Structural Transition of Poly[(R)-3-hydroxybutyrate-co-(R)-3- hydroxyvalerate] Single Crystals on Heating As Revealed by Synchrotron Radiation SAXS and WAXD

Synthesis and physical properties of polyhydroxyalkanoate (PHA)-based block copolymers: A review

Polyhydroxyalkanoates (PHAs) are a group of natural polyesters that are synthesised by microorganisms. In general, their thermoplasticity and (in some forms) their elasticity makes them attractive alternatives to petrochemical-derived polymers. However, the high crystallinity of some PHAs - such as poly(3-hydroxybutyrate) (P3HB) - results in brittleness and a narrow processing window for applications such as packaging. The production of copolymeric PHA materials is one approach to improving the mechanical and thermal properties of PHAs. Another solution is the manufacture of PHA-based block copolymers. The incorporation of different polymer and copolymer blocks coupled to PHA, and the resulting tailorable microstructure of these block copolymers, can result in a step-change improvement in PHA-based material properties. A range of production strategies for PHA-based block copolymers has been reported in the literature, including biological production and chemical synthesis. Biological production is typically less controllable, with products of a broad molecular weight and compositional distribution, unless finely controlled using genetically modified organisms. By contrast, chemical synthesis delivers relatively controllable block structures and narrowly defined compositions. This paper reviews current knowledge in the areas of the production and properties of PHA-based block copolymers, and highlights knowledge gaps and future potential areas of research.

Sectorization of Macromolecular Single Crystals Unveiled by Probing Shear Anisotropy

Polymer single crystals continue to infiltrate emerging technologies such as flexible organic field-effect transistors because of their excellent translational symmetry and chemical purity. However, owing to the methodological challenges, direct imaging of the polymer chains folding direction resulting in sectorization of single crystals has rarely been investigated. Herein, we directly image the sectorization of polymer single crystals through anisotropic elastic deformation on the surface of macromolecular single crystals. A variant of friction force microscopy, in which the scanning direction of the probe tip is parallel with the cantilever axis, allows for high contrast imaging of the sectorization in polymer single crystals. The lateral deflection of the cantilever resulting from shear forces transverse to the scan direction shows a close connection with the in-plane components of the elastic tensor of the polymer single crystals, which is of a fundamentally different origin than the friction forces. This allows for fast, facile, and nondestructive characterization of the microstructure and in-plane elastic anisotropy of compliant crystalline materials such as polymers.

Laser Transmission Welding of Semi-Crystalline Polymers and Their Composites: A Critical Review

The present review provides an overview of the current status and future perspectives of one of the smart manufacturing techniques of Industry 4.0, laser transmission welding (LTW) of semi-crystalline (SC) polymers and their composites. It is one of the most versatile techniques used to join polymeric components with varying thickness and configuration using a laser source. This article focuses on various parameters and phenomena such as inter-diffusion and microstructural changes that occur due to the laser interaction with SC polymers (specifically polypropylene). The effect of carbon black (size, shape, structure, thermal conductivity, dispersion, distribution, etc.) in the laser absorptive part and nucleating agent in the laser transmissive part and its processing conditions impacting the weld strength is discussed in detail. Among the laser parameters, laser power, scanning speed and clamping pressure are considered to be the most critical. This review also highlights innovative ideas such as incorporating metal as an absorber in the laser absorptive part, hybrid carbon black, dual clamping device, and an increasing number of scans and patterns. Finally, there is presented an overview of the essential characterisation techniques that help to determine the weld quality. This review demonstrates that LTW has excellent potential in polymer joining applications and the challenges including the cost-effectiveness, innovative ideas to provide state-of-the-art design and fabrication of complex products in a wide range of applications. This work will be of keen interest to other researchers and practitioners who are involved in the welding of polymers.