Study On Preparation And Application Properties Of Larch Tannin-modified Soybean Meal Adhesive

Soybean meal adhesive is a kind of biomass protein adhesive,which is made of soybean meal powder as the main raw material,adding modifiers,additives.and so on.At present,there are many studies on soybean-based adhesives,but the present situation of their application and popularization is not ideal.The main reason is that the soybean-based adhesives prepared at present are easy to produce mildew,low cross-linking density,and it is difficult to completely replace the cheap aldehyde-based adhesives on water resistance and gluing properties.In this paper,on the basis of reviewing the research progress of soybean-based adhesives,and aiming at the problems of soybean-based adhesives at present,a tannin-modified soybean meal adhesives with high crosslinking density,excellent water resistance and bonding properties and good mildew resistance was prepared by using larch tannin and soybean meal powder as two important forest resources.And the adhesive was used to prepare plywood and MDF with excellent properties.The main contents and results are as follows:1.Preparation of tannin-modified soybean meal adhesiveUsing dicyanamide as tannin modifier,tannin-based curing cross-linking agent was prepared under alkaline conditions,treated as curing agent,and the tannin-modified soybean meal adhesive was prepared by mixing and mixing at room temperature,using soybean meal powder as raw material and complex glue containing active water-soluble macromolecule as liquid phase.The wetting properties,rheological properties,dynamic thermal mechanical properties and microstructure of tannin-modified soybean meal adhesives were studied by FTIR,contact angle measuring instrument,rotary rheometer,DMA and SEM,and the crosslinking mechanism of tannin modified soybean meal adhesive was analyzed.The results show that:In alkaline condition,dicyandiamide and tannin form amides.The introduction of tannin-based curing crosslinking agent increases the viscosity of soybean meal adhesives and decreases the solid content.At the same time,the wetting performance and water resistance of soybean meal adhesives can be significantly improved;Rheological analysis showed that the tannin modified soybean meal adhesive was a pseudoplastic fluid,and with the increase of the tannin-based curing cross-linking dose,the viscosity of the adhesive system increased,showing a certain viscosity;DMA analysis showed that the Tg of tannin-modified soybean meal adhesive decreased first and then increased with the increase of tannin-based curing cross-linking agent.When the addition of tannin-based curing cross-linking agent was 4%,the Tg was the lowest and the curing performance was the best;SEM analysis showed that the introduction of tannin-based curing cross-linking agent made the fracture surface of soybean meal adhesives smooth and the number of small holes reduced.Based on the above characterization results,the tannin-based curing crosslinker reacted with soybean protein isolate and composite glue,forming a three-dimensional interpenetrating network structure.The tannin-based curing crosslinker improved the crosslinking density and water resistance of soybean meal adhesives by its own active groups.2.Application of tannin-modified soybean meal adhesive on plywoodThe plywood was prepared from tannin-modified soybean meal adhesives,and the production process of plywood was optimized.At the same time,the effects of aging time,adhesive keepping time and storage time of tannin-based curing cross-linking agent on the properties of plywood were studied,and compared with MDI-modified soybean meal adhesive in keeping time and hot pressing temperature.The results are as follows:Considering the factors of production cost,bonding performance,safety and environmental protection,the optimum parameters of tannin-modified soybean meal plywood are:4%tannin-based curing cross-linking agent,0.2‰primary viscosity,hot pressing temperature of 120?,hot pressing pressure 1.2 MPa,hot pressing time is 90 s/mm,sizing quantity is 360 g/m~2,Eucalyptus veneer.And the strength of plywood pressed with this process parameter is better than the standard of national?class plate;Compared with MDI-modified soybean adhesive,tannin-modified soybean adhesive has the advantages of low toxicity,long shelf life and excellent bonding performance,but there are still some gaps in curing speed;Aging time has obvious influence on soybean meal plywood,mainly on bonding strength and coating properties.To ensure the properties of plywood,aging time should be controlled within 1 hour;the storage period of tannin-based curing cross-linking agent is 2 months,and the longest aging time of tannin-modified soybean meal adhesives is 90 minutes.In order to ensure the quality of tannin-modified soybean meal plywood,it is necessary to use tannin-modified soybean meal adhesives in time.3.Application of Tannin-Modified Soybean Meal Adhesive on MDFMDF was prepared by tannin-modified soybean meal adhesives,and the production process of soybean meal MDF was optimized.The results are as follows:Considering the production cost and the properties of the sheet,the optimum parameters are soybean meal 100kg/m3,compound glue 60 kg/m3,tannin-based curing cross-linking agent 4%,emulsified paraffin wax 4%,hot pressing time 330 s,hot pressing temperature 190-200 C,moisture content 7%-9%and density 750-840 kg/m3.The IB,MOR,MOE,SS and 24h-TS values of soybean meal MDF prepared by optimum ratio and process parameters can meet the requirements of GB/T11718-2009.4.Inhibitory effect of tannin-modified soybean meal adhesives on aspergillus nigerIn order to study the inhibitory effect of tannin-modified soybean meal adhesives on aspergillus niger,the mildew time,mildew rate,proportion of damaged area and damage value of soybean meal plywood and MDF were studied,and the anti-mildew effect of tannin modified soybean meal adhesives on aspergillus niger was obtained.The results are as follows:The introduction of tannin-based curing cross-linking agent can prevent aspergillus niger to a certain extent,and with the increase of the amount of tannin-based curing cross-linking agent,the beginning mildew time and the complete mildew time of soybean meal plywood and MDF are prolonged,the mildew speed becomes slower,the damage value and the proportion of the damaged area are reduced,and the anti-mildew effect is more obvious.