Preparation Of Lignin Phenol Formaldehyde Resins And Their Properties

Phenol formaldehyde resins (PF) have been widely used in industries because of their exceptional adhesiveness, fire resistance and flame resistance. However, the start materials, phenol and formaldehyde are produced from petroleum. With its depletion and environmental problem, the production of PF from non-petroleum sources was therefore of great interest. Lignin is second only to cellulose in the nature, which widely exists in plant cell walls. It is significant to make full use of lignin for both environment and economy reasons. In consideration of its adhesiveness in plant cell walls and the similar structural characteristics compared with PF, introduction of lignin into PF resins is practicable and significant. The main work of this thesis is as follows.Optimization of the process for preparation of lignin-phenol-formaldehyde (LPF) resins. The structures of lignin varies with their origins, which induce variation of the conditions in LPF preparation. The lignin, derived from corn stalk, was directly incorporated into PF to synthesize LPF resins. The properties of the prepared LPF resins including viscosity, solid content, free formaldehyde content and adhesive strength were tested to evaluate the process. The optimized preparation conditions are NaOH content of 10%, formaldehyde to phenol molar ratio of 1.8:1, reaction time of 4 h, and lignin content of 25%. The properties of the prepared LPF under the optimum conditions are viscosity of 70 mPa·s, solid content of 40.9%, free formaldehyde content of 0.131%, and adhesive strength of 0.72 MPa. The properties all meet the requirement of GB/T 14732 and GB/T 9846-2004It was found that the adhesive strength of LPF is lower than the standard when lignin content was higher than 40%. So, activation or liquefaction of lignin were applied to prepare high quality LPF.Two activation methods, phenolation and hydromethylolation, were used. FT-IR and quantitative analyzation showed phenol and formaldehyde were introduced into lignin through phenolation and hydromethylolation reaction, respectively. The prepared LPF resin has similar physical properties such as viscosity, solid content compared with those of PF, while the free formaldehyde content was higher than PF. The content of phenolic hydroxyl groups of phenolated lignin increased from 4.06% to 4.36% slightly, and the adhesive strength of LPF was not improved obviously. The hydroxyl value of hydromethylolated lignin increased from 48.74 mgKOH/g to 207.89 mgKOH/g, and the adhesive strength of LPF improved from 0.72 MPa to 1.15 MPa.Liquefaction of lignin in sub-critical water without catalyst to prepare degradation of liquified lignin phenol formaldehyde resins (DLPF) was further studied in this thesis. The liquefied products were mainly aromatic organic compounds such as phenols, aldehydes and ketones in sub-critical water (260℃,3.4 MPa). As shown from GCMS analysis, the relative content of phenolic compound dissolved in ethyl acetate exceeds 70%. The DLPF with high contents of lignin content (up to 60%) were synthesized successfully. The physical properties of DLPF resin are similar to those of PF, while the free formaldehyde content of DLPF decrease to 0.104% from 0.131%, and the adhesive strength increase to 1.4 MPa from 0.72 MPa. The improved properties are attributed to the increased reactivity of the degradation of liquified lignin. The structure of DLPF is similar to PF resin, and the activation energy of DLPF considerately decreased from 93.39 kJ/mol to 68.63 kJ/mol.