Degradation Of Enzymatic Hydrolysis Lignin In Isopropyl Alcohol-Water Co-solvent And Its Application In Phenol-formaldehyde Resin

Phenol-formaldehyde (PF) resin is extensively used in the wood industry for their excellent performances including high bonding strength, excellent water resistance, heat resistance and chemical stability. However, it also has limitations:high free phenol content and free formaldehyde content, high cost of petrochemical resources, non-renewable and other shortcomings. As the gradual increase awareness of environmental protection and increasing depletion of fossil resources, several attempts have been made to look for a kind of cheap, environmentally friendly, renewable biomass materials to replace phenol. Lignin, as an important and abundant renewable phenolic compound in the nature, is suitable to substitute phenol. Enzymatic hydrolysis lignin (EHL), a new style lignin obtained from the residue of second generation fuel ethanol, has better chemical activity than other lignin. But compared with phenol, its disadvantages including large molecules, low reactivity and so on, limit its application for a long time.In this paper, enzymatic hydrolysis lignin is obtained from bio-ethanol residue by alkali solution and acid hydrolysis method, and depolymerized to low molecular weight in isopropyl alcohol-water co-solvent. By using single factor experimental method, the influences of reaction temperature, reaction time and solid-liquid ratio on the lignin yield and formaldehyde value were investigated in hydrothermal degradation reaction and degradation reaction with solid base catalyst. Compared two degradation products, lignin were depolymerized in the optimal conditions. Then the lignin was used for partial replacement of phenol to prepare lignin-phenol formaldehyde (DLPF) resin adhesives and pressing into plywood. And the impacts of lignin substitution rate on the properties of DLPF resin were explored. The results showed that:the degradation method can partially degrade enzymatic hydrolysis lignin, reduce the molecular weight of lignin and increase the reaction activity of lignin. At last, lignin-modified phenol-formaldehyde resin can not only improve the performance of phenol formaldehyde resin, but also reduce the phenol dosage.Hydrothermal degradation of enzymatic hydrolysis lignin was carried out in isopropyl alcohol-water co-solvent. Increasing the reaction temperature within a certain range, the yields and formaldehyde values of lignin increased at the same time. There is also discussion of the effect of reaction time and the solid-liquid ratio on the degradation products. The optimal reaction conditions of hydrothermal degradation of lignin in isopropyl alcohol-water co-solvent were confirmed as:reaction temperature of 250℃, reaction time of 60 min, solid-liquid ratio of 1:10. And the degradation products yield and formaldehyde yield value in this condition were 64.38% and 0.2992 g. GPC results show the decrease of molecular weight and FTIR and 1H NMR results show the cleavage of ether linkage (α-O-4, β-O-4) in the process of degradation and the increases of the content of phenolic hydroxyl group and aliphatic hydroxyl group; at the same time, TG and DSC results show that glass transition temperature of lignin decreased compared with the lignin without degradation.Solid base as a catalyst was added into hydrothermal degradation of in isopropyl alcohol-water co-solvent. Being similar to the reaction above, the effect of temperature on the yield and formaldehyde value is remarkable. Rising temperature within a certain range can help to improve yields and increase the formaldehyde value. Meanwhile, the reaction time was optimized and the optimal conditions were got as follows:reaction temperature of 250℃, reaction time of 180 min, solid-liquid ratio of 1:10. In this condition the yield and formaldehyde value of degradation product were 75.8% and 0.3683 g, respectively. The results of GPC, FTIR and 1H NMR showed the reduce of molecular weight, the cleavage of ether bond (a-O-4, (3-0-4, etc.) and the increase of content of phenolic hydroxyl groups and aliphatic hydroxyl groups of the degradation lignin in the process of catalytic hydrolysis lignin degradation. Meanwhile TG and DSC results show that the degradation reaction reduced glass transition temperature of lignin. By comparing the yields, formaldehyde values and characterization results of two types of degradation products, it came to a conclusion: compared to hydrothermal degradation of lignin, catalytic degradation lignin should be more suitable for preparing lignin modified phenol formaldehyde resin adhesives.The results showed that 70% phenol in the resin can be replaced by degradation lignin without damaging the bonding strength of the adhesives (DLPF). Expect free formaldehyde content, all the properties of the adhesives can meet National Standard (GB/T14732-2006), including solids content, free phenol content, brominable substance content and bonding strength. FTIR results showed DLPF resin and PF resin have a similar chemical structure. But on the thermal behavior, TG and DSC revealed that incorporation of lignin can slightly improve thermal stability of PF resin and reduced curing temperature of PF resin. In order to explore the effect of degradation process on the replacement rate of lignin in PF resin’s preparation, the non-degradation lignin modified PF resin (LPF) was synthesized for comparison. With the same degradation lignin or non-degradation lignin substitution, the bonding strength of DLPF resin was superior with respect to the LPF resin. The degradation process of lignin in isopropyl alcohol-water co-solvent could enhanced the substitution rate of lignin and improve PF resin’s performance.