Phosphorylated cardanol prepolymer-grafted carboxylated styrene–butadiene rubber for better processing with enhancing silica filler dispersion Onkar Prabhavale, 1 Denial Mahata , 1 Golok B. Nando 1,2 1 Rubber Technology Centre, IIT Kharagpur, Kharagpur 721302, West Bengal, India 2 School of Minerals, Metallurgical and Materials Engineering, IIT Bhubaneswar, Bhubaneswar 752050, Odisha, India Correspondence to: D. Mahata (E-mail: denial.mahata@gmail.com) and G. B. Nando (E-mail: nandogb@iitbbs.ac.in) ABSTRACT: Cardanol is a byproduct of cashew industry of semiforest origin. It is cheap and available in humongous amount and acts as a multifunctional additive in rubber compounds. It can be oligomerized with orthophosphoric acid to make phosphorylated cardanol prepolymer (PCP). Hence, cardanol has been chemically grafted on to the backbone chain of carboxylated styrene–butadiene rubber (XSBR) by employing melt grafting technique in presence of peroxide initiator to include multifunctional properties. The PCP-grafted XSBR (PCP-g-XSBR) was characterized by using Fourier transform infrared spectroscopy and 1 H-NMR techniques and optimize the grafting conditions such as percent of grafting and grafting efficiency by using Taguchi methodology. PCP-g-XSBR was compounded with silica filler for a comparative study in terms of processing behavior with XSBR. The cure characteristics such as the cure rate and the optimum cure time of the unfilled PCP-g-XSBR compounds were determined by oscillating disc rheometer. The thermal analysis of PCP-g-XSBR vulcanizate exhibits slightly better thermal stability as well as plasticization effect. Morphological behaviors also display the less cracked and filled fracture surfaces with better filler dispersion in PCP-g-XSBR vulcanizate. The mechanical properties of the com- pounded PCP-g-XSBR vulcanizates also improve compare to XSBR vulcanizates. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47528. KEYWORDS: elastomers; functionalization of polymers; grafting; plasticizer; synthesis and processing techniques Received 3 November 2018; accepted 19 December 2018 DOI: 10.1002/app.47528 INTRODUCTION Rubber as a strategic material is widely used in society from birth to death. Most common usage of rubber is mainly in tires, auto- mobiles, mechanical goods, construction industries, textile indus- tries, and biomedical applications. The major components of rubber products are rubber, reinforcing fillers, sulfur, process oils, and other additives like stabilizers, antioxidants, and so forth. Mineral oils such as paraffinic, naphthenic, and aromatic oils have proven their importance as softeners, extender, and process aids in rubber compounds. They improve the processability and also enhance the quality of dispersion of fillers in the rubber matrix. 1 Since January 2010, petrochemically derived mineral oils contain polycyclic aromatic compounds, which are basically car- cinogenic nature. Therefore, European Union and United States of America strictly prohibited on the use of mineral oils in the production of tires. As per EU law, the processed oils containing more than 3% polycyclic aromatic content cannot be used as rub- ber process oils in tire and other rubber products. 2 Therefore, finding a suitable alternatives for mineral oil in rubber processing is necessary to reduce health risk in all rubber industries. Cardanol, a promising natural resource from cashew nut shell liquid and waste of the cashew industry, is a well-established alternative source for replacement of mineral oil in rubber pro- cessing. 3 Chemically, it is known as meta-pentadecenyl phenol carrying a C-15-long lipidic side chain at the meta position of the phenolic ring, which creates the plasticization effect in rubber with easy processing. Phosphorylated cardanol prepolymer (PCP) serves as an excellent “multifunctional additive,” which can replace processing oil plasticizer. It performs various roles such as a plasticizer during compounding, a tackifier, a fire retardant, a coagent for vulcanization, improver of filler dispersion and physicomechanical properties of vulcanizates, as well as crosslink density. It is amphiphilic in nature with a polar phosphate group and a nonpolar C 15 unsaturated side chain. Therefore, PCP can act as a good compatibilizer and can also enhance filler reinforce- ment properties for rubber. In addition, the unsaturation in side © 2019 Wiley Periodicals, Inc. 47528 (1 of 9) J. APPL. POLYM. SCI. 2019, DOI: 10.1002/APP.47528