Polymeric materials hold several advantages over metal components in heat exchangers such as cost savings, lighter weight and corrosion resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability and required strength. Neat polymer resins have inferior mechanical and thermal properties relative to metals, requiring careful consideration of the entire heat exchanger system from materials to system design, to achieve sufficient performance. This review summarizes the physical parameters governing polymer and composite thermal conductivity, as well as the latest research on augmenting thermal conductivity. Highly filled composites containing carbon or metal have achieved thermal conductivity an order of magnitude higher than that of neat polymers. The effects of critical additive characteristics, such as interfacial compatibility, filler shape factor, loading level and processing technique, are reviewed. In addition to lower material costs, high volume processing technologies such as injection molding and extrusion are responsible for the cost savings of

Enzymatic depolymerization of poly(ethylene terephthalate) (PET) has emerged as a potential method for PET recycling, but extensive thermomechanical preprocessing to reduce both the crystallinity and particle size of PET is often conducted, which is costly and energy-intensive. In the current work, we use highcrystallinity PET (HC-PET) and low-crystallinity cryomilled PET (CM-PET) with three distinct particle size distributions to investigate the effect of PET particle size and crystallinity on the performance of a variant of the leaf compost-cutinase enzyme (LCC-ICCG). We show that LCC-ICCG hydrolyzes PET, resulting in the accumulation of terephthalic acid and, interestingly, also releases significant amount of mono(2hydroxyethyl)terephthalate. Particle size reduction of PET increased the maximum rate of reaction for HC-PET, while the maximum hydrolysis rate for CM-PET was not significantly different across particle sizes. For both substrates, however, we show that particle size reduction has little effect on the overall conversion extent. Specifically, the CM-PET film was converted to 99 ± 0.2% mass loss within 48 h, while the HC-PET powder reached only 23.5 ± 0.0% conversion in 144 h. Overall, these results suggest that amorphization of PET is a necessary pretreatment step for enzymatic PET recycling using the LCC-ICCG enzyme but that particle size reduction may not be required.

No abstract

No abstract

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.