Study On Toughening Modification Of Phenolic Resin And Properties Of Poplar Scrimber

In this paper,the toughened phenolic resins were studied and prepared for poplar scrimber.The phenolic resin was modified by diethylene glycol monoethyl ether,bisphenol A and benzyl chloride.The basic properties of the modified phenolic resin were analyzed,the infiltration and bonding properties of the modified phenolic resin were evaluated.Finally,diethylene glycol monoethyl ether modified phenolic and bisphenol A modified phenolic resin were selected to optimize the addition of toughening agents.Poplar scrimber was prepared from modified phenolic resin with the best addition,the physical and mechanical analysis of poplar scrimber before and after aging were carried out.Finally,the strain distribution of poplar scrimbers were analyzed by digital image correlation(DIC).The main contents and conclusions are as follow:(1)The phenolic resin,diethylene glycol monoethyl ether modified phenolic resin,bisphenol A modified phenolic resin and benzyl chloride modified phenolic resin were respectively labeled as PF,M-PF,A-PF,L-PF.L-PF had the highest viscosity and the smallest water mixing ratio.By differential scanning calorimeter analysis(DSC)and thermal gravimetric analysis(TG)of the phenolic resin,it was known that the temperature required for A-PF curing was the smallest.By fourier transform infrared analysis(FTIR)and dynamic thermo-mechanical analysis(DMA),the three toughening agents grafted the soft segment to the phenolic resin to different extents.The toughness of L-PF was the best,M-PF was the second,and A-PF had the least toughness.Tensile specimens prepared by toughening modified phenolic resins had lower tensile strength than ordinary phenolic resin,but still met GB/T 9846.3-2004 "Plywood Part 3: General technical conditions for ordinary plywood" The minimum requirement for the bonding strength of class I plywood(≥0.70MPa).Although L-PF exhibited the best toughness in the three toughened modified phenolic resins,the tensile strength of the tensile specimens was also in line with the standard,but due to its large molecular weight,the mixing ratio was small and poor wettability on the fluffed poplar venner,so it was not suitable as impregnating phenolic resin for preparing poplar scrimber.M-PF and A-PF were selected to analyze effect of different additions of toughening agent on phenolic resin.(2)The modified phenolic resins in which diethylene glycol monoethyl ether were added in an amount of 2 wt%,4 wt% and 6 wt% were labeled as 2M-PF,4M-PF and 6M-PF,respectively;The modified phenolic resins with added amount of bisphenol A of 5wt%,10wt% and 15wt% were labeled as 5A-PF,10A-PF and 15A-PF,respectively.The results showed that with the increase of the addition of diethylene glycol monoethyl ether,the mixing ratio and free formaldehyde content of M-PF decreased,and the gelation time,viscosity increase rate and free phenol content increased.With the addition of bisphenol A increased,the mixing ratio and the content of free formaldehyde of A-PF increased,the gelation time and viscosity increase rate decreased,and the free phenol content changed little.In the tensile strength test,6M-PF and 15A-PF had the highest elongation at break,which were 8.23% and 5.61%,respectively.The elongation at break of 4M-PF was slightly less than 6M-PF,but the tensile strength and elastic modulus were the largest,8.77 MPa and 0.42 MPa respectively;the tensile strength and elastic modulus of 15A-PF were the largest,respectively 17.25 MPa,0.70 MPa.It was indicated that the tensile plasticity of M-PF was better than that of A-PF,but the tensile strength was smaller than that of A-PF.Finally,4M-PF and 15A-PF with better comprehensive performance were selected for the preparation of polar scrimber.(3)The poplar scrimbers prepared by fluffed poplar veneer and four phenolic resins(PF,4M-PF,15A-PF,4M-PF+15A-PF(1:1 blend))were labeled as Ps,Ms,As,MAs;unfluffed poplar veneer prepared poplar scrimber correspondingly labeled: P,M,A,MA.MAs and MA had the highest air-drying moisture content and Ms and M had the largest water-swelling rate.The roughness of polar scrimber was 1.00~2.50μm.The airdry moisture content and thickness water absorption expansion rate of fluffed poplar scrimber were lower than those of unfluffed poplar scrimber.After aging,the air-drying wood moisture content of polar scrimber was reduced,the average density was reduced and the roughness was increased.After aging,the average density of As and A changed the most,and the roughness of Ms and MA was the largest.The MOR,MOE and impact toughness of the fluffed poplar scrimber were smaller than that of the unfluffed poplar scrimber.The impact toughness of poplar scrimbers prepared by three toughening phenolic resins were larger than that of PF,indicating that the three toughening phenolic resins had toughening effect on poplar scrimber.The hardness of the fluffed poplar scrimber was MAs>As>Ms>Ps;the hardness of the unfluffed poplar scrimber was MA>P>A>M.After aging,the MOR,MOE,impact toughness and hardness of poplar scrimber were decreased,and the MOR,MOE and hardness of As and A after aging were the smallest.(4)For the DIC analysis of poplar scrimber,in the three-point bending test,the strain value of poplar scrimber was increased with the increase of load.Under the same load,the strain value of the fluffed poplar scrimber was larger than that of the unfluffed poplar scrimber.The strain values of the fluffed poplar wood was Ps>Ms>As>MAs.The strains of unfluffed poplar scrimber was P>A>MA>M.The energy consumed by the toughened poplar scrimber was higher than that of the common poplar scrimber.Therefore,under the same force,the strain value of the toughened poplar scrimber was smaller than that of the common poplar scrimber.After aging,the surface material of poplar scrimber was changed and the strain distribution was uneven.The tensile strain of Ps,A and MA were greater than the compressive strain.