Abstract:

This paper deals with the properties of lignin-modified phenol-formaldehyde resin ( LPF) adhesive synthesized with lignin partially substituting for phenol under various conditions. Then,the influences of such factors as the substitution rate of lignin for phenol,the sodium hydroxide dosage,the formaldehyde-to-lignin mass ratio and the solid content of the product on the properties of LPF were discussed,and the factors were optimized. Finally,the thermal properties of LPF were analyzed by means of DSC. The results show that the alkali activation and hydroxymethylation help to improve the chemical reactivity of the lignin,that the adhesive prepared under the optimal conditions ( a substitution rate of 50%,a sodium hydroxide dosage of 4. 5%,a formaldehyde-to-lignin mass ratio of 8: 100 and a solid content of 41. 4%) is of high bond strength ( up to 2. 04MPa) as well as low residual formaldehyde and phenol contents ( much less than those regulated by the national standard) ,and that the prepared LPF adhesive is superior to the phenol-formaldehyde resin adhesive because it is of low curing temperature and high curing rate.

Key words: lignin, phenol, phenol-formaldehyde resin, adhesive, bond strength, free formaldehyde