Study On The Preparing For Laccase-Treated Alkali Lignin Adhesive And Its Bonding Mechanism

The objective of this study is to manufacture wood adhesive without the release of residual formaldehyde, solve the waste and pollution problems of black liquor from the paper mill, and explore a new kind of non-toxic, environmentally friendly and green plywood production process. In this paper, we use laccase to oxidative industrial lignin to prepare renewable and environmentally friendly biomass-based laccase / lignin adhesives. Meanwhile, the bonding mechanism of laccase activation lignin has also been investigated.The paper includes four parts. PartⅠ: Research on the technology of preparing laccase-treated industry alkali lignin adhesive, including the single-factor and orthogonal optimization test. The effects of reaction conditions, such as the dosage of laccase, pH, activation temperature, activation time and solution chroma to shearing strength and viscosity of laccase/lignin adhesive has been carried out. It was to be provide possible theories and technical permanents making directly used industry alkali lignin resource as adhesive for veneer; PartⅡ: Research on the comparative technology of lignin catalyzed with laccase for two times has been conducted. Through comparison of shearing strength between laccase/lignin adhesive catalyzed for two times and reference samples dealed with different technic, we want to find a new technology about laccase/lignin adhesive to improve the bonding performance of veneer; PartⅢ: Research on the influence of hot press conditions, such as temperature, time, pressure, the dosage of adhesive to the performance of laccase/lignin adhesive, in order to search the best technical condition of hot press. PartⅣ: The changes of lignin functional group before and after laccase treatment and the reaction mechanisms in the laccase/lignin adhesive systems were investigated in detail by FTIR and UV. The major achievements of this research are following:(1)The dosage of laccase, PH, activation temperature, activation time and solution chroma are the main factors that influence the laccase/lignin adhesive preparation technology. Under single factor experiment, the best parameters and scopes are ensured. As follows: the dosage of laccase 20～30mL/20g lignin, PH value 3.0～4.0, activation temperature 35℃, solution chroma 70%, activation time 7h.(2)Based on the optimum parameters screened out through single factor experiment, we choose the dosage of laccase, pH value, activation temperature and activation time as four influencing factors, which has three levels respectively. Through orthogonal test, we find that the four factors all have significant impact on shearing strength, and the order of significant is: the dosage of laccase > PH value>activation temperature>activation time. According to the orthogonal test results and statistics analyses, the optimum parameters are found out, that is the dosage of laccase 30mL/20g lignin, pH 3.0, activation temperature 35℃, activation time 7h. The corresponding shearing strength can reach the fourth grade plywood requirements according to GB.(3)Through comparison of shearing strength between lignin adhesive catalyzed with laccase for two times and reference samples dealed with different technic, we find that the former is obviously bigger than the latter.(4)Through the research on the influence of hot press conditions to the performance of laccase/lignin adhesive and under single factor experiment, the best parameters and scopes are obtained, that is temperature 160℃, time 15～20min, pressure 1.5MPa, adhesive dosage 0.05～0.06g/cm2.(5)According to the FTIR spectra, the structure of lignin modified by laccase changed obviously which could be described as follows: Firstly, the vibration intensity of hydroxide O-H increased and the wave number of peak value increased; Secondly, the vibration intensity of conjugated carbonyl groups (α-carbonyl groups) increased obviously; Thirdly, band of phenol hydroxyl disappeared, which revealed that phenol hydroxyl of lignin was oxidized to form alcoxy or peroxy radicals after been modified by laccase; Furthermore, methoxy content increased and the intensity of syringyl C―H stretchy of ester bond enhanced significantly.(6)The UV spectra of laccase-lignin suggested that the phenol hydroxyl content of lignin both decreased dealed with laccase and high temperature respectively. It not only indicated that laccase catalysis is conducive to improve the adhesion effect, but also presumed that proper high temperature is advantageous to increase the products intensity in the process of panel production.