Preparation And Properties Of Organic-inorganic Composite Coating On Polymethyl Methacrylate

Polymethyl Methacrylate(PMMA)is a kind of thermoplastic polymer,which has excellent optical properties,mechanical properties,melt processability and high impact resistance.It is widely used in construction,automobile,medical,optical devices,aerospace and other fields.However,the low surface hardness and poor scratch resistance of PMMA restrict its long-term stable use.The common method to solve the above problems is to prepare functional protective coating on its surface to improve the service life.However,there are differences in thermal expansion coefficient and polarity between the coating and the substrate.How to improve the interfacial adhesion and reduce the cracking and shedding of the coating has always been a research hotspot in coating/polymer composites.Compared with the traditional chromic acid modification of PMMA surface,a simple,feasible,green and low-cost H₂O₂surface modification method is first explored in this paper.Taking advantage of the strong oxidability of H₂O₂,the surface of PMMA was modified under hydrothermal conditions to improve its hydrophilicity and enhance the interface adhesion between PMMA and coating.On this basis,the construction and interfacial adhesion mechanism of organic-inorganic siloxane hybrid coatings were studied to minimize the potential risk of inducing coating failure.The purpose is to explore a simple,controllable and engineered method for PMMA surface modification and coating preparation.The main research contents are as follows:(1)H₂O₂hydrothermal modification of PMMA surface and its interfacial adhesion:the modification mechanism of H₂O₂on PMMA surface was studied at room temperature and hydrothermal conditions,and the effect of modification on the interfacial adhesion between PMMA matrix and SiO₂coating was investigated.The results show that the hydrothermal environment of high temperature and high pressure will make the microgap of PMMA molecular chain adsorb a certain amount of H₂O₂molecules which can activate the PMMA surface.The water contact angle of the surface decreased from 73°to 56°after hydrothermal treatment with 30 wt%H₂O₂solution at 60?for 1 h,and the surface is more hydrophilic.The particles of SiO₂coating deposited by magnetron sputtering are uniform and orderly,and prepared by Sol-gel method are compact.The interface between the coatings and PMMA substrate is firmly bonded.(2)Preparation and properties of micro-nanometer high-siloxane hybrid coating:Based on the characteristics of hydrolytic polycondensation of?-aminopropyltriethoxysilane(APTES)to form organic-inorganic siloxides,a high siloxide hybrid coating was prepared on the surface of PMMA which modified by H₂O₂.The results show that the presence of H₂O₂molecules in the micro-gap of PMMA facilitates the adsorption of APTES molecules to the PMMA surface.The quality of the coating formed in a closed environment rich in water vapor and ammonia is better.This method can effectively avoid the problem that siloxane is easy to agglomerate in an alkaline environment.The particle size of the formed silicon-oxygen hybrid coating is in a nanometer scale,and the particles are arranged orderly and have micro gaps,which can effectively resist internal stress.(3)Self-growth layer of amino POSS on the surface of PMMA:the H₂O₂modified PMMA substrate was placed in the POSS initial reaction solution to self-grow to form an amino POSS transition layer.The results show that the amino POSS layer appears on the surface of PMMA after 2 h,and the water contact angle decreases from 73°of the original PMMA to 48°.The increase of wettability is beneficial to the uniform extension of SiO₂sol on the surface of polymer matrix.Many evaluation tests such as cross-cut,temperature change,water vapor and immersion show that the amino POSS transition layer is constructed between the inorganic SiO₂coating and the PMMA surface,which strengthens the interface adhesion between the coating and the substrate.The coating has no problems such as cracking and falling off,which effectively improves the adaptability of PMMA to complex environments and prolongs its service life.(4)Chemical preparation method of POSS deposition layer on PMMA surface:phenyl POSS powder was uniformly dispersed into benign solvent and deposited on PMMA surface by coating method.The results show that the POSS molecules can form an ordered POSS layer along the PMMA texture through solvent regulation,which increases the surface roughness of PMMA and the relative contact area between SiO₂coating and PMMA.At the same time,the micro-gap between the structure can effectively counteract the internal stress,and the cracking and shedding of SiO₂coating is significantly reduced.This method provides a new idea for the preparation of functional protective coatings on PMMA surface.