Thermoplastic Resin Film Used To Prepare Green Plywood After Plasma Treatment

Plywood exhibits excellent performance,low price and simple preparation procedure and has been widely used in indoor decoration.Also,it can replace solid wood,Ttraditional adhesives used in plywood can release a large amount of formaldehyde,which is harmful to the health of producers and consumers.So the problem of formaldehyde release and “white pollution” can be solved by using thermoplastic resin as wood adhesive.But the polarity between thermoplastic resin and wood is quite different,which results in poor interfacial compatibility.Nowdays,the methods used for modification of thermoplastic resin have some problems,which affect their widespread use in production.The physical method is time and energy consuming whereas the chemical method is not friendly to the environment.Plasma treatment is an efficient and environmentally friendly treatment method for surface modification of polymers.In this paper,thermoplastic resins(LLDPE,PP,PVC,waste plastics)were used as wood adhesive to prepare plywood,plasma was used for surface treatment to improve the interface compatibility between resin and poplar veneer.The effects of plasma treatment process on the surface properties of thermoplastic resin were studied,the physical and mechanical properties of plywood and the bonding interface structure were also discussed.The main researches and results are summarized below:(1)LLDPE/poplar plywood was prepared by treating LLDPE film with dielectric barrier(DBD)plasma and radio frequency(RF)plasma,respectively.The results show that oxygen-containing groups(-C=O,C-O and C-O-C)were introduced into LLDPE by plasma treatment.The contact angle of LLDPE surface was reduced and hydrophilicity was improved by plasma treatment.The bonding strength of plywood met the requirement of type II plywood according to the National Standard of GB/T 9846.3-2015.Within 0-4.5 kW of DBD plasma processing power,the oxidation of LLDPE was enhanced and contact angle dropped from 120.63° gradually to 68.45°.Bonding strength of plywood had increased from 0.48 MPa to 0.88 MPa.Further increasing power brings no further improvement in the effect of oxidation due to the probability of collisions between energetic particles increased.Similarly,the modification effect of LLDPE became better with the decrease of processing speed.For RF plasma,with the power increasing,contact angle of LLDPE is reduced to 45.46° while bongding strength up to 0.85 MPa within 0-150 W.In general,the two plasma treatment methods improved the interfacial compatibility between LLDPE film and poplar veneer through oxidation on the surface.By comparing the two processing methods,it was found that the process of DBD plasma was simpler,more convenient and easier to be integrated into the production line for continuous processing as compared with RF plasam.Therefore,DBD plasma was selected as the processing method for subsequent treatment.(2)DBD plasma treatment could improve the compatibility of PP and PVC film with poplar veneer and enhance the bonding strength of plywood.According to FTIR and XPS,the surface of PP,PVC were oxidized by plasma treatment,and oxygen element was introduced into surface of films.However,the surface oxygen element of PVC only increased from 17.35% to 19.53% because of cross-linked structure,while the oxygen element of PP increased from 3.38% to 16.27%.Therefore,the contact angle and surface free energy of PP,PVC film were enhanced,and the surface of PP and PVC changed from polarity to nonpolarity.With processing parameters of 4.5 kW and 8 m/min,contact angle of PP decreased from 99 ° to 76 °and PVC reduced from 100 ° to 70 °.The hydrophilicity and surface free energy of PP and PVC films were improved by increasing the processing power and decreasing the processing speed.The bonding strength of PP/ poplar plywood increased from 0.58 MPa to 0.89 MPa.And after the plasma treatment of PVC,the PVC/poplar plywood met the type II plywood according to the National Standard of GB/T 9846.3-2015,up to 0.79 MPa.(3)The plywood prepared by plasma-treated waste plastics reached the type II plywood according to the National Standard.This method can not only achieve the recycle of waste plastic film but also slove the emission of formaldehyde in plywood at root.According to the analysis of FTIR and XPS,O-C-O,C-O and other oxygen-containing groups were introduced into the surface of waste plastics after plasma treatment,and the content of oxygen increased from 5.28% to 21.57% with the increase of power within 0-4.5 kW.As the rate decreases,the oxygen content increased gradually.Through oxidation,the hydrophilicity of waste plastic film became better,and the contact angle fall from 107 ° to 76 °.The polarity of plasma-treated waste plastic film and poplar veneer was similar,so under the synergy of mechanical interlock and enhanced interfacial compatibilities,the bonding strength of plywood prepared by waste plastics film and poplar,which both treated at 4.5 kW,8 m/min plasma process,increased from 0.49 MPa to 0.82 MPa.