Combining agriculture and energy industry waste products to yield recyclable, thermally healable copolymers of elemental sulfur and oleic acid

Abstract

Sulfur and oleic acid, two components of industrial waste/byproducts, were combined in an effort to prepare more sustainable polymeric materials. Zinc oxide was employed to serve the dual role of compatibilizing immiscible sulfur and oleic acid as well as to suppress evolution of toxic H2S gas during reaction at high temperature. The reaction of sulfur, oleic acid, and zinc oxide led to a series of composites, ZOSx (x = wt % sulfur, where x is 8–99). The ZOSx materials ranged from sticky tars to hard solids at room temperature. The ZOSx compositions were assessed by 1H NMR spectrometry, FTIR spectroscopy, and elemental microanalysis. Copolymers ZOS59‐99, were further analyzed for thermal and mechanical properties by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Remarkably, even ZOS99, comprising only 1 wt % of zinc oxide/oleic acid (99 wt % S) exhibits at least an eightfold increase in storage modulus compared to sulfur alone. The four solid samples (59–99 wt % S) were thermally healable and readily remeltable with full retention of mechanical durability. These materials represent a valuable proof‐of‐concept for sustainably sourced, recyclable materials from unsaturated fatty acid waste products. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1704–1710

Valorization of Lignin as a Sustainable Component of Structural Materials and Composites: Advances from 2011 to 2019

“…Although elemental sulfur itself is quite brittle, durable materials can be obtained for the copolymers comprising up to 90 wt.% sulfur [51][52][53][54]. These efforts have employed a wide range of starting materials including cellulose, lignin, amino acids, terpenoids, algae acids, polystyrene derivatives, and other olefins [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70]. More recently, radical-induced aryl halide/sulfur polymerization (RASP) proved similarly effective for preparation of high sulfur-content materials (HSMs) but employing aryl halides in place of the olefins required for inverse vulcanization.…”

Durable, acid-resistant copolymers from industrial by-product sulfur and microbially-produced tyrosine

“…In contrast to many reported high sulfur-content materials, 30,31,36,39,40 once TTS 50 or TTS 30 were set as solids they could not be remelted or reshaped. To prepare materials of desired shapes, it was necessary to pour the homogenized reaction solutions into a mould for subsequent heating to complete the crosslinking process.…”

Copolymers by Inverse Vulcanization of Sulfur with Pure or Technical‐Grade Unsaturated Fatty Acids

“…The fatty acids present in these low‐value by‐products generally include oleic, linoleic, palmitic, and stearic acid (Chart A) in the highest quantities. We recently reported on high sulfur‐content copolymers comprising oleic acid crosslinked by sulfur, with ZnO added as a compatibilizer ( ZOS x , x = wt % sulfur in monomer feed, Chart ) . The preparation of ZOS x employed the inverse vulcanization mechanism introduced by Pyun in 2013 .…”

“…Although extended sulfur catenates are generally unstable with respect to the orthorhombic (S 8 ring) allotrope at STP (standard temperature and pressure), such extended chains can be stabilized by their confinement within the crosslinked network structure. In this way, stable sulfur catenates averaging from five to over 100 sulfur atoms have been observed, depending on the composition and crosslink density of the network in which the chains are confined . The high crosslink density and extended sulfur catenates present in inversely vulcanized materials, coupled with the thermal reversibility of SS bond formation, have led to materials that can be mechanically strong, recyclable by simple remelt–recast processes, and thermally healable.…”

“…With the addition of only 1 wt % of oleic acid crosslinker, the ZOS x copolymers, for example, exhibited an eightfold increase in storage modulus over sulfur. The ZOS x materials also demonstrated facile thermal healing and retained their full mechanical strength after many recycling trials …”