Study On Self-Bonding Process Of Molded Bamboo Scrimber With Green And Water-Resistant Characteristic

China’s wood resources are scarce,but bamboo resources are abundant.Rational development of bamboo resources is of great strategic significance for ensuring China’s wood safety,promoting ecological civilization construction and rural revitalization.Due to the arc-shaped,hollow structure and large taper of bamboo culm,a large amount of processing residues will be produced in mechanical cutting.For example,when manufacturing bamboo glulam,the material utilization rate is less than 40%,resulting in a huge waste of resources.It is an important research topic how to use bamboo processing residues to produce green and high-performance bamboo restructuring materials.In view of this,this paper takes bamboo processing residues as the research object,and systematically studies the influence of raw material physical parameters and molding forming conditions on the properties of bamboo scrimber by using molding forming and bulk self-bonding technology.The self-bonding characteristics and forming mechanism of molded reconstituted bamboo were explored,and the optimized forming preparation process was obtained,in order to provide scientific ideas and methods for the high value-added utilization of bamboo processing residues.The specific research conclusions of this paper are as follows:(1)The effects of particle size and moisture content of bamboo powder on the properties of molded reconstituted lumber were investigated.With the decrease of bamboo powder particle size,the surface red-green and yellow-blue indexes of bamboo-based molded reconstituted lumber gradually decreased,but the brightness did not change significantly.The surface hardness,water resistance,modulus of rupture and elastic modulus all showed an increasing trend.until the particle size decreased to 60 mesh,the performance tended to be stable.With the increase of the initial moisture content of bamboo powder,the surface red-green and yellow-blue indexes of bamboo-based molded reconstituted lumber increased,while the surface hardness,modulus of rupture,elastic modulus,water absorption and dimensional stability decreased.The optimized bamboo particle size was 60 mesh and the initial moisture content was 10%.(2)The influence of molding conditions on the properties of molded reco nstituted materials was revealed.The influence degree of the three elements of molding on the forming performance of bamboo-based molded reconstituted materials is:molding temperature>molding pressure>holding time.As the molding temperature increases,the weight loss rate and color difference of the sample gradually increase,and the change range decreases when the temperature exceeds 160℃.The dimensional expansion rate,water absorption,elastic modulus,static bending strength and hardness all showed a trend of decreasing first and then increasing.With the increase of molding pressure,the size expansion rate,water absorption,elastic modulus and static bending strength of the sample also showed a trend of decreasing first and then increasing.With the increase of holding pressure,the size expansion rate,water absorption,elastic modulus and static bending strength of the sample also decreased first and then increased.The optimized molding conditions are:temperature 160℃,pressure 55 MPa,holding time 30 min.(3)The optimized forming process of bamboo-based molded reconstituted material was obtained.Based on the optimization method of response surface method,the self-bonding process of bamboo molded reconstituted wood was obtained as follows:molding temperature 157℃,molding pressure 52 MPa,holding time 30min.At this time,the static bending strength of the sample was 51.8 MPa,the water absorption rate of 24 h was 7.6%,and the surface hardness was 29.6 HV,which was basically consistent with the predicted value of the model.The properties of bamboo molded reconstituted wood prepared by the optimized process are much better than those of ordinary wood-based panels.(4)The self-bonding forming mechanism of molded reconstituted materi al was revealed.The chemical composition and physical structure of bamboo will change during high temperature molding.The specific surface area of bamboo powder increases with the decrease of particle size,which promotes the increase of surface reaction sites,thus enhancing the chemical bonding effect of material components.An appropriate amount of water can aggravate the polycondensation reaction between the microfibrils in the amorphous region and the cellulose in the crystalline region,but the water content has no effect on the chemical composition of the sample,only changing the chemical group content.The relative crystallinity of the crystalline region of the sample increases first and then decreases with the increase of temperature.