USE OF AMIDOXIMATED STARCH IN PAPER MAKING

Abstract: The present invention relates to a process for produc­ ing novel cationic starch comprising the step of reacting starch having cyanoethyl groups or starch having cyano­ ethyl groups and quaternary aminoalkyl groups with hy­ droxylamine or the salts thereof to amidoximating the reac­ tion product. The resulting cationic starch of the invention exhibits significant advantages as compared with those of conven­ tional cationic starch as a dry strengthening agent.

Description: BACKGROUND OF THE INVENTION In paper making industry, cationic starch has widely been used by including the same in pulp at the tine of paper making thereof as dry strength agent, retention aid, drainage aid, printability improver and the like. Furthermore such cationic starch has variously been utilized as warp sizing agent and finish in textile industry, besides as flocculant, emulsifier and the like in other industries. As the process for producing cationic starch as described above, generally practiced is such a process which comprises either reacting pasty or slurry starch with an alkylamine halide such as diethylaminoethyl chloride or an aminochlorohydrin compound such as 3-chloro-2-hydroxypropyltrimethylammonium chloride, or with a glycidylamine such as 2, 3-epoxypropyltrimethylammonium chloride in the presence of strong alkali as described in Starch: Chemistry and Technology, vol II, 1967, pp. 403 - 420, Academic Press Co. SUMMARY OF THE INVENTION The present invention contemplates to provide a process for the production of cationic starch having remarkable advantages as a dry strengthening agent which comprises the steps of reacting starch or quaternary aminoalkylated starch with acrylonitrile in the presence of alkali to cyanoethylate hydroxyl groups of the starch, and further reacting the thus cyanoethylated starch with hydroxylamine or the salts thereof to amidoximate the cyanoethyl groups. Such cyanoethylated starch has been publicly known in U.S. Patent No. 2,316,129, and furthermore amidoximating reaction has been publicly known as a method for modifying acrylonitrile polymer in U.S. Patent Nos. 2,959,574 and 2,959,514 as well as British Patent No. 786,960 etc., and such reaction being expressed by the following formula: Such amidoximated starch obtained by reacting cyanoethylated starch with hydroxylamine is cationic starch in which amidoxime groups dissociate in acid condition to exhibit cationic activity. When such cationic starch is included in pulp as a dry strengthening agent and examined, adsorption to the pulp is favorable in acidic paper making so that the cationic starch exhibits remarkable dry strengthening effect. In this respect, the present inventors continued their study and as a result, they have found not only such fact that the amidoxime groups in said amidoximated starch dissociate in acidic condition to afford cationic activity to the starch, thereby permitting the starch to be adsorbable to pulp so that improvement for dry strength due to the starch appears, but also that the amidoxime groups themselves contribute for the dry strength. Namely, dry strengthening effect of conventional cationic starch exhibits some improvement with a rise in degree of cationic activity, but there is, in general, no increase further in such effect, whilst it has been observed in the amidoximated starch according to the present invention that the dry strengthening effect is also substantially continuously elevated. However, since amidoxim group is primary or secondary amine, it does not dissociate in neutral or alkaline condition so that there is no adsorption of amidoximated starch to pulp in case of neutral or alkaline paper making. As a result, no dry strengthening effect was observed in such case as mentioned above. For solving this problem, quaternary aminoalkyl groups are further introduced into said amidoximated starch. Thus it was observed that remarkable improvement in dry strength with an increase in degree of amidoximation in also neutral or alkaline paper making wherein amidoxime groups do not dissociate as in the case of acidic paper making of amidoximated starch without any modification. In this case, since amidoxime groups are not dissociated, it has been found that dry strengthening effect of the amidoxime groups is irrespective of dissociation. Furthermore, quaternary aminoalkylated starch being a starting material of the present invention has been used as a dry strengthening agent in the paper making industry. However, when the present inventors studied effect of quaternary aminoalkylated starch as dry strengthening agent for including the same in pulp in case of neutral or alkaline paper making, it became apparent that quaternary aminoalkyl groups are indispensable for adsorption of starch with respect to pulp, but it was difficult to observe such effect of a dry strengthening agent in the quaternary aminoalkyl groups themselves, and improvement in dry strength was derived from the adsorbed starch. As a matter of course, if quaternary aminoalkyl groups are increased with respect to starch, a degree of cationic activity of such starch rises and adsorption of the starch for pulp increases also, so that some improvement in paper strength may be observed. In essential, however, significant elevation of dry strength cannot be expected from that attained by increasing amount of starch. From the above results, we have found that both of amidoximated starch and quaternary aminoalkylated starch exhibit excelelnt dry strengthening effects in acidic and neutral or alkaline paper making, respectively. It is needless to say that amidoximated one of the latter aminoalkylated starch is also effective for case of acidic paper making. DESCRIPTION OF THE PREFERRED EMBODIMENTS The process for the production of cationic starch having remarkable advantages as a dry strength agent and the application thereof as a dry strengthening agent will be described hereinbelow. Gelatinization is effected in accordance with conventional procedure by adding water to starch to prepare a slurry mixture, and further adding alkali to the slurry mixture. Powdery or liquid quaternary aminoalkylated starch is commercially available. Such quaternary aminoalkylated starch has the following general formula: wherein R₁ is C₁ - C₄ alkylene group, R₂, R₃ or R₄ is C₁ - C₄ alkyl group, X is hydrogen atom or hydroxyl group, and A is acid residue. In the present invention, either such commercially available quaternary aminoalkylated starch may be used as the starting material, or such starch may originally be prepared in accordance with such a manner that starch is gelatinized in alkaline condition, then 2, 3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride is added thereto, and the resulting mixture is warmed at a temperature of around 60°C to react the same. This reaction may also be carried out at the same time or after the undermentioned cyanoethylation. When the aforesaid gelatinized starch liquid or quaternary aminoalkylated gelatinized starch liquid is added a prescribed amount of acrylonitrile in strong alkaline condition and the mixture is reacted with stirring, each of the corresponding cyanoethylates can be obtained. Cyanoethylating reaction is very rapid in strong alkaline condition, i.e., the reaction terminates at room temperature for around 6 hours, and the reactivity thereof reaches 90% or more. The cyanoethylated starch liquid thus obtained is added equimolar hydroxylamine salt with respect to the acrylonitrile added to be adjusted in such that a pH of the solution becomes 7.0 to 9.0. While hydroxylamine is commercially available in the form of hydrochloride or sulfate, it is required in this case to adjust pH in such that hydroxylamine is in free state by adding alkali or acid in case of the reaction in response to an amount of the existing alkali at the time of cyanoalkylation. Amidoximating reaction is carried out at a temperature of 60°C or more. The reaction time thereof depends on the reaction temperature, i.e., about 60% of cyanoethyl groups are amidoximated at 70°C for 3 to 4 hours, and 85°C for around 2 hours, respectively. After the reaction, an acid corresponding to the amidoxime groups is added to the reaction product to neutralize it. Furthermore, when quaternary aminoalkylated starch which has been previously cyanoethylated is subjected to amidoximation, quaternary amidoximated starch may be obtained. The above reaction may be schematically expressed as follows, when quaternary aminoalkylated starch is used as its starting material: A degree of conversion of the amidoximated starch thus obtained can be estimated with respect to the amidoximation thereof in accordance with conventional colloidal titration method. Such colloidal titration method has been reported in J. Poly. Sci., 8 , 243 (1952) in such that a sample corresponding to 10 mg of starch is weighed, diluted with distilled water, and the titration is effected with N/400 potassium polyvinylsulfonate in acetic acid acidified and ammoniacal conditions by using Toluidine Blue as an indicator. As a result of the titration, the total amine and quaternary amine are determined in acetic acid acidified and ammoniacal conditions, respectively. In this reaction, however, carboxylic acid is produced by partial saponification at the time of cyanoethylating and amidoximating reaction, and such carboxylic acid combines intermolecularly with quaternary amine, so that amount of the quaternary amine measured is less than that existing actually. Thus, actually amidoximated amount must be somewhat lower than such a value obtained by subtracting ammoniacally measured value (amount of quaternary amine) from acetic acid acidified measured value (total amine content). In case of starting from starch, it is sufficient that only the acetic acid acidified value (total amine content) is measured. The aforesaid amidoximated starch is included in pulp slurry at the time of paper making as in the case where a usual dry strengthening agent is used. As a result, it was observed that amidoximated ones derived from starch or quaternary aminoalkylated starch and amidoximated ones of quaternary aminoalkylated starch exhibited remarkable improvement in dry strength in acid and neutral or alkaline paper making, respectively, in response to their degrees of amidoximation. Particularly, significant elevation of dry strength was observed with respect to amidoximated ones of quaternary aminoalkylated starch in case of neutral or alkaline paper making as compared with quaternary aminoalkylated starch being the starting material. On the other hand, a rise in degree of aminoalkylation exhibited scarcely advantage in dry strength. Decision of effect for dry strength is made herein in accordance with "Bursting Strength of Paper" TAPPI T 403 OS-76. Pulps such as LUKP, NUKP, corrugated waste pulp and the like other than ordinary LBKP (bleached kraft pulp of soft wood) and NBKP are also effective for those used in the present invention. By the use of the amidoximated cationic starch according to the present invention, not only dry strength attained by including such cationic starch in pulp slurry, but also drainage retention are improved, besides surface strength of papers can be elevated by means of sizing press. It is a matter of course that the cationic starch of the present invention may also be utilized for other general applications of cationic starch. The present invention will be specifically described hereinbelow in conjunction with the following examples, but it is to be noted that the invention is not limited thereto. Example 1 Preparation of Amidoximated Starch (1) Cyanoethylating reaction 46 g of cornstarch (13% moisture content, 0.247 mol starch) are weighed out and placed into a three-necked flask equipped with a stirrer and a reflux condenser. 300 mℓ of distilled water are added to the cornstarch, the mixture is sufficiently dispersed, 30 mℓ of 5N NaOH are added to the dispersion, and they are agitated at 80°C for 30 minutes to gelatinize the same. After the gelatinization, the resulting product is cooled to room temperature, 3.3 g of acrylonitrile (0.062 mol with respect to 25 mol% starch) are added thereto, and the resulting mixture is reacted at room temperature for 6 hours. (2) Amidoximating reaction 5.1 g (0.062 mol) of equimolar hydroxylamine sulfate of said acrylonitrile are dissolved in 20 mℓ of distilled water, the solution is added to the product in (1), and they are reacted at 70°C for 3 hours. At the time of starting the reaction, 16 mℓ of 5N H₂SO₄ are added to adjust pH of the reaction solution to 8.0. After completing the reaction, the product is neutralized by the use of sulfuric acid to obtain a pH of 3.0. The resulting final product will be hereinafter referred to as "Sample I". (3) Measurement for degree of amidoximation A certain amount of sample corresponding to 10 mg of starch was weighed out from Sample I, diluted with 100 mℓ of distilled water, and the resulting solution was titrated with N/400 potassium polyvinylsulfonate (hereinafter referred to simply as "PVSK) in acetic acid acidified condition by utilizing Toluidine Blue as the indicator, whereby a measured value of 4.2 mℓ was obtained. This value corresponds to a rate of addition of amidoxime groups with respect to 17 mol% starch. Example 2 Preparation of Amidoximated Starch The starch sizing solution obtained in accordance with the same manner as that of Example 1 was added 6.6 g (0.124 mol with respect to 50 mol% starch) of acrylonitrile to effect cyanoethylation. Thereafter 10.2 g (0.124 mol) of hydroxylamine sulfate were added to the resulting product thereby amidoximating the same. At the time of amidoximating reaction, 4 mℓ of 5N H₂SO₄ were added to adjust pH to 8.0. The conditions other than those described above are the same with those of Example 1. A PVSK (Potassium salt of Polyvinyl Sulphate consumption of the product was 6.9 mℓ, and a rate of addition for amidoxime groups was 28 mol% to starch. The resulting product will hereinafter be referred to as "Sample II". Example 3 Preparation of Quaternary Amidoximated Starch (1) Quaternary aminoalkylating reaction 46 g of cornstarch (13% moisture content, 0.247 mol starch) are weighed out and placed into a three-necked flask equipped with a stirrer and a reflux condenser. 300 mℓ of distilled water are added to the cornstarch, the mixture is sufficiently dispersed, 30 mℓ of 5N NaOH are added to the dispersion, and they are agitated at 80°C for 30 minutes to gelatinize the same. After the gelatinization, bulk temperature of the product is lowered to 60°C, 7.5 g (0.025 mol with respect to 10 mol% starch) of 50% aqueous 3-chloro-2-hydroxy-propyl-trimethylammonium chloride are added thereto, and the resulting mixture is reacted for 2 hours. As a result of colloidal titration, quaternary aminoalkylation was 6.0 mol% with respect to starch. The product thus obtained will be hereinafter referred to as "Sample A". (2) Cyanoethylating reaction and amidoximating reaction Acrylonitrile and hydroxylamine sulfate were reacted with the quaternary aminoalkylated starch solution of Sample A in accordance with a similar manner to that of Example 1 with each varying amount of both the acrylonitrile and hydroxylamine sulfate as shown in the following Table 1, whereby samples 25-A, 50-A, and 70-A (each charging mol% being shown by a figure) of various degrees of amidoximation were obtained. Example 4 Preparation of Quaternary Amidoximated Starch (1) Quaternary aminoalkylating reaction By varying an amount of 3-chloro-2-hydroxypropyltrimethylammonium chloride (hereinafter referred to simply as "CTA") to be added in Example 3 - (1) as shown in the following Table 2, various quaternary aminoalkylated starch of different amounts of addition were experimentally prepared. Name of Sample 50% CTA Amount Added of Quaternary Amine To Starch Amount Added B 5 mol% 3.8 g 3.2 mol% C 15 mol% 11.3 g 8.5 mol% (2) Cyanoethylating reaction and amidoximating reaction Acrylonitrile and hydroxylamine sulfate were amidoximated with 50 mol% charging with respect to starch in accordance with a similar manner to that of Example 1 by using quaternary aminoalkylated starch solution of said Samples B and C, and the results thereof are shown in Table 3. Name of Sample Analytical Value Degree of Amidoximation Total Amine Quaternary Amine 50-B 32.2 mol% 3.2 mol% 28.0 mol% 50-C 34.4 mol% 8.5 mol% 25.9 mol% (Figure in the Name of Sample indicates charge mol% of acrylonitrile.) Example 5 Dry Strength Test Dry strength tests were made in acid paper making with respect to amidoximated starch Samples I and II prepared experimentally in Examples 1 and 2, and as a control, quarternary aminoalkylated starch Sample A prepared experimentally in Example 3 was added to the tests. Paper making conditions were as described hereinbelow. An LBKP (bleached kraft pulp of soft wood) of 400 mℓ C.S.F. degree of beating was used, and subjected to paper making under condition of 50 g/m² basis weight in accordance with TAPPI standard. The samples were added with respect to pulp in two levels of 0.5% and 1.0%, and 3% alum, respectively, and paper making pH was 5.7. Dry strength is represented by specific burst strength, and the results thereof are shown in the following TAble 4. As is apparent from Table 4, it is observed that there is remarkable improvement in dry strength of the amidoximates starch Samples I and II according to the invention of this application as compared with Sample A corresponding to commercially available cationic starch, and dry strengthening effect is also elevated with the increase of degree of amidoximation. Example 6 Dry Strength Test Dry strength tests were effected in both acid paper making (addition of 3% alum) and alkaline paper making (pH 8.5) with respect to quaternary amidoximated starch prepared experimentally in Example 3 in accordance with a similar manner to that of Example 5. As is apparent from Table 5, it is observed that the cationic starch samples (25-A - 70-A) prepared by amidoximating quaternary aminoalkylated starch (A) according to the present invention exhibit remarkably elevated specific burst strength in both acid and alkaline paper making as compared with the quaternary aminoalkylated starch (A) being the starting material, and advantages of the amidoximated cationic starch of this invention increase with the elevation in degree of amidoxiamtion. Example 7 Dry Strength Test Samples wherein degree of amidoximation is kept at a substantially constant value are used with respect to quaternary cationic starch of various degrees of quaternary aminoalkylation, and dry strength was tested in respect of quaternary aminoalkyl groups in alkaline paper making in accordance with a similar manner to that of Example 5. As is clear from Table 6, it is hardly observed that dry strength is not influenced dependent upon degree of quaternary amination, if the samples have substantially the same degrees of amidoximation with each other. Example 8 Surface Strength Test of Paper Surface strength of the papers which were subjected to alkaline paper making by employing Samples A and 50-A was tested with the use of an IGT tester in accordance with a similar manner to that specified in TAPPI T499 Su-64. Printing conditions for the test were spring A, ink tacking 15, and printing pressure 50 kg/cm², and results of the test were judged by printing speed in respect of fluffing. As is apparent from Table 7, it is observed that the cationic starch (50-A) prepared by amidoximating quaternary aminoalkylated starch (A) exhibits remarkably elevated surface strength of paper in comparison with the quaternary aminoalkylated starch (A) being the starting material. The features disclosed in the foregoing description and in the following claims may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims: The use as a paper strengthening agent of amidoximate starch which is manufactured by reacting starch having cyanoethyl groups with hydroxylamine or a salt thereof to amidoximate cyanoethyl groups. The use according to Claim 1, wherein the starch further has quaternary aminoalkyl groups. The use according to Claim 2, wherein the quaternary aminoalkyl groups have the following formula: wherein each of R1, R2, and R3 represent the same or different C1 to C3 alkyl group. The use according to Claim 2, wherein the quaternary aminoalkyl groups have the following general formula: wherein R represents a C₁ to C₄ alkylene group and R₁, R₂, and R₃ each represent the same or different C₁ to C₃ alkyl group. A method of making paper with enhanced dry strength, which method comprises the steps of including as a paper strengthening agent amidoximate starch which is manufactured by reacting starch having cyanoethyl groups with hydroxylamine or a salt thereof to amidoximate cyanothyl groups, in pulp slurry and effecting paper making therefrom wherein the starch further has quaternary aminoalkyl groups. A method according to Claim 5, wherein the quarternary aminoalkyl groups have the following formula: wherein each of R₁, R₂, and R₃ represents the same or different C₁ to C₃ alkyl group. A method according to Claim 5, wherein the quaternary aminoalkyl groups have the following general formula: wherein R represents C₁ to C₄ alkylene group and R₁, R₂ and R₃ each represent the same or different C₁ to C₃ alkyl groups.

Inventors: MAEKAWA, EIKICHI, MATSUNAGA, YOSHIKI, SUGIYAMA, TOSHIAKI
Applicants: KYORITSU YUKI CO. LTD.
Application year: 1985
Main classification: C08B31
IPC codes: D21H17, C08B31