McChalicher Christopher W J, Srienc Friedrich
Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, MN 55455, USA.
J Biotechnol. 2007 Nov 1;132(3):296-302. doi: 10.1016/j.jbiotec.2007.04.014. Epub 2007 Apr 29.
Mechanical testing of solvent cast films consisting of short-chain-length (SCL) polyhydroxyalkanoate (PHA) films suggested that films consisting of block copolymers retained more elasticity over time with respect to films of similar random copolymers of comparable composition. Two experimental techniques, wide angle X-ray scattering (WAXS) and uniaxial extension, were used to quantitatively investigate the structure-property relationship of bacterially synthesized PHA block copolymers of poly(3-hydroxybutyrate) (PHB) homopolymer and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) random copolymer (PHBV) segments. Uniaxial testing experiments yielded the Young's modulus, ultimate tensile strength, and the elongation until fracture of the films. Percent crystallinity was determined by deconvolution of amorphous and crystalline scattering peaks obtained from WAXS. Two PHBV films containing either 8% 3-hydroxyvalerate monomer (3HV) or 29% 3HV exhibited a quick transition to brittle behavior, decreasing to less than 20% percent elongation at fracture within a few days after annealing. Conversely, the block copolymer samples remained higher than 100% elongation at fracture a full 3 months after annealing. Because block copolymers covalently link polymers that would otherwise form thermodynamically separate phases, the rates and degrees of crystallization of the block copolymers are less than the random copolymer samples. These differences translate into materials that extend the property space of biologically synthesized SCL PHA.
对由短链长度（SCL）聚羟基脂肪酸酯（PHA）制成的溶剂浇铸薄膜进行的力学测试表明，与组成相当的类似无规共聚物薄膜相比，由嵌段共聚物组成的薄膜随时间推移保留了更多弹性。采用广角X射线散射（WAXS）和单轴拉伸这两种实验技术，定量研究了细菌合成的聚（3-羟基丁酸酯）（PHB）均聚物和聚（3-羟基丁酸酯- co - 3-羟基戊酸酯）无规共聚物（PHBV）链段的PHA嵌段共聚物的结构-性能关系。单轴测试实验得出了薄膜的杨氏模量、极限拉伸强度和断裂伸长率。通过对WAXS获得的非晶和结晶散射峰进行反卷积来确定结晶度。两种分别含有8% 3-羟基戊酸酯单体（3HV）或29% 3HV的PHBV薄膜表现出快速转变为脆性行为，并在退火后几天内降至断裂伸长率小于20%。相反，嵌段共聚物样品在退火后整整3个月内的断裂伸长率仍高于100%。由于嵌段共聚物将原本会形成热力学分离相的聚合物共价连接起来，因此嵌段共聚物的结晶速率和结晶度低于无规共聚物样品。这些差异转化为扩展了生物合成SCL PHA性能空间的材料。
