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Accelerating Polymer Degradation using Pro-oxidant Additives
Citation:
Sahle-Demessie, E. AND B. Mezgebe. Accelerating Polymer Degradation using Pro-oxidant Additives. American Chemical Society Annual meetings, Atlanta, Georgia, August 22 - 26, 2021.
Impact/Purpose:
Oxo-degrability of single-use plastics could help reduce the persistence of plastics in the environment, making the plastic biodegradable. We are reporting the use of pro-oxidant (iron stearate and cobalt stearate) for efficient enhancement of biodegradation of polyolefins. Photolytic processes constitute the major route for promoting the eventual degradation and hence biodegradation of plastics in the environment. This process could be enhanced by using pro-oxidant/pro-degradant. additives at low concentrations (typically 1–2% weight) in the formulation of conventional plastic to create oxo-biodegradable materials without any significant change in their original mechanical and optical properties. The pro-oxidant/pro-degradants in plastics initiate polymer degradation producing free radicals that react with molecular O2 from the atmosphere.
Description:
Single use plastics that are commonly used for packaging and service ware, such as bottles, bags, straws and wrappers result in land and marine pollution that as they break down into microplastics. Blending plastics with pro-oxidants could be a promising solution as they accelerate photooxidation to obtain degradable materials whose final ecological and physical footprint are much smaller. In this study, two pro-oxidants, iron stearate (FeSt3) and cobalt stearate (CoSt2), were melt blended with polypropylene (PP) at concentrations of 1 and 2 wt%. Plates of neat and pro-oxidant filled PP were kept in an accelerated weathering chamber that simulates damaging effects of long-term outdoor exposure. Samples were taken out from the test chamber and their properties were measured at selected time interval as they undergo photochemical degradation. Physical, thermal, and chemical properties of pristine and pro-oxidant filled samples were measured, using TGA, differential scanning calorimetry and Fourier transfer IR spectroscopy (FTIR). Within 300 h of aging in the chamber, PP with pro-oxidants were embrittled, cracked and broken into pieces. After 500 h of aging plastics plates showed significant reduction in melting and re-crystallization points indicating polymer chain breaking, rapid depolymerization. Uv-Vis and GC-mass spectroscopic analysis of wash-water samples indicated water soluble degradation products are potently biodegradable and can be assimilated by microorganisms. The study offers a successful approaches where benign filler could significantly reduce the persistent of plastic pollution without creating undesired by-products.