What changes occur to the sizing agent attached to the surface of fiberglass during the drying process?
(1) Before drying. During the drawing process, a layer of sizing agent film is coated on the surface of the fiberglass with a thickness of 0.5~2μm. This film is a multi-phase complex structure, with the homogeneous sizing agent as the continuous phase and the emulsion particles of different sizes as the dispersed phase. At this time, the Si-OH bonds in the coupling agent molecules begin to combine with the Si-OH bonds on the glass surface and concentrate on the glass surface.
(2) Drying process. During the drying process, as the water evaporates continuously, the concentration of the wetting agent increases, the emulsion begins to break, the emulsion particles condense, and the non-ionic lubricant begins to migrate to the liquid-gas interface, i.e., the surface layer. The inorganic salt of the antistatic agent crystallizes due to supersaturation. This process continues until the thickness of the wetting agent film is reduced to 0.05~0.2μm. After the solution is dried, it becomes a continuous phase in a small range, and the particles of different emulsions pile up together and maintain their original particle interface without mutual fusion. At this time, the mechanical properties of the wetting agent film are very poor, the yarn has poor wear resistance, and the stiffness is not high.
(3) After maintaining this temperature for a period of time, the emulsion particles of various film-forming agents begin to reach the melting temperature, and the molecules diffuse with each other. Although they cannot form a completely homogeneous structure (this is related to the solubility parameters of various emulsion resins, the viscosity of the molten resin, the molecular polarity, and the chemical structure similarity between the resins), the interface between the emulsion particles has disappeared, and various emulsion resins and water-soluble resins have merged with each other to form a roughly complete and continuous film. If there is a cross-linking agent in the formula of the wetting agent and film-forming agent, the cross-linking agent begins to work at this time, causing the resin to form a network structure and increase the molecular weight, while the non-ionic lubricant continues to migrate to the surface. At this time, the yarn has good wear resistance, improved stiffness, and the strength also reaches the maximum value. However, over-drying can also cause yarn quality problems, such as yellowing of the surface.
The sizing agent often cannot form a continuous and complete film on the fiberglass single fiber. Because the sizing agent film is too thin and the corresponding latex particles are large, the latex resin particles after drying often protrude from the film surface, and these protrusions or even small spherical particles bond the single fibers together.
