Processing of polypropylene blends

Only two classes of polypropylene (PP) blends have achieved commercial success blends wiA polyolefins and with polyamides (PA). With PP/polyolefin blends, the goal is either to improve the impact resistance of the base resin (impact-modified PPs) or to produce thermoplastic elastomers (d)mamically vulcanized blends). PA/PP blends aim at bridging the property gap between the two pol5oners. Therefore, sigitificant information on processing is available only for these two families of blends. 

In PP/EPDM systems (e.g. Vestolen EM, Hiils), advantage has been taken of the combination of crystalline tmd amorphous polymer properties. The blends are formulated by selecting molecular weights of the components and concentration of the elastic segments in the EPDM. Some of these blends are prepared by dynamic vulcanization. 

Dynamically vulcanized blends ([3, 4] see also the chapter on Thermoplastic dynamic vulcanizates in this book) are produced by melt mixing an elastomer phase with a thermoplastic (the elastomer being the major component) and then curing the elastomer during melt mixing. The resulting blend comprises the thermoplastic resin hlled with high concentration of rubber particles well bonded to the matrix. These blends are usually PP/EPDM (Santoprene ) or PP/polybutadiene (PB), but ex- 

Despite their high viscosity, these PP/EPDM blends are easily extruded. The recommended extruder should have L/D s 24 and the screw a moderate compression ratio, e.g. 2.S-3.5, which is similar to those used for polyvinyl chloride (PVC) or PE extrusion. Temperature settings should be increased with the blend hardness. Owing to the two-phase nature of the blend, the material has relatively high extradate swell which increases with shear stress, i.e. with resin hardness, at constant shear rate. 

Blends of PA-6 or PA-66 with PP (e.g. Oigalloy , Elf Atochem, Ultra-mid JQR, BASF) have flow properties similar to PP. This constitutes an improvement over the flow behavior of neat PA. The PA/PP blends are easier to extrude than PA because the melt viscosity is less sensitive to temperature variations. The processing conditions for PP/PA-66 blends are comparable to those normally used to process PA-66. However, it shovild be noted that (hying of these blends is much slower than that for the neat PA. For single-screw extrusion, the barrel should have L/D s 20, fitted with a standard three-zone screw, with compression ratio of 2.5-3. Excessive shearing may cause destruction of morphology, and thus 

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Manchado M. A. L., Biagiotti J. and Kenny J. M., Rheological behavior and processability of polypropylene blends with rubber ethylene propylene diene terpolymer. J. Appl. Polym. Sci. 81 (2001) pp. 1-10. 

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