Blends of polypropylene (PP) and thermoplastic elastomers (TPE), namely SBS (styrene-butadienestyrene) and SEBS (styrene-ethylene/1-butene-styrene) block copolymers, were prepared to evaluate the effectiveness of the TPE type as an impact modifier for PP and influence of the concentration of elastomer on the polymer properties. Polypropylene homopolymer (PP-H) and ethylene-propylene random copolymer (PP-R) were evaluated as the PP matrix. Results showed that TPEs had a nucleating effect that caused the PP crystallization temperature to increase, with SBS being more effective than SEBS. Microstructure characterization tests showed that in most cases PP/ SEBS blends showed the smallest rubber droplets regardless of the matrix used. It was seen that SEBS is a more effective toughening agent for PP than SBS. At 0°C the Izod impact strength of the PP-H/SEBS 30% b/w blend was twofold higher than the SBS strength, with the PP-R/SEBS 30% b/w blend showing no break. A similar behavior on tensile properties and flexural modulus were observed in both PP/TPE blends. Yield stress and tensile strength decreased and elongation at break increased by expanding the dispersed elastomeric phase in the PP matrix.
SynopsisThe compatibility of poly(ethy1ene oxidehpolflmethyl methacrylate) (PEO-PMMA) blends were examined covering the complete composition range. Up to 20% of PEO content films were transparent and glass transition temperatures were determined by DSC and by refractive index vs. temperature measurements. Only one T, was obtained for these samples and the relationship between T8 and composition has been evaluated. At higher PEO content crystallization took place and the films were opaque. Melting temperatuures of PEO in blends were determined by DSC. Melting point depression was observed for increasing proportion of PMMA and the binary interaction parameter has been calculated.
EXPERIMENTALSeveral samples of commercial PEO were used (2, = 4,000, 6,000, and 10,000 from Atlas Industrias Quimicas S.A.; and Bw = 7,500, 14,000, and 18,500 from Polyscience Inc.). PMMA (B, = 6x lo5) was prepared by conventional suspension polymerization.Physical mixtures of PEO of different molecular weights and PMMA covering the whole range of composition were prepared at room temperature as cast films from chloroform solutions. The resulting films were subjected
Blends of isotactic polypropylene (PP), ethylene-propylene rubber copolymer (EPR), and ethylene-propylene crystalline copolymer (EPC) can be produced through in situ polymerization processes directly in the reactor and blends with different structure and composition can be obtained. In this work we studied the structure of five reactor-made blends of PP, EPR, and EPC produced by a Ziegler-Natta catalyst system. The composition of EPR was related to the ratio between ethylene and propylene used in the copolymerization step. The ethylene content in the EPR was in the range of 50 -70 mol %. The crystallization behavior of PP and EPC in the blends was influenced by the presence of the rubber, and some specific interactions between the components could be established. By preparative temperature rising elution fractionation (P-TREF) analysis, the isolation and characterization of crystalline EPC fractions were made.
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