Thermal and Mechanical Properties of Acrylonitrile-Butadiene Rubber Modified Polybenzoxazine as Frictional Materials

Abstract

Frictional composites based on polybenzoxazine (PBA-a) and acrylonitrile-butadiene rubber (NBR) are developed in this study. Mechanical, thermal and tribological properties of the PBA-a/NBR composites at 0, 2, 5, 10 and 15wt% of NBR particle contents are evaluated. Curing behaviors of the NBR-benzoxazine molding compounds are examined by differential scanning calorimetry to show an exothermic peak of about 222°C compared with that of the benzoxazine resin, i.e. 232°C suggesting curing acceleration of the benzoxazine resin due to the presence of the NBR particles. The storage modulus of the NBR-filled PBA-a is observed to systematically decrease from 5.2 GPa of the neat PBA-a to 2.8 GPa with an addition of 15wt% of the rubber particles. Glass transition temperature (Tg) of the composites evaluated by dynamic mechanical analysis increases with increasing of NBR particle contents, i.e. from 172°C for PBA-a to 186°C for PBA-a/15wt% NBR. Furthermore, the friction coefficients of the composites with 2wt% NBR are determined to be 0.603 for static type and 0.528 for kinetic type. Those values are improved from the value of 0.597 and 0.475 for unmodified polybenzoxazine, respectively. Therefore, the obtained outstanding properties, i.e. storage modulus, glass transition temperature and friction coefficient make the polybenzoxazine composites highly attractive to be utilized as friction materials.

Effects of graphite/partially carbonized hemp hurd particle mass ratios on tribological properties of polybenzoxazine composites

“…The flexural modulus and flexural strength of the friction composite material specimens were determined following ASTM D790-M93 using a universal testing machine, Instron, (model 5567 from Instron (Thailand) Co., Ltd. (Bangkok Thailand)). The dimension of each specimen was 25 × 60 × 3mm 3 . The test was performed in a three-point bending mode with a support span of 48 mm and at a crosshead speed of 1.2 mm/min.…”

“…Benzoxazine resin is one suitable candidate for this application because of its distinctive advantages that are suitable for employing as polymeric binders for non-asbestos organic friction materials (NAO FMs), including very low melt viscosity, good interfacial adhesion with fillers, self-polymerizability upon heating via ring-opening polymerization without catalyst or curing agent, and no by-product release in the curing process [2]. Polybenzoxazines also exhibit outstanding properties contributing to exceptional tribological performances of NAO FMs, including near-zero shrinkage, low water absorption, high glass transition temperature of 170 -340 oC, high thermal stability with degradation temperature at 5% weight loss (Td5) of 315 -350 °C, and excellent mechanical properties, i.e., flexural strength of 126 MPa and flexural modulus of 4.5 GPa [3][4][5][6]. Reinforcement fibers improve the mechanical properties and play a major role in maintaining stiffness, strength, and tribological behaviour of friction composites, fillers are added mainly to reduce cost and maintain the overall composition [7].…”

“…The molding compounds were mixed using an internal mixer at 120 o C for 40-45 min. The free volume of the mixer chamber with cam rotor mounted is 105 cm 3 . Molding compounds including all ingredients with a mass of 50-100 g was put into a mixer chamber to ensure a thorough and uniform mixing.…”