ABSTRACT:The effect of the stearic acid coated fillers and their geometry on the shear/dynamic viscosity and complex viscosity has been investigated using polypropylene (PP) compounds filled with stearic acid uncoated and coated talc, calcite, and mixed talc/calcite particles. The viscosity was measured over a wide range of shear rates (10 Ϫ8 to 10 3 ) using a capillary, cone-plate and sandwich rheometer. Overall, the rheological properties of the compounds exhibited different behavior upon different filler systems, stearic acid involvement, shear stress or strain, and frequencies due to stearic acid involvement. This implies that the stearic acid lowers the interfacial force between the filler surface and the resin matrix, followed by a favorable processing. In addition, at very low shear stresses, the viscosity of talc(un) compounds was higher than calcite(un) ones; at very high shear stresses, on the other hand, talc compounds became lower than calcite(un) compounds. This is interpreted as due to the different geometry between talc and calcite. The yield value as a function of shear stress was observed for all filler systems and exhibited lower than that obtained from the extrapolation. Furthermore, the CoxMerz relation between the complex and shear viscosity for both the stearic acid uncoated and coated compounds is found not valid.

Moisture was treated on a silica surface and it was added into bis(triethoxysilylpropyl)disulfide (TESPD)/carbon black (CB)/S-SBR compound and mixed in an internal mixer. The effects of moisture were investigated with respect to the temperature rise during mixing, processability, cure characteristics, and mechanical properties and two-pass (2P) mixings were compared with conventional three-pass (3P) mixings. Addition of the moisture treated silica into the compound lowered the heat generation during mixing, lowered the drop temperature, decreased the scorch time, lowered the heat build up, lowered the tanδ (E″/E′), increased the Mooney viscosity, increased the torque rise (MH-ML), increased the elongation modulus, increased the blow out time, and increased the deformation%. The properties of each compound were gradually increased with the level of moisture and the 2P mixing procedure generated less heat during mixing and exhibited better mechanical properties than the 3P mixing one. The addition of water molecules improved the silane reaction with silica surface via improved hydrolysis and resulted in an increased level of cross-linking. It also seemed hydrolyzes the benzothiazolesulfenamide accelerator and resulted in a faster scorch and an increased cure rate.

Moisture and temperature effects were investigated on silica/(triethoxysilylpropyl) disulfide (TESPD)/carbon black (CB)/S-SBR compounds with respect to processability, vulcanization characteristics, physical properties, and alcohol residues. The moisture-treated compounds exhibited lower rates of viscous heat generation during mixing, lower discharging temperatures (drop temperatures), lower Mooney viscosities, shorter cure times (T c -90), higher torque rises (M H Ϫ M L ), less heat build ups (HBU), and equal or less alcohol residues than the control. As the drop temperatures of the compound were increased, decreased temperature differences between mixer sensor (set drop) and real (proven) temperatures, increased the scorch times (T s -2), decreased the cure times (T c -90), increased the tensile moduli, and decreased the alcohol residues remaining in the compound. The higher temperature drop compounds (160 and 176°C) exhibited no reversion behavior; however, the lower temperature (120 and 140°C) drop compounds exhibited marching behavior. The treatment of moisture on the silica surface influenced the hydrolysis reaction to the silane and improved coupling on the silica surface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 623-633, 2005

In this study, polypropylene grafted with maleic anhydride (PP-g-MA) and styrene ethylene-co-butylene styrene block copolymer grafted with maleic anhydride (SEBS-g-MA) were used as coupling agents for polypropylene-based wood-plastic composites containing 50 wt % wood flour. Adding up to 5 wt % PP-g-MA to the composite increased the tensile strength of the woodplastic composite (WPC) by almost 100% and the reversed-notch Izod impact strength by more than 100%; the modulus remained essentially unchanged. By contrast, the same amount of SEBS-g-MA had a greater effect on the impact strength but a smaller influence on the tensile strength; in addition, the modulus was reduced. On using a combination of 2 wt % PP-g-MA and 1 wt % SEBS-g-MA, the impact strength of the composite could be increased significantly, but the tensile strength and modulus were not reduced to any appreciable extent relative to the use of PP-g-MA alone. Because WPCs are building products where minimizing costs is extremely important, this finding has important commercial implications.

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