Greenseal: Non-isocyanate curing flexible foam systems

According to the Deinze, Belgium, based company Greenseal NV, there is a trend to develop polyurethane systems, which do not contain free isocyanates, like monomeric MDI, present in One-Component Foam (OCF), having all formulation ingredients in a single (aerosol) can, which after spraying gives a froth with cellular structure that cures by air humidity. Typically, substrates to build OCF formulations are aromatic polyisocyanates, like polymeric MDI (“pMDI”), well known in the construction foam industry.

Upcoming changes in governmental regulations like adjusted safety labelling, disposal as hazardous waste, and a lowering of the free monomeric content below 1 % w/w, all of which are key drivers for industrial manufacturers to develop isocyanate-free PU foam products. To anticipate on these radical changes, the development of an alternative and self-curing foam system which is cured by oxygen from air was pursued. The concept is based on implementing chemistry with smaller ecological footprint and, most importantly, aims at providing a safer solution for polyurethane foams to the user. Inspiration was found in the use of urethane (meth)acrylate prepolymers, which currently find applications in adhesives, electronics, coatings, and flooring among others. Indeed, such materials tend to crosslink with formation of PU networks photochemically or by electron beam.

Obviously, this approach is less useful for PU foam hence a more suitable curing system needed to be designed. Radical initiators active at ambient temperatures, were found to successfully cure the urethane prepolymers. These compounds, alkylboranes, have very low activation energies for reaction with oxygen, giving instant decomposition and radical formation upon exposure to air. The behaviour of these species was fully elaborated by EPR spectroscopy, providing useful mechanistic insights in the underlying chemistry. As such, it was possible to tune reactivity of the curing system to match with selected prepolymers and formulations thereof. Initial trials showed too fast of a curing on the interphase between froth and atmosphere, where obviously oxygen concentration is highest.

Finally, a proof-of-concept level was reached when a urethane acrylate formulation was prepared that fully cured within 2 min after release from the aerosol can. The curing mechanism as investigated was independent of temperature, no post expansion was observed while foam properties were good with uniform cellular structure and structural rigidity. This significantly faster curing, tunable and predictable, now allows to decouple curing efficiency and final foam performance from variables like temperature and air humidity. Moreover, the applied technology is non-toxic, performing and provides perspective for a non-isocyanate future. The technology was patented, with several more applications pending.

Major advantage of the new process is the non-exposure of free isocyanate to DYI and construction workers, when applying these newly developed products.

www.greenseal.be

Contact: Aster de Schrijver Chairman FDS Invest NV, Sint-Martens-Latem, Belgium http://fdsinvest.com/ Chairman of the board Greenseal NV, Deinze, Belgium www.greenseal.be

About Greenseal NV Greenseal was was founded by Aster De Schrijver, OCF foams co-inventor during the 1970s. The company is based in Deinze, Belgium, and represents more than 45 years of dedication to the OCF industry. Greenseal produces a complete assortment of hardware and accessories for the OCF industry, including aerosol valves (tilting and gun valves), PU foam guns (metal and plastic), and accessories (caps, rings, tubes). The company provides technical support and R&D services to OFC producers. It has a fully equipped lab facility in Deinze, Belgium, and joint R&D activities in Belgium, Portugal, Bulgaria, Turkey.