U.S. patent application number 14/175218 was filed with the patent office on 2014-08-14 for sulfonated polyolefin-based flame retardant material.
This patent application is currently assigned to UT-Battelle, LLC. The applicant listed for this patent is UT-Battelle, LLC. Invention is credited to Christopher J. Janke, Amit K. Naskar, Felix L. Paulauskas, Charles David Warren.
Application Number | 20140225051 14/175218 |
Document ID | / |
Family ID | 51296860 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140225051 |
Kind Code |
A1 |
Naskar; Amit K. ; et
al. |
August 14, 2014 |
SULFONATED POLYOLEFIN-BASED FLAME RETARDANT MATERIAL
Abstract
Disclosed herein is a flame retardant composition comprising
sulfonated polyolefin and a SO.sub.2-scavenging material and/or a
flame retardant material that is not a sulfonated polyolefin. Also
disclosed is a flame-resistant composite comprising a host material
in which is incorporated sulfonated polyolefin as a flame retardant
composition. Further disclosed are methods for producing the flame
retardant composition and flame-resistant composites.
Inventors: |
Naskar; Amit K.; (Knoxville,
TN) ; Paulauskas; Felix L.; (Knoxville, TN) ;
Warren; Charles David; (Knoxville, TN) ; Janke;
Christopher J.; (Oliver Springs, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UT-Battelle, LLC |
Oak Ridge |
TN |
US |
|
|
Assignee: |
UT-Battelle, LLC
Oak Ridge
TN
|
Family ID: |
51296860 |
Appl. No.: |
14/175218 |
Filed: |
February 7, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61762489 |
Feb 8, 2013 |
|
|
|
Current U.S.
Class: |
252/601 ;
139/420R; 524/430; 524/442; 524/502; 524/576 |
Current CPC
Class: |
D01F 11/06 20130101;
C08K 3/22 20130101; D06M 10/06 20130101; D06M 10/008 20130101; C08K
3/22 20130101; D06M 11/44 20130101; D06M 11/36 20130101; D06M
2200/30 20130101; C08L 23/32 20130101; C08L 23/32 20130101; C08K
2201/013 20130101; C08K 3/346 20130101; D06M 11/55 20130101; D06M
2101/20 20130101; C08K 3/346 20130101; D06M 11/76 20130101 |
Class at
Publication: |
252/601 ;
524/576; 524/430; 524/442; 524/502; 139/420.R |
International
Class: |
D06M 11/55 20060101
D06M011/55; D03D 1/00 20060101 D03D001/00 |
Goverment Interests
[0002] This invention was made with government support under Prime
Contract No. DE-AC05-000R22725 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A flame retardant composition comprising sulfonated polyolefin
and a SO.sub.2-scavenging material.
2. The composition of claim 1, wherein said SO.sub.2-scavenging
material is incorporated within the sulfonated polyolefin.
3. The composition of claim 1, wherein said sulfonated polyolefin
is in the form of an object which has on its surface a layer of
said SO.sub.2-scavenging material.
4. The composition of claim 1, wherein said SO.sub.2-scavenging
material is comprised of a metal oxide.
5. The composition of claim 4, wherein said metal oxide is a
transition metal oxide.
6. The composition of claim 5, wherein said transition metal oxide
is zinc oxide.
7. The composition of claim 4, wherein said metal oxide is an
alkaline earth oxide.
8. The composition of claim 1, wherein said SO.sub.2-scavenging
material is comprised of ammonium or phosphonium groups serving as
countercations to sulfonate groups residing on or in the sulfonated
polyolefin.
9. The composition of claim 1, wherein said flame retardant
composition is further comprised of a flame retardant material that
is not a sulfonated polyolefin.
10. The composition of claim 9, wherein said flame retardant
material is comprised of a silicate-containing material.
11. The composition of claim 10, wherein said silicate-containing
material is a clay.
12. The composition of claim 1, wherein said polyolefin is selected
from polyethylene, polypropylene, polybutadiene, polyisoprene, and
combinations thereof.
13. The composition of claim 1, wherein the flame retardant
composition exhibits an elongation at break of at least 5%.
14. The composition of claim 1, wherein the flame retardant
composition exhibits an elongation at break of at least 15%.
15. A flame-resistant composite comprised of a host material
requiring flame resistance in which is incorporated sulfonated
polyolefin as a flame retardant composition.
16. The flame-resistant composite of claim 15, wherein said
flame-resistant composite further comprises a SO.sub.2-scavenging
material incorporated therein.
17. The flame-resistant composite of claim 16, wherein said
SO.sub.2-scavenging material is comprised of a metal oxide.
18. The flame-resistant composite of claim 15, wherein said flame
retardant composition further comprises a flame retardant material
incorporated therein, wherein said flame retardant material is not
a sulfonated polyolefin.
19. The flame-resistant composite of claim 18, wherein said flame
retardant material is comprised of a silicate-containing
material.
20. The flame-resistant composite of claim 15, wherein said host
material requiring flame resistance is a fabric.
21. The flame-resistant composite of claim 15, wherein said host
material requiring flame resistance is a plastic.
22. A method for producing a flame retardant composition, the
method comprising combining sulfonated polyolefin with a material
selected from a SO.sub.2-scavenging material, a flame retardant
material that is not a sulfonated polyolefin, and combination
thereof.
23. The method of claim 22, wherein said SO.sub.2-scavenging
material is incorporated into said sulfonated polyolefin.
24. The method of claim 22, wherein said SO.sub.2-scavenging
material is coated onto said sulfonated polyolefin fiber. said
sulfonated polyolefin is in the form of an object which has on its
surface a layer of said SO.sub.2-scavenging material.
25. The method of claim 22, further comprising producing the
sulfonated polyolefin fiber by sulfonating a polyolefin fiber.
26. The method of claim 22, wherein said SO.sub.2-scavenging
material is comprised of a metal oxide.
27. The method of claim 22, wherein said SO.sub.2-scavenging
composition is comprised of ammonium or phosphonium groups serving
as countercations to sulfonate groups residing on the surface of
the sulfonated polyolefin fiber.
28. The method of claim 22, wherein said flame retardant material
is comprised of a silicate-containing material.
29. A method for forming a flame-resistant composite, the method
comprising forming a composite of a sulfonated polyolefin and a
host material in need of flame resistance.
30. The method of claim 29, further comprising incorporating a
SO.sub.2-scavenging material into said flame-resistant
composite.
31. The method of claim 30, wherein said SO.sub.2-scavenging
material is comprised of a metal oxide.
32. The method of claim 30, further comprising incorporating a
flame retardant material that is not a sulfonated polyolefin into
said flame-resistant composite.
33. The method of claim 32, wherein said flame retardant material
is comprised of a silicate-containing material.
34. The method of claim 29, wherein said flame-resistant composite
is a flame-resistant textile, and said flame-resistant textile is
formed by a process comprising weaving or bonding a flame retardant
composition comprising sulfonated polyolefin fiber having an
elongation at break of at least 10% with itself and/or other fibers
of a textile.
Description
[0001] The present application claims benefit of U.S. Provisional
Application No. 61/762,489, filed on Feb. 8, 2013, all of the
contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates, generally, to flame retardant
materials, and more particularly, to sulfonated forms of such
compositions.
BACKGROUND OF THE INVENTION
[0004] Flame retardant materials are produced in large quantities
and incorporated into numerous everyday articles in order to meet
fire safety codes and regulations. Nevertheless, numerous drawbacks
and concerns exist with their use. For example, many flame
retardant substances are either too costly, toxic, or difficult to
incorporate into a particular material of interest. Thus, there is
a continuing effort to find flame retardant materials that are
effective, economical, non-toxic, and can be facilely incorporated
into other materials, such as textiles and fabrics.
SUMMARY OF THE INVENTION
[0005] The instant disclosure describes a new class of flame
retardant compositions based on sulfonated forms of neat or
recycled polyolefin-based fibers. The flame retardant compositions
described herein are advantageously highly effective, cost
efficient, and can be facilely incorporated into a range of
materials to render them flame resistant. In particular, since the
developed fibers can typically exhibit elongation characteristics
of >8%, or 12-15%, the filaments can be weaved to form flame
retardant fabric. Moreover, by appropriate measures, as further
described below, these flame retardant compositions can be rendered
substantially non-toxic without a deleterious effect on their flame
retardant abilities. In particular embodiments, the sulfonated
polyolefin fiber is combined with a SO.sub.2-scavenging material in
order to decompose toxic SO.sub.2 fumes formed when the sulfonated
polyolefin fiber is subjected to a high temperature, such as
provided by a flame.
[0006] In another aspect, the invention is directed to a
flame-resistant composite that includes the sulfonated polyolefin
flame retardant composition described above incorporated into a
material in need of flame resistance. The invention is also
directed to an article (e.g., a textile or fabric) composed
completely of the flame retardant composition described above, or
in combination with at least one other material in need of flame
resistance.
[0007] In yet other aspects, the invention is directed to methods
for producing the flame retardant composition described above, or
for producing a flame-resistant article, such as a flame-resistant
textile or fabric. In a method for producing a flame retardant
composition, the method includes combining sulfonated polyolefin
with a material selected from a SO.sub.2-scavenging material, a
flame retardant material that is not a sulfonated polyolefin, and
combination thereof. For example, the SO.sub.2-scavenging material
and/or flame retardant material can be incorporated into the
sulfonated polyolefin or can be coated onto the sulfonated
polyolefin, or both. The SO.sub.2-scavenging material in the
composition helps to avoid the deleterious exposure to thermal
decomposition products resulting from sulfonated polyolefins. In a
method for forming a flame-resistant composite, the method includes
forming a composite of a sulfonated polyolefin and a host material
in need of flame resistance. For example, in the case where the
flame-resistant composite is a flame-resistant textile, the
flame-resistant textile can be formed by a process including
weaving or bonding a sulfonated polyolefin fiber having an
elongation at break of at least 8%, 9%, or 10% with itself and/or
other fibers of a textile. The fibers can also be rendered flame
resistant before or after weaving into fabric form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1. Schematic of a polyolefin fiber that is partially
sulfonated by diffusion of sulfonating agent(s) from outside, thus
resulting in a sheath-core morphology, where sheath is sulfonated
polyolefin and core is neat or unreacted polyolefin.
[0009] FIG. 2. Thermogravimetric analysis (TGA) data of sulfonated
polyolefin and sulfonated polyolefin coated with SO.sub.2-scavenger
material (ZnO).
[0010] FIG. 3. Derivative thermogravimetric analysis data of
sulfonated polyolefin and sulfonated polyolefin coated with
SO.sub.2-scavenger material (ZnO).
[0011] FIG. 4. DSC melting endotherms of polyethylene fibers before
and after e-beam irradiation, and DSC melting endotherms after
e-beam irradiation under reactive sulfonation conditions.
DETAILED DESCRIPTION OF THE INVENTION
[0012] As used herein, the term "about" generally indicates within
+0.5, 1, 2, 5, or 10% of the indicated value. For example, a
temperature of about 25.degree. C. generally indicates in its
broadest sense 25.degree. C..+-.10%, which indicates
22.5-27.5.degree. C.
[0013] The flame retardant composition described herein includes or
is composed entirely of a sulfonated form of a polyolefin (i.e.,
sulfonated polyolefin). The sulfonated polyolefin is typically in
the form of a fiber; however, particularly as the fiber can be
broken down into particles or powder form, and with appropriate
molding techniques (e.g., melt pressing or extrusion), numerous
other shapes of the sulfonated polyolefin are possible, including
powder, particles, pellets, flakes, platelets, spheres, and the
like.
[0014] The sulfonated polyolefin may, in some embodiments, be any
of the completely or partially sulfonated polyolefin fiber
compositions known in the art as intermediates in the preparation
of carbon fiber, although the sulfonated polyolefin fiber
compositions of the art have heretofore never been considered as
flame retardants since the necessary or optimal characteristics of
sulfonated polyolefins as precursors for carbon fiber vs. their use
as flame retardants are mutually exclusive and generally in
conflict. Significantly, it has herein been found that the
sulfonated polyolefin compositions, optimized as flame retardants,
would, in many cases, be essentially useless as precursors for
carbon fiber. More specifically, many of the sulfonated polyolefin
compositions described herein, effective as flame retardants, would
produce carbon fibers with an extreme degree of brittleness, and
with unacceptably low strength and modulus. Conversely, many of the
sulfonated polyolefin fiber compositions known in the art as useful
precursors for carbon fiber may be substantially sub-optimal,
inferior, or even ineffective as a flame retardant for the instant
purposes.
[0015] The sulfonated polyolefin can be produced by any of the
methods and conditions known in the art, particularly those methods
known in the art for sulfonating polyolefin fibers. The sulfonation
methods and conditions considered herein can be any of the
processes known in the art in which a polymer fiber is exposed to a
source of SO.sub.x species (typically, SO.sub.2, preferably in an
oxidizing environment, such as O.sub.3, and/or SO.sub.3 in an inert
environment) for the purpose of sulfonating the polymer fiber. The
sulfonation methods and conditions considered herein can be, for
example, any of the processes known in the art in which a polymer
fiber is submerged in a sulfonation bath of, for example, sulfuric
acid, fuming sulfuric acid, or chlorosulfonic acid, or their
mixtures, in order to sulfonate the polymer fiber. As further
discussed below, the conditions of the sulfonation step can be
selected to either completely sulfonate or partially sulfonate the
polyolefin fiber. For example, adjustments in residence time,
processing temperature, and reactivity or concentration of the
sulfonating species will also adjust the degree of sulfonation.
Therefore, one or more of these variables can be suitably modified
to achieve a complete, partial, or specific degree of sulfonation.
The foregoing methods, commonly used in the sulfonation of
polyolefin fiber, may also be used in the sulfonation of a
polyolefin object of another shape, such as polyolefin powder,
particles, sheets, pellets, rods, tubes, spheres, flakes,
platelets, and the like.
[0016] When sulfonated by diffusion of sulfonating agents, as
described above, a fiber of cylindrical shape can possess a
morphology characterized by a sulfonated sheath and unsulfonated
core. Such a sheath-core texture of a fiber is schematically shown
in FIG. 1.
[0017] As used herein, the terms "partially sulfonated," "partial
sulfonation," "incompletely sulfonated," or "incomplete
sulfonation" all have equivalent meanings and are defined as an
amount of sulfonation below a saturated (or "complete") level of
saturation. The degree of sulfonation can be determined by, for
example, measuring the thermal characteristics (e.g., softening or
charring point, or decomposition temperature associated with
pyrolysis of incompletely sulfonated polyolefin) or physical
characteristics (e.g., density, rigidity, or weight fraction of
decomposable unsulfonated-polymer segment, or limiting oxygen
index) of the partially sulfonated polyolefin (typically fiber).
Since rigidity, as well as the softening and charring point (and
thermal infusibility, in general) all increase with an increase in
sulfonation, monitoring of any one or combination of these
characteristics can be correlated with a level of sulfonation
relative to a saturated level of sulfonation. In particular, a
polyolefin fiber or other object can be considered to possess a
saturated level of sulfonation by exhibiting a constant thermal or
physical characteristic with increasing sulfonation treatment time.
In contrast, a fiber that has not reached a saturated level of
sulfonation will exhibit a change in a thermal or physical
characteristic with increasing sulfonation treatment time.
Moreover, if the fiber with a saturated degree of sulfonation is
taken as 100% sulfonated, fibers with a lesser degree of
sulfonation can be ascribed a numerical level of sulfonation below
100%, which is commensurate or proportionate with the difference in
thermal or physical characteristic between the partially sulfonated
fiber and completely sulfonated fiber. In different embodiments,
the polyolefin precursor is sulfonated up to or less than a
sulfonation degree of 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%,
50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or 5% relative to a
saturated level of sulfonation taken as 100%. The level of
sulfonation can be further verified or made more accurate by an
elemental analysis. In some embodiments, the polyolefin fiber may
be hyper-sulfonated by use of longer sulfonation time or high
pressure in a gas phase reaction. In such cases, the degree of
sulfonation (in wt %) can be greater than 100%.
[0018] In one embodiment, to sulfonate the polyolefin object (e.g.,
powder, fiber, or a mat or paper preform thereof), the polyolefin
object is submerged into or passed through a liquid containing
sulfur trioxide (SO.sub.3), a sulfur trioxide precursor (e.g.,
chlorosulfonic acid, HSO.sub.3Cl), sulfur dioxide (SO.sub.2), or a
mixture thereof. In particular embodiments, polyolefin fiber is
passed through the liquid by pulling the fiber into the liquid from
a creel of fiber spool either unconstrained or held at a specified
tension. Typically, the liquid containing sulfur trioxide is fuming
sulfuric acid (i.e., oleum, which typically contains 5-30% (or more
particularly, 15-30%) free SO.sub.3) or chlorosulfonic acid, or a
liquid solution thereof.
[0019] In other embodiments, to sulfonate the polyolefin object,
the polyolefin object is contacted with a sulfonating gas in a
gaseous atmosphere (i.e., not in a liquid). For example, the
polyolefin object can be introduced into a chamber containing
SO.sub.2 or SO.sub.3 gas, or a mixture thereof, or a gaseous
reactive precursor thereof, or mixture of the SO.sub.2 and/or
SO.sub.3 gas with another gas, such as oxygen, ozone, or an inert
gas, such as nitrogen or a noble gas (e.g., helium or argon).
[0020] In some specific embodiments, hot melt-spun fiber jets below
the spinneret are exposed to sulfonating gas in a gaseous
atmosphere (i.e., not in a liquid). The hot melt stream of fiber
reacts with the sulfonating gas mixture. The hot, less crystalline
or non-crystalline melt reacts faster with reactive gas to yield
sulfonated polyolefin fiber.
[0021] The sulfonating liquid or gas may also include (i.e., be
admixed with) one or more additional oxidants that may favorably
adjust the density or type of oxidized groups formed on the surface
of the polyolefin object. Some examples of additional oxidants
include ozone, air, oxygen, an inorganic or organic peroxide (e.g.,
hydrogen peroxide, cumene peroxide, or benzoyl peroxide), a peroxy
acid (e.g., a peroxysulfuric or peroxycarboxylic acid), a chromate
or dichromate (e.g., K.sub.2Cr.sub.2O.sub.7), permanganate (e.g.,
KMnO.sub.4), hypochlorite (e.g., HOCl or NaOCl), chlorite,
perchlorate (e.g., NaClO.sub.4), or nitrate (e.g., HNO.sub.3 or
KNO.sub.3).
[0022] In other embodiments, to sulfonate the polyolefin object, a
polyolefin precursor resin is melt-mixed with a sulfonation
additive that evolves a SO.sub.x gas at elevated temperatures in
order to effect sulfonation at the elevated temperature. To form a
precursor fiber, the melt-mixed composite can be spun to produce a
melt-mixed composite fiber, wherein the melt-mixed composite fiber
contains polyolefin precursor resin as an unsulfonated matrix
material within which the sulfonation additive is incorporated. The
resulting melt-mixed composite fiber (i.e., "melt-spun fiber") or
other object is then heated to a desulfonation temperature
effective for the liberation of SO.sub.x gas from the sulfonation
additive. Liberation of SO.sub.x gas from the sulfonation additive
results in complete or partial sulfonation of the polyolefin matrix
under an inert or oxic environment. A particular advantage of this
melt-mixing methodology is that the amount of sulfonation of the
fiber material or other object can be carefully controlled by
precisely quantifying the amount of sulfonation material (e.g., by
weight or molar ratio of the sulfonation material with respect to
total amount of composite material). In some embodiments, a
completely sulfonated object exhibits 1 mole of sulfonate or
sulfate per mole of polyethylene repeat unit. In some embodiments,
a completely sulfonated object gains 0.5 moles of sulfonate or
sulfate per mole of polyethylene repeat unit, through a
diffusion-controlled process. In some embodiments, when
hypersulfonation is conducted, the sulfonated object may gain
greater than 0.5 moles, or at or greater than 0.55 moles, of
sulfonate or sulfate per mole of polyethylene repeat unit.
[0023] The sulfonation additive can be any solid-state compound or
material bearing reactive SO.sub.x-containing groups (typically,
--SO.sub.3H, or sultone, i.e., --(SO.sub.2--O)--, or sulfate
--(O--SO.sub.2--O)-- groups) that function to liberate SO.sub.2
and/or SO.sub.3 under elevated temperatures. In particular
embodiments, the sulfonation additive is an organic (i.e.,
carbon-containing or carbonaceous) sulfonated compound or material.
Some examples of organic sulfonated compounds or materials include
sulfonated graphene, sulfonated diene rubber, sulfonated
polyolefin, polyvinyl sulfate, sulfonated polystyrene, sulfonated
lignin, and sulfonated mesophase pitch. Such organic sulfonated
compounds are either commercially available or can be produced by
methods well known in the art (e.g., by any of the liquid or gas
sulfonation processes known in the art, as discussed above).
Inorganic non-metallic sulfates, such as ammonium sulfate, ammonium
bisulfate, or other such sulfates, can also be used as a
sulfonation additive in the precursor matrix. Moreover, to increase
compatibility of the additive with the polyolefin polymer, the
sulfonation additive (e.g., graphene or other polycyclic aromatic
compound or material) may be functionalized with hydrophobic
aliphatic chains of sufficient length (e.g., hexyl, heptyl, octyl,
or a higher alkyl chain) by methods well known in the art.
[0024] In a particular embodiment, the sulfonation additive is
elemental sulfur, which can be melt-mixed with polyolefin
precursor. To form precursor fibers, the elemental sulfur-mixed
polyolefin resin can be spun into fiber or non-woven mat form. Then
the precursor object is oxidized, such as in air, ozone, or in
oxidizing liquid bath, as described above, to obtain the sulfonated
precursor. In other embodiments, fibers are exposed to electron
beam, microwave, or UV radiation during reaction with sulfonating
agents.
[0025] In still other embodiments, to produce a sulfonated
polyolefin fiber, fibers are produced (e.g., drawn) from a
sulfonated polyolefin resin. The sulfonated polyolefin resin can be
produced by, for example, sulfonating a polyolefin resin by any of
the techniques described above. Fibers can be produced from the
sulfonated polyolefin resin by any of the fiber-producing
techniques known in the art and as herein described, e.g., by
solution spinning, gel-spinning, solvent or plasticizer-assisted
melt-spinning, or melt processing.
[0026] In another embodiment, completely or partially sulfonated
polyolefins are plasticized with a suitable (i.e., plasticizing)
solvent, such as dimethyl sulfoxide, dimethyl formamide, an oil
(e.g., an inorganic oil, such as silicone oil, or an organic oil,
such as vegetable oil) or concentrated or dilute sulfuric acid, at
varied dilutions and processed in the form of a gel at low
temperature in a coagulation bath to obtain solution-spun
completely- or partially-sulfonated fibers. In particular
embodiments, sulfonated additives, such as organic sulfonated
compounds, are incorporated into the fiber by doping them into the
plasticized polymer gel. Sulfonated additives serve as a source of
SO.sub.x gas at elevated temperatures and serve as sulfonating
agents in an oxic environment.
[0027] The period of time (i.e., residence time) that the
polyolefin fiber or other object is exposed to the sulfonating
species at the sulfonating temperature, as well as the temperature
during exposure to the sulfonating species (i.e., sulfonation
temperature) can be suitably adjusted to provide a complete
sulfonation or a level of sulfonation below a complete sulfonation
(i.e., partial sulfonation). In some embodiments, the degree of
sulfonation (DS) can be determined or monitored at points during
the process by use of thermogravimetric analysis (TGA), dynamic
mechanical analysis (DMA), density measuring device, or other
suitable analytical technique.
[0028] The sulfonation temperature is generally below a
carbonization temperature, and more typically, at least 0.degree.
C., 10.degree. C., 20.degree. C., 30.degree. C., 40.degree. C., or
50.degree. C., and up to 300.degree. C. In different embodiments,
the sulfonation temperature is precisely or about 30.degree. C.,
40.degree. C., 50.degree. C., 60.degree. C., 70.degree. C.,
80.degree. C., 90.degree. C., 100.degree. C., 110.degree. C.,
120.degree. C., 130.degree. C., 140.degree. C., 150.degree. C.,
160.degree. C., 170.degree. C., 180.degree. C., 190.degree. C.,
200.degree. C., 210.degree. C., 220.degree. C., 230.degree. C.,
240.degree. C., 250.degree. C., 260.degree. C., 270.degree. C.,
280.degree. C., 290.degree. C., or 300.degree. C., or a sulfonation
temperature within a range bounded by any two of the foregoing
values (for example, at least or above 30.degree. C., 40.degree.
C., 50.degree. C. and up to or less than 200.degree. C.,
250.degree. C., or 300.degree. C.; or at least or above 50.degree.
C. and up to or less than 160.degree. C., 170.degree. C., or
180.degree. C.; or at least or above 70.degree. C. and up to or
less than 120.degree. C., 140.degree. C., 160.degree. C., or
180.degree. C.).
[0029] The residence time at sulfonation is very much dependent on
several variables, including the sulfonation temperature used,
concentration of sulfonating agent in the reaction medium, level of
applied tension (if any), crystallinity of the precursor polymer,
and the thickness of the polyolefin fiber or other object. The
residence time is also dependent on the sulfonation method used
(i.e., liquid or gas phase processes). As would be appreciated by
one skilled in the art, the degree of sulfonation achieved at a
particular sulfonating temperature and residence time can be
replicated by use of a higher sulfonation temperature at a shorter
residence time, or by use of a lower sulfonation temperature at a
longer residence time. Similarly, the residence time required to
achieve a degree of sulfonation in a polyolefin fiber or other
object of a certain thickness may result in a higher degree of
sulfonation in a thinner fiber or smaller object and a lower degree
of sulfonation in a thicker fiber or larger object with all other
conditions and variables normalized.
[0030] Generally, for polyolefin fibers having a thickness in the
range of 0.5 to 50 microns, a residence time at sulfonation of up
to about 90 minutes provides a partial sulfonation (i.e., where
sulfonation has not occurred through the entire diameter of the
fiber through the core, thus producing a surface-sulfonated
polyolefin fiber), whereas a residence time above 90 minutes
generally provides a complete sulfonation for the indicated
thickness. In different embodiments, depending on such variables as
the sulfonation temperature and fiber thickness or object size, the
residence time at sulfonation may be suitably selected as
precisely, about, up to, or less than 360 minutes, 300 minutes, 240
minutes, 180 minutes, 150 minutes, 120 minutes, 90 minutes, 60
minutes, 30 minutes, 20 minutes, 10 minutes, 5 minutes, or 1
minute, or a residence time within a range bounded by any two of
the foregoing values. During sulfonation, which is a diffusion
controlled process, a tensile stress of any suitable degree can be
employed, such as a tensile stress of 0, 1, 5, 10, or 15 MPa, or
within a range thereof. Precursor crystallinity depends on the
nature of the polymer and molecular orientation in the fiber form
and typically has a value from 0 to 80%.
[0031] Generally, for polyolefin fibers having a thickness in the
range of 15 to 20 microns, complete sulfonation (i.e., to the core
of the fiber) will occur at: a sulfonation temperature of
150.degree. C. or greater when employing a sulfonation residence
time of about 5-10 minutes or greater; or a sulfonation temperature
of 140.degree. C. or greater when employing a residence time of
about 10-15 minutes or greater; or a sulfonation temperature of
130.degree. C. or greater when employing a residence time of about
15-20 minutes or greater; or a sulfonation temperature of
120.degree. C. or greater when employing a residence time of about
20-25 minutes or greater; or a sulfonation temperature of
110.degree. C. or greater when employing a residence time of about
25-30 minutes or greater; or a sulfonation temperature of
100.degree. C. or greater when employing a residence time of about
30-35 minutes or greater; or a sulfonation temperature of
90.degree. C. or greater when employing a residence time of about
35-40 minutes or greater; or a sulfonation temperature of
70.degree. C. or greater when employing a residence time of about
40-45 minutes or greater. Therefore, for any of the foregoing
examples, a reduction in sulfonation temperature or residence time
should generally have the effect of achieving a partial sulfonation
(i.e., a surface sulfonation) for polyolefin fibers having a
thickness in the range of 15 to 20 microns.
[0032] The above exemplary sulfonation temperatures and residence
times are not meant to be taken precisely, but as approximate and
typical for polyolefin fibers having a thickness in the range of 15
to 20 microns. For polyolefin fibers having a thickness below the
aforesaid range, lower sulfonation temperatures and/or lower
residence times may be used to achieve the same effect or if a
partial sulfonation is desired; and likewise, for polyolefin fibers
having a thickness above the aforesaid range, higher sulfonation
temperatures and higher residence times can be used to achieve the
same effect, or the same or lower sulfonation temperatures and/or
residence times may be used to achieve a partial sulfonation.
Moreover, generally, for polyolefin fibers having a thickness in
the range of 15 to 20 microns, a residence time at sulfonation of 2
minutes is too short to achieve complete sulfonation (to the core
of the fiber) at a sulfonation temperature of 160.degree. C. or
less, and a residence time of 1 minute or less is generally too
short to achieve complete sulfonation at a sulfonation temperature
of 200.degree. C. or less. In particular embodiments, a partially
sulfonated tow of filaments of 1 to 30 micron thicknesses is
produced by varying one or more of the above parameters. The
foregoing exemplary combinations of sulfonation temperatures and
residence times are particularly relevant to liquid phase and gas
phase sulfonation processes described above.
[0033] In particular embodiments, a partial sulfonation process is
employed on the polyolefin object. Particularly when a liquid phase
or gas phase sulfonation process is used, the partial sulfonation
process results in a surface-sulfonated polyolefin fiber or other
object (i.e., which possesses an unsulfonated core). The
surface-sulfonated polyolefin object is achieved by judicious
selection of sulfonation temperature and residence time,
appropriate for the fiber thickness or object size, that halts
sulfonation before the entire core of the object becomes
sulfonated. Generally, this is achieved by limiting the residence
time at a particular sulfonation temperature to a time below that
which would result in complete sulfonation through the core.
Moreover, by adjusting the residence time, the thickness of the
unsulfonated core and sulfonated surface can be correspondingly
adjusted. For example, increasing the residence time at a
particular sulfonation temperature would have the effect of
thickening the sulfonated surface and narrowing the unsulfonated
core, while decreasing the residence time at a particular
sulfonation temperature would have the effect of reducing the
thickness of the sulfonated surface and thickening the unsulfonated
core.
[0034] If desired, the thickness of the sulfonated surface and
unsulfonated core can be further adjusted by including an
autocatalytic solid-state desulfonation-sulfonation step (i.e.,
"desulfonation step" or "desulfonation process") at the interface
of the sulfonated sheath and unsulfonated core (i.e., "sheath-core
interface"). During the desulfonation-sulfonation process, the
aforesaid interface gradually propagates towards the core. In the
desulfonation process, the surface-sulfonated polyolefin object is
heated to a desulfonation temperature effective for the liberation
of SO.sub.x gas from the sulfonated surface. As the sulfonated
sheath is rigid and becomes crosslinked after desulfonation, in the
sulfonation phase, SO.sub.x gas molecules liberated from the
surface migrate toward the core of the object, thereby partially
sulfonating additional polymeric material toward the core. This
results in a narrower unsulfonated core and thicker sulfonated
surface, or eventually, partial sulfonation throughout the object
including through the core. The higher the temperature and the
longer the residence time at the desulfonation temperature, the
narrower the unsulfonated core and the thicker the crosslinked
sheath. In some embodiments, the desulfonation temperature is
employed for a period of time less than the time required for the
entire polyolefin object to be partially sulfonated through the
core. The instant application also includes the possibility of
employing a desulfonation step for a period of time effective to
partially sulfonate the polyolefin object through the core. In the
foregoing embodiment, no unsulfonated core remains.
[0035] When a desulfonation process is employed, the desulfonation
temperature can independently be selected from any of the
sulfonation temperatures and residence times provided above (e.g.,
at least 30.degree. C., 40.degree. C., 50.degree. C., 60.degree.
C., or 70.degree. C., and up to or less than 120.degree. C.,
140.degree. C., 160.degree. C., 180.degree. C., 200.degree. C.,
250.degree. C., or 300.degree. C.). Moreover, a desulfonation
(inverse sulfonation) process is generally practiced herein in the
absence of an external sulfonating source, thereby not further
adding sulfonating species to the polyolefin object, but limiting
the amount of sulfonating species to the amount present in the
sulfonated surface or the amount incorporated into the sulfonated
polyolefin object on completion of the sulfonation process. The
desulfonation process is generally practiced herein in an
oxygen-containing (i.e., O.sub.2-containing or oxic) environment,
such as air or an artificial oxygen-inert gas atmosphere, which may
be conducted at either standard pressure (e.g., 0.9-1.2 bar),
elevated pressure (e.g., 2-10 bar), or reduced pressure (e.g.,
0.1-0.5 bar). In other embodiments, a pressure of precisely, about,
or at least 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 bar, or
a pressure within a range therein, is employed.
[0036] In some embodiments, the sulfonation and/or desulfonation
process includes exposing the fiber or other object (before,
during, and/or after the sulfonation or desulfonation process) to
radiative energy. The radiative energy can be, for example,
electromagnetic radiation (e.g., ultraviolet, X-ray, infrared, or
microwave radiation) or energetic particles (e.g., electron or
neutron beam). In the case of electromagnetic radiation, the
radiation may be dispersed or collimated, as in a laser. In some
embodiments, the radiative energy is ionizing, while in other
embodiments it is not ionizing. The polyolefin fiber or other
object may alternatively or additionally be exposed to radiative
energy before, during, or after sulfonation. In some embodiments,
electromagnetic or energetic particle radiation is not
employed.
[0037] In some embodiments, in the case of a polyolefin fiber, the
sulfonation and desulfonation processes are practiced without
applying a stress (tension) along the length of the fiber. In other
embodiments, either the sulfonation or desulfonation process, or
both, are practiced by applying a stress along the fiber length.
The stress can be applied to, for example, avoid fiber shrinkage or
to improve the strength or modulus of the fiber.
[0038] The polyolefin precursor to be sulfonated can be, for
example, a poly-.alpha.-olefin, such as polyethylene,
polypropylene, polybutylene, polyisobutylene, ethylene propylene
rubber, or a chlorinated polyolefin (e.g., polyvinylchloride, or
PVC), or a polydiene, such as polybutadiene (e.g.,
poly-1,3-butadiene or poly-1,2-butadiene), polyisoprene,
dicyclopentadiene, ethylidene norbornene, or vinyl norbornene, or a
homogeneous or heterogeneous composite thereof, or a copolymer
thereof (e.g., EPDM rubber, i.e., ethylene propylene diene
monomer). In the case of polyethylene, the polyethylene can be any
of the types of polyethylene known in the art, e.g., low density
polyethylene (LDPE), linear low density polyethylene (LLDPE), very
low density polyethylene (VLDPE), high density polyethylene (HDPE),
medium density polyethylene (MDPE), high molecular weight
polyethylene (HMWPE), and ultra high molecular weight polyethylene
(UHMWPE). In the case of polypropylene, the polypropylene can also
be any of the types of polypropylenes known in the art, e.g.,
isotactic, atactic, and syndiotactic polypropylene. The polyolefin
precursor may or may not also be derived from, or include segments
or monomeric units of other addition monomers, such as styrene,
acrylic acid, methacrylic acid, methyl acrylate, methyl
methacrylate, vinyl acetate (as well as partially or fully
hydrolyzed derivatives of vinyl acetate, such as vinyl alcohol),
terephthalate (e.g., as polyethylene terephthalate, or PET), and
acrylonitrile. In some embodiments, these other addition monomers
are included in no more than, or less than, for example, 50, 60, or
70% by monomer number or weight in the polyolefin precursor. The
polyolefin may also be either in virgin, compounded, or recycled
form.
[0039] The sulfonated polyolefin object (or polyolefin precursor)
can have any desired thickness (i.e., diameter, particularly for
the case of a fiber) or size. For example, in different
embodiments, the fiber can have a thickness of precisely, about, at
least, above, up to, or less than, for example, 0.1, 0.2, 0.5, 1,
2, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100 microns, or a
thickness within a range bounded by any two of these values. In
some embodiments, the fiber is in the form of a tow, while in other
embodiments the fiber is in the form of a single filament.
Continuous filaments or tows from very low count (<500) to very
high counts (>50 k) are considered herein. Such fibers may also
be stapled or chopped (short-segment). The polyolefin fiber
precursor may also be in the form of a fiber, film, yarn, fabric,
mesh, or felt. In the case of a non-fibrous sulfonated polyolefin
object, the object may have one or more of its dimensions
independently selected from any of the thicknesses provided above,
or it may have one, two, or all of its dimensions substantially
larger, e.g., 250, 500, 750, 1000, or 1500 microns.
[0040] The polyolefin fiber precursor can be produced by any of the
methods known in the art. In some embodiments, the fiber precursor
is produced by a melt-spinning (i.e., melt-extrusion) or other
variants of melt-processing (i.e., melt-blowing). In other
embodiments, the fiber precursor is produced by a solution-spinning
process (fiber is produced by coagulation of solid fiber from
solution of the polymer in a solvent). The conditions and
methodology employed in melt-spinning and solution-spinning
processes are well-known in the art. Moreover, the fiber precursor
may be produced by a single or bi-component extrusion process. The
conditions and methodology employed in single or bi-component
extrusion processes are also well-known in the art.
[0041] The sulfonation of polyolefin materials induces flame
retardancy. The higher the degree of sulfonation, the higher the
flame-resistance. Thus, depending on the degree of sulfonation, or
depending on the composition of the material, the limiting oxygen
index of the material can be tailored. However, a sulfonated
material during thermal exposure (above 100.degree. C.) generally
produces SO.sub.x. For example, a sulfonic acid derivative of a
polyolefin is known to produce SO.sub.2 and H.sub.2O. The release
of SO.sub.x is generally known to induce toxic effects in a human;
thus, its mitigation, as described herein, is of great
importance.
[0042] In some embodiments, the sulfonated polyolefin object,
described above, is combined with a SO.sub.2-scavenging material.
The SO.sub.2-scavenging material can be any material, generally a
solid, but possibly a liquid, that functions to scavenge SO.sub.2
and/or a related gas (e.g., any sulfur-containing or SO.sub.x gas
or liquid) formed during decompositional heating of the sulfonated
polyolefin.
[0043] In a first set of embodiments, the SO.sub.2-scavenging
material is selected from one or a combination of metal oxides,
particularly those having an effective or pronounced ability to
scavenge SO.sub.2 and related gases. The metal oxide can be, for
example, an alkaline earth oxide (e.g., MgO or CaO), or a
transition metal oxide, particularly oxides of the first row of
transition metals, such as oxides of Sc, Ti, V, Cr, Mn, Fe, Co, Ni,
Cu, or Zn, wherein ZnO is particularly preferred.
[0044] In a second set of embodiments, the SO.sub.2-scavenging
material is a carbonate or bicarbonate compound, such as a metal,
ammonium, or phosphonium carbonate or bicarbonate. Any of the
metals described above are considered herein in their carbonate or
bicarbonate form, such as the alkaline earth metal carbonates and
bicarbonates (e.g., MgCO.sub.3 and CaCO.sub.3, e.g., limestone), as
well as the alkali metal carbonates and bicarbonates (e.g.,
Na.sub.2CO.sub.3 and NaHCO.sub.3).
[0045] In a third set of embodiments, the SO.sub.2-scavenging
material is a hydroxide compound, such as a metal, ammonium, or
phosphonium hydroxide. Any of the metals described above are
considered herein in their hydroxide form, particularly the alkali
metal hydroxides (e.g., LiOH, NaOH, and KOH), alkaline earth
hydroxides (e.g., Mg(OH).sub.2, Ca(OH).sub.2, Sr(OH).sub.2, and
Ba(OH).sub.2), main group hydroxides (e.g., Al(OH).sub.3), and
transition metal hydroxides.
[0046] In a fourth set of embodiments, the SO.sub.2-scavenging
material is a compound containing ammonium or phosphonium groups.
When such compounds are combined with the sulfonated polyolefin, it
is believed that the positively charged ammonium or phosphonium
groups form a complex with negatively charged sulfur-containing
(e.g., sulfonate) groups in the sulfonated polyolefin. Without
being bound by any theory, it is believed that the formed complex
substantially inhibits the sulfur-containing groups from
decomposing into SO.sub.2 fumes.
[0047] The ammonium group can be, for example, inorganic ammonium
(i.e., NH.sub.4.sup.+), or an organic ammonium of the formula
NR.sub.4.sup.+, wherein the four R groups are independently
selected from H and hydrocarbon groups (for example, methyl, ethyl,
n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, t-butyl, benzyl,
and phenyl), with at least one R group being a hydrocarbon group.
Some specific examples of organic ammonium groups include
methylammonium, dimethylammonium, trimethylammonium, and
tetramethylammonium, and ammonium groups in which one or more of
the methyl groups in the foregoing examples are independently
replaced with any of the other exemplary hydrocarbon groups
mentioned above.
[0048] The phosphonium group can be, for example, of the formula
PR.sub.4.sup.+, wherein the four R groups are independently
selected from H and hydrocarbon groups (e.g., as provided above)
with at least one R group being a hydrocarbon group. Some specific
examples of phosphonium groups can be derived by substituting
nitrogen with phosphorus in examples provided above for ammonium
groups.
[0049] In other embodiments, the ammonium or phosphonium group is
cyclic or bicyclic in nature, i.e., a cyclic hydrocarbon group
having one or more ring nitrogen or phosphorus atoms. Some examples
of ammonium ring groups include piperidinium, pyrrolidinium,
imidazolium, pyridinium, and pyrazinium groups. An example of a
phosphonium ring group is a charged phosphabenzene or P-spiro
bicyclic phosphonium group.
[0050] The anion in the ammonium and phosphonium compound can be
any anion, but preferably an anion that permits the facile exchange
with sulfur-containing anions in the sulfonated polyolefin and that
does not adversely affect the flame-resisting and physical
properties of the sulfonated polyolefin. The anion can be, for
example, a halide (e.g., chloride, bromide, or iodide), hydroxide,
nitrate, sulfate, hydrogensulfate, phosphate, hexafluorophosphate,
carbonate, formate, acetate, and triflate.
[0051] In some embodiments, any two or more of the above
SO.sub.2-scavenging materials can be used in combination. In other
embodiments, one or more of any of the above-mentioned classes or
specific types of SO.sub.2-scavenging materials are excluded from
the above-described sulfonated flame retardant composition or
excluded from a flame-resistant composite in which the sulfonated
flame retardant composition is incorporated.
[0052] By having the sulfonated polyolefin and SO.sub.2-scavenging
material in a combined state is meant that the SO.sub.2-scavenging
material is in physical contact with at least a portion of the
sulfonated polyolefin composition. The sulfonated polyolefin
composition is made to be in contact with the SO.sub.2-scavenging
material in any suitable manner and by any suitable means, provided
that the SO.sub.2-scavenging material is not substantially hindered
or obviated from scavenging SO.sub.2 gas produced by the sulfonated
polyolefin at a temperature at which SO.sub.2 gas is produced.
Moreover, as the development of SO.sub.2 fumes is desirably
substantially eliminated or prevented, the SO.sub.2-scavenging
material is preferably included in an amount and spatial
arrangement that permits the substantial elimination or prevention
of SO.sub.2 fumes from the entire sulfonated polyolefin object used
monolithically or as a fire retardant in another material.
[0053] By a first particular embodiment, the SO.sub.2-scavenging
material can be incorporated within the sulfonated polyolefin
object by, for example, admixing, blending, or compounding (i.e.,
combining) a sulfonated polyolefin and SO.sub.2-scavenging material
to form a sulfonated composite. The resulting composite may be
substantially homogeneous or relatively or substantially
heterogeneous in its distribution of SO.sub.2-scavenging material.
A substantially homogeneous distribution of SO.sub.2-scavenging
material generally possesses particles of SO.sub.2-scavenging
material having a size of up to or less than, for example, 1
micron, 500 nm, 100 nm, 50 nm, or 20 nm in size evenly distributed
in the sulfonated polyolefin matrix. Alternatively, the
substantially homogeneous distribution may not be a distribution of
SO.sub.2-scavenging particles, but a distribution of
SO.sub.2-scavenging molecules. A heterogeneous distribution of
SO.sub.2-scavenging material generally possesses particles having a
size greater than 1 micron, or at least or greater than 2, 5, 10,
50, 100, 200, or 500 microns in the sulfonated polyolefin matrix.
Using shaping techniques, such as cutting, powderizing, molding,
and/or pressing techniques known in the art, various shapes of the
sulfonated composite material can be made.
[0054] By a second particular embodiment, the SO.sub.2-scavenging
material is in the form of a coating (i.e., layer) on the surface
of the sulfonated polyolefin fiber or other object. The coating
may, in some embodiments, completely cover the entire surface of
the sulfonated polyolefin object, whereas in other embodiments, the
coating may cover a portion, typically at least 50%, 60%, 70%, 80%,
90%, or 95% of the surface, of the sulfonated polyolefin object. In
different embodiments, the coating of the SO.sub.2-scavenging
material can have a uniform or average thickness of about, at
least, greater than, up to, or less than, for example, 0.1, 0.2,
0.5, 1, 2, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100
microns, or a thickness within a range bounded by any two of these
values.
[0055] The SO.sub.2-scavenging material can be coated onto the
sulfonated polyolefin object by any suitable means. In particular
embodiments, the sulfonated polyolefin object is contacted with a
fluidized bed of a powderized form of the SO.sub.2-scavenging
material in order to deposit a layer of the SO.sub.2-scavenging
material onto the sulfonated polyolefin object. The powderized form
of the SO.sub.2-scavenging material can be made of particles having
any suitable uniform or average diameter, including diameters
corresponding to any of the exemplary coating thicknesses provided
above, or a smaller uniform or average diameter of at least,
greater than, up to, or less than, for example, 5, 10, 15, 20, 30,
40, or 50 nm. In other embodiments, a layer of the
SO.sub.2-scavenging material is deposited by contacting the
sulfonated polyolefin object with a liquid solution in which the
SO.sub.2-scavenging material is dissolved, dispersed, or suspended,
and then drying the liquid coating, with optional re-application of
the liquid solution followed by drying, if desired, to provide a
coating of desired thickness. Thus, the SO.sub.2-scavenging
material can be applied on sulfonated fibers, films, or fabrics by
deploying a method similar to that of the textile sizing or finish
application process.
[0056] In some embodiments, after an initial or final layer of the
SO.sub.2-scavenging material has been deposited, the layer may be
subjected to a post-processing step in which the layer is made to
coalesce into a resilient layer and/or become strongly adhered with
the sulfonated polyolefin. The post-processing step may include,
for example, exposure to a crosslinkable resin, followed by curing.
In some embodiments, curing can be achieved by alternative
cross-linking methods similar to deposition of external energy
(such as electron beam) for short duration. Alternatively, the
sulfonated polyolefin object may be pre-treated, prior to
deposition of a layer of the SO.sub.2-scavenging material, with a
substance that forms or facilitates a strong bonding interaction
between the sulfonated polyolefin and the SO.sub.2-scavenging
material.
[0057] The SO.sub.2-scavenging material can be included in or on
the sulfonated polyolefin object in any suitably effective amount.
In different embodiments, the SO.sub.2-scavenging material is
included in or on the sulfonated polyolefin object in an amount of
about, at least, above, up to, or less than, for example, 1, 2, 3,
4, 5, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45, or 50 wt %, or a wt %
within a range bounded by any two of the foregoing exemplary
values, wherein the wt % is with respect to the combined weight of
the SO.sub.2-scavenging material and sulfonated polyolefin.
[0058] In some embodiments, the sulfonated polyolefin object,
described above, with or without a SO.sub.2-scavenging material, is
combined with a flame retardant material that is not a sulfonated
polyolefin. The term "combined", used herein, may have any of the
same meanings as provided above for the SO.sub.2-scavenging
material, such as being incorporated within (e.g., dispersed as
particles, fibers, or molecules in the sulfonated polyolefin
matrix) or as a layer on the sulfonated polyolefin object.
Moreover, any of the methods for incorporating an
SO.sub.2-scavenging material into the sulfonated polyolefin, as
described above, are also applicable for incorporating the flame
retardant material into the sulfonated polyolefin. In some
embodiments, the flame retardant material has the same composition
as the SO.sub.2-scavenging material; thus, one substance may
function as both a SO.sub.2-scavenging material and a flame
retardant material. In other embodiments, the flame retardant
material has a composition different than the SO.sub.2-scavenging
material. In the latter embodiment, the flame retardant material
normally does not have SO.sub.2-scavenging ability, and the
SO.sub.2-scavenging material normally does not have flame retarding
ability.
[0059] The flame retardant material can be any of the inorganic or
organic flame retardant materials known in the art, except that it
preferably does not adversely affect the physical properties of the
sulfonated polyolefin for use as a flame retardant, and can be
easily integrated into or on the sulfonated polyolefin. Some
examples of flame retardant materials include metal hydroxides or
hydrates (e.g., aluminum hydroxide or magnesium hydroxide), red
phosphorus, boron compounds (e.g., borates and boric acid),
organochlorides, organobromides (e.g., decabromodiphenylether and
tetrabromobisphenol A), organophosphorus compounds (e.g.,
organophosphates), carbonate minerals (e.g., huntite), antimony
compounds (e.g., antimony trioxide, sodium antimonate, and antimony
pentoxide), and combinations thereof. In other embodiments, the
flame retardant material is a silicate-containing compound or
material, such as a silicate-containing mineral, such as silica,
feldspar, talc, olivine, tourmaline, serpentine, chrysotile,
amphibole, crocidolite, asbestiform, asbestos, mullite, or a clay
(e.g., a kaolin, serpentine, montmorillonite, illite, mica,
glauconite, chlorite, vermicullite, attapulgite, or sepiolite). In
yet other embodiments, the flame retardant material is a form of
elemental carbon with significant barrier properties, such as
graphenes, exfoliated graphite, carbon black, amorphous carbon, or
carbon nanofibers (e.g., nanotubes), or a carbide (e.g., silicon
carbide).
[0060] It is well known in the art that some flame retardant
materials may not work alone, but may need to be in combination
with another flame retardant chemical to function effectively or
optimally as a flame retardant. For example, halogenated flame
retardants are often used in combination with antimony oxide. In
other embodiments, one or more of any of the above-mentioned
classes or specific types of flame retardants are excluded from the
above-described sulfonated flame retardant composition or excluded
from a flame-resistant composite in which the sulfonated flame
retardant composition is incorporated.
[0061] The flame retardant is typically either in solid or liquid
form when incorporated in or onto the sulfonated polyolefin object.
In solid form, the flame retardant is typically incorporated as
particles or fibers, which are preferably homogeneously dispersed
throughout the sulfonated polyolefin matrix or formed as a layer on
the surface of the sulfonated polyolefin fiber. The flame retardant
particles or fibers can have any suitable diameters, such as any of
the diameters provided above for the SO.sub.2-scavenging material.
In fibrous form, the flame retardant can have any suitable length,
which may correspond to the diameters provided above, or may be
significantly longer, e.g., at least, above, or up to 200, 300,
400, or 500 microns.
[0062] The flame retardant material can be included in or on the
sulfonated polyolefin object in any suitably effective amount. In
different embodiments, the flame retardant material is included in
or on the sulfonated polyolefin object in an amount of about, at
least, above, up to, or less than, for example, 1, 2, 3, 4, 5, 10,
12, 15, 18, 20, 25, 30, 35, 40, 45, or 50 wt %, or a wt % within a
range bounded by any two of the foregoing exemplary values, wherein
the wt % is with respect to the combined weight of the flame
retardant material and sulfonated polyolefin.
[0063] Significantly, the inclusion of a flame retardant can
advantageously permit a significantly lowered amount of sulfonation
for the sulfonated polyolefin object. The lower required amount of
sulfonation can be particularly advantageously by, for example,
reducing the time and cost of the sulfonation process.
[0064] By controlling the conditions used in the sulfonation
process, as well as choice and manner of integration of the
SO.sub.2-scavenging material or flame retardant, the mechanical
properties of the sulfonated polyolefin object, which may or may
not be combined with a SO.sub.2-scavenging material or flame
retardant material (other than a sulfonated polyolefin), can be
tailored. Some mechanical properties that can be tailored, as
particularly applicable to a sulfonated polyolefin fiber, include
tensile strength, modulus, elongation at break (i.e., break
strain), and toughness. The sulfonated polyolefin object produced
herein, which may or may not be combined with a SO.sub.2-scavenging
material or flame retardant material (other than a sulfonated
polyolefin), can have a tensile strength of about, at least,
greater than, up to, or less than, for example, 2, 5, 7, 10, 12,
15, 18, 20, 25, or 30 ksi. In different embodiments, the sulfonated
polyolefin object, which may or may not be combined with a
SO.sub.2-scavenging material or flame retardant material (other
than a sulfonated polyolefin), has a modulus of precisely, about,
at least, greater than, up to, or less than, for example, 0.1, 0.2,
0.3, 0.4, 0.5, 0.6, 0.7, or 0.8 Msi. The sulfonated polyolefin
object, which may or may not be combined with a SO.sub.2-scavenging
material or flame retardant material (other than a sulfonated
polyolefin), can have an elongation at break of precisely, about,
at least, greater than, up to, or less than, for example, 1, 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
22, 23, 24, or 25%.
[0065] In another aspect, the invention is directed to
flame-resistant composites that contain the above-described
sulfonated polyolefin as a flame retardant component incorporated
into or integrated with a host material to be rendered flame
resistant, wherein the sulfonated polyolefin may or may not be
combined with a SO.sub.2-scavenging material or flame retardant
material (other than a sulfonated polyolefin) when it is
incorporated in the material to be rendered flame resistant. The
host material can be any material requiring flame resistance in
which the sulfonated polyolefin fibers can be incorporated. The
host material can be, for example, a layer, sheet, film, or other
shape of a plastic, polymer, fabric, or cellulosic material. If the
host material is meltable, the sulfonated polyolefin can be mixed
with the melted host followed by solidification. If the host
material is not meltable, or melting is to be avoided, the
sulfonated polyolefin can be introduced by, for example,
powderizing or pelletizing the host material, mixing it with the
sulfonated polyolefin fiber or other object, and melt-pressing or
pressure-welding. The sulfonated polyolefin can be included in any
suitable amount in the flame resistant composite, which can be an
amount over 0% and under 100%. In different embodiments, the
sulfonated polyolefin can be included in an amount of precisely,
about, at least, above, up to, or less than, for example, 1%, 2%,
5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, 75%,
80%, 85%, 90%, or 95% by weight of the flame resistant composite.
The amount of sulfonated polyolefin may also be within a range
bounded by any of the foregoing exemplary values.
[0066] In a first set of embodiments of the flame resistant
composite, if a SO.sub.2-scavenging material or flame retardant
material is included in the flame resistant composite, either or
both of these materials are either incorporated into the sulfonated
polyolefin objects or are a coating on the sulfonated polyolefin
objects that are incorporated into or integrated with the host
material. In a second set of embodiments of the flame resistant
composite, if a SO.sub.2-scavenging material or flame retardant
material is included in the flame resistant composite, either or
both of these materials, or a portion thereof, are not in contact
with the sulfonated polyolefin objects, but instead are
incorporated (e.g., dispersed) separately in the host material. Any
of the means, described above, for incorporating sulfonated
polyolefin into a host material can be used for incorporating a
SO.sub.2-scavenging material or flame retardant material into the
host material.
[0067] In particular embodiments, the material to be rendered flame
resistant is a textile. The textile can be, for example, a woven or
non-woven fabric composed of strands of a textile material. In
particular embodiments, the fabric is a fabric used in clothing,
furniture, upholstery, flooring, rugs, or mats. Some examples of
fabrics that can be rendered flame resistant include cotton,
polyester, nylon, silk, wool, rayon, cellulose acetate, spandex,
and blends thereof. In other embodiments, the strands of the fabric
are composed solely of sulfonated polyolefin fiber, which may also
include a SO.sub.2-scavenging material or flame retardant material.
The flame resistant textile can be produced by, for example,
weaving sufficiently flexible sulfonated (or partially sulfonated)
polyolefin in fiber form with either itself or other fibers of a
textile by methods well known in the art.
[0068] In another embodiment, the flame resistant textile or other
flame resistant article is made by chemical or physical bonding of
the sulfonated polyolefin objects (e.g., powder, particles,
pellets, or fibers) with each other and/or with a material to be
rendered flame resistant. Chemical bonding can be accomplished by,
for example, including a bonding agent, such as a curable polymeric
resin, that bonds the sulfonated polyolefin objects with each other
and/or with a material to be rendered flame resistant. Physical
bonding can be accomplished by, for example, pressure, heat, or a
radiative source (e.g., electromagnetic or particle bombardment) to
induce bonding.
[0069] In a particular embodiment, the sulfonated polyolefin
objects are bonded with each other by inducing strong inter-object
or interfilament bonding between sulfonated polyolefin objects,
such as particles or fibers. In some embodiments, the strong
interfilament bonding is induced by contacting the sulfonated
polyolefin objects with water. Without being bound by any theory,
the strong interfilament bonding is believed to be mediated by the
presence of sulfur-containing and possibly other oxidized groups on
the surface of the sulfonated polyolefin objects that likely form
extensive hydrogen bonding interactions with each other
particularly when they interact with water molecules.
[0070] As used herein, the term "water" can be relatively or
substantially pure water, or alternatively, an aqueous solution.
Relatively or substantially pure water is generally composed
completely of water, except for trace elements that may normally be
found in water of relative or substantial purity. In some
embodiments, the water may be ultrapure (i.e., up to 14, 16, or 18
MOhm). An aqueous solution, if used, may include one or more
additional solvents or a solute, as long as the additional
components in the water do not substantially hinder or adversely
affect the ability of the sulfonated polyolefin objects to bond.
The additional solvent or solute may function, for example, as
wetting agents, surfactants, agglomerating agents, or bonding
agents. The solvent is necessarily a polar protic or aprotic
solvent miscible in water, such as an alcohol (e.g., methanol,
ethanol, or isopropanol), dimethylformamide, dimethylacetamide,
dimethylsulfoxide, acetone, glycerol, or ethylene glycol. The
solute can be, for example, an inorganic compound or salt (e.g.,
lithium, sodium, and potassium salts of a halide, hydroxide,
nitrate, or mineral acid), an inorganic polymeric material (e.g., a
polysiloxane or sol-gel), an organic polymeric material (e.g., a
polyacrylate or polyacrylamide), or an organic compound (e.g., a
fluorinated surfactant, wetting agent, polyol, or polyalkylene
glycol). In some embodiments, any one or all of the additional
solvents or solutes described above (or any additional solvent or
solute altogether) are excluded. In other embodiments, any one or a
combination of the above-listed solvents may be used instead of
water to make contact with the sulfonated objects in order to
effect a strong inter-object (or interfilament) bonding.
[0071] In some embodiments, the sulfonated fibers or other objects
are soaked in aqueous mineral acids such as hydrochloric acid,
sulfuric acid, nitric acid, chlorosulfonic acid, or aqueous
alkaline solutions of metal hydroxides or nonmetallic hydroxide
(e.g., ammonium hydroxide) in order to effect hydrogen or ionic
bonding in dried agglomerations or filament bundles of preferred
orientation or random orientation. In embodiments where sulfonated
filaments are used, the filaments can be in continuous or chopped
forms of finite lengths.
[0072] In some embodiments, the sulfonated polyolefin objects are
contacted with water by immersing the sulfonated polyolefin objects
in water or an aqueous solution. The sulfonated polyolefin objects
can be immersed in water or aqueous solution by, for example,
submerging the sulfonated objects into water or an aqueous
solution, passing water or an aqueous solution over the sulfonated
objects, or spraying the sulfonated objects with water or an
aqueous solution. Generally, excess water (i.e., water or aqueous
solution beyond that which coats the fibers) is removed either by
filtration, draining, or drying, or a combination of these. The
resulting sulfonated objects, after removal of excess water, become
strongly bonded to form a mat or paper preform. In embodiments
where sulfonated polyolefin fibers are used, the sulfonated
polyolefin fibers can be passed through a slit die, during or after
contact with water, in order to orient the fibers in a special
arrangement to make a mat or paper preform. When being passed
through a slit die, the fibers are generally in the form of a
viscous suspension and then placed under pressure in a hot chamber
where solvents volatilize. Generally, after excess water is
removed, the sulfonated polyolefin objects are dried or annealed
either under ambient conditions (e.g., 20-35.degree. C.) or at an
elevated temperature, such as a temperature of precisely, about, at
least, up to, or less than 40, 50, 60, 70, 80, 90, 100, 120, 150,
175, 200, 250, or 300.degree. C., or a temperature within a range
bounded by any two of the foregoing values.
[0073] In other embodiments, the sulfonated polyolefin objects are
contacted with water by contacting the sulfonated polyolefin fibers
with water vapor. Any gaseous atmosphere containing water vapor is
applicable herein. Typically, the humidity level of the
water-containing atmosphere is precisely, about, or at least, for
example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or
100%. The water-containing atmosphere generally includes, besides
water vapor, those gases normally found in air, or an inert
atmosphere, such as nitrogen, argon, or carbon dioxide. The
water-containing atmosphere may or may not also include one or more
reactive gases that function, for example, to further encourage
inter-object (or interfilament) bonding or alter the surface
chemistry of the sulfonated objects.
[0074] The sulfonated polyolefin objects and/or the water
contacting the sulfonated polyolefin objects may be held at any
suitable temperature during contact of the sulfonated objects with
water or an aqueous solution. In some embodiments, the sulfonated
objects and/or water are at room temperature, such as precisely or
about 20, 25, 30, or 35.degree. C. In other embodiments, the
sulfonated objects and/or water are at an elevated temperature,
such as precisely or about 40, 50, 60, 70, 80, 90, or 100.degree.
C. In other embodiments, the sulfonated objects and/or water are at
a depressed temperature, such as precisely or about 0, 10, or
15.degree. C. In some embodiments, the temperature of the
sulfonated objects and/or water is within a range bounded by any
two of the exemplary temperatures provided above.
[0075] One or more additional steps or conditions can be employed,
besides contact with water, to promote inter-object or
interfilament bonding in the sulfonated polyolefin objects. The one
or more additional steps or conditions can be, for example, any of
the chemical or physical bonding techniques generally discussed
above and as known in the art. In a particular embodiment, a hot
stamping process or mechanical pinning, as well known in the art,
is applied to the sulfonated polyolefin objects. The sulfonated
polyolefin objects may also be coated with a plasticizer, which can
be any suitable plasticizing compound or material, such as a polyol
(e.g., ethylene glycol, diethyleneglycol, or glycerol) or organic
solvent. In some embodiments, the sulfonated polyolefin objects are
subjected to a hot stamping process, mechanical pinning, or
plasticization without first exposing (or ever exposing) the
sulfonated objects to water.
[0076] To produce the mat or paper preform, partially or completely
sulfonated polyolefin fibers may be arranged in a non-woven mat or
paper form, and then bonded, as described above, to form the
preform. In other embodiments, unsulfonated polyolefin fibers are
arranged in a non-woven mat or paper form, and then bonded, by any
of the chemical or physical techniques described above (e.g., hot
stamping, partial melting, or plasticization) to form a preform
that is then subjected to sulfonation conditions to partially or
completely sulfonate the preform. In yet other embodiments, a
non-woven mat or paper preform composed of partially sulfonated
polyolefin fibers is subsequently further sulfonated. In particular
embodiments, unsulfonated polyolefin fibers are arranged in a
non-woven mat or paper form, and then bonded by any of the
processing techniques known in the art for producing a spun-bonded
or melt-blown mat, before being sulfonated.
[0077] Examples have been set forth below for the purpose of
illustration and to describe certain specific embodiments of the
invention. However, the scope of this invention is not to be in any
way limited by the examples set forth herein.
Example 1
Preparation of Sulfonated Polyolefin (LLDPE) Fiber
[0078] An as-spun tow of neat LLDPE of 1560 filaments (18
micrometer filament diameter) was continuously processed through a
two-part reactor containing (1) concentrated sulfuric acid, and (2)
oleum with 20% SO.sub.3. The speed of the fiber was adjusted to
attain proper residence time. A tensile stress of 5 MPa was applied
to the fiber during semi-continuous processing. For the
concentrated sulfuric acid bath, the temperature was maintained at
115.degree. C. A temperature below 100.degree. C. in the
concentrated sulfuric acid bath did not result in an infusible
fiber even after 12 hours of treatment. For the oleum bath (which
is a concentrated sulfuric acid bath containing dissolved SO.sub.3
gas), the temperature was maintained at 90.degree. C. A residence
time of 4 hours and 40 minutes was used for the concentrated
sulfuric acid and oleum baths, respectively, which resulted in
infusible fibers that were found to be hygroscopic under ambient
conditions.
[0079] The oleum-based sulfonated LLDPE fibers treated at 70, 80,
90, and 97.degree. C. resulted in 1.21, 1.49, 1.55, and 1.61 g/cc
densities, respectively, in the resulting sulfonated fibers. The
mechanical properties of the fibers are displayed in the table
below.
TABLE-US-00001 TABLE 1 Mechanical properties of the sulfonated
LLDPE fibers Tensile Density Diameter strength Modulus Elongation
Fiber (g/cc) (mm) (ksi) (Msi) (%) As-spun LLDPE 0.94 16-20 20-25
0.1-0.3 100 Sulfonated -- 20 12 0.1 12 by conc. H.sub.2SO.sub.4 at
97.degree. C. for 12 hours Stabilized by 1.61 20-25 7 0.2 15 oleum
at 97.degree. C. for 4 hours
[0080] As shown in Table 1, the sulfonated filaments exhibit
greater than 10% ultimate elongation, which is important for
conversion of tow into fabric by proper fabrication technique, such
as knitting or weaving. The completely sulfonated fibers with high
densities are thermally infusible and do not catch fire in open
flame under ambient conditions. Sulfonated filaments with a density
above 1.45 g/cc tend to exhibit flame-resistance.
[0081] However, the thermal treatment causes release of SO.sub.2
gas, which is known to be toxic. For sequestration or adsorption of
SO.sub.2 gas, the sulfonated fiber was coated with ZnO powder by
passing the fiber through a fluidized bed of ZnO. The sulfonated
filaments were dispersed in ZnO suspension in tetrahydrofuran
solvent. After soaking for 2 minutes in ZnO suspension, the fibers
were removed from the liquid medium by use of a tweezer.
[0082] The TGA data (scanned at 10.degree. C./min under nitrogen)
of the sulfonated fiber and ZnO coated sulfonated fibers are shown
in FIG. 2. It was observed that the presence of a ZnO coating
reduced the SO.sub.2 release kinetics, and the derivative
thermogravimetric (DTG) analysis peak maxima (as shown in FIG. 3)
shifted to higher temperature by 12.degree. C. The pyrolysis of ZnO
coated sulfonated fibers above 400.degree. C. was found to be more
intense than that in neat sulfonated fibers. Thus, the presence of
a SO.sub.2-scavenger retards desulfonation and forms an adduct
containing SO.sub.x that finally decomposes above 850.degree. C.
(FIG. 2).
Example 2
Preparation of Sulfonated Polyolefin (LLDPE) Fiber Using E-beam
Irradiation
[0083] The LLDPE fiber tow discussed in Example 1 was e-beam
irradiated at 10-1000 kGy to reduce the melting temperature, which
in turn accelerated the sulfonation kinetics during subsequent
sulfonation reaction. As shown in FIG. 4, increasing radiation
dosage results in a reduction in melting temperature of
polyethylene fibers with overall heat of fusion, i.e.,
crystallinity, of the fibers remaining unchanged, even when they
were irradiated at 1000 kGy dosage. However, when polyethylene
fiber was irradiated in the presence of a SO.sub.2 gas and at 500
kGy dose, a significant reduction in crystallinity was observed, as
also shown in FIG. 4. This indicates crosslinking of the polymer by
the SO.sub.2 gas and e-beam. The highly irradiated fibers were
dissolved in the sulfonation bath due to vigorous reaction.
However, unlike the neat PE fiber sample described in Example 1,
the 10 kGy irradiated fiber, when treated with concentrated
H.sub.2SO.sub.4 for 12 hours at 97.degree. C., resulted in an
infusible fiber. Thus, it was herein found that generation of free
radicals in the polyolefin accelerates the sulfonation kinetics and
more quickly converts the flame retardant material.
[0084] While there have been shown and described what are at
present considered the preferred embodiments of the invention,
those skilled in the art may make various changes and modifications
which remain within the scope of the invention defined by the
appended claims.
* * * * *