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.ABSTRACT
Cure curve of (A) non-filler, (B) carbon black–filled, and (C) silica-filled compounds.
Stress–strain curve of (A) non-filler, (B) carbon black–filled, and (C) silica-filled compounds.
Relationship between nitrogen contents and swelling degree of non-filler (█), carbon black–filled (▵), and silica-filled (•) compounds.
Number of sulfur bonding and amount of bonding sulfur of (A) non-filler, (B) carbon black–filled, and (C) silica-filled vulcanizates determined by the conventional swelling method. ▵, polysulfide (mol/cc); •, disulfide (mol/cc); █, monosulfide (mol/cc); ×, amount of bonding sulfur (%).
13C FG-MAS NMR spectrum for carbon black–filled compounds. The overview chemical shift for HANR is described in the top of the figure. The enlarged spectrum ranging from 30 to 70 ppm for (A) HANR, (B) DPNR(U), (C) DPNR(E), (D) PFNR, and (E) Pureprena.
Relationship between nitrogen contents and intensity ratio (%) of the signal at 57 ppm for carbon black–filled compound, normalized with the signal at 23 ppm as a reference.
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