Study On Construction And Performance Of Organic-inorganic Composite Coating On Polycarbonate Surface

Polycarbonate(PC)is a transparent engineering plastic commonly used in packaging,automotive,food,medical and aerospace fields.It has excellent optical properties,melt processability,thermal stability,high impact resistance,and low cost.However,PC has low hardness,is not resistant to scratches,and is easily aging by ultraviolet radiation,which seriously affects its long-term use.On the premise of maintaining the original performance of PC,a common method to solve these problems is to prepare protective or functional coatings on its surface to improve the overall performance of material.However,the thermal expansion coefficient,surface energy and other physical properties between the coating and substrate are different.How to improve the interfacial adhesion and reduce the cracking and peeling of coatings has always been the research focus of coating/matrix composites.In this paper,the interface adhesion between inorganic coating and polymer matrix was enhanced by surface modification of PC.Polyhedral oligomeric silsesquioxane(POSS)has the characteristics of organic-inorganic hybrid materials.By constructing POSS between the coating and polymer matrix,the problems of coating cracking and peeling caused by thermal expansion can be alleviated.Research contents are as follows:1.Preparation of POSS transition layer on PC surface by magnetron sputtering and its anti-atomic oxygen(AO)properties:Taking advantage of similar polarity between dodecyl phenyl POSS and PC,a transition layer of POSS was deposited on the surface of PC by magnetron sputtering.The effects of sputtering power and time on the target material and transition layer were studied.On this basis,Si O₂/POSS/PC samples were prepared.The results show that a dense POSS transition layer can be formed by sputtering under 50 Sccm argon flow rate and 90 W for 2 h.The composite coating formed by POSS and Si O₂has good AO resistance.2.Study on improvement of interfacial adhesion between Ti O₂coating and PC substrate by POSS:Si O₂target was treated with Na OH solution to enhance its surface adhesion.POSS powder was uniformly pressed on the surface of Si O₂target to prepare POSS sputtering target.Ti O₂/POSS composite coating was prepared on PC surface by magnetron sputtering.The results show that after depositing a POSS layer,the water contact angle of PC surface decreases from 80°to 27°,and the wettability is improved,which is beneficial to the deposition of Ti O₂coatings.After irradiating with 365nm ultraviolet light for 40 hours,the water contact angle of Ti O₂/POSS/PC surface decreased from 64°to 5°,showing super hydrophilicity and self-cleaning.3.Silane coupling agent(SCA)and plasma strengthen the adhesion of Si O₂coating and PC substrate:The feasibility of improving the interface adhesion between Si O₂coating and PC substrate by using the reactivity or compatibility of SCA functional groups with organics was studied,to improve the bonding strength between coating and PC and alleviate the internal stress caused by temperature change.A surface modification method with controllable polarity was obtained by combining plasma surface treatment with SCA.The results show that the water contact angle of PC samples decreases from 80°to 59°treated by H₂O₂and KH-550 solvothermal process.After treated with Ar plasma and SCA,a homogeneous hydrolytic layer was formed on PC surface.After temperature changing from 80°C to-5°C for 5 times,the coating remains intact without peeling off and deformation,which effectively alleviates the internal stress caused by thermal expansion and cold contraction.4.Effect of silicon-based composite coating on environmental stress cracking(ESC)resistance of PC:Silicon-based composite coatings with different compositions were prepared from tetraethyl orthosilicate(TEOS),methyltrimethoxysilane(MTMS),dimethyldimethoxysilane(DMDMS),aminopropyl isobutyl POSS and trihydroxyphenyl POSS as starting materials.The anti-ESC properties of PC in ethanol solution were evaluated by three point bending stress relaxation method.The results show that the silicon-based coating improves the ESC resistance of PC samples to a certain extent,the stress-relaxation in ethanol environment is significantly slower than that of original PC,and there is no crack on the sample surfaces.