Effect of fiber surface characteristics on foam properties

Besides natural fibers, synthetic fiber filaments are increasingly used in papermaking industry nowadays. As long fiber is used as raw material, it is necessary to design a process to prevent fiber flocculation. As a result, foam forming emerges as a technology that can effectively disperse fiber and subsequently improve papers’ evenness. Whether they are small nano-particles or large-size long fibers, foam forming technology has opened up an innovative application of its approach. The relationship between fiber surface characteristics and foam forming was studied in this paper. The results showed that fibers with hydrophilic surfaces could combine well with bubbles on the solid–liquid interface. The physical strength of the liquid film is enhanced and its surface viscosity is increased. As a result, such foams have a high stability. The foam half-life was 5.0 min for softwood fiber, which was slightly increased compared with a pure foam system, whose half-life was 4.5 min. However, the foam half-life was drastically decreased with addition of Polyethylene Terephthalate (PET) fiber (1.5 min) and Polypropylene (PP) fiber (1.0 min), whose contact angles were 80.04° and 130.26° respectively. Meanwhile, the bubble size has been decreased and mostly concentrated in the range of 0–50 microns. In addition, the effect of exerted pressure on the foam structure was also obtained. The results of the present study indicated that the generated foam gradually transferred from polyhedron to a spherical structure under moderate pressure conditions. Furthermore, when the pressure difference was higher than 10,000 Pa, bubble ruptured quickly.