SynopsisCrystallization of polypropylene (PP) in the blends of PP with styrene+thylene butylene-styrene triblock copolymer (SEBS) is studied through differential thermal analysis (DTA) and X-ray diffraction measurements. Analysis of crystallization exotherm peaks in terms of crystallization nucleation and growth rates, crystallite size distribution, and crystallinity revealed differences in the morphology of PP component in the blend in the different regions of blend composition. Crystallinity determined by X-ray diffraction and DTA showed identical variations with blend composition. Variations in tensile properties of these blends with blend composition are also reported. Correlations of the various tensile properties with the crystallization parameters, viz., the crystallinity and crystallite size distribution, are presented, which confirm the influence of crystallization of PP component on the tensile properties of these blends. INTRODUCTIONIt has been shown1 that blending of polypropylene (PP) with high density polyetheylene (HDPE) or reinforcement with short glass fiber affects the crystallization and morphology of PP. An understanding of the crystallization behavior of PP is of great importance to explain the mechanical properties of polyblends and composites involving PP as the major component.Blends of PP with various other polymers have been r e p~r t e d~-~ to show improvements in mechanical and rheological properties suited to many applications. SEBS (styrene-ethylene butylene-styrene) triblock copolymer, obtained by hydrogenation of the butadiene sequence, is a recently developed thermoplastic elastomer. Blends of SEBS with HDPE and polystyrene (PS) and the development of thermoplastic interpenetrating polymer networks (IPN) with SEBS were recently reported.6 Lindsey, Paul, and Barlow7 found that addition of SEBS to the binary HDPE-PS blends improved the ductility, toughness, and various mechanical properties but lowered the strength and modulus. In the case of thermoplastic IPN's, Siegfried, Thomas, and SperlingG developed the two types of thermoplastic IPN's (chemically blended and mechanically blended) with styrene, methacrylic acid, and isoprene monomers. TheyG found a dual phase continuity after ionomer formation in both types of these IPNs, while the melt viscosity was lower in the chemically blended IPN than the mechanically blended one. Blends of SEBS with PP, reported8 recently by us, have shown considerable improvement in the melt rheological properties of PP, favorable from the point of view of processing.In this paper we present a study of crystallization of PP in the blend of PP and SEBS, with SEBS content varying from 5 to 25 wt %. The crystallization be- havior and the degree of crystallinity are determined through the differential thermal analysis (DTA) and X-ray diffraction measurements. Use of thermal analysis techniques (DTA or DSC) for the study of crystallization kinetics of PP is illustrated in the literaturel~~ DTA or DSC thermogram of PP shows welldeveloped crystallization exot...

Improving the processability and physical properties of sustainable biobased polymers using biobased fillers is essential to preserve its biodegradability and make them suitable for different end user applications. Herein, we report the use of spray-dried lignin-coated cellulose nanocrystals (L-CNCs), a biobased filler, to modify the rheological and thermo-mechanical properties of poly­(lactic acid) (PLA) composites. The lignin coating on CNCs not only improved the dispersion of CNCs but also enhanced their interfacial interaction with the PLA matrix, resulting in a significant improvement in rheological and thermo-mechanical properties. The rheological percolation threshold concentration obtained by power law analysis for PLA/L-CNC composites was found to be 0.66 wt %, which is significantly lower than the reported values for other PLA/CNC composites. Such a low rheological percolation concentration of L-CNCs can be attributed to excellent dispersion of L-CNCs in the PLA matrix. Addition of only 0.5 wt % L-CNCs to the PLA matrix resulted in an almost 60% improvement in storage modulus, relative to neat PLA, as measured by dynamic mechanical analysis. This improvement in mechanical properties can be attributed to a significant increase in the degree of crystallinity of the PLA. Excellent dispersion and compatibility of L-CNCs with PLA allowed generation of a high density of nucleating sites resulting in an increase in the degree of crystallinity of the PLA matrix. Improvement in the storage modulus at higher loading of L-CNCs can be attributed to both high crystallinity and reinforcement by L-CNCs. We have readily prepared a fully biobased transparent and potentially biodegradable PLA film through film blowing by addition of just 0.3 wt % L-CNCs in the PLA matrix. This present study clearly demonstrates that L-CNCs can serve as excellent fillers for PLA for the development of fully biobased composites.

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Tensile yield behavior of the blends of polypropylene (PP) and styrene–ethylene butylene–styrene block copolymer (SEBS) is studied in blend composition range 0–25 wt % SEBS. Three sets of samples, (i) solution‐blended compression‐molded (SBCM), (ii) melt‐blended compression‐molded (MBCM), and (iii) melt‐blended injection‐molded (MBIM), were studied to investigate the relative merits of solution blending and melt blending and the effect of subsequent mixing during injection moulding. Systematic changes with varying blend composition were found in stress–strain behavior in the yield region, viz., in yield stress, yield strain, width of yield peak, and work of yield. Growth of shear bands before necking also showed some systematic variation with blend composition. Shapes and sizes of dispersed‐phase (SEBS) domains at various blend compositions were studied by scanning electron microscopy. Analysis of yield stress data on the basis of the various expressions of first power and two‐thirds power laws of blend composition dependence and the porosity model (i.e., the exponential law) led to consistent results from all expressions about the variation of stress concentration effect in these sample sets; the stress concentration effect increased in the following order: MBIM < SBCM < MBCM. Furthermore, in addition to revealing relative suitability of the various expressions to the present system, this analysis also showed a transition around the blend composition 5 wt % SEBS from a continuous to a discontinuous structure. Solution blending produces lower degree of discontinuity in the structure of this two‐phase blend than the melt blending, and this discontinuity in melt blended samples is reduced on subsequent mixing during injection‐molding process.

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