melt spinning of poly(vinyl alcohol) plasticized …
TRANSCRIPT
(43) Vol.38, No. 2 (1982) T-61
(Received July 1, 1981)
MELT SPINNING OF POLY(VINYL ALCOHOL) PLASTICIZED WITH GLYCERIN
By Piao Dong-shwi* and Toshio Kitao
(Kyoto University of Industrial Arts and Textile Science, Matsugasaki, Kyoto 606)
PVA compounds plasticized by various amounts of glycerin were spun into fibers by melt process
and followed by the extraction with methanol and the drawing in a hot air. The structure and
properties of the fibers were studied by a x-ray instrument, a polarizing light microscope, a density
gradient column, a differential thermal analyser and a tensile tester. The best spinnability was found
for the compound containing 27 wt %glycerin. However, the exact glycerin content of the as-spun
fiber prepared from this compound was 11 wt%. The drastic decrease in glycerin content might be
attributed to the vaporization during the melt spinning and the bleeding after the melt spinning.
The extracted fiber could be drawn by around 7 times at 220•KC, while the plasticized as-spun fiber
was drawable up to 6 times. The drawn extracted fiber had the higher anisotropy evaluated by
polarized microscopy but the lower crystalline orientation by x-ray analysis than those of the
extracted fiber. This may be responsible to the mobility and the orientation of amorphous chains
in both plasticized and extracted fibers.
INTRODUCTION
The three techniques for producing fibers of synthetic linear polymers have been established:
melt, dry and wet spinnings. If a polymer can be fusible under reasonable conditions, the melt spin
ning is preferred because this is most convenient and simplest.
Poly(vinyl alcohol) (PVA) is currently spun into fibers by either wet or dry process since the de
composition temperature of PVA is very close to
the melting point. These solution techniques seem to be much complicated than the melt spinning. For example, the wet process is made up of many
sub-processes; i. e., the. preparation of spinning dope, the control of coagulant, the washing of
resultant fibers, etc. Many researchers, therefore, have challenged to
the melt spinning of PVA applying a variety of
techniques. Uzumaki et al. 1) studied the melt spinning of a fully saponified PVA of which degree of polymerization ranged from 1,000 to
2,000 and obtained fine fibers in a small scale. According to their patent, however, the spinning speed was limited to 30 m/min. Many attempts
have been made on the improvement of the spinnability of PVA. Kawakami et al.2) melt-spun some partially saponified PVA and then com
pleted the saponification after melt spinning. Matsumoto et al.3) studied the melt spinning of
poly(vinyl alcohol-ethylene) copolymer and found that the copolymer had to contain at least 50 mole%
of ethylene for smooth spinning. Kato et al.4)
made a fiber from a polymer blend of 30 wt% nylon 6 with 70 wt% PVA. However, it is obvious
that the chemical and/or the physical properties of the spun fibers must differ from the fiber of pure PVA.
Another catelogy of investigations is characterized by the use of additives. Sakamoto et al.5)
employed water vapor as a plasticizer of PVA to reduce the melt viscosity and to spin fine fibers
at higher take-up speeds. Yamada et al.6) also used water together with chemicals such as ethylene glycol, glycerin, and phthalic esters. These ideas have been extensively developed by Mashio et al.7) They used plasticized commercially avail
able PVA's with either ethylene glycol, ethylene urea, or glycerin and succeeded in the high speed melt spinning up to 500 m/min for a compound
comprising 10 parts of PVA and 5 parts of ethylene
urea. They also described that another mixture
* On leave from The Institute of Chemical Fibers, Changchun City, Jilin Province, China
T-62 SEN-I GAKKAISHI (報 文) (44)
containing 60 parts of PVA and 40 parts of
glycerin could be spun at 300m/min. These fibers could be hot-drawn, annealed, and acetalized
in the conventional manner. In their patent, how
ever, no attempt was made on the elimination of
plasticizer from the resultant fibers. They have also mentioned that the tensile strength of the
fiber plasticized with glycerin was 8g/d. It implies
that the plasticizer might play an important role
on the molecular orientation in the course of
hot-drawing.
Unfortunately, the details of the procedure and
the properties have not been revealed in the
patents. In the present paper PVA's plasticized with varying amount of glycerin were melt spun
into fibers and then glycerin was extracted from
the fibers. The hot drawing of the fibers was made
on both the plasticized and the extracted samples.
The orientation behavior was estimated by using
x-ray diffraction analysis and polarized microscopy.
EXPERIMENTAL
MATERIALS
A PVA was supplied by UNICHIKA Co. Ltd.
According to UNICHIKA, the average degree of
polymerization was 1,700, the saponification de
gree was 99.91mole%, and the residual sodium
acetate was around 0.5 mole%.
Prior to the fabrication, the PVA powder was
washed with large amounts of water and methanol
to eliminate the residual sodium acetate and then
dried in an air oven. The 70 parts of glycerin
(reagent grade) was mixed with 30 parts of distilled
water, as a swelling agent to PVA and the carrier
of glycerin. A predetermined amount of this
glycerin-water mixture was sprayed onto the PVA
powder. After being aged at about 95•KC for 24
hrs, the compound was dried in a vacuum oven at
105•KC for 24 hrs to eliminate the water. The
residual water results in the formation of bubbles
during the melt spinning at elevated temperatures.
The dry compounds prepared were allowed to
stand for two more days in a desiccator with silica
gels. The glycerin content of the final compounds
was varied from zero to 45 wt%.
MELT SPINNING
Melting point of various glycerin plasticized
PVA's was first determined by using a differential
thermal analyser (DTA), Model DT-20B, Shimadzu
Co. Ltd. The heating rate was 20•KC/min.
The spinnability of these plasticized PVA's was
qualitatively estimated by using a plunger type
extruder equipped with a spinneret having a 1.0
mm orifice, which was designed in our laboratory.
The actual melt-spinning experiments were per
formed with an another laboratory spinning instru
ment equipped with a 25 mm single screw extruder,
a spinneret with twelve 0.5 mm nozzles, and a
conventional take-up device.
The glycerin in the as-spun fibers was extracted
with boiling methanol in a Shoxlet apparatus for
more than 14 hrs. The drawing was made in a
Bistron instrument, Iwamoto Machinary Ltd.,
which was basically designed for the biaxial draw
ing of plastic films.
MICROSCOPIC OBSERVATIONS
The surface structures of the resulting fibers
were observed with a scanning electron microscope.
Gold-sputtered samples were subjected to the
observations and a standard technique was em
ployed.
O RIENTATION
The overall degree of orientation of fibers was
estimated with a polarizing microscope equipped
with a Berek compensator. The measurement was
made under the sodium D-line, of which wave
length is 589 nm. The crystalline orientation was
estimated from wide angle X-ray scattering (WAXS)
studies radiated by the nickel filtered Cu-ku beam
through a tubular collmetor with 0.5 mm slit.
DENSITY AND CRYSTALLINITY
Assuming the simple two phase model, the
degree of crystallinity was estimated by the densi
ty, measured in a n-heptane-carbon tetrachloride
density gradient column. The density D is related
to the crystallinity X using a common equation:
1/D=(X/Dc)+(1-X)/Da where suffices c and a
refer to the crystalline and amorphous, respective
ly. The crystalline and the amorphous densities
have been reported by many researchers. Among
them, in the present study, we chose the values
proposed by Sakurada et al.8), namely Dc=1.345
g/cm3 and Da=1.269g/cm3
TENSILE PROPERTIES
Tensile experiments were run at room tempera
ture by using an Instron type tensile tester,
Shinkoh Model TOM 200D. Guage length was
30mm and cross head speed was 30 mm/min.
(45) Vol.38, No.2 (1982) T-63
RESULT AND DISCUSSION
Figure 1 shows the variation of the melting
point of PVA as a function of the weight fraction
of glycerin, indicating that the melting point is a
linear decreasing function of the glicerin content.
The spinnability of these PVA-glycerin compounds
was qualitatively examined by using a small plunger
type extruder. Table 1 summarizes the spinnability
of various compounds. The best spinnability was
found for two samples which contained 27 and
35wt% glycerin. For all samples the optimum
spinning temperature was approximated to be
thirty degrees higher than their melting point, i. e.,
(Tm+30)•KC. When the spinning was conducted at
temperatures lower than (Tm+30)•KC, the polymer
stream emerged through the spinneret orifice be
haved as an elastomer and was hardly melt-drawn
into fine fibers. Whereas when the spinning tem
perature raised to higher, the extrudates colored
brownish and decomposed just below the spinneret.
Although the compound containing 35wt% glycer
in was almost equally spinnable to that of 27wt%
glycerin, the latter was subjected to the further
experiments in order to minimize the plasticizer
Fig. 1. The variation of melting point as
a function of glycerin content.
content.
In the melt spinning with a screw extruder, the
temperature of the spinneret was fixed at 232•KC
which was just 30•KC higher than the melting point
of this compound. Under such conditions of the
spinning, the compound was very good at the
spinnability and hence the fiber having the diame
ter less than 60 microns could be obtained at the
take-up speed of 300m/min or faster. For the
convenience of handling, however, the rates of
extrusion and taking-up were controlled to obtain
an as-spun fiber of 150 microns.
Since the bleeding of glycerin was apparently
observed on the surface of the as-spun fibers, the
fibers thus prepared were stored in a desiccator
with silica gel for more than three weeks to equi
librate the glycerin content. The amount of
glycerin in the as-spun fiber was cross-checked by
both Shoxlet extraction and DTA techniques. The
actual glycerin content determined from the ex
traction experiment was about 11wt%. This
amount was in good agreement with the result of
DTA, i. e. the melting point of 220•KC measured
with DTA. (c. f. Fig. 1)
This drastic decrease of glycerin from 27 to 11
wt% must be caused not only by the bleeding from
the as-spun fibers but also by the evaporation in
the course of melt-spinning. The bleeding of
glycerin from the as-spun fibers was confirmed
from its moisture regain behavior. When the as
spun fiber was allowed to stand in a desiccator
conditioned at 20•KC and 65%RH, the sample
weight increased significantly as represented in
Curve 1 of Figure 2. In the earlier stage, the
increase is rapid and fairly linear with respect to
the time stored. But the rate of increase gradually
slows down and finally levels off on prolonged
storage. This suggests that the sorption of water
must be governed by two different mechanisms:
Table I. Spinnability of PVA plasticized by various amount of glycerin.
Note; -indicates the skip of the examination.
T-64 SEN-I GAKKAISHI (報 文) (46)
Fig. 2. The plot of moisture regain against the
time stored at 20•KC and 65%RH for
as-spun (_??_) and extracted (_??_) fibers.
in the earlier stage of the rapid increase, water
must be sorbed into the glycerin which bled on
the surface of the fibers. After the saturation of
water in this glycerin layer, the diffusion of water
from glycerin to the fiber may be attributed to
the apparent rate of the weight increase.
Some samples of the as-spun fibers were ex
tracted in a Shoxlet apparatus to get extracted
fibers and the rest was subjected to drawing
without extraction. Both the plasticized and
extracted fibers were drawn in the Bistron instru
ment at various temperatures. The maximum draw
ratio varied markedly with temperature as shown
in Figure 3. It is shown that the drawability of the
extracted fiber was always greater than that of the
plasticized one. This is possibly attributed to the
molecular relaxation during the course of extrac
tion.
Figure 4 shows the variation of the fiber density
with draw ratio. The density of glycerin at 30•KC
is 1,26g/cm3 which is very close to the amorphous
density of PVA 1,269g/cm3, given by Sakurada
et al.8). Assuming that glycerin locates only in
amorphous region, we can adopt the conventional
equation: (1/D)_??_(X/Dc)+(1-X)/Da. The density
(and hence the crystallinity) of the extracted fiber
was independent to the draw ratio, whereas that
of the plasticized fiber increased monotonically
with increasing draw ratio.
In usual melt spinning the cross section of the
resulting fiber is almost circular, as the volumetric
retraction due to the solidification is rather small.
It is interesting to see whether the fibers prepared
Fig. 3. The effect of draw temperature on the drawability of plasticized (_??_) and extracted (_??_) fibers.
Fig. 4. The effect of drawing at 220•KC on the
density and the crystallinity of plasti
cized (_??_) and extracted (_??_) fibers.
in the present study have circular cross section or
not, even after the elimination of glycerin. The
SEM photographs shown in Figure 5 indicate that
all the fibers are circular and no detectable defect
can be seen on their surfaces. So, the anisotropy
of the fibers was determined by using a conven
tional polarizing microscope.
Figure 6 shows the relation between birefrin
gence and draw ratio for both the plasticized and
extracted fibers. Before drawing, the birefringence
of the plasticized fiber is slightly greater than that
of the extracted one. The difference may be
attributable to the molecular relaxation during the
extraction of glycerin, as was mentioned above.
The birefringence of the extracted fiber increased
with drawing and reached to 38•~10_??_3 at draw
ratio of 7. The birefringence of the plasticized
fiber tends to increase only in the early stage of
(47) Vol. 38, No. 2 (1982) T-65
(A)
(B)
(C)
(A)
(B)
(C)
(D)
(E)
(F)
(G)
(H)
Fig. 5. The SEM photographs of various PVA fibers: (A) plasticized and undrawn
(60x), (B) extracted and undrawn (60x), (C) extracted and drawn by 7 times (120x).
Fig. 6. The effect of drawing on the birefringence of plasticized (_??_) and extracted (_??_) fibers.
Fig. 7. The WAXS patterns of various drawn fibers: (A) plasticized and undrawn, (B) plasticized and drawn by 2.1, (C) plasticized and drawn by 4.0, (D) plasticized and drawn by 5.0, (E) extracted and undrawn, (F) extracted and drawn by 2.1, (G) extracted and drawn by 4.0, and (H) extracted and drawn by 5.0.
drawing and soon levels off to 22•~10-3.
Figure 7 shows the wide angle X-ray scattering
patterns of various PVA fibers. It is clear from
Figure 7(A) and 7(E) that the use of the plasticizer
does not modify the crystalline form but reduces
the crystal size. In other words, the plasticizer
does not induce any unfavourable effect on the
T-66 SEN-I GAKKAISHI (•ñ•¶) (48)
crystallization of PVA. On drawing, the crystallites in the both fibers tend to orient along the fiber axis. The WAXS patterns obtained for the drawn extracted fibers seem to be more diffused than those of the drawn plasticized ones. Indeed, in the patterns taken for the extracted fibers the
(101) reflection comes in contact with the broad (200) arc. On the other hand, those of the drawn plasticized fibers are obviously distinguished each other. In addition, the azimuthal intensity distributions of the (101) and (200) reflection are sharper for the plasticized fibers than for the extracted ones.
The situation is just opposite to the result obtained by the polarizing microscopy. The difference in the orientation behavior must be explained in terms of the mobility of their amorphous chains. The plasticizer may facilitate the reorganization of crystallites during the drawing but may enhance the relaxation of amorphous chains after the fibers were released from the drawing force.
Figure 8 shows the typical stress-strain curves of drawn fibers. As was expected, the drawn extracted fiber has the greater tensile strength, the
Fig. 8. The stress-strain relation for plasticized
(1) and extracted (2) fibers.
higher initial modulus and the smaller elongation
at break. Numerical values of the tensile properties
of the fibers are given in Table II.
Finally the extracted drawn fibers were acetalized
in the ordinary manner. The softening temperature
in water for the unacetalized fiber was 81.4•KC.
ACKNOWLEDGEMENT
The authors indebted to Drs. T. Yasui and A.
Kubotsu of Kurare Co. Ltd. for obtaining the SEM
photographs.
REFERENCES
1) M. Uzumali, E. Shimoda, and M. Takamura; Jpn. Patent s36-12559 (1961)
2) H. Kawakami, H. Fujii, and H. Takachi; Jpn. Patent s47-22099 (1972)
3) T. Matsumoto et al.; Kobunshi Kagaku, 23, 610 (1971), Sen-i Gakkaishi, 30, T391 (1974), ibid, 30, T398 (1974), and ibid, 31, T152 (1975)
4) H. Kato, K. Fujiwara, and U. Anzai; Jpn. Patent s48-22833 (1973)
5) T. Sakamoto, H. Kizu, Y. Yokomaku, S. Hibara, I. Otsubo, and S. Kitagawa; Jpn.
Patent s23-1140 (1948) 6) M. Yamada, T. Kinoshita, and T. Inoue; Jpn.
Patent s25-356 (1950) 7) F. Mashio, K. Yamaoka, H. Kawakami, and
E. Sato; Jpn. Patent s37-9768 (1962) 8) I. Sakurada, K. Nukushina, and Y. Sone;
Kobunshi Kagaku, 12, 506 (1955) 9) H. Kawase; "Sen-i Binran", Maruzen, Tokyo
(1968), p. 659 10) E. Nagai; ibid, p. 659
Table II. Tensile properties of fibers.
(49) Vol. 38, No.2 (1982) T-67
グ リセ リンで可塑 化 した ポ リビニル アル コール の溶融 紡 糸
京都工芸繊維大学繊維化学科 朴 東旭,北 尾敏男
グ リセ リンを 種 々の割合 で混 合 したPVA配 合物 を溶
融紡 糸 した。 この繊 維 を メタノール紬 出 しグ リセ リンを
除去 した後,加 熱 空気 中で延伸 した。繊 維の 構造 およ び
性 質を,X線回 折,偏 光顕微鏡,密 度 勾配管,DTA,
および引張試験機 に よ り評価 した。 グ リセ リンを27wt
%含 む試料 が最 も良 好 な紡糸性 を示 した。 この配合 物か
ら作 った未延 伸繊維 は,紡 糸お よび保存 過程 におい て グ
リセ リンの一部 を失 ってお り,延 伸 に供 した 試料中 には
11wt%の グ リセ リンが残 って いた。 メ タノール抽 出に
よ り完全 に グ リセ リンを 除いた繊 維 は,約7倍 延伸す る
ことがで きた 。グ リセ リンを除 いた繊維 は グ リセ リンを
含 む繊維 よ りも大きい 複屈折 と小 さい結 晶勾 配度を示 し
た 。 この原 因 は,非 晶質 の配向度 の相達 によ って説明 さ
れ た。