Final Report: Isocyanate-Free Polyurethane Coatings

EPA Contract Number: EPD15030
Title: Isocyanate-Free Polyurethane Coatings
Investigators: Bolskar, Robert D
Small Business: TDA Research Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: September 1, 2015 through February 29, 2016
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2015) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Toxic Chemicals

Description:

Polyurethanes are polymers that are widely used in a variety of industrial and consumer applications including foams, insulation and coatings.  The annual production of polyurethanes in the U.S. is about 7 billion pounds. Two-component polyurethanes are high performance protective coatings used in automotive, aerospace, and corrosion protection applications, and they dominate many markets because of their unmatched physical and chemical properties. Aliphatic polyurethanes are considered the best performing coatings for applications that require outdoor durability, color stability, high gloss, and/or exceptional chemical resistance. Unfortunately, their use presents significant problems because the isocyanate derivatives that are used in the standard route to make polyurethane materials are toxic and alternatives to using isocyanates as precursors to polyurethanes are sought. In this project, TDA Research, Inc. (TDA) is developing a new non-isocyanate two-part polyurethane chemistry to eliminate isocyanate toxicity and health and safety problems of current polyurethanes. Our technology is simple to use, does not produce volatile organic chemical (VOC) emissions, and should lower the cost of applying polyurethane coatings. Most importantly, the composition of the coatings can be identical to those used today, but no isocyanates will be used to form them.

The standard route to polyurethane coatings is based on reactions of two components, one of which has two or more hydroxyl (-OH) groups (in a diol or polyol), while the second has two or more isocyanate (-NCO) groups. Isocyanate derivatives are toxic and cause irritation of skin and mucous membranes, chest tightness, and difficult breathing, even at trace quantities that are well below permissible exposure levels. Additionally, some isocyanates are classified as potential human carcinogens and cause cancer in animals. Non-volatile isocyanates  are harmful irritants to the eyes and respiratory tract and powerful sensitizers. Not only is the isocyanate component a powerful irritant, but sensitized subjects can suffer severe asthma attacks and even death when exposed to trace quantities that are well below permissible exposure levels. The hazard is particularly significant to those that apply polyurethane paints, as this process involves spraying both components onto a surface where the cross-linking reaction occurs. Isocyanate workers can become sensitized to isocyanates and diisocyanates, leading to occupational asthma and significant claims for compensation. Therefore, isocyanate sensitization has a significant impact on the work force and a high cost in health and workers compensation benefits to the companies that make and use them. Furthermore, the processes used to manufacture isocyanates typically employ highly toxic chemicals such as phosgene, which is yet another drawback of isocyanates.

Another significant problem with current polyurethane systems is that these products typically contain high levels of volatile organic compounds (VOCs), which are added to reduce the viscosity of one or both of the components. Unfortunately, the solvent is volatilized as the urethane compounds are combined during processing, causing excessive VOC emissions. Increasingly stringent regulations have put pressure on the coatings industry to reduce worker exposure to toxic chemicals and lower the emission of VOCs. The industry has responded by looking for ways to modify its manufacturing and formulation processes, including developing other dual cure chemistries and high-solid one-component paints. Several strategies have also been developed to reduce the VOC content of two-part coatings. These include isocyanate cross-linkers that are compatible with waterborne formulations; reactive diluents which reduce viscosity but also react during cure (which prevents them from evaporating); solvent-free low viscosity acrylic polyols; low viscosity highly functional isocyanate cross-linkers; and finally new VOC-exempt solvents. Although these strategies have permitted ultra-low VOC two-part polyurethanes to be manufactured, they have also created  other hazards. For  example, reducing the viscosity of the isocyanate polymer usually is accomplished by using a lower molecular weight monomer, which also increases its volatility and therefore the potential for worker exposure. In addition, the density of isocyanate groups is generally higher in these newer, less viscous materials, which further increases the potential hazard to workers. Clearly, there is a need to develop a low VOC product that, in the finished or cured state, has the composition and the well-established and trusted performance of highly optimized two-part polyurethane coatings, but can be made without using the highly toxic and sensitizing isocyanate compounds.

Thus, for numerous reasons, it will be beneficial to replace isocyanate-based polyurethane processes with less hazardous alternatives, especially for two-part polyurethane formulations. However, the less-hazardous coating chemistries tried to date either offer insufficient performance, cure too slowly or are too expensive.

In Phase I of the project we have shown that our method has the potential to serve as an isocyanate-free drop-in replacement of traditional isocyanate-based two-part polyurethane- forming processes. Our synthetic efforts in Phase I emphasized not only the proof-of-concept reaction to make polyurethanes, but also the synthesis and characterization of new precursor derivatives because most of them are not yet commercially available. In Phase II TDA will optimize the precursor chemistry and polymerization processes, and demonstrate that our isocyanate-free polyurethanes are suitable replacements for today’s high performance paints.

A successful project will result in a cost-effective drop-in technology that allows the elimination of isocyanate from current two-part polyurethane coating formulations without the need for reformulation and requalification. This will allow a rapid transition to the market. Eliminating reactive isocyanate groups from polyurethanes will clearly eliminate toxicity and industrial health and safety problems associated with current polyurethanes, and will reduce the high cost of health and workers’ compensation benefits that today arise from worker sensitization. Furthermore, TDA’s approach may reduce both the cost of the polyurethane coating and the VOC emissions.

Commercial prospects for non-isocyanate polyurethane coating technologies are very high. Urethane coatings are one of the fastest-growing sectors of the worldwide paint and coatings industry. Despite their relatively high cost, their excellent durability, resistance to corrosion and abrasion, pleasing optical properties and flexibility make urethane coatings suitable for a range of  high-performance  applications.    Dominant  markets  include  automotive  refinishes,  wood finishes and high-performance anticorrosive coatings. The worldwide market for automotive refinish coatings was valued in 2007 at $5.12 billion and that of field applied, room temperature- cure industrial maintenance coatings were valued at $3.0-$4.5 billion. The 2015 world market for polyurethane military aerospace coatings was $316 million. Even a modest 1% penetration of this market would represent $100M revenues from the technology resulting from this project.

SBIR Phase II:

Isocyanate-Free Polyurethane Coating  | Final Report