Effect of soft and hard segments ratio of waterborne polyurethane on the properties of modified basalt fiber reinforced polypropylene composites

Abstract The interaction between fiber and polymer matrix is crucial for the properties of fiber‐reinforced composites. This paper explored the use of end‐capped waterborne polyurethanes (WPU) modified basalt fiber (BF) to reinforce the polypropylene (PP), aiming to improve interfacial interaction and mechanical properties. Furthermore, the effect of the ratio of soft and hard segments in the end‐capped WPU and the fiber content on the comprehensive properties of the composites have been thoroughly investigated. Three kinds of capped aqueous polyurethanes with different soft‐to‐hard segment ratios were prepared, corresponding to isocyanate indices ( R ) of 1.3, 1.4, and 1.5, respectively. The results indicated that the fracture section images of the composites confirmed the modification effect of BF and the good interfacial compatibility between end‐capped WPU modified BF (W‐BF) and PP. Moreover, the composite with R = 1.4 end‐capped WPU modified BF exhibited the optimum mechanical properties, fatigue properties and thermal deformation temperature. Specifically, the tensile strength, fatigue performance and heat distortion temperature achieved value of 47.7 MPa, 55,000 cycles and 142.5°C, which represent increases of 32.5%, 400%, and 10.9%, respectively, compared with the unmodified fiber‐reinforced composites, respectively. This efficient interface modification strategy will provide a novel method for high‐performance fiber reinforced composites. Highlights Waterborne polyurethanes improve the surface roughness of BF. Chemical and physical interaction between WPU and BF. WPU modification to enhance BF‐PP interfacial interaction. WPU and BF increase the tensile strength by 40%. Stronger interfacial interactions lead to higher thermal stability.