Filler dispersion is a critical factor in determining the properties of filled rubber composites. Silica has a high density of silanol groups on the surface, which lead to strong filler-filler interactions and a poor filler dispersions. A cure accelerator, N-tert-butyl-2-benzothiazole sulfenamide (TBBS), was found to improve filler dispersion in silica-filled natural rubber (NR) compounds. For the silica-filled NR compounds without the silane coupling agent, the reversion ratio generally increased with increase in TBBS content, whereas those of the silica-filled NR compounds containing the silane coupling agent and carbon black-filled NR compounds decreased linearly. The tensile strength of the silica-filled NR vulcanizate without the silane coupling agent increased as the TBBS content increased, whereas carbon black-filled samples did not show a specific trend. The experimental results were explained by TBBS adsorption on the silica surface and the improvement of silica dispersion with the aid of TBBS.
The electrospinning of sodium alginate, a natural biopolymer, was performed from aqueous solutions by blending with PEO, a biodegradable polymer. The conductivity and surface tension of solutions of sodium alginate and PEO were investigated by standard methods. The morphology, thermal, and mechanical properties of the electrospun nanofibers were studied using field emission scanning electron microscopy (FE‐SEM), fourier transform infrared spectroscopy (FT‐IR), energy dispersive X‐ray (EDX), differential scanning calorimetry (DSC) and tensile testing. Uniform, smooth, and ultra‐fine nanofibers with diameters of ∼140–190 nm were obtained with solution concentrations of 6–7.2% and sodium alginate/PEO volume ratios of 30:70–50:50. The mechanical strength of the electrospun sodium alginate/PEO mats with good morphology was 21 MPa compared to PEO mats which had a strength of only 10 MPa. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers
ABA-type block copolymers composed of poly(6-benzyloxycarbonyl-L-lysine) (PCLL) as the A component and poly(ethy1ene oxide) as the B component were synthesized by polymerization of 6-benzyloxycarbonyl-L-lysine N-carboxyanhydride initiated by primary amino groups located at both ends of the PEO chain. From circular dichroism measurements in solution, as well as from infrared spectra measurements in the solid state, it was found that the polypeptide block exists in the a-helical conformation, as in PCLL homopolymer. The intensity of wide-angle X-ray diffraction patterns of the block copolymers depends on the PEO content and shows basically similar reflections as the PCLL homopolymer. The morphology examined by transmission electron microscopy and differential scanning calorimetry revealed microphase-separated structure.
SYNOPSISTWO new thermotropic liquid crystalline polymers (LCPs) were synthesized. One is a dimesogenic LCP having a flexible hexamethylene spacer in the main chain, the other is a rigid-type main-chain LCP having alkoxy side groups on the terephthaloyl moiety of the polymer. Blends of LCP with poly(buty1ene) terephthalate were melt-spun a t different LCP contents and different draw ratios to produce a monofilament. Maximum enhancement in the ultimate tensile strength was observed for the blends containing 5% LCP at any draw ratio, and decreased with further increase in LCP content. The initial modulus monotonically increased with increasing LCP content. The tensile properties of the rigid-type LCP blends were higher than those of the flexible main-chain LCP blends. 0 1996 John Wiley & Sons, Inc. I NTRO D UCTlO NThermotropic liquid crystalline polymers (LCPs) have been the subject of considerable research due to their specific chemical structures, high strength, high modulus, low viscosities, and other good mechanicalIn the molten state, LCP shows the increased mechanical strength and stiffness of a thermoplastic matrix polymer. Moreover, even relatively small amounts of LCP may induce a reduction in the melt viscosity, and thus improve processability. LCP may also improve other properties of thermoplastics, such as dimensional and thermal stability?Blending conventional thermoplastic polymers with LCPs can lead to easier processing and reinforcement of the matrix. Much work has been done in the area of blending LCPs with engineering therm o p l a s t i c~.~-~ It has been shown for some pairs of polymers that one can obtain so-called self-reinforced composites in which LCP phase in situ forms * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 60, 939-946 (1996) 0 1996 John Wiley & Sons, Inc.CCC 00Zl-S995/96/070939-08 reinforcing fibers in a matrix of an engineering therr n o p l a~t i c .~*~-~~ Recent literature has shown that flexible spacers or flexible side-groups in the rigid backbone of the LCPs may have a positive influence on the adhesion, and mechanical properties of the LCP blends may be Rodlike LCPs, e.g., the fully aromatic polyesters (Vectra, etc.), will therefore probably be replaced in many cases by LCPs containing flexible elements, designed to fit just one matrix polymer.This paper deals with the physical and mechanical properties of two new thermotropic LCP blends. A structural main-chain LCP with a flexible spacer (Main-LCP) was prepared from 1,6-dibromohexane, hydroquinone and p-hydroxybenzoic acid; and a rigid LCP having dialkoxy side groups (Side-LCP) was synthesized from dialkoxyterephthalic acid and biphenol. The properties of the Main-LCP blends were compared with those of blends prepared from the Side-LCP and poly(buty1ene terephthalate) (PBT). We also describe the mechanical properties of the in situ composites obtained from the blends. To improve tensile properties, the optimum processing parameters such as draw ratio and the LCP content 939 940 CHA...
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