Preparation And Photoaging Performance Research Of UV Coating On PBO Fibers Surface

In recent years, Poly-p-phenylenebenzobisthiazole (PBO) fiber as reinforcingmaterial has been extensively used in resin-matrix composite, due to its superiormechanical properties including high-specific strength and high-specific modulus,as well as unique characteristics such as low density, high thermal and chemicalstabilities. However, the sensitivity to solar light, especially ultraviolet (UV), whichcan deteriorate structures and properties of PBO fiber and corresponding composites,seriously affects the safety and reliability of PBO fibers-composite materials.Therefore, research on the anti-UV protection of PBO fiber becomes a fascinatingfield. In the present research, organic-molecule and inorganic-nanoparticleUV-absorbed agents were used, and three different surface protective coatings wereprepared on PBO fiber surface by plasma modification method, sol-gol andself-assembly technology for improving UV-resistance of PBO fiber. The structureof coating on PBO fiber surface was characterized, and the properties of materialespecially photo-aging property were studied.PBO fiber surface is smooth, and non-polar. PBO fiber was activated byoxygen plasma modification for the successful preparation of coating. Theinfluences of voltage and time of plasma treatment on activation were evaluated.Results show that increasing power and time of plasma treatment both make surfaceroughness of fiber increase, surface free energy and IFSS between fiber and epoxyresin matrix first increase and then decrease. The optimal treatment condition wereobtained: voltage is175W and time is10min.2-(2-hydroxyphenyl)-benzotriazole (BTZ) was selected as organic-moleculeUV-absorbed agent after experimental optimization, and added into sizing agent ofepoxy resin for creation of anti-UV coating on PBO fiber surface. The similarity ofmolecular strcture between sizing agent and epoxy resin improves the wettabilitybetween PBO fiber and matrix. UV accelerated aging test shows that coating createdby pure epoxy resin based sizing agent can not protect fiber body, whereas coatingcreated by UV-absorbed organic-molecue containing sizing agent can effectivelyabsorb incident UV light, and relieve aging degradation of fiber body. After480hUV-accelerated aging, tensile strength (TS) retention and intrinsic viscosity (IV)retention of original PBO fiber is29.2%and72.0%, respectively. TS retention andIV retention of PBO-I fiber treated by sizing agent containing1.0wt%BTZ isincreased to52.7%and81.7%, respectively.Plasma induced vapor surface grafting technology and surface coatingmethod of sol nanoparticle were combined to prepare coating with photostability on PBO fiber surface. PBO fiber surface was activated through oxygen plasma inducedacrylic acid grafting reaction, Roughness, functional group content and surface freeenergy on PBO fiber increase, tensile strength decrease in a small extent, andinterface bonding between PBO fiber and epoxy resin increase. With the extensionof grafting time, polyacrylic acid coating on PBO fiber surface becomes moreperfect, fiber surface becomes more rough, surface free energy and IFSS both firstincrease and then decrease. The best result was obtained when vapor grafting time is10min. The average size of TiO2and ZnO sol nanoparticles is38nm and50nm.Small size and narrow size distribution of these particles can completely meet withthe demand of fiber surface coating. A photo-shielded inorganic nanoparticle layerwas formed on fiber surface after surface coating of nanoparticle. Increased surfaceroughness and surface functional group content of fiber cause surface free energy offiber increase, and interface shear strength (IFSS) between fiber and epoxy resin isimproved. With the increase in number of surface coating, nanoparticle protectivelayer becomes denser, coating thickness become greater, and increased TiO2andZnO content on fiber surface supply coating with a efficient absorption for UV ray.Accelerated aging test proved that inorganic nanoparticles on fiber surface build aeffective barrier between UV ray from external environment and fiber body, providefiber with high tensile strength retention and intrinsic viscosity retention, and thisprotective effect is more significant with coating thickness increase. TS retentionand IV retention of PBO-II-1fiber and PBO-II-2fiber is56.8%and53.8%,82.6%and79.8%, respectively.Coordinative usage of plasma surface active treatent and layer-by-layerself-assembly technology to create coating with photostability on PBO fiber surface.Protective coating of (PAA/BPEI)m/(PAA/TiO2)nor (PAA/BPEI)m/(POSS/TiO2)nwas prepared on fiber surface by virtue of self-assembly. After treatment, surfaceroughness and surface functional group content increase, surface free energyincrease, IFSS between fiber and epoxy resin also increase. Characteristicabsorption peaks of Ti and Si element appear on XPS spectrum, and element contentincreased with the increase in number of self-assembly. UV accelerated aging testshowed the increase in number of self-assembly can increase the thickness ofcoating, and increased thickness of inorganic nanoparticle coating can moreeffectively protect fiber. By comparing TS retention and IV retention of untreatedand treated PBO fiber after accelerated aging, a phenomenon is found that anti-UVstability of treated PBO fiber is better. After480h UV accelerated aging, TSretention and IV retention of PBO-III-1fiber and PBO-III-2fiber can reach56.0%and60.7%,81%and82.3%, respectively. With the increase in thickness of coating, TS retention and IV retention of fiber gradually increase, this result indicate thatpreparing a certain thickness of coating on fiber surface can effectively protectintegrity of fiber.