Dispersion of 24-mm staple fibers with foam

Abstract

In addition to carding and airlaid processes, nonwovens are produced from staple fibers by a wet-laid process. A drawback of this process is the necessity to use very dilute fiber suspensions to avoid fiber entanglement and consequent poor fiber web uniformity. As a result, flow volumes are very high and process speeds are rather low compared to water forming used in the paper and board industry. A promising option for making nonwovens is foam laying. The bubbles in foam keep the fibers apart until the foam is removed, and much higher fiber weight consistencies can be used compared to traditional wet laying. A key challenge in foam forming of nonwovens is to obtain uniform dispersion of the fibers in the foam. In this work, we studied this with 24-mm staple fibers, and analyzed the homogeneity of the obtained foams by making fibrous sheets from them in a laboratory sheet mold. We found that dispersion was highly dependent on the mixing conditions, such as mixing time, foam air content, and fiber weight consistency. Remarkably, excellent fiber disintegration and uniform sheets were obtained without mechanical pre-treatment of staple fibers, with fiber consistencies as high as 0.3%. By comparison, conventional wet-laid processes typically operate with fiber consistencies lower than 0.05%. Thus, at an industrial scale, foam forming promises production of uniform webs from stable fibers with clearly lower water volumes and possibly also higher machine speeds compared to conventional wet-laid forming.

Foam forming of fiber products: a review

“…where l is suspension viscosity. Figure 7a shows as an example the viscosity of an SDS foam as a function of shear rate with air content of 70% together with corresponding fit by Equation (10). We see in Figure 7a that the inclusion of hardwood fibers or microfibrillated cellulose (MFC) does not change the power law index of the foam.…”

“…It was concluded that textile-like nonwovens could also be made with foam forming when mechanical bonding, like hydroentanglement, was used. Asikainen et al [10] studied the mixing of 24-mm staple fibers with foam, and made fibrous sheets from the fiberladen foam in a laboratory sheet mold. They found that the quality of final fiber sheets was very sensitive to mixing time, foam air content, and fiber weight consistency.…”

“…Foam forming is a process that enables the making of a variety of fiber products, [1] ranging from paper [2][3][4][5][6] and lightweight packaging [7] to nonwoven fabrics [8][9][10] and insulation, [11][12][13][14][15] filtering [13,16,17] and construction materials. In this method, the advantages of traditional water-forming technology are combined with the improved ability of handling very different kinds of raw materials such as long fibers [10,18] or particles with varied densities. Moreover, the foam process is generally efficient in terms of raw material, energy, and water use.…”

Process simulation-based evaluation of design and operational implications of water-laid paper machine conversion to foam technology

“…At the pilot scale, all the published studies have thus far been performed at the VTT Technical Research Centre of Finland Ltd. (VTT). Many aspects of foam forming have already been studied, including 1) the generation of foam and resulting foam properties, such as air content, bubble size, and half-life time (Al-Qararah et al 2013, 2015b; 2) the nature and behavior of the foaming agent (Lappalainen et al 2014;Gottberg et al 2019); 3) methods for evaluating the bubble size distribution (Lappalainen and Lehmonen 2012;Koponen et al 2019); 4) the macroscopic properties of foam-formed products (Lehmonen et al 2013;Vähä-Nissi et al 2018); 5) the pore structures of fiber networks of foam-formed fiber suspensions (Al-Qararah et al 2015aKoponen et al 2017); 6) foam forming of long fibers (Koponen et al 2016;Asikainen et al 2020); and 7) the operational performances of individual process steps, such as foam generation (Koponen et al 2018), forming (Koponen et al 2016(Koponen et al , 2018Lehmonen et al 2020), pressing (Torvinen et al 2015;Järvinen et al 2018;Lehmonen et al 2020), and drying (Timofeev et al 2016).…”