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

   https://doi.org/10.1039/c9ra06213k  

   Thiounn, Timmy ; Tennyson, Andrew G. ; Smith, Rhett C. ( October 2019 , RSC Advances)

   The search for alternative feedstocks to replace petrochemical polymers has centered on plant-derived monomer feedstocks. Alternatives to agricultural feedstock production should also be pursued, especially considering the ecological damage caused by modern agricultural practices. Herein, l -tyrosine produced on an industrial scale by E. coli was derivatized with olefins to give tetraallyltyrosine. Tetraallyltyrosine was subsequently copolymerized via its inverse vulcanization with industrial by-product elemental sulfur in two different comonomer ratios to afford highly-crosslinked network copolymers TTSx ( x = wt% sulfur in monomer feed). TTSx copolymers were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis (DMA). DMA was employed to assess the viscoelastic properties of TTSx through the temperature dependence of the storage modulus, loss modulus and energy damping ability. Stress–strain analysis revealed that the flexural strength of TTSx copolymers (>6.8 MPa) is more than 3 MPa higher than flexural strengths for previously-tested inverse vulcanized biopolymer derivatives, and more than twice the flexural strength of some Portland cement compositions (which range from 3–5 MPa). Despite the high tyrosine content (50–70 wt%) in TTSx , the materials show no water-induced swelling or water uptake after being submerged for 24 h. More impressively, TTSx copolymersmore »are highly resistant to oxidizing acid, with no deterioration of mechanical properties even after soaking in 0.5 M sulfuric acid for 24 h. The demonstration that these durable, chemically-resistant TTSx copolymers can be prepared from industrial by-product and microbially-produced monomers via a 100% atom-economical inverse vulcanization process portends their potential utility as sustainable surrogates for less ecofriendly materials.« less
2. Robust, remeltable and remarkably simple to prepare biomass–sulfur composites

   https://doi.org/10.1039/d0ma00538j  

   Lauer, Moira K. ; Karunarathna, Menisha S. ; Tennyson, Andrew G. ; Smith, Rhett C. ( October 2020 , Materials Advances)

   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,more »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.« less
3. Copolymerization of a Bisphenol a Derivative and Elemental Sulfur by the RASP Process

   https://doi.org/10.3390/suschem1020013  

   Thiounn, Timmy ; Lauer, Moira K. ; Karunarathna, Menisha S. ; Tennyson, Andrew G. ; Smith, Rhett C. ( September 2020 , Sustainable Chemistry)

   Fossil fuel refining produces over 70 Mt of excess sulfur annually from for which there is currently no practical use. Recently, methods to convert waste sulfur to recyclable and biodegradable polymers have been delineated. In this report, a commercial bisphenol A (BPA) derivative, 2,2′,5,5′-tetrabromo(bisphenol A) (Br4BPA), is explored as a potential organic monomer for copolymerization with elemental sulfur by RASP (radical-induced aryl halide-sulfur polymerization). Resultant copolymers, BASx (x = wt% sulfur in the monomer feed, screened for values of 80, 85, 90, and 95) were characterized by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Analysis of early stage reaction products and depolymerization products support proposed S–Caryl bond formation and regiochemistry, while fractionation of BASx reveals a sulfur rank of 3–6. Copolymers having less organic cross-linker (5 or 10 wt%) in the monomer feed were thermoplastics, whereas thermosets were accomplished when 15 or 20 wt% of organic cross-linker was used. The flexural strengths of the thermally processable samples (>3.4 MPa and >4.7 for BAS95 and BAS90, respectively) were quite high compared to those of familiar building materials such as portland cement (3.7 MPa). Furthermore, copolymer BAS90 proved quite resistant to degradation by oxidizing organic acid, maintaining its full flexuralmore »strength after soaking in 0.5 M H2SO4 for 24 h. BAS90 could also be remelted and recast into shapes over many cycles without any loss of mechanical strength. This study on the effect of monomer ratio on properties of materials prepared by RASP of small molecular aryl halides confirms that highly cross-linked materials with varying physical and mechanical properties can be accessed by this protocol. This work is also an important step towards potentially upcycling BPA from plastic degradation and sulfur from fossil fuel refining.« less
4. Valorisation of waste to yield recyclable composites of elemental sulfur and lignin

   https://doi.org/10.1039/C9TA03222C  

   Karunarathna, Menisha S. ; Lauer, Moira K. ; Thiounn, Timmy ; Smith, Rhett C. ; Tennyson, Andrew G. ( January 2019 , Journal of Materials Chemistry A)

   Lignin is the second-most abundant biopolymer in nature and remains a severely underutilized waste product of agriculture and paper production. Sulfur is the most underutilized byproduct of petroleum and natural gas processing industries. On their own, both sulfur and lignin exhibit very poor mechanical properties. In the current work, a strategy for preparing more durable composites of sulfur and lignin, LSx , is described. Composites LSx were prepared by reaction of allyl lignin with elemental sulfur, whereby some of the sulfur forms polysulfide crosslinks with lignin to yield a three-dimensional network. Even relatively small quantities (<5 wt%) of the polysulfide-crosslinked lignin network provides up to a 3.4-fold increase in mechanical reinforcement over sulfur alone, as measured by the storage moduli and flexural strength determined from dynamic mechanical analysis (temperature dependence and stress–strain analysis). Notably, LSx composites could be repeatedly remelted and recast after pulverization without loss of mechanical strength. These initial studies suggest potential practical applications of lignin and sulfur waste streams in the ongoing quest towards more sustainable, recyclable structural materials.
5. Halloysite infused jute fiber/poly (3-hydroxy-butyrate-co-3-valerate) bionanocomposites: Thermal, mechanical and fire retardant properties

   https://doi.org/10.1177/00219983221127062  

   Hasan, Kamrul SM ; Zainuddin, Shaik ; Turner, Azizi J. ; Hosur, Mahesh V. ; Jeelani, Shaik ( September 2022 , Journal of Composite Materials)

   Biocomposites have become more mainstream over the past decades for preserving the environment and producing sustainable materials as a potential substitute to synthetic polymer based composites derived from scarce petroleum materials. However, it is essential to investigate their mechanical, thermal and fire retardancy performance to answer the question of their suitability in automobile, biomedical, construction, film packaging, and commercial industries. In this work, we have studied one such promising biocomposites, jute fiber/poly (3-hydroxy-butyrate-co-3-valerate) (PHBV) and investigated their aforementioned properties. At first, 3–15 wt% halloysite nanotubes (HNTs) were dispersed in PHBV/chloroform mixture using an ultrasound process. PHBV/HNTs thin films were then prepared using the solvent casting method. Finally, jute fiber/PHBV-HNTs bionanocomposites were prepared using the compression mold method. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests were performed to study the thermal and fire retardancy properties. Uniaxial tensile and flexure tests were also performed to investigate the mechanical properties. In addition, scanning electron microscopy (SEM) was carried out to analyze the fracture surfaces of flexure tested samples. Results of jute/PHBV composites showed a significant increase in thermal and mechanical properties at 5 wt% HNTs loading in comparison to neat composites (without HNTs). In contrast, the composites with 15 wt% loading showed superior firemore »retardancy. SEM images of flexure tested samples showed enhanced interfacial bonding and less fiber pullout when compared to neat counterparts.

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