Review Articles

Due to the societal appeal in carbon emission reduction and neutralization, chemical recycling of waste polyester for valuable chemicals has attracted attention in an increasing number of applications. Research on chemical recycling of polyester wastes is currently rising sharply and becoming a hot spot gradually. Many technical and fundamental questions still need to be addressed, such as harsh depolymerization conditions (high temperature, long reaction time, low yields, etc.) and techno-economy and environmental sustainability matters. The chemical recycling protocol and optimization of degradable polyester wastes are systemically investigated along with short discussions on non-degradable ones. The thermoset polyurethane and epoxy adhesives derived from depolymerized waste polyesters for contributing to wood-based structural composite materials (e.g., laminated plywood, fire retarded wood coating, and transparent wood composites) along with life-cycle assessment and techno-economic analysis are also critically evaluated and analyzed. These novel insights are expect to open a new avenue to develop wood-based structural materials via value-added chemicals from polyester waste recycling, which contribute to the sustainable society along with prompting further research and extension in forestry biomaterials and renewable natural resources.

Graphical Abstract

Chitin is the second most abundant natural polysaccharide after cellulose and consists of N-acetyl-D-glucosamine units linked by β-1,4-glycosidic bonds. In nature, chitin does not accumulate due to the synergistic action of chitinolytic enzymes. Based on their catalytic domains, chitinases are classified into glycosyl hydrolase families GH18 and GH19. They are widely produced by bacteria and filamentous fungi. Different types of chitinolytic enzymes, including endochitinases, exo-acting enzymes, and N-acetylglucosaminidases, have been reported to exhibit antimicrobial and insecticidal activities, making them valuable tools for controlling phytopathogenic fungi and insect pests. Chitin degradation generates chitooligosaccharides (COS), which possess diverse biological properties such as antimicrobial, antioxidant, anti-inflammatory, and antitumor activities, contributing to improved human health. Microbial chitinases are also applied in several industrial and environmental processes, including protoplast formation, single-cell protein production, and dye removal. Advances in recombinant expression and genetic engineering have enhanced chitinase production, stability, and catalytic efficiency. Moreover, recombinant chitinases have been successfully utilized in biocontrol strategies and in developing transgenic plants with increased resistance to phytopathogens. This review highlights the broad agricultural, industrial, and biomedical applications of chitinases and their crucial role in promoting environmental sustainability and advancing bio-based industrial processes.