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.