Effects of resin and curing parameters on the degree of cure of resole phenolic resins and woodflour composites

Abstract

SynopsisThe degree of cure of various resole phenolic resins was assessed from their resistance to acetone extraction. Cured woodflour composites of resoles were also characterized by dynamic mechanical tests in linear viscoelastic behaviour regions. Acetone extraction is not a sensitive discriminator between highly cross-linked resins. In addition, residual basic catalyst promotes aldol condensation reactions of acetone to produce materials that are absorbed in the phenolic resin so as to provide negative weight loss data on extraction. Despite its inaccuracies, however, this solvent resistance test is still useful as a go/no-go specification technique. Dynamic mechanical tests were performed on molded resole/woodllour composites. This is a useful method for characterizing degree of cure and residual reactivity of the phenolic resin. Degree of cure increases with curing time, temperature and resin pH, with pH being the most important variable. Resins cured at pH's near neutral are linked by ether linkages rather than the more stable methylene bridges. The final degree of cure of woodflour composites depends heavily on the curing conditions (pH, time, temperature). It does not appear to be crucial how the initial resoles were made (i.e., catalyst, phenol/formaldehyde mole ratio or duration of the condensation reaction time) so long as the resoles have relatively high molecular weight. Curing should preferably be at temperatures below 180°C to minimize degradation of the polymer.

Relationship between different mechanical properties of phenol formaldehyde SLG-reinforced composites

“…It was also discovered that curing phenolic resins should preferably be at temperatures below 180°C to minimize degradation of the polymer. 27 The curing temperatures for composites used in this study were at or below 100°C to ensure degradation will not happen but the curing time of 10 h was too long and higher temperature and shorter curing time should be attempted in the future; the degree of cure as indicated by dynamic mechanical thermal analysis (DMTA) was 90%. 28 However, it was found that the curing process was unaffected by any additives.…”

Ligneous resole adhesives for exterior-grade plywood

“…For the extraction setup, a round-bottom flask was filled with 250 mL acetone and the thimble was placed in a 100 mL Soxhlet extractor. The resin powder was then extracted for 48 h, as proposed in previous work (So and Rudin 1990;Schmidt and Frazier 1998). Subsequently, the thimbleincluding the insoluble resin and the extractive was dried and weighed to determine the soluble amount of the cured adhesives.…”

Effect of Fiber Treatments on Mechanical Behavior of Short Fique Fiber-reinforced Polyacetal Composites

“…The natural fiber composites have been used with thermoset matrices such as unsaturated polyester [16][17][18], epoxy [19,20], and phenolic resins [21][22][23]. Thermoplastic matrices such as polypropylene [24][25][26], polyethylene [27][28][29], polystyrene [30], and polycarbonate [31] have also been extensively investigated.…”