Melt Processing Pretreatment Effects on Enzymatic Depolymerization of Poly(ethylene terephthalate)

Abstract

Poly­(ethylene terephthalate) (PET) is a common thermoplastic material, used in a wide variety of applications (i.e., bottles, fabrics, packaging, electronics, and automotive components). Increasing demand for PET has precipitated a need for improved recycling technology, especially for single-use PET waste. Recently, enzymatic depolymerization has shown promise as an environmentally responsible alternative for PET chemical recycling that yields economically useful products (e.g., terephthalic acid, adipic acid, and ethylene glycol). However, the depolymerization system still suffers from low rates on crystalline PET substrates, and effects of realistic waste streams are not known. In our work, PET waste is pretreated using an ultra-high-speed twin-screw extruder system. PET substrates were modified by various processing pretreatments to allow enzymes better access to depolymerize substrate materials. The effect of varying throughput and mechanical shear on structural properties of the PET waste was analyzed using molecular weight and thermal characterizations. These pretreated samples exhibit modifications in molecular weight, glass transition temperature, crystallinity, and specific surface area. The unpurified leaf-branch compost cutinase enzyme produced from the fed-batch fermentation of Escherichia coli BL21­(DE3) was used in enzymatic depolymerization, where a faster reaction was observed as crystallinity was decreased and the specific surface area was increased. The rate of terephthalic acid production was also significantly higher for samples processed at lower mechanical shear with higher throughputs. This work demonstrates the potential for tailoring pretreatments in pursuit of faster and more energy efficient PET recycling using enzymes, with facile adaptation to the industrial scale for the circular economy.

Dynamic Docking-Assisted Engineering of Hydrolases for Efficient PET Depolymerization

“…It has been reported that PET will recrystallize rapidly at temperatures above 72 °C and is undesirable for depolymerization . We found that the conventional PET pretreatment method using the extruder reduced the molecular weight of PET, , and the low molecular weight PET tended to recrystallize . To avoid this situation, oven melting was used to pretreat the PET substrate.…”

Enzyme selection, optimization, and production toward biodegradation of post‐consumer poly(ethylene terephthalate) at scale

“…The Extruded RPET (ExPET) was obtained by extrusion of RPET using twin screw extrusion at 200 rpm with a throughput of 9 g min −1 (15 mm diameter screws 60:1 L:D, Technovel Japan). [ 30 ] The types of poly(ethylene terephthalate) (PET) materials used in this study and their properties are listed in Table 2 . Glass transition temperature ( T g ), melting temperature ( T m ), and crystallinity (%) values were acquired using Differential Scanning Calorimetry (DSC) analysis.…”

Bottlenecks in biobased approaches to plastic degradation

“…Some of these bottlenecks include high crystallinity, the inclusion of additives, and the often mixed/layered composition of plastics. The challenge of polymer crystallinity is a considerable roadblock for biological recycling and has led to many attempts at developing preprocessing methods [20][21][22][23][24] . However, while these preprocessing methods increase enzymatic degradation efficiency, many are not commercially/economically scalable.…”