Improvement of film formation abilities of waterborne latex particles for coating applications

Resumen

Waterborne paints, which use latices as binders, constitute the biggest share by technology to the worlds coating market. However, even modern waterborne paints need VOCs as plasticisers to obtain a desirable coating quality. The used co-solvents are acting as temporary plasticizers decreasing the minimum film formation temperature (MFFT) without changing the TG of the polymers. The objective of the present thesis was to reduce solvents out of latex paints, maintaining or increasing the final mechanical properties of the films. To achieve this goal, new zero emission plasticizers were developed: temporary hydro plasticisers (THP) and temporary oligomer plasticisers (TOP). In the case of THPs, grafted compounds presented the best performances, being itaconic acid (ITA) the one showing the best results reducing the MFFT of a latex with a TG of 30ºC, down to 12 - 16 °C with only small impact on the final latex film properties. The effect of the THP was also proven by following the film formation process by wet DSC.In the case of the TOPs, a method was optimized to produce the oligomers in-situ in the polymer particles with the aid of a chain transfer agent (CTA). Films produced with TOP showed better mechanical properties, for films dried at lower temperatures. The combination of THP and TOP concepts reduced the MFFT down to 5ºC, showing the promising behavior of the combined approach.The concepts tried at lab scale were then upscaled to industrial application trials, which showed the need to produce oligomers with lower TG than the main polymer. This new approach provided improved final properties at lower VOC content, compared with a benchmark latex dried in the presence of higher VOC content. It was demonstrated by Pyrene Excimer Fluorescence (PEF) spectroscopy that TOP plasticizers achieve this improvement by enhancing the polymer chain interdiffusion in the last steps of the drying process.