The Polyurea Development Association Europe held its annual conference in London, near Heathrow Airport in November 2017. Simon Robinson paid a visit.
A wide range of papers were presented at the two-day Polyurea Development Association Europe meeting in west London in November 2017, from the importance of operator training, dust exposure regulations and the interaction between European fire regulations and polyurea-based coatings.
The papers are available to members of PDA Europe, and here we concentrate on three: a versatile three-step process to polyurea composites, surface coating polyureas and vapour blasting. The last is a technique to prepare surfaces which, proponents say avoids many of the problems with wet and dry blasting.
Tamas Balogh, technical director of Polinvent, Budapest offered a different, indirect approach to creating polyurea using a 50% water solution of waterglass such as sodium silicate (component ‘A’).
He explained that this way of making ‘indirect’ polyurea has been known in the mining and tunnel construction and rock stabilisation sectors for more than 30 years. Polinvent has tuned the resins to have long and well-controlled pot life. The user can choose among the ‘B’ component types to find pot life and viscosity that fit to the technology and to the expected weather conditions. Waterglass solution is delivered by large manufacturers; Polinvent does not produce it in house.
In this process, the water in which the waterglass is dissolved reacts with isocyanate to produce amines and carbon dioxide; there is then a part-reaction between the sodium hydroxide component of waterglass which produces carbon dioxide and sodium carbonate, and finally a reaction between the amine formed in the first reaction with the rest of isocyanate to produce polyurea.
The carbon dioxide generated in the amine reaction is dissolved into the aqueous medium and reacts with the strongly alkaline waterglass, producing small soda crystals.
In practice, this is done by mixing waterglass and an MDI-based blend together to create a two-phase system. The reaction starts on the surface of the waterglass droplets suspended in the MDI-blend. This gives a mixture with a pot life of between 5 and 150 minutes, and can be used to make composites, Balogh said. Glass fibre, aramid, basalt and carbon fibres have all been used successfully to make composites, he added. The mixtures’ viscosity is between 150 and 3000 mPa/s, depending on the resin, and solids content is typically between 85 and 90%.