text: Although they have excellent environmental credentials, waterborne polyurethane dispersions tend to suffer from lower mechanical strength than other resins. The use of polycarbonate based polyols in the synthesis can help overcome this weakness. The wear and corrosion resistance is also not as good and hence they are often hybridized. Other strategies used to overcome some of the weaknesses include molecular design and mixing/compounding with inorganic rather than polymeric materials. The use of an anionic or cationic center or indeed a hydrophilic non-ionic manufacturing technique tends to result in a permanent inbuilt water resistance weakness. Research is being conducted and techniques developed to combat this weakness. Simple blending has also been employed. This has the advantage in that if no new molecule has been formed but merely blending with existing registered raw materials, then that is a way around the work required to get registration of the material under various country regimes such as REACH in Europe and TSCA in the United States. Because of the surface tension of water being so high, pinholes and other problems of air-entrainment tend to be more common and need special additives to combat. They also tend not to be manufactured with biobased polyols because vegetable based polyols don't have performance enhancing functional groups. Modification is possible to achieve this and enable even greener versions.
  Drying, curing and cross-linking is also not usually as good and hence research is proceeding in the area of post crosslinking to improve these features.