Highly Transparent Thermoplastic Elastomer From Isotactic Polypropylene and Styrene/Ethylene-Butylene/ Styrene Triblock Copolymer: Structure-Property Correlations Zubair Ahmad, 1 K. Dinesh Kumar, 1 Madhumita Saroop, 2 Nisha Preschilla, 2 Amit Biswas, 2 Jayesh R. Bellare, 3 Anil K. Bhowmick 1 1 Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302, India 2 Polymer Research & Technology Centre, Reliance Industries Ltd., Mumbai 400071, India 3 Department of Chemical Engineering, Indian Institute of Technology, Mumbai 400076, India Polypropylene (PP) is one of the most useful general purpose plastics. However, the poor transparency and brittleness of PP restricts its applications in the field of medical and personal care where silicone and polyvinyl chloride (PVC) are presently used. This work concen- trates on developing highly transparent elastomeric PP blends and also thermoplastic elastomer by blending isotactic polypropylene (I-PP) with styrene/ethylene- butylene/styrene (SEBS) triblock copolymer. PP/SEBS blend derived from high melt flow index (MFI) PP and high MFI SEBS exhibit remarkable transparency (haze value as low as 6%) along with good percentage of elongation and processability. The reduction in differ- ence of refractive index (RI) between PP and SEBS has been observed by blending SEBS with PP. The wide angle X-ray diffraction studies show that there is sig- nificant reduction in the percentage crystallinity of PP by the addition of SEBS block copolymer. Tempera- ture-dependent polarized light microscopy studies reveal the reduction in spherulites size by the addition of SEBS block copolymer. Transmission electron micrographs show that the SEBS polymer forms a fine lamellar structure throughout the PP matrix with phase inversion at higher SEBS concentration. Development of phase morphology, crystalline morphology, and crystallinity in different blends has been analyzed and microstructure-haze correlations have been develo- ped. POLYM. ENG. SCI., 50:331–341, 2010. ª 2009 Society of Plastics Engineers INTRODUCTION Silicone and polyvinyl chloride (PVC) polymers are widely used in medical and personal care products requir- ing good transparency [1]. Silicone has excellent high temperature performance and chemical resistance. How- ever, silicone is very expensive material. On the other hand, PVC is a low cost material with wide processing window. However, there is a growing recycling concern over PVC. Polypropylene (PP) is one of the most familiar poly- mers used in industry and in daily life. Although PP exhibits superior mechanical properties, the poor transpar- ency and brittleness of PP restricts its applications in the field of medical and personal care, where silicone and PVC are presently used [2]. Therefore, it is of great im- portance to explore methods to increase the softness and transparency of PP. There are several ways to increase the transparency of PP [3], e.g., (1) to increase the frac- tion of amorphous phase, (2) to reduce the size of spheru- lites, and (3) to destroy spherulite structure by stretching. To increase the transparency, crystalline polymers are usually thermally quenched or crystallized by adding nucleating agents. Thermal quenching, however, reduces the dimensional stability of the polymers. Nucleation agents bring a contamination problem when the polymer is used as a container or as wrapping film for food, drugs, and so on. Consequently, it is very important to increase the transparency of PP without thermal quenching or nucleating agents. Therefore, enhancing the transparency of PP by increasing the fraction of amorphous phase could be an excellent choice among the various available options. In literature, there are several reports which examine different TPEs based on PP especially for automotive and industrial applications [4–10]. Various types of thermo- plastic elastomers (TPEs) based on rubber-plastic blends [11–16] have been reported from our laboratory. Correspondence to: A.K. Bhowmick; e-mail: anilkb@rtc.iitkgp.ernet.in DOI 10.1002/pen.21540 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2009 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2010