Preparation And Properties Of Soy Protein Based Adhesive

In the wood processing and manufacturing industry,wood-based panels are widely used in the manufacturing of furniture,building materials,and laminate flooring due to their good processibility and economic benefits.Adhesives are the essential components during the manufacturing of wood-based panels,and are usually developed from non-renewable petroleum resources,which during service life can give rise to unwanted detrimental organic compounds.Therefore,it is significant to develop an eco-friendly and biomass-derived adhesive for the wood processing industry.As an agricultural by-product,soy protein is an ideal material to be processed into adhesives because of its extensive availability,low price and environmentally friendly.However,the pristine soy protein adhesive exhibits an inferior bonding strength and poor water resistance due to the weak internal bonding strength,inherent hydrophilic nature and ignitability,which limit its practical application in the wood processing industry.Based on this,the soy protein adhesive was modified to improve the bonding strength and water resistance,and endow flame retardant performance,and thus developed a high performance and multi-functional bio-based adhesive.The crosslinker(BHTA)with multiple epoxy groups and flexible long chains was prepared by the ring-opening reaction of 1,6-hexanediol glycidyl ether(BEPH)and triethylenetramine(TETA)in a one-pot strategy without solvent and catalyst.Then,the BHTA was introduced to prepare soy protein-based adhesive.The epoxy groups of BHTA could react with the soy protein molecules to form crosslinking network structures,which significantly enhanced the gel content,thermal stability and hydrophobicity of the cured soy protein adhesive,and the flexible long chain could improve toughness.In addition,the optimal processing conditions of plywood prepared by soy protein adhesive were obtained via orthogonal test as pressure 3 MPa,time 12min and temperature 120℃.Consequently,the dry and wet bonding strength were increased from 1.1 MPa and 0.2 MPa to 2.8 MPa and 1.1 MPa,respectively,marking increments of 155%and 450%when compared to the pristine soy protein-based adhesive,which were beyond the standard of type Ⅱ plywood(≥0.7 MPa,GB/T 9846-2015).Then,tannic acid(TA)was gradually deposited on the surface of CNCs by oxidative self-polymerization,and then octadectadecamine(DA)was reacted with TA in situ by Michael addition and Schiff base to obtain modified cellulose nanoparticles CTDA,which was proved by FT-IR,TGA and XPS.Moreover,WAC showed that CTDA nanoparticles had excellent hydrophobic properties,which was related to the introduction of long-chain alkyl groups.Subsequently,CTDA,as reinforcer and hydrophobic element,was added into soy protein to prepare adhesive.The results of FT-IR,XRD,TGA,SEM and sol-gel tests presented that dense crosslinking network structures were formed between CTDA and soy protein molecules.Meanwhile,CTDA was used as a filler phase to repair the discontinuous adhesive layer,thus forming a stable and complete cured adhesive layer.Therefore,compared with pristine SPI adhesive,the dry and wet strength of the plywood prepared by SMPI/CTDA adhesive increased from 1.1 MPa and 0.2 MPa to 2.9 MPa and 1.4 MPa,respectively,which rose by 160%and600%.In addition,SMPI/CTDA adhesives could be used to bond different substrates,which expanded the application of soy protein adhesives.Finally,organic/inorganic compounds were used to improve the performance of soy protein adhesive.Phenylphosphodichloride(BPOD)was firstly used to react withγ-aminopropyl triethoxysilane(KH550)to remove the harmful halogen and thus obtained the silanized phenylphosphodichloride(BPOD(Si)).Then,the tannic acid(TA),as the multifunctional reactive platform,was used to induce the hydrolysis/condensation of siloxane under the alkaline condition to form hybridization(TBD(Si))with stable silication interface.The chemical structure and surface morphology of the TBD(Si)hybrids were studied by ~1H NMR,FT-IR,XPS,TGA and SEM,proving successful preparation.Then,A stable protein bonding/flame-retardant system was constructed by incorporating the core-shell TBD(Si)hybrids,which acts as reinforcer,crosslinker and flame retardant to improve the performance of soy protein-based adhesives.Therefore,these physical/chemical crosslinking networks were constructed,which improved the thermal stability,gel content and cohesive strength of the adhesive,and reduced the crystallinity and moisture uptake value.The particleboards fabricated by the SPI/D/C/TBD(Si)-10 adhesive showed a rupture modulus of 15 MPa,elasticity modulus of 1950 MPa,internal bonding strength of 0.44 MPa,marking the increments of 110%,110%and 145%when comparing to the pristine SPI adhesive,respectively,and displayed good water resistance and dimensional stability after water immersion,which satisfied the requirements of furniture particleboard manufacturing.In addition,the SPI/D/C/TBD(Si)particleboard showed pre-eminent flame resistance with LOI value of 27.6%due to introducing flame retardance.