Mechanical properties and cross-linking structure of cross-linked natural rubber

Enhancement in antimicrobial efficacy and biodegradation of natural rubber latex through graphene oxide/nickel oxide nanoparticles

This work aims to fabricate antibacterial natural rubber latex composites by introducing different ratios of graphene oxide (GO) and nickel oxide (NiO) nanoparticles. The nanocomposites were prepared using latex mixing and a two-roll mill process, followed by molding with a heating hydraulic press. Detailed analyses were conducted to evaluate the rheological, chemical, physical, thermal, mechanical, and electrical performance of the composites. Fourier transform infrared spectroscopy (FTIR) was employed to analyze the interaction among different components, while the surface morphology was examined through the field emission scanning electron microscopy (FESEM) technique. The composites with a loading ratio of 1:2 of GO to NiO (optimized concentration) exhibited the highest tensile strength (24.9 MPa) and tear strength (47.4 N/ mm) among all the tested samples. In addition, the composites demonstrated notable antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. The thermal stability of the composites was observed up to 315 °C, and their electrical resistivity lies in the insulating range across a temperature span of 25 °C to 50 °C. The research uncovers critical insights into advancing composite materials suitable for diverse applications, featuring inherent antibacterial attributes, robust mechanical properties, resilience to solvent, UV shielding properties, and controlled electrical resistivity capabilities.

PROTEIN INFLUENCE ON THE MECHANICAL PROPERTIES OF NR

Effect of protein on vulcanization of NR, obtained from Hevea brasiliensis, was investigated by analyzing the crosslinking structure of the resulting vulcanizates prepared from untreated NR, deproteinized natural rubber (DPNR), and protein-free natural rubber (PFNR) by swelling methods and rubber-state NMR spectroscopy. The proteins present in NR were removed by three methods: deproteinization with enzyme, urea, or urea–acetone in the presence of sodium dodecyl sulfate. The amount of proteins present in NR, approximately 0.238 w/w%, was reduced to 0.000 w/w% by urea–acetone deproteinization, whereas it was reduced to approximately 0.003 and 0.019 w/w% by enzyme and urea deproteinizations, respectively. Hardness, swelling degree, and crosslinking structure depended on the amount of proteins. Changes in mechanical properties for the vulcanizates prepared from not only non-filler compounds but also carbon black–filled and silica-filled compounds were attributed to the amount of proteins.

Bacterial and enzymatic degradation of poly(cis-1,4-isoprene) rubber: Novel biotechnological applications

Poly(cis-1,4-isoprene) rubber is a highly demanded elastomeric material mainly used for the manufacturing of tires. The end-cycle of rubber-made products is creating serious environmental concern and, therefore, different recycling processes have been proposed. However, the current physical-chemical processes include the use of hazardous chemical solvents, large amounts of energy, and possibly generations of unhealthy micro-plastics. Under this scenario, eco-friendly alternatives are needed and biotechnological rubber treatments are demonstrating huge potential. The cleavage mechanisms and the biochemical pathways for the uptake of poly(cis-1,4-isoprene) rubber have been extensively reported. Likewise, novel bacterial strains able to degrade the polymer have been studied and the involved structural and functional enzymes have been analyzed. Considering the fundamentals, biotechnological approaches have been proposed considering process optimization, cost-effective methods and larger-scale experiments in the search for practical and realistic applications. In this work, the latest research in the rubber biodegradation field is shown and discussed, aiming to analyze the combination of detoxification, devulcanization and polymer-cleavage mechanisms to achieve better degradation yields. The modified superficial structure of rubber materials after biological treatments might be an interesting way to reuse old rubber for re-vulcanization or to find new materials.

Connecting caddisworm silk structure and mechanical properties: combined infrared spectroscopy and mechanical analysis

The underwater silk of an aquatic casemaking caddisfly larvae (Hesperophylax occidentalis) is viscoelastic, and displays distinct yield behaviour, large strain cycle hysteresis and near complete recovery of its initial strength and stiffness when unloaded. Yield followed by a stress plateau has been attributed to sequential rupture of serial Ca(2+)-cross-linked phosphoserine (pS) β-domains. Spontaneous recovery has been attributed to refolding of the Ca(2+)/pS domains powered by an elastic network. In this study, native Ca(2+) ions were exchanged with other metal ions, followed by combined mechanical and FTIR analysis to probe the contribution of pS/metal ion complexes to silk mechanical properties. After exchange of Ca(2+) with Na(+), the fibres are soft elastomers and the infrared spectra are consistent with Cv3 symmetry of the -[Formula: see text] groups. Multivalent metal ions decreased the -[Formula: see text] symmetry and the symmetric stretching modes (vs) split in a manner characteristic of ordered phosphate compounds, such as phosphate minerals and lamellar bilayers of phosphatidic acid lipids. Integrated intensities of the vs bands, indicative of the metal ion's effect on transition dipole moment of the P-O bonds, and thereby the strength of the phosphate metal complex, increased in the order: Na(+) < Mg(2+) < Sr(2+) < Ba(2+) < Ca(2+) < Eu(3+) < La(3+) < Zn(2+) < Fe(2+) With a subset of the metal ion series, the initial stiffness and yield stress of metal ion-exchanged fibres increased in the same order: [Formula: see text] [Formula: see text] establishing the link between phosphate transition dipole moments and silk fibre strength.

Self-tensioning aquatic caddisfly silk: Ca2+-dependent structure, strength, and load cycle hysteresis

Caddisflies are aquatic relatives of silk-spinning terrestrial moths and butterflies. Casemaker larvae spin adhesive silk fibers for underwater construction of protective composite cases. The central region of Hesperophylax sp. H-fibroin contains a repeating pattern of three conserved subrepeats, all of which contain one or more (SX)n motifs with extensively phosphorylated serines. Native silk fibers were highly extensible and displayed a distinct yield point, force plateau, and load cycle hysteresis. FTIR spectroscopy of native silk showed a conformational mix of random coil, β-sheet, and turns. Exchanging multivalent ions with Na(+) EDTA disrupted fiber mechanics, shifted the secondary structure ratios from antiparallel β-sheet toward random coil and turns, and caused the fibers to shorten, swell in diameter, and disrupted fiber birefringence. The EDTA effects were reversed by restoring Ca(2+). Molecular dynamic simulations provided theoretical support for a hypothetical structure in which the (pSX)n motifs may assemble into two- and three-stranded, Ca(2+)-stabilized β-sheets.