Crystal morphologies and enzymatic degradation of melt-crystallized thin films of random copolyesters of (R)-3-hydroxybutyric acid with (R)-3-hydroxyalkanoic acids

Crystallization of microbial polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs), produced by the microbial fermentation, is a promising green polymer and has attracted much attention due to its excellent biocompatibility, complete biodegradability, and non-cytotoxicity. The physical properties of PHAs are closely related to their chemical and crystalline structure. Therefore, deep understanding and regulating the structure and crystallization of PHAs are the key factors to improve the performance of PHAs. This review first provides a brief overview of the development history, chemical structure, and basic properties of PHAs. Then, the crystal structure, crystal morphology, kinetics theories and crystallization behavior of nucleation-induced PHAs are systematically summarized to provide a theoretical foundation for improving PHAs crystallization rate and physical properties. In the end, the outlook on the crystallization and application prospects of PHAs is also addressed.

Biological degradation of plastics: a comprehensive review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegradation is necessary for water-soluble or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degradation of natural and synthetic polymers in order to understand what is necessary for biodegradation and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochemical changes involved. Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. This paper reviews the current research on the biodegradation of biodegradable and also the conventional synthetic plastics and also use of various techniques for the analysis of degradation in vitro.

Enzymatic degradation processes of lamellar crystals in thin films for poly[(R)-3-hydroxybutyric acid] and its copolymers revealed by real-time atomic force microscopy

Enzymatic degradation processes of flat-on lamellar crystals in melt-crystallized thin films of poly[(R)-3-hydroxybutyric acid] (P(3HB)) and its copolymers were characterized by real-time atomic force microscopy (AFM) in a phosphate buffer solution containing PHB depolymerase from Ralstonia pickettii T1. Fiberlike crystals with regular intervals were generated along the crystallographic a axis at the end of lamellar crystals during the enzymatic degradation. The morphologies and sizes of the fiberlike crystals were markedly dependent on the compositions of comonomer units in the polyesters. Length, width, interval, and thickness of the fiberlike crystals after the enzymatic degradation for 2 h were measured by AFM, and the dimensions were related to the solid-state structures of P(3HB) and its copolymers. The width and thickness decreased at the tip of fiberlike crystals, indicating that the enzymatic degradation of crystals takes place not only along the a axis but also along the b and c axes. These results from AFM measurement were compared with the data on crystal size by wide-angle X-ray diffraction, and on lamellar thickness and long period by small-angle X-ray scattering. In addition, the enzymatic erosion rate of flat-on lamellar crystals along the a axis was measured from real-time AFM height images. A schematic glacier model for the enzymatic degradation of flat-on lamellar crystals of P(3HB) by PHB depolymerase has been proposed on the basis of the AFM observations.