Polyethylene terephthalate (PET) is one of the most commonly used polyester plastics worldwide but is extremely difficult to be hydrolyzed in a natural environment. PET plastic is an inexpensive, lightweight, and durable material, which can readily be molded into an assortment of products that are used in a broad range of applications. Most PET is used for single-use packaging materials, such as disposable consumer items and packaging. Although PET plastics are a valuable resource in many aspects, the proliferation of plastic products in the last several decades have resulted in a negative environmental footprint. The long-term risk of released PET waste in the environment poses a serious threat to ecosystems, food safety, and even human health in modern society. Recycling is one of the most important actions currently available to reduce these impacts. Current clean-up strategies have attempted to alleviate the adverse impacts of PET pollution but are unable to compete with the increasing quantities of PET waste exposed to the environment. In this review paper, current PET recycling methods to improve life cycle and waste management are discussed, which can be further implemented to reduce plastics pollution and its impacts on health and environment. Compared with conventional mechanical and chemical recycling processes, the biotechnological recycling of PET involves enzymatic degradation of the waste PET and the followed bioconversion of degraded PET monomers into value-added chemicals. This approach creates a circular PET economy by recycling waste PET or upcycling it into more valuable products with minimal environmental footprint.

Polyamides (PAs) are repeatedly exposed to environments of varying humidity throughout their service life. Due to their hygroscopic nature, moisture diffusion can alter the polymer properties, sometimes irreversibly. It has been previously found that the effect of transport of water on the structure, morphology, and physical properties of polymers is not negligibly small. In certain semi-crystalline polyamides, the diffusion coefficient has been shown to be governed by the local chain dynamics (β relaxation). The final molecular weight of PAs achieved after melt processing is a result of the equilibrium between the forward and reverse polycondensation depending on the water concentration. With the growing demand for unreinforced and reinforced polyamides as well as polyamide fibers in high-performance applications, it is critical to understand the physics of the interaction between water molecules and polymer or composite systems. This article reviews the existing literature about polyamide-water interactions with a focus on the governing physical laws of moisture transport within the polyamide matrix, drying kinetics, and dynamics of water in the polymer system. The implications of moisture on the processing and properties of the polyamides class of materials are also discussed, suggesting the need for best practices in instrumentation and control.

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate “smart fertilizers” for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the “bottleneck” for nitrogen–phosphorous–potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers.