Weathering performance of mulberry wood with UV varnish applied and its mechanical properties

Mulberry wood is used in carpentry, fences, turnery, and garden architecture. In this study, various mechanical properties (modulus of rupture, modulus of elasticity, Janka hardness, and screw holding resistance) of mulberry (Morus alba) wood and its weathering performance after applying 3- and 5-layer UV system parquet varnishes with different surface applications were investigated. The varnished materials were aged using UV lamps for 252 h and 504 h, and the aged specimens were compared with non-aged specimens. The results of the variance analyses found that all tests were significant. According to the results, it was found that while the yellow color (b*) tone value, lightness, and glossiness (perpendicular (⊥) and parallel (║) direction at 20°, 60°, and 85° angles) values decreased for both varnish applications, the pendulum hardness value increased. The adhesion strength (pull-off) test (MPa) to the surface first decreased and then increased.

Effects of artificial weathering on the color, gloss, adhesion, and pendulum hardness of UV system parquet varnish applied to doussie (Afzelia africana) wood

An important wood species in the furniture and parquet industry today is “doussie” wood. In this study, the effects of artificial weathering on ultraviolet-cured varnish (3 coats and 5 coats) applied to doussie (Afzelia africana) wood were investigated. The samples of the UV system cured varnishes were exposed to aging effects for 252 h and 504 h via an UV-A 340 nm lamp. The coated specimens were exposed to UV-A 340 nm fluorescent lamp in a QUV accelerated weathering tester for 252 h and 504 h. The surface adhesion strength, color (L*, a*, b*, ∆E*, ∆L*, ∆a*, and ∆b*) parameters, pendulum hardness, and glossiness (parallel (//) and perpendicular (⊥) at 20°, 60°, and 85°) of UV varnishes coated samples were quantified before and after weathering. According to the results, while the a* value increased, the adhesion, L*, b*, and glossiness values decreased with aging. As a result, it was concluded that doussie wood can be used in the production of flooring with UV-cured varnish.

Pendulum hardness of polyurethane coatings during curing

Purpose – This paper aims to disclose the evolution of pendulum hardness of two-component acrylic polyurethane coatings during the cure process and attempts to describe the quantitative relationship between pendulum hardness and curing time. These findings are helpful for the study of fast curing acrylic polyurethane coatings. Design/methodology/approach – The pendulum hardness method was used to monitor the hardness of two-component acrylic polyurethane coatings during curing. The quantitative relationship between pendulum hardness and curing time can be obtained with Avrami equation. Findings – The evolution of coating pendulum hardness can be divided into three stages. By using the Avrami equation that explained the influence of both the acid value and the curing temperature on the drying speed of hydroxyl acrylic resin, the evolution of coating pendulum hardness during curing can also be accurately described. Research limitations/implications – It should be noted that the physical meaning of the Avrami exponent, n, is not yet clear. Practical implications – The results are of great significance for the development of fast-curing hydroxyl-functional acrylic resins, with the potential to improve the drying speed of the coatings used in automotive refinish. Originality/value – It is novel to divide the pendulum hardness into three stages, and, for the first time, the Avrami equation is utilized to describe the evolution of coating pendulum hardness during curing.