Preparation, characterization of cardanol grafted natural rubber and evaluation of technical properties of its vulcanizates

摘要

Cardanol is chemically known as m-pentadecenyl phenol obtained by double vacuum distillation of cashew nut shell liquid, a by-product of cashew industry. It is a proven multifunctional additive (MFA). Grafting of cardanol onto natural rubber will impart inherent MFA characteristics to the natural rubber. The objective of this work is to graft cardanol onto natural rubber (NR) in the condensed phase in a Brabender Plasticorder. Grafting is confirmed by infrared spectroscopy and nuclear magnetic resonance spectroscopy. Grafted rubber is characterized by evaluation of its plasticity, Mooney viscosity and Limiting Oxygen Index. Plasticity of the grafted rubber is higher than the raw natural rubber and is found to be comparable to rubber containing 5～7phr of aromatic process oil. Thermal characterization using differential scanning calorimetry has been carried on the raw NR and cardanol grafted NR. Comparative study of technical properties of the vulcanizates obtained from natural rubber by varying the dose of process oil (3, 5 and 7phr) and vulcanizates obtained from cardanol grafted natural rubber have been carried out. Green compound of the grafted rubber showed faster curing behavior reflected in the increased cure rate and decreased cure time. Vulcanizate of the grafted rubber exhibited higher tensile strength, elongation at break and tear strength in comparison to vulcanizates of virgin natural rubber. Other technical properties such as resilience and compression set have also been evaluated and are found to be better than 3～5 phr oil plasticized NR vulcanizates. Results of ageing test show that vulcanizates of the grafted rubber have 10% higher retention of tensile strength and elongation at break than the vulcaniztes of virgin natural rubber. Thus cardanol acts as plasticizer, cure promoter, an antioxidant in addition to enhancement in tensile properties when grafted onto the backbone of natural rubber.