Nitroarene-Mediated Photo-oxidative Deconstruction and Upcycling of Unsaturated Rubber Waste

TL;DR

A new method converts rubber waste into high-value materials with better strength and water resistance using light and a chemical oxidant.

Contribution

A photo-oxidative method for upcycling unsaturated rubber waste into functional materials with tunable properties.

Findings

Unsaturated rubbers are converted into carbonyl-terminated oligomers under LED light and a nitroarene oxidant.

The resulting materials show improved tensile strength and hydrophobicity when cross-linked with p-phenylenediamine.

Oligomers can be further modified into carboxylic acids or hydroxyl groups for use as polymer additives.

Abstract

Transforming waste polymers into materials with improved
properties
offers a compelling strategy for advancing the sustainable use of
polymers, echoing the Chinese proverb: “Blue comes from indigo
but surpasses it in blueness.” Herein, we report a photo-oxidative
deconstruction and upcycling method for unsaturated rubber waste.
Under 390 nm LED irradiation at room temperature, in the presence
of a nitroarene oxidant, diverse unsaturated polymersincluding
natural rubber, polybutadiene, nitrile rubber, styrene–butadiene
rubber, and even cross-linked nitrile glovesare selectively
converted into carbonyl-terminated oligomers. The aldehyde-functionalized
products are cross-linked via dynamic imine chemistry with p-phenylenediamine to yield reprocessable elastomers with
markedly improved tensile strength (from 12.9 to 16.7 MPa) and surface
hydrophobicity (contact angle from 23 ± 2° to 83 ±
3°). Furthermore, the aldehyde groups on the oligomers can be
selectively oxidized to carboxylic acids or reduced to hydroxyl groups,
enabling their versatile use as polymeric additives including curing
agents, chain extenders, and toughening agents. This strategy demonstrates
a versatile route for converting rubber waste into high-value functional
materials.

Figures