ABSTRACT:The hydrogenation of natural rubber (NR) and various epoxidized natural rubbers (ENR) was investigated by using diimide generated in situ from the thermal decomposition of p-toluenesulfonylhydrazide (TSH) in oxylene solution at 135°C.1 H-NMR analysis indicated that approximately 85-95% of hydrogenation was performed with a twofold excess of TSH. FT-IR and Raman spectroscopy were employed to confirm the microstructure characteristics of the hydrogenated rubbers. The cis-trans isomerization was also observed by 1 H-and 13 C-NMR. The signal in 1 H-NMR of the epoxide group of the ENR disappears after hydrogenation while the signal of the opened epoxide ring product was detected. This may be due to the epoxide ring opening reaction caused by the p-toluenesulfinic acid by-product. The high temperature of the reaction condition leads to chain degradation in both NR and ENR. Thermal behaviors of the hydrogenated rubbers characterized by differential scanning calorimetry showed that the glass transition temperatures of the hydrogenated rubbers were increased about 10 -20°C compared with the starting rubbers.

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The sol-gel reaction of tetraethoxysilane in natural rubber (NR) latex was conducted to produce in situ silica-filled NR latex, followed by adding sulfur cross-linking reagents to the latex in a liquid state. The latex was cast and subjected to sulfur curing to result in a unique morphology in the NR composite of a flexible film form. The contents of in situ silica filling were controlled up to 35 parts per one hundred rubber by weight. The silica was locally dispersed around rubber particles to give a filler network. This characteristic morphology brought about the composite of good dynamic mechanical properties. Synchrotron X-ray absorption near-edge structure spectroscopy suggested that the sulfidic linkages of the sulfur cross-linked composites were polysulfidic, S x (x ≥ 2), and a fraction of shorter polysulfidic linkages became larger with the increase of in situ silica. The present observations will be of use for developing a novel in situ silica-filled NR composite prepared in NR latex via liquid-phase soft processing.

Stereocomplex polylactide (scPLA) films were prepared by melt blending of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) with and without an epoxy-based chain extender before compression molding. The obtained scPLA films were characterized through differential scanning calorimetry, X-ray diffractometry (XRD), tensile testing and dimensional stability to heat. XRD patterns revealed that all the scPLA films had only stereocomplex crystallites. The obtained results showed that the chain-extension reaction improved mechanical properties of the scPLA films, however, it suppressed stereocomplexation and heat resistance.

Mechanical properties of partially hydrogenated natural rubber (HNR) vulcanizates were evaluated regarding their chemical structure and crystallizable nature of HNR, and are reported here, to the best of our knowledge, for the first time. HNRs of three levels of hydrogenation (20.6, 29.0, and 40.6 mol%) were successfully prepared by the chemical modification of natural rubber (NR) latex using N 2 H 4 and H 2 O 2 as reagents, in a sufficient amount for preparing sulfur-crosslinked samples to be subjected to mechanical and structural measurements. The three HNR vulcanizates were found to be crystallizable upon stretching; it is noted that even 40.6 mol% hydrogenation did not prevent HNR vulcanizates from crystallization upon stretching, while their onset strain of crystallization was higher than that of NR vulcanizate. The hysteresis loss and residual strain up to a stretching ratio of 2 for the HNR vulcanizates tended to become larger with the increase in the degree of the hydrogenation. Tensile and dynamic mechanical properties of 20.6 mol% hydrogenated HNR vulcanizate were comparable to those of NR vulcanizate. From differential scanning calorimetry and temperature dispersion of dynamic modulus or loss, the glass transition temperatures of HNR vulcanizates were found to be almost the same as that of NR vulcanizate, which is also notable. The thermal stability of HNR vulcanizates was better than that of NR vulcanizate. Thus, this chemical modification seems to give a promising NR derivative whose properties can be equivalent or even better than the mother polymer.