Study On Preparation And Properties Of High Hydrostatic Pressure Assisted Modified Soybean Protein Adhesives

With the rapid development of the wood industry,the amount of wood adhesives is increased greatly.Traditional industrial adhesives are mostly "trialdehyde" adhesives such as urea-formaldehyde,phenol-formaldehyde and melamine,which release toxic gases such as formaldehyde during use,and this seriously endangers the environment and human health.Toxic-free and environmental friendly bio-based adhesives have become a research hotspot in recent years.Among them,soy protein is a rich raw material and highly reactive.Soy protein has more-COOH,-NH2 and some hydrophilic groups,which has poor water resistance which limit their real application as wood adhesive.High hydrostatic pressure(HHP)treatment is a novel food sterilization and enzyme inactivation technology.HHP can cause the changes of the structure of biological macromolecules such as proteins,which will affect the physical chemical as well as the functional properties of proteins.This work here explores the effect of HHP on the structural characteristics of Soybean Protein Isolate(SPI),Also we investigated the effect of the addition of urea and cellulose composite on the HHP treated SPI based adhesives.The structure and performance are studied.The main research contents and conclusions are as follows:(1)The SPI solution was treated at 0.1,200,400,and 600 MPa for 5 min.The fluorescence scanning results showed that the surface hydrophobicity increased after HHP treatment and reached the maximum at 400 MPa.The results of circular dichroism showed that HHP treatment caused the α-helix content of the protein decreases,the βsheet content increases,the ordered structure of the protein is destroyed,and the hydrophobic groups are exposed.(2)After treatment at 0.1,200,400,and 600 MPa for 5 min,0.2%(wt)hexamethylenetetramine was added into the SPI solution as a crosslinking agent to form adhesive.The maximum dry and wet bonding strengths measured at 400 MPa are 5.109 and 2.011 MPa,which are greatly improved compared with at air pressure;the viscosity ranges from 230 to 420 mPa·s.The prepared adhesive has better flowability and wettability,but compared with at air pressure,the viscosity of the adhesive increased after HHP treatment,and wetting performance slightly decreased.(3)Urea was added into SPI solution to obtain the urea pre-modified soy protein solution,it was treated at 0.1,200,400,and 600 MPa for 5 min,followed by adding 0.2%(wt)hexamethylenetetramine as a crosslinking agent to form adhesive;The maximum dry and wet bonding strengths of the obtained adhensives measured at 600 MPa are 7.105 and 2.238 MPa;viscosity ranges from 220 to 590 mPa·s,the obtained adhesive at 0.1 MPa has poor wetting performance.(4)1%(wt)crystalline cellulose solution was added to SPI solution for micro modification,and was treated at 0.1,200,400,and 600 MPa for 5 min,followed by adjusting the pH to 10 to form adhesives;It was found that the maximum dry and wet bonding strengths of the obtained adhensives at 600 MPa which are 6.444 and 1.912 MPa respectively;the viscosity ranges from 140 to 270 mPa·s,which has good fluidity and wettability.