Tuning solvent strength can fractionate PVC into ultra-low molecular weight material with low dispersity†

Abstract

The drive towards a circular economy in plastic materials has become a worldwide goal. It is apparent that conventional recycling alone falls well short of achieving circularity in plastic materials due to the complex formulations of commercial products. Poly(vinyl chloride) (PVC) is a post-consumer plastic that is especially challenging to recycle mechanically. However, compared to other commodity plastics, PVC is potentially well-suited for chemical recycling, especially via dissolution processes that selectively remove additives. Solvent-based recycling of PVC would circumvent thermomechanical processes that cause degradation of the polymer backbone. Yet, solvent-based recycling has its own set of considerations. Recycling a “Katamari” of mixed products of unknown origins (and potentially widely varying molecular weight distributions) might yield a purified PVC product that is of low value and/or without obvious utility. Thus, solvent fractionation of the feed into two or more products of relatively narrow molecular weight distributions may be required instead of bulk dissolution of the entire mass of polymer. In this work, we demonstrate solvent-based fractionation of PVC as both single-step and sequential processes. Two solvent systems were considered: acetone–methanol and tetrahydrofuran–methanol. The content of methanol in the solvent systems was varied to adjust the overall “strength” of the solvent system, thus controlling the molecular weight of the recovered soluble and insoluble fractions of PVC. Sequential fractionation proved capable of producing PVC fractions with dispersities (Đ) as low as 1.14. Further, sequential fractionation of commercial PVC, containing additives, was highly promising for removing additives from the bulk (76.9%) of recovered PVC.