The present paper examined the positive temperature coefficient (PTC) property of carbon black (CB) filled isotatic polypropylene which was crystallized isothermally at 150°C, the fusion property of the matrix polymeric crystals and the distribution of CB particles in the matrix during spherulitic growing, then found out their relation. Two melting peaks were observed in thermograms of differential scanning calorimetry of these samples. The area of the lower melting peak decreased with increasing of crystallization time, outstripped area of higher melting peak at 25h. PTC peak temperature from lower melting peak shifted to higher melting peak at 25h, PTC intensity increased till 25h, suddenly decreased at 25h, again mildly increased after 25h. It was found from optical micrographs that 25h was just right a critical time, at which the spherulitics first contacted each other, CB particles crowded together around the spherulitic porphyries.

View full abstract

The thermodynamic interactions of rubbers (EPR and NBR) with various solvents (probes) were investigated by inverse gas chromatography (IGC) over a wide range of temperature from 60°C to 200°C.
Rubbers were coated on the Support (Chromosorb WAW DMCS (60_??_80 mesh)) as a thin layer film with various concentrations. The Support was carefully packed in the stainless steel column (2.2mm inner diameter×2000mm length).
Retention diagrams (R.D.) of rubber/solvent system were obtained by using the specific volumes (V⁰_g) obtained at 1/w→0 on the lnV_g vs. 1/w plopts. The R. Ds of rubbers showed linear lines in the whole temperature range. Values of the rubber/solvent interaction parameters (χ₁₂) were calculated from the V⁰_gs. The χ₁₂, at 60, 100, and 180°C for EPR with n-C₆H₁₂ were 0.22, 0.15, and -0.22, and for NBR, 1.31, 0.84, and 0.65, respectively. It should be understood that the EPR is more soluble in n-C₆H₁₂ than NBR. The χ₁₂ of other alkane such as n-C₅H₁₂ and n-C₁₀H₂₂ for NBR, were also larger than those for EPR.
The partial molar heat of sorption (_??_H^s₁) of alkane for EPR was larger than for NBR. These data indicate that EPR could adsorb alkane more strongly than NBR.

View full abstract

Wear properties of short fiber reinforced chloroprene rubber (SFRR) composites were examined when the SFRR were rubbed against four abrasive papers that had different surface roughness. The rubbing experiments were conducted in the longitudinal (L), transverse (T) and normal (N) directions of the oriented fibers to study the effect of fiber orientations on the wear rate, and the effect of roughness of the mating abrasive paper. The effects of diameters and materials of the reinforced fiber on the wear were also examined. When rubbed against fine abrasive papers, the wear rates of the SFRR tended to be much lower than those of the unreinforced rubber (CR). When rubbed against coarse abrasive papers, the difference in the wear rates between the SFRR and the CR became small, because the wear rates of the SFRR increased by reason of easy cutting or easy detachment of the reinforced fibers in the L and T directions of the SFRR. The transfer of rubber to the fine abrasive paper was observed in the experiments of the SFRR reinforced by large fibers in diameter. Then the wear rate was low and the frictional coefficient was high. For these facts, the surface roughness dependence on the wear rates of the SFRR was larger than those of the CR. Minimum frictional coefficient was observed when rubbed against abrasive paper having medium surface roughness. The plowing term of the friction became large with increasing the mating surface roughness, and the adhesion term of the friction also became large with decreasing the mating surface roughness.

View full abstract