Impact of impregnation and bleaching on the surface hardness of oak (Quercus petraea L.) wood

The impact of impregnation and bleaching on the hardness of varnish layers on oak (Quercus petraea L.) wood was investigated. A number of solutions [sodium hydroxide (NaOH) and hydrogen peroxide (H2O2); NaOH, calcium hydroxide, and H2O2; NaOH, magnesium sulfate, and H2O2; sodium bisulfate and H2C2O4 · 2H2; sodium silicate and H2O2; and potassium permanganate, sodium bisulfate, and H2O2] were applied at a concentration of 18% to bleach both impregnated [Tanalith‐CBC (T‐CBC) or Imersol‐WR 2000 (I‐WR 2000)] and unimpregnated (natural) wood panels. Subsequently, a water‐based varnish (WB) was coated over the samples, and the hardness of the varnished layers was determined in accordance with ASTM D 4366. Among the samples that were varnish‐coated without bleaching, T‐CBC/WB yielded the highest hardness (59.50), whereas I‐WR 2000/WB exhibited the lowest (49.17). However, among the samples varnish‐coated after bleaching, the highest (56.50) and lowest (40.83) varnish hardness values were obtained with T‐CBC/solution 2/WB and I‐WR 2000/solution 4/WB, respectively. All the chemicals used for the bleaching process reduced the surface hardness. However, after the varnish coating, except for solutions 4 and 6, all the solutions showed hardness values similar to those of varnish‐coated natural (control) samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 498–504, 2004