Study On DBD Low-temperature Atmospheric Plasma Enhanced Nano SiO₂ Coating On PCTG Surface

Polyethylene terephthalate 1,4-cyclohexanedimethanol ester（PCTG）has good light transmittance,impact resistance and meets the environmental requirements of food grade,so it can be widely used in the market and has great development potential in new products.But because the surface hardness is low at room temperature,it is easy to produce scratches,which greatly affects the beauty and service life of its products.In order to effectively improve the surface hardness of PCTG,it is a very convenient and reliable scheme to deposit coating on the surface of PCTG.Firstly,nano Si O₂ coating was prepared by sol-gel method to improve the surface hardness and heat and weather resistance of the material,and the hybrid treatment of nano Si O₂ changed the wettability of the material,providing and improving a variety of properties for the surface of PCTG.However,due to the low surface energy of PCTG,extremely smooth surface and lack of polar functional groups on the surface,the surface wettability is poor,and it is difficult to deposit and bond the coating.Therefore,the surface of PCTG is premodified.DBD plasma technology is a typical"cold"non-equilibrium low temperature plasma with high electron temperature and low macroscopic temperature.The working conditions of DBD plasma used in this paper are atmospheric pressure and room temperature,and the working medium gas is air.Therefore,the non-equilibrium plasma created in this experiment is a simple and convenient,low cost and effective scheme which can be used in practical production.The low macroscopic temperature generated by DBD low atmospheric plasma provides the possibility of surface modification of PCTG.In this paper,Si O₂ nanoparticles were prepared by St?ber method using ethyl orthosilicate（TEOS）and APTES were added to improve the adhesion of the coating.Nano Si O₂ coating solution was prepared by sol-gel method,and the coating was deposited by vertical lifting method.However,the PCTG surface needs to be pre-modified to enhance the effect of coating deposition before deposition.Using DBD low temperature atmospheric plasma technology,the fixed parameters were set at 60 KV,1 A,to explore the surface chemical groups,surface roughness,surface wettability,surface hardness and surface transmittibility under the treatment time of60 s,120 s and 180 s.Secondly,after the treatment time of DBD low temperature atmospheric plasma is 60 s,120 s and 180 s respectively,the best treatment time of deposition coating is found by environmental scanning electron microscopy,EDS and surface hardness analysis.The experimental results show that:The surface treatment of PCTG by DBD low-temperature atmospheric plasma produces a large number of polar oxygen-containing functional groups on the surface of PCTG,which leads to the intensified crosslinking of molecular chains on the surface of PCTG.When the treatment reaches 120 s,the number of polar oxygen-containing functional groups reaches the peak,and many point bumps are generated on the surface of PCTG,which increases the surface roughness of PCTG.In the treatment of 120 s,the point-like protrusions on the surface are more three-dimensional,and in the treatment of 180 s,most of the point-like protrusions are fused into massive protrusions.Due to the introduction of polar functional groups and the change of surface roughness,the surface wettability of PCTG also becomes very good,and the surface water contact Angle decreases from the initial 89.6゜to 30.8゜at 120 s.Through the measurement of Vickers hardness tester,it is found that the DBD low temperature atmospheric plasma treatment,the surface hardness of PCTG increased slightly.According to the analysis of UV-Visible-near-infrared absorption spectrometer,the treatment of DBD low-temperature atmospheric plasma does not affect the transmittance of visible light,and can improve the protection ability of UV light.The transmittance of UV light decreases with the increase of processing time.When the DBD low temperature atmospheric plasma is treated for 120 s,the comprehensive effect of nano-Si O₂ coating deposition is the best.When the content of nano-Si O₂ is enough,the coating distribution is very uniform,and the average hardness of the material surface increases the most,by 66.9%.It can protect the surface of PCTG,increase its service life,and effectively improve its application range and prospect.