Green colour protection of makino bamboo (Phyllostachys makinoi) treated with ammoniacal copper quaternary and copper azole preservatives

The objectives of this study were to search for appropriate low-toxicity preservatives to be used as green colour protectors for makino bamboo (Phyllostachys makinoi) culms, and to find appropriate conditions and process, especially an alkali-pretreatment-free and a solvent-free process, for treating makino bamboo to achieve green colour protection. The influence of various green colour protection reagents and treatment conditions on the colour of bamboo culms was examined using a colour difference meter. Two water-borne copper-based preservatives, namely ammoniacal copper quaternary compound-type B (ACQ-B) and copper azole (CuAz), were tested as protectors. In addition to heating in a water bath, the ultrasonic heating method was also employed. Results revealed that, without alkali-pretreatment, an excellent green colour protection (a* = −11.0) was obtained when the makino bamboo culms were treated with 2% aqueous ACQ-B solution in a 60 °C water bath for 1 h, and that CuAz has no effect on green colour protection (a* = 3.9) under the same conditions. Compared with conventional heating in a water bath, improvement on the green colour protection can be achieved with a shorter treatment time by using ultrasonic heating. The a* value of bamboo culms after the treatment with 2% ACQ-B at a 60 °C ultrasonic bath for 15 min was −10.0.