Search

Successive modification of starch with octenyl succinic anhydride (OSA) and plant-derived geraniol allows for a largely bio-derived starch derivative that can undergo facile reaction with elemental sulfur to generate sustainable composite materials.

Herein we report a route to sulfur–starch composites by the modification of corn starch with octenyl succinic anhydride (OSA, degree of substitution = 2.6%) and its subsequent reaction with elemental sulfur through an inverse vulcanization process to generate OSSx (where x = wt% sulfur, either 90 or 95). This work represents an expansion into a previously untapped biomass source for the preparation of recyclable thermoplastic materials by this process. Composites OSSx are comprized of 83–89% by mass of extractable sulfur, and have reasonable thermal stability (Td = 214–216 °C) and Tm (DSC) of 118 °C. The starch modification strategy employed herein allowed for lower degree of substitution of the starch than was feasible for other bioploymers, leading to materials with high strength despite relatively low crosslink density relative to that in previous biopolymer–sulfur composites. The low crosslink density resulted in relatively long polysulfur catenates, thus producing materials with impressive flexural strengths (5.3–5.4 MPa) and highlighting the potential for biomass–sulfur materials to exhibit a range of mechanical properties depending on the biopolymer scaffold and modification strategy.

The extent to which lignocellulose biomass particle size influences the properties of biomass–sulfur composites prepared from these particles was evaluated. For this purpose several materials were prepared by the reaction of sulfur with peanut shell particles that had been fractionated into narrow size ranges using ASTM certified sieves. Eight particle size fractions with an upper cutoff range of 710 microns were thus used to prepare a series of eight composites PSS-1 to PSS-8. The use of biomass particles having defined size ranges allowed for a 36-fold faster reaction rate relative to the analogous reactions employing unfractionated biomass, while the resultant composites still maintained excellent strength characteristics. Composites prepared with smaller biomass particles exhibited the most uniform dispersion, yet similar ultimate strength characteristics were observed for most of the composites irrespective of the biomass particle size. The strength characteristics of these materials could be rationalized by the interplay of the dispersion of filler in the network versus the unfavorable interactions between the hydrophilic biomass filler and hydrophobic sulfur network. This work highlights the importance of quantifying filler effect for microscopically non-homogeneous composite materials and provides insight on simple strategies for drastically impacting the time and energy expenditures for biomass composite synthesis and resultant properties.

A composite was prepared from biomass and waste sulfur from fossil fuel refining. The composite has higher compressive and flexural strength than portland cement. Avoiding expensive biomass separation and achieving metrics exceeding those of commercial products is a notable step towards a green economy.

Renewably-sourced, recyclable materials that can replace or extend the service life of existing technologies are essential to accomplish humanity's quest for sustainable living. In this contribution, remeltable composites were prepared in a highly atom-economical reaction between plant-derived terpenoid alcohols (10 wt% citronellol, geraniol, or farnesol) and elemental sulfur (90 wt%). Investigation into the microstructures led to elucidation of a mechanism for terpenoid polyene cyclization initiated by sulfur-centered radicals. The formation of these cyclic structures contributes significantly to understanding the mechanical properties of the materials and the extent to which linear versus crosslinked network materials are formed. The terpenoid–sulfur composites can be thermally processed at low temperatures of 120 °C without loss of mechanical properties, and the farnesol–sulfur composite so processed exhibits compressive strength 70% higher than required of concrete for residential building. The terpenoid–sulfur composites also resist degradation by oxidizing acid under conditions that disintegrate many commercial composites and cements. In addition to being stronger and more chemically resistant than some commercial products, the terpenoid–sulfur composites can be used to improve the acid resistance of mineral-based Portland cement as well. These terpenoid–sulfur composites thus hold promise as elements of sustainable construction on their own or as additives to extend the operational life of existing technologies, while the cyclization behaviour could be an important contributor in other polymerizations of terpenoids.

Lignocellulosic biomass holds a tremendous opportunity for transformation into carbon-negative materials, yet the expense of separating biomass into its cellulose and lignin components remains a primary economic barrier to biomass utilization. Herein is reported a simple procedure to convert several biomass-derived materials into robust, recyclable composites through their reaction with elemental sulfur by inverse vulcanization, a process in which olefins are crosslinked by sulfur chains. In an effort to understand the chemistry and the parameters leading to the strength of these composites, sulfur was reacted with four biomass-derivative comonomers: (1) unmodified peanut shell powder, (2) allyl peanut shells, (3) ‘mock’ allyl peanut shells (a mixture containing independently-prepared allyl cellulose and allyl lignin), or (4) peanut shells that have been defatted by extraction of peanut oil. The reactions of these materials with sulfur produce the biomass–sulfur composites PSx, APSx, mAPSx and dfPSx, respectively, where x = wt% sulfur in the monomer feed. The influence of biomass : sulfur ratio was assessed for PSx and APSx. Thermal/mechanical properties of composites were evaluated for comparison to commercial materials. Remarkably, unmodified peanut shell flour can simply be heated with elemental sulfur to produce composites having flexural/compressive strengths exceeding those of Portland cement, an effect traced to the presence of olefin-bearing peanut oil in the peanut shells. When allylated peanut shells are used in this process, a composite having twice the compressive strength of Portland cement is attained.