Various approaches to sustainable and continually recyclable Cross-Linked Polymers

 

 In recent year, effort has focused on the development of recycling strategies for cross-linked polymers. Various approaches were discussed on recycling of cross-linked polymers and also on future challenges that must be overcome to enable widespread, viable, and more sustainable and practical implementation of these materials, these include the sustainable sourcing of feedstocks, long-term environmental stability of these polymers, attempt to move forward various synthesis and recycling methods.

Cross-linked polymers, often referred to as thermosets, are another class of materials comprising around 15–20% of polymers produced. Traditional recycling of cross-linked polymers via mechanical reprocessing is impractical because their structures preclude flow, even at elevated temperatures. Their insolubility also precludes solution reprocessing. Although some of these materials are down-cycled into lower value products, most thermosets are incinerated, landfilled. Still, the high strength and chemical stability of thermosets renders them essential for use in tires, engineering composites, foams, adhesives, and many other applications. Developing strategies to recycle these materials without compromising their performance represents a formidable challenge.

Recently, the incorporation of dynamic interactions such as hydrogen bonding, electrostatic interactions, or dynamic covalent bonds into both linear polymers and polymer networks has enabled the design of polymers that heal spontaneously.While these materials have great potential to enhance the longevity of polymeric materials or enable new technologies due to their stimuli-responsiveness, their dynamic nature under ambient conditions could pose challenges in applying these polymers as structural materials. Therefore, significant attention has focused on controlling the dynamics of covalent bonds and incorporating them in robust cross-linked materials. In this way, desirable mechanical properties can be achieved under service conditions, while reprocessability can be induced under certain stimuli that are independent of the service conditions. Despite rapidly growing interest in reprocessable cross-linked polymers, other aspects of sustainability i.e., renewability and degradability are rarely integrated into their development. Some researchers will highlight promising approaches for continually recycling cross-linked polymers via depolymerization strategies or dynamic exchange reactions. They provide insight into the outstanding challenges these materials face toward replacing traditional nonrecyclable thermosets and limiting the adverse environmental impacts of this important class of materials.