Grantee Research Project Results
Final Report: Waterborne NIPU Epoxy Hybrid Coating
EPA Grant Number: SU840158Title: Waterborne NIPU Epoxy Hybrid Coating
Investigators: Zhou, Qixin , Ling, Zichen , Huang, Kuan-Chen
Institution: University of Akron
EPA Project Officer: Page, Angela
Phase: I
Project Period: December 1, 2020 through November 30, 2021
Project Amount: $25,000
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2020) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Chemical Safety
Objective:
This project is investigating an innovative approach to generate a waterborne non-isocyanate polyurethane (NIPU) coating, which provides a solution for “Non-toxic paints and coatings” in the research area “Chemical Safety.” The green and sustainable approach to produce polyurethane coating protects the environment, benefits the health of people in surrounding communities, and creates economic benefits.
Polyurethane coatings—which are high-performance coatings widely used for automotive, aerospace, and corrosion protection applications—are produced using hazardous and toxic isocyanates as the primary building blocks. Isocyanates and isocyanate derivatives have generated serious concerns due to their environmental, health, and safety-related issues. Although research on non-isocyanate polyurethane has received extensive development in recent years, NIPU synthesis is still faced with a major problem—low reactivity. In addition, the development and research on waterborne NIPU is still in its infancy. The innovation of this project is intended to fill the gap. The project aims to combine the features of the NIPU approach and waterborne coating to develop a waterborne NIPU epoxy hybrid coating from a bio-based resource. The new approach will not involve the use or production of isocyanates; also, it will reduce voltaic organic compounds (VOCs) by using water as a solvent. The objectives of the project are to (1) prepare a waterborne NIPU epoxy hybrid coating; (2) study the structure-property relationships of the waterborne NIPU; and (3) investigate the performance of the newly developed waterborne NIPU coating.
Relationship to People, Prosperity, and the Planet
This green solution for non-toxic coatings promotes sustainability for People, Prosperity, and the Planet (P3). From a social standpoint, the green approach avoids worker exposure to an isocyanate environment, protecting workers’ health and preventing any potentially harmful effects associated with isocyanates. From an economic standpoint, the non-isocyanate process reduces expenditures related to healthcare and workers’ compensation benefits, safety precautions in manufacturing and application, and disposal or treatment fees for isocyanate-based polyurethane coatings. From a marketing standpoint, due to demands for sustainable and environmentally friendly coatings, the market share for a waterborne NIPU is expected to grow in the future year, especially as regulations for using isocyanates become stricter.
Summary/Accomplishments (Outputs/Outcomes):
The outcome of this project is a green approach to produce waterborne NIPU epoxy hybrid coating and the approach is feasible, practical, and desirable. The reaction is monitored by Fourier-transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (NMR), and 13C NMR to characterize the chemical structures of the products to determine the reaction time.
Waterborne NIPU epoxy hybrid coating synthesis
The process includes the synthesis of cyclic carbonate, synthesis of amine-terminated NIPU prepolymer, the polymer chain extension, neutralization, and dispersion in water. The first step, synthesis of bisphenol A diglycidyl ether (DGEBA) cyclic carbonate, was at 130 °C for 96 h. FTIR, 1H NMR, and 13C NMR were used to characterize the chemical structure of DGEBA. The second step, synthesis of amine-terminated NIPU prepolymer, was at 75 °C for 8 h. FTIR was used to monitor the signal strength of C=O of the cyclic carbonate group (around 1800 cm-1) during this step. Next, the epoxy resin was added into the amine-terminated NIPU prepolymer at room temperature with magnetically stirring for 1h. Then, acetic acid was added to the mixture to neutralize the product. Finally, the NIPU polymer was dispersed in water under vigorous stirring followed by solvent removal.
Waterborne NIPU epoxy hybrid coating formulation
The solid content of waterborne NIPU coatings was controlled to around 20 wt.%. The molar ratio of cyclic carbonate group/epoxy group/amine group is 1:1:2. Details of the formulation of different waterborne NIPU coatings are listed in Table 1 in Summary of Phase I Results.
Waterborne NIPU epoxy hybrid coating characterization
The DGEBA and amine-terminated NIPU was successfully synthesized confirming by FTIR, 1H NMR, and 13C NMR. After the curing process of waterborne NIPU epoxy hybrid coatings, the functional groups of the coating films were characterized by FTIR. The appearance of the C=O stretching further verified the formation of the urethane group.
Thermogravimetric analysis (TGA) was utilized to analyze the thermal stability of waterborne NIPU epoxy hybrid coating films. The mechanical properties of NIPU coatings were characterized by the tensile test. The general coating properties were studied in terms of coating film hardness (by pendulum hardness and pencil hardness), solvent resistance (ethanol), impact resistance, and adhesion (cross-hatch adhesion and pull-off adhesion). All of the evaluations demonstrate that the waterborne NIPU epoxy hybrid coatings possess excellent properties in thermal stability, mechanical property, and general properties. The tunable thermal and mechanical properties can be achieved by adjusting the fatty acid content and the ratio of soft to hard segments.
Actual accomplishments consistent with the anticipated objectives
Based on the experimental results, a conclusion can be drawn that project results meet the expected outcomes in the original proposal: (1) the green approach for waterborne NIPU is feasible; (2) the green approach for waterborne NIPU is practical; and (3) the green approach for waterborne NIPU is desirable.
Conclusions:
The waterborne NIPU epoxy hybrid coating developed in this project is a polyurethane coating with tunable thermal and mechanical properties, durability, and corrosion resistance. In addition, the reactions occur at low or room temperature and the coating is waterborne containing minimized VOCs—thus, it is a green, sustainable, and cost-effective process that can substitute for the traditional isocyanate-based polyurethane process.
The waterborne NIPU coating developed in this project supports the EPA’s priorities in developing non-toxic coatings and paints. The synthesis process, which is completely free of isocyanates, will allow EPA to be proactive in regulating isocyanates and potentially would enable EPA to ban the use of isocyanates.
Supplemental Keywords:
green chemistry, environmentally benign substitute, non-isocyanates, polyurethane coating, waterborne coating, bio-based coating, low VOCsThe 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.