Online measurement techniques for nanocellulose films and coatings

There has been an inclination in industrial coatings towards the utilization of more eco-friendly, renewable, and biodegradable solutions. Among these solutions, a material of special interest is nanocellulose, which, owing to its biodegradable and renewable nature in addition to properties such as mechanical robustness, flexibility, low density, non-toxicity, and surface modification ability, has become an extremely popular research topic.

This work dealt with non-contact measurement of coating thickness for nanocellulose-based films and coatings. Knife coating was used throughout the work. Three non-contact methods, viz. NIR spectroscopy, IR thermography, and optical confocal displacement sensing were used to measure thickness of nanocellulose coatings, both in dry and wet state. Two different types of nanocellulosic materials, namely, microfibrillated cellulose (MFC) and cellulose nanofibrils (CNF) were used in the study. Polypropylene, polyether sulfone membrane, and stainless steel were used as substrates.

Optical confocal displacement sensing was found to be the most accurate technique for measuring the thickness of MFC films with an RMS error of 9.3% for wet films and 29.1% for dry films. For CNF films, IR thermography produced best results with an RMS errors of 26.1% and 13.2% for wet and dry films respectively. As evident, the measurements were lacking industry-standard accuracy, which leaves the scope for improvement in future work.