| Polymer materials prepared from renewable forest resources have attracted an increasing attention recently, predominantly owing to the needs of environmental protection and substitutes of petroleum. About 0.14 billion tons of cellulose are separated from plants every year in pulp and paper industry, and at the same time 50 million tons of lignin are obtained from pulping waste liquor. But so far, less than 20% of lignin by-product has been effectively utilizatized. Phenolic resin ,with excellent performance, has been widely used to manufacture plywood. Lignin-phenol-formaldehyde(LPF) resin, in which part of toxic petrochemical phenol is substituted, can not only reduce the consumption of phenol, but also achieve the aim of waste utilization.LPF was prepared by blending of hydroxymethylated alkali lignin or lignosulfonate with phenol-formaldehyde resin, and by copolymerization of alkali lignin with phenol and formaldehyde. The preparation, structure and properties of a variety of LPF resins were investigated. The main results were described as follows:1. Characteristics of alkali lignin and LignosulfonateThe composing component, functional groups, element contents and thermal behavior of alkali lignin and lignosulfonate were analyzed by chemical titration, FT-IR,NMR and TGA. Both of alkali lignin and lignosulfonate have higher sugar and ash contents,and the effective lignin content is less than 30%.The amount of total hydroxyl,phenolic hydroxyl and alcoholic hydroxyl of alkali lignin are 6.19%,2.47% and 3.72% respectively, While the amount of total hydroxyl,phenolic hydroxyl and alcoholic hydroxyl in lignosulfonate are 5.89%,3.67% and 3.28% respectively.Element analysis shows that both of alkali lignin and lignosulfonate have high C/H ratio and high oxygen content. FT-IR and 13C NMR results show that the main structure of alkali lignin and lignosulfonate are guaiacyl and syringyl respectively. TGA shows that two lignins begin to decompose at 200℃,and the residual rate of lignosulfonate is lower than that of alkali lignin, because of its lower ash contents。 2. Study on composite adhesive of hydroxymethylated lignosulfonate /phenol-formaldehyde resin(HLPF)HLPF was prepared by blending modified lignosulfonate and phenol-formaldehyde resin. The lignosulfonate, without pre-treatment by extractation and purification, was modified by hydroxymethylation to increase its reactivity. The optimal conditions of hydroxymethylation are as follows: the mass ratio of lignin-formaldehyde 3:1, the amount of catalyst 0.25%. FT-IR and 13C NMR showed that the amount of hydroxymethyl group was increased significantly by hydroxymethylation reaction and reduced with increasing the amount of lignin. When 30%~40% of phenol-formaldehyde resin(PF) was replaced by hydroxymethylated lignins, the adhesive thus formulated showed lower free formaldehyde and free phenol. The bonding strength could meet the standard of type I plywood and the formaldehyde emission of the plywood was less than 0.3mg/L, up to the standard of E0 degree plywood. The best pressing plate conditions are: assembly time 4~8h, pressing temperature 135±5℃.3.Study on composite adhesive of hydroxymethylated alkali lignin /phenol-formaldehyde resin(KPF)KPF was prepared by blending modified alkali lignin and phenol-formaldehyde resin. The alkali lignin, taking no extracted purification, was modified by hydroxymethylation to improve its reactivity, The optimal conditions of hydroxymethylation are as follows: the mass ratio of lignin-formaldehyde is 3:1, the amount of catalyst is 0.25%. FT-IR and 13C NMR show that the amount of hydroxymethyl group was increased after hydroxymethylation reaction and reduced with increasing the amount of lignin. When 30%~50% of phenol-formaldehyde resin(PF) was replaced by hydroxymethylated lignins, the adhesive thus formulated showed lower free formaldehyde, simple manufacture process, good reproducibility and low free phenol. The bonding strength could meet the standard of type I plywood and the formaldehyde emission of the plywood was less than 0.2mg/L, up to the standard of E0 degree plywood. When 30% of PF was replaced by hydroxymethylated lignins, the curing speed of KPF was faster than PF. The contact angle of KPF on wood was less than 90. The thermal stability of KPF declines as the amount of lignin increases.4. Study on Lignin-Phenol-formaldehyde ResinThe lignin-phenol-formaldehyde resin(KLPF) adhesives were synthesized by replacing part of phenol with technical kraft lignin and introducing the technical kraft lignin at initial reaction stage. The optimal preparation conditions of KLPF are as follows: the reaction temperature 80℃,the solid content (47±1)%.The adhesive thus formulated showed good reproducibility with the benefit of low cost. When 30%~50% of phenol was replaced by lignin, the bond strength could meet the requirement of type I plywood and the formaldehyde emission of the plywood was less than 0.3mg/L, up to the standard of E0 degree plywood. FT-IR and 13CNMR results showed that lignin participated in the copolymerization of phenol and formaldehyde. TGA and DSC results showed that modified KLPF had faster curing speed and lower heat-resistance.5. Pilot experimentA pilot experiment was carried out in Jiashan Zhongjia Chemical Industry Co.,Ltd and the KLPF adhesives were synthesized by replacing 38% of phenol with technical kraft lignin in 2t reactor, The properties of the resulted KLPF are as follows: solid content 48.9%,viscosity(25℃) 189mPa.s, free formaldehyde 0.26%,free phenol 0.16, pH value 11.5 and storage period >20d. The formaldehyde emission of the plywood manufactured with the KLPF was less than 0.3mg/L and the bond strength could meet the requirement of type I plywood both by rapid determination method and 28h cycle determination method.
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