Silk/Natural Rubber (NR) and 3,4-Dihydroxyphenylalanine (DOPA)-Modified Silk/NR Composites: Synthesis, Secondary Structure, and Mechanical Properties

Abstract

Silk composites with natural rubber (NR) were prepared by mixing degummed silk and NR latex solutions. A significant enhancement of the mechanical properties was confirmed for silk/NR composites compared to a NR-only product, indicating that silk can be applied as an effective reinforcement for rubber materials. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and wide-angle X-ray diffraction (WAXD) analysis revealed that a β-sheet structure was formed in the NR matrix by increasing the silk content above 20 wt%. Then, 3,4-dihydroxyphenylalanine (DOPA)-modified silk was also blended with NR to give a DOPA-silk/NR composite, which showed superior mechanical properties to those of the unmodified silk-based composite. Not only the chemical structure but also the dominant secondary structure of silk in the composite was changed after DOPA modification. It was concluded that both the efficient adhesion property of DOPA residue and the secondary structure change improved the compatibility of silk and NR, resulting in the enhanced mechanical properties of the formed composite. The knowledge obtained herein should contribute to the development of the fabrication of novel silk-based elastic materials.

Unexpected Toughening of Poly(lactic acid) by Microwave-Assisted Devulcanization of Waste Latex Rubber

“…With an increase of MAD duration from 0 to 16 min, gradual gains in the intensity and area were obtained for the first halo centered at 2θ = 12.6°, as accompanied by the contrary transformation occurring for the second harmonic. The variations were primarily a result of the decreased intrachain correlation distance, offering evidence for the accumulative proportions of newly formed short and de-cross-linked chains . In addition, there were no obvious variations for the graphene-evoked diffraction peaks located at 26.6°, suggesting that the MAD process did not affect the structural features of the incorporated graphene nanosheets.…”

“…The variations were primarily a result of the decreased intrachain correlation distance, offering evidence for the accumulative proportions of newly formed short and decross-linked chains. 32 In addition, there were no obvious variations for the graphene-evoked diffraction peaks located at 26.6°, 33 suggesting that the MAD process did not affect the structural features of the incorporated graphene nanosheets. It was therefore assumed that the graphene nanosheets could steadily serve as the nanoabsorbers of microwave irradiation, 34 providing the critical prerequisite for the execution of our MAD approach.…”

Recent advances of natural fibers based green rubber composites: Properties, current status, and future perspectives

“…The main component of silk is silk fibroin, a filament core protein with excellent mechanical properties and biodegradability 53–54 . Smitthipong et al 55 reported that silk fibers (SIFs) can enhance the tensile strength of whole NR and purified NR.…”

A silk composite fiber reinforced by telechelic-type polyalanine and its strengthening mechanism

“…12 β-Sheets were thought to be finally involved in the crystalline or semicrystalline regions of silk fibers. 13 To improve the mechanical properties, natural rubber (NR), 14 collagen, 15 hydroxyapatite (HA), 16,17 poly(lactic acid) (PLA) 18 and graphene 19 were added to silk fibroins for biomedical applications. Although these additives are usually biocompatible or biodegradable to meet various application requirements, the problem of building strong interfacial cohesion between silk fibroins and additives remains largely unsolved.…”