The Synthesis Of Biochemical Modified Soybean Protein Adhesives And Application Research

The soybean protein adhesives as a typical of biological adhesive,has been continuously study for acentury. But because of it has all the defects that will be existing in the biological adhesives,such as lowbond strength,easy to rotten,high viscosity,short storage life,poor water resistance,etc.So that the peoplehave lost the enthusiasm for the study of the soybean protein adhesive,and turned to develope ormodified the relatively good performance of organic synthesis adhesives.However,due to the continuousimprovement of living standards and environmental awareness gradually increased, as a user, they arenot just pursuit the quality of the products,but also are increasingly concerned about if it will harmfultheir health and living environment or not.Not only that,governments are aware of the hazards offormaldehyde and volatile organic compounds,so they organization formulated or revised a series ofmandatory national standards of adhesive products,to safeguard their people’s health and a good livingstandard.So, to develop one or more low formaldehyde organic synthetic adhesives,even is thezero-formaldehyde environment friendly biological adhesives become the focus of our research.But inthe long run,due to the limited petroleum resources and irrefragable,thus the organic synthetic adhesivesbased on the petroleum as a raw material,there are limitations and unsustainable.So to develop one orseveral environmental friendly biological adhesives have become a inevitable thing.And now,on behalfof the environmental friendly biological adhesives, the soybean protein adhesives have been researchedin full swing.This research mainly use the soybean meal that is a by-product after extract the oil from thesoybean as the main raw material.Through the biological modification and chemical crosslinkingtreatment with the soybean protein,so the environment friendly soybean protein adhesives are madeout,and then we analyzed it application on bamboo floor.In the development process of soybean proteinadhesives,i use the infrared spectrum analysis as the method to analyze the effect of differentmodification methods of soybean protein chemical structure.Also studied the approach of pepsinhydrolysis of soybean protein,and make out the soybean protein hydrolysate that used for preparationproduce the soybean protein adhesives.Studied the optimum process of polyvinyl alcohol crosslinkingof soybean protein,as well as the optimum hot-pressing process of the application of soybean proteinadhesives to produce bamboo flooring.Conclusions are as follows: (1) Thermal modification did not affect the primary structure of soybean protein,but it will madethe soy protein thermal denaturation,the soybean protein combined with each other which caused thesolution viscosity increasing;The enzyme could hydrolyze the peptide bond of the polypeptide chain orthe amide bond to some extent,and the intramolecular or intermolecular crosslinking of the peptidechain increased;Acid-modified partially hydrolyzed peptide bond,but it could not cause a big impact onthe peptide chain,and acid could dissociated soybean globulin which cause the solution viscosityreducing;Alkali could greatly hydrolyze of peptide bonds or amide bonds which made many polargroups exposing,these groups could have the crosslinking reaction under the catalysis of alkali whichgenerated the greater molecular weight molecules,and it made the viscosity of solution increasingsharply.(2) The optimum process conditions of pepsin hydrolysis of soybean meal solution is temperature37℃,pH1.8,and when the high substrate concentration of soybean meal at the condition ofhydrolysis,the hydrolysis degree will increase with the adding amount of enzyme or to extend thetime;The soybean meal after heat-moisture treatment,soybean protein will expose more point ofapplication of enzyme,it can accelerate the enzyme rection which is favorable for the hydrolysisreaction,and can improve the degree of hydrolysis;The20%soybean meal solution after preheatedtreatment10minutes at90℃,the hydrolysis degree of soybean solution can reach to23.4%underhydrolysis temperature37℃,pH1.8,the adding amount of enzymes14000U·g-1,hydrolysis time3hours,and at this time,the most of molecular weight of hydrolyzed soybean protein molecular is1000D,and the hydrophobic groups also exposed mostly, which can be used as the soybean proteinhydrolysate for preparing the soybean protein adhesives.(3) Through the biological and chemical modification,the properties of soybean protein gotsignificantly improved, and the best technology of chemical modification is:18%POVAL,4%SDBS,3%sodium sulfite,15%glycerin, at this time, the viscosity of the soybean adhesive is61605mpa·s, the dry state shear strength is1.81MPa, the wet state shear strength is0.97MPa,this is upto the national standard(GB/T17657-1999). The curing temperature of the modification soybeanadhesive is between100℃~150℃, the hydrophilic group of modification soybean adhesive decreasedsignificantly, the soybean protein molecules and polyvinyl alcohol molecules produce the crosslinkingreaction,so it improve the water resistance performance of the soybean protein adhesive. (4) In the selected level range,the hot-pressing temperature is the main factor that influence theproperties of bamboo flooring, and then is hot-pressing time and hot-pressing press.Comprehensiveconsideration to the actual production,starting from the production energy consumption and productioncycle,the best hot-pressing process of bamboo flooring is:temperature130℃,time1.5min,pressure3MPa,and at this time,the static strength of bamboo flooring is122MPa, impregnated peel is20mm,formaldehyde emission is0.06mg/L that both reached the national standard of GB/T17657-1999and GB/T20240-2006.