| Acid hydrolysis ligneous residue (AHLR), produced from acid hydrolysis of hardwoods, was investigated to partially replace phenol for synthesis of exterior-grade phenol-formaldehyde (PF) resins. An AHLR was chemically modified by phenolysis reaction under acidic conditions to increase its reactivity relative to resinification with formaldehyde. The AHLR and phenolated-acid hydrolysis ligneous residues (P-AHLR) were characterized by {dollar}sp1{dollar}H, {dollar}sp{lcub}13{rcub}{dollar}C-NMR and FTIR, and the degree of phenolation was determined based on {dollar}sp{lcub}13{rcub}{dollar}C NMR spectroscopy. The degree of phenolation of 1.9 per average AHLR unit was achieved under optimum phenolation conditions. The P-AHLR polymers reacted with formaldehyde in a homogenous dilute sodium hydroxide solution (pH = 11) through hydroxymethylation and partial resinification to form phenolated-acid hydrolysis ligneous residue-formaldehyde (P-AHLR-F) resins. The performance of P-AHLR-F resins was evaluated by thermal analysis of the curing process and by a hard maple shear block compression test. Differential Scanning Calorimetry (DSC) was used to compare kinetic parameters for the curing of neat PF and P-AHLR-F resins. Results from dynamic DSC revealed that curing temperature of P-AHLR-F resins was generally lower than that of the neat PF resin at constant heating rates, and activation energies showed essentially no difference between PF and P-AHLR-F adhesives. The isothermal DSC at 150{dollar}spcirc{dollar}C indicated that P-AHLR-F resins cured faster than the neat PF resin. Used as adhesive the shear bond strengths of the P-AHLR-F resins were superior in both dry and accelerated aging tests to those of a commercial, exterior-grade, PF type resole resin used for comparative purpose. A cyclical process was developed to reuse solvent and unreacted phenol. This process was tested through three cycles for manufacturing phenolated-acid hydrolysis ligneous residue-formaldehyde resins. The resins produced in these cycles, like those produced in a single cycle, gave properties (compressive shear test, both dry and accelerated aging) superior to those of the commercial, exterior-grade PF resole resin. |
