Study On Properties And Evaluation Of Adhesive Used In Bamboo-based Structural Materials

It is necessary to develop bamboo-based panels. For it can take full advantage of domestic plenty bamboo resource, decrease the deforestion and protect the natural forest effectively, accelerate the development of rural economics as well as help farmer to increase income. Bamboo-based panels for structural engineering material need high bonding strength. Based on the requirement from economic situation and actual market the research started. The aim of the research is that resolve the quality problem of bamboo-based structural materials such as the high ratio of delamination and the short use periods of production. According to bamboo's properties, we should research on special resin for bamboo use and properties evaluation of adhesive system of bamboo-based structural materials. As a result, the bonding strength of bamboo-based structural materials is improved.In this research, the materials were bamboo strips and bamboo board.Using the automatic contact angle meter, the surface free energy of bamboo strips and bamboo board was investigated, the change of surface free energy after being treated by four kinds of coupling agent was investigated as well. The effects of concentration of coupling agent CA5, the hot compress time and the compress temperature on physical-mechanical properties of Laminated bamboo strips lamber (LBSL) were researched, especially the bonding strength of LBSL. The changing of shear strength of bamboo board after being treated by four kinds of coupling agent was studied. The preparatory mechanism of silane coupling agent improving bonding strength of PF resin using on bamboo materials was researched by FTIR.In order to increase the bonding strength of the hot curing resin used on bamboo, the resorcin was used to modify the PF resin into PRF resin. The changing of synthesize condition of hot curing PRF adhesive effects on properties of resin and physical- mechanical properties of LBSL were investigated as well as the effects of different PRF resin on bonding strength of bamboo boards. The thickness and assembly orientation of bamboo curtain effects on physical-mechanical properties of LBSL were investigated either. The optimized cold curing PRF adhesives were gained by investigating different factors effects on properties of resin.The surface free energy of bamboo strips and bamboo board were increased which treated by coupling agent CA5, KH560 and KH602. The surface wettability was improved as well. However, the result is opposite which treated by coupling agent KH550. While all of the bonding strength which surface of bamboo pretreated by 4 kinds of coupling agent was increased. When concentration of KH550 was 0.5% the shear strength was increased significantly. With adding the concentration of KH550, first the shear strength of bamboo board was increased and then decreased. While with adding the concentration of KH560 and KH602, the shear strength of bamboo board was increased. Especial when the concentration of KH560 was 2%, the shear strength up by 400%.About research of the preparatory mechanism of silane coupling agent improving PF bonding bamboo, the result showed that three kinds of silane coupling agent used in the test all can react with the hydroxide group and form chemical bond. The hydroxide group is from the cellulose, hemicellose and lignin of bamboo as well as the PF and PRF resin. The optimized technology was gained to prepare the LBSL which is made of bamboo strips treated by coupling agent CA5.The technology is that density of LBSL board was 0.8g/cm3, concentration of CA5 2%, hot compress temperature 160℃, hot compress time 14min. According to the technology, the properties of LBSL board were as following: modulus of rupture(MOR) 181.2MPa ,modulus of elasticity(MOE)11000.41 MPa, ratio of delamination 0.66%, Thickness swelling after 24 hours water absorption 4.36%.The values of boards were higher than value of standard.Resorcin could increase the shear strength of modified PF adhesive on bamboo board significantly. The shear strength increased up to 50%. However, as the concentration of resorcin change from 1% to 3%, the shear strength of PRF resin changed a little bit. The optimized variable factors of synthesizing PRF adhesive are that: the concentration of resornic was 1.5%, molar ratio of formaldehyde and phenol was 2.0, the concentration of adhesives used to immersion bamboo strips was 30%. According to the technology, the properties of LBSL board were as following: modulus of rupture(MOR) 185.2MPa ,modulus of elasticity(MOE)10800.35 MPa, ratio of delamination 0.58%, Thickness swelling after 24 hours water absorption 4.20%.The values of boards were higher than value of standard.When the cold curing PRF adhesives were synthesized, the more concentration of resorcin the higher the wood failure measuring the dry shear strength, It means that the better bonding strength. However, the effect on 28h boiling water shear strength was small.9% was a critical concentration of resorcin in PRF adhesive. The change of ratio of composition influenced the shear strength and curing time of the PRF adhesive obviously. The molar ratio of phenol and formaldehyde influenced the stability of adhesive significantly, the stability of adhesive was best when the molar ratio of phenol and formaldehyde was 1.5. As the curing agent polyformaldehyde were added more the shear strength and wood failure of specimens were descended rapidly and the curing time of adhesive were shorted. When the concentration of polyformaldehyde was 6%, the shear strength of PRF adhesive was best.The concentration of resornic was 10.5% and 9%, which the two kinds of optimized cold curing PRF adhesives. The shear strength was up to the standard of JAS SE-9.The thickness of bamboo strips effected significantly on physical-mechanical properties of LBSL. With decreasing of the thickness of bamboo strips, the thickness swelling after 24 hours water absorption (24hTS) of LBSL and the ratio of delamination (DR) was decreased obviously. While the MOR , MOE and density of LBSL were increased. The optimized thickness of bamboo strips is 0.8-1.4mm.Orientation of bamboo curtain effected obviously on physical-mechanical properties of LBSL. When bamboo curtains were assembled crossly layer by layer, Each of physical-mechanical properties of LBSL become worse than that of bamboo curtains were assembled parallely. Especially 24hTS and DR of LBSL changed rapidly.