ELSEVIER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Polymer Degradation and Stability 61 (1998) 303-307 0 1998 Elsevier Science Limited. All rights reserved Printed in Great Britain PII: SO141-3910(97)00214-O 0141-3910/98/W front matter Effectiveness of a plant polymer as an antioxidant zyxwvutsrqponm B. C. Bag, A. K. Ghosh, B. Adhikari & S. Maiti* zyxwvutsrqponmlkjihgfedcbaZYXW Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302, India (Received 5 April 1997; revised version received 18 August 1997; accepted 10 September 1997) A renewable polymer collected as a gum from a local plant (M oringa oleifera) was blended with styrene butadiene rubber (SBR). Tensile properties like 200% modulus, 300% modulus, elongation at break (%), tensile strength and hardness of filled vulcanizates were measured before and after isothermal aging at 100°C for 24, 48 and 72 h in presence of air. The results are compared with a non- polymeric antioxidant additive N-phenyl-N’-isopropyl-p-phenylene diamine (IPPD). The plant polymer is only slightly less effective than IPPD as an anti- oxidant. 0 1998 Elsevier Science Limited. All rights reserved 1 INTRODUCTION Oxidation of a polymer can occur at all stages, i.e. from synthesis to final use, causing undesirable changes in mechanical, aesthetic, and electrical properties. To protect the polymer from oxidation, low molecular weight phenolics, amines, organo- sulfur and organophosphorus compounds are used.lp2 These compounds have some drawbacks like surface blooming and volatilization, with a consequent loss of activity.394 Other problems with these compounds may be toxicity, leaching and migration in contact with solvents/chemicals, and reduction of mechanical properties of the vulcani- zate by causing disruption of the stress propaga- tion through the polymer chains. These problems can be solved by using a poly- meric antioxidant which is thermally stable, non- toxic and compatible with the base polymer. The main aim of this investigation was to evaluate the performance of a plant polymer (PP) to be blended with SBR as an antioxidant and to compare its effectiveness with the conventional antioxidant IPPD. The characteristics of the plant polymer have been included in a separate communication.5 The gummy plant polymer from Moringu olezfera is highly polar with tin of 6630 and &f, of 9268. It contains carbon, hydrogen, oxygen, phosphorus and calcium and is soluble in highly polar aprotic *To whom correspondence should be addressed. 303 solvents. Although the gum could not be struct- urally characterized completely, the presence of phosphorus and the fire retardancy property of the gum were the main reasons behind the investiga- tion of antioxidant property of the plant polymeric gum because phosphoric acid esters are known to be heat stabilizers in polymers.’ Some additional advantages of this plant polymer are thermal stabi- lity, compatibility with NR, SBR, CR, etc. and resistance to leaching.5 2 EXPERIMENTAL 2.1 Materials Styrene butadiene rubber (SBR, 1502). N-cyclo- hexylbenzthiazyl sulfenamide (CBS) (ICI India), zinc oxide (E. Merck), carbon black (N 330) (Phi- lips Carbon Black Ltd.) spindle oil (MCI, India), stearic acid (LR, Wilson Laboratory, India), sulfur (LR, Qualigens, India), IPPD (ICI, India) were used as obtained. 2.2 Compounding Compounding of filled stocks of SBR with com- mercial antioxidant (IPPD) and plant polymer (PP) was carried out separately following a standard laboratory procedure (ASTM Dl5-54T, 1954) on a two-roll rubber mixing mill at a friction ratio 1.2. Rubber was first masticated to form a band on the