Polymer upcycling

With plastic production and consumption rates increasing across the world, new means of dealing with post-consumer plastic waste such as chemical upcycling are necessary. We have several projects to overcome these barriers including:

  1. Using ionic interactions (i.e., the attraction of opposite charges) to force polymers to mix.

  2. Developing catalysts and mechanical mixing in combination to break down polymers into smaller, reusable molecules.

Ionic Blend Compatibilization

A major impediment to plastic recycling is the immiscibility of chemically dissimilar polymers, resulting in poor physical properties when different plastics are mixed. This is a fundamental property to polymers as these long molecules tend to have a very small entropy of mixing and a very large enthalpic penalty.

A recent, intriguing theory predicts the suppression of macrophase separation upon the installation of a single positive charge on one polymer and a single negative charge on a second polymer, and a widening of the homogeneity window with increasing charge density. The Segalman group, as part of a collaborative effort with other UCSB groups, seeks to exploit ionic interactions as a tool for polymer compatibilization, recycling and upcycling.

 

Blending of sparsely, oppositely charged polymers provides a sustainable pathway to obtain new materials with desirable physicochemical properties, coupled with a vast design space that allows for flexibility in materials design.

 

In our group, we have recently demonstrated the blend compatibilization of highly immiscible polymer pairs through ionic interactions, namely a 1) PS/PDMS pair through an acid/base end-group functionalization, and a 2) PnBA/PDMS pair through sparsely charged pendant group functionalization.

(left) A reactive end-group functionalized PDMS-base/PS-acid blend demonstrates improved optical clarity compared to its pristine counterparts. (right) An ionically pendant functionalized PDMS/PnBA blend coacervates after counter-ion removal.

For further reading, click here to access our Perspective article on the ionic compatibilization of polymers!

Catalytic and Mechanical Upcycling

To develop energy-efficient and easily scalable routes to plastic waste processing, it is important to combine the development of new catalytic processes with an understanding of polymer physics and rheology. In our projects in this domain of polymer upcycling, the Segalman group harnesses fundamental insights into polymer reactivity and dynamics to develop effective upcycling routes for targeting commercial polyolefins.

  • Owing to the high bond energy of the C-C bond and the lack of any reactive centers, polyolefin molecules require high energy input for chemical conversions. Additionally, the high viscosity of these polymer melts lead to processing challenges. Chain scission implemented by mechanical forces generated during flow can reduce energy demand for bond scission as well as make polymer melts more processible. We seek to understand the exact ways in which flow-induced scission occurs and then utilize this insight to design particle-polymer mixtures that undergo scission when triggered by flow.

  • The catalyst pore structures commonly used to convert small- to medium-size molecules may not be ideal in the depolymerization of long, entangled macromolecules. Due to their slow diffusion in the melt phase, polymer chains require alternative catalyst architectures that optimize interactions between active sites and bonds in the polymer backbone. Designing catalysts for this application requires an understanding of how molecular weight and pore size influence polymer rheology. Using nano-rheological tools, we aim to track the dynamics of pore-confined polymers undergoing catalytic degradation.