WO2022019863A1

WO2022019863A1 - Dry resistance additive substance for paper products

Info

Publication number: WO2022019863A1
Application number: PCT/TR2021/050550
Authority: WO
Inventors: Semih Durmus; Gokhan SENEL
Original assignee: Ak Kim Kimya San. Ve Tic. A. S
Priority date: 2020-07-21
Filing date: 2021-06-08
Publication date: 2022-01-27
Also published as: TR202011610A2

Abstract

The invention relates to a water-soluble glyoxalated polyacrylamide polymer containing (a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer, to be used as a dry resistance additive substance in paper products.

Description

DRY RESISTANCE ADDITIVE SUBSTANCE FOR PAPER PRODUCTS

Technical Field

The invention relates to dry resistance additive substances used in paper production.

State of the Art

The use of cellulose in paper production continues to be dominant throughout the world. Despite various developments and improvements, expensive, time-consuming and environmentally unfriendly procedures are used to improve the strength of cellulose fibres.

Paper resistance is generally characterized by dry and wet resistance, among other properties. The dry resistance of the paper is measured as a function of the tensile resistance when the paper is in a dry sheet state and after conditioning under conditions of uniform humidity and room temperature prior to testing.

The most commonly used dry resistance chemical in the paper industry is starch. As it is a powder, starch is not used directly. Starch, which needs to be boiled at high temperatures, may lose its activity as a result of bad boiling. It becomes difficult for the starch that has lost its activity to react with the paper, and thereby more starch use is needed. The increase in the amount of usage increases the operating costs. Also, boiled starch needs to be used immediately. If not used immediately, the product can be spoiled, and this will add more costs to the enterprise.

The facts that the shelf life of the starch solution is short and the charge carrying capacity of the starch is low are also among the problems addressed within the state of the art.

Paper manufacturers generally add dry resistance additive substances during the manufacturing process to increase the dry resistance of the paper product. Many of these additive substances are cationic polymers. For example, cationic starches are frequently added in the paper manufacturing process to increase the dry resistance without increasing the wet resistance. However, many research and development studies towards new additive substances that can be used instead of cationic starch to improve dry resistance properties continue to be conducted. For instance, US Patent No US 3,332,834 describes a dry resistance system with a molecular weight of between about 1.000 and about 30.000, comprising one anionic polyacrylamide, alum and a water-soluble cationic resin.

Although there are dry resistance additive substances in the state of the art, the need for dry resistance additive substances with improved performance continues.

The Aim of the Invention

The present invention relates to a dry resistance enhancing additive substance in paper production and a process for its preparation, which meets the aforementioned requirements and brings some additional advantages.

Boiled starch should be used immediately. The product may degrade when not in use. The primary aim of the invention is to provide a dry resistance additive substance with an extended shelf life in paper production.

As it is a powder, starch cannot be used directly. It needs to be boiled at high temperature. Also, if not boiled properly, starch loses its activity. Starch which has lost its activity will be react with the paper and thereby causes more starch to be used. The increase in the use causes an increase in the enterprise costs. Another aim of the invention is to provide a dry resistance additive substance that decreases the raw material and enterprise costs, eliminates the additional processes like boiling and saves time and energy.

Starch can carry a limited charge due to its complex structure. As the charge density on it cannot be increased, it becomes difficult for the starch to adhere to the paper in some paper manufacturing processes. Another aim of the invention is to provide a dry resistance additive substance the charge density of which can be adjusted as desired.

The structural and characteristic features of the invention and all its advantages will be understood more clearly thanks to the figures given below and the detailed explanation written with reference to these figures, and therefore the evaluation should be made by taking these figures and detailed explanation into consideration.

Detailed Description of the Invention

Cellulose fibres used for the preparation of paper products have anionic charges in their natural state. With the present invention, electrostatic interaction with cellulose has been improved and a polymeric structure with cationic charges has been obtained to be used as a dry resistance enhancing additive substance in paper products. It has been determined that the said polymeric structure performs synergistically better in paper products compared to starch and acrylamide based additive substances.

The glyoxalated polyacrylamide polymer of the invention contains (a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer.

In the present application, the expression "cationic vinyl monomer" is used to mean a polymerizable vinyl monomer that gains a positive charge to the polymer. Preferred cationic vinyl monomers include dialkyl ammonium quaternary salts (e.g., diallyl dimethyl ammonium chloride), 2-(dimethylamino)ethyl acrylate, trimethyl p-vinylbenzyl)ammonium chloride, dimethylaminopropyl acrylamide, 3-acrylamido-3-methylbutyl trimethyl ammonium chloride and combinations thereof in certain proportions. The most preferred cationic vinyl monomer is diallyl dimethyl ammonium chloride (DADMAC). Commercially, DADMAC is relatively more viable and DADMAC is readily available industrially.

In the present application, the expression "acrylamide monomer" is used to mean a primary amide containing monomer. Preferred acrylamide monomers include acrylamide, methacrylamide, ethylacrylamide, crotonamide, N-methyl acrylamide, N-butyl acrylamide, N- ethyl methacrylamide and combinations thereof in certain proportions. The most preferred acrylamide monomer is acrylamide. The cost of acrylamide is relatively low and industrially acrylamide is readily available industrially.

The glyoxalated polyacrylamide polymer of the invention is obtained from the reaction of glyoxal with a terpolymer containing a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer. In the reaction, the glyoxal substituents are attached to the pendant amide groups provided by the acrylamide monomer in the terpolymer's structure. Accordingly, said terpolymer has amide substituents that can react with glyoxal. In a preferred embodiment of the invention, the said terpolymer essentially consists of (a) acrylamide monomer, (b) acrylic acid and (c) cationic vinyl monomer units.

To obtain the desired terpolymer structure, the proportion of acrylamide monomer in the terpolymer is 1-60%, preferably 2-40% by mass; the proportion of acrylic acid in the terpolymer is 1-30%, preferably 2-10%, by mass; the proportion of cationic monomer in the terpolymer is 1-30%, preferably 1-15%, by mass; and the proportion of glyoxalin in the terpolymer is 0,1-15%, preferably 0,1-8% by mass. By the use of monomers in the specified ranges, glyoxalated polyacrylamide polymer with desired properties can be obtained. The ratios of monomers used ensure that the final product is water-soluble to be used as an additive substance in paper production. In addition, the monomers used in the specified ratios increase the adhesion of the polymer to the paper and extend the shelf life of the additive substance product.

To prepare the terpolymer, (a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer are reacted in an aqueous solution in the presence of a polymerizing catalyst. The polymerization is carried out preferably in aqueous medium by free radical polymerization. The polymerizing catalyst is preferably a free radical catalyst. Preferred catalysts include peroxidic catalysts (e.g., hydrogen peroxides, water- soluble organic peroxides, hydroperoxides) persulfate salts such as potassium and ammonium persulfate; water-soluble azo catalysts (e.g., 2,2'-azo-bis(amidinopropane) hydrochloride) or mixtures thereof in certain proportions. The most preferred catalyst is potassium persulfate and/or ammonium persulfate.

Said terpolymer is prepared by a process comprising the following steps:

(i) providing a first monomer mixture comprising at least one acrylamide monomer and acrylic acid or a salt thereof, wherein at least one acrylamide monomer is acrylamide;

(ii) providing an aqueous second monomer mixture comprising at least one cationic vinyl monomer, wherein said at least one cationic vinyl monomer is a diallyl dimethyl ammonium salt;

(iii) continuously adding the first monomer mixture obtained in step (i) to the second monomer mixture in step (ii) at a certain rate, wherein the temperature is set at 75-80°C; and

(iv) continuously adding at least one polymerizing catalyst together with the first monomer mixture to the second monomer mixture of step (ii) in an amount and at a rate sufficient to obtain the desired terpolymer.

By the addition of monomers at a certain rate, it becomes easier to synthesize the polymer with the best molecular weight and to control the molecular weight.

In a preferred embodiment of the invention, the acrylamide monomer added in step (i) is 0,5- 10 moles; the acrylic acid added in step (i) is 0,1-5 moles; and the cationic vinyl monomer added in step (ii) is 0,1-5 moles. The addition time of the first monomer mixture in step (iii) to the second monomer mixture is at least 1 hour. As catalyst, preferably 0,05-3 moles of potassium persulfate and/or ammonium persulfate is added.

The temperature of the reaction mixture during polymerization should be between 75°C and 80°C. If the temperature exceeds 80°C, cooling is required. In order to obtain a terpolymer with the desired chemical composition and monomer distribution, the first monomer mixture and the second monomer mixture are prepared separately, and the first monomer mixture is added to the second monomer mixture at the same time and speed with the catalyst.

The resulting terpolymer is then reacted with glyoxal and glyoxalated using a method known in the art, for example the condensation reaction. Glyoxalin aldehyde groups react with amide groups in the cationic vinyl monomer copolymer parts of the terpolymer by condensation and form pendant glyoxalated groups. The resulting polymer will hereinafter be referred to as "glyoxalated polyacrylamide polymer" or "glyoxalated polyacrylamide terpolymer".

The terpolymer obtained from step (iv) above is reacted with glyoxal at pH 6-9 to glyoxalate the resulting terpolymer. For this, first the reaction mixture in step (iv) is allowed to cool at ambient temperature until its temperature reaches 35-40°C. Then, the pH of the mixture is adjusted to 6-9 by adding base. An aqueous solution of glyoxal is added to the reaction mixture. The amount of glyoxal added is 0,01-40%, preferably 0,1-10%, based on the molar ratio of acrylamide. The use of glyoxal at rates higher than this range may cause an increase in viscosity in the product and may adversely affect product stability. When the desired viscosity is achieved, the pH of the reaction mixture is brought between 2-4 by adding acid. The viscosity of the glyoxalated terpolymer obtained at 22C is 10-500 cp, preferably 50-100 cp. The resulting glyoxalated terpolymer is essentially water-soluble.

Among the bases that can be used are alkali metal hydroxides, carbonates and bicarbonates, alkaline earth metal hydroxides, trialkyl amines, tetraacrylammonium hydroxides, ammonia, organic amines, alkali metal sulphides, alkaline earth sulphides, alkali metal alkoxides, alkaline earth alkoxides and at least one of or combinations at certain rates of the alkali metals phosphates such as sodium phosphate, potassium phosphate. Preferred bases include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide or alkali metal carbonates such as sodium carbonate and potassium carbonate. More preferably, sodium hydroxide (NaOH) is used as the base.

Acids that can be used include sulphuric acid, hydrochloric acid and formic acid. In another preferred embodiment of the invention, the acrylamide monomer added in step (i) is 0,5-10 moles; the acrylic acid added in step (i) is 0,1-5 moles; and the cationic vinyl monomer added in step (ii) is 0,1-5 moles. The addition time of the first monomer mixture in step (iii) to the second monomer mixture is at least 1 hour. As catalyst, preferably 0,05-3 moles of potassium persulfate or ammonium persulfate is added. After the reaction ends, 0,05-3 mol of glyoxal is added to the reaction mixture.

The resulting product mixture can be added to the pulp as a dry resistance additive substance in the manufacturing of paper products. The said mixture can be diluted before adding it to the pulp. As an additive, the polymer is generally applied at a rate of 1-30 kg per 1 ton of paper. The dry resistance additive substance of the invention interacts with anionic cellulose electrostatically with the cationic charges it carries on the polymeric structure. It forms hydrogen bonds with cellulose due to the hydroxyl (-OH) groups it carries. Due to its high molecular weight, it adheres to cellulose well. By this way, it also increases the dry resistance property of the paper product.

Example 1 - Preparation of terpolvmer

50 g of 50% acrylamide solution and 5 g of acrylic acid were mixed in a tank. In a separate reactor, water and 15 g of 60% DADMAC monomer were prepared. The reactor temperature was increased to 75-80°C. 2 g of potassium persulphate solution was prepared.

Prepared acrylamide and acrylic acid solutions are dosed into the reactor to be in minimum 1 hour. Potassium persulphate persulphate solution prepared at the same time was dosed into the reactor at the same duration.

After the polymerization ended, the polymer was cooled. The pH of the polymer was adjusted to 6-9 with sodium hydroxide.

Example 2 - Glvoxalation of Terpolvmer

After pH adjustment, 8 g of glyoxal was added to the reaction vessel. When the viscosity was 100-200 cp at 25-30°C, the pH of the reaction was adjusted to 2-4 with sulphuric acid. Polymer with 20-30% active substance (ie about 20-30% polymer and about 80-70% water) was obtained.

Example 3 - Performance of qlvoxalated polyacrylamide polymer

Performance results in laboratory conditions obtained when 10 kg of each product was applied to 1 ton of paper are given in Table I.

Table I

Claims

1 . A water-soluble glyoxalated polyacrylamide polymer to be used as the dry resistance additive substance in paper products comprising (a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer, wherein said at least one acrylamide monomer is acrylamide and said at least one cationic vinyl monomer is a diallyl dimethyl ammonium salt; the proportion of the acrylamide monomer in the polymer is 1-60% by mass, the proportion of the acrylic acid is 1-30% by mass, and the proportion of the cationic vinyl monomer is 1-30% by mass.

2. Polymer according to Claim 1 , wherein the the proportion of the glyoxal in the polymer is 0,1-15% by mass.

3. The polymer according to Claim 1 or 2, wherein the polymer is obtained by the reaction of glyoxal with a terpolymer containing (a) at least one acrylamide monomer, (b) acrylic acid and (c) at least one cationic vinyl monomer.

4. The polymer according to any of the preceding Claims, wherein it is obtained from a free radical polymerization reaction in an aqueous medium of a monomer mixture comprising (a) at least one acrylamide monomer, (b) acrylic acid or a salt thereof, and (c) at least one cationic vinyl monomer.

5. The polymer according to any of the preceding Claims, wherein the said terpolymer essentially consists of (a) acrylamide monomer, (b) acrylic acid and (c) cationic vinyl monomer units.

6. Process for the preparation of a water-soluble glyoxalated polyacrylamide polymer for use as a dry resistance additive substance in paper products, comprising the steps of:

(iii) continuously adding the first monomer mixture obtained in step (i) to the second monomer mixture in step (ii) at a certain rate, wherein the temperature is set at 75- (iv) continuously adding, together with the first monomer mixture, at least one polymerizing catalyst to the second monomer mixture of step (ii) in an amount and at a rate sufficient to obtain the desired terpolymer; and

(v) glyoxalating the terpolymer obtained in step (iv) by reacting with glyoxal.

7. The process according to Claim 6, wherein the pH is adjusted to 6-9 by adding base to the reaction mixture before the said step (v).

8. The process according to Claims 6 or 7, wherein the amount of glyoxal added is 0,01-40% based in the molar ratio of the acrylamide monomer.

9. An additive substance obtained by the process according to any of the Claims 6 to 8 to increase the dry resistance in paper products.

10. A paper product containing the additive substance according to Claim 1 or 9.

11. A method to process the pulp in a paper machine, characterized in that it comprises adding the additive substance according to Claim 1 or 9 as dry resistance enhancer during the processing of the said pulp.

12. A method according to Claim 11 , wherein no other dry resistance additive substance is added to the pulp.