Study On The Formation Of Lignin-based Dopa Structure And Its Enhancement Of Soybean Protein Adhesives

In order to solve the problem that the active crosslinker of soy protein adhesive depends on fossil resources inspired by the high adhesion structure of mussel protein the methoxyl group on the aromatic ring of enzymatic lignin was removed by n-dodecyl mercaptan and ultrasound.which was replaced by p Henol hydroxyl group to form catechol structure and then used to modify soy protein adhesive to prepare whole biomass adhesive.The effects of treatment methods and conditions on the structure and structure of lignocellulosic catechol and the effects of the introduction of lignocellulosic catechol structure on the functional groups pyrolysis behavior cross-section morp Hology residual rate toughness bonding strength and other properties of soy protein adhesive and the enhancement mechanism were studied.The conclusion is as follows:(1)Using n-dodecyl mercaptan as the demethoxy reagent.the enzyme hydrolyzed lignin was modified by demethoxy and the demethoxy lignin was obtained by reaction at 90 ? for 1H.Compared with the unmodified lignin,the content of methoxyl decreased by 39.1% and the content of p Henolic hydroxyl increased by 34.9%.After modification,the activity of enzymatic hydrolysis of lignin increased by 27% compared with that of unmodified lignin.Some methoxyl groups in guaiac and Syringa structural units of enzymatic hydrolysis lignin are removed and p Henolic hydroxyl groups are formed thus forming lignin catechol structure.(2)After ultrasonic treatment for 20 minutes,the structure of lignin changed obviously,and the content of methoxy group decreased 29.6% the content of p Henolic hydroxyl increased by19% and the content of alcohol hydroxyl increased 38.4% In addition the molecular weight of the enzyme hydrolyzed lignin after ultrasound was significantly reduced and the reaction activity of the enzyme hydrolyzed lignin was 23% higher than that of the unmodified lignin forming the lignin catechol structure.(3)The apparent viscosity of soy protein adhesive modified by demethoxylin was determined by 136700 m Pa.s Down to 100600 m Pa.s the adhesive residue rate reached 88.6% Compared with the unmodified adhesive the water resistance of the adhesive is increased by 70% and the water resistance of the adhesive is improved 0.89 MPa The water-resistant gluing of plywood made ofpure soybean protein adhesive Increased intensity 67.9% After modification the thermal stability of soy protein adhesive was improved and the peak value was from two hundred and 294.10° C to310.36 ? degradation rate from zero point six one three Reduce to zero point five three four The crosslinking system is more stable than before.Demethoxyenzymatic hydrolysis of lignans can effectively reduce the brittleness of soy protein adhesive and improve the crosslinking density of the adhesive.This is because:(1)lignin itself contains a large number of active groups which can form hydrogen bond with soybean protein to enhance the bonding strength;(2)after demethoxylation treatment part of the methoxyl is removed to form new p Henol and alcohol hydroxyl groups and the reaction activity of lignin is greatly improved.(3)The structure of pyrocatechol is formed by demethoxylin,which is oxidized to o-benzoquinone in the process of hot pressing.The quinone structure further reacts with the amino group of soybean protein to form covalent cross-linking so as to improve the water-resistant adhesive strength of the adhesiv.