Low or no VOC polyurethane dispersions with good performance are achievable
Pittsburgh, June 18, 2008 -- The search for ultra low VOC polyurethane dispersions that are safer for the environment while also continuing to deliver high-end results has yielded new formulations and procedures that are free of the co-solvent n-methylpyrolidone (NMP). The desire to develop the safest products possible has directed scientists at Bayer MaterialScience (BMS) to delve further into the chemistry behind the new low-VOC materials - including cross-linking mechanisms such as UV cure and cure with water-dispersible isocyanates - and the improvement of properties through these reactions. Improving hardness, stiffness and solvent resistance through two methods of croslinking polyurethane dispersions (PUDs) was presented by a BMS scientist at the recent American Coatings Show and Conference (ACS) held in Charlotte, N.C.
New formulations and procedures have been developed that result in ultra low and zero VOC polyurethane dispersions. These new products can be formulated into ultra low VOC coatings systems. Improving the properties of coatings from these systems was the subject of this paper. The chemistry behind these materials, including cross-linking mechanisms, were presented. The cross-linking mechanisms include oxidative cure, UV cure, and cure with water-dispersible isocyanates. Improvement of properties through these reactions was demonstrated.
Taking Ultra Low VOC Polyurethane Dispersions to the Next Level of Performance was presented by Pete Schmitt, Bayer MaterialScience (BMS) LLC, during the event's Polyurethanes session. The paper was co-authored by colleagues William Corso and Bob Wade, BMS LLC, and Rolf Gertzmann and Christoph Irle, BMS AG.
The ACS presentation described the challenges and processes of creating finished products free of co-solvents through the acetone process. Through various studies, crosslinking PUDs improved the overall quality. This was further discussed by Schmitt at ACS, specifically UV cure and the addition of polyisocyanate crosslinkers.
"We found that through the acetone process, a variety of co-solvent free PUDs were developed to be employed as coatings for a multitude of substrates," said Schmitt. "We were also able to document the effects of both UV and polyisocyanate cures on film properties of waterbourne polyurethanes."
Through UV curing, polymers are high enough in molecular weight to develop a film through ambient drying, and when an increase of the strength of films is required, polyisocyanate crosslinkers are added. Adding a polyisocyanate to increase the solvent resistance and tensile strength in PUDs ultimately creates a polyurea that becomes a penetrating system, improving the properties of the polyurethane.
Advances in the synthesis of ultra low VOC polyurethane dispersions are demonstrated through the various processes. Low or no VOC dispersions with good performance are possible through crosslinking PUDs via UV cure, polyisocyanate cure or a mixture of the two. Assessing the desired properties of the finished product will ultimately help scientists decide which method is most applicable.
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Thomas Erdner, Phone: 412-777-5200
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