Grantee Research Project Results

Final Report: Cool Roof Coatings Incorporating Glass Hollow Microspheres for Improved Solar Reflectance

EPA Grant Number: SU834300
Title: Cool Roof Coatings Incorporating Glass Hollow Microspheres for Improved Solar Reflectance
Investigators: Barsoum, Michel , Biamah, Michael , Jerbarsi, Anthony , Kocher, William , Kownurko, Devin , Krall, Ryan , Mox, Daniel , Wilson, Mathew , Zoules, Dimitri
Institution: Drexel University
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2009 through August 14, 2011
Project Amount: $61,829
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2009) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities

Objective:

Elastomeric cool-roof coatings can be applied to buildings to decrease heat gain, yielding energy savings and mitigating the “urban heat island” effect. Most cool-roof formulations are based on titanium dioxide (TiO₂). While TiO₂, and several TiO₂ replacements, perform according to ASTM reflectance standards, the infrared (IR) absorption properties of these materials is rarely discussed. Carefully designed TiO₂ replacements have the potential to effectively scatter visible and infrared wavelengths, increasing the overall reflectance of a coating beyond the upper limits defined by ASTM standards. This project has demonstrated that the introduction of voids, through the inclusion of glass hollow microspheres at high volume loadings can effectively scatter selected wavelengths.

The second phase of this project involves a further investigation into the efficacy of coatings formulated using glass hollow microspheres. This will include field-testing, ASTM standard testing for reflectivity, tensile strength, weathering, and other properties, and additional formulation work. The research team also plans to implement the coating in various areas in the City of Philadelphia to study cool roof impacts on the urban heat island.

Test and implement an elastomeric cool roof coating developed for improved reflectance in the near infrared region. Increase community awareness on energy saving potential and environmental impacts of cool roof coatings. Further study how the infrared radiative properties of titanium dioxide replacements can increase the efficacy of roofing materials.

Summary/Accomplishments (Outputs/Outcomes):

 Two groups, or teams of freshman, worked on the project in the latter stages, and their objectives were to develop two formulation mixtures for cool roof coatings that would simultaneously pass both tensile and reflectance ASTM standards. One team focused on using diatomaceous earth (DE) to increase the tensile strength, while the other team focused on incorporating glass hollow microspheres into cool roof coatings to increase the reflectance. A Perkin Elmer Lambda 950 was used in conducting the reflectance tests on a range from 2502500 nm, while the tensile tests were carried out on a uniaxial tensile tester in accordance with ASTM standards. 

A.    Diatomaceous Earth Team

 Initially, different formulations and mixtures were made using different types of DE. The types of diatomaceous earth that were used were Celite 266, Celite 400D and Permaguard. Celite 266 was great for elongation, but did not meet the ASTM D6083 1.4 MPa tensile strength standard. Similarly, permaguard showed good tensile strength, however it failed to meet the ASTM D6083 200% elongation standard. Celite 400D yielded the best results for tensile tests, and the results indicate that it passed the ASTM elongation standards. Thus, additional formulations using different ratio percentages of Celite 400D were made. 

The Celite 400D with the highest tensile strength ranged from 1.6 to greater than 2 MPa, which exceeds the ASTM D6083 standard for tensile strength of 1.4 MPa. The elongation of this same sample met the ASTM standards, making this particular sample a potential alternative to TiO₂ in cool roof coatings for tensile strength. Celite 400D was not only the best sample in tensile strength tests, but also the most reflective of the samples involving diatomaceous earth. While the team has evaluated many grades and sources of diatomaceous earth, a grade that results in higher reflectance than TiO₂ based controls has yet to be found.

B.     Microspheres Team

 Formulations were prepared at several volume fractions and four different types of glass hollow microspheres, which were blended in acrylic elastomeric roof coatings. By incorporating glass hollow microspheres, sufficient reflectance was achieved for use as a cool roof coating, with some samples exhibiting higher reflectivity than TiO₂ based controls. The highest reflectance sample contained approximately 30% of glass hollow microspheres by volume. Although embedding glass hollow microspheres in the samples improved reflectance, the tensile strength of these samples did not meet the 200% elongation or 1.4 MPa tensile strength required by ASTM D6083. The glass hollow microspheres may be an alternative to using TiO₂ for reflectance; however, the material’s use may be limited to roof coating and membrane systems which are applied to a reinforced substrate.

Conclusions:

Replacing TiO₂ in cool roof coatings with diatomaceous earth could result in a 10% cost reduction in raw materials. However, incorporating glass hollow microspheres in a roof coating compromises the tensile strength while enhancing the reflectivity, depending on the volume and diameter of the microspheres. Both studies show that TiO₂ could be replaced by either diatomaceous earth or glass hollow microspheres to yield better tensile strength or reflectivity. Further studies and experiments are needed to investigate the possibility of combining the results from both groups, and producing a sample that would meet the ASTM standards for tensile strengths and reflectance, while being a good replacement for TiO₂ in cool roof coatings. 

Supplemental Keywords:

Building envelope, insulation, UHI

Progress and Final Reports:

Original Abstract

2010 Progress Report

P3 Phase I:

Cool Roof Coatings Incorporating Glass Hollow Microspheres  | Final Report