Curing reaction kinetics of paper-based phenolic resin laminates—from laboratory measurements to inline quality control

We describe a comprehensive analysis of the drying and curing kinetics of resol phenol-formaldehyde (PF) resin utilizing multiple different thermophysical and optical measurement techniques and combinations thereof to gain a comprehensive understanding of the physicochemical processes that take place during large-scale production of paper-based PF laminates. This included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier-transform infrared evolved gas analysis (FTIR-EGA), and near-infrared (NIR) spectroscopy. In particular, the tailored integration of TGA with simultaneous near-infrared (NIR) spectroscopy in reflection geometry facilitated the evaluation of NIR spectroscopy's suitability for monitoring the ongoing process. This led to the implementation of an NIR-based real-time measurement setup at an industrial production site for a feasibility assessment. NIR spectroscopy in combination with partial least squares (PLS) regression modeling showed highly promising results highlighting the advantages of NIR spectroscopy as a tool for real-time inline quality control for large-scale production of PF resin laminates.