聚羟基脂肪酸酯（PHA）是一类完全由微生物合成的生物高分子，具有生物相容性、生物可降解性、光学活性和压电性等优异性能，受到研究者们广泛关注。为了改善PHA材料结晶速率慢、室温下存在二次结晶以及高成本限制应用等不足，本文通过引入成核剂、研发新型聚合物、改善加工工艺进行PHA结构的调控和性能优化；同时通过功能化改性PHA，寻求新型高附加值的应用领域。围绕PHA的结构、性能和应用，本文进行了以下研究：针对3-羟基丁酸和4-羟基丁酸的共聚物P3HB4HB结晶速率慢的问题，发现尿嘧啶可以显著加快P3HB4HB的结晶。实验结果表明随着尿嘧啶含量的增加，P3HB4HB的结晶温度Tc升高，球晶尺寸减小，同时成核密度提高。引入1 wt%尿嘧啶，可以使P3HB4HB在95°C的等温结晶半结晶时间降至2.37分钟，仅为纯P3HB4HB半结晶时间的3.5%。原位变温红外光谱的结果发现尿嘧啶和P3HB4HB分子链具有显著的相互作用，有助于初级晶核的形成。本文系统研究了分段补料方法生产的P3HB4HB的组成和结构。该P3HB4HB显示出多重熔点，并表现出等温结晶温度和非等温结晶升温速率的依赖性。通过分级沉淀的方法获得六个分级组分。随着4HB比例的升高，材料的断裂伸长率增加，拉伸强度和杨氏模量降低，降解速率加快。针对P3HB4HB材料的二次结晶问题，本文设计了三种拉伸工艺来探究加工工艺对P3HB4HB结构和性能的调控，结果显示三种拉伸膜的拉伸强度可以在一个月内保持相对稳定，明显改善P3HB4HB的二次结晶现象。最后，为了克服PHA材料的高成本对其推广的限制，本文对PHA进行功能化改性。通过相分离的方法成功制备了表面具有特殊浸润性的3-羟基丁酸和3-羟基己酸共聚物PHBHHx膜。随着PHBHHx溶液的浓度的增加，PHBHHx膜的表面微观结构依次为网络状、叶片状、花朵状和多孔球状。在实验中本文成功制备了接触角大于150°的超疏水PHBHHx膜。在水油分离实验中，超疏水PHBHHx膜具有高度选择性和吸附能力。在细胞、血小板和细菌的粘附实验中也显示出优异的抗生物粘附性能，可以进一步开发为医用植入材料。
Polyhydroxyalkanoates (PHAs) are a family of biopolyesters synthesized by various microorganisms. They have attracted increasing attentions due to their outstanding biocompatibility, biodegradability, optical activity and piezoelectricity. This study aims to increase the crystallization rate of PHA, overcoming secondary crystallization and reducing the limitation on high cost of PHA. Effective nucleating agents are targeted, new polymer for improving performance of PHA has been successfully developed and three kinds of drawing methods are designed. On the other hand, functional PHA for high value-added applications were prepared. This study focused on the structure, performance and applications of PHA with the following results:It was found that uracil can significantly accelerate the crystallization of random copolymers of 3-hydroxybutyrate and 4-hydroxybutyrate (P3HB4HB). It was shown that the crystallization temperature (Tc) of P3HB4HB increased with increasing uracil content. The size of spherulites was reduced and the nucleation density was increased. The crystallization half-times (t1/2) of P3HB4HB decreased significantly in the presence of uracil. With addition of 1 wt% uracil, the t1/2 value of P3HB4HB crystallized at 95°C was 2.37 min, only 3.5% of the neat polymer crystallization time. In-situ FTIR spectra revealed the interactions between uracil and P3HB4HB in composites that helped induce some precursory structures.The composition and structure of the novel polymer P3HB4HB produced via fed-batch were investigated. P3HB4HB showed multiple melting points during studies on isothermal crystallization and non-isothermal crystallization. The melting points exhibited dependences on the temperature of isothermal crystallization and on the rate of non-isothermal crystallization. Subsequently, six fractions were generated from a fractional precipitation method. As the proportion of 4HB increased, the elongation at break of the block copolymer material increased, the tensile strength and Young's modulus decreased and the degradation rate was increased. In order to overcome the secondary crystallization for improving the ductility of P3HB4HB, three drawing processes were developed to explore the regulation of the structure and properties of P3HB4HB. Mechanical property studies showed that the tensile strength of the three stretched P3HB4HB films became relatively stable within one month, this significantly prohibited the secondary crystallization of P3HB4HB. Finally, functionally modified PHA were developed to expand the application of PHA into high value-added fields to overcome the limitation on the high PHA cost. Random copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx) films with special wetting properties was prepared via phase separation. With the increase of PHBHHx concentrations, structures of leaf-shapes, flowers-like patterns, domains and microspheres were formed, respectively. A superhydrophobic PHBHHx film with a contact angle larger than 150° was obtained. The results of water/oil separation shown that the superhydrophobic PHBHHx film has a high selectivity and adsorption capacity in water/oil separation. It also showed excellent anti-bioadhesive properties in adhesion experiments of cells, platelets and bacteria, which can be further developed into medical implant materials.
