U.S. patent application number 10/497374 was filed with the patent office on 2004-12-30 for catalyst system and method for preparing flame resistant materials.
Invention is credited to Yang, Charles Q.
Application Number | 20040261191 10/497374 |
Document ID | / |
Family ID | 27766026 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040261191 |
Kind Code |
A1 |
Yang, Charles Q |
December 30, 2004 |
Catalyst system and method for preparing flame resistant
materials
Abstract
Presently, multifunctional carboxylic acids, such as
1,2,3,4-butanetetracarboxylic acid (BTCA) are used to bond a
hydroxyl-functional organophosphorous oligomer to cotton fabric in
the presence of a catalyst, such as sodium hypophosphite
(NaH.sub.2PO.sub.2). However, the free carboxylic acid groups bound
to the cotton fabric form a calcium salt during home laundering,
thus diminishing the flame retardant properties of the treated
cotton fabric. Disclosed herein is a new catalyst system consisting
of hypophosphorous acid (H.sub.3PO.sub.2) and a nitrogen-containing
organic base such as triethanol amine (TEA). When the catalyst
system is present together with the polycarboxylic acid, TEA
esterifies the free carboxylic acid groups under curing conditions,
thus reducing calcium concentration on the fabric during home
laundering. It also provides nitrogen-phosphorous synergism to
enhance the flame retardant performance of the organophosphorous
compound. The cotton fabric treated with BTCA and the
hydroxyl-functional organophosphorous oligomer in the presence of
this new catalyst system demonstrate flame retardant properties
superior to that treated with NaH.sub.2PO.sub.2 as a catalyst.
Inventors: |
Yang, Charles Q; (Athens,
GA) |
Correspondence
Address: |
GREENLEE WINNER AND SULLIVAN P C
5370 MANHATTAN CIRCLE
SUITE 201
BOULDER
CO
80303
US
|
Family ID: |
27766026 |
Appl. No.: |
10/497374 |
Filed: |
August 6, 2004 |
PCT Filed: |
February 20, 2003 |
PCT NO: |
PCT/US03/05087 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60358938 |
Feb 22, 2002 |
|
|
|
Current U.S.
Class: |
8/115.51 |
Current CPC
Class: |
D06M 13/44 20130101;
D06M 15/667 20130101; D06M 13/282 20130101; D06M 13/46 20130101;
D06M 2200/30 20130101; D06M 13/192 20130101 |
Class at
Publication: |
008/115.51 |
International
Class: |
D06M 010/00 |
Claims
I claim:
1. A method of binding a flame retardant compound or composition to
cellulose comprising: applying a composition comprising a
hydroxyalkyl-functionalized flame retardant, a polycarboxylic acid,
hypophosphorous acid and a nitrogen-containing organic base to a
cellulose-containing material.
2. The method of claim 1, further comprising curing the
cellulose-containing material at a temperature of between 200 to
100.degree. C. for a time of between 20 seconds and 10 minutes.
3. The method of claim 1, wherein said flame retardant is a
hydroxylalkyl-functionalized organophosphorous compound.
4. The method of claim 3, wherein said hydroxylalkyl-functionalized
organophosphorous compound is Fyrol 51.
5. The method of claim 1, wherein said polycarboxylic acid is
1,2,3,4-butanetetracarboxylic acid.
6. The method of claim 1, wherein said nitrogen-containing organic
base is TEA.
7. The method of claim 1, wherein said nitrogen-containing organic
base is hydroxylalkyl functionalized.
8. The method of claim 1, wherein said flame-retardant is present
in the composition at 2 to 40 weight percent.
9. The method of claim 1, wherein said polycarboxylic acid is
present in the composition at 1 to 20 weight percent.
10. The method of claim 1, wherein said hypophosphorous acid is
present in the composition at 1 to 12 weight percent.
11. The method of claim 1, wherein said nitrogen-containing organic
base is present in the composition at a weight percent which
maximizes the esterification of cellulose-containing material.
12. The method of claim 11, wherein said nitrogen-containing
organic base is present in the composition at 1 to 15 weight
percent.
13. The method of claim 1, further comprising adjusting the pH to
between 2 to 4.5.
14. A catalyst system for applying flame retardants to fabric
comprising hypophosphorous acid and a nitrogen containing organic
base.
15. The catalyst system of claim 14, wherein said nitrogen
containing organic base is triethanolamine.
16. The catalyst system of claim 14, wherein said nitrogen
containing organic base is selected from the group consisting of:
triethanolamine, diethanolamine, and ethanolamine.
Description
BACKGROUND OF THE INVENTION
[0001] The durable flame retardant finishes for cotton and other
cellulosic fabrics commonly used by the industry include the
tetrakis-(hydroxylmethyl)phosphonium chloride (THPC)--based system
with the commercial name of "Proban", and dimethyl
(N-hydroxylmethylcarbamoyle- thyl) phosphonate and its analog,
known as reactive organophosphorous chemicals with the trade name
of "Pyrovetax CP" (1-2). However, the THPC technology requires an
expensive amination chamber and strict application condition
control to assure consistent performance. It is not compatible with
the overwhelming majority of the existing textile finishing
equipment, therefore is not considered to be practical for
mass-market production. The reactive organophosphorous chemicals
technology involves the use of a N-methylol phosphorous-containing
flame retardant agent and a N-methylol crosslinking agent, and both
compounds lead to the emission of high levels of formaldehyde, a
known carcinogen, during the application of the finish to cotton
fabric as well as during the use of finished cotton products by
consumers. Therefore, the flame retardant chemicals for cotton
commercially available to the textile industry are very
limited.
[0002] Polycarboxylic acids, such as 1,2,3,4-butane-tetracarboxylic
acid (BTCA), have been used as nonformaldehyde crosslinking agents
for cotton and wood pulp cellulose (4-5). Alkali metal salts of
phosphoric, phosphorous and hypophosphorous acids, such as sodium
dihydrogen phosphate (NaH.sub.2PO.sub.4), sodium phosphite
(Na.sub.2HPO.sub.3), and sodium hypophosphite (NaH.sub.2PO.sub.2),
have been used as catalysts for the esterification and crosslinking
of cellulose by polycarboxylic acids (6-9). In the presence of
those catalysts, a polycarboxylic acid molecule esterifies
cellulose and forms multiple ester linkages with cellulose, thus
crosslinking cellulose and imparting wrinkle resistance to cotton
fabrics (10).
[0003] U.S. Pat. No. 6,309,565 (Oct. 31, 2001) reports fabric
treatments with a formaldehyde-free hydroxylalkyl-functional
organophosphorous flame retardant compound (FR) and a cross-linking
agent such as 1,2,3,4-butanetetracarboxylic acid (BTCA). BTCA
apparently functions as a binding agent between the flame retardant
compound and cotton cellulose. It is reported that a catalyst such
as NaH.sub.2PO.sub.2 may be used if adequate cross-linking is to be
achieved.
[0004] Because the use of cotton in apparel and home furnishing has
became increasingly popular and new federal mandatory standards for
fabric flammability have emerged (3), there is an urgent need to
develop new and formaldehyde-free durable flame retardant finishes
for cotton and cotton blends to meet the increasing demand of the
market.
SUMMARY OF THE INVENTION
[0005] The present invention relates to a catalyst system for a
nonformaldehyde durable flame retardant finish for fabrics. One
preferred flame retardant finish comprises a
hydroxylalkyl-functional organophosphorous compound (FR) and a
polycarboxylic acid. The new catalyst system comprises (1)
hypophosphorous acid (H.sub.3PO.sub.2) or salts thereof and (2) a
nitrogen-containing organic base, such as triethanolamine (TEA).
The nitrogen-containing organic base reacts with H.sub.3PO.sub.2 in
an aqueous solution to form a salt of hypophosphorous acid (Scheme
1), which functions as the catalyst for the esterification of a
carboxylic acid with cellulose and FR. 1
[0006] More specifically, provided is a method of binding a flame
retardant compound or composition to cellulose comprising: applying
a composition comprising a hydroxyl-functional flame retardant, a
polycarboxylic acid, hypophosphorous acid and a nitrogen-containing
organic base to a cellulose-containing material. This method may
further comprise curing the cellulose-containing material. Also
provided is a catalyst system for bonding flame retardants to
fabric through a polycarboxylic acid comprising hypophosphorous
acid and a nitrogen-containing organic base.
[0007] As used herein, "polycarboxylic acid" includes any organic
structure with more than one carboxylic acid functional group. Some
examples of polycarboxylic acids include
1,2,3,4-butanetetracarboxylic acid, citric acid, poly(maleic acid),
poly(itaconic acid), copolymer of maleic acid and itaconic acid,
poly(fumaric acid) or mixtures of two or more of these acids. As
used herein, "nitrogen containing organic base" does not include
ammonia and other bases that do not contain carbon. A preferred
nitrogen containing organic base is triethanolamine (TEA).
[0008] Various fabrics and materials can be treated with the
compositions and methods of the invention as long as they contain
cellulose. Various salts of hypophosphorous acid may be used, as
known in the art. The flame retardant compound is any of a number
of flame retardants known in the art, such as a
hydroxylalkyl-functionalized organophosphorous compounds.
[0009] Monomeric, oligomeric (which generally contain from about
two to ten repeat units) and polymeric (which generally contain
over about ten repeat units) hydroxyalkyl-functional
organophosphorus flame retardant additives are intended for use
herein.
[0010] A reactive oligomeric phosphorus-containing flame retardant
of the type that is described in U.S. Pat. No. 3,695,925 to E. D.
Weil and U.S. Pat. Nos. 4,199,534, 4,268,633, and 4,335,178 to R.
B. Fearing is an example of one of the hydroxyalkyl-functional
organophosphorus flame retardants that can be used in accordance
with the present invention. A preferred embodiment has the
following structure: 2
[0011] where R.sub.1 is independently selected from methyl and
hydroxyethyl, R.sub.2 is independently selected from methyl,
methoxy, and hydroxyethoxy, and n is equal to or greater than 1.
This embodiment is made by a multistep process from dimethyl
methylphosphonate, phosphorus pentoxide, ethylene glycol, and
ethylene oxide and is available under the registered trademark
FYROL.RTM. 51 from Akzo Nobel Chemicals Inc. The endgroups are
principally hydroxyl groups.
[0012] Another class of materials for use herein includes water
soluble oligomeric alkenylphosphonate materials, examples of which
are described in U.S. Pat. Nos. 3,855,359 and 4,017,257, both to E.
D. Weil. The presence of alkenyl substituents in these materials
provide an additional mechanism for permanence utilizing free
radical curing conditions (described in the patents above). A
preferred species of this type is available under the trademark
PYROL.RTM. 76 from Akzo Nobel Chemicals Inc. and is produced by
reacting bis(2-chloroethyl) vinylphosphonate and dimethyl
methylphosphonate with the substantial elimination of methyl
chloride.
[0013] Another type of hydroxyalkyl-functional organophosphorus
flame retardant that can be employed are oligomeric phosphoric acid
esters that carry hydroxyalkoxy groups as described in U.S. Pat.
Nos. 2,909,559, 3,099,676, 3,228,998, 3,309,427, 3,472,919,
3,767,732, 3,850,859, 4,244,893, 4,382,042, 4,458,035, 4,697,030,
4,820,854, 4,886,895, 5,117,033, and 5,608,100.
[0014] Although Applicant does not wish to be bound by theory, it
is believed the nitrogen-containing organic base is bound to cotton
through its esterification with the polycarboxylic acid. It also
has the following functions:
[0015] (1) It provides phosphorous-nitrogen synergism for the FR
compound, thus improving the performance of FR.
[0016] (2) It reacts with the free carboxylic acid groups of the
polycarboxylic acid on cotton fabric under curing conditions, and
significantly increases the amount of ester and reduces the
formation of calcium salts of the carboxylic acid on the cotton
fabric. The introduction of positive charge to the cotton fabric
through TEA is thought to also replace calcium cations and prevent
them from forming salt with the free carboxylic acid groups on the
fabric. It was found that the formation of calcium salt on the
cotton fabric treated with FR and BTCA during home laundering
diminishes the performance of FR on the fabric. The reduced calcium
concentration on the fabric as a result of the use of the
nitrogen-containing organic base enhances the flame retardant
performance of the treated cotton fabric during home
laundering.
[0017] (3) It raises the pH of a finish solution, therefore
improves the strength retention of the treated cotton fabric.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1. The calcium concentration on the cotton fabric
treated with 9.6% BTCA and 4.8% NaH.sub.2PO.sub.2, cured at
185.degree. C. for 2 min, and finally treated with CaCl.sub.2
solutions of different concentrations.
[0019] FIG. 2. The calcium concentration on the cotton fabric
treated with 9.6% BTCA and 4.8% NaH.sub.2PO.sub.2, cured at
185.degree. C. for 2 min, and finally washed in tap water as
function of the HLWD cycles.
[0020] FIG. 3. The pH of the cotton fabric treated with 9.6%
BTCA/4.8% NaH.sub.2PO.sub.2 suspended in water as a function of the
added volume of the 0.10 M CaCl.sub.2 solution.
[0021] FIG. 4. The calcium concentration on the cotton fabric
treated with 24% FR, 9.6% BTCA and 4.8% NaH.sub.2PO.sub.2, cured at
185.degree. C. for 2 min, and finally treated with CaCl.sub.2
solutions as a function of the calcium concentration of the
CaCl.sub.2 solutions.
[0022] FIG. 5. The calcium concentration on the cotton fabric
treated with 24% FR, 9.6% BTCA and 4.8% NaH.sub.2PO.sub.2 and cured
at 185.degree. C. for 2 min as a function of the number of the HLWD
cycles.
[0023] FIG. 6. The titration curve of H.sub.3PO.sub.2.
[0024] FIG. 7. The ester carbonyl band intensity of the cotton
fabric treated with 24% FR, 9.6% BTCA, % H.sub.3PO.sub.2 in
combination with different concentrations of TEA, and cured at
185.degree. C. for 2 min as a function of the TEA
concentration.
[0025] FIG. 8. The calcium concentration on the cotton fabric
treated with 24% FR, 9.6% BTCA, 7% H.sub.3PO.sub.2 in combination
with TEA of different concentrations, and cured at 185.degree. C.
for 2 min, and finally treated with 0.5M CaCl.sub.2 for 30 min as a
function of the TEA concentration.
[0026] FIG. 9. The LOI (%) of the cotton fabric treated with 24%
FR, 9.6% BTCA, 7% H.sub.3PO.sub.2 in combination with TEA of
different concentrations, and cured at 185.degree. C. for 2 min and
finally subjected to 5 HLWD cycles as a function of the TEA
concentration.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The following nonlimiting examples will assist in
understanding the invention.
[0028] Materials
[0029] The fabrics used in the investigation include: (1) a dark
brown 100% cotton twill weave fabric weighing 246 g/m.sup.2; (2) a
white 60/40 cotton/polyester blend plain weave fabric weighing 136
g/m.sup.2. The flame retardant agent (FR) was a hydroxyl-functional
organophosphorous oligomer with the trade name of Fyrol 51 supplied
by Akzo Nobel Chemical Corporation, New York. BTCA, hypophosphorous
acid (H.sub.3PO.sub.2), triethanolamine (TEA), and sodium
hypophosphite (NaH.sub.2PO.sub.2) were reagent-grade chemicals
supplied by Aldrich, Wis. The melamine-formaldehyde crosslinker
with the trade name of Ecco Rez M-300 was supplied by Eastern Color
& Chemical Company, Greenville, S.C.
[0030] Fabric Treatment and Home Laundering Washing/Drying (HLWD)
Procedures
[0031] The fabric was first immersed in a finish solution
containing FR, BTCA, and the catalyst, then passed through a
laboratory padder with two dips and two nips, dried at 90.degree.
C. for 3 min, and finally cured in a Mathis curing oven at a
specified temperature. All the concentrations presented here are
based on weight (w/w, %). The wet pick-up of the cotton and
cotton/polyester blend fabrics was approximately 85 and 80%,
respectively. After curing, the treated fabric was first subjected
to a washing/drying cycle without use of a detergent (specified
here as "water wash") to remove FR and BTCA not bound to cotton and
the catalyst. The home laundering wash/dry process was done
according to AATCC Test Method 124-1996 (Appearance of Fabrics
After Repeated Home Laundering). The detergent used was a
commercial Tide detergent without bleach. The water temperature was
approximately 45.degree. C.
[0032] Fabric Performance Evaluation
[0033] The vertical flammability of treated cotton fabric was
measured according to ASTM Standard Method D6413-99. The limited
oxygen index (LOI) of the treated cotton fabric was measured
according to ASTM Standard Method D2863-97. The breaking strength
in filling direction of the treated cotton fabric was measured
according to ASTM Standard Method D5035-95.
[0034] Infrared Spectroscopy Measurement
[0035] All the infrared spectra presented are diffuse reflectance
spectra collected with a Nicolet Magna spectrometer and a Specac
diffuse reflectance accessory, and are presented in absorbance mode
(-log R/R.sub.0) for quantitative analysis. Resolution for all the
infrared spectra is 4 cm.sup.-1, and there were 100 scans for each
spectrum. Potassium bromide powder was used as a reference material
to produce a background diffuse reflectance spectrum. The treated
and cured cotton fabric was first washed in water to remove FR and
BTCA not bound to cotton and the catalyst, then treated with a 0.1
M NaOH solution at room temperature for 4 min to convert the free
carboxylic acid group on the fabric to a carboxylate anion. The
fabric sample thus treated is dried at 80.degree. C. for 5 min. To
improve sample uniformity, the fabric sample was finely ground in a
Wiley mill to form a powder before infrared spectroscopy analysis.
The ester carbonyl band intensity in the infrared spectra was
normalized against the 1318 cm.sup.-1 band associated with a C--H
bending mode of cellulose.
[0036] Determination of Phosphorous and Calcium Concentration on
the Treated Cotton Fabric
[0037] Approximately 2 g of treated cotton fabric taken from
different parts of a larger fabric specimen were ground in a Wiley
mill into a powder to improve sample uniformity. 2 ml concentrated
H.sub.2SO.sub.4 were added to 0.1 g of cotton powder. 10 ml 30%
H.sub.2O.sub.2 were added dropwise to the mixture, allowing the
reaction to subside between drops. The reaction mixture was then
heated on a hotplate at approximately 250.degree. C. to digest the
powder and to evaporate the water until dense SO.sub.3 vapor is
produced. The completely digested cotton sample as a clear solution
was transferred to a 50-ml volumetric flask, then diluted with
distilled/deionized water. The sample thus prepared was analyzed
with a Thermo-Farrell-Ash Model 965 induced current plasma atomic
emission spectrometer (ICP/AES) to determine the % concentrations
of phosphorous and calcium.
[0038] Formation of Calcium Salt on the Cotton Fabric Treated with
BTCA
[0039] The cotton fabric treated with 9.6% BTCA and 4.8%
NaH.sub.2PO.sub.2 was cured at 185.degree. C. for 2 mm. The treated
fabric was first washed in water to remove the catalyst and BTCA
not bound to cotton, then treated in CaCl.sub.2 solutions of
different concentrations at room temperature for 30 min. The
calcium concentration of the CaCl.sub.2 solutions ranged from 0.10
to 4.00%. The cotton fabric thus treated was thoroughly washed in
deionized water for 30 min to remove any residual calcium ions not
bound to the fabric, and finally dried.
[0040] The calcium concentration on the cotton fabric determined by
ICP/AES is plotted against the calcium concentration of the
CaCl.sub.2 solutions used to treat the fabric (FIG. 1). One
observes that the calcium concentration on the fabric increased as
the calcium concentration of the solution increased (FIG. 1). The
calcium concentration on the fabric reached approximately 0.3% when
the calcium concentration of the solution was increased to 1.00%,
and it stabilized at the 0.3% level as the calcium concentration of
the solution increased further (FIG. 1). Thus, the data indicate
that the calcium cations form salt with the free carboxylic acid
group on the fabric, which has low solubility in water (Scheme 3).
The formation of calcium salt on the treated cotton fabric reached
saturation when the calcium concentration in the solution was
increased to 1.00% as shown in FIG. 1. 3
[0041] The cotton fabric treated with 9.6% BTCA/4.8%
NaH.sub.2PO.sub.2 and cured at 185.degree. C. for 2 min was also
washed in tap water in the presence of a detergent. The calcium
concentration on the cotton fabric is plotted against the number of
the home laundering washing/drying (HLWD) cycles (FIG. 2). One
observes that the calcium concentration on the fabric increased as
the number of HLWD cycle was increased, and it reached
approximately 0.28% after 5 HLWD cycles (FIG. 2). The data show
that the calcium cations of the tap water form salt with the free
carboxylic acid group bound to the treated cotton fabric.
[0042] The cotton fabric treated with 9.6% BTCA/4.8%
NaH.sub.2PO.sub.2 and cured at 185.degree. C. for 2 min was ground
into a powder. 0.1 g of the powder sample was suspended in 50 ml
distilled water, and then titrated with a 0.10 M CaCl.sub.2
solution. The pH of the fiber/water mixture was plotted against the
volume of the CaCl.sub.2 solution added to the mixture (FIG. 3).
The pH of the fiber/water mixture decreased as the volume of the
added CaCl.sub.2 solution increased. The steady decline in pH value
was evidently a result of the formation of calcium salt on the
fiber as shown in Scheme 3, which liberated the proton from the
carboxylic acid groups on the fabric. The pH value stabilized at
approximately 4.65 when the volume of the CaCl.sub.2 solution was
increased to 14.0 ml, indicating the formation of calcium salt on
the fiber reached saturation. All the data demonstrated that
calcium cation reacts with the free carboxylic acid bound to the
cotton fabric to form insoluble salt.
[0043] Formation of Calcium Salt on the Cotton Fabric Treated with
FR and BTCA
[0044] The cotton fabric was treated with 24% FR, 9.6% BTCA, and
4.8% NaH.sub.2PO.sub.2, and then cured at 185.degree. C. for 2 min.
The treated fabric was washed in water to remove the FR and BTCA
not bound to cotton. The fabric was then treated in CaCl.sub.2
solutions of different concentrations at room temperature for 30
min. The calcium concentration on the cotton fabric is plotted
against the calcium concentration of the CaCl.sub.2 solutions (FIG.
4). One observes that the calcium concentration on the treated
cotton fabric increased as the calcium concentration of the
solution increased, and it stabilized at 0.4-0.5% when the calcium
concentration in solution was increased to 0.50% and above. The
cotton fabric treated with FR and BTCA was also washed in tap water
in the presence of a detergent. The calcium concentration on the
cotton fabric increased as the number of the HLVVD cycles was
increased as shown in FIG. 5. All the data presented above show
that the free carboxylic acid group on the fabric treated with FR
and BTCA also form insoluble calcium salt (Scheme 4). 4
[0045] The cotton fabric was treated with 16% FR and BTCA of
different concentrations. The fabric thus treated was subject to 10
HLWD cycles, followed by thoroughly rinsing in deionized water for
30 min to remove the calcium physically absorbed on the fabric. The
calcium concentration on the treated cotton fabric before and after
10 HLWD cycles are presented in Table 1. The calcium concentration
on the fabric before washing is insignificant, and it became
substantially larger after 10 HLWD cycles. One also observes that
the calcium concentration after laundering also increased as the
BTCA-to FR ratio was increased. Evidently, larger number of
carboxylic acid groups on the cotton fabric as a result of higher
BTCA concentration used to treat the fabric led to the increased
calcium concentration after home laundering.
[0046] The cotton fabric was treated with 24% FR, 9.6% BTCA and
4.8% NaH.sub.2PO.sub.2, cured at 185.degree. C. for 2 min, then
subjected to different number of HLWD cycles. The LOI, char length,
percent phosphorous retention, and calcium concentration of the
fabric thus treated is shown in Table 2. In spite of the fact that
the fabric still retained 89% of phosphorous on the fabric after 3
HLWD cycles, the char length exceeded 300 mm and LOI also decreased
significantly. One observes that the calcium concentration
increased from 0.008% to 0.110% after 3 HLWD cycles (FIG. 5). The
diminished flame resistance of the treated cotton fabric is due to
the formation of calcium salt of carboxylic acid on the fabric
during the laundering process. The combustion and pyrolysis of
cotton ultimately converts FR to phosphoric acid, which leads to
dehydration of cellulose via phosphorylation-dephosphorylation
cycle and retards burning (12). The calcium ions on the fabric
react with phosphoric acid and form calcium phosphate, which does
not function as a flame retardant agent. Consequently, the
flame-resistance of the treated cotton fabric deteriorates as the
amount of calcium bound to the cotton fabric increases.
[0047] When the cotton fabric was treated with 24% FR and 11.2%
melamine-formaldehyde crosslinker (M-F), and cured at 165.degree.
C. for 2 min. The treated cotton fabric was then subjected to
different number of HLWD cycles. The LOI, char length, percent
phosphorous retention and calcium concentration of the fabric thus
treated is presented in Table 3. The data indicated that the
calcium concentration of the fabric remained practically unchanged
during the home laundering process. After 5 HLWD cycles, the LOI
for the cotton fabric treated using M-F as a crosslinking agent was
29.2 with 65% of original phosphorous retained on the fabric,
whereas LOI of the fabric crosslinked by BTCA was only 24.7 with
84% of original phosphorous on the fabric. The BTCA treated fabric
failed the vertical flammability test after 3 HLWD cycles, whereas
the char length for the M-F treated fabric was only 135 mm after 15
HLWD cycles in spite of the fact that only 62% of phosphorous
remained on the fabric. Evidently, the formation of insoluble
calcium salt on the fabric is associated with the free carboxylic
acid groups, not with any phosphate group formed as a result of
possible hydrolysis of FR on the fabric. It was concluded that when
a polycarboxylic acid is used a crosslinking agent for the FR, the
free carboxylic acid group form insoluble calcium salt during the
laundering process, thus diminishing the flame retardant properties
of the treated cotton fabric.
[0048] New Catalyst System
[0049] NaH.sub.2PO.sub.2 has been the most effective catalyst for
esterification and crosslinking of cotton by a polycarboxylic acid.
In this research, the combination of H.sub.3PO.sub.2 and TEA was
used as a new catalyst system to replace NaH.sub.2PO.sub.2. 20 ml
of a 0.30 M H.sub.3PO.sub.2 was titrated with 0.30 M TEA. The pH of
H.sub.3PO.sub.2 is presented as a function of the volume of TEA
added (FIG. 6). H.sub.3PO.sub.2 is a relatively strong acid with
K.sub.a value of 5.9.times.10.sup.-2 whereas TEA is a weak base
with K.sub.b value of 5.75.times.10.sup.-7. The original pH of
H.sub.3PO.sub.2 was 1.56 before the titration was started.
H.sub.3PO.sub.2 was neutralized to form TEA salt as TEA was
gradually added as shown in Scheme 1.
[0050] The titration reached equivalent point when the volume of
added TEA reached approximately 20.30 ml. The pH was drastically
increased from 2.98 to 6.01 around the equivalent point (pH=4.8)
when only 1.00 ml of TEA (from 19.80 to 20.80 ml) was added. (FIG.
6). Based on the pH titration curve, it was calculated that
approximately 97% of H.sub.3PO.sub.2 were neutralized when the pH
reached 3.0. Since all the finish solutions containing
H.sub.3PO.sub.2/TEA were maintained at pH 3.0, the overwhelming
majority of the catalyst is in the form as TEA salt of
H.sub.3PO.sub.2.
[0051] The esterification of cotton cellulose by a polycarboxylic
acid proceeds in two steps: formation of a 5-membered cyclic
anhydride intermediate by dehydration of two adjacent carboxylic
acid groups, and the reaction between cellulose and the anhydride
intermediate to form ester (12-13). In previous research, it was
found that TEA esterifies the anhydride intermediate formed on the
cotton fabric treated with a polycarboxylic acid under curing
conditions. Consequently, the amount of anhydride not reacted
decreased whereas the amount of ester on the fabric increases
(14).
[0052] The cotton fabric was treated with 24% FR, 9.6% BTCA, 7%
H.sub.3PO.sub.2 in combination with different concentrations of
TEA. The pH of all the finish solutions was adjusted to 3.0 using
either NaOH or HCl solutions. The fabric was cured at 185.degree.
C. for 2 min, and washed in deionized water to remove any FR, BTCA
and TEA not bound to cotton. Before the fabric samples were
analyzed by FT-IR spectroscopy, the samples were treated with 0.1 M
NaOH to convert the free carboxylic acid groups to carboxylate
anions so that the ester carbonyl band was not overlapped by the
carboxylic carbonyl, therefore could be measured quantitatively
(15). The ester carbonyl of the cotton fabric thus treated is
plotted against the TEA concentration in FIG. 7. The amount of
ester formed on the treated cotton fabric increased notably as the
TEA concentration was increased, and the ester carbonyl band
intensity reached its maximum when the TEA concentration was
increased to 8%. The infrared spectroscopy data evidently show that
addition of TEA to the finish system resulted in esterification of
BTCA with TEA during the curing process, thus increasing the total
amount of ester formed on cotton. A further increase in the TEA
concentration from 8% to 14% reduces the ester carbonyl band
intensity (FIG. 7). This was because that both TEA and cotton
cellulose competed to react with BTCA, a further increase in the
esterification between TEA and BTCA led to the decrease in the
esterification between cotton and BTCA, thus reducing the total
ester bound to cotton.
[0053] The calcium concentration of the cotton fabric treated with
24% FR, 9.6% BTCA, 7% H.sub.3PO.sub.2 in combination with different
concentrations of TEA and cured at 185.degree. C. for 2 min was
treated in a 0.5 M CaCl.sub.2 solution for 30 mins. The calcium
concentration of the fabric thus treated is plotted against the TEA
concentration (FIG. 8). One observes a significant decrease in
calcium concentration as the TEA concentration was increased, and
the calcium concentration reached its minimum when the TEA
concentration was increased to 8%. Previously, it was found that
ester formation reached its maximum when TEA concentration was
increased to 8%. The reduction in calcium concentration on the
fabric as shown in FIG. 8 is obviously due to the reduction in the
amount of free carboxylic acid on the treated cotton fabric as a
result of increased esterification of BTCA by TEA. One also
observes that further increase in the TEA concentration from 8% to
14% in the finish bath did not cause further reduction in calcium
concentration.
[0054] The LOI (%) for the cotton fabric treated with FR, BTCA and
H.sub.3PO.sub.2 without the presence of TEA was only 24.1. It
increased to 30.7 when 5% TEA was presented in the finish and it
reached its maximum (31.1) when TEA concentration was 10%. The same
trend remained after the treated cotton fabric was subject to
different number of home laundering cycles. The LOI (%) of the
treated cotton fabric after 5 laundering cycles is presented as a
function of the TEA concentration in the finish system (FIG. 9).
The increased LOI is attributed to two factors: the reduction in
calcium concentration as shown in FIG. 8 and the increase in
nitrogen concentration as a result of more TEA bonding to cotton
through its esterification with BTCA. The data also indicate that a
further increase to 12% in TEA concentration reduced the LOI (FIG.
9). This is consistent with the change in ester carbonyl band
intensity as demonstrated in FIG. 7.
[0055] Based on the data presented above, it was concluded that the
TEA added to the finish system esterifies the free carboxylic acid
group, thus reducing the calcium concentration on the treated
fabric. The TEA bound to cotton through its esterification with
cellulose also provides phosphorous-nitrogen synergism.
Consequently, the H.sub.3PO.sub.2/TEA catalyst system significantly
enhances the flame retardant properties of the treated cotton
fabric.
[0056] The Performance of the Cotton Fabric Treated with FR, BTCA,
and H.sub.3PO.sub.2/TEA
[0057] The cotton fabric was treated with 28% FR, 14% BTCA and 7%
H.sub.3PO.sub.2 in combination with TEA of different
concentrations. The pH of the finish solutions was adjusted to 3.0
using either NaOH or HCl solutions. The treated fabric was cured at
185.degree. C. for 2 min. The calcium concentration and LOI of the
fabric treated with different TEA concentrations are presented in
Table 4. The data show that calcium concentration increased as the
number of laundering cycles were increased. When TEA is present,
however, the calcium concentration on the fabric was drastically
reduced and LOI was increased. One also observes that TEA
concentration at 8-10% resulted in the highest LOI. This is
consistent with the data presented in FIG. 9.
[0058] The same FR/BTCA/H.sub.3PO.sub.2 finishing system with TEA
concentration ranging from 5% to 12% was applied to a 60/40
cotton/polyester blend fabric. The treated fabric was cured at
185.degree. C. for 2 min. The calcium concentration and LOI of the
cotton fabric thus treated is presented in Table 5. It is
interesting to note that the finishing system considerably improved
the flame retardant performance of the polyester/cotton blend. The
data also show that TEA concentration of 10% led to highest LOI and
the lowest calcium concentration.
[0059] The performance of the FR/BTCA finish with different
catalysts was compared. The cotton fabric was treated with 28% FR
and 14% BTCA in the presence of two different catalysts: (1) 7%
H.sub.3PO.sub.2 in combination of 10% TEA and (2) 7%
NaH.sub.2PO.sub.2. The fabric was then cured at 185.degree. C. for
2 min. The calcium concentration, LOI, and char length of the
cotton fabric thus treated are presented in Tables 6, 7, and 8,
respectively. The calcium concentration on the fabric after 5 HLWD
cycles was increased to 0.196% when NaH.sub.2PO.sub.2 was used as
the catalyst, whereas it was only 0.045% when H.sub.3PO.sub.2/TEA
was used. Evidently, the esterification of TEA with BTCA reduces
the formation of calcium salt on the fabrics. The fabric treated
with FR, BTCA, and H.sub.3PO.sub.2/TEA showed considerably higher
LOI and shorter char length than that treated with FR, BTCA, and
NaH.sub.2PO.sub.2 (Tables 7 and 8, respectively). The treated
fabric failed the vertical flammability test after 3 HLDW cycles
when NaH.sub.2PO.sub.2 was used as the catalyst, whereas the char
length was only 91 mm after 5 HLWD cycles when H.sub.3PO.sub.2/TEA
was used (Table 8). The data clearly demonstrate that the combined
effects of reduced calcium concentration on the fabric and
phosphorous-nitrogen synergism significantly improved the flame
retardant properties of the treated cotton fabric.
[0060] Although the description contained herewith contains many
specificities, these should not be construed as limiting the scope
of the invention but as merely providing illustrations of some of
the presently-preferred embodiments of this invention. For example,
compounds other than those specifically mentioned may be used and
are included in the invention, as long as they perform the same
function. Also, times and concentrations other than those
specifically described may be used and are included in the
invention. All references cited herein are hereby incorporated by
reference to the extent not inconsistent with the disclosure
herewith.
REFERENCES
[0061] 1. E. D. Weil, "Phosphorous Flame Retardants", in
"Kirk-Other Encyclopedia of Chemical Technology", 4th ed., M.
Grayson Ed., New York, John Wiley & Sons, 1995, vol. 10,
pp976-998.
[0062] 2. M. Lewin, "Flame Retardance of Fabrics", in "Handbook of
Fiber Science and Technology: Vol II. Chemical Processing of Fibers
and Fabrics, Functional Finishes Part B", M. Lewin and S. B. Sello,
Eds, Mercel Dekker, New York, pp78-91 (1984).
[0063] 3. Federal Register, 1-1-00 ed., 16CFR Ch. 11, pp. 1610-1616
(2000).
[0064] 4. C. M. Welch, Formaldehyde-Free Durable Press Finishes,
Review of Progress in Coloration, 22, 32-41 (1992).
[0065] 5. C. M. Welch, "Tetracarboxylic Acids as Formaldehyde-free
Durable Press Finishing Agents", Textile Res. J. 58, 480-486
(1988).
[0066] 6. C. M. Welch and B. A. K. Andrews, "Catalysts and
Processes for Formaldehyde Free Durable Press Finishing of Cotton
Textiles with Polycarboxylic Acids", U.S. Pat. No. 4,820,307 (Apr.
11, 1989).
[0067] 7. C. M. Welch and B. K. Andrews, "Catalysts and Processes
for Formaldehyde Free Durable Press Finishing of Cotton Textiles
with Polycarboxylic Acids", U.S. Pat. No. 4,936,865 (Jun. 26,
1990).
[0068] 8. C. M. Welch and B. K. Andrews, "Catalysts and Processes
for Formaldehyde Free Durable Press Finishing of Cotton Textiles
with Polycarboxylic Acids", U.S. Pat. No. 4,936,865 (Dec. 4,
1990).
[0069] 9. B. K. Andrews, N. M. Morris, D. J. Donaldson and C. M.
Welch, "Catalysts and Processes for Formaldehyde Free Durable Press
Finishing of Cotton Textiles with Polycarboxylic Acids", U.S. Pat.
No. 5,221,285 (Jun. 4, 1990).
[0070] 10. C. Q. Yang and D. Wang, "Evaluation of Ester
Crosslinking of Cotton Cellulose by A Polycarboxylic Acid Using
Acid-Base Titration", Textile Res. J., 70, 615-620 (2000).
[0071] 11. J. K. Stowell, E. W. Weil, W. L. Coble,
"Formaldehyde-Free Flame Retardant Treatment for
Cellulose-Containing Materials", U.S. Pat. No. 6,309,545 (Oct. 31,
2001).
[0072] 12. M. Levin, "Flame Retardance of Fabrics", in "Handbook of
Fiber Science and Technology: Chemistry Processing of Fibers and
Fabrics", Vol. 2, Part B., ed., M. Lewin and S. B. Sello, Marcel
Dekker, New York, 1984, p86.
[0073] 13. C. Q. Yang, "Ft-IP Spectroscopy Study of the Ester
Crosslinking Mechanism of Cotton Cellulose" Textile Res. J. 61,
433-440, 1991.
[0074] 14. C. Q. Yang, "Infrared Spectroscopy Studies of the Cyclic
Anhydride as the Intermediate for Ester Crosslinking of Cotton
Cellulose by Polycarboxylic Acids. I. Identification of the Cyclic
Anhydride Intermediate", J. Polym. Sci., Part A. Polym. Chem. 33,
1187-1193 (1993).
[0075] 15. C. Q. Yang, "Infrared Spectroscopy Studies of the Cyclic
Anhydride as the Intermediate for Ester Crosslinking of Cotton
Cellulose by Polycarboxylic Acids. III. Molecular Weight of A
Crosslinling Agent", J. Polym. Sci., Part A. Polym. Chem. 35,
557-564 (1997).
[0076] 16. C. Q. Yang and G. Bakshi, "Quantitative Analysis of the
Nonformaldehyde Durable Press Finish on Cotton Fabric: Acid-Base
Titration and Infrared Spectroscopy" Textile Res. J. 66, 377-384
(1996).
1TABLE 1 The Calcium Concentration on the Cotton Fabric Treated FR
and BTCA with different BTCA-to-FR Ratio FR BTCA Ca Concentration
(%) Concentration Concentration BTCA-to-FR before after 10 (%) (%)
Ratio washing HLWD cycles 16 2.0 0.125 0.008 0.191 16 4.0 0.250
0.000 0.202 16 6.0 0.375 0.000 0.262 16 8.0 0.500 0.005 0.302 16
12.0 0.750 0.006 0.353
[0077]
2TABLE 2 The LOI, Char Length and Percent Phosphorus Retention of
the Cotton Fabric Treated with FR and BTCA. Number of HLWD Cycles
before water after water Fabric Property wash wash 1 3 5 10 15 LOI
(%) 29.0 26.5 25.8 25.3 24.7 24.1 23.2 Char Length (mm) 85 144 176
>300 >300 >300 >300 % Phosphorus Retention -- 96 88 89
84 82 75 Calcium Concentration(%) -- -- 0.110 0.102 0.196 0.240
0.297
[0078]
3TABLE 3 The LOI, Char Length, Percent Phosphorus Retention and
Calcium Concentration of the Cotton Fabric Treated with FR and
Hydroxymethylated Melamine. Number of HLWD Cycles after Fabric
Property water wash 1 5 10 15 LOI (%) 32.1 29.7 29.2 28.7 27.8 Char
Length (mm) 79 84 81 94 135 % Phosphorus -- 70 65 66 62 Retention
Calcium -- 0.044 0.039 0.029 0.024 Concentration (%)
[0079]
4TABLE 4 The LOI and calcium concentration of the 100% Cotton
Fabric Treated with 28% FR, 14% BTCA and 7% H.sub.3PO.sub.2 in the
presence of Different Concentration with TEA LOI(%) Calcium
concentration(%) TEA After After 1 After 5 After After 1 After 5
Concentration(%) water wash HLWD cycle HLWD cycles water wash HLWD
cycle HLWD cycles 0 24.1 23.6 23.5 0.041 0.101 0.196 5 30.7 29.2
27.9 0.015 0.019 0.056 8 30.9 30.2 28.1 0.003 0.011 0.021 10 31.1
30.0 28.6 0.003 0.011 0.045 12 30.2 29.7 26.3 0.006 0.007 0.031 pH
was adjust by NaOH or H Cl
[0080]
5TABLE 5 The Calcium Concentration and LOI of the 40/60
Polyester/cotton Fabric Treated with 28% FR, 14% BTCA and 7%
H.sub.3PO.sub.2 in the presence of Different Concentration with TEA
LOI(%) Calcium concentration(%) TEA After After 1 After 5 After
After 1 After 5 Concentration(%) water wash HLWD cycle HLWD cycles
water wash HLWD cycle HLWD cycles 5 27.4 26.3 25.2 0.032 0.034
0.064 8 27.6 26.7 25.7 0.001 0.012 0.037 10 28.6 27.7 25.8 0.007
0.006 0.010 12 27.6 26.3 24.7 0.000 0.008 0.035 pH was adjust by
NaOH or H Cl
[0081]
6TABLE 6 The Calcium Concentration on the Fabric Treated with FR
and BTCA in the presence of Different Catalyst System Calcium
Concentration (%) FR BTCA Catalyst Before After After 1 After 5
Concentration Concentration Concentration pH Water wash Water wash
HLWD cycle HLWD cycles 28% 14% H.sub.3PO.sub.2 7% 3.0 0.000 0.003
0.011 0.045 adjusted by TEA 28% 14% NaH.sub.2PO.sub.2 7% 2.8 0.002
0.040 0.110 0.196 adjusted by NaOH
[0082]
7TABLE 7 The LOI of the Fabric Treated with FR and BTCA in the
presence of Different Catalyst System LOI(%) FR BTCA Catalyst
Before After After 1 After 5 Concentration Concentration
Concentration pH Water wash Water wash HLWD cycle HLWD cycles 28%
14% H.sub.3PO.sub.2 7% 3.0 34.3 31.1 30.0 28.6 adjusted by TEA 28%
14% NaH.sub.2PO.sub.2 7% 2.8 29.2 26.9 25.8 24.7 adjusted by
NaOH
[0083]
8TABLE 8 The Char Length of the Fabric Treated with FR and BTCA in
the presence of Different Catalyst System Char Length(mm) FR BTCA
Catalyst Before After After 1 After 5 Concentration Concentration
Concentration pH Water wash Water wash HLWD cycle HLWD cycles 28%
14% H.sub.3PO.sub.2 7% 3.0 66 70 78 91 adjusted by TEA 28% 14%
NaH.sub.2PO.sub.2 7% 2.8 88 133 176 >300 adjusted by NaOH
* * * * *