Grantee Research Project Results
Final Report: Enabling Electrostatic Painting of Automotive Polymers with Low Cost Carbon Nanofibers
EPA Contract Number: EPD06037Title: Enabling Electrostatic Painting of Automotive Polymers with Low Cost Carbon Nanofibers
Investigators: Burton, David
Small Business: Applied Sciences, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $69,924
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Safer Chemicals , SBIR - Pollution Prevention
Description:
Automotive manufacturers are on a quest to reduce weight, increase fuel efficiency, and eliminate corrosion from automotive parts and body panels while maintaining their capability to compete based on cost, appearance, and performance. To meet those goals, manufacturers want to use more polymer matrix composites, particularly in body panels. Unfortunately, existing structural polymers (e.g., vinyl ester) are not amenable to electrostatic painting (ESP), the industry-standard practice for finishing metals. To use ESP on polymers, primers that contain environmentally detrimental volatile organic compounds (VOCs) are required, and processes must be adopted that add complexity and cost to manufacturing. These factors currently limit the extent to which polymer matrix composites are employed.
To solve these problems, Applied Sciences, Inc. (ASI) proposed a simple, solvent-free method that endows polymers with sufficient electrical conductivity so that they can be painted in the same manner as metals. ASI dispersed low concentrations of inexpensive carbon nanofibers (CNF) into the polymer matrix resin to impart sufficient electrical conductivity for the ESP process. The benefits of this approach are manifest, both for automotive manufacturers and the public.
Enabling direct ESP of polymers will eliminate approximately 18 percent of VOCs from the process and reduce costs by about $100 per vehicle. The net present value of this innovation conservatively is estimated at $500 million for the industry over the next 15 years (Pelsoci, 2005). Ultimate savings could reach $2 billion and 4 million pounds of VOCs annually. The improved economic viability of composites also will expand their use beyond the current level of only approximately 35 percent of automobile surface area, thereby increasing fuel efficiency (Gregus, 2001). It is calculated that the 1 percent reduction in vehicle weight that would result from replacement of the remaining steel body panels would lead to a 0.6 percent reduction in gasoline consumption and thus a savings to the U.S. economy of approximately $1.5 billion per year.
Currently, about 30 percent of automotive surface area is composed of composites, with much of the inroads in unpainted parts (bumpers, truck beds, trim) and components that do not require exact color match to metal components. Enabling ESP of composites by the exact techniques used for metal will extend their use into side panels and hoods, and dramatically increase their share of vehicle coverage. The successful demonstration of this approach will have favorable environmental and cost implications at all points in a vehicle’s life cycle.
Summary/Accomplishments (Outputs/Outcomes):
Incorporating carbon nanofiber into polymers at low loadings is known to create composites that can carry electrical currents while simultaneously increasing mechanical properties (Tibbetts, et al., in press; Boyce Components). Composites produced from a variety of composite fabrication techniques (injection molding, compression molding, long fiber thermoplastics processing, sprayable gelcoat), different polymers (PP, PEEK, PC, Nylon, PE), and carbon nanofiber types and grades were tested under this program. The composites tested all had electrical conductivities between 10-4 to 10-6 S/cm with loadings as low as 2 weight percent of CNF. The conductive composites were painted using ESP techniques and then tested for surface finish quality, adhesion, and abrasion resistance. The conductive composites received the paint with no alterations in the painting process and behaved similarly to metal. The CNF did not affect the surface quality nor did it impact the adhesion of the paint to the composite surface. The best nanofiber variant proved to be the XT version. The best processing methods were the long fiber thermoplastic process and the sprayable gelcoat. The sprayable gelcoat allows the ability to selectively place conductivity at the surface of the composite.
Composites fabricated with the new XT product have the same conductivity as the old CNF product, but at much lower loadings. The XT product is easier to disperse and therefore, retains more of its original length before processing, resulting in more conducive composites.
Conclusions:
Electrostatic painting holds substantial environmental and economic advantages for painting and finishing in the automotive industry; however, automotive components are increasingly manufactured from polymer composites that are not electrically conductive, and must be coated with conductive primers to enable electrostatic painting. The use of carbon nanofiber to impart electrical conductivity to the composite part could eliminate the requirement for a conductive primer on the composite surface.
To test the feasibility of this concept, four composite designs were fabricated of typical candidate reinforcement/polymer combinations that are, or could be used in, automotive composites. The composites were tested for electrical conductivity, paintability, surface finish, and adhesion. All composites fabricated showed no limiting changes in processing of the composites, and demonstrated excellent electrical conductivity and low percolation threshold with respect to CNF loading. All composites demonstrated good paintability performance and surface finish. Two of the composites were found to have 100 percent adhesion when tested using the ASTM standard, and three were found to show some delamination. The adhesion performance reflects the compatibility of the paint and composite and is not affected by the presence of the CNF. The XT variant of the carbon nanofiber provided sufficient conductivity at the lowest loading of all fiber variants. The XT material will be the grade of CNF used for all future ESP work.
The processing methods that show the most promise for generating conductive composites at the lowest loadings are the long-fiber thermoplastics (LFT) and the process developed by Boyce Components for making conductive gelcoats. A cost comparison shows that for composite parts thicker than a 1/10 of an inch, it is more economical to apply a thin gelcoat (5 mils thick) than to incorporate CNF throughout the volume of the part. The cost savings are a result of concentrating the most expensive component of the composite, the nanofiber, to the surface where the charging for electrostatic painting will occur. Preliminary estimates are that a savings of nearly $100 dollars per vehicle would be realized assuming approximately 50 percent of the vehicle surface is a composite material.
Overall, the program was successful in demonstrating that composites made conductive with the addition of CNF can be electrostatic painted without the addition of a conductive primer coat. Elimination of the conductive primer would eliminate approximately 0.23 pounds of VOC emission per automobile, or about 18 percent of the total VOC emissions related to painting and finishing. Future research and development will enable the development of other applications such as electronic enclosures, composite electrostatic precipitators, anti/de-icing heaters for aircraft, and antistatic flooring, countertops, and truck bed liners.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectSupplemental Keywords:
SBIR, small business, EMI shielding, nanotube, conductive polymers, nanocomposites, decreased VOC emission, improved fuel economy,, RFA, Scientific Discipline, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, automotive coating, electrostatic spray painting, environmentally benign coating, nanocoatings, nanocomposite, air pollution control, nanotechnology, VOC removal, emission controls, nanomaterials, nanofiberSBIR Phase II:
Enabling Electrostatic Painting of Automotive Polymers With Low Cost Carbon Nanofibers | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.