MODIFIED FILLER COMPOSITION AND PAPERMAKING PROCESS USING THE SAME

Abstract

A modified filler composition used in papermaking is provided. The modified filler composition contains microfibrillated cellulose, filler, and latex having a glass transition temperature of less than 20° C. The dry weight of the microfibrillated cellulose is about 0.1% to about 10% that of the filler; the dry weight of the latex is about 0.1% to about 15% that of the filler.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to People's Republic of China Patent Application No. 201310045150.X, filed Feb. 5, 2013, which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a modified filler composition used in the field of papermaking, and a papermaking process using the modified filler composition.

2. Description of Related Art

Microfibrillated cellulose is cellulose microfibrils defibrillated from cellulosic materials by mechanical methods and/or the TEMPO catalytic oxidation method. The microfibrillated cellulose contains water-soluble cellulose and water-insoluble cellulose. The microfibrillated cellulose has dimensions of about 100 nm to about several millimeters in length, and about 3 nm to tens of micrometers in diameter. Due to a large number of carboxyl groups of the microfibrillated cellulose, high aspect ratio, and good flexibility, the microfibrillated cellulose made by the TEMPO catalytic oxidation method is generally added into paper pulp to improve the strength properties of the paper made using the same.

In the field of papermaking, adding filler to the paper pulp can effectively lower down the cost. However, if both filler and microfibrillated cellulose were added into the paper pulp, the filler would inhibit the hydrogen bonding of the microfibrillated cellulose. In addition, the negatively charged microfibrillated cellulose would repel the negatively charged or neutral filler, causing the finer filler particles to easily aggregate. Therefore, adding both filler and microfibrillated cellulose to the paper pulp leads to a non-uniform distribution of filler particles on the microfibrillated cellulose, thus decreasing the filler retention.

Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE FIGURE

Many aspects of the disclosure can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the disclosure.

FIG. 1 is a scanning electron micrograph of a modified filler composition of Example 1.

FIG. 2 is a scanning electron micrograph of a filler composition of Comparative Example 1.

DETAILED DESCRIPTION

The microfibrillated cellulose used in this disclosure is made by the TEMPO catalytic oxidation method.

One example for preparing the microfibrillated cellulose by the TEMPO catalytic oxidation method may include the following steps: (1) providing bleached kraft pulp (BKP) and beating the pulp; (2) providing the beaten pulp having an amount by dry weight of 100 parts, and adjusting the concentration of the beaten pulp to about 2%; (3) adding a catalyst having an amount by dry weight of about 0.001 part to about 1 part to the above pulp, the catalyst being TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) or a derivative of TEMPO; (4) adding an assistant catalyst having an amount by dry weight of about 0.01 part to about 10 parts into the pulp, the assistant catalyst consisting of iodides, bromides, borates, or a mixture thereof; (4) adding an oxidant (sodium hypochlorite) having an amount by dry weight of about 0.1 part to about 20 parts into the pulp and stirring, keeping the pH value of the pulp to be in a range from about 9.5 to about 11; (5) the pulp and the oxidant reacting for about 0.5 hours to 4 hours to obtain a mixture containing oxidized celluloses, TEMPO, catalyst, and water; (6) removing the residual catalyst and TEMPO from the mixture; (7) mechanically treating the oxidized celluloses by ultrasonication or high-pressure homogenization.

During the reaction process of the cellulose and the oxidant, some hydroxyl groups (—OH) on the chains of glucose of the cellulose are selectively oxidized to carboxyl groups (—COOH), which have stronger negative charges than the hydroxyl groups. Thus, the oxidized cellulose molecules easily delaminate and defibrillate cellulose microfibrils due to the strong electrostatic repulsion in the cellulose molecules.

The microfibrillated cellulose made by the TEMPO catalytic oxidation method has strong negative charge due to the carboxyl groups. The content of the carboxyl groups of the microfibrillated cellulose is in the range from about 0.06 to about 1.7 mmol/g. The microfibrillated cellulose has a complex composition, which substantially contains both water-soluble cellulose and water-insoluble cellulose. The water-soluble cellulose further contains nanocrystalline cellulose (NCC), nanofibrillated cellulose (NFC), and oligosaccharides, for example. The water-soluble cellulose (such as NFC) may position on the cell wall of the water-insoluble cellulose.

The modified filler composition in this disclosure contains microfibrillated cellulose and latex, wherein the dry weight of the microfibrillated cellulose in the modified filler composition is about 0.1% to about 10% that of the filler, and the dry weight of the latex in the modified filler composition is about 0.1% to about 15% that of the filler. The modified filler composition may further contain water.

The microfibrillated cellulose in the modified filler composition is made by the TEMPO catalytic oxidation method. The content of carboxyl groups of the microfibrillated cellulose is in the range from about 0.06 to about 1.7 mmol/g. The microfibrillated cellulose contains water-soluble cellulose having a mass percentage of 0.1% to 50% and water-insoluble cellulose having a mass percentage of 10% to 99.9%.

The filler is composed of ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, talc, or any combination thereof. In this embodiment, more than 50% of the filler has a particle diameter less than or equal to 2 μm.

The latex has a glass transition temperature (T_g) of less than 20° C. In one embodiment, the T_g of the latex is less than 10° C. The latex is an emulsion, and the latex is consisted of polybutadiene latex, styrene-butadiene latex, carboxylic butadiene-styrene latex, cationic butadiene-styrene latex, polyvinyl acetate latex, or any combination thereof.

The latex in the modified filler composition makes the filler particles distribute uniformly on the surface of the microfibrillated cellulose. A possible mechanism for this is illustrated as following: (1) the ambient temperature of the modified filler composition is higher than the T_g of the latex, so the latex becomes unstable and demulsifies; (2) the filler particles have a large specific surface area, so easily adsorb the demulsified latex; (3) thus, carbon-carbon double bonds (—[C═C]—) of latex distribute on surfaces of the filler particles. Carbon-carbon double bonds easily react with microfibrillated cellulose. Therefore, the latex is equivalent to a binder or a media for coupling the microfibrillated cellulose and the filler together.

The modified filler composition may further contain a cross-linking agent. The cross-linking agent is a borate cross-linking agent, a borax cross-linking agent, or dialdehyde cross-linking agent (such as oxaldehyde or glutaric dialdehyde). The dry weight of the cross-linking agent is about 0.1% to about 15% that of the latex. The cross-linking agent promotes the cross-linking between the latex and the microfibrillated cellulose to form a network structure, which is beneficial for increasing the filler retention on the microfibrillated cellulose.

The modified filler composition can be made by directly mixing the filler, the microfibrillated cellulose, and the latex together. During the mixing process, the temperature of the composition is maintained in a range from 20° C. to 110° C. In this embodiment, the temperature of the composition is kept in a range from 20° C. to 70° C. In other embodiments, the temperature of the composition is kept in a range from 30° C. to 50° C.

One example for preparing the modified filler composition may include the following steps: (1) providing a filler suspension; (2) adding the microfibrillated cellulose into the filler suspension to obtain a mixture, the dry weight of the microfibrillated cellulose being about 0.1% to about 10% that of the filler; (3) adding the latex into the above mixture, the dry weight of the latex being about 0.1% to about 15% that of the filler; (4) stirring the mixture with a speed of about 800 revolutions per minute (RPM) for about 5 min between about 20° C. to about 110° C.

The filler adsorbing on the surface of the microfibrillated cellulose has a particle size uniformity of less than 10. The particle size uniformity is calculated by dividing the standard deviation of the particle diameter by the mean particle size.

A papermaking process using the above modified filler composition includes the following steps.

Step 1: providing a paper pulp.

Step 2: adding the above modified filler composition into the paper pulp, and selectively adding or not adding unmodified filler to the paper pulp.

Thus, the filler in the paper pulp is either all from the modified filler composition, or is a combination of the modified filler composition and the unmodified filler. The total weight of the filler added into the paper pulp is 10% to 300% of the dry weight of the pulp fiber. The weight of filler from the modified filler composition is 80% to 100% of the total weight of the filler in the paper pulp. The microfibrillated cellulose from the modified filler composition is a portion of the pulp fiber.

Step 3: adding at least one auxiliary additive into the paper pulp.

The auxiliary additive may contain starch, retention aids, or the like. The starch is consisted of anionic starch, oxidized starch, grafted starch, amphoteric starch, or any combination thereof. The retention aids are either one-component retention aids or three-component retention aids. For example, the nanocrystalline cellulose (NCC) and/or the microfibrillated cellulose can be used as an anionic retention aid.

Step 4: employing the paper pulp to make paper.

Paper made by the above papermaking process has an ash retention of about 60% to about 95%, and a first-pass ash retention of about 55% to about 90%. Note: conventional paper has an ash retention of about 45% to about 90%, and a first-pass ash retention of about 40% to about 85%.

The paper made by the above papermaking process has a high ash retention. The reason may include one or more of the following:

(1) The microfibrillated cellulose made by the TEMPO catalytic oxidation method has a complex composition and contains both water-soluble cellulose and water-insoluble cellulose. The water-insoluble cellulose has many carboxyl groups, causing it to delaminate due to the electrostatic repulsion. Thus, the fine filler particles and latex particles easily incorporate into the inside of the water-insoluble celluloses.

(2) The temperature of the modified filler composition is higher than T_g of the latex, so the latex demulsify; the demulsified latex acts as a binder or a media for coupling the microfibrillated cellulose and the filler together.

(3) Some of the water-soluble cellulose adsorbs the filler particles, which improves the dispersion ability of the filler, so the filler disperses uniformly in the modified filler composition. In case that the modified filler composition is kept static in a container for about 4 hours, there will be no or few filler particles at the bottom of the container.

(4) The surface of the filler particles adsorbs some of the water-soluble cellulose, improving the chemical reactivity of the filler. Thus, the filler with reactive functional groups chemically bonds with the pulp fiber.

The disclosure provides a modified filler composition containing latex, the latex having a low glass transition temperature. The latex acts as a binder for coupling the microfibrillated cellulose and filler together, which makes the filler particles uniformly distribute on the surface of the microfibrillated cellulose. The paper pulp added with the modified filler composition has a high filler retention. Thus, paper made by the paper pulp has a high ash retention.

EXAMPLE 1

In this embodiment, the modified filler composition was prepared by the following steps: (a) providing a microfibrillated cellulose aqueous dispersion containing 2 g of microfibrillated cellulose by dry weight; (b) adding 20 g of filler (GCC) to the microfibrillated cellulose aqueous dispersion, more than 95% of the filler by weight having a particle size of less than 2 μm; (c) adding 0.2 g of styrene-butadiene latex having a T_g of about 10° C. to the microfibrillated cellulose aqueous dispersion to obtain a mixture; (d) stirring the mixture at a temperature of about 50° C. for about 5 minutes, thereby making the modified filler composition. A scanning electron micrograph of the modified filler composition is shown in FIG. 1.

COMPARATIVE EXAMPLE 1

A comparative filler composition was made by mixing microfibrillated cellulose and filler together by stirring at about 600 RPM for about 5 minutes, wherein the weight of the filler is 10 times the dry weight of the microfibrillated cellulose. The filler is uniformly dispersed GCC, and more than 95% of the filler by weight has a particle size of less than 2 μm. A scanning electron micrograph of the comparative filler composition is shown in FIG. 2.

FIG. 2 shows obvious aggregation of the filler particles on the surface of the microfibrillated cellulose, while FIG. 1 shows that the filler particles distribute much more uniformly on the microfibrillated cellulose, with little aggregation.

The fillers in Example 1 and Comparative Example 1 were tested, and the test results are listed in Table 1 below. The test results demonstrate that the filler in Example 1 has a much more uniform particle size. Note: the particle size uniformity is a value calculated by dividing the standard deviation of the particle diameter by the mean particle size.

TABLE 1
Test type	Comparative Example 1	Example 1
particle size uniformity of	11.9	7.42
filler
Average particle size of	4.5 μm	3.9 μm
filler

EXAMPLE 2

The above modified filler composition in Example 1 containing 2 g of microfibrillated cellulose and 20 g of filler was added into a Leaf Bleached Kraft Pulp (LBKP) having a dry weight of about 10 g; 2 g of starch was added into the above pulp; the pulp was diluted and employed to make paper.

COMPARATIVE EXAMPLE 2

20 g of filler were added into a LBKP having a dry weight of about 10 g; 2 g of starch were added into the above pulp; the pulp was diluted and employed to make comparative paper.

The papers made in Example 2 and Comparative Example 2 were tested, and the test results are listed in Table 2 below. The test results show that the ash retention and the first-pass ash retention of the paper in Example 2 are much higher than those of the paper in Comparative Example 2.

TABLE 2
Test type	Comparative Example 2	Example 2
Basis weight g/m2	72.3	73.1
Thickness μm	94.7	85.7
Paper bulk cc/g	1.31	1.17
Air permeability s	10.5	33.5
Fold endurance test, number	3	4
of folds (1.0 kg)
Bursting index kPa · m2/g	0.84	0.99
Tensile index N · m/g	17.4	21.8
Cohesion kg · cm	0.53	0.99
Ash content %	45.74	51.4
First-pass ash retention %	42.1	63.3
ash retention	68.7	82.2

EXAMPLE 3

In this embodiment, the modified filler composition was prepared by the following steps: (a) providing a filler suspension containing 2 g of filler (calcium carbonate) by weight; (b) adding microfibrillated cellulose having a dry weight of 0.002 g into the filler suspension; (c) adding 0.002 g of styrene-butadiene latex having a T_g of less than 10° C. into the filler suspension to obtain a mixture; (d) stirring the mixture at a temperature of about 50° C. for about 5 minutes, thereby making the modified filler composition.

A mixed pulp containing 10 g of Needle Bleached Kraft Pulp (NBKP) by dry weight and 10 g of alkaline peroxide mechanical pulp (APMP) by dry weight was provided. The above modified filler composition in Example 3 was added into the mixed pulp; 0.08 g of starch was added into the above mixed pulp; the mixed pulp was diluted to a concentration of about 0.3% and employed to make paper.

COMPARATIVE EXAMPLE 3

A mixed pulp containing 10 g of NBKP by dry weight and 10 g of APMP by dry weight was provided and adjusted to a concentration of about 4%. Then, 2 g of filler (calcium carbonate) and 0.08 g of cationic starch was added into the mixed pulp; the mixed pulp was diluted to a concentration of about 0.3% and employed to make comparative paper.

EXAMPLE 4

In this embodiment, the modified filler composition was prepared by the following steps: (a) providing a filler suspension containing 5 g of filler (calcium carbonate) by weight; (b) adding microfibrillated cellulose having a dry weight of 0.005 g into the filler suspension; (c) adding 0.005 g of styrene-butadiene latex having a T_g less than 10° C., and 0.005 g of a cross-linking agent (borax) into the filler suspension to obtain a mixture; (d) stirring the mixture at a temperature of about 50° C. for about 5 minutes, thereby making the modified filler composition.

A mixed pulp containing 10 g of NBKP by dry weight and 10 g of APMP by dry weight was provided and adjusted to a concentration of about 4%. The above modified filler composition in Example 4 was added into the mixed pulp; 0.08 g of starch was added into the above mixed pulp; the mixed pulp was diluted to a concentration of about 0.3% and employed to make comparative paper.

COMPARATIVE EXAMPLE 4

A mixed pulp containing 10 g of NBKP by dry weight and 10 g of APMP by dry weight was provided and adjusted to a concentration of about 4%. Then, 5 g of filler (calcium carbonate) and 0.08 g of cationic starch were added into the mixed pulp; the mixed pulp was diluted to a concentration of about 0.3% and employed to make paper.

The papers made in examples 3, Example 4, comparative example 3, and Comparative Example 4 were tested, and the test results are listed in Table 3 below. Compared with the paper in comparative example 3, the ash retention and the first-pass ash retention of the paper in example 3 are significantly improved. Compared with the paper in comparative example 4, the ash retention and the first-pass ash retention of the paper in Example 4 are also significantly improved.

TABLE 3
	Comparative		Comparative
Test type	Example 3	Example 3	Example 4	Example 4
Basis weight g/m2	76.1	74.7	81.5	77.6
Thickness μm	184.5	179.4	184.2	190.8
Paper bulk cc/g	2.42	2.40	2.26	2.46
Air permeability s	4.1	3.5	4.1	4.0
Fold endurance test,	59	92	40	62
number of folds
(1.0 kg)
Bursting index	2.38	2.53	2.22	2.28
kPa · m2/g
Tensile index	43.8	46.1	40.0	42.1
N · m/g
Cohesion kg · cm	0.97	1.02	0.85	0.92
Ash content %	3.86%	5.49%	9.94%	12.54%
First-pass ash	40.1%	58.1%	55.2%	71.7%
retention %
ash retention %	42.5%	60.4%	59.6%	75.2%

EXAMPLE 5

In this embodiment, the modified filler composition was prepared by the following steps: (a) providing a filler suspension containing 60 g of filler (calcium carbonate) by weight; (b) adding microfibrillated cellulose having a dry weight of 4 g into the filler suspension; (c) adding 9 g of styrene-butadiene latex having a T_g less than 10° C. into the filler suspension to obtain a mixture; (d) stirring the mixture at a temperature of about 50° C. for about 5 minutes, thereby making the modified filler composition.

A mixed pulp containing 10 g of NBKP by dry weight and 6 g of APMP by dry weight was provided and adjusted to a concentration of about 4%. The above modified filler composition in Example 5 containing 60 g of filler and 4 g of microfibrillated cellulose were added into the mixed pulp; 0.4 g of cationic starch was added into the above mixed pulp; the mixed pulp was diluted to a concentration of about 1%; a three-component retention aid containing 300 PPM cationic polyacrylamide, 3600 PPM bentonite, and 800 PPM anionic polyacrylamide was added into the mixed pulp, the pulp being employed to make paper.

COMPARATIVE EXAMPLE 5

A mixed pulp containing 10 g of NBKP by dry weight, 6 g of APMP by dry weight, and 4 g of microfibrillated cellulose by dry weight was provided and adjusted to a concentration of about 4%. Then, 60 g of filler (calcium carbonate) and 0.4 g of cationic starch were added into the mixed pulp; the mixed pulp was diluted to a concentration of about 1%; a three-component retention aid containing 300 PPM cationic polyacrylamide, 3600 PPM bentonite, and 800 PPM anionic polyacrylamide was added into the mixed pulp, the pulp being employed to make comparative paper.

The papers made in Example 5 and Comparative Examples 5 were tested, and the test results are listed in Table 4 below. Compared with the paper made in Comparative Example 5, the ash retention and the first-pass ash retention of the paper in Example 5 are significantly improved, and the number of folds, tensile index, and cohesion of the paper made in Example 5 also improved.

TABLE 4
Test type	Comparative Example 5	Example 5
Basis weight g/m2	107.9	112.0
Thickness μm	134.9	72.0
Paper bulk cc/g	1.25	0.64
Fold endurance test, number	2	11
of folds (1.0 kg)
Air permeability s	18.9	51.4
Tensile index N · m/g	7.2	16.6
Cohesion kg · cm	0.64	2.25
Ash content %	59.6	62.4
First-pass ash retention %	49.2	84.0
ash retention %	79.5	95.5

It is believed that the exemplary embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.

Claims

1. A modified filler composition, comprising:

microfibrillated cellulose,

filler, and

latex having a glass transition temperature of less than 20° C.,

wherein the dry weight of the microfibrillated cellulose is about 0.1% to about 10% of that of the filler, the dry weight of the latex is about 0.1% to about 15% of that of the filler.

2. The modified filler composition as claimed in claim 1, wherein the microfibrillated cellulose has negative charge and comprises carboxyl groups, the content of carboxyl groups of the microfibrillated cellulose is in the range from about 0.06 to about 1.7 mmol/g.

3. The modified filler composition as claimed in claim 2, wherein the microfibrillated cellulose comprises water-soluble cellulose having a mass percentage of about 0.1% to about 50% and water-insoluble cellulose having a mass percentage of about 10% to about 99.9%.

4. The modified filler composition as claimed in claim 3, wherein the water-soluble celluloses comprises nanocrystalline cellulose, nanofibrillated cellulose, and oligosaccharide.

5. The modified filler composition as claimed in claim 1, wherein the latex has a glass transition temperature of less than 10° C.

6. The modified filler composition as claimed in claim 1, wherein the latex is selected from the group consisting of polybutadiene latex, styrene-butadiene latex, carboxylic butadiene-styrene latex, cationic butadiene-styrene latex, polyvinyl acetate latex, and any combination thereof.

7. The modified filler composition as claimed in claim 1, wherein the filler adsorbing on the surface of the microfibrillated cellulose has a size uniformity of less than 10.

8. The modified filler composition as claimed in claim 1, wherein more than 50% of the filler has a particle diameter of less than or equal to 2 μm.

9. The modified filler composition as claimed in claim 1, wherein the modified filler composition further comprises a cross-linking agent.

10. The modified filler composition as claimed in claim 9, wherein the cross-linking agent is borate, borax, glutaric dialdehyde, or oxaldehyde; the dry weight of the cross-linking agent is about 0.1% to about 15% of that of the latex.

11. A papermaking process, comprising:

providing a modified filler composition, the modified filler composition comprising microfibrillated cellulose, filler, and latex having a glass transition temperature of less than 20° C., the dry weight of the microfibrillated cellulose being about 0.1% to about 10% of that of the filler, the dry weight of the latex being about 0.1% to about 15% of that of the filler.

providing a paper pulp;

adding the modified filler composition into the paper pulp;

employing the paper pulp to make paper.

12. The papermaking process as claimed in claim 11, wherein the modified filler composition is prepared by mixing the microfibrillated cellulose, filler, and latex together.

13. The papermaking process as claimed in claim 11, wherein the process further comprises a step of adding unmodified filler to the paper pulp prior to employing the paper pulp to make paper.

14. The papermaking process as claimed in claim 13, wherein the total weight of the filler in the modified filler composition and the unmodified filler in paper pulp is about 10% to about 300% of the dry weight of the pulp fiber, the weight of filler in the modified filler composition is about 80% to about 100% of the total weight of the filler in the modified filler composition and the unmodified filler.

15. The papermaking process as claimed in claim 11, wherein the microfibrillated cellulose has negative charge and comprises carboxyl groups, the content of carboxyl groups of the microfibrillated cellulose is in the range from about 0.06 to about 1.7 mmol/g.

16. The papermaking process as claimed in claim 11, wherein the microfibrillated cellulose comprises water-soluble cellulose having a mass percentage of about 0.1% to about 50% and water-insoluble cellulose having a mass percentage of about 10% to about 99.9%, the water-soluble celluloses comprises nanocrystalline cellulose, nanofibrillated cellulose, and oligosaccharide.

17. The papermaking process as claimed in claim 11, wherein the latex has a glass transition temperature of less than 10° C.

18. The papermaking process as claimed in claim 11, wherein the latex is selected from the group consisting of polybutadiene latex, styrene-butadiene latex, carboxylic butadiene-styrene latex, cationic butadiene-styrene latex, polyvinyl acetate latex, and any combination thereof.

19. The papermaking process as claimed in claim 11, wherein the filler adsorbed on the surface of the microfibrillated cellulose has a size uniformity of less than 10.

20. The papermaking process as claimed in claim 11, wherein more than 50% of the filler has a particle diameter of less than or equal to 2 μm.

21. The papermaking process as claimed in claim 11, wherein the modified filler composition further comprises a cross-linking agent, the cross-linking agent is borate, borax, glutaric dialdehyde, or oxaldehyde; the weight of the cross-linking agent is 0.1% to 15% of that of the latex.

22. The papermaking process as claimed in claim 11, wherein the process further comprises a step of adding auxiliary additive to the paper pulp prior to employing the paper pulp to make paper.