US3027224A

US3027224A - Polyvinyl alcohol fibers having improved elasticity

Info

Publication number: US3027224A
Application number: US784092A
Authority: US
Inventors: Osugi Tetsuro; Tanabe Kenichi; Kawabe Yotaro; Yabe Hisashige; Morimoto Osamu; Miyazaki Sadamaru
Original assignee: Kurashiki Rayon Co Ltd; Air Reduction Co Inc
Current assignee: Kurashiki Rayon Co Ltd; Airco Inc
Priority date: 1958-12-31
Filing date: 1958-12-31
Publication date: 1962-03-27
Anticipated expiration: 1979-03-27

Description

March 96 TETSURO OSUGI ETAL 3,

POLYVINYL ALCOHOL FIBERS HAVING IMPROVED ELASTICITY Filed Dec. 31, 1958 POLYVINYL ALCOHOL SPINNING SOLUTION SPINNING ZONE STRETCHING ZONE HEAT TREATMENT ZONE ACETALIZAT] ON ZONE STRETCH 1 N6 ZONE HEAT TREATMENT ZONE PRODUCT FIBERS INVENTORS TETSURO OSUGI KENICHI TANABE YOTARO KAWABE H ISASHIGE YABE OSAMU MORIMOTO SADAMARU MIYAZ AKI BY 9UM6X ATTORNEY red States This invention relates to the preparation of improved polyvinyl alcohol fibers. More specifically, the invention relates to the preparation of polyvinyl alcohol fibers which have excellent elastic recovery and which have good stability and wet heat resistance.

It is well-known that fibers of polyvinyl alcohol can be obtained by dry or wet spinning from aqueous solutions thereof. However, such fibers show undesirable sensitivity to water, especially hot Water. The fibers generally shrink more than of their length in water at room temperatures, and dissolve in hot water at 70- 90 C.

In order to improve the properties of polyvinyl alcohol fibers, the fibers are generally stretched during or after spinning. Additionally, the fibers are generally heat treated to further improve the properties thereof. The heat treatment is usually carried out at temperatures in the range ZOO-250 C. After stretching and heat treatment, the polyvinyl alcohol fibers are acetalized with formaldehyde or other aldehydes to further improve the properties of the fibers. Although the strength and wet heat resistance of polyvinyl alcohol fibers obtained by such treatment are good, the elastic recovery of the said fibers is usually fairly low.

It is an object of the present invention to provide a process for the production of polyvinyl alcohol fibers having improved elastic recovery properties.

It is a further object of the invention to provide a process for the production of polyvinyl alcohol fibers having improved elastic recovery properties and high wet heat resistance.

Other objects of the invention will be apparent from the instant specification and claims.

The block diagram of the figure is illustrative of the steps which may be employed in practicing the present invention.

In accordance with the present invention, polyvinyl alcohol fibers having high elastic recovery are produced by subjecting polyvinyl alcohol fibers to stretching after the fibers have been acetalized. It has been found that the elastic recovery of the acetalized fibers is greatly improved by this stretching after acetalization. In an especially preferred practice of the invention, the polyvinyl alcohol fibers are acetalized at least in part with a ring containing mono-aldehyde prior to stretching.

Polyvinyl alcohol which is used in the invention is a linear synthetic polymer consisting of at least about 98% vinyl alcohol units -CH --CHOH. Polyvinyl alcohol having a degree of polymerization greater than 800 and preferably in the range 1000-3000 is employed.

According to the invention, the polyvinyl alcohol is formed into fibers. Wet or dry spinning techniques are suitably employed. A particularly preferred wet spinning process is described in copending application Serial No. 336,166 filed February 10, 1953, of Tomonari et 211., now Patent No. 2,988,802. Other spinning techniques can be used. During and/or after formation of the polyvinyl alcohol spinning solution into fibers, it is desirable to stretch the fibers to a draw ratio in the range of about atent 3,027,224 Patented Mar. 27, 1962 ice 2:1 to 12:1 to improve the strength and. other properties thereof.

The oriented fibers are preferably heat-treated prior to acetalization at temperatures in the range of about 210-250 C. for about 2 seconds to 5 minutes to improve the Wet heat resistance of the fibers. Alternatively, the heat treatment prior to acetalization can be omitted and the fibers heat treated after acetalization and subsequent stretching. Further, the fibers can be heat-treated both before acetalization and after acetalization and stretching. The heat treatment can be carried out in air or inert gases such as nitrogen, in steam, in inert molten materials such as paraffin or Woods metal, or the like.

In accordance with the invention, the oriented fibers are acetalized with a mono-aldehyde to a 560% degree of acetalization; that is, the fibers are reacted with a mono-aldehyde until 5-60% of the vinyl alcohol units contained therein have been reacted. The acetalization is carried out preferably in aqueous media in the presence of an acid catalyst. Preferably the aqueous system contains 02-10% aldehyde, 5-20% acid such as sulfuric acid, and 0-25 sodium sulfate or ammonium sulfate. Other acids such as hydrochloric acid, nitric acid, and phosphoric acid together with the salts: thereof can be used. Suitably the acetilization is carried out at temeratures in the range 4080 C. for times ranging from a few minutes, e.g. 10 minutes, to a number of hours, e.g. 20 hours.

In especially preferred practice of the invention, the polyvinyl alcohol fibers are acetalized to a degree of acetalization of at least 5% with a ring-containing monoaldehyde. The use of ring-containing aldehydes results in the production of fibers having improved stability and elastic recovery. Examples of ring-containing monoaldehydes which are suitably used include furfural, benzaldehyde, hexa-hydrobenzaldehyde, tetra-hydro-benzaldehyde, ortho-, meta-, and para-chlor-benzaldehyde, 2,4- dichlor-benzaldehyde, trichlor, tetrachlor and pentachlor benzaldehyde, ortho-, meta-, and para-nitrmbenzaldehyde, salicylaldehyde, terephthalic acid aldehyde; vanillin, tolualdehyde, phenylacetaldehyde, cinnamic aldehyde, naphthaldehyde, diphenyl aldehyde and the like.

Non-cyclic mono-aldehydes can also be used to acetalize the polyvinyl alcohol fibers in carrying out the present invention. Mixtures of cyclic and non-cyclic aldehydes can be used. Examples of non-cyclic aldehydes which can be used include formaldehyde, acetaldehyde, butyraldehyde, valeraldehyde, hexaldehyde, heptaldehyde, acetylaldehyde, nonylaldehyde, =laurylaldehyde, stearaldehyde, unsaturated derivatives thereof, methoxy-, ethoxy-, hydroxy-, chlor-, brom-, cyano-, carboxy-, sulfo-, and amino-substituted derivatives thereof, and the like. Generally, aldehydes having up to about 20 carbon atoms are suitably employed.

After the polyvinyl alcohol fibers have been acetalized, the said fibers are stretched in accordance with the invention to produce fibers having improved elastic recovery. The temperature at which the said stretching can be carried out can vary depending upon factors such as the type of mono-aldehyde employed in the acetalizetion, the degree of acetalization, and the like. Temperatures as low as 70-80 C. can be used but higher temperatures in the range -220" C. generally give best results.

It is usually desirable to stretch the acetalized fibers about 5 to 50% of their length although the fibers can be stretched amounts outside this range. It is advantageous to heat treat the acetalized fiber after stretching since such heat treatment improves the stability and wet heat resistance of the fibers. Temperatures up to about 220 C. can be used in this heat treatment. Longer times and higher temperatures for this heat treatment favor imaeeaaae proved stability and wet heat resistance. It is also advantageous to permit the fibers to shrink an amount not exceeding the stretch given after acetalization during the heat treatment.

The following illustrates the advantageous efiects attained through practice of the invention:

Polyvinyl alcohol fibers were prepared by wet spinning. The fibers were heat treated and acetalized with formaldehyde to 30% degree of acetalization. Various portions of the fibers were stretched at 70 C., 100 C., 150 C., and 200 C. respectively in air for 3 minutes. Another portion of the fibers was stretched 20% in 3 minutes in air at 150 C. and subsequently heat-treated at 210 C. for 2 minutes during which the fibers shrank The following table shows the treating conditions as well as the properties of the said fibers. Also presented for comparison purposes are the results for polyvinyl alcohol fibers spun and heat-treated similarly to those above but acetalized to 28% degree of acetalization with benzaldehyde.

TABLE 1 had a tenacity of 3.1 g./d., elongation of 24%, and elastic recovery at 3%, 5% and 7% elongation of 54%, 48% and 46% respectively.

Part of the acetalized fibers were stretched 10% in 2 minutes in air at 170 C. Upon standing for a number of days in a room maintained at 20 C. and 65% relative humidity, the fibers shrank 1.5%. Elastic recovery of the resulting fibers at 3%, 5% and 7% elongation were 81%, 79% and 76%.

Another part of the acetalized fibers were stretched 28% in 2 minutes in air of 180 C. These fibers upon standing as above indicated shrank 2.6%. The fibers had a tenacity of 4.6 g./d., elasticity of 1.2% and elastic recovery of 94% and 90% respectively at 3% and 5% elongation.

Example II Polyvinyl alcohol fibers, spun and heat treated as described in Example I, were acetalized in a water solution containing by Weight 2% n-butyraldehyde, 10% sulfuric Formalized Fibers Benzalized Fibers Stretching after acetalization:

Temp, Amount, percent Heat treatment after st Temp, C Shrinkage, percent Maximum Shrinkage, percent Shrinkage after standing, percent Shrinkage in Water after 30 minutes, percent:

20 C. water 0. water 80 0. water Elastic Recovery, percent:

3% elongation 7% elongation In the above table, the shrinkage upon standing was recorded after the fibers were maintained without stretching for a number of days at 20 C. in a room wherein the relative humidity was The elastic recovery was measured by stretching the fibers to the desired elongation through use of a KS Serirneter with a load velocity of 10 g. per minute, and after maintaining the fibers at the desired elongation for 30 seconds, releasing the load at a velocity of 10 g. per minute.

The results presented in the above table illustrate the improved elastic recovery of fibers stretched after acetalization in accordance with the invention. Generally greater stretching resulted in greater elastic recovery. Both the formalized and benzalized fibers had improved elastic recovery properties. The benzalized fibers also possessed high wet heat resistance together with very high elastic recovery properties, the elastic recovery properties thereof being higher than that of wool (88% and 83%) and nylon (86%) as measured by the same method.

As can be seen from the results illustrated above, the stability and wet heat resistance of the fibers is improved after stretching by subjecting the fibers to heat treatment. The advantageous improvement in elastic recovery of the stretched acetalized fibers is retained during such subsequent heat treatment. Fibers produced in accordance with the instant invention find application where the properties of high elastic recovery are necessary.

The following examples illustrate the invention:

Example I Polyvinyl alcohol fibers were prepared by wet spin ning. The fibers were heat treated at constant length for 3 minutes in air at 230 C. The heat treated fibers were acetalized in a water solution containing by weight 5% formaldehyde, 15% sulfuric acid and 15% sodium sulfate at 60 C. for 1 hour. The degree of acetalization of the resulting fibers was 32%. The acetalized fibers acid, and 20% methanol at 60 C. for 15 hours. The resulting fibers had a degree of acetalization of 25%.

The acetalized fibers were stretched 10% in 30 secends in a liquid parafiin bath; the fibers were further heat treated in the paraffin bath at 150 C. for 20 seconds at constant length.

The resulting fibers shrank 2.8% upon standing at room temperature and normal humidity. The fibers had an elastic recovery of 82% and 78% respectively at 3% and 7% elongation.

Example III A dry spun polyvinyl alcohol fiber was cold drawn to 130% elongation and then hot drawn to elongation in 5 seconds in hot air of 230 C. The fiber was further heat-treated in hot air of 235 C. during which treatment the fiber shrank 20%.

The resulting fiber was acetalized in an aqueous solution containing by weight 3% formaldehyde, 1% nonylaldehyde, 10% sulfuric acid and 60% methanol at 60 C. for 1 hour.

The acetalized fiber was drawn 16% in a Woods metal bath at C. in 10 seconds. The fiber was further heat treated in the same bath at C. for 10 seconds whereby the fiber shrank 3%.

The resulting fiber shrank 1.5% upon standing at room temperature and humidity. The fiber shrank 4.6% when immersed in water for 30 minutes. The elastic recovery of the fiber at 3% elongation was 92%. When immersed in 7885 C. water for 1 hour, the fiber shrank 13%. The tensile strength and elasticity of the fiber were almost equal to those of the fiber not stretched after acetalization. Spun yarn of the acetalized and stretched fiber was blended with viscose staple fiber and was dyed in a dyeing bath at 75-85 C. to obtain bulk yarn.

Example IV Polyvinyl alcohol fibers were prepared by wet spinning. The fibers were heat treated in air of 230 C. for 2 minutes without stretching. The fibers were divided into portions A, B, C, and D, and were treated as follows:

Portion A was acetalized to a degree of acetalization of 35% in an aqueous solution containing by weight formaldehyde, 15% sulfuric acid, and 15% sodium sulfate at 60 C. for 1 hour.

Portion B was acetalized to a degree of acetalization of 32% in an aqueous solution containing by weight 1.8% nonylaldehyde, 5% sulfuric acid, and 60% ethanol at 70 C. for 1 hour.

Portion C was acetalized to a degree of acetalization of 31% in an aqueous solution containing by weight 4% benzaldehyde, sulfuric acid, and 50% methanol at 60 C. for 1 hour.

Portion D was acetalized to a degree of acetalization of 26% in an aqueous solution containing by weight 5% phenylacetaldehyde, 10% sulfuric acid and 50% methanol at 70 C. for 1 hour.

Subsequently the above fibers were hot drawn to various degrees of elongation in air. The following table shows the drawing conditions and also presents the properties of the fibers obtained.

at 90 C. for 30 minutes, the elastic recovery thereafter being 90% and 85% at 3% and 7% elongation respectively.

We claim:

1. The method of preparing polyvinyl alcohol fibers having improved characteristics including high elastic recovery properties, which comprises spinning a polyvinyl alcohol solution into fibers, modifying said fibers by subjecting the fibers to the following steps in sequence, first acetalizing 5-60% of the vinyl alcohol units of said fibers by subjecting said fibers to reaction with a rnonoaldehyde having up to carbon atoms in an acetalization Zone, removing the fibers from the acetalization zone, and second stretching the acetalized fibers 55 0% of their length in a medium selected from the group consisting of air, liquid parafiin and Woods metal at a temperature in the range or" 100-220 C. whereby acetalized fibers having improved elastic recovery characteristics are produced.

2. The method of preparing polyvinyl alcohol fibers having improved characteristics, including high elastic re cover properties which comprises spinning a polyvinyl alcohol solution into fibers, modifying said fibers by subjecting the fibers to the following steps in sequence, first TABLE 2 Drawing Shrinkage, minutes in water Elastic Recovery,

percent Fiber Portion Elonga- Time, Temp, 3% Elon- 7% Elontion, min. C. C. C. C. C. gation gation percent talized fibers to 4.4 g./d. for the fibers drawn 20% in 2 minutes at 180 C. The elasticity of these fibers decreased from 28% to 14%.

The fibers of portion A stretched 30% in 2 minutes at 180 C. when soaked in water for 30 minutes decreased in elastic recovery to 63% at 3% elongation and 48% at 7% elongation. On the other hand, the fibers of portion C stretched 20% in 2 minutes at 180 C. retained the improved elastic recovery even after treatment in water acetalizing 5-60% of the vinyl alcohol units of said fibers by subjecting said fibers to reaction with a rnonoaldehyde having up to 20 carbon atoms in an acetalization zone, at least 5% of the said vinyl alcohol units being acetalized by reaction with a ring-containing rnonoaldehyde having up to 20 carbon atoms, removing the fibers from the acetalization zone, and second stretching the acetalized fibers 550% of their length in a medium selected from the group consisting of air, liquid paraffin and Woods metal at a temperature in the range of l00220 C. whereby acetalized fibers having improved elastic recovery characteristics are produced.

References Cited in the file of this patent UNITED STATES PATENTS 2,636,803 Cline et al Apr. 28, 1953 2,895,786 Schlack July 21, 1959 FOREIGN PATENTS 799,815 Great Britain July 24, 1957

Claims

1. THE METHOD OF PREPARING POLYVINYL ALCOHOL FIBERS HAVING IMPROVED CHARACTERISTICS INCLUDING HIGH ELASTIC RECOVERY PROPERTIES, WHICH COMPRISES SPINNING A POLYVINYL ALCOHOL SOLUTION INTO FIBERS, MODIFYING SAID FIBERS BY SUBJECTING THE FIBERS TO THE FOLLOWING STEPS IN SEQUENCE, FIRST ACETALIZING 5-60% OF THE VINYL ALCOHOL UNITS OF SAID FIBERS BY SUBJECTING SAID FIBERS TO REACTION WITH A MONOALDEHYDE HAVING UP TO 20 CARBON ATOMS IN AN ACETALIZATION ZONE, REMOVING THE FIBERS FROM THE ACETALIZATION ZONE, AND SECOND STRETCHING THE ACETALIZED FIBERS 5-50% OF THEIR LENGTH IN A MEDIUM SELECTED FROM THE GROUP CONSISTING OF AIR, LIQUID PARAFFIN AND WOOD''S METAL AT A TEMPERATURE IN THE RANGE OF 100-200*C. WHEREBY ACETALIZED FIBERS HAVING IMPROVED ELASTIC RECOVERY CHARACTERISTICS ARE PRODUCED.