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Okazaki, Japan

Chaikumpollert O.,Nagaoka University of Technology | Chaikumpollert O.,National Metal and Materials Technology Center | Wakisaka O.,Tokai Rubber Industry Ltd | Mase A.,Tokai Rubber Industry Ltd | And 3 more authors.
Rubber Chemistry and Technology

Decelerated fermentation of natural rubber latex was performed to investigate the relationship between the morphology and mechanical properties of natural rubber. Natural rubber latex was preserved with sodium hydroxymethylglycinate, as a bactericide, to decelerate the fermentation of nonrubber components such as proteins, phospholipids, carbohydrate, and so forth. Gradual increases in the viscosity of the latex and gel content of the resulting rubber took place as the preservation period was prolonged, which were distinguished from less change in the viscosity of high-ammonia natural rubber (HANR) and high gel content of its rubber. The particle size distribution was dramatically changed during decelerated fermentation, although that of the HANR latex did not change. The pH and nitrogen content of the rubbers were independent of the preservation time. Morphology of the fermented natural rubber and the HANR was observed with scanning probe microscopy. Fewer mechanical properties of the fermented natural rubber were related to the destruction of the nanomatrix structure of the nonrubber components, which resulted from the decrease in the fatty acid ester groups with bacteria as compared with the good mechanical properties of the HANR. Source

Chaikumpollert O.,Nagaoka University of Technology | Sae-Heng K.,Rajamangala Institute of Technology | Wakisaka O.,Tokai Rubber Industry Ltd | Mase A.,Tokai Rubber Industry Ltd | And 2 more authors.
Polymer Degradation and Stability

Low temperature degradation of natural rubber was performed with potassium persulfate (K2S2O8, KPS) in the latex stage at 30 °C to accomplish a good processability of the rubber. Various grades of natural rubbers were used as a source rubber. Gel content, molecular weight and chemical structure of the rubbers were characterized by swelling method, size exclusion chromatography and 1H NMR spectroscopy, respectively. The well characterized natural rubber was subjected to oxidative degradation with KPS at 30 °C. Mooney viscosity decreased when the latex was degraded with 1.0 phr of KPS and it was dependent upon the amount of KPS. Molecular weight and gel content of the degraded natural rubber were about one-half as low as those of the source rubber. Chemical structure of the rubber was analyzed through Fourier transform infrared and 1H NMR spectroscopic methods. The degraded natural rubber was found to contain carbonyl and formyl groups as an evidence of the oxidative degradation. Tensile strength of a vulcanizate prepared from the degraded natural rubber was the same as that prepared from the source rubber, even though the gel content and the molecular weight of the degraded rubber were distinguished from those of the source rubber. © 2011 Elsevier Ltd. All rights reserved. Source

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