双向拉伸与成核剂诱导P34HB多尺度微观结构演变

Polyhydroxylalkanoates (PHA) are a group of biopolyesters pro-duced by various bacteria, and they have attracted increasing attentions due to their outstanding biocompatibility, biodegradability and thermal processibility. Among them, P34HB (poly(3-hydroxybutyrate-co-4-hydroxybutyrate)) is the most promising fourth-generation commercial product. Via adjusting 4HB monomer ratios, P34HB can exhibit properties ranging from semi-crystalline plastic to complete amorphous elastomer. Polymer films can be oriented by biaxial stretching, as a consequence, the changes of microstructure give the drastic change in mechanical properties as well as other performances such as high-gloss, transparency, excellent gas barrier, etc. In industrial film processing, simultaneous biaxial stretching modes are widely used. In this work, P34HB with different nucleating agents will be fabricated through a cast film process and then uniaxial and biaxial stretched on a laboratory stretcher under different temperature. The microstructures evolution during uniaxial and biaxial stretching of neat and nucleated P34HB will be investigated by FTIR, in-situ Wide angle X-ray scattering (WAXS) and small angle X-ray scattering SAXS. The deformation mechanism will be studied, which may shed new light on the relationship between process, structure and mechanical property of P34HB oriented film.

聚羟基脂肪酸酯（PHA）是一类由微生物合成的羟基脂肪酸组成的线性聚酯，由于其出色的生物相容性、可降解性和热加工性而备受关注。众PHA产品中，3-羟基丁酸和4-羟基丁酸共聚酯（P34HB）最有希望成为第四代商业化产品。根据组成单体3HB与4HB 比例的不同，P34HB 具有从非常硬的高度结晶体到软的弹性体等一系列不同的材料学性质。聚合物膜在经历双向拉伸取向之后，随着微观结构的改变，机械性能、光学性能和阻隔性能等都会得到大幅度提升。在聚合物膜生产过程中，同步双向拉伸技术已经得到广泛的应用。在本工作中，以原位广角X射线衍射、小角X射线散射和红外光谱为主要研究手段，揭示加入不同成核剂的P34HB流延膜在温度、单双向拉伸外场作用下的多尺度微观结构演化机制，建立“外场-结构-性能”关系，进而指导高性能P34HB双向拉伸膜的生产。

双向拉伸聚酰胺6（BOPA6）薄膜广泛应用于包装领域，但常规BOPA6薄膜的阻隔性能相对于铝箔等高阻隔材料仍有一定差距，通过熔融共混引入具有高阻隔性的乙烯-乙烯醇共聚物（EVOH），流延成膜并进一步双向拉伸，建立PA6/EVOH薄膜热力场下的微观结构变化机制和 “外场-结构-性能”关系，进而可为高性能PA6/EVOH双向拉伸膜的生产提供理论依据。工作主要分为以下三个部分：.（1）PA6/EVOH复合材料。通过熔融共混法将EVOH与PA6基体均匀混合制备PA6/EVOH复合材料。研究发现，EVOH阻碍薄膜中PA6的γ型晶体的生成，促进α型晶体的生成，提高结晶度。PA6和EVOH之间具有较好的相容性，并且在EVOH的添加量达到15 wt%时，复合材料内部形成微观相分离结构。.（2）通过挤出流延制备PA6/EVOH（15 wt%）预制膜，而后双向拉伸。研究表明，单向拉伸促使PA6晶体的（020）晶面垂直于MD方向（MD为拉伸方向），而双向拉伸进一步促使（002）晶面平行于MD-TD平面。拉伸不仅促进PA6/EVOH薄膜结晶而且促进其晶体取向，随着拉伸比的增加，晶体的取向度增加。单向拉伸薄膜在MD的拉伸强度随着拉伸比的增加而提高，TD的拉伸强度降低，而双向拉伸薄膜的力学性能在MD和TD方向上平衡均化。此外，单向和双向拉伸均能提高薄膜的阻隔性能，且双向拉伸后的薄膜其阻隔性能更佳。.（3）制备拉伸比为3×3的PA6/EVOH双向拉伸薄膜。EVOH的引入使得，PA6/EVOH双向拉伸薄膜的阻隔性能显著增加，当EVOH的含量为35 wt%时，薄膜的阻隔性能提高超过一倍，PA6/EVOH双向拉伸薄膜的强度、模量和韧性都有所提高。由此可见，PA6/EVOH双向拉伸薄膜具备优异的力学和阻隔性能，有望作为高阻隔并具有优异综合性能的薄膜应用于包装领域。