(270a) Thermoplastic Polyurethane Gel Quality Improvement Based on Pilot Line Filter Evaluation

Gel quality in thermoplastic polyurethane (TPU) is a critical customer requirement in several applications including films, fibers, easy-to-extrude, and sheet. Gels are visual defects that have several root causes including large agglomerations of TPU hard segments and various foreign contaminates. While the agglomerations of TPU hard segments are significantly impacted by the mixing profile during the initial reaction of the TPU, the amount of agglomerations and size distribution of those agglomerations can be affected by the filter type, media type, and nominal pore size before the TPU is pelletized. However, even with filtration, often the magnitude of impact is not sufficient make a TPU with the desired gel quality outcome for the applications. The aim of this study was to predict the filtration impact on production TPU gel quality based on pilot scale gel quality results and determine the scaling correlation. Not only would this be beneficial to implement new filter types in production for existing products, but having a correlation would also be instrumental in new product commercialization. Early in the development phase, a project could be redirected or stopped if the gel quality could not be met on the production scale based on the available equipment. There is also a safety factor of evaluating new filtration equipment on the pilot scale with lower throughput while generating less waste and eliminating production down time. Factors to consider for the correlation are flow rate per square meter of filter media, pressure through the filter unit, amount of material that can be produced before a filter change, and impact on the TPU properties. An additional challenge to overcome was for a given TPU, the gel quality would change as the equipment size changed, from the 25mm pilot extender, to the 40mm pilot extruder, and to the 92mm production extruder. Through data analysis and trials on production and pilot scale, a correlation was established. From this work, a new filter was successfully implemented in production after extensive testing on the pilot line that reduced the number of gels in the product.