Surface Ageing Of Polyethylene Wood Plastic Composites Treated By Jet Plasma

Polyethylene wood-plastic composite is one of the most widely used wood-plastic composites.Its products have excellent properties,such as light weight and corrosion resistance.Usually,polyethylene wood-plastic composites are prepared by extrusion process,which makes the non-polar polyethylene components accumulate on the surface of the material,resulting in low surface energy and difficult to be bonded.Therefore,in order to achieve seamless bonding of polyethylene wood-plastic composites,it is necessary to modify the material surface.Jet plasma surface treatment technology can rapidly change the surface composition and properties of polyethylene wood-plastic composites and improve the surface bonding properties of materials.But there is a certain ageing for plasma surface treatment.The content of wood powder,polishment process,the kind of plasma atmosphere and storage environment all affect the ageing of jet plasma treatment.In this paper,the surface treatment of polyethylene wood-plastic composites was carried out by jet plasma treatment technology.The effect of content of wood powder,polishment process,the kind of plasma atmosphere and storage environment on ageing of plasma treatment were studied by contact angle test,bonding strength test,infrared spectrum analysis and X-ray photoelectron spectroscopy(XPS)analysis.After jet plasma treatment,-OH,C=O,C-O and other oxygen-containing polar groups were introduced into the surface of polyethylene wood-plastic composites.These oxygen-containing polar groups can not exist stably on the surface of the material.With the prolongation of the storage time,the number of oxygen-containing polar groups on the surface of the material will gradually decrease,and plasma modification shows a certain ageing effect.The influence of different factors on the ageing of jet plasma treatment is also different.After air jet plasma treatment,the surface contact angle of polyethylene wood-plastic composites with 40%,50%and 60%content of wood powder decreased from 108?,950and 81°to 71°,70°and 71°respectively,and the bonding strength increased from 1.00 MPa,1.37 MPa and 1.39MPa to 10.07 MPa,10.64 MPa and 10.76 MPa respectively.With the prolongation of storage time,the number of polar groups on the surface of treated samples decreased,the contact angle increased and the bonding strength decreased slightly,but still reached about 9.00 MPa,which was much better than that of untreated samples.The surface properties of polyethylene wood-plastic composites varied with the change of wood powder content.The higher wood powder contained in the composites,the smaller change of surface properties and ageing effect of jet plasma treatment.The bonding strength of the non-polished and polished wood-plastic composites treated by air jet plasma increased to 10.76 MPa and 11.24 MPa respectively,and the surface contact angle decreased from 91°to 71°and 81°respectively.After polishment and plasma treatment,more oxygen-containing polar groups can be formed on the surface of composites,which is beneficial to the improvement of bonding properties.With the intend of storage time,the changes of surface contact angle,the number of oxygen-containing polar groups and the bonding strength of polished-composites treated by plasma are smaller than those treated only by plasma,showing a smaller ageing effect.The bonding strength of plasma treated specimens is much better than that of untreated specimens despite the ageing effect.The bonding strength of polyethylene wood-plastic composites treated by oxygen plasma,nitrogen plasma and air plasma increased significantly from 1.39 MPa to 10.87 MPa,11.35 MPa and 11.37 MPa respectively.The contact angle decreased significantly from 91°to 71°,31°and 33°respectively.The bonding strength of samples treated by oxygen and nitrogen plasma increased more significantly and the contact angle decreased significantly.With the prolongation of storage time,the number of polar groups on the surface of samples treated by oxygen plasma decreased slightly;the bonding strength and the contact angle changed less,showing better ageing effect.The treatment effect and ageing effect of air plasma are almost the same with that of oxygen plasma,but the treatment effect of nitrogen plasma is good,but the ageing effect of treatment is obvious.Humidity,temperature and air isolation all affect the ageing on plasma surface treatment of polyethylene wood-plastic composites.The bonding strength of polyethylene wood-plastic composites treated by air plasma decreased from 10.76 MPa to 10.19 MPa,8.65 MPa,and the contact angle changed from 71°to 80°and 63°respectively.The number of polar groups on the surface of samples placed in low humidity environment decreased slightly,showing less ageing effect.High humidity environment can cause laterial softening and deformation,which has a great influence on the ageing of jet plasma treatment.The bonding strength of polyethylene wood-plastic composites treated by air plasma decreased from 10.76 MPa to 10.19 MPa and 9.96 MPa scperately at low and high temperatures,and the contact angle increased from 71°to 80°and 82°respectively.The polar groups on the surface of the composites treated by air plasma decreased less and showed less ageing effect.The bonding strength of polyethylene wood-plastic composites treated by air plasma decreased from 10.76 MPa to 10.19 MPa and 10.06 MPa respectively in vacuum and non-vacuum environments,and the contact angle increased from 71°to 84°and 80°respectively.The number of polar groups on the surface of polyethylene wood-plastic composites placed in vacuum environment changed less and showed less ageing effect.Compared with temperature and air isolation,humidity has a greater influence on the ageing of polyethylene wood-plastic composites treated by jet plasma.