Combined bio-carbonization and dyeing of wool:: A possibility of using cell wall-degrading enzymes and 1:1 metal-complex dyes

This study was undertaken to investigate the possibility of a new process to remove plant residues from wool, using enzymes as biocatalysts together with a dyeing process in a two-step exhaustion process, performed in a single bath. The enzymes were selected in order to hydrolyze the polysaccharides in primary plant cell walls and middle lamella, resulting in more fragile residues easier to be removed. Commercial enzymatic preparations of Trichoderma reesei and Aspergillus aculeatus were used, after appropriate optimization. A total enzyme loading of 1.0 mL/L of each enzymatic preparation yielded an equivalent amount of 241.2 mg of glucose per gram of plant residue, under the optimal conditions: 40.5 degrees C, pH 4.0, and 0.75 mL/L of a non-ionic wetting agent. Reducing groups of the total released sugars were determined with the Miller reactive 3,5-dinitrosalicilic acid (DNS), which has been used for the indirect measurement of the efficiency of the process. Furthermore, to enhance the degradation of the plant residues, dyeing processes using the incubation bath and several acid and metal-complex dyes, usually applied on wool dyeing, were tested. The dyeing procedure with 1:1 metal-complex dyes adjusted to pH 1.9 with sulfuric acid has promoted a higher degradation of the plant residues without damaging wool fibers. Accordingly, higher concentration of glucose was detected by the DNS reagent and higher weight losses of the plant residues were obtained when compared to enzymatic treatment without dyeing. The low pH used in the dyeing procedure increases the degradation of the cell wall polysaccharides, by acid catalysis. Also, scanning electron microscopy was used to show the plant cell wall degradation.