A Biobased, Zero-VOC Coalescent for Architectural and Industrial Coatings
By Zuzanna Donnelly, Arkema
In the coatings industry, the concept of sustainably is becoming increasingly important, whether to meet regulatory requirements or growing customer and consumer expectations.1,2 Sustainability is also a significant driver for coatings innovations.3,4,5
The United Nations has adopted a list of 17 “Sustainable Development Goals”6 that seek to define a blueprint for sustainability on a global scale. Many of these relate to sustainability in coatings, such as reducing volatile organic compounds (VOCs) and greenhouse gases and replacing fossil fuel-based products with biosourced materials.7,5
With these UN Sustainable Development Goals in mind, a new coalescent technology for waterborne paints that meets the zero-VOC requirement as measured by ASTM D6886 and has a high biobased carbon content of 96% as measured by ASTM D6866 has been developed.
This goal of the study described in this article is to evaluate the performance of this product in several representative architectural and industrial waterborne paint formulations and benchmark performance against other VOC and zero-VOC coalescents available on the market.
Performance of this new coalescent was evaluated in a range of waterborne binder chemistries, including all acrylic, vinyl acrylic, styrene acrylic hybrid, and self-crosslinking acrylic systems in several architectural and industrial maintenance paint formulations.
This new coalescent technology was found to compare favorably with commercial zero-VOC coalescents in architectural coatings formulations. In industrial coatings formulations, substitution of VOC solvents, in whole or in part, with this new technology allows for significant lowering of overall formulation VOC while maintaining good coating performance. Improved metal adhesion and impact properties were observed with retention of high gloss and good corrosion resistance.
Viscosity and Heat Age Stability: The initial Stormer viscosity—measured with a Krebs Stormer viscometer according to ASTM D562 and reported as Krebs Unit (KU)—was measured at room temperature prior to placing the paint can into a 120 °F oven. The can was removed after 2 weeks and allowed to return to room temperature. The Stormer viscosity in KU was measured again.
Gloss measurements and yellowness index: Gloss and yellowness of paint films were measured using micro-TRI-gloss and color-guide 6805 (both meters from BYK-Gardner), respectively.
Minimum Temperature Film Forming (MFFT) testing: MFFT testing was carried out on a Rhopoint instrument equipped with a variable temperature MFFT bar. A temperature range of -4.5 °C to 13 °C was used. Latex films were drawn down at 75 microns thickness and allowed to dry under flowing N2 gas for 30 minutes. MFFT temperature readings were taken at the point where the latex film transitioned from clear cohesive film to white powder.
Tint strength: Five grams of Colortrend Phthalo Blue was weighed into a half-pint can containing 250 grams of test paint. After the colorant was added, the paint can was shaken on a Red Devil shaker for 3 to 5 minutes. Paint drawdowns using the tinted paint compositions were then prepared on Leneta B charts using a 3 mil bird bar. These were allowed to dry for 1 day in a controlled temperature and humidity chamber at 25 °C and 50% relative humidity. The Y% brightness value was measured on a colorimeter and the percent tint strength was calculated by the Kubelka-Munk (KM) formula.
Washability and Stain Removal: Paints were applied at a wet film thickness of 7 mils to black Leneta Scrub Charts and allowed to dry for a minimum of 3 days. CIELAB color values were measured prior to application of stains. Stains were allowed to set for 2 hours and excess stain was removed by rinsing under cold water. Samples were placed into a Garner Straight Line Washability and Wear Abrasion Machine and scrubbed for 50 cycles with the addition of 10 mL of Formula 409 solution to the premoistened sponges. Samples were rinsed with water and dried. CIELAB color values were measured on areas where the samples were scrubbed and delta E values are reported.
Mudcracking: Paint drawdowns were made using a Sag bar on 1B Leneta charts and allowed to dry for 24 hours. The greatest thickness that did not show cracking is reported.
Dry Adhesion: The test paints were applied to untreated aluminum, cold rolled steel and galvanized steel using a 4 mil Bird applicator. The paints were allowed to dry for 7 days before the lattice pattern described in ASTM D3359B was cut and the pressure sensitive tape applied. The removal of the coating from the substrate was rated using the classification charts described in the ASTM Standard.
Flash Rust: The cold rolled steel panel from the adhesion test was examined after drying overnight. The panels were rated on a scale where 10 = no rust and 0 = heavy rust.
Other standard test methods used: Scrub Resistance ASTM D2486-06, Test Method B; Wet Adhesion to alkyd paints ASTM D6900; Block Resistance ASTM D4946; Chemical Resistance, ASTM D1308, 1 Hour Contact; Impact Resistance, ASTM D2794, 1 Week, R612 CRS Panels; Humidity Resistance, ASTM D2247, R46 Panels; ASTM B117-09 Standard Practice for Operating Salt Spray (Fog) Apparatus – R46 Panels; Prohesion, ASTM G85 Annex, R46 Panels.
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