HK1186169B - Acoustic building material employing chitosan - Google Patents

Abstract

A cast ceiling tile and method for manufacture incorporates chitosan in an amount sufficient to provide improved strength and to enhance the dewatering of the slurry used to form the tile.

Description

Acoustic building material using chitosan

This application is a continuation-in-part application of U.S. application serial No.13/294,200 filed on 15/11/2011, which in turn claims priority to U.S. provisional application No.61/427,643 filed on 28/12/2010.

Technical Field

The field relates to building materials for construction, and more particularly to ceiling tiles comprising chitosan uniformly dispersed within the structure of the tile.

Background

Building materials or ceilings are used in the construction industry to provide original ceiling structures or to replace covered ceiling structures. The ceilings may be mounted directly to the building surface or they may be mounted in a suspended ceiling fabric using a mesh support secured to the building structure. These panels are prepared from a slurry of fibers, fillers and binders.

Of particular interest herein are panels made using compositions and casting procedures such as those disclosed in U.S. Pat. Nos. 5,395,438 and 1,769,519. According to these patent teachings, molding compositions comprising fibers, fillers, colorants and binders, particularly starch gels, are prepared for molding or casting ceiling bodies. The mixture or composition is placed on a suitable tray and the composition is then scraped to the desired thickness with a scraper or roller. The tray with the composition is then placed in an oven to dry or cure the composition. The dried board is removed from the tray and may be treated on one or both sides to provide a smooth surface to achieve the desired thickness and prevent warping. The sheet is then cut into panels of the desired dimensions.

Chitosan or poly-D-glucosamine is commercially available as a deacetylated form of chitin, which is a structural component in the cell walls of crustacean outer bones and certain fungi. It is a cationic polymer similar to cellulose. Chitosan has been found to promote blood coagulation and has been used in bandages. It is a biocide and has special properties that enhance antimicrobial and antifungal behavior. Chitosan is also used as a flocculant in heavy metal water filtration. Chitosan is also indicated to absorb formaldehyde and odor.

Disclosure of Invention

Chitosan has been found to be a multifunctional additive for fiber boards that can be directly incorporated into the slurry formulation. The chitosan was dissolved in acid and added directly to the slurry as a dilute solution. In this way, the chitosan was uniformly dispersed through the plate structure and did not significantly change in the manufacturing process.

The use of chitosan in ceiling structures enables the resulting articles to have a number of advantages. For example, a chitosan concentration of less than about 10wt% provides structural reinforcement sufficient to allow for a reduction in the amount of binder. This results in cost savings because the binder is an expensive component of the fiber board composition.

Another advantage of incorporating chitosan in the board structure is that it strengthens and helps the components to bond and enables increased recycling content. I.e. the amount of binder can be reduced and an increased amount of recycled cellulose can be used.

Most unexpectedly, it has also been found that chitosan is incorporated in the board structure to enhance dewatering or water removal from the board structure as they are formed and to reduce drying requirements. In the casting process, dewatering from the plate structure is improved prior to the oven drying step and the amount of drying required is reduced. In the plate structure comprising chitosan according to the present invention, the amount of water removed in the dewatering step before oven drying is increased compared to the same plate structure and treatment except for the addition of chitosan. Thus, the amount of water to be removed in the final oven drying step is reduced according to the invention. Reduced oven drying requirements save energy and expense.

The biocidal properties of chitosan are particularly useful in ceiling applications where high humidity, condensation or other sources of moisture may wet the board. This environment favors the undesirable growth of microorganisms and fungi that may be deposited by air transfer.

It is believed that the ability of chitosan to absorb formaldehyde reduces the formaldehyde level of the process and article. The odor-removing properties of chitosan are particularly useful in article applications.

Detailed Description

As noted above, chitosan has been found to provide desirable properties to building materials, particularly cast ceiling tile compositions, as a multifunctional additive. For convenience, the invention is described hereinafter with particular reference to cast ceiling panels.

The ceiling tile contemplated herein comprises a base fiber that is typically a mineral fiber such as mineral wool or similar inorganic fiber. The filler is typically perlite, clay, calcium carbonate, glass beads, stucco (calcium sulfate hemihydrate), or gypsum. The binder is typically starch, latex or similar material. These materials or ingredients as described above are typically mixed in an aqueous slurry and processed in a water felting process.

In a typical composition, the fiber and filler components comprise the major components. However, a wide variety of compositions may be used. For example, the following chart summarizes typical cast ceiling tile compositions. It should be recognized that the composition may include one or more of the indicated types of fibers, fillers, or binders as set forth in the following table. Percentages herein are weight percentages based on solids, unless otherwise indicated by note or context.

The fiber, filler and binder components are mixed in the aqueous slurry in a known manner at a level of about 65% to 75% solids. Chitosan was dissolved in an acidic aqueous solution and homogeneously blended into the slurry. For example, chitosan in the form of powder or flakes may be dissolved in 2-4 vol% acetic acid solution and then added to the slurry. The amount of chitosan solution added provides a final product weight basis of 1% to 6% based on the solids contained in the slurry.

It is believed that the presence of hydrophilic OH and NH groups in the chitosan enhances the uniform distribution and thorough penetration and/or contact of the fibers and filler slurry ingredients by the chitosan. Furthermore, it is believed that chitosan with cations interacts with starch. Furthermore, the chitosan appears to form a fibrous structure that is interwoven and/or otherwise interacts with the other fibrous components of the panel to provide structural reinforcement, which enables the amount of binder to be reduced and there is an acceptably limited change in panel physical properties.

As noted above, the addition of chitosan to the board structure of a ceiling tile or the like reduces the amount of water that remains in the structure as it is formed prior to oven drying. The casting process may include natural draining, application of vacuum to the plate, and/or rolling to remove water prior to oven drying. The use of chitosan in accordance with the present invention has been found to be effective in enhancing water removal when used in conjunction with one or more of the previously described pre-oven drying processes. Thus, chitosan-containing panels according to the invention contained less water prior to oven drying than the same formed panel structure with the same composition but without the addition of chitosan.

The following illustrative examples compare panels corresponding to the core of the panel and not including the outer coating, apertures, or other surface treatment. The board composition comprises mineral wool, corn starch, stucco, and boric acid. The board composition was varied here to incorporate different amounts of chitosan to verify the binding and reinforcing properties of chitosan.

The absolute amounts of the components contained in the prepared panels are shown in table 1 below.

TABLE 1 formulation

Panel 1 provides a comparative panel with no added chitosan but with typical amounts of starch. Plates 2-5 contain increasing amounts of chitosan.

The properties of the panels 1-5 are shown in Table 2.

Table 2: properties of

Test panels 1-5, the results are shown in Table 2 above. The test results given in table 2 were determined using the following test procedure.

The flexural modulus MOR test is a 3-point bend test. The test procedure herein is similar to the ASTM C367 Standard test method for Strength Properties of Prefabricated structural Acoustic tiles or Embedded ceilings. The hardness test illustrates the ability of the ceiling to withstand indentations that may occur during installation or post-installation. The 2 "ball hardness test used herein is similar to the ASTM C367 standard test method for strength properties of prefabricated structural acoustic panels or embedded ceiling tiles.

Comparison of panels 1 and 2 shows an increase in strength and stiffness as indicated by the increased MOR and stiffness results. The comparison included the same amount of binder and 1% chitosan was added to panel 2. Thus, chitosan improves these physical properties.

Panels 3 and 4 showed a further increase in strength as indicated by increased MOR. Panel 5 showed a decrease in strength and MOR after 10% addition. It is believed that an increase in strength or MOR and/or acceptable physical property values may be achieved by the addition of chitosan in an amount greater than 5% and up to about 10% or more. The currently preferred range of chitosan is from about 2% to about 8%. As used herein, acceptable physical properties means that the physical property values tested are at least equal to about 95% of the values provided by the same formed ceiling tile using the same ingredients but without the addition of chitosan.

Even though it may result in somewhat lower property values, it should be recognized that the amount of more expensive starch ingredients may be reduced in achieving structures of increased strength or MOR properties and/or hardness. In addition, the amount of recycled newsprint can be increased instead of a reduced amount of starch, thereby increasing the recycled and post-industrial/post-consumer content in the board.

The panel 5 is characterized by a reduction in strength and stiffness of greater than 5% of the comparative value. It is currently believed that this drop exceeds acceptable physical property values.

The following panels were prepared using the casting procedure described above to evaluate mold resistance. The plate composition based on total dry ingredients is summarized in table 3 below.

Table 3: composition based on total dry ingredients

Panels 6-7 were prepared according to the previous formulation and tested for their mildew resistance based on ASTM D3273-00 (re-approved in 2005). Plate 6 is a control plate, without chitosan; plate 7 contained 5% chitosan and plate 7 contained 10% chitosan. The front and back of the panel were evaluated after two and four weeks of exposure. The front and back sides of the panel were observed and rated at a value of 0-10, where 0 represents continuous damage across the sample surface and 10 represents complete absence of damage to the sample by particulate matter. The test results are shown in table 4 below.

Table 4: resistance to mold

As shown in table 4, the use of chitosan inhibited mold growth. The surface of the plate is not substantially damaged. Chitosan improves mold resistance and increases strength and MOR values.

Additional comparisons, 5% chitosan and 10% chitosan formulations are given below.

It should be apparent that the present disclosure is by way of example and that various changes may be made by adding, modifying or omitting details without departing from the fair scope of the teaching contained in this disclosure. Therefore, the invention is not to be limited to the specific details of this disclosure except to the extent that the following claims are necessarily so limited.

Claims (21)

1. A cast ceiling tile formed from the dried acoustical product of an aqueous slurry of ingredients consisting essentially of fiber, filler, binder selected from the group consisting of starch and latex, and chitosan uniformly dispersed throughout the aqueous slurry for interaction with the slurry ingredients, whereby the cast ceiling tile formed by drying water from the aqueous slurry is structurally reinforced by the interaction of chitosan with the fiber ingredients in the slurry as compared to a similarly formed ceiling tile of the same slurry ingredients except for chitosan.

2. The cast ceiling tile of claim 1, wherein said chitosan interacts with said ingredients to provide a ceiling tile with enhanced physical properties, including MOR, as compared to a ceiling tile identically formed from the same slurry ingredients except for chitosan.

3. The cast ceiling tile of claim 1, wherein the chitosan is present in an amount of 0.5 wt% to 10wt% based on the total weight of solids in the aqueous slurry.

4. The cast ceiling tile of claim 1, wherein the chitosan is dissolved in an acid solution for addition to the slurry.

5. The cast ceiling tile of claim 1, wherein the slurry comprises a reduced amount of binder corresponding to the amount of chitosan added to maintain acceptable physical properties and an increased amount of cellulose fiber recycled material corresponding to the reduced amount of binder, thereby increasing the post-industrial/post-consumer content of the tile.

6. The ceiling tile of claim 5, wherein the acceptable physical properties include MOR and hardness.

7. The cast ceiling tile of claim 1, wherein the chitosan interacts with the slurry composition during dewatering to remove an increased amount of water from the ceiling tile as compared to a cast ceiling tile identically formed from the same slurry composition except for the chitosan.

8. The cast ceiling tile of claim 1, wherein the fibers are mineral wool and the filler is selected from perlite, calcium carbonate, clay, and stucco.

9. The cast ceiling tile of claim 1, wherein said chitosan tends to increase the mold resistance of the ceiling tile.

10. The cast ceiling tile of claim 1, wherein the ceiling tile has a composition comprising by weight:

60 to 80 percent of fiber, and the fiber,

15 to 70 percent of filler,

3% to 12% of a binder, and

0.5 to 10 percent of chitosan,

provided that the sum of the percentages of the above components is equal to or less than 100%.

11. An acoustic building material comprising a dried product of an aqueous slurry of ingredients consisting essentially of mineral fiber, filler, starch binder, and chitosan, the chitosan being uniformly dispersed throughout the aqueous slurry, the chitosan interacting with the slurry ingredients, whereby the acoustic building material is structurally reinforced by the chitosan interacting with at least the starch binder as compared to an identically formed acoustic building material of the same slurry ingredients except for the chitosan.

12. The building material of claim 11, wherein the chitosan interacts with the slurry ingredients to provide a building material having enhanced mechanical properties, including MOR, as compared to a building material identically formed from the same slurry ingredients except for chitosan.

13. The building material of claim 11, wherein the chitosan is present in an amount of 1 wt% to 6 wt% based on the total weight of solids in the aqueous slurry.

14. The building material of claim 11, wherein the slurry comprises a reduced amount of binder corresponding to the amount of chitosan added to maintain acceptable physical properties and an increased amount of cellulose fiber recycled material corresponding to the reduced amount of binder.

15. The building material of claim 11, wherein the chitosan interacts with the slurry component during dewatering to remove an increased amount of water from the building material as compared to a building material identically formed from the same slurry component except for the chitosan.

16. The building material of claim 11, wherein the fibers are selected from the group consisting of mineral wool, glass fibers, and cellulose fibers, and the filler is selected from the group consisting of perlite, calcium carbonate, clay, and stucco.

17. A method of making a ceiling tile from an aqueous slurry of dry acoustic material in a casting process, comprising: forming the aqueous slurry of ingredients consisting essentially of mineral fiber, filler selected from perlite, calcium carbonate, clay and stucco, uniformly dispersing the chitosan in the aqueous slurry, dewatering and drying the slurry to form the acoustic material, the chitosan interacting with the starch binder and/or mineral fiber slurry ingredients, thereby reinforcing the resulting panel compared to a cast panel structure identically formed of the same ingredients except for chitosan.

18. The method of claim 17, wherein the chitosan is dissolved in an acid solution and added to the slurry.

19. The method of claim 18, wherein said chitosan interacts with said component to provide said cast slab with increased MOR and hardness as compared to a cast slab also formed from the same component except chitosan.

20. The method of claim 17, wherein the step of dewatering the slurry comprises removing an increased amount of water due to the presence of chitosan as compared to a casting slab also formed from the same composition except for chitosan.

21. The method of claim 17, wherein the chitosan is present in an amount of 0.5 wt% to 10wt% based on the total weight of solids in the aqueous slurry, and the slurry comprises a reduced amount of binder corresponding to the amount of chitosan added to maintain acceptable physical properties, and an increased amount of cellulose fiber recycled material corresponding to the reduced amount of binder, thereby increasing the post-industrial/post-consumer content of the building material.