JOURNAL OF MATERIALS SCIENCE 24 (1989) 688-692 Scanning electron microscopic studies on the tear fracture of polyethylene filled natural rubber vulcanizate J. KURIAN, S. AKHTAR, G. B. NANDO, S. K. DE Rubber Technology Centre. Indian Institute of Technology, Kharagpur 721 302. India Tear failure of natural rubber (NR) filled with high density polyethylene (HDPE) was studied by scanning electron microscopy (SEM). The tear strength of NR was increased by the addition of HDPE. It was found that HDPE forms physical links with NR. The retention of tear strength by ageing attains an optimum value with HDPE loading. 1. Introduction The service life of rubber products depends on their resistance to various types of failure modes, an import- ant one of which is tear. Many theories have been proposed to describe the tear fracture of filled and unfilled rubber vulcanizates [1-5]. Thermoplastic filled elastomers have the advantage of good processing properties like lower die swell, better finish of extruded and calendered products and also higher green strength. Over the last two decades, FORCE ~x~CRACK "\PROPAGATION -b -~ CUT TABLE I Formulations of the mixes Ingredients Mix 1 Mix 2 Mix 3 Mix 4 Natural rubber 100.00 I00.00 I00.00 100.00 Zinc oxide 5.00 5.00 5.00 5.00 Stearic acid 2.00 2.00 2.00 2.00 Sulphur 2.50 2.50 2.50 2.50 2 Vulkacit CZ 1.00 1.00 1.00 1.00 3HDPE 0.00 10.00 30.00 50.00 Tear strength (kNm -~) 36.5 35.9 41.4 50.8 I ISNR-5, supplied by Rubber Research Institute of India, Kottayam, India. 2N-cyclohexyl-2-benzothiazyl sulphenamide, supplied by Bayer (India) Limited, Bombay, India. 3High Density Polyethylene - HOSTALEN GA 7260, obtained from Polyolefins Industries Limited, Bombay, India. Melting point 128-132 ° C; Density 0.960 g cm-3; Melt Flow Index (DIN 53735) - 16. several patents have appeared where thermoplastic semicrystalline materials have been blended with vulcanizable rubbers to obtain composites with improved properties [6-9]. This paper examined the mechanism of tear fracture in natural rubber vulcanizates filled with high density polyethylene. The effect of heat ageing on the tear strength of these vulcanizates has also been studied. Scanning electron microscopy (SEM) has been successfully used by FORCE Tear SCAN AREA Fracture surface Figure 1 Tear test specimen. 688 Figure 2 Tear fractograph of unfilled NR vulcanizate (100 x ). 0022-2461/89 $03.00 + .12 © 1989 Chapman and Hall Ltd.