Research and development activities directed toward commercial production of cellulosic ethanol have created the opportunity to dramatically increase the transformation of lignin to value-added ...products. Here, we highlight recent advances in this lignin valorization effort. Discovery of genetic variants in native populations of bioenergy crops and direct manipulation of biosynthesis pathways have produced lignin feedstocks with favorable properties for recovery and downstream conversion. Advances in analytical chemistry and computational modeling detail the structure of the modified lignin and direct bioengineering strategies for future targeted properties. Refinement of biomass pretreatment technologies has further facilitated lignin recovery, and this coupled with genetic engineering will enable new uses for this biopolymer, including low-cost carbon fibers, engineered plastics and thermoplastic elastomers, polymeric foams, fungible fuels, and commodity chemicals.
Additive manufacturing is distinguished from traditional manufacturing techniques such as casting and machining by its ability to handle complex shapes with great design flexibility and without the ...typical waste. Although this technique has been mainly used for rapid prototyping, interest is growing in direct manufacture of actual parts. For wide spread application of 3D additive manufacturing, both techniques and feedstock materials require improvements to meet the mechanical requirements of load-bearing components. Here, we investigated short fiber (0.2–0.4mm) reinforced acrylonitrile–butadiene–styrene composites as a feedstock for 3D-printing in terms of their processibility, microstructure and mechanical performance. The additive components are also compared with traditional compression molded composites. The tensile strength and modulus of 3D-printed samples increased ∼115% and ∼700%, respectively. 3D-printing yielded samples with very high fiber orientation in the printing direction (up to 91.5%), whereas, compression molding process yielded samples with significantly lower fiber orientation. Microstructure–mechanical property relationships revealed that although a relatively high porosity is observed in 3D-printed composites as compared to those produced by the conventional compression molding technique, they both exhibited comparable tensile strength and modulus. This phenomenon is explained based on the changes in fiber orientation, dispersion and void formation.
Dynamic covalent crosslinking such as disulfide bonds, Diels-Alder (DA) reactions are widely used for healing applications. Herein, we report a simple approach involving the metal-ligand reversible ...interactions in diverse nature, which helps in developing a robust and self-healable carboxylated nitrile (XNBR) rubber by employing low cost and the commercially obtainable materials. Self-healing performance and mechanical properties were organized by introducing the various metal-ligand domains into the XNBR rubber. The network of XNBR, in-situ cross-linked via metal-ligand complexes, consists of strong and weak coordination bonds. The strength of various metal-ligand modified coordination bonds, healing performance, and mechanical properties primarily depend on the type of metal ions. The Fourier transform infrared spectroscopy (FTIR) makes the various metal-ligand coordination bond formation into the XNBR rubber visible. The coordination crosslinked XNBR rubber with 4 phr of Zn and Co metal ion exhibits high tensile strength (4.3±0.6 and 10.3±1.1 MPa) with excellent healing efficiency (100 and 88%), which is far higher than the most reported non-covalent supramolecular modified elastomers. The various metal-ligand coordination bonds are fully reconstructed during the rebuilding process and exhibiting excellent self-healing property.
Textile grade polyacrylonitrile (PAN) was used as a precursor material for carbon fiber preparation. E-beam irradiated polyacrylonitrile grafted carbon nanofibers were dispersed in polyacrylonitrile ...solution (dissolved in dimethyl formamide). Carbon nanofibers (CNF) infused polyacrylonitrile solution was wet spun on a lab-scale wet-spinning setup to form 50 to 70 µm diameter fibers with 3.2 wt.% CNF-PAN, 6.4 wt.% CNF-PAN, and neat PAN. Precursor fibers were characterized for thermal, mechanical and morphological properties using various techniques. Drawing the precursor fibers further enhanced polymer chain orientation and coalesced the voids, enhancing tensile strength and modulus by more than 150% compared to those of the undrawn fibers. Precursor composite fibers on carbonization showed enhanced strength, compared to that of pristine PAN fibers, by four times and stiffness by 14 times. The carbon–carbon composite fibers were further characterized with SEM/FIB, XRD and tensile strength. The property improvements were dependent on the uniform distribution of carbon nanofibers, and surface modification of carbon nanofibers further enabled their dispersion in the composite fibers. Furthermore, 3.2 wt.% CNFs in PAN fibers showed maximum improvement in properties compared to 6.4 wt.% CNF in PAN fibers, indicating that the property enhancements go through a maximum and then drop off due to challenge in getting uniform distribution of nanofibers.
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•Super TPV based on XNBR and PA12 via the application of novel cyclic peroxide.•Highest mechanical properties and thermal stability of TPV of 50:50 XNBR-PA12.•Superior performance ...behaviour with reference to heat and oil aging study.
Thermoplastic vulcanizates (TPVs) are special classes of thermoplastic elastomers, in which dynamic vulcanization of the rubber phase takes place during melt mixing with a semi-crystalline thermoplastic matrix phase at elevated temperature. TPV is characterized by processing behaviour like thermoplastic at elevated temperature and performance properties of vulcanized rubber at ambient temperature. High performance TPVs or super TPVs are new generation TPVs which exhibit high heat resistance as well as excellent oil resistance property suitable for automotive under-the-hood applications. In the present work, a new super TPV based on carboxylated acrylonitrile butadiene rubber (XNBR) and polyamide (PA12) has been developed. (XNBR:PA12) TPVs of different blend ratios have been prepared by using a fixed concentration of novel cyclic monofunctional peroxide. Final morphology of TPVs varies from either a co-continuous to a dispersed one depending on the blend ratio. TPV of 50:50 XNBR-PA12 shows the highest mechanical properties as well as superior thermal stability among all other TPVs. From differential scanning calorimetric (DSC) study, it can be clearly seen that the glass transition temperature (Tg) of XNBR has shifted to high temperature range in case of all TPVs as compared to that of uncrosslinked blend system. Dynamic mechanical analysis (DMA) also demonstrates that tanδ values of all the TPVs are lower and the storage moduli are higher than the uncrosslinked blend system. Lowest tanδ peak of TPV of 50:50 blend ratio of XNBR:PA12 indicates the highest degree of crosslinking and this is also supported by the swelling studies. The highest level of mechanical properties and superior thermal stability support that phenomenon. Heat aging and oil resistance study have also been carried out in details to understand the performance behaviour of these super TPVs at service condition.
In the present work, the development and characterization of an intrinsically self-healable material based on butyl imidazole modified bromobutyl rubber (BIIR)/natural rubber (NR) blends, which are ...filled with carbon nanotubes (CNTs) are reported. It was found that the addition of CNTs and the blending with NR significantly enhance the tensile strength of the BIIR composites. The use of butyl imidazole as physical cross-linker for the BIIR phase provides the blend composites the non-covalent bondings, which are responsible for their self-healing properties. Owing to the increase of the viscosity of the BIIR phase upon its physical crosslinking the island-matrix morphology of the blend changes over to a co-continuous structure. The preferential wetting of the CNT surface by the low-loading NR phase in the NR/BIIR blends can be explained by the good rubber-filler interaction between the linked phospholipids of the NR molecules and the π-electrons of the CNT surface. As a result, the favored localization of the CNTs in the NR phase strongly improves the electrical properties of the blends according to the double percolation theory. On the other hand it does not deteriorate the self-healing of the BIIR phase. The high electrical conductivity provides us a possibility to heat the blend by application of an electrical voltage in order to accelerate the self-healing process.
Carbon fibers having unique morphologies, from hollow circular to gear‐shaped, are produced from a novel melt‐processable precursor and method. The resulting carbon fiber exhibits microstructural and ...topological properties that are dependent on processing conditions, rendering them highly amenable to myriad applications.
Novel thermoplastic vulcanizates (TPVs) based on silicone rubber (PDMS) and polyamide (PA12) have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of ...various types of peroxides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP), 3,3,5,7,7-pentamethyl 1,2,4-trioxepane (PMTO) and cumyl hydroperoxide (CHP) were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide) had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indicate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High storage modulus (E') and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.
The ZSM‐5 zeolite powders were prepared through in situ extraction (extraction and conversion in single step process) of silica from rice husk ash in the presence of other aqueous‐based precursors ...(sodium aluminate and tetrapropyl ammonium hydroxide) following a simple hydrothermal condition at 130°C–170°C. The powders were characterized by X‐ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR) spectroscopy, N2 physisorption measurements, and field emission scanning electron microscopy (FESEM). Crystallizations of ZSM‐5 were noticed at 130°C/96 h, 150°C/24 h, and 170°C/12 h. The exothermic peak at 422°C in DTA curve indicated the removal of tetrapropyl ammonium ions (TPA+) used as structure directing agent (SDA). The vibration bands at around 550 and 1221 cm−1 indicated the presence of double 5‐ring in ZSM‐5. The 150°C–170°C‐treated samples exhibited higher BET surface area and pore volume compared to those of 130°C‐treated powders. The FESEM images showed coffin‐shaped morphology of the powders, and their sizes increased with increase in both reaction temperature and time.
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