Study On Preparation Technology And Properties Of Plywood Manufactured By Poplar Veneer And Discarded Polypropylene Filter

In the post-COVID-19 era,wearing masks remains an effective way to prevent the spread of the disease.It has become an urgent need to find a low-carbon and economical reuse method of discarded disposable medical masks(DMM).In this study,polypropylene filter membrane(PPF)in waste DMM was used as raw material to study the feasibility of using PPF to prepare plywood.The mechanical properties of poplar/PPF plywood were improved by high voltage electrostatic field induction technology,The findings in this study provide theoretical basis for the reuse of waste DMM and PPF,and scientific guidance for the performance improvement of aldehyde-free plywood.In this paper,the structure,chemical properties,thermal properties and surface properties of the pasteurized PPF were analyzed systematically,and the poplar/PPF plywood was prepared.The feasibility of PPF as a adhesive for plywood was discussed.The effects of different chemical modification treatments(modifier type and concentration)on the surface activation of PPF were studied.Based on the high voltage electrostatic field induction technology,the"two-step method"(high voltage electrostatic field induction followed by hot pressing)and"one-step method"(high voltage electrostatic field induction and hot pressing simultaneously)were used to prepare the high strength poplar/PPF plywood.Advanced equipment and means such as dynamic mechanics analyzer(DMA),nano-indentation instrument and digital image correlation technology(DIC)were integrated to understand the strengthening mechanism of poplar and PPF bonding interface induced by high voltage electrostatic field.The main conclusions of this paper are as follows:(1)After sterilization,PPF can be used as bonding materials for plywood.The optimum hot-pressing parameters for the preparation of poplar/PPF plywood were:hot pressing temperature 165℃,hot pressing time 3min,hot pressing pressure 1.3MPa,PPF dosage 6 layers.Under the optimum hot pressing parameters,the adhesive strength of poplar/PPF plywood was 0.76MPa,met the requirements for Class II plywood.(2)After chemical modification,the surface wettability of PPF was significantly improved.After high voltage electrostatic field induction,oxidation reaction occurred on the surface of PPF,the number of oxygen-containing functional groups on the surface of PPF gradually increased.Based on the"two-step"and"one-step"methods,the adhesive strength of the plywood was 1.13MPa and 1.23MPa,respectively.Correspondingly,the elastic modulus was 5718MPa and 6381MPa,and the static bending strength was 59.71MPa and 65.05MPa.The uniform and dense adhesive layer was formed under the induction of high voltage electrostatic field,and the adhesive layer density was significantly increased.The peak adhesive layer density of the one-step method(910kg/m~3)was higher than that of two-step method(885kg/m~3).(3)The formaldehyde emission of poplar/PPF plywood was about 0.07mg/L,lower than the plywood made by formaldehyde-based adhesive.(4)DMA results showed that the linear viscoelastic region(LVR)of plywood prepared by one-step method or two-step method was greater than that of poplar veneer.The LVR of plywood prepared by the one-step method was higher(0.20%).In the heating process,compared with the"two-step"method,the"one-step"method plywood had higher stiffness retention,higher melting temperature of PPF,less viscoelastic deformation,and better thermal-and hygro-resistances.(5)DIC and nanoindentation test results showed that the mechanical properties of cell walls at the glued interface were effectively improved by the induction of high voltage electrostatic field,improving its bearing capacity and promoting stress transfer at the glued interface during loading.The elastic modulus and hardness of wood fiber cell wall at the gluing interface were increased by 45,33 105 and 90%,respectively.The elastic modulus and hardness at the corner/intercellular layer were increased by 53 and 41%,and 97 and 78%,respectively.(6)After three wet-freeze-thermal cycle tests,the adhesive strength,static bending strength and static bending elastic modulus retention of plywood prepared by"one-step"and"two-step"methods were significantly improved.The one-step plywood had the highest retention rates of 77,88 and 85%,respectively,which were attributed to the effective penetration of PPF into wood cell walls.