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Open AccessFeature PaperArticle

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

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Biomacromolecules Research Team, RIKEN Center for Sustainable Resource Science, 2-1, Saitama, Wako 351-0198, Japan
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Materials Structure Group I, Research & Utilization Division, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
*
Author to whom correspondence should be addressed.
Academic Editor: Yasumoto Nakazawa
Molecules 2020, 25(1), 235; https://doi.org/10.3390/molecules25010235
Received: 13 December 2019 / Revised: 26 December 2019 / Accepted: 2 January 2020 / Published: 6 January 2020
(This article belongs to the Special Issue Silk Fibroin Materials)
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. View Full-Text
Keywords: silk; natural rubber (NR); composite; enzymatic modification; 3,4-dihydroxyphenylalanine (DOPA) silk; natural rubber (NR); composite; enzymatic modification; 3,4-dihydroxyphenylalanine (DOPA)
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Sogawa, H.; Korawit, T.; Masunaga, H.; Numata, K. Silk/Natural Rubber (NR) and 3,4-Dihydroxyphenylalanine (DOPA)-Modified Silk/NR Composites: Synthesis, Secondary Structure, and Mechanical Properties. Molecules 2020, 25, 235.

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