Foam forming of long fibers

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.