A cantilever deflection technique was used to monitor stress in sim during drying of cellulose acetate coatings. Porosity was introduced in some coatings using dry-cast phase separation. Stress and weight loss profiles for dense coatings, a coating that contained small (∼1 μm) pores, and a coating that contained small (∼1 μm) pores and macrovoids (∼200 μm) are compared. In-plane tensile stress after drying ranged from 30 MPa (dense coatings) to 5 MPa (macrovoid-containing coating). The stress profiles for dense coatings feature a period of rapidly and then slowly increasing stress due to constrained shrinkage. For a coating that formed small pores, drying and stress development are delayed, stress rises and then drops a small amount due to capillary pressure relief. The stress profiles for the small pore and macrovoid-containing coatings are similar, except for a stress plateau at early stages of drying, which may be caused by macrovoid growth.
Bibliographical noteFunding Information:
The authors acknowledge the University of Minnesota Graduate School, through its Doctoral Dissertation Fellowship, and the Industrial Partnership for Research in Interfacial and Materials Engineering along with its industrial supporters, through the Coating Process Fundamentals Program, for financial support of this research. The authors also acknowledge K. Zhang for his expertise and help with SEM imaging and T. Baraniak and W. Suszynski for their technical assistance. Finally, helpful discussions with C. Miller are gratefully acknowledged.
Copyright 2018 Elsevier B.V., All rights reserved.
- Coating stress
- Dry-phase separation