Compatibilization of Low Molecular Weight Polypropylene in High Molecular Weight Matrix Via Solvent Swelling

TL;DR

A new method improves the mechanical properties of recycled polypropylene blends by promoting co-crystallization without additives.

Contribution

A solvent immersion annealing method is introduced to compatibilize low and high molecular weight polypropylene blends.

Findings

Solvent immersion annealing promotes co-crystallization in PP blends.

The method increases extensibility of PP blends over sixfold.

Improved mechanical performance enables reuse of low MW PP.

Abstract

Mechanical recycling of polypropylene (PP) causes chain
scission
during high-temperature, high-shear processing, resulting in lower
molecular weight (MW) fragments, which contain fewer tie chains between
crystalline lamellae. This change can lead to significantly reduced
mechanical performance, making the use of post-consumer recycled PP
in new materials particularly challenging, especially as recent government
policies mandate the use of recycled content at increasing levels.
Previous strategies in addressing these needs rely on chemically crosslinking
or introducing additives, which can be time-consuming, cost-prohibitive
at scale, and/or further complicate waste streams. In this work, we
demonstrate a solvent immersion annealing method that swells PP blends
containing high and low MW fractions, promoting their co-crystallization,
which leads to significantly improved mechanical performance of the
blended materials. Specifically, our results show an over 6-fold increase
in extensibility of PP blends, effectively enabling their reuse and
extended lifetime. This work presents an innovative and straightforward
method to address the recycling challenges of low MW PP without the
need for additives, potentially opening new avenues for future research
in blend compatibilization for addressing plastic circularity challenges.

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