Special Issue: 9 th INTERNATIONAL PAPER AND COATING CHEMISTRY SYMPOSIUM / INTERNATIONAL PAPER PHYSICS CONFERENCE Nordic Pulp & Paper Research Journal Vol 31 no (2) 2016 239 Foam forming of long fibers Antti Koponen, Katariina Torvinen, Ari Jäsberg and Harri Kiiskinen KEYWORDS: Crowding number, Flocculation, Foam forming, Formation, Long fibers SUMMARY: The paper industry is continuously seeking possible solutions for new fiber based products to widen their product portfolio and to develop more valuable products. For the current products the technologies enabling the reduction of the raw material consumption and improvement of the energy and water efficiency are under great interest. This is a challenging goal since the quality of the end product should simultaneously remain intact. In a water-laid process the challenge to improve formation increases with increasing fiber length. To date the only solution has been to decrease the forming consistency. However, when using foam as a carrier fluid flocculation of fibers is decreased and fiber length can be increased. Foam forming studies have been performed with long fibers in realistic process conditions at VTT’s pilot environment. Our scope is on long-fiber suspensions that can still be run on existing paper machine geometries. The average fiber length and foam density were the main variables in these trials. The formation of papers made of short fibers was always very good. For longer fibers formation improved with decreasing foam density and was much better than that of water-laid samples. Long fibers were found to increase the bulk and the tensile index, but to decrease the z-strength. ADDRESSES OF THE AURHORS: VTT Technical Research Centre of Finland Ltd. P.O.Box 1603, FIN- 40101 Jyväskylä, FINLAND. Corresponding author: Antti Koponen (antti.koponen@vtt.fi) There is a growing urgency to develop novel bio-based products and technologies as a solution to reduce our reliance on non-sustainable fossil fuels. Lignocellulosic fibers represent the most suitable alternative to address this challenge. In addition to being renewable, many inherent lignocellulosic fiber properties (e.g. strength, stiffness, structuring capability) surpass those of products based on petroleum-based polymers. The existing paper and board raw materials and processes, however, have been fundamentally the same for 150 years and the changes that are required by industry to respond to related needs have fallen short to revolutionize practices in bio based fibers usage. Throughout the history of papermaking, using water as the carrier fluid has completely dominated the industry. During early 70’s a few unprejudiced engineers tried to shake this paradigm by studying the possibility of replacing water with foam in paper making (Radvan, Gatward 1972; Smith et al. 1974; Smith, Punton 1975). As a result, the Radfoam process was developed (Tringham 1974). In principle this was an attractive idea: foam forming gives the web an outstanding uniformity, and it is also possible to use higher headbox consistency (Punton 1975b). Moreover, foam forming can be used to obtain more bulky structures with a given raw material base (Punton 1975a). However, despite of its potential advantages, foam forming was not adopted in the paper industry at that time. After a long silent period, the prospects of using wet foams as carrier phase to replace water has captured increased interest (Hellén et al. 2013). In addition to improving the efficiency of existing processes and to allow better uniformity in material, a wide variety of raw materials of different size and type can be adopted (Poranen et al. 2013; Torvinen et al. 2015). Moreover, foam structure and rheology can be varied to tune the density (Madani et al. 2014; Jahangiri et al. 2014; Alimadadi, Uesaka 2015) and microporous structure (Al- Qararah et al. 2015) of the foam formed product. The properties of nonwoven materials range from textile like to paper-like (Russell 2007). These materials are composed of longer textile fibers, but especially wet- laid nonwovens have structure similar to that of paper with random fiber orientation. In specialty papers long man-made fibers can be combined with a pulp fiber sheet to give textile-like properties to it. Inclusion of long fibers can improve e.g. such paper properties as tear strength, bulk, and moldability. The process speed of these products would preferably be comparable with traditional paper machines. However, such suspensions are prone to strong flocculation due to the exceptionally wide fiber length distribution and the high length to width ratio of the long fibers (Hubbe 2007). Thus making of such nonwovens with water forming is typically possible only in very diluted conditions which decreases the energy and water efficiency of the process considerably (Keith 1994; Das et al. 2012). On the other hand traditional nonwoven technologies such as carding or spun-laying are also impractical here. However, foam forming is a promising process candidate here as reasonably high fiber consistencies can be used without making big compromises in formation. In this paper we will present some results on foam forming studies with long fibers that have been performed in realistic process conditions at VTT’s pilot environment (Poranen et al. 2013; Torvinen et al. 2015). Our scope is with such long-fiber suspensions that can be still run on existing paper machine geometries. We present first the materials and measurement methods used in this study. Then we discuss briefly the effect of crowding number (Kerekes, Schell 1992) on flocculation and formation. Next we present and discuss our results on the dependence of formation, bulk and strength properties of paper on some process parameters. Finally, we present our conclusions. Materials and methods Furnishes Bleached unrefined hardwood kraft (BHK) with SR level (Schopper-Riegler freeness) of 18, bleached unrefined softwood kraft (BSK), with SR level of 13, and 6 mm TENCEL® fibers by Lenzing AG were used in various mixtures in the trials. TENCEL® is a lyocell fiber and it is of botanic origin - its raw material is extracted from Brought to you by | Lancaster University Authenticated Download Date | 4/12/19 4:59 AM