Abstract
Terpenoids are potentially sustainable replacements for petrochemical olefins. Sulfur is a waste product produced in large quantities from fossil fuel refining. Several composites with attractive properties have recently been made from terpenoids and sulfur. This report details the extent to which the ratio of sulfur to terpenoid and the terpenoid olefin content influences the thermal and mechanical properties of such terpenoid-sulfur composites. The terpenoids selected were diunsaturated geraniol and triunsaturated farnesol that, upon their inverse vulcanization with elemental sulfur, yield composites GerSx and FarSx, respectively (x = wt % sulfur). The wt % sulfur in the monomer feed was varied from 30–95 for this study, providing twelve materials. Mechanical analysis of these materials was undertaken by compressive and tensile strength techniques. Differential scanning calorimetric analysis revealed both polymeric and orthorhombic sulfur present in the materials with glass transition temperatures (Tg) of −37 °C to −13 °C and melt temperatures (Tm) of 119 to 104 °C. The crystallinity of composites decreases as the weight fraction of sulfur decreases and composites having the highest olefin content exhibit no detectable crystalline microstructures. The compressive strength of the materials showed increasing strength for higher olefin-content materials for both GerSx (with compressive strength of up to 32 MPa) and FarSx (with compressive strength of up to 43 MPa). The improved strength with increasing olefin content levels off at around 80–85% of terpenoid, after which point both tensile and compressive strength diminish.
Highlights
Accepted: 23 September 2021Terpenoids are biologically-sourced olefins that hold great promise for supplanting fossil fuel-derived olefins in tars and bitumen used in asphalt, in polymers, and in related composite materials [1,2,3,4,5,6,7,8,9]
In previous work we demonstrated that monoalkene, diene and triene terpenoids react with sulfur to yield durable composites having compressive strengths that can exceed that of ordinary Portland cement (OPC) [10,11]
When sulfur is used as the majority component in reactions with olefins, high sulfur-content materials (HSMs) are formed in a process known as inverse vulcanization [12,13,14,15,16,17]
Summary
Accepted: 23 September 2021Terpenoids are biologically-sourced olefins that hold great promise for supplanting fossil fuel-derived olefins in tars and bitumen used in asphalt, in polymers, and in related composite materials [1,2,3,4,5,6,7,8,9]. When sulfur is used as the majority component in reactions with olefins, high sulfur-content materials (HSMs) are formed in a process known as inverse vulcanization [12,13,14,15,16,17] These HSMs are often composites wherein some free sulfur is trapped within a cross-linked network of organics linked by oligomeric or polymeric sulfur catenates [11,18,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]. When trapped within a network solid, the polymeric catenates can be stabilized, affording the composite with strength typical of more traditional carbon-catenate-backbone materials
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