Enzymatic deinking: Effectiveness and mechanisms

Enzymatic deinking represents a new approach for processing waste paper into quality products. The objectives of the present research were to clarify the role of factors affecting effectiveness of cellulase treatment, and to identify the mechanisms underlying ink removal. A commercial cellulase preparation was used to deink a highly crosslinked soybean oil-based ink from a newsheet consisting of 17% semibleached kraft pulp (SBKP) and 83 % thermomechanical pulp,(TMP). Ink detached via enzymatic treatment, water controls and conventional chemical deinking was removed from pulp suspensions in a standard laboratory flotation cell. Effects of various process parameters were investigated in fractional factorial trials. Effectiveness was evaluated in terms of handsheet brightness, residual ink counts, and ink areas before and after flotation. Several process parameters proved significant, but the most important were disintegration time and enzyme concentration. Cellulase treatment increased brightness and reduced ink counts and areas to values significantly lower than those of wafer controls. Deinking results, however, did not match those obtained via chemical deinking. Apparently enzymatic treatment fostered removal of large ink particles by hastening and increasing the separation of fibrous materials covered by large areas of ink. Trials with unprinted paper confirmed that cellulase treatment accelerated separation of fibrous materials Scanning electron micrographs, prepared after treatment of pure SBKP and TMP papers, showed that SBKP fibers were most affected by cellulase treatment Some localized degradation was observed, but external fibrils were not removed with any great frequency. Effects of cellulase treatment on TMP fibers were lesser, and restricted primarily to occasional shortening and/or removal of fibrils. Similar effects were noted in photomicrographs of fibers from newsheet Based on these findings, the primary role of cellulases in deinking appears to involve separation of ink-fiber agglomerates, and simple dislodging or breaking of ink particles as fibrous materials separate in response to mechanical action during disintegration. Understanding the role of cellulases in deinking, nonetheless, requires clear appreciation of their effects on the different types of fibers present in waste paper. Although not investigated during the present research, fines of both pulp types are also involved by virtue of their significant presence in ink-fiber agglomerates. Given their high specific surface area, fines are subject to preferential attack by cellulases. The role of fines in enzymatically enhanced separation of ink-fiber agglomerates is the subject of future research.