RECYCLING Nordic Pulp & Paper Research Journal Vol 30 no (1) 2015 189 Indicator paper for detecting microstickies in recycle mill process water Ved Naithani, Lucian A. Lucia, and Sujit Banerjee KEYWORDS: Chromatography, Dyes, Microstickies, Polyacrylates, Stickies SUMMARY: An indicator paper based on a mailing label treated with a mixture of two dyes changed color in the presence of microstickies in water. The indicator paper consisted of a polyacrylate-coated mailing label that was dipped in a mixture of Safranin O and Astrazon Green dyes and dried. The treated label was then dipped in process water and re-dried. The color on the adhesive side of the label changed in the presence of microstickies. Optical (RGB, red, green, blue) analysis confirmed the stickies-induced color changes. During re-drying, the microstickies chromatographically separated the two dyes to a small extent across the thickness direction of the label leading to the color change. The theoretical detection limit for microstickies is 150 ppm, while the practical limit is about 400 ppm. ADDRESSES OF THE AUTHORS: Ved Naithani (vpnaithani@hotmail.com), Lucian A. Lucia (lalucia@ncsu.edu): Qilu University of Technology, Key Laboratory of Pulp & Paper Science and Technology, Jinan 250353 P.R. China; North Carolina State University, Department of Wood & Paper Science, Raleigh, NC 27695, USA Sujit Banerjee (vpnaitha@gmail.com) Georgia Institute of Technology, School of Chemical & Biomolecular Engineering, Atlanta, GA 30332, USA Corresponding authors: Lucian A. Lucia, Sujit Banerjee Stickies are adhesive polymeric materials that enter recycle mills with recovered paper. These materials are typically hot melts, binders, and pressure sensitive adhesives (PSAs) and combinations thereof. They can deposit on the surfaces of machines and dryer cans, press felts, forming fabrics and other equipment in a recycle mill and compromise the performance, and hence, the economics of the process. PSAs originate from envelopes and from various types of labels, and are the main culprits for most stickies-related operational problems. The nature and distribution of stickies are similar across various mills as shown in a survey of twenty-five facilities (Douek et al 2003). Stickies are classified as microstickies if they can pass through a 0.15 mm screen; larger particles are referred to as macrostickies. Methods for determining macrostickies are usually based on physical separation (screening), staining, and imaging (Ingede 2013). The detection and control of microstickies has long been an industry priority and several test methods have been described (Dykstra et al. 1998; Oullette 1995; Cathie et al 1991; Sithole et al. 1997; Ben et al. 2014; de Jong 2005). In general, these procedures are based on (a) deposition where a hydrophobic sorbent collects the hydrophobic stickies, (b) direct determination of stickies or their surrogates, and (c) agglomeration of micro- to macrostickies with subsequent detection. All these methods have limitations, and a standard technique has not yet been recognized (Ingede 2011). The sorbent in the first case can be a paper machine wire (Doshi et al. 2003) or other hydrophobic surface. However, stickies are not the only hydrophobic materials that can deposit and there is no certainty that all the stickies would be captured. Direct determination is difficult because no one solvent extracts all the stickies potentially present. Surrogates for stickies such as fractionated total organic carbon (TOC) developed by Koskinen et al. (2003) correlate with runnability (Haynes 2011), but the TOC can include materials that are not stickies. However, this method is useful because stickies are likely to predominate in process waters that have stickies issues, which is why the method correlates with filtrate tack. The method has been applied extensively by Haynes (2007; 2011) to profile the water systems of several mills. Most of these analyses are conducted offline and turnaround is slow. Some procedures require a processing period of up to three weeks (de Jong 2005). The quartz crystal microbalance (QCM) procedure (Goto et al. 2007), the fractionated TOC method (Koskinen et al. 2003), and a flow cytometry procedure (Wang et al. 2012) can be used online. We now describe a simple and robust indicator paper (analogous to litmus paper for pH determination) for rapid onsite detection of stickies. The procedure is only semi-quantitative; its purpose is to swiftly identify a “high stickies” situation so that corrective action can be taken rapidly. Materials and Methods Whitewater was obtained from a mill that processed old corrugated containers (OCC). Carbotac 26171, a commercial polyacrylate emulsion, was obtained from B.F. Goodrich. The defoamer, Bubreak 4444, was received from Buckman. Polyvinyl acetate (PVAc) was obtained from MP Biomedicals. It was dissolved in methanol and an aliquot added to water with vigorous stirring such that the methanol content in water was less than 5%. The principal base indicator paper was an Avery 5160 mailing label coated on one side with a polyacrylate adhesive. The thickness of the label was 0.1 mm. Avery 5436 and Dennison 43-551 S1648 labels surfaced with styrene/isoprene were also used in one set of measure- ments. Safranin O (SO) and Astrazon Green (AG) dyes were purchased from Marker Gene Technologies, Eugene, OR. They were prepared as mixtures at 0.05% each in the final solution. This concentration is typical for these dyes; small changes in concentration did not affect the trends. The labels were dipped in the dye mixture for about two minutes and then either air-dried or dried at 60°C. The treated labels were dipped in water containing microstickies for about two minutes and then dried as Brought to you by | Uppsala University Library Authenticated Download Date | 9/18/19 12:27 PM