Jet Plasma Treatment And Bonding Of Polyethylene Wood Plastic Composites

Wood-plastic composites(WPCs)are widely used in various fields of national economy,which emerged as a generation of energy-saving and environment-friendly materials.However,the low surface energy and non-polar polyethylene components lead to the poorly adhesion of polyethylene wood-plastic composites,the surface of wood-plastic composites need to be treated before bonding to achieve perfect seamless bonding.This study selects the jet plasma discharge to process the polyethylene wood-plastic composite surface,by optimizing the atmosphere and time to produce groups on the surface that can react with the adhesive,achieving the good adhesive performance of adhesive joint.Investigated the effects of treatment time and atmosphere on the surface properties and durability of PE-WPC,and analyzed the mechanism of surface treatment and water resistance failure of PE-WPC by a combination of water absorption test,bonding strength test,surface morphology observation,surface contact angle analysis,Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS).The optimization result of the jet plasma treatment process shows that the nitrogen jet plasma discharge treatment changed the surface polarity and surface wetting properties of the material and improved the adhesion significantly,by the generation a large amount of polar nitrogen-containing and oxygen-containing groups.During the experimental processing time range,the surface properties of the material change periodically with the prolongation of the processing time,which is owing to the physical etching of the nitrogen jet plasma.The research on the surface treatment of wood-plastic composites by different atmosphere jet plasma shows that the nitrogen atmosphere jet plasma treatment is most efficient,generation the more effective nitrogen and oxygen groups,and decreased the surface contact angle significantly,the bonding strength and water resistance of the bonded samples are the best among them;the oxygen group treatment introduces the polar group content second,but the etching degree is the highest,the bonding strength and water resistance are in the middle;the air atmosphere made the highest contact angle and the poorly wettability there's less polar groups of it introduced on the surface,bring the bonding the lowest strength and water resistance of the bonded sample.Jet plasmas of different atmospheres occupy different dominant roles in the treatment process,oxygen atmospheres are mainly oxidized and etched,while nitrogen atmosphere is dominated by chemical modification,and air atmosphere is weakly combined with the above two effects.By analyzing the mechanism of nitrogen gas jet plasma treatment on the PE-WPC surface,it's easy to known that the chemical modification of PE-WPC surface is mainly to the introduction of more HN-C=O/-C=O groups in the PE component,while the oxidative etching of the plasma removes some polyethylene component of surface and exposes the internal wood component,a large number of-OH,-COOH,-NH groups are introduced through the oxidation of the active particles.These polar oxygen-containing and nitrogen-containing groups can promote the reaction between the surface of the wood-plastic composite material and the adhesive to form chemical bonds,thus greatly improving the bonding performance.The water resistance test results of polyethylene wood-plastic composite adhesive joints show that the water resistance properties of polyethylene wood-plastic composites bonded joints treated by different atmospheric jet plasmas are different,and the nitrogen atmosphere treatment generated more polar groups on the surface which can forms more effective chemical bonding with the adhesive during the bonding process,thus has the best water resistance..The epoxy resin adhesive has excellent water resistance,and forms a strong interfacial bonding force with the polar groups introduced on the surface of the treated material,so the water-repellent property of the bonded sample is better.However,reactive polyurethane hot melt adhesive can cure with water molecules.Although the water-resistant property of the adhesive after long-term water immersion is not as good as that of epoxy resin,it has a fast bonding speed and can realize the rapid bonding of wood-plastic composite materials.The extreme water immersion test of wood-plastic composite samples treated by nitrogen jet plasma showed that the surface properties of PE-WPC material treated by nitrogen jet plasma were changed during the water immersion,the change of the glue interface property is also the primary cause for the endurance failure of the glue joint.The durability failure of polyethylene wood-plastic composite bonded joints in water environment is mainly due to the decrease of interfacial adhesion caused by hydrolysis of chemical bonds of water molecules on the bonding interface and cracks with the internal stress at the-bonding interface derived from the continuous water absorption expansion of wood components.