BFRL: 2008 Program Information (V 1.1)

Program Manager:
Jonathan Martin
Revised: 11/6/2007

BFRL Goal:
High Performance Construction Materials and Systems

Relevant Links

SLP: Service Life Prediction of Nanostructured Polymeric Materials

To validate the reliability-based methodology and to develop models for service life prediction of nanostructured polymeric materials (NPMs), and to develop metrologies/methodologies for the characterization of NPMs. This program contributes to the BFRL goal on High Performance Construction Materials and Systems, and also to NIST initiatives on Nanotechnology.

Over the last few decades, polymeric materials have made tremendous inroads into numerous industry sectors, including transportation, aerospace, building, and construction. While possessing light weight, high specific strength and stiffness, processability, and low cost, polymeric materials are susceptible to degradation by a number of environmental factors, including ultraviolet radiation, high temperatures, and moisture. The lifetime of a polymeric component is greatly influenced by these factors, as well as by its own molecular composition and the presence of additives/fillers.

At the present time, polymer durability testing utilizes both real-time field and accelerated laboratory testing, but the majority of these tests lack a scientific basis, and are not capable of quantitatively predicting service life. In general, service life prediction, as opposed to materials comparison testing or material rank-ordering, is extremely difficult to achieve using conventional methods due to fundamental flaws in the design of the experiments and the metrologies utilized. In order to obtain data that is high enough in quality to incorporate into mathematical models, specimens exposed in both outdoor and accelerated laboratory testing must be characterized on the basis of absorbed dosage, not time as is conventionally done, and environmental variables must be characterized exactly the same way for both locations.

Service life prediction research is a problem that is not addressed in industry or academia at a fundamental scientific level. The absence of such a methodology has hindered product development and innovation, acceptance of polymeric materials into new applications, and the ability of polymeric materials to realize their full potential as structural materials.

In 2006, the Polymeric Materials Group became the first research team to successfully link field and laboratory exposure results for a neat, model epoxy coating using a reliability-based methodology. Unlike conventional methodologies, the reliability-based methodology is a quantitative and scientifically-based methodology. The premises underlying this methodology, however, essentially challenge every aspect of the premises underlying the conventional methodologies. Success in applying this methodology in predicting the service life of the epoxy coating has provided the Polymeric Materials Group with an opportunity to move into the study of nanostructured systems, which includes polymers filled with nanoscale materials.

Our initial focus will be on metal oxide particles and carbon nanotubes, which are nano-scale fillers that are of interest to our customers. One example of a metal oxide filler is titanium dioxide, widely used in a wide variety of polymeric building products. It is also a semiconductor and photocatalytically active, which has important and scientifically interesting ramifications on performance and lifetime of the polymeric matrices. Carbon nanotubes also are being increasingly utilized in a wide variety of applications, yet the properties of nanotubes and the impact of nanotubes on initial and long-term properties of materials are not fully understood. This proposed research is both challenging and pioneering, and has already gained strong industrial support.

The projects comprising the service life prediction program can be divided into three broad subject areas, which address the major objectives of this program:

1. Validation of the reliability-based methodology and development of models for service life prediction of nanostructured polymeric materials (NPMs),
2. Development of metrologies/methodologies for the characterization of NPMs, and
3. Application projects.

In 2006, Polymeric Materials Principal Investigators gave a number of keynote presentations highlighting the linkage made between field and laboratory exposure results for a polymeric system.

The Polymeric Materials Group was the first research team to provide data proving that, using the NIST SPHERE, reciprocity is valid for an epoxy coating over a wide range of exposure temperatures and relative humidities.

Nanoscale characterization of filled polymeric systems and their degradation with AFM, laser scanning confocal microscopy, SEM, nanoindentation and x-ray scattering and neutron scattering has been successfully carried out, laying the groundwork for future detailed studies in this area.

Protocols for measuring multi-scale structure (i.e., from nanometers to micrometers) and particulate dispersion in polymer suspensions and films using light and neutron scattering have been successfully developed, and the results have been presented at the 2007 ACS Spring meeting. Polymeric Materials Group researchers demonstrated the quantitative relationship between dispersion and mechanical property uniformity as well as weathering durability.

An experimental protocol for assessing the photoreactivity of nano- and pigmentary titanium dioxide particles using Electron Paramagnetic Resonance (EPR) measurements and nitroxide spin-traps has been developed and optimized. This protocol is equal in sensitivity, but simpler and less laborious, than current industrial practice for measuring pigment photoreactivity. Spectrophotometric assay methods also have been developed and used to assess the photoreactivity of nanostructured titanium dioxide.

An optical metrology has been developed for quantifying the scratch resistance of polymeric coatings and plastics using instrumented indentation and optical scattering measurements. For the first time, optical scattering measurements have quantified the effect of scratch width in the specular and off-specular scattering from a coating surface. A draft scratch test method relating nano-scratching and optical scattering has been submitted for industry review.

The construction, installation, and optical alignment of a novel Scanning Wavelength Illumination System have been completed, providing color capability to our current optical scattering technology.

A method has been developed to effectively functionalize carbon nanotubes and nanoclays with isocyanate (NCO) group that will form covalent bonds with polymer matrices; this will increase the degree of dispersion of the CNTs, and also increase the CNT/matrix interfacial strength and stress transfer in CNT/polymer composites. A patent disclosure has been submitted for this discovery.

A methodology to covalently couple CNTs with quantum dots (QDs) for probing dispersion of CNT in polymer solution and solid materials has been successfully demonstrated.

Construction of an Automated Analytical Laboratory (AAL) within BFRL was initiated in 2006. This laboratory has been equipped with a 7-axis robotic arm along with five analytical instruments.

Data demonstrating that applied mechanical strain affects the solubility of rubber systems was collected, analyzed and presented. It also was demonstrated that two weeks on the SPHERE was able to reproduce the failure of a commercial sealant product that took six weeks in the field, when exposed to moisture and mechanical strains.

Critical experiments were carried out that demonstrate that a critical relative humidity level exists for optimal polymer/substrate adhesion. The value of this critical relative humidity is a function of the bulk polymer solubility, and is not a surface phenomenon as previously believed.

Selected Publications and Presentations: Polymeric Materials Group researchers are highly active in both archival publications and presenting in scientific forums. In FY 2007, the project leaders in this group have given over thirty technical talks, seventeen of which were invited or keynote presentations.

A selection of the publications is listed below.

L. Sung, X. Gu, C. Clerici, H. Hu, E. Loizou, and D.L. Ho, “Effect of Pigment Dispersion on Optical Properties and Durability of a TiO2 Pigmented Epoxy Coating,” Proceedings of the 232nd American Chemical Society Meeting (2007).

L. Sung, C. A. Michaels, A. M. Forster, J. Lucas, J. Comer, and P.L. Drzal, “Correlating Surface Morphology to Damage Response in Polymer Coatings through Instrumented Scratch Testing,” FSCT•ICE 2006 Proceedings of the 84th Annual Meeting Technical Program, New Orleans, LA, November 2006.

L. Sung, J. Comer, A. M. Forster, H. Hu, B. Floryancic, L. Brickweg, and R.H. Fernando, “Scratch Behavior of a Nano-Alumina/Polyurethane Coating,” FSCT•ICE 2006 Proceedings of the 84th Annual Meeting Technical Program, New Orleans, LA, November 2006.

I-Hsiang Tseng and Stephanie Watson, “Evaluating Photoreactivity of TiO2 Using EPR Spectroscopy,” Proceedings of the North American Catalysis Society, 20th North American Meeting, Houston, TX, June 2007.

T. Nguyen, X. Gu, D. Martin, M. VanLandingham, R. Ryntz, and J. W. Martin, “Degradation Mode of Coatings in Photolytic, Hydrolytic and Corrosive Environments – A Nanoscale Study,” FSCT•ICE 2006 Proceedings of the 84th Annual Meeting Technical Program, New Orleans, LA, November 2006.

Xiaohong Gu, Chris Michaels, Peter L. Drzal, Joan Jasmin, David Martin, Tinh Nguyen, and Jonathan Martin, “Probing photodegradation beneath the surface: A depth profiling study of UV-degraded polymeric coatings with micro-chemical imaging and nanoindentation,” JCT Research, in press (2007).

Aline Granier, Tinh Nguyen, Alexander Shapiro, and Jonathan W. Martin, “Polyurethane composites reinforced by isocyanate-functionalized multi-walled carbon nanotubes and carbon nanofibers,” Proc. Adhesion Society Meeting, Feb. 2007, Tampa, Florida, 228-230.

Aline Granier, Tinh Nguyen, Naomi Eidelman, and Jonathan W. Martin, “Covalent Functionalization of Carbon Nanotubes with Diisocyanate for Polyurethane Nanocomposites,” Proc. Adhesion Society Meeting, Feb. 2007, Tampa, Florida, 346-348.

Aline Granier, Tinh Nguyen, Ha-Jin Lee, Alex Shapiro, and Jonathan W. Martin, “A Novel Method to Covalently Functionalize Carbon Nanotubes with Isocyanate for Polyurethane Nanocomposite Coatings,” Proc. Asian Pacific Coating Conference and Show, Bangkok, Thailand, June, 2007.

A.M. Forster, S. S. Watson, A. L. Forster, and P. L. Drzal., “Quantifying Surface Mechanical Properties of Filled Coatings Exposed to Accelerated Weathering Conditions,” Journal of Coatings Technology Research, in press.

A. M. Forster, B. Morgan, J. Lucas, "Material Stiffness and Surface
Roughness Factors in Polymer Indentation," Proceedings of the 29th Annual Adhesion
Society, Tampa, FL, 2007.

Joannie Chin, Eric Byrd, Cyril Clerici, Mounira Oudina and Li-Piin Sung, “Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor: Temperature and Humidity Aging,” NISTIR 7373, January 2007, also Polymer Degradation and Stability, in press.

Joannie Chin, Eric Byrd, Brian Dickens, Robert Clemenzi, Rusty Hettenhouser, Art Ellison, Jason Garver, Debbie Stanley, Vincent Colomb, and Jonathan Martin, “A High Throughput System for Accelerated Weathering and Automated Characterization of Polymeric Materials,” Polymer Preprints, March 2007.

Joannie Chin, Donald Hunston, and Aaron Forster, “Thermo-viscoelastic analysis of ambient cure epoxy resins used in construction applications,” NISTIR 7429, June 2007.

Joannie Chin, “Durability of Composites Exposed to UV Radiation” in Durability of Composites for Civil Structural Applications,” Vistap Karbhari, editor (Woodhead Publishing Ltd., 2007).