Mechanism of Action of Wood Fiber in Powder Materials
Release Time:
2020-05-18
Source:
Mechanism of Action of Wood Fiber in Powder Materials
Wood fiber is a versatile additive that can be used in powdered materials such as cement, gypsum, and lime. It is extracted from wood pulp through a series of processes—chopping, neutralization, bleaching, and pressing—to completely remove lignin and hemicellulose, as these components can adversely affect the hydration and strength of cement and gypsum. The resulting material is then screened to produce finished products with varying fiber lengths and diameters, tailored to meet the specific requirements of different applications. While wood fiber shares certain functions with cellulose ethers, such as thickening and viscosity enhancement, it is an insoluble natural material (whereas cellulose ethers are water-soluble). Consequently, wood fiber provides stronger reinforcement for powdered materials and is significantly more cost-effective than cellulose ethers.
Wood fibers come in a variety of grades, differing in fiber length, density, and purity, with lengths ranging from 10 µm to 2,000 µm. Their bulk density is approximately 0.8–1.3 g/cm³. Wood fibers are exceptionally strong, with a surface texture remarkably similar to that of asbestos; moreover, they are entirely non-toxic and harmless. The saturation moisture content of wood fibers is about 10–12%, while their normal moisture content typically falls within the range of 4–8%. Consequently, they should be stored in a dry environment, as they do not absorb moisture from the air in a way that would compromise their performance. They are insoluble in water and organic solvents and exhibit resistance to dilute acids as well as to both acidic and alkaline conditions. The alkalinity of cement does not harm them or adversely affect the properties of the powdered materials. Wood fibers are highly inert: in powdered formulations, they do not react with any other constituents, but rather exert only physical effects. Furthermore, wood fibers possess excellent freeze-thaw resistance, with no frost-heave damage.
Mechanism of Action of Wood Fiber in Powder Materials
1. Strong thickening and reinforcement effect. Wood fibers exhibit robust cross-linking capabilities. When mixed with other materials, the fibers immediately interlock like a blanket, forming a three-dimensional network that traps water or other liquids within its structure. The longer the fibers, the more pronounced the thickening effect.
2. The structural viscosity of wood fibers can enhance workability. When shear forces are applied—such as during troweling, mixing, or pumping—some of the liquid is expelled from the fiber network into the matrix, resulting in a reduction in viscosity and improved workability. Once the shear force is removed, the fiber structure rapidly reconstitutes, reabsorbs the moisture, and restores the original viscosity.
3. Excellent liquid retention capability. Wood fibers can absorb 100% to 200% of their own weight in liquid and, due to their structure, can adsorb an additional 2 to 6 times their weight in liquid.
4. Crack resistance. The mechanical energy generated during curing or drying is mitigated by the fiber reinforcement.
5. Low shrinkage. Wood fibers exhibit excellent dimensional stability, which prevents the mixture from shrinking and settling and enhances its crack resistance.
6. Anti-sagging: During construction and the drying process, no sagging occurs, enabling thicker plaster layers to be applied in a single pass. Moreover, wood fibers exhibit excellent thermal stability even under high-temperature conditions.
7. Extended open time. Due to the capillary action of the fibrous structure, internal moisture is rapidly transported to the slurry surface and interface, resulting in a uniform distribution of moisture throughout the slurry system. This significantly reduces skinning and markedly enhances both bond strength and surface strength. Furthermore, this mechanism also effectively mitigates cracking during drying by reducing tensile stress.
