Note: Descriptions are shown in the official language in which they were submitted.
~ 1~0~13
D.D. I~itney-C.F. Mur~hy-
G.C. Daul 1-14-3
-- 2 --
This invention relates to a process for the production
of high performance, high wet modulus rayon filaments and
fibers.
Regular low wet modulus rayons normally are prepared
from a viscose containing 8 or 9g cellulose and 5 to 6~ caustic
soda; the acid in the spin bath usually being much in excess
of that required to neutralize the alkaline caustic soda -
6.5% to as high as 9% or more of acid. Low modulus rayons
when converted to fabrics have a tendency to shrink when
laundered, the principal cause of shrinkaye beipg their low
resistance to stretching when wet ti.e. low modulus1. Rayon
researchers have found tha~ when the wet modulus of rayon
is sufficiently high (over 0.5 g~d), progressive~shrinkage
is essentially controlled and a more stable fabric and garment
reslllt.
On the other hand, in the production of high wet
modulus (HW~) rayon fibers, that is fibers having a wet ;~ `
strength of at least about 0.5 grams per denier, it is
customary to use a "rich" viscose composition in which the
a~ount of caustic soda is essentially equal to the amount of
cellulose. For example, U.S. Patent 3,720,743, assigned to
the present assignee, discloses a process for the production
of HWM rayon fibers having a number of desirable properties
in addition to high ~7et strength. The Patent indicates that~
a balanced ratio, for example, of 7.5~ cellulose and 7.5%
~'
- 2 ~
1 1~0413
D.D. ~qhitney-C.F. ~lurphy-
G.C. Daul 1-14-3
caustic soda should be used. U.S. Patents 3,632,468 and
4,121,012 are similarly directed to ~M rayon fibers prepared
from balanced ratios of caustic and cellulose.
So-called polynosic rayons, having high strength
5 and modulus, are prepared from relatively smaller (and
unbalanced) amounts of cellulose and caustic. However,
the polynosic rayons differ from other ~r,~ rayons in both
their properties and their preparation. Because of the
high degree of polymerization of the cellulose required
for these rayons, high viscosity viscoses are used. High
salt indices (about 20) and very large amounts of CS2 are
`necessary to effect solubility and good spinnability. Low
concentrations of acid at low temperatures in the spin bath
are also necessary to form the fibrillar polynosic structure.
Such fibers, while they have high wet modulus properties,
have low elongations, in the range of 7 to 10~, which
result in difficulties in conversion to yarn and fahric.
~olynosic fibers made by such processes are usually brittIe
and have accordingly achieved only limited commercial
acceptance.
Thus, it would be desirable to produce dimensionally
stable, strong high performance rayons with high wet
modulus, using, however, more economical conditions than
have heretofore been thought possible.
It is accordin~ly a primary object of this invention
D.D. ~lhitney- C.F. Murphy
l 160413 G.C. Daul 1-14-3
-- 4 --
to provide a process for the production of high wet modulus
rayon filaments and fibers with reduced amounts of caustic
and acid~
It is an additional object of this invention to provide
a process in which the ranges of caustic soda relative to
acid can be adjusted to produce HWM fibers with a variety
of properties, cross-sections and shapesO
It is still an additional object of this invention
to provide a process for producing rayon filaments and
fibers which combine more economical process conditions
with improved fiber properties.
It has been found quite unexpectedly that high per-
formance, HWM rayon fibers having a desirable level of elon-
gation may be produced by the use of an unbalanced ratio of
cellulose and caustic in the viscose if it is accompanied by
~ reduced amount of acid in the primary spin bath. More
specifically, the pxocess of the invention involves the
production of crimped high tenacity rayon filaments and fibers
having a wet modulus of at least 0.5 g/d and a wet elongation
Of about 11-17% comprising preparing a viscose solution
containing a mixture of viscose modifiers which substantially
retard regenaration, said modified viscose solution having
a salt index between 2.5 and 6, prepared from an unbalanced
ratio by weight of sodium hydroxide to cellulose ranging
from 0,6~ to 0.87, spinning said viscose solution into a
coagulating spin ba~l containing from 0.8 to 3.9~ by weight
of sulfuric acid, from 1 to 6~ by weight zinc sulfate and from
10-20~ by weight sodium sulfate, the ratio by weight of acid
r~ 4
11 6 0 ~ 1 3 D D Whi~ney-C,F Murph~-
in the spin bath to sodium hydroxide in the viscose solution
ranging from 0.20 to 0,66. The ~esulting incompletely
regenerated filaments are immediately stretched and the
regeneration is completed in an acid bath maintained
above 80C and the tension of said cellulosic filaments
relaxed to permit crimp development.
It should be noted that the reduction of only a
percentage or two in the amount Gf caustic soda and acid
used in the viscose processhas considerable economic
significance. These are two of the major raw materials
used, which when neutralized, produce water and salts.
Evaporation of the water and recovery of the salt are
energy intensive operations. Be reducing the quantities
of the raw materials used in the process, significant
energy and cost savings are effected.
It was quite surprising to find that HWM fibers of
outstanding quality could be spun from leaner viscose
compositions, i.e. viscose compositions containing less
caustic by weight than cellulose. The key to HWM properties
was thought to be high caustic. Ordinarily, when the
caustic content is lowered and all other spinning conditions
are held constant, the wet elongation increases and the
wet modulus properties of the resulting fiber deteriorate
dramatically. Most commercially produced HWM fibers are
spun at acid levels which cannot be lowered without encoun-
tering spinnability problems. o~ten poor spinning, under
normal ~M process conditions, can be improved simply by
increasing the primary bath acid concentration and this is
- 5 -
l 160~13
D . D, ~lhitney-C. F . Murphy-
G.C. Daul 1-14-3
frequently done in commercial spinning operations. ~e have
now found that for high wet modulus production, the reduced
caustic requires less acid, not only less acid resulting
from less caustic requiring neutralization, but less acid
so that the fibers set up more slowly, an~ stretchability
is improved. With balanced ratios of caustic and cellulose,
the acid concentration cannot be lowered without adversely
impacting fiber spinning, resulting in a condition known
to the art as slubbing. The present invention involves the
discovery that the caustic level may~be reduced i~ the
viscose only if the ~evel of acid in the s~in bath is
also reduced. Not only does this prevent adverse impact on
spinnability and fiber properties, but the fiber properties,
principally wet modulus, are actually improved. ; ~;~
lS Generally, the process of the invention involves the ~;
preparation of a viscose solution from cellulose xanthate.
Purified chemical cellulose, such~as bleached sulfite and
prehydrolyzed kraft wood pulps as well as cotton linters
having a relatively high uniform degree of polymerization ;~
are converted into alkali cellulose by steeping in sodium
hydroxide, aged to a cuene I.V. (intrinsic viscosity) of
from 2.0 to 3.6 dl/g (decaliters/gram) and xanthated with
26 to 40% by weight of carbon disulfide, based on oven dried
cellulose weight, at approximately ambient temperatures
(e.g. 20-30C). The amount of carbon disulfide is not
~ \
l ~ ~0413
D.D. r~lhitney-C.F~ ?-lurphy-
G.C. Daul 1-14-3
-- 7 --
critical as long as the salt index is correct and viscose
filterability is satisfactory. The viscose solution is
modified with a regeneratin retardant of ~he type shown,
for exam~le, in U.S. Patent 2 t 942,931 and which preferably
comprises from 0.5 ~o 2.5~ each of dimethylamine and poly-
ethylene glycol. Alternatively, modifiers such as ethoxylated
amines sold under the trademarks Ethomeen C-25 and Leomi~-,
AC80 can be used in place of dimethylamine, and branched
chain polyglycols such as those sold ~nder the trademark
Berol Visco 399 may be substituted for polyethylene glycol.
The salt in~ex of the viscose spinning solution should be
between 2.5 and 6 and the gamma number between about 20
and about 45 when spun with ripening selected to attaLn~
this level. The specific salt index~and gamma~number depend
lS upon the amount of carbon disulfide used in xanthation~and~
the temperature and time of ripening used. The viscos~ity
of the spinning solution is not particularly critical and
~ : ~
can range between about 50 and 150 ball fall seconds, or
between 75 and 225 poise, measured at 20C. The viscose
solution is prepared from an unbalanced ratio by weight
of sodium hydroxide to cellulose ranging from 0.60 to 0.87
and preferably from 0.65 to 0.80. The amount of cellulose
should be from 5-9%, preferably 6-~%, by wei~ht of the
solution. The amount of sodium hydroxide should be from
4-7%, preerably from 5-6~, also by weight of the solution.
_ 7 _
l ~60~13
D,D. ~itney-C.F. '~urp~y-
G.C. Daul 1-14-3
The coagulating spin bath contains a sulfuric acid
concentration of from 0 R to 3.9%, preferably 2.5 to 3.5%
by wei~nt of the bath. The ratio by weight of acid in the
spin bath to sodi~ hydroxide in the viscose spinning
solution should range from 0.20 to 0.66, preferably from
0.40 to 0.60. The spin bath should also contain about
l to 6% by weight of zinc sulfate and from 10-20% by
weight of sodium sulfate. It may also contain from 0.01
to 0.1 percent by weight of a surface active agent or
lubricant such as lauryl pyridinium chloride, and a modicum
of regeneration retardants carried in with th.e tow.
The deaerated viscose is spun through a spinnerette
into a coagulating spin bath at about 30 to 45C. Travel
of the filament through the primary spin bath should be
li~ited to that re~uired to develop sufficient strength
for stretching, in order to avoid any unnecessary regene-
ration, with the greater percentage of stretch achieved
prior to substantial reseneration. Immediately after
leaving the spin bath, the filaments as a group or towj
and ~hile thev are substantiall~ soluble in dilute alkali,
are stretched from about lO0 to 300 percent. ~o effect
this stretch, the tow is drawn frorl the bath the desired
distance, passed several times around a driven godet to
~revent slippage and then several times around one or more
stretch rolls driven at a sufficiently greater speed to
.
l 1~0413
D.D. I~hitney-C.F. ~lurphy-
G.C. Daul 1-14-3
g _
provi~e the ~esired continuous stretching.
Since filaments made by the procedures described
above are highly plastic and relatively strong immediately
upon extrusion into the coagulation bath, it is important
to stretch as quickly and as much as possible prior to
reqeneration in order to obtain the desired high wet
modulus. The strongest filaments with the highest wet
modulus are produced when the stretching takes place
immediately after the onset of coagulation in a gradual
fashion. For example, when only one godet and one stretch
roll are used, the stretching occurs on, or as the tow ;
leaves, the first roll and is then completed as the tow
of filaments passes through the regeneration bath or baths.;~
To facilitate stretching and to regenerate the
coagulated filament tow, it is conducted through one or
more hot regeneration baths of suffIcient length which
contain hot dilute acid. We prefer dilute acid baths for
our purpose, maintained at 80 to 100C (preferably about
95-98C), in any event, sufficiently hot to substantially
regenerate the newly formed filaments in the tow. The
stretch bath or baths contain from about O.5 to 3.0 percent
sulfuric acid and a stabilized modicum of salts carried
over from the preceding coagulation bath.
After the filaments are substantially regenerated,
tension is reduced or removed to permit crimp development.
g _
~ ~60413
D.D. '!Ihitney-C.F. Murphy-
G.C. Daul 1-14-3
-- 10 --
Following rela~ation, the filaments are treated with hot
dilute acid, desulfurized, neutralized, washed, finished
and dried by conventional techniques.
Alternatively, the filaments can be cut into staple
fibers which develop a high degree of crimp on relaxation.
~hese highly crimped staple fibers are acidified, desul-
f~rized, neutralized, washed, finished and dried by
conventional techniques. Cutting of the tow into staple t
fibers is usually performed in the acid state.
The finishing of the crimped filaments and staple
fibers should be balanced to preserve crimp, high ~odulus
and high strength, while building adequate elongation for
good conversion properties and good wear and abrasion-
resistance in end-products. Use of a commercially
available staple fiber finishing agent is advantageous
to insure processability for efficient conversion to
yarn and fabric.
Fibers produced in accordance with the invention
may have a variety of cross-sectional configurations and
degrees of crimp, primarily dependent on the amount of
acid used in the spin bath for a given caustic to cellulose
ratio in the viscose. The cross-sectional configuration
may vary from essentially circular and with the least amount
of crimp, spun at acid concentrations within the lower
portio.; of the claimed range, to bilobal filaments at
-- 10 --
l 160413
D.D. Whitney-C.F. ilurphy-
G.C. Daul 1-14-3
intermediate acid levels having the most crimp. At the
higher end of the acid range, multilobal cross-sections
are obtained. The properties or the fibers produced in
accordance with the invention are at least the equivalent
of high performance fibers produced from prior art, rich
caustic, viscose solutions and higher acid spin baths,
while the wet modulus properties are in many instances
higher. Properties of the fibers of the invention will
have the following general ranges:
Wet modulus 0,5-1.2 g/d
S6.5 maximum 12%
Conditioned Tenacity 3-4 g/d
Conditioned Elongation lQ-15
Wet Tenacity 2-3 g/d
Wet Elongation Ll-l7%
Wet modulus as measured herein LS the ~et tenacity
in grams per denier at 5~ elongation. The minimu~ and
maximum wet modulus values have been roun~ed off to the ~ ;
first decimal place. ~hus, a wet modulus value of 0.46
is considered to fall within the above range. "S6.s" is
a measure of the fiber's resistance to laundering and
specifically the solubility of the fiber in 6.5~ ~laOH at
20C, he tenacity values axe in accordance with AST!-I
test number D-1577-66, using 1~2 inch gauge length. The
~5 elongation values are in accordance with ASTM test number
-- 11 -- .
1 160413
D.D ~itney-C.~. Murphy-
G.C. Daul 1-14-3
- 12 -
D-540-64.
The following examples illustrates the practice of
the invention. Unless other~7ise indicated, all parts and
percentages are by weight.
E~.~LE 1
This example shows the preparation of a prior art
H~l fiber produced by a process similar to that described
in the aforesaid U.S. Patent 3,720,743. A modified v scose
spinning solution was produced from chemical cellulose whlch
was prepared by steeping a high purity wood pulp, having
an Slo of 2.~ percent and an S18 of 1.4 percent. (Slo and
S18 are a measure of the solubility of the fiher in~l0~
and 18~ NaO~, respectively, at 25C~. The thus formed
alkali cellulose contained, after being pressed,~34% ~;
lS cellulose and 15~ sodium hydroxide. The alkali cellulose
was shredded and aged to a cuene I.V~ of about 3.0 dl/g.
It was then reacted with 32% carbon disulfide, based on
the weight of cellulose, at 30C to form cellulose xanthate~
~lhich was dissolved in sodium hydroxide at 10C and mixed
for two hours to rovide a balanced viscose soluticn con-
taining 7.5% cellulose and 7.5~ sodium hydroxide. To this
viscose solution, 1.3~ dimethylamine and 1.3~ polyethylene
glycol of ~l.l7. 1540 (both based on the weight of cellulose)
were added. The viscose solution was ripened to a salt
(~aCl) index of 5Ø
- 12 -
1 160413
D.D. I~hitney-C.~. ~'urphy-
G.C. Daul 1-14-3
- 13 -
The well-deaerated viscose then was extruded
through a cluster of spinnerettes with 24,200 holes -
0.0025 inch diameter each, into a primary acid coagulating-
type spin bath containing 5.0% sulfuric acid, 15~ sodium
sulfate, and 2.8~ zinc sulfate at a temperature of 40C.
The coagulated filament tow was wrapped around a godet
and led through a hot secondary acid bath to a wash reel
on which it was wrapped several times to prevent slippage.
The secondary acid bath contained 3.0~ sulfuric
acid and residues of salts carried over from the primary
bath. It was maintained at about 95 to 98C. The tow
was spun at 30 meters per minute and stretched through
the secondary bath at 120%.
The tow was collected wet, cut in~to staple fiber
lengths, washed, desulfurized, and finished in the usual
manner with a staple fiber finish. After dryina and
conditioning, single filament test were run under standard
pxocedures. The sin~le filament fiber physical property ~
test results are sho~m in Table I. ~ ;
The ratio of ~laOH/cellulose in this E~ample was
1:1 and the ratio of H2SO4 in the spin bath to NaOH;ln
the viscose was 0.67.
E ~ ~I2 2
The process of Example 1 was substantially repeated
2s except that the primary bath sulfuric acid concentration
- 13 -
l 160413
D,D, Whitney-C.F. ~ur?hy-
G.C. Daul 1-14-3
- 14 -
was reduced to 3.5%. The lower acid level resulted in
unacceptable extrusion occurring at~the spinnerette face
in the primary bath (i.e. slubbing) which resulted in
unregenerated, uncoagulated viscose in the tow which
prevented it from being cut into staple or processed
properly.
EX~LE 3
The rayon fiber of this example is typical of
commercially produced regular rayon staple. ~
A viscose spinning solution was produced by steeping
a chemical cellulose wood pulp, ha~ing an Slo~ of 8.8 and
an Slg of 4.4. The thus formed alkali cellulose was pressed,~
shredded, and aged to a cuene I.V. of 2.2 dl/g. It was
then reacted with 28% carbon dlsulfide, based on ~the~-eight
of cellulose, to orm cellulose xanthate which was dissolved
in sodium hydroxide and mixed to produce a viscose solution
containing 9.0% cellulose and 5.0~ sodium hydroxide.
The viscose was ripened to a salt (,~aCl) inde~ of 4.0 and
deaerated.
It was then extruded through a spinnere~tte into a
primary acid coaguIating-type spin bath containing 6.8
sulfuric acid, 21~ sodium sulfate, and 1.0% zinc sulfate
at a temperature of 55C. The coagulated to~7 was wrapped
around a godet several times to prevent slippage and
~5 stretched 50~ while spinning at lOO meters per minute.
l ~6~413
D.D. Whitney-C.F. Murphy-
G.C. Daul 1-14-3
- 15 -
The tow was collected wet, cut into staDle fiber
lengths, washed, desulfurized, and finished in the usual
manner with a staple fiber finish. After drying and
conditioning, single filament fiber physical tests were
run under standard procedures. The results are given
in Table I.
The ratio of NaOI-I to cellulose in this Exam~le was
0.56 anA the ratio of H2SO4 in the spin bath to NaOH ln
the viscose was 1.36.
E ~ ~LE 4
This example illustrates the practice of the present~
invention. The H~M rayon of this example was ~roduced by
the process of Example l except that an unbalanced vis~cose
composition of 7 . 5Qo cellulose and 4.5% sodium hydroxide
was used.
It was spun under the same conditions e~cept that
1.0~ sulfuric acid was contained in the primary spin bath.
All other process variables were the same. Flber physical
~est results are listed in Table I.
The ratio of l~laOH to cellulose was 0.6 and the ratio
:
of H25O4 in the spin bath to NaOH ln the viscose was 0.22.
EX~ E 5
The HWM rayon of this example was produced by a
process similar to that in Example 4 except that an
unbalanced viscose composition of 9.0~ cellulose and 6.0%
- 15 -
l 160~13
D.D. ~itney-C.F. ~urphy-
G.C. Daul 1-14-3
- 16 -
sodium hydroxide was used and was prepared at a cellulose
I.V. of 2.3 dl/g and ripened to a 4.9 salt (~aCl) index.
It was spun under the same conditions except that
the primar~ bath contained 3.5~ sulfuric acid. All other
process variables were the same except that stretch was
130~, Fiber physical test results are given below in
Table I with results from fibers produced as described
in Examples 1-4.
TABLE I
Ex. 1Ex. 2 Ex. 3Ex. 4 Ex. 5
Ratio~
~aOH/Cellulose
in viscose 1.0 1.0 0.560.6 ~ 0.67
Ratio:
H2SQ4 in spin
bath~NaOH in
viscose 0.670.47 1.360.22 0.42 ;
Tenacity g/d
Conditioned 3.5 would 2.8 3.5 3.7
Wet 2.2 L.5 2.2 2.4
Elongation
Conditioned 13 not 20 13 12
Wet 15 25 15 13
Wet Modulus g/d 0.5 0.2 0.5 0.8
25 Full ~ave s~in
Crimps/in. 15 10 20 18
::
- 16 -
l 160413
D~D~l~hitney-c~F~Mur~h
G.C.Daul 1-14-3
- 17 -
E ~ ~LE 6
A process similar to that of Example 4 was used to
produce the fiber of this example except that an unbalanced
viscose composition of 8.5~ cellulose and 6.0~ soaium
hydroxide was used to prepare the viscose. The cellulose
in viscose was at I.V. 2.2 dl/g; it was ripened to a 5.1
salt (NaCl) index, and 1.3% Ethomeen C-25 (an ethoxylated
amine) and 1.3% polyethylene glycol were added (based on -
the weight of cellulose) as regeneratlon retardants.
The viscose was spun into~a primary bath contain1ng
2.9~ sulfuric acid. All other process variables were the
.
same. Fiber physical test results are given in Table II.
The ratio of acid in the spin bath to NaOH in the visoose ;
was 0.48. ;
lS E~A~T~ 7
The ~IW~ rayon produced in this example was prepared
similar to that of Example 6, using similar viscose composi-
tion, cellulose cuene I.V., and other parameters, except
that the regeneration retardants used were dimethylamine
an~ a branched polyglycol, Berol Visco 399 (1.3% of each~.
All other viscose and spinning conditions were the same.
The fiber physical ~est results are listed in Table II
together with those of ~xample 7.
- 17 -
~ 160413
D . D . Whitney-C.F. Murphy-
G.C. Daul 1-14-3
- 18 -
TABLE II
Example 6Example 7
Ratio:
NaOHfCellulose in viscose 0.71 0.71
S Ratio:
H2So4 in spin bath/
NaOH in viscose 0.48 0.48
Modifiers Ethomeen C-25 dimethylamine
polyethylene serol Visco 399
glycol
Tenacity~ g/d
Conditioned 3.5 3.6
Wet 2.2 2.3
Elongati~n,% . ~ :
Conditioned 15 13 : :
Wet 17 15~ ~ :
Wet Modulus, g/d 0.5 0.7
Full Wave
Crimps/in~ 22 18
EXAMP~E 8
In this example, fibers were prepared with progressive-
ly decreasing amounts of acid and acid to caustic ratios.
A modified ~iscose spinning solution was produced in
much the same manner as in Example 1 including steeping,
pressing, shredding, aging, xanthating, and mixing
- 18 -
l 1~0413
D.D. I~lhitney-C.F. ~urphy-
G.C. Daul 1-14-3
-- 19 --
operations. IIowever, an unbalanced viscose composition of
7.5% cellulose and 6.0~ sodium hydroxide was used. The
viscose was ripened to a salt (.laCl) index of 5.2 with a
cuene I.V. of 2.8 dl/g resulting in a viscosity of 100 ball
~all seconds at 20C. The modifiers~, dimethylamine and
polyethylene glycol were added to the viscose at 1.3~ each
based on the weigh~ of cellulose. 30% carbon~disulfide
was injected durlng xanthation. ~ ~
The deaerated viscose was extruded throu~h a cluster
of spinnerettes with 24,200 holes (0.0020 inch diameter each)
into a primary acid coagulating-type spin bath containing~
2.9~ sulfuric acid, 15% sodium sulfate, and 2.~ zinc
sulfate at a temperature o 40C. The coaguIated~tow~was~
wrapped around a godet and led through a hot secondary
acid bath to a wash reel on which it was wrapped~several
times to prevent slippage.
The secondary acid bath contained about 2.0~ suIfuric
acid and residues of salts carried over from the primary
bath. It was maintained at about 95 to 98C, and the
tow was spun at 30 meters per minute and stretched 130%
through the secondary bath.
The tow was collected wet, cut into staple fiber
lengths, washed, desulfurized, an~ finished in the usual
manner with a staple fiber finish. After drying and con-
ditioning, single filament tests were run under standard
-- lg --
1 ~60~13
D.D. T~h~ tney-C.F. ~ur~hy-
G.C. Daul 1-14-3
- 20 -
procedures. The single filament fiber physical property
test results are shown in Table III as a family of fibers
with different primary bath acid concentrations. The acid
level had a direct effect on secondary bath stretch ancl
fiber wet elongation and modulus; i.e., the lower the acid
concentration with respect to caustic in viscose, the
hi~gher the ~odulus.
In Table III, Sample 1 is outside the scope of the
invention. At acid levels of 4% and higher, the wet elongation
is too high a~ there is some sacrifice of wet modulus. It
will be noted from this table that wet modulus and wet
elongation propertles are directly related to acid level.
The lower the acid, the lower the wet elongation and the
higher the wet modulus. The relationship is essentially
linear with respect to both of these properties. The
invention thus makes possible the ability ~o control wet
elongation and modulus by control of aci~ level. Insofar'
as is known, this has never previously been possi~le.
- 20 -
~ 1~0413
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-- 21 --
