Abstract:

By means of phenol liquefaction (or phenolation) in the presence of sulfuric/phosphoric acids as catalyst, the soy flour translated into raw material for water-resistant wood adhesive. The techniques of GPC, HPLC, FTIR and plywood evaluation were employed to characterize the phenolated soy flours (PSF) and the PSF-formaldehyde (PSFF) adhesives. It indicated that more than 90% of soy flour translated into phenolated resultants with molecular weight ranged 250-7 250 after the soy flour liquefied at 130-150 ℃ for 90min with phenol/soy flour ratio ranged from 3/1 to 2/1, and some phenol was bonded to soy flour via 1,4- and 1,2- substitutions after liquefaction. Phenolation not only unfolded the globular structure of soy protein but also increased the quantity of reactive groups in PSF, therefore a low-free-formaldehyde adhesive with good bond strength and water resistance was prepared with PSF. The plywood panels manufactured with the PSFF adhesives resulted in 28 h boiling-dry-boiling wet bond strength from 1.24 to 1.81 MPa. The phenol/soy flour ratio had various effects on the many properties of phenolated soy flour and PSFF adhesives, and the PSFF adhesive prepared with phenol/soy flour ratio of 3 had the best bond strength.

Key words: soy flour, phenol liquefaction, wood adhesive, characterization