Final Report: A Green and Unique Thermosetting-Thermoplastic PolycarbonateEPA Contract Number: EPD17037
Title: A Green and Unique Thermosetting-Thermoplastic Polycarbonate
Investigators: Cameron, Randy E.
Small Business: Instrumental Polymer Technologies, LLC
EPA Contact: Manager, SBIR Program
Project Period: September 1, 2017 through February 28, 2018
Project Amount: $99,990
RFA: Small Business Innovation Research (SBIR) - Phase I (2017) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Manufacturing
The purpose of this project is to develop a new class of plastics we call thermosetting thermoplastic. There are 300 million tons of plastics used to form structural materials, composites, adhesive and sealants. Manufacturers have to choose between using a thermoplastic or thermosetting plastic. Thermoplastics are long chained polymers that can easily melt processed, but the resulting material is susceptible to solvent attack and deforms under stress. If more structural integrity and chemical resistance is needed, a thermosetting plastic is chosen in which polymer segments react together to form a crosslinked matrix. The problem is thermosets are more costly to process. The precursor reactants need to be separated, cooled or blocked to keep them from reacting before processing. Energy in the form of heat or light is then needed to activate the cure. Furthermore, the crosslinking of a thermoset is irreversible. Currently both thermoplastics and thermoset plastics are derived from petroleum byproducts and can last 100 years before biodegradation. Though there is significant effort to recycle thermoplastics, of the 33.6 million tons of plastic discarded only 9.5% of it is recycled.
In this project we are developing an aliphatic polycarbonate that will be a benefit for both the manufacturer and for the environment. This thermosetting thermoplastic is a crosslinked thermoset resin at room temperature, but when heated over 120°C, the polymer network fragments into a low viscosity liquid that can be easily processed. Upon cooling the material once again crosslinks. This provides a wide range of cost savings for those using thermoset resins. It also provides better chemical resistance and structural integrity for those who use thermoplastics. This thermosetting plastic can also be recycled like a thermoplastic. Furthermore, this technology is made from sustainable raw materials and will biodegrade faster than current plastics.
During Phase I of this program we were not only able to demonstrated the technical soundness of this technology, but found that it would form a broader application platform than we had expected. We synthesized both dendrimeric and hyperbranched versions of the polycarbonate polymer. Samples prepared with reactive hydroxyls on their backbone crosslinked to form a solid resin upon cooling to room temperature, as expected. Those samples were found to have excellent chemical resistance. Upon heating to 120°C the crosslinked polymer fragment to form a liquid that can be processed and shaped, as expected. Upon cooling those samples once again crosslinked, suggesting the technology could be used as a recyclable thermoset resin. However, we also found that samples prepared without reactive hydroxyls on their backbone remained liquid at room temperature until exposed to moisture in air. The moisture in the air initiated a ring opening polymerization cure. Those samples, once exposed and cured, underwent the same reversible crosslinking and fragmentation under heat. This revealed that this technology could also be designed for moisture cured coatings, adhesives and composites. In other words, this technology is not limited to applications which could handle solid materials. For example, we thought powder and hot melt coatings and adhesives could be made, however, liquid moisture curing coatings and adhesives can now also be designed.
We performed physical testing on all the material after crosslinking and found them to have excellent strength, chemical resistance and adhesion. Due to the high crosslink density, the particular polymer formed had elongation which is typical for a thermosetting epoxies and unsaturated polyesters, but not high enough to be a replacement to polycarbonate or acrylonitrile butadiene styrene, (ABS). Biodegradation studies have only been performed for a month and a half, however, results already show that this polycarbonate degrades faster than commercially available polycarbonate, though not as good as cellulose, which was used as a positive control.
The commercial applications for the hydroxyl terminated polycarbonates developed in Phase I are low temperature curing powder coatings, hot melt coatings and adhesives and composites. The polycarbonates capped with carbonates have commercial applications in moisture curing coatings and adhesives as well as replacing baked polyurethane coatings using blocked isocyanates. The crosslink density of samples made so far does not offer the elongation required for its use to compete with current thermoplastics, but during Phase II we plan to us extenders to provide that elongation.