Non-toxic wood preservation
US2006045978
A method for the protection of wood, increasing the strength and
load-bearing capacity of wood, and increasing the capacity of wood
to generate friction with adjacent soils, by treating wood with
one or more minerals of low toxicity mixed with an aqueous medium,
to provide wood that retains the infused minerals for an extended
period of time while avoiding the detrimental environmental
effects of conventional chromium or copper-based inorganic salt
preservation and organic chemical methods.
[0001] The present invention relates to a mineral compound and its
use in a method for preserving and protecting wood against decay
and insect infestation, and fire, increasing the strength and
load-bearing capacity of wood, and increasing the capacity of wood
to generate friction with adjacent soils. The invention is useful
in both hardwoods and softwoods.
[0002] On a commercial scale, the method of the present invention
is preferably conducted using a treatment cylinder of a sufficient
size to be both economically practical and convenient.
BACKGROUND OF THE INVENTION
[0003] Preservation of wood materials with chemicals and mineral
compounds has often posed a significant hazard to the environment.
Various water-soluble salts, such as borax, copper and chromium
salts, zinc chlorides, and sodium fluoride have been used to
provide wood preservative properties. These salts offer protection
against mold, fungi and insect infestation.
[0004] Unfortunately, wood treated with the types of water-soluble
inorganic salts described above are susceptible to leaching of the
salts into the surrounding environment, and the treated wood often
becomes susceptible to microbial or insect attack over time as
salt concentration decreases in the treated wood.
[0005] Chromated-copper-arsenic (CCA) compositions are used in the
conventional treatment of wood products. CCA acts as a
preservative and also protects the wood surface from softening
when exposed to sun and rain. However, chromium and arsenic salts
are highly toxic and any leaching action contaminates the
surrounding environment. Accordingly, governmental agencies of
various countries are regulating and/or prohibiting use of such
materials.
[0006] The leaching of both water-soluble inorganic salts and CCA
compositions commonly employed in the wood preservation industry
shorten the economic life of the treated wood. The present
invention seeks substantially to reduce leaching and to increase
the economic life of the treated wood, thereby alleviating the
world's demand for timber and slowing the rate of de-forestation.
[0007] Unlike water-soluble salts, organic chemicals used to treat
wood do not tend to leach out of treated lumber to a significant
extent, but these materials are generally toxic and are also
increasingly subject to restrictions on use and disposal mandated
by governmental agencies.
[0008] Preservation of wood to enhance its fire-resistant capacity
is the subject of U.S. Pat. No. 4,612,050 to Hicks, which
describes a process for preparation of a liquid solution of sodium
silicate, mineral water, and citric or malic acid, which forms a
gel within wood following application of the liquid solution as an
exterior coating. This patent is based on a formulation and
chemical reaction different from that made by means of this
application and does not utilize pressure treatment to maximize
mineral impregnation.
[0009] The present invention seeks to improve upon the prior art
wood treatment methods by providing a treatment that is of low
toxicity, is made up of highly stable minerals, reduces undesired
viscosity and corrosion effects encountered in other wood
preservative treatment processes, does not leach active
ingredients out of impregnated wood materials significantly over
time, improves strength, load-bearing capacity and friction
capacity of wood, decreases combustibility and ignition
temperature, and protects the treated wood from degradation by
microorganisms, mold, fungi, insects, wood-boring marine
organisms, and fire.
STATEMENT OF INVENTION
[0010] The present invention relates to a method for treatment of
wood by (a) contacting wood material with an aqueous treatment
solution containing one or more minerals to provide impregnated
wood material, and (b) separating the impregnated wood material
from the aqueous treatment solution.
[0011] In a preferred embodiment, the present invention further
provides for subjecting the impregnated wood material to a
pressure treatment during step (a).
DETAILED DESCRIPTION
[0012] As used herein, the following terms have the designated
definitions, unless the context clearly indicates otherwise.
[0013] As used herein, the terms "wood" and "wood material" shall
mean all forms of wood, for example, solid wood (such as timber or
lumber in the form of logs, beams, plants, sheets and boards),
wood composite materials (such as wood fiber board, chip board,
and particle board) and all products made from wood and
wood-composite materials (such as mill frames, decking, siding,
truss joists, foundation piers, pilings, flooring, siding,
cladding, roof shingles and utility poles).
[0014] As used herein, the term "water" shall mean one or more of
seawater, saltwater, brines, brackish water, and fresh water.
[0015] As used herein, the term "microbicide" refers to a compound
capable of inhibiting the growth of or controlling the growth of
microorganisms at a locus; microbicides include, for example,
bactericides, fungicides, and algaecides.
[0016] The mineral combinations of the present invention include
one or more of the following: (a) 0.1% to 100% by weight limestone
(CaCO3); (b) 0.1% to 100% by weight dolomite (CaMg(CO3)2); (c)
0.1% to 100% by weight brucite (Mg(OH)2); (d) 0.1% to 100% by
weight calcium hydroxide, commonly called slaked lime (Ca(OH)2);
(e) 0.1% to 100% by weight Portland cement; (f) 0.1% to 100% by
weight diatomaceous earth (Si(OH)4), and (g) 0.1% to 100% by
weight rock powder (including basalt and granite), where the
weight percentages of the above components (a) through (g) are
based on the ratio of (x) the weight of the component to (y) the
total weight of all minerals applied to treat the wood.
[0017] The mineral combinations that are the subject of this
invention may be incorporated into the wood material by treatment
methods that involve contact of the wood with aqueous solutions,
emulsions or suspensions of the aforementioned mineral
combinations, either in combination or individually, added in any
order. Suitable methods of contact include, for example, brushing,
spraying, dipping, pressure and other similar treatments. With
respect to wood material such as particle board or plywood, the
mineral combinations may also be introduced in a glue-mixing
process. Preferably, application of the mineral combinations to
wood materials is by pressure treatment using a treatment cylinder
of sufficient size to be both economically practical and
convenient, using two or more atmospheres of pressure.
[0018] Impregnation of the mineral combinations into the wood
material may be accomplished by use of an aqueous carrier
solution. Preferably, the agent solution is an aqueous solution of
one or more of saltwater, seawater, brines, brackish water, and
freshwater.
[0019] The soaking of wood and other materials can be done at
standard pressure, by use of vacuum-pressure cycles, pressure or
other standard wood preservation processes. Use of vacuum-pressure
or pressure techniques reduces treatment time and increases the
level of penetration of the mineral into the wood product, thereby
increasing the effectiveness of the preservative treatment.
Preferably the treatment is conducted by subjecting the
impregnated wood material to a pressure treatment during contact
of the wood material with the aqueous treatment solution for a
sufficient time, preferably from about 5 minutes to about 72
hours.
[0020] For the aqueous mineral agent solutions, the concentration
of the mineral combination in the water varies. Choice of mineral
concentration may depend on a variety of factors, including the
species, size, type, form and other characteristics of the wood to
be treated as well as the intended end use of the treated material
and the solubility of the minerals used.
[0021] Optional treatments include addition of one or more of the
following adjuvants during the treatment process: surfactants,
acids, bases, dispersants, defoamers, corrosion inhibitors, wax,
water-repellent polymer agents, and fire retardants (such as
phosphoric acid salts, sulfuric acid salts, carbonates, borates,
nitrates, chlorides, and bromides.)
[0022] For some applications, additional optional ingredients may
be included in the method of the present invention. For example
one or more microbicides and pesticidal agents may be added to the
treatment solutions used in the method of the present invention,
thereby providing additional advantages and effectiveness. When
treatment solutions containing microbicides (such as algicides,
bactericides, fungicides and marine antifouling agents) or
pesticides (such as insecticides) are employed, the proportions
that are used will depend upon the relative efficacy of compounds
in the mixture with respect to the amount of wood material to be
treated and the targeted condition or pests to be controlled.
EXAMPLES
[0023] Some embodiments of the invention are described in detail
in the following Examples. Reference to "weight" in the Examples
refers to the percentage of the weight of all substances
(including water) applied to the wood. The Examples illustrate the
invention.
Example 1
[0024] There is formed a mixture of
3.5% by weight of limestone,
3.0% by weight of brucite,
1.0% by weight of calcium hydroxide, and
92.5% by weight of water.
Example 2
[0029] There is formed a mixture of
60% by weight of Portland cement,
10% by weight of diatomaceous earth, and
30% by weight of water.
Example 3
[0033] There is formed of a mixture of
40% by weight of dolomite,
10% by weight of brucite,
5% by weight of calcium hydroxide, and
45% by weight of seawater, brine, or fresh water.
Example 4
[0038] There is formed a mixture of
40% by weight of diatomaceous earth,
15% by weight of brucite,
3% by weight of calcium hydroxide,
3% by weight of dolomite, and
39% by weight of water.
Example 5
[0044] There is formed a mixture of
7.5% by weight of Portland cement,
0.5% by weight of brucite, and
92% by weight of water.
[0048] The mixtures in the above examples, applied using pressure
for a period of from about 5 minutes to 72 hours at a temperature
of from about 40[deg.] F. to about 250[deg.] F., will impregnate
wood with the indicated components to make the treated wood: (i) a
less desirable food for mold, fungi, bacteria, other
microorganisms, wood-boring marine organisms, and insects, (ii)
more resistant to fire, by reason of a reduced combustibility and
a raised ignition temperature, (iii) stronger and of a higher
load-bearing capacity, and (iv) more desirable to use in friction
pile foundations, as the exterior surface of the treated wood will
generate greater friction with adjacent soils. As to Examples 1
and 3 to 5, when the treated wood is placed in calcareous soil,
the brucite will chemically react with the soil to form limestone,
to create even more friction.
