BACKGROUND ART Cellulose-based products made from cellulosic fibers, chips, and shavings make up a significant portion of the building product market because they are cost effective, easy to work with, and environmentally friendly. Cellulose-based products provide structural support, act as roofing substrates, and dampen unwanted noise. Unfortunately, traditional cellulose-based products are also flammable. A number of methods have been developed to reduce the flammability of such materials, but many current methods are inadequate at providing fire- retardancy, are too expensive, or have some other shortcoming.

For example, U. S. Patent No. 6,518, 333 issued to Liu et al., on Feb. 11,2003, teaches a fire-retardant cellulosic product comprising: a cellulosic material, at least one polymeric binder resin, and fire retardant solid particles compressed together to form a panel. While products produced according to Liu have some degree of fire-retardancy,-they fail to qualify for the Class A rating for ASTM E-84. Furthermore, products that use polymeric resins can sometimes create toxic off gases when exposed to flames for extend periods time.

U. S. Patent No. 5,840, 105 issued to Helmsetter et al., on Nov. 24,1998, discloses a fire- resistant solution for application to the surface of cellulosic materials comprising: water, pure white clay, fine mica and sodium silicate. Surface coatings like that described in Helmsetter'105 provide flame resistance to the surface of cellulosic materials, however, they fail provide full. depth fire protection.

A need exists for a method that provides reliable, full-depth fire-retardancy to cellulose- based particle products that is cost effective, and is non-toxic.

DISCLOSURE OF INVENTION The present invention imparts fire-retardancy upon cellulosic products utilizing a cost- effective, non-toxic, and reliable process. Unlike previous methods which impart superficial fire- retardant coatings upon finished products, the present process treats the individual particles (i. e.

fibers, chips etc. ) that make up cellulose-based particle products. Treating the individual particles provides fire-retardancy throughout the entire length and width of the final product.

This full-depth retardancy provides superior protection, especially in catastrophic fires where the' surface coat of product is often compromised.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention imparts full-depth fire-retardancy upon cellulosic particle products utilizing a cost-effective, non-toxic, and reliable process. For the purpose of this disclosure, the term'cellulosic particle products' ("CPPs") is defined as any product that is made from cellulosic (or lignin-cellulosic) materials like wood fibers, wood chips, sawdust, bagasse, pulp extracts and other cellulosic fibers, particles and waste. CPPs encompass fiberboards, particleboards, medium density fiberboard (MDF), furniture board, fire-resistant panels, and other cellulosic particle products. It is important to note that the process may also be used to impart fire- retardancy to a number of non-cellulosic particulate products as well as cellulosic hard boards, The method of the present invention generally comprises the following: 1. Mixing a cellulosic (or lignin-cellulosic) material with an aqueous solution (i. e. water) and a phosphate (i. e. MKP), forming a phosphate-cellulose slurry; 2. Mixing a metal oxide composition with the phosphate-cellulose slurry forming a phosphate-oxide-cellulose slurry, the slurry containing treated cellulosic material ; 3. Removing the treated cellulosic material from the aqueous portion of the phosphate-oxide cellulose slurry; 4. (optional) Compressing the'cellulosic rnaterial forming a compressed ceituiosic .. material ; 5. Drying the compressed cellulose material.

The order of the steps of the method can be changed. For example the cellulosic material can be mixed with an aqueous solution (i. e. water) and a metal oxide to form a metal oxide-cellulose slurry first followed by the addition of a phosphate compound (MKP or MKP plus a silica containing compound) to the aqueous metal oxide-cellulose slurry to form the oxide- phosphate cellulose slurry. The oxide-phosphate-cellulose slurry has similar characteristics as the phosphate-oxide cellulose slurry described herein. Other steps are also similar to what is described below.

Mixing a cellulosic (or lianin-cellulosic) material with an aqueous solution and a phosphate, to form a phosphate-cellulose slur The first step of the present invention involves mixing a cellulose material with an aqueous solution and a phosphate to create a phosphate-cellulose slurry, The three components of the phosphate-cellulose slurry can be combined in any order. In a preferred

embodiment of the invention the cellulosic material is mixed with the aqueous solution (i. e. water) prior to the addition of the phosphate. Once combined, all three components are mixed for between 30 seconds and 20 minutes, or for sufficient time to ensure a relatively homogeneous mixture. Mixing can be achieved using a variety of methods including agitation.

The aqueous solution is preferably water. Alternatively, the phosphate and aqueous solution may be combined prior to the addition of the cellulose material.

Table 1. Exemplary weight percents for the phosphate-cellulose slurry Phosphate (i. e. MKP) Aqueous Solution Cellulose Material (ie. water) Exemplary Range 0.5-40 wt. % 50-99 wt. % 0. 5-40 wt. % Preferred Range 1-15 wt. % 75-98 wt. % 1-15 wt. % Commercial Range 1-7 wt, % 83-97 1-10 wt. % Table 1 provides exemplary weight percent ranges for the various components present in the phosphate-cellulose slurry. Generally the cellulose materials comprise between approximately 1-40 weight percent of the phosphate-cellulose slurry. The amount of cellulose present will depend on a variety of factors. When using small cellulosic fibers a preferred weight percent range for the cellulose material is generally between 1-15 wt. % of the mixture, more preferably 1-10 wt. %. The cellulose-based material can be virtually any type of cellulose material, however, it is preferably comprised of fibers, shavings, small chips or other fine cellulose particles with high surface-area to weight ratios. The high surface-area to weight ratio allows the materials to absorb the : aqueous solution (and the added phosphates and oxides) inore vapidly and to a grëater degree :'It shouid also be : noted thät various non-cellulpsic materials can be used in place of cellulose materials. Treating hardboards (or similar large products) may cause the percentages to vary.

As noted in Table 1 the aqueous solution (i. e. water) is generally present at between 50- 99 wt. percent of the phosphate-cellulose slurry, preferably at a range of between 75-98 wt. %.

Increasing the amount of water generally reduces the cost of production and increases the flowåbility of the slurry. A suitable temperature range for the water (aqueous solution) is between 40-180°F, more preferably between 60-160°F.

As described in Table 1, the phosphate is present at between 0.5-40 wt. percent of the phosphate-cellulose mixture, a more preferred range being between 1-15 weight percent.

Suitable phosphates include phosphoric acid and, phosphoric acid salts including but not limited to mono-potassium phosphate ("MKP"), sodium phosphate, ammonium phosphate, aluminum phosphate and combinations thereof. MKP (KH2PO4) is the most preferred phosphate. Dry phosphates are generally utilized but other forms can also be envisioned.

Addition of the Metal Oxide Composition A metal oxide mixture is added to, and mixed with the phosphate-cellulose slurry to form a phosphate-oxide-cellulose slurry. The phosphate-oxide-cellulose slurry is mixed for between 30 seconds and 20 minutes, or until the slurry is well-mixed. Mixing can be achieved by several techniques well known in the art including but not limited to agitation. The metal oxide reacts with the phosphate in the cellulose slurry in an exothermic reaction. Evidence of the reaction can be seen in a rise in the slurry temperature and pH. Dry oxide (or hydroxides) are used but other forms can also be employed.

Table 1-Exemplary weight percents of the phosphate-oxide cellulose slurry Phosphate Aqueous Solution Cellulose Metal Oxide Mixture (i. e. water) Material Exemplary Range 0 5-35 wt. % 50-98 wt. % 0. 5-40 wt. % 0. 5-30 wt. % Commercial 1-10 wt. % 70-98 wt. % 1-10 wt. % 1-10 wt. % Range Table 2 provides exemplary weight percents for the phosphate-oxide cellulose slurry. In general a higher percentage of phosphate and metal oxide corresponds to higher level of protection. However when the process is being used in large scale commercial production it is cost effective to reduce the amount of phosphate and metal oxide mixture as they are the most expensive reagents. Surprisingly, it was found that phosphate and metal oxide amounts can be reduced to a few weight percent (when weight percent ratio between the cellulose and phosphate + oxide is approximately 2: 1 or less and possibly as high as 5: 1 or 10: 1) of the phosphate-oxide-cellulose slurry white maihtain) ng fire-retardancy. The percentages can be varied according to conditions and desired resutts...

Metal Oxide Mixture As indicated in table 2, the metal oxide mixture is generally present at between 0.5-30 wt.

% of the phosphate-oxide-cellulose mixture, preferably between 1-10 wt. %. MgO is the preferred metal oxide, however, other metal oxides can be utilized in place of MgO, including but not limited to FeO, AI (OH) 3, Fe203, TiO, ZrO, and Zr (OH) 4. It is believed that the metal oxide reacts with the phosphate present on the surface of (and possibly inside) the cellulose material.

The reaction between the metal oxide and phosphate is believed to create a coating which imparts fire-retardancy upon the individual pieces of cellulose material.

It may be beneficial to use MgO that is part light burned (calcined at between 700- 1000°C) and part hard burned (calcined at between 1000-1500°C). The ratio between the hard and light burned generally between (0.5-2) : 1 A salient feature of the present invention is the weight percent ratio between the phosphate (i. e. MKP) and the metal oxide/hydroxide (i. e. MgO). A preferred embodiment has a

weight percent ratio between MKP and MgO between 5: 1 and 1: 5, more preferably between approximately 2: 1 and 1: 1. The weight ratio between MKP and MgO influences the reaction rate between the metal oxide and phosphate and thus the ability of each to attach to and coat the cellulosic particles.

Another important aspect of the invention is the weight percent ratio between the cellulose material and the combination of phosphate and metal oxide (i. e. MKP + MgO).

Generally, the ratio should be less than 10: 1, preferably less than 5: 1 and more preferably around 2 : 1. A proper ratio between the phosphate, oxide and cellulose ensures that all the cellulose material is adequately treated.

Silica-Containina Compound A salient feature of the invention is the presence of a silica-containing compound in the phosphate-oxide cellulose mixture. The silica-containing compound can be added at any step prior to removal of the cellulose material from the slurry. Generally the silica containing compounds is present at between 0.5 and 20 wt. % of the phosphate-oxide-cellulose mixture.

In one preferred embodiment the silica containing compound is mixed with the metal oxide prior to the addition of the metal oxide composition to the phosphate cellulose slurry. The metal oxide-silica mixture comprises: a metal oxide and a silica containing compound where the weight ratio between the metal oxide and silica containing compound is generally between (0.5- 2): 1. Suitable silica containing compounds (s) include but are not limited to: silica powder, silica fume, crushed rice hulls, small particle fly ash, and combinations thereof. Silica powder is proffered. The silica containing compound is believed. to act as carrier for the'MgO (or phosphate) l assisting in the reaction between the meta ! oxide and the phosphate, Holding Times/Additiona) mixing Each mixing step may be held for a period of time to ensure adequate absorption/reaction of the mixtures components. A series of mixing/holding steps can be employed to ensure optimal reactivity and homogeneity. Hold times can vary. Exemplary hold times ranges from 30 second to 20 minutes. Alternatively, the slurry can be allowed to sit for a period following mixture.

Additives Various additives can be added to the phosphate-oxide cellulose mixture. The additives can be added at any step prior to removal of the cellulose material from the phosphate-oxide- cellulose-slurry. Suitable additives include but are not limited to: mullite, alumina, sand, clay, volcanic glasses, kyanite, bauxite, aluminum oxide, silicon oxide, chrome oxide, iron oxide, and mixtures thereof. Preferred additives include calcium containing compounds including but not limited to: tricalcium phosphate, hydroxyapatite, biphasic calcium phosphate, tetracalcium

phosphate, CaSiO3, and combinations thereof. Tricalcium phosphate, hydroxyapatite, CaS103 and combinations thereof being the most preferred.

Removing cellulose material from phosphate-oxide cellulose slurry After sufficient mixing the treated cellulose material is removed and separated from the aqueous portion of the phosphate-oxide-cellulose slurry. The cellulose materials can be removed by a number of techniques well known in the art including but not limited to physical removal from the solution, and draining off the aqueous solution. In one embodiment the cellulose materials are physically taken out in clumps and spread out for on a porous support for drying. In another embodiment the phosphate-oxide cellulose slurry can be transferred (i. e. pumped) into a moving (or stationary) draining bed in which the aqueous solution is drained away from cellulose material by gravity or other means. Other separation means can also be employed including straining the cellulose material from the aqueous portion of the slurry.

Compression After the cellulose materials have been removed and drained from the phosphate-oxide- cellulose slurry certain types of cellulose materials (i. e. fibers, particles) can be compressed using a variety of methods well known in the art including the use of rollers. The cellulose materials can be compressed into variety of shapes, sizes, lengths and widths.

Drying Cellulose Material Drying the cellulose material can be achieved by several techniques known in the art including heating in an oven or a series of ovens. The cellulose material should be heated at temperature and'for. a time period sufficient to produce cellulose products with a water content of less than. 10% by weight, more preferably less than 5% by weight. Exempiaryrtemperatures are between 100-1000°F : : Suitable. time ranges are between. 5 minutes and 2 hours.'-.. : Commercial Production The present process can be utilized in conjunction with other known methods of manufacturing cellulose particle products like fiberboard, particle board and the like. See, U. S.

Patent Nos. 6,197, 414; 4,935, 457; 4,597, 928; 4,311, 555; 4,190, 492 which are hereby <BR> <BR> incorporating by. reference in their entirety. The fibers, . chips, or other cellulose particles can be treated first using the present process and can then be used known manufacturing process.

Alternatively, known processes can incorporate the present process.

A suitable temperature range for the water being mixed with the phosphate powder is between 40-180°F. The temperature of the water is related to the mixtures reactivity, thus the rate of the reaction can be controlled to some degree by the temperature of the water being added. Warm water tends to speed up the reaction while cool water tends to slow it down.

The temperature of such reagents, like that of water can affect the reactivity of the

mixtures and can be used to regulate the reaction to a limited degree. Again, warm reagents may speed up the reaction while cool reagents tend it slow them down.

Coating the compressed cellulose material with an additional fire-retardant coatings.

Mixing Containers The invention can be mixed in a variety of container types. The container is preferably non-reactive with the slurry components and can vary in size and shape according to desired results. An alternate embodiment uses a series of containers. The steps of the invention can be repeated to increase effectiveness.

The examples below provide exemplary formulations for various embodiments of the present invention.

Example I-is one preferred embodiment of the invention Water + Cellulose Material + (MgO/Silica Powder mixture) 60,000 Ibs of water having a temperature of approximately 140°F was combined with 3000 Ibs of cellulosic fiber forming a cellulosic slurry having a pH between 3.1 and 3.2. 1000 Ibs of MKP was added to, and mixed with the cellulosic slurry until formation of a phosphate cellulose mixture having a pH of between 3.9 and 4.0. The phosphate-cellulose slurry was then held for 5 minutes. 1 0001bs of a MgO/Silica composition was added to, and mixed with, the phosphate-cellulose slurry until formation of a phosphate-oxide cellulose slurry having a pH of between 5.8 and 6.0. The phosphate-oxide cellulose slurry was held 5 minutes. The MgO/Sitica composition was composed of (2501bs hard burned MgO, 2501bs light burned MgO and 5001bs of silica powder : Mixing was achieved by agitation. After mixing the treated cellulose fibers were separated from the aqueous portion of the slurry (by draining the solution),. compressed. through a series of rollers and dried using a series of ovens.

Example II MKP + Water + Cellulose Material + (MgO/Silica Powder mixture) 3g of MKP were mixed with 90g of water to form a well-mixed aqueous phosphate solution. 4g of cellulose fibers was added to the aqueous phosphate solution and hand mixed , for 2 minutes forming a well-mixed phosphate-cellulose slurry. 3g of MgO/Silica mix was added to the phosphate-cellulose slurry and hand mixed for another 2 minutes forming a phosphate- oxide cellulose slurry. The MgO/Silica slurry was composed of (0.75 g hard burned MgO, 0. 75 g of light burned MgO and 1.5 g of silica powder. After mixing was complete, the aqueous portion of the phosphate-oxide-cellulose slurry was drained and the cellulose fibers were dried in an oven at approximately 500°F.

Alternative Embodiments

Method for imparting fire-retardancy upon materials comprising: a. Mixing a cellulose material with a first aqueous solution forming a first cellulose slurry ; b. Removing the cellulose material from the first cellulose slurry; c. Mixing the removed cellulose-based material with a second aqueous solution forming a second cellulose slurry, the second slurry containing treated cellulose material. d. Removing the treated cellulose material from the second cellulose slurry, The first aqueous can be either an aqueous phosphate solution or an aqueous metal oxide solution. The second aqueous solution can also be either a phosphate or metal oxide solution, however, it should be different than the first slurry. For example if the first slurry contains a phosphate solution than the second should contain a metal oxide and vis versa. The aqueous phosphate solution is generally between 0.5-40 wt. percent phosphate and 60-99 wt. percent water, preferably between 1-10 wt. percent phosphate and 90-99 wt. percent water. The aqueous metal oxide (hydroxide) solution is general 1-40 wt. percent metal oxide and 60-99 wt. percent water, preferably between 1-10 wt. percent metal oxide and 90-99.5 wt. percent water.

The cellulose generally comprises 0.5-45 wt. percent of the first and second slurry, preferably between 0. 5-10 wt. percent. The types of phosphate and oxides, ratios and other general features are similar to the embodiment already described.

Having described the basic concept of the invention, it will be apparent to those skilled in the art. that the'foregoing'detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications are intended to be., suggested and are within the scope and spirit of the present invention. Additionally, the recited' order of the elements or sequences, or the use of numbers, letters or other designations therefor, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.

All publications and patent documents cited in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication or patent document were so individually denoted.