Development of ballistic armor based on Kevlar[trademark] fiber and fumed silica-filled polybenzoxazine composites

Abstract

The aim of this study is to develop a ballistic armor produced from the matrix of polybenzoxazine (PBZ) modified with fumed silica (nano-SiO[subscript 2]), and the reinforcing Kevlar[superscript TM] fiber. From our previous research, polybenzoxazine has been reported to be a versatile polymer being tailor-made for many purposes. The outstanding properties of polybenzoxazine are its outstanding mechanical and thermal properties as well as its good processability. One of the unique properties of this polymer is its compatibility with many kinds of fillers. In this study, fumed silica was selected to mix with polybenzoxazine in order to modify its rigidity which is related to its sound propagation velocity. The property is important in ballistic impact resistant mechanism. The suitable condition for the preparation of the polybenzoxazine-fumed silica molding compounds and composites was investigated. The results revealed that the processing condition of the molding compounds to attain their fully cured stage was by heating at 160ํC for 2 hours, 180ํC for 2 hours (in the hydraulic hot-press machine, at 25 MPa), followed by post-curing at 200ํC for 4 hours (in an oven). The experimental results also revealed that the optimal nano-SiO[subscript 2] content in the polybenzoxazine was at 7wt% the Kevlar composite preparation. In addition, the polybenzoxazine matrix modified with 7wt% of the nano-SiO[subscript 2] was able to increase the flexural modulus from 5.98 GPa of the pure polybenzoxazine up to about 7.52 GPa in the composite. The thermal properties were found to increase with increasing the nano-SiO[subscript 2] contents. In the ballistic composite sample, the optimal weight ratio of fiber and modified polybenzoxazine matrix was approximately 75:25. The armor composite with 7wt% nano-SiO[subscript 2] at this composition ratio was able to render desirable ballistic performance up to NIJ standard of level IIIA. The thickness of the polybenzoxazine armor composite that can resist a ballistic impact of the NIJ standard at this level was 30 piles or higher. In addition, it was found that the first plate with the thickness of at least 15 piles was crucial to sufficiently destroy the projectiles of this high level.