Abstract
A series of substituted polybenzoxazines was synthesized and studied as binders in non-asbestos friction composite materials. The structures of the polybenzoxazines were varied in a systemic fashion by increasing the number and position of pendant alkyl (methyl) groups and was accomplished using the respective aromatic amines during the polymer synthesis step. By investigating the key thermomechanical and tribological characteristics displayed by the composite materials, the underlying structure-properties relationships were deconvoluted. Composite friction materials with higher thermomechanical and wear resistance properties were obtained from polybenzoxazines with relatively high crosslink densities. In contrast, polybenzoxazines with relatively low crosslink densities afforded composite friction materials with an improved coefficient of friction values and specific wear rates.
Highlights
Over the past 30 years, developments in the automotive industry have provided vehicles with impressive acceleration and speed capabilities
There was a significant increasing tendency in friction coefficient and wear rate values for all composites when braking temperatures increased to 200 or 250 ◦ C, accompanying the polymer matrix converted from glassy state to rubbery state
It was found that the coefficient of friction and wear rate of polybenzoxazine friction composites were found to be inversely correlated with the polybenzoxazine crosslink density of each type
Summary
Over the past 30 years, developments in the automotive industry have provided vehicles with impressive acceleration and speed capabilities. The reinforcement fibers contribute to composite strength, resistance wear rate, impact and thermal degradation, and other properties of friction materials. Phenolic resins are commonly used as binders for composite friction materials in part because they are available at low cost and possess moderate thermal stability at elevated temperatures, typically up to 300 ◦ C [11]. Cracking is often observed during the resin curing step because ammonia gas and other toxins are emitted as by-products [18] It is brittle and is not resistant to high temperature, which often results in wear loss and fade under 350 ◦ C for the friction materials [14,19]. Glass-to-rubber transition of polymers often leads to substantial change in stiffness, strength, and wear performance of composite friction materials as reported by Wu et al (2012) [21].
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