Preparation And Properties Of Bullet-penetration Resistant Polyurethane Composites

With the improvement of science and technology development level,high lethality weapons were emerging,so it was significant to research and develop composite protective materials with high protective performance,flexible,lightweight and high energy absorption.In this paper,different structures of polyurethane（PU）and surface modification of aramid fiber（AF）were designed to improve the bullet-proof performance of its composites.The process consisted of three steps:First,prepared polytetramethylene ether glycol（PTMG）based PU,and then introduced polycarbonate glycol（PCDL）containing ester group to improve the properties of PU.PU was compounded with AF,aramid weftless cloth（UD cloth）,poly（p-phenylene benzoxazole）（PBO）fiber and carbon fiber to prepare bullet-proof composite target plate.Finally,the surface of AF was modified by secondary functionalization of various silane coupling agents（SCA）and polydopamine（PDA）,and the bullet-proof target plate meeting the requirements was prepared.The structure of polyurethane elastomer（PUE）was designed.PTMG was used as the soft segment of the prepolymer method,and the prepolymer（PUP）was formed by reaction with dicylocyhexylmethane diisocyanate（HMDI）.Then,a series of PUEs with different soft segment contents were prepared by using dimethylthionyltoluene diamine（DMTDA）,3,3’-dichloro-4,4’-diaminodiphenyl methyl（MOCA）and other diamine chain extenders.The micro and macro effects of soft segment contents of PUEs were analyzed by fourier transform infrared spectroscopy（FTIR）,wide-angle X-ray diffraction（WAXD）,differential scanning calorimetry（DSC）,dynamic mechanical analysis（DMA）and stress-strain curves.The results showed that the introduction of PTMG could improve the microphase separation,crystallization properties and low temperature resistance of PUE,and reduced the tensile and dynamic mechanical properties of PUE.PCDL/PTMG polyurea（PUA）was prepared by adding PCDL based on the above PUE.After comparing the performance of PUA and PUE,a bullet resistant target plate was prepared by combining PUA with four types of fibers.The results showed that the introduction of polar ester group-COO-promoted the formation of hydrogen bonds in the hard segment of-NH,resulting in the general improvement of the microphase separation degree,amino hydrogen bonding index and mechanical properties of PUA compared with PUE.The increase of hard segment content will increase the degree of micro-phase separation,dynamic mechanical properties and tensile strength of PUA,but will reduce its low temperature resistance and crystallinity.Through scanning electron microscopy（SEM）and live fire target testing,it was found that UD cloth had the best bullet penetration resistance due to its high surface roughness and the best interfacial bond strength with PUA.In order to compensate for the shortcomings of AF such as smooth surface and few active functional groups,The surface of AF was grafted with reagents such as Ca Cl₂ethanol solution,SCA,PDA aqueous solution,and the effects of different reagents on its microstructure and macroscopic properties were investigated through SEM,X-ray photoelectron spectroscopy（XPS）,FTIR,thermogravimetric（TGA）,single fiber tensile strength test,and H extraction test.The results showed that all kinds of reagents were successfully grafted on AF surface,which increased the roughness of fiber surface and the active groups such as-OH and epoxide,and effectively improved the interface bonding strength between AF and PUA.The secondary functional modification of PDA can further improve the mechanical properties and interface strength of AF.The tensile strength of AF-PDA-KH570 can reach 251.05 MPa,the adhesion between AF-PDA-KH550 and PUA reached 172.79 N.Through live fire target testing,the ultimate penetration speed of the AF-PDA-KH570 composite target plate was increased by 52.88 m/s compared to the original AF composite target plate,indicating that modified AF can indeed improve its resistance to bullet penetration.