Effects of chromated-phosphate treatment process on the green color protection of ma bamboo (Dendrocalamus latiflorus)

Ma bamboo (Dendrocalamus latiflorus Munro) treated with chromated phosphate (CP) exhibits an excellent green color. To understand the effects of the treatment sequence of CrO3 and H3PO4 and their interactions regarding green color protection, CrO3-H3PO4 and H3PO4-CrO3 two-step treatments plus a H3PO4-CrO3-H3PO4 three-step treatment were carried out in this study. Results revealed that the treatment sequence of CrO3 and H3PO4 definitely affects the effectiveness of bamboo color protection. Green color protection of ma bamboo culm could not be achieved by treating it with CrO3 or H3PO4 alone or with the H3PO4-CrO3 two-step treatment. Only by treating it with the CrO3-H3PO4 two-step treatment or the H3PO4-CrO3-H3PO4 three-step treatment did ma bamboo exhibit an excellent green color. The results indicated that bamboo reacts first with CrO3 and then forms an insoluble complex with H3PO4, which produces the green color on its epidermis. Chlorophyll analyses demonstrated that chlorophyll is not a key factor for green color protection. The green pigment was also formed when chlorophyll-free bamboo was treated with 2% CP at 60degreesC for 3 h.