U.S. patent application number 14/931766 was filed with the patent office on 2017-05-04 for method for reducing elemental sulfur in gypsum products.
The applicant listed for this patent is CertainTeed Gypsum, Inc.. Invention is credited to John W. College, George Glavin, Chris Hilton, Helen Ilyashenko, Yu-Zhi Kiang, Choung-Houng Lai, Sang-Ho Lee.
Application Number | 20170121183 14/931766 |
Document ID | / |
Family ID | 58634351 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170121183 |
Kind Code |
A1 |
College; John W. ; et
al. |
May 4, 2017 |
Method For Reducing Elemental Sulfur In Gypsum Products
Abstract
Disclosed are various methods for reducing levels of elemental
sulfur within gypsum products such as wall board. Gypsum sometimes
includes increased levels of elemental sulfur. Such sulfur can be
corrosive and otherwise harmful at elevated levels. The disclosure
contemplates reacting the elemental sulfur with copper to copper
sulfide. This reaction has the benefit of reducing the levels of
elemental sulfur present within the final gypsum product. The
copper can be added at any of a variety of locations in the
manufacturing process. This is a very efficient method for reducing
elemental sulfur in the production of gypsum products.
Inventors: |
College; John W.;
(Pittsburgh, PA) ; Lee; Sang-Ho; (North Grafton,
MA) ; Hilton; Chris; (Vancouver, CA) ; Kiang;
Yu-Zhi; (Vancouver, CA) ; Lai; Choung-Houng;
(Acton, MA) ; Glavin; George; (Amherst, MA)
; Ilyashenko; Helen; (Northborough, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CertainTeed Gypsum, Inc. |
Tampa |
FL |
US |
|
|
Family ID: |
58634351 |
Appl. No.: |
14/931766 |
Filed: |
November 3, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 28/145 20130101;
C04B 11/007 20130101; C01F 11/466 20130101; C04B 2111/0062
20130101; C04B 2111/10 20130101; C01G 3/12 20130101; C01G 1/12
20130101; C04B 28/145 20130101; C01F 11/468 20130101; C04B 24/10
20130101; C04B 14/42 20130101; C01P 2006/80 20130101; C04B 38/10
20130101; C04B 24/383 20130101; C04B 22/14 20130101; C04B 2103/0016
20130101; C04B 24/08 20130101; C04B 2103/20 20130101 |
International
Class: |
C01F 11/46 20060101
C01F011/46 |
Claims
1. A method for reducing of presence of elemental sulfur in a
gypsum product, the method comprising the following steps:
providing stucco to be used in the production of the gypsum
product, the stucco including a level of elemental sulfur; mixing
copper into the stucco; allowing the copper to react with the
elemental sulfur, the reaction reducing the level of elemental
sulfur within the stucco; utilizing the stucco with the reduced
level of elemental sulfur in the production of gypsum product.
2. The method as described in claim 1 wherein the reaction between
the copper and the elemental sulfur produces copper sulfide
(Cu.sub.2S).
3. The method as described in claim 1 wherein the reaction between
the copper and elemental sulfur produces copper monosulfide
(CuS).
4. The method as described in claim 1 wherein the reaction between
the copper and elemental sulfur produces copper disulfide
(CuS.sub.2).
5. The method as described in claim 1 wherein the level of
elemental sulfur within the gypsum following the reaction is below
that described in ASTM C1396M-14a.
6. A method for reducing elemental sulfur in a gypsum product, the
method comprising the following steps: forming a gypsum slurry
comprising calcium sulfate hemihydrate (CaSO.sub.41/2H.sub.2O) and
water, the gypsum slurry also including an amount of elemental
sulfur; mixing an amount of fine copper powder into the gypsum
slurry; allowing the copper to react with the elemental sulfur
within the gypsum slurry, the reaction producing copper sulfide
(Cu.sub.2S); the production of the copper sulfide (Cu.sub.2S)
reducing the amount of elemental sulfur present in the gypsum
slurry; utilizing the gypsum slurry in the production of the gypsum
product.
7. The method as described in claim 6 wherein the slurry includes a
starch and a retarder.
8. The method as described in claim 6 wherein the slurry further
comprises one or more of the following: foam, wax, glass fibers,
and sugars.
9. The method as described in claim 6 wherein the level of
elemental sulfur within the gypsum following the reaction is below
that described in ASTM C1396M-14a.
10. The method as described in claim 6 wherein the gypsum product
is a wall board.
11. A method for reducing elemental sulfur in gypsum wallboard, the
method comprising the following steps: providing a volume of
calcium sulfate dihydrate (CaSO.sub.4 2H.sub.2O) containing an
amount of elemental sulfur; crushing the calcium sulfate dihydrate
(CaSO.sub.4 2H.sub.2O) in a mill; heating and calcining the crushed
calcium sulfate dihydrate (CaSO.sub.4 2H.sub.2O) to produce calcium
sulfate hemihydrate (CaSO.sub.41/2H.sub.2O), the calcium sulfate
hemihydrate (CaSO.sub.41/2H.sub.2O) containing an amount of
elemental sulfur; mixing an amount of fine copper powder with the
calcium sulfate hemihydrate (CaSO.sub.41/2H.sub.2O), with the
weight ratio between the fine copper powder and the elemental
sulfur in the gypsum being in the range of approximately 1 to 1 to
approximately 4 to 1; allowing the copper to react with the
elemental sulfur within the heated calcium sulfate hemihydrate
(CaSO.sub.41/2H.sub.2O), the reaction producing copper sulfide
(Cu.sub.2S); the production of the copper sulfide (Cu.sub.2S)
reducing the amount of elemental sulfur (S) present in the calcium
sulfate hemihydrate (CaSO.sub.41/2H.sub.2O); utilizing the calcium
sulfate hemihydrate (CaSO.sub.41/2H.sub.2O) in the production of
gypsum wallboard.
12. The method as described in claim 11 wherein the method further
comprises the step of collecting ground fines and wherein the
copper powder is added after the ground fines are collected.
13. The method as described in claim 11 wherein zinc (Zn), iron
(Fe), manganese (Mn), nickel (Ni), or Cobalt (Co) are used in place
of the copper powder (Cu).
14. The method as described in claim 11 wherein metallic oxides are
used in place of the copper powder.
15. The method as described in claim 11 wherein the copper powder
is added to the gypsum feed stream.
16. The method as described in claim 11 wherein the copper powder
is added immediately after the formation of a stucco slurry.
17. The method as described in claim 11 wherein the copper powder
is directly added after calcination.
18. The method as described in claim 11 wherein the copper powder
is added via a stucco feed stream.
19. The method as described in claim 11 wherein a board dryer is
used to increase the efficiency of the reaction between the copper
and the elemental sulfur.
20. The method as described in claim 11 wherein the efficiency of
the reaction between the copper and the elemental sulfur is
increased via residence times within a silo.
21. The method as described in claim 11 wherein the weight ratio
between the fine copper powder and the elemental sulfur in the
gypsum is in the range of approximately 1 to 1 to approximately 4
to 1.
22. The method as described in claim 11 wherein the copper powder
is added to the calciner feed stream.
23. A method for producing a gypsum product with enhanced physical
properties, the method comprising: providing a volume of gypsum,
the gypsum containing an amount of elemental sulfur; mixing an
amount of copper powder with the gypsum; allowing the copper to
react with the elemental sulfur in the gypsum; utilizing the gypsum
in the production of the gypsum product.
24. The method as described in claim 23 wherein the amount of added
copper is greater than 500 ppm and the enhanced physical property
in the gypsum product is inhibited mold and mildew growth.
25. The method as described in claim 23 wherein copper is added in
range of approximately 20 ppm to approximately 1000 ppm and the
enhanced physical property in the gypsum product is inhibited mold
and mildew growth.
26. The method as described in claim 23 comprising the further step
of calcining the gypsum and wherein the step of mixing the copper
powder is carried out before the calcining step.
27. The method as described in claim 23 comprising the further step
of calcining the gypsum and wherein the step of mixing the copper
powder is carried out after the calcining step.
Description
TECHNICAL FIELD
[0001] This disclosure relates to a method for reducing elemental
sulfur in gypsum products. More specifically, the disclosure
relates to reducing elemental sulfur in gypsum via the addition of
copper.
BACKGROUND OF THE INVENTION
[0002] Gypsum board is one of the most widely used and versatile
building materials in the world. The basic construction for gypsum
building boards has remained unchanged for quite some time. This
construction includes a core of calcium sulfate dihydrate
(CaSO.sub.4 2H.sub.2O) that is sandwiched between opposing paper
sheets.
[0003] The gypsum can be either artificially produced or mined.
Naturally occurring gypsum must be ground and crushed in a mill
prior to use. Thereafter the ground gypsum is heated in a kettle
whereby it is calcined to produce calcium sulfate hemihydrate
(CaSO.sub.41/2H.sub.2O) (or stucco) in accordance with the
following equation:
CaSO.sub.42H.sub.2O+Heat.fwdarw.CaSO.sub.41/2H.sub.2O+11/2H.sub.2O
[0004] The calcined gypsum is thereafter mixed with water to form a
stucco slurry. Other additives can be included such as
accelerators, retarders, or starches. The slurry is advantageous
because it allows the gypsum to be formed into any of a variety of
shapes or sizes. In the manufacture of gypsum building boards, the
slurry is poured out over a bottom sheet in a manufacturing line. A
top sheet is then used to enclose the gypsum. The edges of the
lower sheet can be turned up to form the edges of the wallboard.
Further forming can take place via the use of rollers, guides, or
hinge plates that are spaced out over a series of forming
tables.
[0005] As the board passes over the forming tables, the water
reacts with the stucco to reverse the above noted equation. As a
result, the calcium sulfate hemihydrate (CaSO.sub.41/2H.sub.2O) is
converted to calcium sulfate dihydrate (CaSO.sub.4 2H.sub.2O) in
accordance with the following equation:
CaSO.sub.41/2H.sub.2O+11/2H.sub.2O.fwdarw.CaSO.sub.42H.sub.2O+Heat
[0006] After the gypsum completely sets, the boards are delivered
to a gypsum board dryer where additional water vapor is driven out
of the board. Finally, the boards are cut into desired lengths.
[0007] A significant problem has arisen regarding certain drywall
that was imported into the United States from the People's Republic
of China. Chinese drywall was imported into the United States
during the housing boom starting around 2004. The gypsum used to
produce this drywall had increased amounts of elemental sulfur.
This elemental sulfur remained in the final gypsum wallboard. The
suspicion was that the elemental sulfur produced sulfurous gas
emissions, such as carbon disulfide, carbonyl sulfide, and hydrogen
sulfide. Homeowners have reported that these emissions resulted in
various household items becoming corroded. A litany of adverse
health effects were also claimed as a result.
[0008] In response, the United States Congress passed the Drywall
Safety Act of 2012 (DSA). The DSA was signed into law in 2013, Pub.
L. No. 112-266, 126 Stat. 2437 (2013). The DSA directed the
Consumer Products Safety Commission (CPSC) to promulgate a rule
regarding acceptable levels of elemental sulfur in wallboard. In
early 2015, the CPSC determined that ASTM C1396M-14a, "Standard
Specification for Gypsum Board" was an acceptable standard that
conformed to the requirements of the DSA and was consistent with
elemental sulfur levels not associated with elevated rates of
corrosion in the home. ASTM C1396M-14a was developed by
Subcommittee C11.01 on Specifications and Test Methods for Gypsum
Products of ASTM International. The CPSC's determinations mean that
the elemental sulfur content limit in ASTM C1396M-14a shall soon be
treated as a consumer product safety rule promulgated under the
Consumer Product Safety Act (CPSA). ASTM C1396M-14a states that
Gypsum board shall contain not greater than 10 parts per million
(PPM) of orthorhombic cyclooctasulfur (S.sub.8), when tested in
accordance with Test Methods ASTM C471M.
[0009] The problems associated Chinese drywall have created a need
to find ways to reduce or eliminate elemental sulfur from gypsum
wall board. The present disclosure relates to methods of reducing
elemental sulfur in gypsum via the addition of copper. The
background art discloses various uses for copper in building
materials.
[0010] For example, U.S. Pat. No. 8,926,855 to Thomas discloses
building materials that include a dampening layer containing a
plaster and a viscoelastic polymer. In certain embodiments, the
dampening layer also includes a high atomic weight material, a high
molecular density material, or a combination thereof. One example
of such material is copper powder.
[0011] U.S. Pat. No. 6,676,744 to Merkley discloses fiber cement
composite materials using cellulose fibers loaded with inorganic or
organic substances. Copper is disclosed as one possible loading
substance for the cellulose fibers.
[0012] U.S. Pub. App. 2015/0030532 to Sahin discloses an
antimicrobial material comprising a metal ion charged with
synthesized zeolite. Silver, zinc, and copper metal ion-charged
zeolites can be used. The new construction materials are
antimicrobial and prevent microorganism growth.
[0013] Although the above referenced inventions achieve their own
individual objectives, none of the background art discloses
reducing elemental sulfur in gypsum via the addition of copper.
SUMMARY OF THE INVENTION
[0014] The method of the present disclosure provides an advantage
by producing gypsum products with reduced levels of elemental
sulfur.
[0015] An advantage is realized by mixing copper with calcined
gypsum, whereby elemental sulfur in the gypsum reacts with the
copper at an elevated dry solids temperature.
[0016] Yet another advantage is achieved by mixing copper with the
stucco prior to the addition of the water at the mixer, whereby
elemental sulfur in the slurry reacts with the copper. The slurry
typically contains 30% to 50% water. The slurry is thereafter
violently mixed to ensure good sulfur/copper contact.
[0017] A further advantage is attained by reacting copper with
heated gypsum within a board dryer to increase the reaction between
the copper and any elemental sulfur within the gypsum.
[0018] The present disclosure realizes yet another advantage by
efficiently and economically producing a gypsum product that
contains levels of elemental sulfur that are compliant with ASTM
C1396M-14a.
[0019] Another advantage is that by reducing levels of elemental
sulfur, minerals containing up to 800 ppm of elemental sulfur can
be successfully used in the production of gypsum products.
[0020] Various embodiments of the invention may have none, some, or
all of these advantages. Other technical advantages of the present
invention will be readily apparent to one skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] For a more complete understanding of the present disclosure
and its advantages, reference is now made to the following
descriptions, taken in conjunction with the accompanying drawings,
in which:
[0022] FIG. 1A is diagram of a calcination apparatus.
[0023] FIG. 1B is diagram of an additional calcination
apparatus.
[0024] FIG. 1C is a diagram of a gypsum board forming line.
[0025] FIG. 2 is a graph showing the levels of elemental sulfur
present at various points during calcination.
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] The present disclosure relates to methods for reducing
levels of elemental sulfur within gypsum products such as wall
board. Natural gypsum often includes increased levels of elemental
sulfur. Such elemental sulfur can be corrosive and otherwise
harmful at elevated levels. The disclosure contemplates reacting
the elemental sulfur with copper to produce copper sulfide. This
reaction has the benefit of reducing the levels of elemental or
orthorhombic cyclooctasulfur (S.sub.8) present within the final
gypsum product. The copper can be added at any of a variety of
locations in the manufacturing process. For example, the copper may
be added prior to any calcining of the gypsum, at the output of a
calciner, prior to the mixer, or within the mixer. The various
methods of the present disclosure are described hereinafter.
[0027] FIG. 1A illustrates an apparatus for calcining gypsum 20.
Apparatus 20 includes a gypsum conveyor 22 for transporting a
volume of gypsum from a source of stored gypsum (not shown). The
stored gypsum can be natural or synthetic gypsum or combinations
thereof. The gypsum is in the form of calcium sulfate dihydrate
(CaSO.sub.4 2H.sub.2O). It is known that calcium sulfate dihydrate
sometimes contains elevated levels of elemental sulfur (S) that can
remain in the finished gypsum product. For example, in mineral form
calcium sulfate dihydrate may contain up to 800 mg/kg (or 800 ppm)
of elemental sulfur. Processed or recycled calcium sulfate
dihydrate may contain up to 50 mg/kg (or 50 ppm) of elemental
sulfur.
[0028] In the traditional process, the stored gypsum is ground in a
mill then transported to a kettle 23 via conveyor 22, where the
gypsum is heated and calcined. The calcining kettle 23 may be
replaced by an impact mill for grinding and calcining. Calcination
can also be carried out via calcidynes and Claudius Peter (CP)
Mills. Kettle 23 includes a discharge conveyor 24 for subsequent
transport of the calcined gypsum to a hot silo or to a stucco
cooler and ultimately to a storage silo 28. An admix screw can be
provided at 29 for the purpose of transporting the calcined gypsum
to a mixer.
[0029] FIG. 1B illustrates an alternative calcining apparatus 40.
Apparatus 40 likewise includes a gypsum conveyor 42 for
transporting a volume of gypsum. This gypsum is then crushed and
calcined in an impact mill or CP mill 44. A downstream cyclone 46
and bag house 48 are also included as is known in the art. The
resulting stucco is then transported via screw 52 to storage silo
54. An additional conveyor 56 is included for transporting the
stored stucco to the admix screw as needed.
[0030] As is known, heating the ground gypsum causes calcination to
produce calcium sulfate hemihydrate (CaSO.sub.41/2H.sub.2O) (or
stucco). Calcination temperatures are generally about 300 to
320.degree. F. Calcination produces calcium sulfate hemihydrate
(CaSO.sub.41/2H.sub.2O) and water vapor in accordance with the
following equation:
CaSO.sub.42H.sub.2O+Heat.fwdarw.CaSO.sub.41/2H.sub.2O+11/2H.sub.2O
[0031] The calcium sulfate hemihydrate (CaSO.sub.41/2H.sub.2O)
likewise contains elevated amounts of elemental sulfur. This
elemental sulfur level is reduced by mixing an amount of fine
copper powder (Cu) with the calcium sulfate hemihydrate following
the calcination. In one embodiment, the copper is added to kettle
23 following calcining. However, in the preferred embodiment, the
copper is added along the discharge conveyor 24 of the calcining
kettle 23 (FIG. 1A). This allows for optimal contact between the
copper and elemental sulfur while the stucco is at an elevated
temperature. In a similar fashion, with reference to FIG. 1B, the
copper can be added to mill 44 or along conveyor 52. The amount of
copper added can range from approximately 20 ppm to approximately
1000 ppm. Once mixed, the copper chemically reacts with the
elemental sulfur within the calcium sulfate hemihydrate to produce
copper sulfide (Cu.sub.2S) in accordance with the following
equation.
2Cu+S.fwdarw.Cu.sub.2S
[0032] It is preferable that the weight ratio between the fine
copper powder and the elemental sulfur is approximately 4 to 1.
However, ratios within the range of approximately 1:1 to
approximately 4:1 can also be used. It has further been discovered
that the reaction is most efficient if carried out while the
calcium sulfate hemihydrate is still heated following calcination.
A dry reaction temperature of about 300.degree. F. has proven
effective. In this part of the process, there is good mixing in
conveyors and long reaction times in the storage silos. It must
also go through other optimum areas like the mixer and the board
dryer.
[0033] The production of copper sulfide is advantageous because it
reduces the levels of elemental sulfur present in the calcium
sulfate hemihydrate. The treated calcium sulfate hemihydrate can
then be converted into a slurry and formed into a gypsum product.
For example, the slurry can be used in a production line 26 to
produce gypsum wall board (FIG. 1C). It has been discovered that
utilizing the disclosed method reduces the amount of elemental
sulfur within the final gypsum product to levels that comply with
industry standards, such as ASTM C1396M-14a.
[0034] FIG. 1C illustrates a production line for forming gypsum
boards. The line 26 includes a supply of calcined gypsum or stucco
28. Stucco is then delivered by an add screw 32 to a mixer 34. Add
screw 32 can be used to mix water, accelerators, retarders,
starches, and other constituents. This results in the formation of
a gypsum slurry. In accordance with an alternative method of the
present disclosure, the copper powder is added via the add mix
screw 32 to the gypsum slurry. This again results in a reaction
between the elemental sulfur and copper to form copper sulfide
(Cu.sub.2S). The elemental sulfur may also react with the copper to
form either copper monosulfide (CuS) or copper disulfide
(CuS.sub.2).
[0035] The formation of copper sulfide, in turn, reduces the levels
of elemental sulfur both within the slurry and in the final gypsum
product. As is known in the art, the formed gypsum panels are
delivered to one or more dryers to completely dry the gypsum panel
before it is cut. It has been discovered that heating the panels
results in a further reaction between the copper and sulfur and
further reductions in the amount of elemental sulfur present within
the board. This also improves the efficiency of the added copper
resulting in less copper being needed to achieve the goal of 10
ppm.
[0036] The present inventors conducted various trials in which
gypsum boards were produced in accordance with the present
invention. The trials were carried out on a conventional gypsum
board production line. Various types of boards were produced,
including 5/8'' Type X fire resistant board and 1/2'' Easi-Lite.TM.
Board. Easi-Lite.TM. is a lightweight gypsum board made by
CertainTeed Gypsum, Inc. Copper powder was added to the gypsum
slurry at varying rates. The trials were conducted at varying
conveyor speeds and varying rates. The goal was to achieve an
elemental sulfur content in the resulting board of less than 10
ppm. During the first trial, as noted in Table 1, with no copper
added, the resulting elemental sulfur levels in the board ranged
from 37.3 ppm to 52.0 ppm. Neither result complies with ASTM
C1396M-14a. However, the elemental sulfur content was reduced below
the 10 ppm threshold with the addition of copper in the amount of
about 166 ppm. Further reductions were realized with copper amounts
of up to about 532 ppm.
TABLE-US-00001 TABLE 1 Testing Data from Plant Trial No. 1 Copper
Total Resulting Speed of Addition Amount Elemental Sample Board
Conveyor Rate of Copper Sulfur Number Grade (fpm) (lb/min) (ppm)
(ppm) 1 5/8 X 108 0.164 166 6.2 2 5/8 X 108 0.328 332 6.3 3 5/8 X
108 0.328 332 5.6 4 1/2 FBC 125 0.519 532 3.6 5 1/2 FBC 125 0.519
532 4.6 6 5/8'' n/a control 0 37.3 7 1/2'' n/a control 0 52.0
[0037] Subsequent trials were carried out on 1/2'' Easi-Lite.TM.
Board and a set conveyor speed of 145 fpm (Table 2). Again, as
expected, with no copper added, the resulting elemental sulfur
content was in excess of the targeted amount of 10 ppm. 172 ppm of
copper resulted in an elemental sulfur content of between 3.31 ppm
and 3.82 ppm.
TABLE-US-00002 TABLE 2 Testing Data from Plant Trial No. 2 Copper
Total Resulting Speed of Addition Amount Elemental Sample Board
Conveyor Rate of Copper Sulfur Number Grade (fpm) (lb/min) (ppm)
(ppm) 1 1/2 Easi-Lite 145 control 0 35.5 2 1/2 Easi-Lite 145
control 0 39.5 3 1/2 Easi-Lite 145 0.14 172 3.31 4 1/2 Easi-Lite
145 0.14 172 3.82 5 1/2 Easi-Lite 145 0.255 314 1.00 6 1/2
Easi-Lite 145 0.255 314 1.70 7 1/2 Easi-Lite 145 0.43 530 1.61 8
1/2 Easi-Lite 145 0.43 530 1.62 9 1/2 Easi-Lite 145 0.154 189 2.13
10 1/2 Easi-Lite 145 0.154 189 2.37 11 1/2 Easi-Lite 145 0.246 303
1.12 12 1/2 Easi-Lite 145 0.246 303 1.53
TABLE-US-00003 TABLE 2 Testing Data from Plant Trial No. 2 Copper
Total Resulting Speed of Addition Amount Elemental Sample Board
Conveyor Rate of Copper Sulfur Number Grade (fpm) (lb/min) (ppm)
(ppm) 13 1/2 Easi-Lite 145 0.429 528 1.24 14 1/2 Easi-Lite 145
0.429 528 1.35 15 1/2 Easi-Lite 145 control 0 35.1 16 1/2 Easi-Lite
145 control 0 43.4
[0038] FIG. 2 illustrates that rates of elemental sulfur (shown in
parts per million "ppm") are reduced by facilitating the
copper-sulfur reaction via increased calcination temperatures.
Calcination generally takes place at about 320.degree. F. However,
further reductions in elemental sulfur can occur if temperatures
are increased to 500.degree. F. (260.degree. C.), 572.degree. F.
(300.degree. C.) and 662.degree. F. (350.degree. C.). FIG. 2
illustrates the effect of calcining at these temperatures for about
30 min. As illustrated, the levels of elemental sulfur present in
unprocessed gypsum is about 130 ppm.
[0039] The addition of copper power (Cu) can also be used to
enhance other physical properties of the resulting gypsum product.
For example, copper has also been found to be a strong
anti-microbial and mold inhibitor. By adding copper power to the
gypsum or gypsum slurry, the resulting gypsum products have an
increased ability to resist mold and mildew growth.
[0040] The present inventors conducted a series of tests on gypsum
boards constructed in accordance with the present invention. The
testing was carried out in accordance with ASTM D3273, entitled
"Standard Test Method for Resistance to Growth of Mold on the
Surface of Interior Coatings in an Environmental Chamber." The
contents of ASTM D3273 are incorporated herein by reference. Tables
3 and 4 below indicate that varying levels of copper were added to
the subject boards. The rate of copper addition varied from 0 ppm
to 500 ppm. The tests were conducted over a span of four weeks. In
accordance with ASTM D3273, the presence of mold or mildew was
rated from 0 to 10. A score of 10 indicates that no mold growth was
detected and a score of 9 indicates that 10% of the sample showed
mold growth, and so on.
TABLE-US-00004 TABLE 3 Mold or Mildew Resistance according to ASTM
D3273 Front Side of Board 0 PPM 100 PPM 200 PPM 500 PPM Week No. Cu
Cu Cu Cu 1 10 10 10 10 2 9 10 10 10 3 7 9 10 10 4 6 7 9 10
TABLE-US-00005 TABLE 4 Mold or Mildew Rate according to ASTM D3273
Back Side of Board 0 PPM 100 PPM 200 PPM 500 PPM Week No. Cu Cu Cu
Cu 1 10 10 10 10 2 9 10 10 10 3 8 8 10 9 4 7 6 9 8
[0041] The tests reveal that without any added copper, mold and
mildew start growing on the board within two weeks with slightly
higher levels of growth on the back side of the board. However,
this growth is inhibited with copper levels of 100 ppm. Mold and
mildew are completely eradicated when copper levels approach 500
ppm. The inventors believe that the added copper acts as a mold
inhibitor in the resulting gypsum product. The added copper also
reacts to produce copper sulfide (Cu.sub.2S), which may also act as
a mold inhibitor.
[0042] The present method describes adding copper to produce copper
sulfide (Cu.sub.2S) and thereby reduce levels of elemental sulfur.
The creation of other metal sulfide products may likewise suffice
to reduce elemental sulfur levels. For example, adding zinc (Zn),
iron (Fe), manganese (Mn), nickel (Ni), cobalt (Co), or metal
oxides in place of the copper powder (Cu) may achieve similar
beneficial results in terms of both reducing elemental sulfur and
inhibiting mold.
[0043] Table 5 reflects additional testing carried out in
accordance with the present invention. This testing was carried out
by adding the copper via the admix screw at a location just before
the mixer. Although it may be preferable to add the copper upstream
of this point, adding it immediately before the mixer represents
the easiest point of introduction. The "Sample ID" reflects that
the tests were carried out on 1/2'' Easi-Lite.TM. Board. It appears
that a specified copper addition rate of 300 ppm yields targeted
results of less than 10 ppm of elemental sulfur (S). It is
envisioned that this addition rate could be brought down to
approximately 200 ppm while still achieving beneficial results.
TABLE-US-00006 TABLE 5 Additional Testing Data from Plant Estimated
Cu Measured (ppm) Elemental Sample Board (Based upon Measured Cu
Sulfur No. Grade feeder rate) (ppm) (ppm) 1 1/2 Easi-Lite 200 126
14.4 2 1/2 Easi-Lite 200 163 10.3 3 1/2 Easi-Lite 300 164 10.4 4
1/2 Easi-Lite 300 159 9.4 5 1/2 Easi-Lite 500 391 6.1 6 1/2
Easi-Lite 500 377 5.3
[0044] Although this disclosure has been described in terms of
certain embodiments and generally associated methods, alterations
and permutations of these embodiments and methods will be apparent
to those skilled in the art. Accordingly, the above description of
example embodiments does not define or constrain this disclosure.
Other changes, substitutions, and alterations are also possible
without departing from the spirit and scope of this disclosure.
* * * * *