Effect of melt viscosity of polypropylene on fibrillation of thermotropic liquid crystalline polymer in in situ composite film

 Various grades of polypropylene were melt blended with a thermotropic liquid crystalline polymer, a block copolymer of p-hydroxy benzoic acid and ethylene terephthalate (60/40 mole ratio). The blends were extruded as cast films at different values of draw ratio (slit width/film thickness). Fibrillation of TLCP dispersed phase with high fiber aspect ratio (length/width) was obtained with the matrix of low melt flow rate, i.e., high viscosity and with increasing film drawing. Melt viscosities of pure components and blends measured using capillary rheometer were found to decrease with increasing shear rate and temperature. Viscosity ratios (dispersed phase to matrix phase) of the systems being investigated at 255 °C at the shear rate ranged from 10² to 10⁴ s⁻¹, were found to lie between 0.04 and 0.15. The addition of a few percent of elastomeric compatibilizers; a tri-block copolymer SEBS, EPDM rubber and maleated-EPDM, was found to affect the melt viscosity of the blend and hence the morphology. Among these three compatibilizers, SEBS was found to provide the best fibrillation. Received: 10 January 2000/Accepted: 24 January 2000     

Mechanical characteristics of hydrogenated natural rubber vulcanizates

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 N₂H₄ and H₂O₂ 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. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic Study of Di-Imide Hydrogenation of Natural Rubber

The diimide hydrogenation of natural rubber (NR) was studied by using p-toluenesulfonylhydrazide (TSH) as a diimide-releasing agent. The microstructure and the percentage of hydrogenation were studied by Raman, ¹H-NMR and ¹³C-NMR spectroscopic techniques. Quantitative measurements on fraction of hydrogenated part gave the results in good agreement by using these techniques. The results indicated that percent hydrogenation increased with increasing of reaction time and about 80-85 % hydrogenation was achieved when a two-fold excess of TSH was used. The vibrational characteristic of C=C bond of NR is strongly Raman active and noted at 1663 cm⁻¹. The decrease of this signal was clearly observed during the progress of hydrogenation but the vibrational frequency of the cis and trans structures of the trisubstituted olefin unit of NR can not be differentiated by this technique. While ¹H- and ¹³C-NMR analysis showed that cis-trans isomerization of carbon-carbon unsaturation of NR occurred during hydrogenation.