Surface sizing introducing carbon nanotubes for interfacial bond strengthening of basalt fiber–reinforced polymer composites

In order to solve the problem of poor interfacial bonding between the smooth and inert basalt fibers (BFs) and the polyamide 6 (PA6) matrix, carboxylated carbon nanotubes (CNTs) were modified onto the surface of BFs using a simple, environmentally friendly, continuously processable, and non-damaging fiber skeleton sizing method via water-soluble polyurethane dispersion. It was found that the highly chemically active carboxylated CNTs were uniformly dispersed on the surface of BFs with adjustable surface roughness and wettability. With enhanced interfacial bonding effect between the BFs and PA6 matrix by surface sizing of 1.5 g/L CNTs, the tensile strength and tensile modulus of the BF-reinforced composites were improved by about 17.5% and 32.6%, and the flexural strength and flexural modulus increased by about 36.0% and 62.5%, with a higher storage modulus and lower loss factor. With the sizing modification of CNTs, the friction and wear reduction properties of the BF-reinforced PA6 composites were also enhanced, and the wear resistance improvement was up to 40.5%. The introduction of CNTs could make a tight bond between the BFs and PA6 matrix to bear frictional shear damage and produce small size abrasive chips. The CNT sizing–modified BF-reinforced PA6 composites presented shallow and narrow 3D wear surface with low surface roughness parameters. The roughened and activated BFs may form a mechanically engaging interface with the polymer matrix molecular chain segments, which could bear more shear damage and relieve the fatigue wear and adhesive wear for the CNT sizing–modified BF-reinforced composites. The above simple and effective strategies and research laws for enhancing interfacial bonding could promote wider applications of BF-reinforced polymer composites in lightweight and high strength, friction and wear reduction, and high temperature resistance.