Study On Cellulose Nanofibers Modifying Hydroxy-methylated Lignosulfonate/Phenol Formaldehyde Adhesive

This paper select Sodium Ligno-sulfonate(SLS)as filler to add into Phenol Formaldehyde resin(PF)for manufacturing Lignin-Phenol Formaldehyde resin(LPF)adhesive.SLS and Formaldehyde were used to complete hydroxymethylation to increase the activity to obtain Hydroxymethylated Lignosulfonate Formaldehyde(HLF).Hydroxy-methylated Lignosulfonate/Ph enol Formaldehyde resin(HLPF)adhesive were manufactured by mixing HLF and PF in a certain proportion.The physical and chemical properties of LPF and HLPF adhesive were studied.Through orthogonal test,the optimum hot pressing process was determined.Ce llulose Nanofibers(CNF)was prepared by acid hydrolysis,and it was used as active filler to modify HLPF adhesive,and thus Cellulose nano-fiber modifying HLPF resin(CNF-HLPF)adhesive was manufactured.The bonding interface of poplar plywood which was glued together by HLPF and CNF-HLPF was analyzed.Several adhesives were studied and analyzed in terms of structure property and viscoelastic properties.This article also take digital speckle correlation method(D SCM)to compare,calculate and analyze strain distribution.In this paper,we made full use of rich biomass materials to prepare a new wood adhesive with comprehensive excellent performance.In addition,it expend news ways for industrial lignin and cellulose and the other paper industry by-product of the comprehensive uti lization.The main contents and conclusions are as follow:1.Composition analysis of lignin and filler modifying PFThe composition of SLS was test and analyzed.SLS was used as active filler to add into PF to prepare LPF.It was found that when the fill er percentage was 10%,LPF had most excellent physical and chemical properties with solid content 53.84%,p H value 11.16,viscosity 2389 m Pa·s,free formaldehyde content 0.1 6%,hydroxymethyl content 18.34%,free phenol content 0.31%,bonding strength 0.94 MPa and qualified content 73.3% respectively.However the qualified content was too low to reach the stand value 80%.Thus,the gluing performance of plywood prepared by LPF adhesive was respectively poor,so the SLS should be taken an activation.2.Study on HLPF and study on hot pressing processWe selected SLS as test material,took hydroxylmethylation to it with formaldehyde.Then HLF was obtained,mixing HLF and PF in a certain proportion to prepare HLPF.Through test and analysis,the best activation p rocess and the best mixing proportion were determined.The best activation process was SLS activ ing with formaldehyde under following condition: The alkali content was 0.1%,the mass ratio of SLS and formaldehyde was 3:1,the active temperature was 80 degr ee Celsius,and the reaction time was 3 hours.The best mixing proportion was HLF and PF 1.5:3(mass ratio).After test,the bonding strength and qualified content meet the requirements of Class I plywood.A four-factor three-level orthogonal experiment was designed for HLPF adhesive.Four factors were hot pressing temperature,time,pressure and coating weight,respectively.And the optimum hot pressing process was determined with temperature 160 degree Celsius,time 1min/mm,pressure 1MPa,and coating weight 150g/m2.3.CNF modifying HLPFand Structure properties and viscoelastic properties of adhesiveCNF was prepared by acid hydrolysis to obtain CNF-HLPF adhesive.Bonding strength before and after aging process was tested,and it was analyzed in the bondin g interface,and it concluded that 2% is the proportion for CNF to HLPF.Through spectral analysis,we can conclude that SLS was mainly composed of syringyl benzenze propane units.After hydroxyl-methylation,the hydroxyl and methylene content of HLF increased.It was found that there exist the molecular chain after reaction by phenol and formaldehyde,and SLS with formaldehyde.Observing the CNF spectrum,it was found that there exist stretching vibration absorption peak of hydroxyl of cellulose,cellu lose skeleton and inner ether.This article take DSC for PF,LPF and HLPF adhesive,and the curing temperature of each resin was obtained and they are 135.7,130.9 and 135 degree Celsius,respectively,which indicated the addition of SLS lowered the curing temperature and increased the curing rate.Combined with hot pressing process,it concluded that 135~140 degree Celsius was the best hot pressing temperature.DMA test were taken to PF,LPF,HLPF and CNF-HLPF to analyze the viscoelastic of each resin.It can be easily found that under room temperature HLPF had the best elasticity,and HLPF had longest mechanical relaxation process.And PF had highest mechanical relaxation process strength,which indicating the largest internal friction.Compare the loss f actors of the resins,we can obtained the glass transition temperature(Tg),and they are 104.6,113.3,122.9and 90.5 degree Celsius,respectively.It can be inferred that viscosity size was CNF-HLPF>LPF>HLPF>PF.Choose HLPF resin as material to research t he storage modulus,loss modulus and loss factor under different frequency with 1,5 and 10 Hz,respectively.The result showed that variation of storage modulus under different frequency was smaller,the resin exhibited strong rigidity under high frequency,and internal friction was higher with larger viscosity under lower frequency,and the frequency enlargement moved Tg in high temperature direction.4.DSCM analysis of gluing interfaceMake a utilization of DSCM to compare,calculate and analyze strain distribution before and after aging process to poplar plywood which was glued by PF,LPF,HLPF and CNF-HLPF adhesive.With 400 N loading,the maximum shear strain of glue line appeared at each end which was close to notch,and the maximum strain of plywood appeared at the position close to notch in core board.Changes ocuured on the amount of strain-concentrated region and strain value on the inner board before and after aging process,which indicated that aging process had a great impact on the strain distution.Take DSCM to gluing interface of four kind plywood,and we can conclude that LPF had a weak interface with the other three had strong one.The technical specifications of HLPF meet the requirements of the national class I board.Utilization of nanoc ellulose modification on HLPF can not only improve bonding strength,but also enhance bonding interface.