Wear-induced mechanical degradation of plastics by low-energy wet-grinding

Publication date: Available online 31 October 2018Source: Polymer Degradation and StabilityAuthor(s): Kartik Ravishankar, Praneeth Srivanth Ramesh, Balaji Sadhasivam, Dhamodharan RaghavachariAbstractMechanical degradation of polymers reported so far, utilize cutting, impact or attrition for size reduction, which is very different from the low-magnitude forces experienced by the polymers during their service life. In this work, we have studied the effect of such low-magnitude forces, on the polymeric articles, using a low-energy rolling compression-type wet-grinder. The rolling compression action produces shear and compression on the polymer article, leading to abrasion and resulting in the formation of crazes, micro-cracks and chip-offs, akin to the wearing. Measurements using Raman spectroscopy showed that the shear forces, generated upon grinding, produced strains on the polymer backbone, which upon sufficient build-up, results in chain scission at the points of physical entanglement. These homolytic chain scissions produced "mechano"radicals, which were confirmed by radical-scavenging using DPPH. The ensuing reduction in the molecular weight was further analyzed using GPC, light scattering and viscometry. Surprisingly, XRD measurements showed strain-induced crystallization as well. In order to theoretically validate the studies, a probabilistic model, explaining the "complex" response of the molecular weight distribution and the PDI upon mechanical degradation, has also be...

Source: Polymer Degradation and Stability - October 31, 2018 Category: Chemistry Source Type: research