Rocher Lison, Ylitalo Andrew S, Di Luccio Tiziana, Miscioscia Riccardo, De Filippo Giovanni, Pandolfi Giuseppe, Villani Fulvia, Zak Alla, Menary Gary H, Lennon Alex B, Kornfield Julia A
School of Mechanical and Aerospace Engineering, Queen's University Belfast, Belfast BT9 5AH, UK.
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Polymers (Basel). 2021 May 27;13(11):1764. doi: 10.3390/polym13111764.
In situ synchrotron X-ray scattering was used to reveal the transient microstructure of poly(L-lactide) (PLLA)/tungsten disulfide inorganic nanotubes (WSNTs) nanocomposites. This microstructure is formed during the blow molding process ("tube expansion") of an extruded polymer tube, an important step in the manufacturing of PLLA-based bioresorbable vascular scaffolds (BVS). A fundamental understanding of how such a microstructure develops during processing is relevant to two unmet needs in PLLA-based BVS: increasing strength to enable thinner devices and improving radiopacity to enable imaging during implantation. Here, we focus on how the flow generated during tube expansion affects the orientation of the WSNTs and the formation of polymer crystals by comparing neat PLLA and nanocomposite tubes under different expansion conditions. Surprisingly, the WSNTs remain oriented along the extrusion direction despite significant strain in the transverse direction while the PLLA crystals (c-axis) form along the circumferential direction of the tube. Although WSNTs promote the nucleation of PLLA crystals in nanocomposite tubes, crystallization proceeds with largely the same orientation as in neat PLLA tubes. We suggest that the reason for the unusual independence of the orientations of the nanotubes and polymer crystals stems from the favorable interaction between PLLA and WSNTs. This favorable interaction leads WSNTs to disperse well in PLLA and strongly orient along the axis of the PLLA tube during extrusion. As a consequence, the nanotubes are aligned orthogonally to the circumferential stretching direction, which appears to decouple the orientations of PLLA crystals and WSNTs.
原位同步辐射X射线散射被用于揭示聚（L-丙交酯）（PLLA）/二硫化钨无机纳米管（WSNTs）纳米复合材料的瞬态微观结构。这种微观结构是在挤出的聚合物管的吹塑过程（“管材膨胀”）中形成的，这是制造基于PLLA的生物可吸收血管支架（BVS）的重要步骤。对这种微观结构在加工过程中如何形成的基本理解与基于PLLA的BVS中两个未满足的需求相关：提高强度以实现更薄的器件，以及提高射线不透性以在植入过程中实现成像。在这里，我们通过比较不同膨胀条件下的纯PLLA管和纳米复合材料管，关注管材膨胀过程中产生的流动如何影响WSNTs的取向和聚合物晶体的形成。令人惊讶的是，尽管横向存在显著应变，但WSNTs仍沿挤出方向取向，而PLLA晶体（c轴）沿管的圆周方向形成。虽然WSNTs促进了纳米复合材料管中PLLA晶体的成核，但结晶过程的取向与纯PLLA管基本相同。我们认为，纳米管和聚合物晶体取向异常独立的原因源于PLLA和WSNTs之间的良好相互作用。这种良好的相互作用使WSNTs在PLLA中分散良好，并在挤出过程中沿PLLA管的轴强烈取向。因此，纳米管与圆周拉伸方向正交排列，这似乎使PLLA晶体和WSNTs的取向解耦。
