(183a) Microwave-Assisted Heating of Polymers

Plastics have become an essential part of daily life. Plastic usage is surging, and the yearly production was 380 million tonnes in 2020. Most of the plastic is ending in landfills and some leaking into the oceans. The level of risk exposed by waste plastics is growing. Therefore, recycling of waste plastics is essential. Thermochemical catalytic conversion of waste plastics to valuable products is an appealing recycling strategy. In the literature, conventional, microwave, ultrasound, radiofrequency heating modes have been employed for processing the waste plastics.^1-3 Recently, microwave heating has received significant attention due to its energy-efficient volumetric and non-contacting energy transfer.^4,5 Despite the low microwave absorbing capability of plastics, microwave heating plays a vital role in resource recovery from waste plastics.

This paper discusses the microwave-assisted heating of polyolefins, polystyrene and PET using microwave absorbing materials (susceptors) to understand the effects of particle size, mass, and contacting pattern on heating. A good susceptor should possess high thermal resistance, chemical inertness, abundance, low-cost, and excellent microwave absorbing properties. Different contacting patterns of polymer and susceptors as well as susceptor particle size were considered to maximize the heating rates. Polystyrene (PS) demonstrated a peculiar heating behavior, resulting in a shoot-up of temperature due to its amorphous nature. High heating rates were measured for particle sizes of the order of millimeters and a suitable reactor length. Structured reactors heating was also demonstrated. Our work demonstrates heating as high as 200 ^oC min^-1. The effect of heating rate on depolymerization is also discussed.

Acknowledgements:

This work is being supported by Center for Plastics Innovation, which is supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences under Award Number DE-SC0021166.