Effect of variation of biobased phenolic resin content in natural rubber blend on rheological, thermal and tribological properties

A biobased copolymer, phenol-cardanol-formaldehyde (PCF928), was prepared by condensation reaction between phenol, cardanol, and formaldehyde. The mixture (P) of phenol and cardanol (92:8 w/w) was mixed with formaldehyde (F) in the molar ratio of 1:0.8 (P:F), and using oxalic acid as a catalyst, the reaction was carried out. This resin (PCF928) was blended with natural rubber in various proportions (like 5, 10, 20, and 30 phr), and four samples were prepared that had the same amounts of C-black as filler and all other ingredients. These were vulcanized in the presence of hexamethylene tetramine and sulfur together. These samples were characterized by density, hardness, and crosslink density. The blends possess higher crosslink density, hardness, and density than that of the pure rubber compound. Mechanical properties of the blends were greater than those of the pure natural rubber (NR) compound. All the blend samples were found equally stable up to 400⁰C. Storage and loss modulus of the blends improved with an increase in PCF928 content when measured by varying the frequency at a constant temperature (125⁰C). Wear resistance of the blends increased with a simultaneous reduction in the coefficient of friction due to the increase in the resin content in them.