| With the social progress and economic development,the environment has been worse.Among them,the release of harmful carcinogens substances formaldehyde from the traditional wood adhesives is a threat to human health.So the study of environmentally friendly starch-based wood adhesive is imminent.However,most of the starch-based wood adhesives have the disadvantages of poor adhesion and poor storage stability.In view of these ubiquitous problems,this paper has experimented and used different characterization methods to study starch-based wood adhesives.In this paper,the influence of different methods on the properties of starch adhesive was studied on the basis of the synthetic technology.Related research contents and results are as follows:1.In view of pretreatment,different durations(0h,0.5h,1h,1.5h,2h,2.5h and 3h)of starch was studied.The optimum acid hydrolysis treatment time was 2h.The shear strength in dry state of the starch adhesive was 6.65 MPa,while the shear strength in wet state was 3.6 MPa,and the grafting reaction was also improved.In addition,the results of Fourier transform,dynamic time scanning and low-field nuclear magnetic resonance(NMR)show that the adhesive can inhibit the regeneration of starch by suppressing the rearrangement of the starch molecular chain and locking the water molecules in the adhesive system.The Acid hydrolysis destroys the hydrogen bond between starch molecules to a large extent to improve the viscosity stability and bonding capacity of starch adhesives,especially after repeated freeze-thaw cycles.2.The effects of different types of emulsifiers on the properties of adhesives were studied from the view of promoting the grafting of adhesives.The results show that the viscosity of the adhesive added with the emulsifier SE is moderate,between 3-8Pa.s,which ensures the flow ability and does not cause the waste of the adhesive during the sizing process.The results of shear strength also show that the addition of emulsifier SE increases the shear strength in dry state of the adhesive from 2.58 MPa to 7.44 MPa,and the shear strength in wet state increases from 1.14 MPa to 3.23 MPa.Moreover,compared with the control group,starch adhesive with addition of emulsifier shows storage stability at low temperature.Especially the adhesive with addition of SE still has mobility after ten freeze-thaw cycles.XRD results show that the addition of emulsifier makes the crystallization zone of starch change to the amorphous region,which provides a larger space for the grafting of the system.Therefore,the grafting rate increases with the addition of emulsifier.Grafting rate of the adhesive with SE increased to 75%.The results of low field NMR show that the addition of emulsifier makes the relaxation time less obvious,and the regeneration of starch is inhibited to a certain extent,which makes the adhesive system more stable.The different emulsifiers have different effects on starch adhesives.Overall,SE is a relatively good choice of emulsifier.3.The effects of different contents of nano-silica particles on the starch-based wood adhesives were studied.The shear strength of dry state increased from 7.44 MPa to7.99 MPa,and the shear strength of wet state increased from 3.23 MPa to 4.87 MPa,which obviously improved the adhesive ability and water resistance of the adhesive.The thermogravimetric curves of the samples show that the degradation temperature Tp of the degradation temperature of the samples with the addition of nanoparticles increased from298.5 ℃ to 302.7 ℃,and the weight loss rate decreased from 25.01% to 24.38%,which indicated that the nanoparticles enhance the thermal stability of the adhesive.The rheological properties indicate that the adhesive is a pseudoplastic fluid,and the presence of silica enhances the plasticity of the adhesive,which facilitates the contact between the adhesive and the wood and enhances the application of the adhesive.The SEM image of the surface of the sample shows that the silica is evenly fused in the adhesive system. |
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