Studies On Improving The Performance Of Starch-based Wood Adhesive By Emulsifier And Nano-motmorillonite

Starch-based wood adhesive is an environmental friendly adhesive and has a broadmarket prospect. However, due to the starch retrogradation, the starch-based adhesive hadshown poor storage stability and weak shear strength, which seriously restricted itsapplication. Therefore, in order to improve the performance of the starch-based adhesive aswell as to realize its industrial production, emulsifier and nano-motmorillonite (NM) wereused to improve the mobility, storage stability, dry shear strength and wet shear strength of thestarch-based adhesive in the study, and the factory pilot test was also conducted in this paper.Firstly, the effects of sodium dodecyl sulfate (SDS) and cetyl trimethyl ammoniumbromide (CTAB) on shear strength, mobility and storage stability of starch-based woodadhesive were studied. The action mechanisms were preliminarily discussed. It is shown that,although SDS and CTAB addition resulted in a slight decrease in shear strength, the mobilityand storage stability were significantly enhanced. The proper addition level of emulsifier was1.5%~2%(w/w). Possible mechanisms of the specific action of SDS and CTAB werediscussed. It was proved that the amylose-emulsifier complexes were formed in starch-basedwood adhesive by using blue value or differential scanning calorimeter (DSC) analysis. Theformation of amylose-emulsifier complexes and emulsifiers absorbed on starch moleculesmight hinder the aggregation of latex particles, as shown by the scanning electron microscopy(SEM) images and Zeta analysis, and inhibit the retrogradation of starch, as observedby DSC analysis.Therefore, the results suggested that the formation of amylose-emulsifiercomplexes and emulsifiers absorbed on starch molecules might hinder the aggregation oflatex particles and inhibit retrogradation of starch during the storage, leading a good mobilityand storage stability of the starch-based adhesive.Secondly, the nano-motmorillonite (NM) was added into the starch-based adhesive bymelt blending to improve the performance of the starch-based adhesive with SDS addition,and the influences of NM on the dry and wet shear strength were primarily investigated. It isshown that, the dry and wet shear strength were significantly enhanced with the NM addition,compared with control adhesive, the shear strength of starch-based wood adhesive with5%ofNM increased by86.5%in dry state and108.2%in wet state. Possible mechanisms of thespecific action of NM were discussed. The result of X-ray diffraction (XRD), SEM, FTIR,TGA and rheologic measurement suggested that the action mechanism might be that theformation of the exfoliated structure of NM and hydrogen-bond interaction enhanced thenetwork of the starch-based wood adhesive, improved the cohesion of the the starch-basedwood adhesive, and formed water-barrier in the starch-based wood adhesive.Thirdly, the NM and organic nano-motmorillonite (ONM) were added into thestarch-based adhesive by in-situ polymerization to improve the performance of thestarch-based adhesive with CTAB addition, and the influences of NM and ONM on the dryshear strength, wet shear strength and viscosity were investigated. It was shown that, the dryand wet shear strength of adhesive could be improved significantly by the ONM, especially,the bonding strength of starch-based wood adhesive with3%of ONM increased by100%in dry state and36.8%in wet state, while the NM did not improve the shear strength in dry andwet state; both the NM and ONM could significantly decreased viscosity of the starch-basedwood adhesive. The results of XRD and DSC suggested that the enhancement observed stemfrom a completely exfoliated structure of ONM formed in the starch-based adhesives andconnected with the starch molecules by CTAB. The optimum adding amount of them byorthogonal design: CTAB is1.5%(w/w, dry starch basis), ONM is3%(w/w, dry starch basis).Finally, the optimum formula of the starch-based adhesive was used for the factory pilotexperiment.The performance of the modified starch-based adhesive exceeded the industrystandard of HG/T2727-2010for the commonly used adhesive and exceeded the merchantadhesive. It’s raw material cost below the PVAc wood adhesive. Therefore, it will have a goodextended value and market prospect.