Final Report: Silane-Terminated Aliphatic Polycarbonate Dendrimer Solutions for Environmentally Green CoatingsEPA Contract Number: EPD10028
Title: Silane-Terminated Aliphatic Polycarbonate Dendrimer Solutions for Environmentally Green Coatings
Investigators: Cameron, Randy E.
Small Business: Instrumental Polymer Technologies, LLC
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Nanotechnology
The environmental impact of polyurethane coatings does not stop at the 1.6 billion pounds of volatile organic solvents (VOCs) released, globally, during their application. The truly stunning impact is noticed when one considers the solvents and cleaners required during application, toxic corrosion inhibitors used, waste during application and the petrochemical footprint of the raw materials. Polyurethane coatings are generally a two-component system, including an isocyanate and polyol component, which is applied over a primer, also a two-component system. Two-component coating systems lead to waste due to difficulty estimating required paint volume and application time. The environmental impact of this is amplified by the fact that most components of these coatings are sourced from petrochemical feedstock with a trail of hazardous waste in their path. Unfortunately, for many applications, two-component polyurethane coatings are needed to meet the performance requirements.
The goal of this project is to use dendrimeric polymers, a type of nanotechnology, to develop a one component, 0VOC aqueous coating that would adhere directly to different substrates including wood, concrete, and steel without the use of a primer. The resin system would be renewably sourced and would yield a coating with performance properties similar to a urethane coating system. The unique spherical shaped dendrimers, acting as molecular cells, also will be used to stabilize hydrophobic nontoxic corrosion inhibitors in the aqueous solution.
For this project INSTRUMENTAL POLYMER TECHNOLOGIES, LLC (IP TECH) is using its proprietary method, called evolution polymerization, to produce dendrimeric aliphatic polycarbonate polyols at low cost. Dendrimers, which are polymers that branch out from a central core to form a sphere, similar to a molecular cell, offer unique opportunities for low-VOC coatings systems. Within this project, IP TECH's dendrimeric polycarbonate polyols are terminated with silanes, the silanes hydrolyzed, and the resulting alcohol distilled away to yield a 0VOC resin system. The resulting aqueous solution then would contain silane terminated dendrimers, which could condense in a sol gel fashion to yield a high performance coating. It was expected that the silane termination would offer adhesion and hardness qualities of sol gel coatings. However, it also was expected that the aliphatic polycarbonate core would reduce the brittleness and inability to apply thick coatings, which has kept sol gel coatings from being used in the general coatings market.
Also, within this project the core of the polycarbonate dendrimer was derivatized with alkyl groups to help stabilize hydrophobic, nontoxic corrosion inhibitors, for use over steel. This uses the dendrimer's unique ability to act as a molecular surfactant and stabilize hydrophobic molecules in an aqueous environment. This is in an effort to make the silane terminated dendrimers practical for use as a primerless topcoat over steel. Knowledge obtained during this study also will help exploit the unique ability of dendrimers to carry hydrophobic materials in aqueous solution.
It was recognized that the success of this project is dependent on how well the performance of the dendrimeric solution compared to properties of two-component urethane coatings when applied over primer. Furthermore, the cost needs to be competitive with polyurethane coatings. An increase in cost is marketable because of the reduction in costs during application relative to current technology; however, a price less than $10/lb is assumed necessary for general market acceptance.
The first goal was to produce a silane terminated dendrimer that was hydrolyzed and stable in an aqueous solution. This was easily done by derivatizing the dendrimer directly with isocyanatopropyl triethoxysilane or the much less expensive aminopropyltrimethoxysilane, followed by hydrolysis under the appropriate conditions.
This was a major step towards a successful project. Optimization of the production process, including the minimization of steps required to derivatize the dendrimer, ultimately led to a silane terminated, 0VOC dendrimer solution at 60 percent solids that could be produced for less than $5.00/lb. This proved the technology is marketable as long as the cured coatings performed.
Application of the dendrimers revealed a dried coating could be formed at typical urethane coating thickness without any signs of cracking. Initially the coatings were very slow to dry and required heating. However, optimizing the catalyst resulted in a 0VOC aqueous dendrimeric solution that cured at room temperature within 12 hours.
The ultimate performance of the dried coatings was much better than anticipated and yielded abrasion resistance and chemical resistance admired of sol gel coatings, but with less brittleness. Unlike sol gels, the dendrimeric solution could dry without cracking at thick film build. Coatings were tested against BOEING's BMS 10-72 exterior coatings specification, known to be one of the most rigorous tests for two-component polyurethane coating systems. Hydrolytic stability, adhesion, impact resistance and chemical resistance were all found to be competitive or better than required in the specification.
Unfortunately, the best properties were found when the coatings were heat cured. Ambient curing, though achieving reasonable properties, was very slow. Work will be done in Phase II of this project to accelerate the cure at room temperature and widen the technology's potential market.
During this project, IP TECH also demonstrated that the best method to stabilize hydrophobic corrosion inhibitors within the core of the dendrimer is to incorporate long alkyl hairs within the core. This truly made the dendrimer a molecular surfactant with a hydrophobic core and hydrophilic, and reactive, surface. Aside from absorbing corrosion inhibitor, it was found the hairs also aided in corrosion protection of steel.
IP TECH will sell this technology through the same distribution network already in place to sell its polycarbonate polyols. The three distributors, who cover the United States market, have agreed to distribute these waterborne silane terminated dendrimers.
Though work will continue to be done on accelerating the cure under ambient conditions, the technology is ready to launch into many market areas. Several coatings companies already have shown interest in testing IP TECH's dendrimeric solutions for use in their coatings. Of immediate applicability are coatings that are force cured as well as coatings that are applied thin. This ranges from coatings for aircraft to coatings for fibers. The coating dries much faster when applied thin, and considering the high abrasion resistance of the coating, a thick film for many applications is not always necessary or even advantagous.
A couple of resin companies have interest in using these dendrimers within the water-based emulsions and solutions they currently sell. Another company is interested in using the technology of this project to blend with their own ceramic sol gels in order to improve their performance.
The process used in the laboratory to produce these dendrimeric solutions is suitable for the reactors currently used by IP TECH to produce its standard polycarbonate polyols. Scale up will be an important part of the Phase II effort.
Phase I of this project was a great success in that it revealed the technology is not only technically feasible, but also is cost effective and ready to commercialize for some markets, while having high future potential in others. The performance of coatings made from these dendrimeric solutions was better than current urethane coating technology with respect to abrasion resistance, adhesion, and chemical resistance. Phase II will focus on accelerating the cure time under ambient conditions, further exploiting the unique character of the dendrimers in the performance of the coatings, as well as reducing production costs. Several potential customers have been identified from various industries who will be able to evaluate the technology during Phase II.