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 (H 2 O 2 ); NaOH, calcium hydroxide, and H 2 O 2 ; NaOH, magnesium sulfate, and H 2 O 2 ; sodium bisulfate and H 2 C 2 O 4 · 2H 2 ; sodium silicate and H 2 O 2 ; and potassium permanganate, sodium bisulfate, and H 2 O 2 ] 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