Effects of Alkyl-Substituted Polybenzoxazines on Tribological Properties of Non-Asbestos Composite Friction Materials

Our plain-English summary of Effects of Alkyl-Substituted Polybenzoxazines on Tribological Properties of Non-Asbestos Composite Friction Materials, by A. Wongpayakyotin, C. Jubsilp, S. Tiptipakorn, et al (Polymers, 2021).

The study

• Authors: A. Wongpayakyotin, C. Jubsilp, S. Tiptipakorn, P. Mora, C.W. Bielawski, S. Rimdusit
• Journal: Polymers
• Published: 2021;13(4)
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This laboratory study tested brake friction materials made without asbestos. It did not study asbestos, human exposure or health. The authors made five benzoxazine resins from bisphenol A and different aromatic amines: aniline, o-toluidine, m-toluidine, p-toluidine and 3,5-xylidine. They used each resin as the binder (10% by weight) in a composite that also contained aramid pulp, carbon, glass and steel fibers, rubber and fillers. They then measured heat resistance, stiffness, strength, friction and wear. The composite made with 3,5-xylidine had the highest crosslink density and the one made with o-toluidine had the lowest. Composites with higher crosslink density were stiffer, more heat resistant and wore less at 25 °C. Friction values at 25 °C ranged from 0.25 to 0.36 and were lower in stiffer composites. The aniline-based composite was also tested from 100 to 350 °C. Its wear rate rose from 0.09 to 0.33 (times 10 to the minus 7 cm3 per N·m) between 100 and 300 °C, and reached 0.66 at 350 °C. The authors concluded that these values met the standard requirement for passenger-car brake pads.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory materials experiment (synthesis and testing of non-asbestos brake friction composites); no human or animal subjects
• Who was studied: Five friction composites, each using a benzoxazine resin made from bisphenol A and one of five aromatic amines (aniline, o-toluidine, m-toluidine, p-toluidine, 3,5-xylidine), made and tested in Thailand
• Exposure: No asbestos exposure was studied. The non-asbestos composites contained benzoxazine resin 10 wt%, aramid pulp 3.75, carbon fiber 1.25, glass fiber 10, steel fiber 25, barium sulfate 10, nitrile butadiene rubber 4, cashew dust 4, graphite 10 and zirconium silicate 25 wt%
• Main results:
  • Crosslink density was highest for the 3,5-xylidine composite (F-BA-35x, 9.86) and lowest for the o-toluidine composite (F-BA-ot, 8.72); the table gives units of 10 to the minus 3 mol/cm3
  • Glass transition temperatures of the composites ranged between 185 and 260 °C
  • Temperature at 5% weight loss ranged from 401 to 414 °C and correlated with crosslink density
  • Flexural strength ranged between 46.1 and 68.5 MPa and flexural modulus between 6.6 and 15.1 GPa
  • At 25 °C, average coefficient of friction ranged between 0.25 and 0.36 and was inversely proportional to storage modulus
  • At 25 °C, wear rate ranged from 2.13 to 0.62 (times 10 to the minus 7 cm3 per N·m) and decreased as crosslink density increased
  • For the aniline-based composite (F-BA-a), wear rate rose from 0.09 at 100 °C to 0.33 at 300 °C and 0.66 at 350 °C (times 10 to the minus 7 cm3 per N·m), described as within the standard requirement of less than 3.5 times 10 to the minus 7
• The authors' conclusion: The authors concluded that thermomechanical properties correlated with crosslink density, that friction and wear were inversely correlated with crosslink density, and that the aniline-based composite's friction and wear values agreed with the standard requirement for passenger-car brake pads

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