Molecular Weight Determination of Polyolefin Deconstruction Products by Thermal Analysis

Plastics are an indispensable class of materials found in countless consumer products. Yet, their growing use and limited recycling strategies have led to a rapid accumulation of plastics waste and devastating environmental impacts. Thus, efforts to improve the end-of-life strategies to address plastics pollution are expanding. Polyolefins, which comprise over half of new plastic production, can be chemically recycled into more valuable carbon feedstocks, such as oils and lubricants. This deconstruction process is not trivial and requires fundamental understanding of the physical principles that correlate to the molecular weights, molecular weight distributions, and architectures assigned to the vast array of polyolefin feedstocks. High temperature gel permeation chromatography is the standard approach to determine the molecular weight distribution of these products, but accessibility to this technique is a challenge. To address this accessibility gap, we propose a method to determine the molecular weight distribution of polyolefin deconstruction products using differential scanning calorimetry (DSC). The molecular weight decreases during polyolefin deconstruction correlates to a change in the melting temperature, leading to identification of molecular weight dependent chain lengths and enabling thermal fractionation. For example, longer polymer chains exhibit minimal melting point dependence, however, their entanglement and diffusion behavior reduce their crystallization kinetics, which can be identified using DSC. It is envisioned that expanding the accessibility of techniques to probe deconstruction products will enable tailored identification that, although not as precise as chromatographic techniques, is tolerant to a range of molecular weights, architectures, and additives.