Objective Phenolic formaldehyde (PF) resins as thermoset polymers possess outstanding bonding properties, dimensional stability and exceptional heat stability with major limitations – high brittleness and shrinkage. These physical properties can be enhanced with the inclusion of particulate fillers or elastomeric materials. Coal, as a filler, has been used to improve both the thermal and mechanical properties of polymer materials. With respect to phenolic resins, the innate aromatic structure in coal suggests improved bonding is possible due to matching functionalities. However, prior to fabricating coal-phenolic composites, the effect of coal type and amount on the heat-curing of the phenolic resin needs to be characterized. In this paper, thermal analysis will be used to better understand the curing kinetics of an acid-based phenolic resin based on the filler type and composition. Methodology A commercial PF resin (Hexion Novolak) will be combined with two types of coal (semi-anthracite and sub-bituminous rank). Curing kinetics will be evaluated using Dynamic Scanning Calorimetry under inert conditions and at various heating rates and filler compositions. The heat flow from the DSC will be used to establish degree of cure profiles and these isoconversional analyses will be used to calculate activation energies based using differential (Friedman) and integral (Kissinger) methods from literature. Results Initial analyses using semi-anthracite coal mixed with the Novolak resin at 20wt.% showed the degree of cure at 4 heating rates with the primary cure intervals occurring between 10% and 80%. At the latter stage (80% - 100%), the curing profiles for the different heating rates, is observed to have a series of overlap, which suggests negligible change in conversion with respect to time. The decrease in the activation energy values as the conversion increases indicates an increase in the curing kinetics as we approach complete conversion during phenolic curing. The results comparing the pure PF resin to the PF resin mix with coal, would be presented at the conference.

Understanding the curing kinetics of phenolic composites based on filler content and composition

ACS Spring 2022

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