In-situ cure monitoring of isocyanate adhesives using microdielectric analysis

Recent advances in microelectronics have produced small electrodes that can be used for remote dielectric measurements. These miniature sensors are small enough to be embedded in a composite panel during manufacture with little disturbance to the manufacturing process. Small particleboard panels (5 by 4.5 by 0.25 in.) were manufactured with 6 percent polymeric diphenylmethane diisocyanate resin in a laboratory hot-press. A dielectric sensor was embedded in the core of each panel to measure both temperature and dielectric responses. The curing behavior of the particleboard furnish was also examined using dielectric analysis in a controlled oven and differential scanning calorimetry. Close agreement was found between the curing response detected by both these techniques. In addition, the curing response of particleboard furnish in a controlled oven was remarkably similar to that seen in situ during particleboard manufacture using four different platen temperatures. The contribution of moisture changes during pressing to the dielectric signal was evaluated. Finally, two different sensor designs were evaluated on a limited basis.

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