GB2152944A - Cellulose acetate graft copolymer and yarn formed therefrom - Google Patents

Abstract

Cellulose acetate having free hydroxyl groups is modified by the ring-opening graft polymerization of a cyclic ester such as a lactone, particularly epsilon -caprolactone. This modified cellulose acetate is suitable material for use in production of a yarn. The yarn is spun after melting the modified cellulose acetate, and has improved stability at melt-spinning temperatures, together with satisfactory fibre properties, as compared with unmodified or plasticized cellulose acetate.

Description

SPECIFICATION Cellulose acetate graft copolymer and yarn formed therefrom The invention relates to a process for preparing a graft copolymer relates to a process for preparing a graft copolymer from a cellulose derivative having a hydroxyl group, such as cellulose acetate and a cyclic ester, and the use of the copolymer as a yarn. The yarn is formed by melt-spinning the graft copolymer which shows improved stability in a molten state.

Cellulose acetate is widely used for textiles and cigarette filters. At present, in industry, it is formed into yarn by a dry spinning process. In this dry spinning process, spinning is performed using a large amount of a diluted solvent, so that a large quantity of energy is necessary to carry out the spinning and solvent recovery and accordingly a large plant is necessary. Therefore, the production cost becomes relatively high. In contrast, a melt spinning process has advantages that the energy cost is low, and that it is convenient for spinning fine-denier yarn or hollow yarn. The reason why the melt spinning process has not been applicable to cellulose acetate despite these advantages is that cellulose acetate undergoes heat decomposition when heated to near its melting point.

Spinning of cellulose acetate at temperature lower than its decomposition point is possible by mixing it with a substance which has the effect of plasticizing it and of lowering its melting point, that is, a plasticizer.

Studies directed at the production, using plasticizers, of hollow yarn especially, have recently been carried out (see, for example, Japanese Patent Publication No. 11564/1978 and Japanese Patent Laid-Open No.

100604/1981).

However, if a plasticizer remains in the yarn after spinning, the yarn generally has poor properties, e.g.

mechanical and thermal properties, and therefore is not always suitable for use. Thus, when spinning hollow yarn by the above process, measures are taken to prevent the plasticizer remaining in the yarn, for example, by removing the plasticizer by treating the yarn with a solvent. In this case, however, the cost for recovering the solvent and the plasticizer is added.

The inventors of the present invention have made extensive studies into the modification of cellulose acetate by internal plasticization so that it may be melt-spun, without undergoing heat decomposition, to obtain yarn which has properties nearly comparable to those of yarn obtained by dry-spinning unmodified cellulose acetate. As a result of these studies, we have found that a modified cellulose acetate, obtained by reacting a cyclic ester with cellulose acetate is excellent in such properties as melt spinnability, processability and yarn properties.

According to the present invention there is provided a process for preparing a graft copolymer which comprises ring-opening polymerization of a cyclic ester in the presence of a catalyst and cellulose acetate having a hydroxyl group.

According to the present invention there is also provided a process for forming a yarn which comprises the steps of melting the modified cellulose acetate, the graft copolymer as defined above, at 170 to 3500C and spinning the melt into the open air.

The reaction of the cellulose acetate and the cyclic ester takes place between the hydroxyl group of the cellulose acetate and the ester group. The polymerization is preferably effected by forming a substantially homogeneous reaction mixture of (1) a cyclic ester, (2) an effective amount of a catalyst for effecting the ring-opening polymerization reaction of said cyclic ester, and (3) a cellulose acetate, said cellulose acetate having a residual hydroxyl group in the molecule and being dissolved in said cyclic ester; then subjecting the reaction mixture to polymerization conditions effective to cause the ring-opening polymerization of the cyclic ester, whereby to obtain a graft copolymer in which a polymer derived from the ring opening of the cyclic ester is grafted to the cellulose acetate.In the process, the weight ratio of the cellulose acetate to the cyclic ester may be from 1/99 to 95/5, and the polymerization temperature may be from 120 C to 230"C, preferably from 140"C to 21 00C. The reaction may be conducted in an atmosphere of dry nitrogen gas. The reaction mixture may further contain (4) an organic solvent which does not contain an active hydrogen in the molecule and has a high compatibility with the cellulose acetate and the cyclic ester, such as xylene. The cellulose acetate preferably has a degree of substitution of 2.0 to 2.7.

Examples of catalysts which may be used in the process are organic acids, inorganics acids, alkali metals, e.g. sodium and potassium, and their derivatives, tertiary amines, e.g. pyridine, alkyaluminium and its derivates represented by triethylaluminium, alkoxytitanium compounds represented by tetrabutyl titanate [C4HgOTi], organometallic compounds e.g. tin octylate and dibutyltin laurate, and metal halides e.g. tin chloride. These catalysts for the ring-opening polymerization reaction are also disclosed in "Koza Jugo Hanno-ron (6), Kaikan Jugo (II) "Lecture, on Polymerization Reaction (7), Ring-Opening Polymerization (II)" by Takeo Saegusa (Kagaku Dojin, 1973), p.p. 107 - 131.They are also illustrated in Japanese Patent Publication Nos. 5294/1959 and 41656/1981 and Japanese Patent Laid-Open Nos. 75422/1980 and 104315/1980.

Examples of the cyclic esters which may be used are lactones e.g.8-valerolactone, -caprolactone, enantholactone and dodecanolactone, and alkyl side chain-containing lactones, e.g. ci-methyl-e- caprolactone and ,3-methyl--caprolactone. Among these, -caprolactone is particularly suited for the purpose of the present invention, because the reaction can proceed relatively easily, because its effect of internally plasticizing cellulose acetate is large and because the product has, for example, good solvent solubility and heat resistance.

The amount of the cyclic ester to be reacted with cellulose acetate is suitably 0.5 to 4.0 mol per anhydroglucose unit of cellulose acetate. When the mole number of the ester reacted is below 0.5, the internally plasticizing effect produced by the reaction of the cyclic ester is small, and when it exceeds 4.0, the product loses the characteristic properties of cellulose acetate.

The effect of the internal plasticization of cellulose acetate, which can be brought about by the reaction with the cyclic ester, is to lower the melting temperature of the product and, in addition, to increase its heat decomposition temperature. This increase in the heat decomposition temperature is distinctive and is not observed in modified cellulose acetates produced by other modification processes, and the process of the present invention for the formation of yarn makes use of this thermal property of the modified, cellulose acetate.

The following experiment was performed in orderto clarify the thermal properties of the modified cellulose acetate. Unmodified cellulose acetate, mixtures of it and a plasticizer, and its corresponding modified cellulose acetate were heated separately in test tubes to examine their heat decomposition initiating temperature and spinnability developing temperatures (defined below).

In each case about 2g of a sample was placed in a test tube. While the sample was being agitated with a 4mm diameter glass thermometer, the temperatue was increased at a rate of 5 to 1 0C/min. The thermometer was withdrawn from time to time to observe the state of the sample. After the sample had approached the temperature at which it developed spinnability, the rate of the temperature increase was changed to a bout 2 C/min. When the thermometer to which the melt adhered was withdrawn from the sample by about 10 cm at a speed of about 10 cm/min, the temperature at which the strand of melt between the thermometer and the bottom of the tube could be spun without breaking was designated the spinnability developing temperature.

The temperature was increased further at a rate of about 2"C/min, and the temperature at which a smell of burning or a marked colouration was adopted as the heat decomposition initiating temperature. Table 1 shows the results of these observations.

This heating test can be applied to establish the temperature at which melt-spinning of a particular modified cellulose acetate should take place. A temperature falling within the range of from the spinnability developing temperature to the heat decomposition initiating temperature can be adopted as the melt-spinning temperature.

The results of Table 1 show that unmodified cellulose acetate could not be melt-spun without adding a plasticizer and that even when a plasticizer was added, the establishment of a melt-spinning temperature was difficult technically, because the range of selection was too narrow. In contrast, cellulose acetate which has been modified by the reaction with cyclic ester showed a wide range of temperature at which it could be spun stably and, therefore, could be easily spun. Although the melt-spinning temperature of the modified cellulose acetate varies with the manner in which it was modified, it can be set within the range of from 170 to 350or. In Table 1 DS stands for 'degrees of substitution' and MS stands for 'Molar substitution".

The yarn obtained by melt-spinning the modified cellulose acetate had a tenacity and an elongation that were nearly equal to those of the yarn obtained by dry-spinning unmodified cellulose acetate and of the yarn obtained by melt-spinning unmodified cellulose acetate containing a plasticizer and subjecting the formed yarn to a treatment for removing the plasticizer, and the modified cellulose acetate yarn had properties which were satisfactory for actual use.

Further, this modified cellulose acetate, together with another synthetic polymer, can also be formed into sheath-core or side-by-side conjugated yarn by a melt-spinning process, and can provide means for obtaining various highly functional yarns.

TABLE 1 Spinnability Heat decomposition Composition developing initiating temperature temperature PC) PC) Cellulose (DS 2.43) 200 200 Cellulose acetate + dimethyl phthalate 100 parts 25 parts 140 180 Cellulose acetate + diethyl phthalate 100 parts 25parts 150 170 Cellulose acetate + triacetin 100 parts 25 parts 160 190 Cellulose acetate + PEG-100 (polyethylene glycol) 100 parts 25 parts 150 160 Cellulose acetate + sulfolane 100 parts 25 parts 150 180 e-Caprolactone-modified cellulose acetate degree of acetylation 2.1 MS ofcaprolactone addition 1.1) 160 270 The present invention will now be described with reference to Examples.

Comparative Example 1 100 parts by weight of cellulose acetate of a degree of acetylation of 2.43 and a degree of polymerization of about 180 was mixed with 35 parts by weight oftriacetin as a plasticizer and 1.3 parts by weight of an equivalent mixture of EP OMIC-R-140 (a product of Mitsuj Petrdchemical Industries, Ltd.) and Irganox 1010 (a product of Ciba Geigy) as a stabilizer. The resulting mixture was molten at 190 C, spun through spinneret holes with a hole diameter of 0.35 mm into an atmosphere at room temperature and taken up at a speed of 350 m/min. Table 2 shows the properties of the filament obtained.

EP OMIC-R-140 is an epoxy resin of epichlorohydrin and bisphenol A and I RGANOX is tetrakis (methylene-3,5-di-tert-butyl-4-hydroxy, hydroxy cinnamate) methane.

Comparative Example 2 Afilament was prepared in the same manner as that in comparative Example 1 except that 40 parts by weight of PEG-400 was used as a plasticizer instead of triacetin and that the take-up speed was 470 m/min.

Comparative Example 3 The filament obtained in Comparative Example 2 was immersed in a large volume of water at room temperature and then dried. During this immersion, the extraction bath containing extracted plasticizer was renewed four times. Table 2 shows the properties of the filament obtained.

Examples 1 and2 Caprolactone-modified cellulose acetate was produced as follows.

Awfully dried reactor fitted with a stirrer, thermometer and reflux condenser was charged with 10 parts by weight of fully pre-dried cellulose acetate (a product of Daicel Chemical Industries, Ltd., degree of acetylation of 2.2), 60 parts by weight of -caprolactone, and 80 parts by weight of xylene, and the mixture was dissolved at 140 C. 66 mg of a xylene solution of 1% tetrabutyl titanate, (C4H90)4 Tir was added to the solution in an atmosphere of dry nitrogen, and the resulting mixture was reacted under agitation at 1400for 19 hours. The product, a light-yellow transparent polymer, was dissolved in acetone and reprecipitated by adding carbon tetrachloride.The precipitated polymer was washed well with carbon tetrachloride and vacuum-dried to obtain lactone-modified cellulose acetate. Proton NMR and determination of acetyl groups on the product revealed that the product had the following degrees of substitution: a degree of acetylation of 2.1 and an MS of lactone addition of 1.1.

The modified cellulose acetate was molten, heated to 250"C and spun through spinneret holes of a hole diameter of 0.3 mm into an atmosphere at room temperature and taken up at speeds of 2.2 m/min (Example 1) and 3.6 m/min (Example 2) to obtain monofilaments.

Example 3 Caprolactone-modified cellulose acetate was produced as follows by using the same apparatus as that used in Example 1. 100 parts by weight of cellulose acetate (a product of Daicel Chemical Industries, Ltd., degree of acetylation of 2.4), 95 parts by weight of e-caprolactone and 60 parts by weight of xylene were dissolved. 95 mg of a xylene solution of 1% tetrabutyl titanate was added to this solution, and the resulting mixture was reacted at 145"C for 22 hours. The other conditions followed those in Example 1 to obtain a modified cellulose acetate having degrees of substitution: a degree of acetylation of 2.2 and an MS of lactone addition of 2.0.

The modified cellulose acetate was spun under the same conditions as those in Example 1 to obtain a monofilament.

Comparative Examples 4 and5 The same lactone-modified cellulose acetate as that produced and melt-spun in Example 1 was dry-spun.

This lactone-modified cellulose acetate was dissolved in acetone containing a small amount of water so that the resulting solution had a concentration of 27%, and was spun into the open air at 70"C through a 14-hole spinneret having a hole diameter of 0.11 mm (Comparative Example 4) and a hole diameter of 0.08 mm (Comparative Example 5) and was taken up at a speed of 320 m/min.

Table 2 summarizes the results of the measured properties of the filaments obtained in the above Examples and Comparative Examples.

From the above description, it was recognized that the modified cellulose acetate prepared by ring opening graft polymerization of epsilon-caprolactone onto cellulose acetate could be dissolved and spun stably, and that the properties of the filaments produced therefrom were nearly comparable to those of the filaments obtained by dry-spinning unmodified cellulose acetate and the filaments obtained by meltspinning unmodified cellulose acetate containing a plasticizer and subjecting the yarn to a treatment for removing the plasticizer, and had a tenacity and an elongation which were satisfactory for actual use.

TABLE 2 Filament properties Item Spinning composition Fineness Tenacity Elongation (d) (gird) (%) Comp. Cellulose acetate + triacetin 600 0.46 51.2 Ex. 1 melt spinning Comp. Cellulose acetate + PEG 126 0.55 41.8 Ex.2 melt spinning Comp. yarn obtained by subjecting the yarn of Compar. Ex. 2 to 61 1.18 29.0 Ex. 3 plasticizer removing treatment Comp. Cellulose acetate Ex.4 dry spinning 15 1.05 27.7 Comp. Cellulose acetate Ex.5 dryspinning 8 1.07 23.2 Ex. 1 Modified cellulose acetate caprolactone(MSof1.1) 50 1.19 20.0 Ex.2 Do. 29 1.24 18.1 Ex. 3 Modified cellulose acetate caprolactone (MS of 2.0) 105 0.92 20.9

Claims (8)

1. A process for preparing a graft copolymer which comprises ring-opening polymerization of a cyclic ester in the presence of a catalyst and cellulose acetate having a hydroxyl group.

2. A process as claimed in claim 1, in which said cyclic ester is epsilon-caprolactone.

3. A process as claimed in claim 1 or 2, in which the cellulose acetate has a degree of substitution of 2.0 to 2.7.

4. A graft copolymer which has been obtained by the process as defined in claim 1.

5. A process for forming a yarn which comprises the steps of melting the modified cellulose acetate, the graft copolymer as defined in claim 3, at 170 Cto 350"C and spinning the melt into the open air.

6. A process as claimed in claim 5, in which the cyclic ester in epsilon-caprolactone.

7. A process as claimed in claim 5 or 6, in which the cyclic ester is used in an amount of from 0.5 to 4.0 moles, per anhydroglucose unit.

8. A yarn which has been obtained by the process as claimed in claim 5,6 or 7.