the melting crystallization kinetics. The Avrami exponent was kept around 2; this indicated that the crystallization mode was not affected by the blending. The equilibrium melting temperature decreased from 144 to 140 C for the 80/20 and 70/30 blends P(3HB-co-11%-4HB)/ P(3HB-co-33%-4HB). This hinted that the crystallization tendency decreased with a higher P(3HB-co-33%-4HB) content.