| With the increasing consumption of non-renewable resources and awareness of human environmental protection,the development of biomass adhesives has gradually been attracted attention.Soy protein adhesive is a typical green biomass adhesive,as it displays rich source of raw materials,renewablility,simple preparation,and excellent performance,which has been increasingly used in the industrial production of wood-based panels.However,petroleum-based crosslinkers are often used to prepare soy protein adhesives with excellent water resistance,which is not conducive to the sustainable development of biomass adhesives.In addition,soy protein adhesives are vulnerable to microbial invasion and poor aging resistance,which greatly limits its practical application in wood industry.In this paper,the lignin epoxy polymers(lignin-epoxidized soybean oil system,EHL-ESO and epoxy polymer of lignin,EPL)with high reactivity were successfully prepared by grafting lignin with epoxy monomer,and then crosslinked with soy protein to obtain soy protein adhesives.The effects of water resistance of soy protein adhesives modified by the different lignin epoxy polymers were studied to construct the soy protein modified by lignin epoxy polymers system,thus preparing the high performance modified soybean meal adhesive(SM/EPL)used soybean meal(SM)as raw material.Then,the effects of thermal-wet treatment on the chemical structure,thermal stability,mold growth and wet shear strength of the modified soybean meal adhesives were studied,and the mildew resistance effect of EPL on the modified soybean meal adhesives was evaluated.Finally,the influence of humidity-heat aging on the chemical structure,crystallinity and thermal stability of the modified soybean meal film was investigated,and the variation rule of the adhesion strength of the plywood treated under humidity-heat conditions was explored,thus evaluating the durability of the modified soybean meal adhesive.The results are as following:(1)The thermal stability and adhesion properties of the soy protein adhesives were significantly improved by the lignin epoxy polymers.When the amount of EHL-ESO was 7%,the wet shear strength of the modified soy protein isolate(SPI)adhesive reached the maximum value of 1.07 MPa.When the amount of EPL was 9%,the wet shear strength of SM/EPL adhesive reached the maximum of 1.02 MPa,and the preparation method is simple and easy to operate,which has a prospect of industrial application.(2)Pure SM adhesive was susceptible to mildew under thermal-wet conditions,while SM/EPL adhesive had excellent mildew resistance,and adding the compound preservatives into SM/EPL adhesive can further improve the mildew resistance;After being treated for 30 days,microorganism and stripping were observed on the glueline of the plywood bonded by pure SM adhesive,while no microorganism and stripping were found on that of SM/EPL adhesive,indicating that plywood bonded by the modified soybean meal adhesive had excellent mold resistance.(3)The main characteristic structure of SM/EPL film was significantly affected by humidity-heat conditions.In the early stage of aging treatment,the post-curing cross-linking reaction was main,and then the hydrolysis and oxidation reaction were dominant,which leaded to the decrease in the cross linking density and the crystallinity of the film;The wet shear strength of SM/EPL adhesive decreased gradually with the increase of aging time,but the plywood bonded by SM/EPL adhesive still showed good durability.After being treated for 1200 hours,the adhesion strength still met the bonding strength requirement according to the China National Standard(GB/T 9846-2015). |
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