Quantifying microstickies via a new agglomeration technique

Despite the recognized importance of microstickies to the various deposition problems experienced in pulping, papermaking, and printing operations, there is still no consensus on a proper method to quantify them. One proposed method is to agglomerate microstickies in a pulp sample by long cold storage or by exposure to reduced pressure conditions followed by a classification step to isolate them from the pulp as macrostickies. In this paper, we tested this approach, but using a more effective agglomeration method to convert microstickies into macrostickies. We found that microstickies in mill samples could be agglomerated into macrostickies by boiling whole pulp suspension. The best agglomeration conditions occurred on 1% consistency pulp stirred at 250 rpm during heating, at a heating time of 45 min, with subsequent maintenance of boiling for 60 min followed by a cooling period of 3 h at room temperature. Polyacrylate type microstickies appeared to respond best to the boiling agglomeration method. To see how effective the boiling method was in agglomerating microstickies into macrostickies, a model pulp with a known quantity of model stickies was made. Using this model stickies suspension, the boiling method was proven to be very efficient for agglomerating microstickies into macrostickies by converting up to 70% of the microstickies into macrostickies. Photomicrographs clearly demonstrated that the macrostickies collected after boiling treatment were mainly formed by microstickies agglomeration.