The Effect of Microfibrillated Cellulose on Mechanical Properties and Performance of Acrylic Elastomeric Roof Coatings

摘要

Of late, there has been increased interest in waterborne acrylic elastomeric roof coatings, because they reduce the heat absorption of buildings compared to traditional asphalt roofs. In addition to heat prevention and energy savings, acrylic roof coating protects the underlying material from water, ultraviolet (UV) radiation, chemicals, and wear. Waterborne acrylic roof coatings are traditionally thickened with cellulosics such as hydroxyethyl cellulose (HEC) and associative thickeners such as hydrophobically modified ethoxylated urethanes (HEUR) and hydrophobically modified alkali swellable emulsions (HASE). The use of these thickeners often leads to challenges with both water resistance and water absorption of the coating. Additionally, the control of syneresis and sagging is often challenging. Microfibrillated cellulose (MFC), a biobased and multifunctional product made of cellulose is a new alternative to traditional thickeners. MFC consists of fibrils with lateral dimensions in the nanoscale and lengths up to micron scale. These strong and rather stiff fibrils form strong films (tensile strength up to 210 MPa). Once MFC is added to a paint, it is usual to see a noticeable effect on the mechanical properties of the final coating. In addition to the effect on mechanical properties, its unique rheological properties allow for increased stability as well as an easy to apply paint. The high yield stress of MFC prevents settling of heavy particles as well as floating of hollow microspheres, whereas the strong shear thinning allows the spraying of thick formulations. This exceptionally thixotropic behavior leads to excellent sag resistance combined with good leveling. The aim of this work was to evaluate the effect of MFC on the key properties of acrylic elastomeric roof coatings, such as tensile strength, water resistance, mudcracking, and adhesion to metal and concrete surfaces. Commonly used thickeners (HEC and HEUR) were used as references. Different fibrillation degrees and dosage levels of MFC were used to clarify the impact of MFC on tensile strength and elongation as well as the relationship between these two parameters. We will demonstrate how MFC increases the tensile strength of elastomeric acrylic roof coating without sacrificing the elongation and performance of the coating.