10.4 Development of Acrylic-Grafted Hybrid Polyurethane Dispersions
(Room 240-242)
10 Apr 18
4:00 PM
-
4:30 PM
Tracks:
Session 10: Polyurethanes II, Session 10: Protective Coatings
Polyurethane Dispersions (PUD) are known to offer high performance, especially in terms of their combination of toughness, abrasion resistance, flexibility and chemical resistance. However, their use has not been expanded to some applications due to high cost in comparison with other water-borne systems such as acrylic latex, which offer good performance at a considerably less cost. The need to reduce the cost of polyurethane dispersions has led the use of blending of Acrylic Latex (AC) and PUD in a coating package, but often it leads to films of lower quality, which is frequently attributed low compatibility between the two resin systems. However, the development of hybrid systems containing chemically bonded polymer structures is expected to lead to better compatibility between components. This study contemplates the synthesis of Polyurethane/acrylic hybrid dispersions using two different grafting techniques.
An NCO terminated pre-polymer was reacted with 50% of the stoichiometric amount of hydroxyethyl acrylate (HEA) to obtain a pre-polymer containing both NCO and acrylate functionality. This polymer has been used for the synthesis of acrylic/PUD hybrids dispersions by two methods - (a) Emulsion polymerization: The pre-polymer is neutralized, dispersed in water and chain-extended with ethylenediamine (EDA), resulting dispersion is used as a seed for conventional emulsion polymerization, with acrylic monomers. (b) Monomer mixing process: pre-polymer is mixed with acrylic monomers and free radical initiator and then is neutralized, dispersed in water and chain extended using EDA. Temperature is then raised to the initiation temperature, and radical polymerization of monomers, within the stabilized droplets, is carried out. The acrylic to urethane ratio was kept at 50:50 by weight in both processes.The grafting efficiency is tested by acrylic monomer depletion using Fourier transform infrared (FTRI), and by comparison of mechanical and chemical properties of the films. Samples also have been evaluated for their emulsion stability (particle size analysis and visual observation). The properties of hybrid dispersion will be compared with the straight acrylic emulsion, straight polyurethane dispersion, and corresponding physical blends.