Fiber cement composite material using biocide treated durable cellulose fibers

Abstract

A fiber cement composite material providing improved rot resistance and durability, the composite material incorporating biocide treated fibrous pulps to resist microorganism attacks. The biocide treated fibers have biocides attached to inner and outer surfaces of individualized fibers to protect the fibers from fungi, bacteria, mold and algae attacks. The biocides selected have strong affinity to cellulose and do not interfere with cement hydration reactions. This invention also discloses the formulation, the method of manufacturing and the final fiber cement products using the biocide treated fibers.

Description

RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 09 / 969,964 filed Oct. 2, 2001 which claims the benefit of U.S. Provisional Application No. 60 / 241,212, filed on Oct. 17, 2000, which are hereby incorporated by reference in their entirety.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to cellulose fiber reinforced cement composite materials using biocide treated cellulose fibers, including fiber treatment methods, formulations, methods of manufacture and final products with improved material properties relating to the same. [0004] 2. Description of the Related Art [0005] Ordinary Portland cement is the basis for many products used in building and construction, primarily concrete and steel reinforced concrete. Cement has the enormous advantage that it is a hydraulically settable binder, and after setting it is little affected by water, compared to gypsum, wood, wood particle boards, fiberboard...

AI Technical Summary

Benefits of technology

[0021] The above described needs are addressed by the preferred embodiments of the present invention in which partially or completely delignified and individualized cellulose fibers are pre-treated with selective inorganic or organic biocides, thereby producing an engineered cellulose fiber. When used in fiber cement composite materials, this engineered fiber retains the advantages of regular cellulose fibers of refining, autoclaving, and manufacture without pressing, but the resultant fiber cement material also can approach or even exceed the performance advantages of artificial fibers such as PVA, in terms of biological durability when used in fiber reinforced cement composite materials. The enhancement in the desirable biodurability is accomplished without any significant reduction in the important physical properties of the material, such as strength and toughness.

[0023] Thus, the use of these engineered rot-resistant fibers imparts to the composite material the enhanced biodurability properties, and therefore constitute an alternative technology that, when fully implemented, has the potential to maintain mechanical properties and the workability with the material in building and construction, while improve the durability of the products in the high humidity and rot-prone environments, regardless of the means of manufacture. They are particularly suitable to the Hatschek process that requires a refine-able fiber (to catch solid particles) and to the autoclave curing cycle that allows the replacement of cement with fine ground silica, although they may also be of use in the air cured products, in conjunction with PVA, to reduce the necessity of the expensive process pressing.

[0025] Embodiments of the present invention will impart the fiber cement composite material with improved biodurability. Incorporation of the biocide treated fibers will increase the retention of the cellulose fiber when the fiber cement matrix is subjected to rot-prone high humidity environment. In one embodiment, the loss of fibers over 6 months of underground exposure was reduced from about 78% to about 32% when the biocide treated fibers are used. The high retention of fibers is indicative of better retention of reinforcement efficiency of the fibers in the fiber cement composite materials.

[0028] Some of these steps can be omitted or rearranged, and other steps may be provided. The step of treating the fibers comprises treating the fibers with inorganic and organic biocides, or combinations thereof by means of techniques such as chemical reactions and / or physical deposition processes such as pressure or temperature impregnation and concentration diffusion. In this step, partially or completely delignified and individualized cellulose fibers are used for the fiber treatment. The effective biocides are attached to the fibers to provide enhanced biological resistances. The biocides that can be used for this purpose include a number of inorganic and organic chemicals and the combinations thereof.

[0030] Incorporation of the biocide treated fibers in the fiber cement matrix in accordance with the embodiments of the present invention improves rot resistance and durability of the final composite materials. The scope of the invention is not limited to particular types of cement, aggregates, density modifiers or additives, nor to their ratios in the formulations. These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.

Problems solved by technology

The disadvantage of these products was that the high-density matrix did not allow nailing, and methods of fixing involved pre-drilled holes.

Since silica, even when ground, is much cheaper than cement, and since the autoclave curing time is much less than the air cured curing time, this became a common, but by no means universal manufacturing method.

However, cellulose reinforced cement products are more susceptible to water induced damages and biological attacks, compared to asbestos cement composite materials.

Hence, asbestos reinforced fiber cement products are themselves strong, stiff (also brittle), and could be used in many hostile environments, except highly acidic environments where the cement itself is rapidly attacked chemically.

This product is air-cured, since PVA fibers are, in general, not autoclave stable.

The great disadvantage of these products is a very large increase in material and manufacturing process costs.

Thick organic coatings are also expensive, and the hydraulic pressing is a high cost manufacture step.

However, cellulose fiber cement materials can have performance drawbacks such as lower rot resistance and poorer long-term durability compared to asbestos cement composite materials.

These drawbacks are due in part to the inherent properties of natural cellulose fibers.

As such, cellulose fibers are susceptible to bio-decay or rot attack when incorporated into fiber reinforced cement composite materials, which also happen to be highly porous.

The microorganisms will break down cellulose polymer chains, resulting in significant loss in the fiber strengths.

The cleavages of cellulose fiber chains by the microorganisms eventually reduce the reinforcement efficiency of the fibers and adversely affect the long-term durability of fiber cement materials.

The primary problem with this technology is increased material and manufacturing cost.

However, the problems associated with this technology include higher porosity of the product and higher susceptibility to biological attacks when compared to asbestos fiber cement materials.

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