Sill~-Lilce Fiber K-6 (chinon) S. MORIMOTO
A cry1oni trile is grafted to proteins to produce Chinon
orldwide and for a number of years, there have W been many attempts to produce synthetic fibers to match the properties of natural silk. Forty years ago the Toyobo Co. tried making ‘(regenerated silk” from silk wastes. The goal then, as now, was to produce a silk-like synthetic fiber. I n 1956 one of the Toyobo chemists, Dr. Yamamoto, decided to try grafting vinyl monomers on proteins and started basic research on the synthesis and formation of a fiber polymer. His research has resulted in the development of K-6 fiber or Chinon (trade name). Table I shows that even though the rest of the world is slowly increasing its production of raw silk, still as of 1967 Japan was producing over 50%. At the same time, Japan is consuming 55y0 of the world consumption, followed by 11.4% for China and 9.8% for the United States. Most of the silk in Japan goes into the traditional kimono, a fact which explains Japan’s interest in silk and the effort she has put into research in silk and/or silk-like fibers.
TABLE 1.
PRODUCTION O F SILK
( A ) World, tom/yr
( B ) Japan, tons/yr
BIA,
Year 1938
56,457
43,152
76.4
1957
31,260
16,666
60.4
%
1958
33,635
20,014
59.2
1959
32,610
19,120
56.6
1960
31,356
16,047
57.6
1961
31,813
18,676
56.7
1962
33,000
19,696
60.3
1963
31,005
16,079
56.3
1964
32,823
19,456
59.3
1965
33,231
1 9,106
57.5
1966
33,02 1
16,694
56.6
1967
34,240
16,921
55.3
VOL. 6 2
NO. 3
MARCH 1 9 7 0
23
TABLE II.
AMINO ACID COMPOSITION IN SILK FIBROIN AND CASEIN
Amino acid
H
(Wt %)
SilkJibrin
HzA~-l'-COOH
Silk fbrin
Silk plastin
Glycine
H
39.9
25.5
1.5
Alanine
-CHB
29.0
23.6
2.5
Serine
-CH20H
13.8
12.6
5.2
Tyrosin
9.2
10.5
5.2
Valine
3.32
2.30
5.9
0.1 9
5.95
6.1
0.76
5.27
3.7
1.14
3.44
19.7
0.77
3.44
13.2
...
2.32
4.5
0.61
1.76
4.2
...
1.36
7.2
...
0.86
8.9
...
...
2.7
...
2.5
I
R
R
Aspartic acid
-CH2COOH
Arginine
-CH2CH,CH
Glutamic acid
-CH
Leucine
+ isoleucine
Phenyl alanine
CH,COOH /CH,
,CH,
-CH2CH, CH,
-C
H
-CH2-
2
-C\CH2CH.
a
CH,
I
OH
-CH,CHoCH CH,-
Proline
/ " '
\kH
Threonine Lysine
NH-C
I
CH,
Casein
CH,KH2
CH,
I
\
Histidine Methionine
-CH,CH,SCH,
...
Tryptophane
"E,,i
...
e . .
1.5
H -CH&
Cystine
-CHS
I
Total
24
INDUSTRIAL A N D ENGINEERING CHEMISTRY
...
...
96.7
96.9
0.29 95.3
Silk fibroin, the principal part of silk, consists of 80% crystalline silk fibrin and 20% amorphous silk plastin. The amino acid residues in fibrin (Table 11) consist of small side chains such as glycine, alanine, and serine. The amino acid residues in the plastin area of the fiber are made up, to a considerable degree, of large side chains, resulting in the amorphous characteristics of the final material. The essentially crystal structure of silk due to fibrin furnishes the mechanical properties of the material. Plastin, or the amorphous area, furnishes the dyeability and soft handling of silk. Chinon is a polymer fiber obtained by grafting acrylonitrile on casein. Casein is made up of large amounts of amino acid residues, with large side chains and little of the amino acid residues with small side chains. Casein, then, forms the amorphous regions of Chinon, but not the crystalline regions. Casein contains many residues susceptible to dyes and therefore contributes greatly to the dyeability of Chinon.
TABLE 111. FIBER PROPERTIES OF S I L K AT VARIOUS POSITIONS IN COCOON
Position, M5
B WS,
3.28
Elongation, % 24.3
3.46
3.64
24.3
25.4
450
3.1 6
4.03
23.5
18.5
650
2.98
3.89
22.7
17.8
250
50
a
Strength, Denier 3.74
g/d
%b
31.9
850
2.40
4.33
23.5
14.2
1050
1.30
5.3 1
20.5
19.2
Av.
2.84
4.08
23.1
21.3
Distance from outside end of silk in cocoon DWS; Decrease in weight at scouring.
History of Protein Fibers (U.S. and Europe)
Characteristics of Natural Silk Silk fiber is one of the finest yarns used for clothing materials. Table I11 shows the denier, the strength, the elongation, and the decrease in weight at scouring a t various positions (distances from outside end of silk in a cocoon). Although the average value of the denier is 2.84 d, a very fine part, 1.3 d, exists inside the cocoon. I t is the mixing of these various deniers which gives us a fiber of excellent handling. T h a t a cross section of silk fiber is nearly triangular is a second characteristic. Third, silk fiber is chemically unstable. While it exhibits good moisture retention and good dyeability, the resistance to chemical reagents and to weather is not satisfactory. Fourth, silk fabric is given its very soft handling by the removal of sericine. The fiber is composed of a double structure, fibroin within surrounded by an outer layer of glue-like sericine. So-called “t;ilk-like” handling is achieved by removing the sericine layer by an alkaline scouring after the fiber is woven into fabric. Now Japanese chemists are attempting to get silk-like fibers by synthetically manufacturing these four features into a fiber. Table I V indicates the different approaches made by various companies, as well as the processes and features of each. Table V shows the properties of each compared to silk. Methods for making silk-like fibers may be classified into several types : fibers from new polymer, modification of existing fibers, and modification in fiber assembly. O n the whole, the problem has proved particularly
Year
Company
-
Fibers from glue 1857 Fibers from casein 1904 1935 Production of fiber from casein SNIA 1936-8 Production of fiber from casein Courtaulds 1938 Production of fiber from I.C.I. peanut protein Use fabrics made from wool1939 Ford Motor Co. soybean protein fiber blends 1948 Production of fiber from zein Virginia-Carolina Chemical
1923 1929 1931 1932 1933 1935 1937 1938 1938 1940 1949
History of Protein Fibers (Japan) Study of regenerated silk yarn Kanegafuchi Spinning Co. (Kanebo) Study of regenerated silk yarn Toyobo Pilot plant Kanebo Pilot plant Toyobo Production of regenerated silk Toyobo yarn, 0.5 T / D Production of regenerated silk Kanebo yarn, 1 T / D Study of fiber from soybean Showa Sangyo Co. protein Study of fiber from soybean Nippon Oil and Fat protein co. Shinko Jinken Co. Study of fiber from soybean protein Shinko Jinken Co. Production of fiber from soysoybean protein, 3 T / D Manshu Daizu ChemStudy of fiber from soybean protein ical Industry
AUTHOR S. Morimoto is in charge of research at the Katata Research Institute, Toyobo Co., Ltd., 7300-7, Honkatata, Otsu, Shiga, Japan. This paper was presented as part of the Symposium on Novel Processes and Technology of the European and Japanese Chemical Industries, 758th Meeting of the American Cfiemical Society, New York, N. Y., September 7-72, 7969. VOL. 6 2
NO. 3 M A R C H 1970
25
TABLE IV.
Trade name
Company
SILK-LIKE FILAMENT YARN
Start to produce current output
Structure and process
Features
Vinylon filament
Vilon
Nippon Vinylon
Fall '63 9.5 t/doy
Filament yarn of amino-acetalized PVA b y dry spinning
Fine denier light color Good feeling and luster
Acryl filament
Pulon
Asahi Chemical Industry
4 t/day
Filament yarn of polyacrylonitrile b y wet spinning
Excellent luster tight color Good feeling like silk
Proiein-AN Copolymer
Chinon (K-6)
Toyobo
October '69 1 t/day
Filament yarn of AN grafted casein b y wet spinning
Excellent feeling and luster like silk Good resistance to chemicals Good crease recovery
Polyesler-ether
A-Tell
Nippon Rayon
April '68 1 t/day
Repeating
spinning
Repeating
Qiana
DuPont June '68
Luster like silk Good light resistance Good resistance to chemicals Good feeling and luster like silk Good crease resistance and dimensional stability
Qco-3-
+CH,CH20 Melt
Cycloaliphatic polyamide
unit
unit
f
-~H++cH2@-~~j0
0
n = 9,10,12
Polyester filament
Sil-Pearl Teijin Sil-Look Toyo Rayon
'65 500 t/m
Triangle cross-section filament yarn
Mixed yarn (NY 4cell-acetate)
Mixcell
Fall '68
Yarns of NY-6 and cellulose acetote mixed b y means of static electricity
Teijin
TABLE V.
Fiber Silk Chinon (K-6) Nylon Pulon (acryl filament) Vilon (PVA filament) Sil-Pearl (PET filament) A-Tell (polyetherester) Cell-Aeetate
26
Strength, gld
Luster like silk
PROPERTIES OF SILK-LIKE FILAMENTS
Elongation,
70
Young's modulus, kg/mm2
Spec t>c gra2zQ
Boiling water shrinkage, m /O
11.0 5-6 4.5 2.0 5.0 0.4
0.9 2.5-4.5 12-14 8.0 2.6 6.2
3.0-4.0 4.0-5.2 4.8-6.4 3.3-4.3 2.9-3.0 4.9
15-25 15-25 28-42 13-20 19-21 22.6
650-1 200 400-1 000 200-450 400-900 700-780 1015
4.0-5.3
15-25
700-900
1.34
0.4-0.5
1.2-1.4
25-35
350-550
1.32
6.5
INDUSTRIAL A N D ENGINEERING CHEMiSTRY
1.33-1.45 1.20 1.14 1.17 1.28 1.38
Oj?cial regazn, 7c
7.5
0.7
Melti;g point, C
... 21 5
...
225 255 228
difficult because many of the synthetic fibers proved to be nonabsorbent or slippery, or they exhibited a tendency to be electrostatic, or proved to be poor in dyeability. Of all the manufactured fibers, however, Chinon was exceptionally close to silk in its properties (Tables VI, VII, and VIII). Artiflcial Protein Fiber
Because natural silk has had excellent properties for textile end-use, it has always been high priced. Therefore for a long time there were many attempts to produce artificial silk yarn from low-priced proteins such as soybeans, peanuts, and zein. These attempts are outlined as follows: T h e greatest defect of these protein fibers was that their mechanical properties were quite insufficient for practical use. T h e strength and elongation of the typical artificial protein fibers are as follows:
TABLE VI. PROPERTIES OF CHINON COMPARED W I T H THOSE OF OTHER FIBERS
Chinon
Properties
Cellulose Meritriacetate nova
Silk
4.0-5.2
3.0-4.0
1.2-2.9
Wet strength, g/d
3.5-4.0
2.1 -2.8
0.8-1
15-25
15-25
25-35
30-50
16-27
27-33
30-40
80
1.O-2.0
2.9
1.0-1.2
Dry elongation, Wet elongation,
% %
Knot strength, g/d Young’s modulus, kg/rnrn2
400-1 000
650-1 200
300-500
9
2.5-3.5
5-6
Moisture percent-
.O
Specific gravity
1.20
Shrinkage in boiling water, %
TABLE V I I .
1.33-1.45
0- 1
2.5-4.5
1.30 0.7
.., ...
ELECTROSTATICITY OF CHINON
Kind of texture
Resistance,
Chinon Silk Polyester Nylon
Crepe de chine Habutoe Crepe de chine Taffeta
8.0 X 1 O’O 1.5 X 1O’O 1.0 1012 1.0 10’2
TABLE VIII.
Afinity, fastness
0. G
Dry elongation Wet elongation
15-20 20-25
Chinon History
... . ,. ...
Fiber
1
Dry strength Wet strength
0.3
age, %, 20°c, 60 RH
%
g/d
0.7
Dry strength, g/d
n
Chinon was called “K-6” in the first stages of its research and development. K stands for the Japanese word “Kaihatsu” which means development, and the G refers to the sixth program in the several projects started at the same time in 1956. I t was decided that to manufacture a silk-like fiber, the amorphous part of the semicrystalline materials used must determine the feel and the esthetic properties of the natural thread. Based on this concept, tremendous basic research was done on the introduction of natural protein, such as that in soybeans, peanuts, zein, and milk casein, into the amorphous part of the fiber. Finally milk casein was used for the development because of its excellent characteristics and its economic superiority. Much effort was required for the solution of problems, concerning the properties and uniformity of the fiber
x x
DYEABILITY OF CHINON FOR VARIOUS CLASSES OF DYES“
Acid dyes
Premetalited dyes
Mordant dyes
Direct dyes
Basic dyes
Disfiersed dyes 0
Affinity
0
0
0
0
0
Buildup property
0
0
0
0
0
A
0
0
0
0
0
0 - A
Chinon Fastness to light
Silk
Fastness to washing
Fastness to rubbing a
0 Good.
A
Fair.
0
0
A - X
-
A - X
0 A-X
0 - A
Chinon
0 - A
0
0
Silk
A-X
A
0
X
X
A-X
-
Chinon
0
0
0
0
0
0
Silk
0
0
0
0
0
I
X Bad.
VOL. 6 2
NO.
3
MARCH 1970
27
Figure 7,
Flow sheet of polymerization process for Chinon
Figure 2. Flow sheet of jber-making process for Chinon
A
Figure 3.
Cross sections of Chinon
A . Left, X400 B . Right, X5000 28
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
product and the scale-up of the processing equipment to a production and stable operating level. Chinon fiber shows excellent mechanical properties with a considerable amount of casein (30 wt %). This fact suggests that protein must be uniformly dispersed in the fiber. Flow sheets of the production processes are shown in Figures 1 and 2. Chinon Properties
The general properties of Chinon, in comparison to those of other fibers, are listed in Table VI. Chinon comparable to silk except in knot strength and shrinkage in boiling water but is superior to Merinova developed by SNIA Viscosa and composed of casein only. I n general, the fiber from a globular protein, such as casein, is inferior in fiber-forming properties and consequently is poor in mechanical properties. Containing a considerable amount of casein, Chinon fiber shows excellent mechanical properties and is comparable or often superior to those fibers of a general acrylic type. If the protein dispersed in the fiber reacted only to the same extent as in protein fiber alone, Chinon would be less in strength than an acrylic fiber. T h a t is not the case. There are two possible explanations. One is that the protein may act as a plasticizer to aid orientation and crystallization of the polymer. The other is that the protein molecule may have some interaction with the polyacrylonitrile molecule in the fiber. The problem will continue to be studied. The conjecture is that the protein dispersed uniformly in the fiber of acrylonitrile plays an important role in achieving the desired properties. At any rate, cross sections of Chinon fiber in Figure 3, A and B, show protein dispersed uniformly in it. Elasticity. The elastic recovery property of Chinon is shown in Figure 4 to be superior in comparison to that in either silk or cellulose triacetate. This property is related to the good crease resistance of its fabric. Light resistance. One of the most significant defects of silk is its poor resistance to light. Compared to silk, Chinon is much more stable to sunlight (Figure 5), and, in fact, is foremost among synthetics in this respect,
80
-,\"
Y
z
8
60
4
w
40
k 0 c-
6
t;
[z
20
3 RADIATION TIME (HRS) Figure 5. Comparison of light resistance, Chinon and silk (radiated with Xenon Fade-Meter) Retention of strength of Chinon Retention of elongation of Chinon Retention of strength of silk Retention of elongation of silk
50
40 I00
-s
3.0
>
LL
f
80
0
20
2U
0 r
9
60
-1 I
1.0
40 0
I
2
3
4
5
0
ELONGATION W e )
Figure 4. Comparison of elastic recovery of Chinon with those of silk and cellulose triacetate
Fig VOL. 6 2
NO. 3 M A R C H 1 9 7 0
29
5.0
4.0
e
c
9 3.0 I
b z k!
t;;
2.0
1.0
0
Figure
I OC
s
80
I
v
W
>
0
86 0 z 0
b 2 I40 X
w
20
0
"
40
60 80 DYEING TEMPERATURE
IO0
Figure 8. Effect of dyeing temperature for acid dye Dye, Suminol leuel, Rubinol 3 GS $ H o j dye bath, 3.0 Liquid ratio, 7.50 Dyeing time, 60 min 30
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Heat reaction. Figures 6 and 7 demonstrate the effect of temperature on the stress-strain (S-S) curve of Chinon in water and fluid paraffin, as well as the S-S curves of silk, all in comparison to the acrylic filament. Acrylic fiber decreases in strength and increases in elongation as temperature increases in the wet state. When we compare the S-S curve of Chinon with that of the acrylic fiber in water a t 96"C, we note that the modulus a t the initial state shows not much difference, but Chinon shows considerably higher strength and smaller elongation a t the breaking point. In comparison with the change in the curve of silk in hot water, Chinon shows a larger decrease in strength and modulus and is inferior to silk. This behavior may be attributed to the physical properties of the fiber components. Therefore in hot-water handling of the fiber, care is necessary. The S-S curve of Figure 8 in fluid paraffin corresponding to a dry heating state, shows that Chinon, in its mechanical property a t high temperature, is superior to the acrylic filament. Electrostaticity. Table VI1 demonstrates that although Chinon is a little higher in electrostatic property than silk, it is much lower in electrostaticity than either polyester or nylon. Therefore among synthetic fibers, Chinon must be classified as best in this property. Dyeability. One outstanding characteristic of Chinon is its dyeability. As the noncrystalline part of Chinon consists of polypeptide, the dyeing behavior of Chinon is distinguished from other synthetic fibers. Table VI11 shows that Chinon has excellent affinity for various classes of dyes-acid, premetalized, mordant, direct, basic, and disperse dyes-and exhibits fine buildup properties so that Chinon can be dyed to deep shades, except with disperse dyes. The fastness of the dyed fibers is superior to that of silk as shown in the table. Although Chinon has an affinity for these various classes of dyes, in practice acid dyes are chiefly used. This is a n excellent quality of Chinon because we can obtain the same colored dyed materials as silk, and we can dye blends of Chinon and silk as well. Furthermore, Chinon can be dyed with basic dyes to meet a user's requirements-for example, the requirement of fluorescent brilliant colored materials. Chinon is a n easily dyed fiber and can be taken to dark shades a t 100°C without using a carrier or high temperature. Figure 8 shows the effect of dyeing temperature on acid-dye uptake. Acid dyes can diffuse into Chinon at low temperatures, and the diffusion rate of dye into Chinon increases in proportion to the rise of dyeing temperatures. However, the dyeing temperature is sufficient a t 100°C to get deep-dyed materials. An acrylic fiber, in contrast to Chinon, cannot be dyed below 80"C, its transition temperature, but the dyeing rate increases remarkably above this level, resulting in a fully dyed material. However, the existence of a dyeing transition temperature-the sudden change of dyeing rate-causes uneven dyeing. Chinon, on the other hand, does not exhibit a transition tem-
TABLE I X . DYE SITE OF CHINON I N COMPARISON TO NYLON AND SILK, MEQ/KG
Class of @e
Chinon
Nylon
Silk
Acid dye Basic dye
200 190
40
290 150
..
MIGRATION PROPERTIES OF CHINON, SILK, AND NYLON
TABLE X.
Degree of migration, % Chinon
Silk
Nylon
Acid Blue 25
77.5
99.7
36.9
Acid Red 135
50.4
81.8
12.3
Acid Red 85
24.3
20.6
0.5
12.5
5.6
0.6
Dye structure
CI No.
I
PH
Acid Blue 170
TABLE XI.
Concentration, Chemicals
HCOOH
NanCOa
RESISTANCE TO CHEMICALS
Treatment condition Temjerature,
%
OC
Time, min
Retention of tenacity Chinon SiK
1
90
60
94
76
20
20
300
100
100
1
90
60
100
90
20
20
300
00
78
1
90
60
90
70
20
20
300
00
90
20
20
300
91
Dissolve
HzOz
1
90
120
a9
03
NaHSOa
1
90
120
96
96
NazSn04
1
90
120
93
95
CCl4
100
20
300
100
100
CI2C=CCLz
100
20
300
100
100
NaOH
VOL. 6 2
NO. 3
MARCH 1970
31
80
IO0 h
-8 70
8
Y
w
Y
2i
W
0
z
3 60 =I
z 0 50
111
m
tn3
50
4X
W
20
60
80
EXCITATION PURITY (%)
0 70 80 90 DYEING TEMPERATURE OC
60 Figure 9.
IO0
Figure 7 7 . Color Yellox RS)
.pc$CUfzon
of Chinon (dje: Sumilight Supra
Efect of djeing temperature f o r basic dye
Sumiacryl Nuuy Blue G, 27, 0 W F CH&OOH, 7% 0 WE C H ~ C O O N Ug570 , 0 MF ’ Liquid ratio, 1.50 Dyeing time, 60 miri
50
40
3 30
v
W 0
z Q, --I
120
ik
IO
Figure 70. Color specification of Chinon (dye: Sumilight Supra Yellow RS) 32
40
INDUSTRIAL A N D ENGINEERING CHEMISTRY
perature (Figure 9 ) . For this reason, the absorbance of dye into Chinon is achieved slowly in proportion to the rise of the dyeing temperature. The result is an evenly dyed Chinon. Dye sites of Chinon for acid dye and basic dye are listed in Table IX. The saturation dye absorption of Chinon for acid and basic dyes is almost the same as that of silk. The “Rrocking phenomenon” takes place in the dyeing of nl‘lon by an acid dye mixture owing to the low number of dye sites in nylon. Chinon has a high number of dye sites for both acid and basic dyes, so that the “Brocking phenomenon” does not take place. The result is evenly dyed fibers. Migration is related to the even dyeing properties of a fiber and is a most important attribute to achieving even dyeing. The degree of migration depends on the dye structure. I n comparison with nylon, Chinon is much closer to natural silk (Table X) in respect to migration. In general, color brilliancy of a dyed material depends on the chemical and physical properties of the fiber. Figures 10 and 11 show the brilliancy of dyed Chinon in comparison with silk. Chinon can be dyed a deeper shade than silk having an equal quantity of dye inside the fibers, and it exhibits a higher brilliance than silk under conditions of the same excitation purity. The casein existing in the noncrystalline part of Chinon may prevent dye aggregation and may take the dyed fiber into brilliancy. The resistance of Chinon to chemicals in comparison to silk is shown in Table XI, Chinon has good resistance to acid, to organic solvent, but is stained yellow with alkali without a decrease in tenacity. In Chinon, with its uniform qualities, we think we have achieved the long-sought goal of manufacturing a fiber close to the natural cocoon silk.
