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Cottonwood pulp filter paper, as a historically significant filtering material, has deep roots in the oil filtration industry. In past industrial oil filtration, precision filtering often shifted from metal mesh to this plant fiber filter paper, making cottonwood pulp paper the star of the filtration world at that time.
Compared to modern synthetic fiber, glass fiber, and metal fiber filter materials, cottonwood pulp filter paper has a relatively rougher, uneven fiber structure that appears flat. However, it is this rough and irregular appearance that gives it a unique advantage in particle adsorption. That said, the uneven fiber thickness also limits its adsorption capacity, as the fineness of the fibers is crucial to the filtering effect. From the microscopic images of plant fiber filter paper, we can see that the longitudinal section of the fibers arranges from sparse to dense, which means the fiber gaps on the oil-facing side are larger and more conducive to ash storage.
While the filtration precision of cottonwood pulp filter paper is somewhat limited, its maximum can reach around 10μm, rarely exceeding 8μm. The filtration precision test results of some typical domestic and international filter paper models are reflected in Table 11-3.
One major drawback of cottonwood pulp filter paper is its low strength, which cannot compare with woven mesh. To enhance its strength, resin impregnation is typically used. Among them, alcohol-soluble phenolic resin is widely favored for its softness, foldable corrugation properties, and enhanced strength after continuous curing. Moreover, heat-resistant phenolic resin and chemically resistant epoxy resin are also available choices. Filter paper treated with impregnated resin not only significantly improves in strength but also slightly enhances filtration precision, improves air permeability, and effectively prevents fiber shedding.
With continuous technological advancements, although cottonwood pulp filter paper may be somewhat inadequate in certain aspects, it remains an irreplaceable choice in some special occasions. Meanwhile, we look forward to future filter material developments that can integrate the advantages of cottonwood pulp filter paper with modern technology to create more efficient, environmentally friendly new filter materials to meet the ever-changing market demands.
