Changes in color and structure of birch wood (Betula pendula) caused by bleaching with hydrogen peroxide solution

Abstract

Abstract The effect of bleaching with a hydrogen peroxide (H2O2) solution on coloring of secondary xylem of kiln-dried birch wood (B. pendula) was investigated with CIELAB color measurements. Structure of unbleached and bleached wood pieces was studied by light microscopy (LM), environmental scanning electron microscopy (ESEM), and transmission electron microscopy (TEM). In addition, hardness and surface roughness of unbleached and bleached wood pieces were characterized with Brinell hardness and contact angle measurements. The results indicated that surface bleaching with H2O2 solution changed the color of birch wood toward white and less red, simultaneously increasing the porosity and roughness of the uppermost surface as well as decreasing the hardness of bleached wood pieces. With embedding bleaching for 24 h with H2O2, the color of the wood pieces could be changed further; however, microscale defects were detected in fiber secondary cell walls. Consequently, complementary to results obtained from microscopic studies, lower hardness values supported the degradation of fiber secondary cell wall in bleached wood pieces. In addition, contact angle measurements indicated increased surface roughness of wood pieces after embedding bleaching with H2O2.