PRODUCTION METHOD THEREOF

Technical Field

The present invention relates to high-strength paper containing modified polymer and production method thereof

Background Art

Currently, Industrial growth in Asian countries affects gradually increasing demand of paper pulp usage for packaging production. As a matter of fact, most of the paper pulps from Asian countries contain short fibres, which is weaker comparing with the European's long fibre pulps. In addition, most of the paper pulps utilized in the production of paper for packaging are obtained from recycling paper pulp, of which the strength of the fibre is continuously decreasing by each round of recycling. Thus, many producers are attempting to create and develop the paper which has improved strength properties in order to meet the demand of pulp and paper industrial community and other relating industrial communities.

At present, there are abundant technologies using for increasing strength of pulp and paper. Mostly, natural starch obtained from cassava, maize, and other plants; or modified starch as cationic starch or amphoteric starch is used. Apart from these said modified starch, in order to increase pulp and paper strength, synthetic polyacrylamide with different molecular weights are used; or, in order to increase the efficiency of reaction with pulp, synthetic polyacrylamide which has been structurally modified, for example, synthetic cationic polyacrylamide, synthetic glyoxylated polyacrylamide, etc. is used.

Prior arts, especially patent documents, which disclosed modified polymers using for improving strength properties of paper and pulp are as follows:

US 4,029,544 A disclosed the method of production starch derivatives and products produced by said method. According to this prior art, additives including starch derivatives with defined amount of cationic aminoalkyl ether group or quaternary ammonium ether group are used together with sulfo succinate group. Degree of substitution (DS) of cationic starch and the amount of sulfosuccinate group is preferably in the range of 0.02-0.04 and 0.02-0.06 respectively. In this case, the amount of starch derivatives is in the range of 0.05-2.0% by weight of dry pulp. As a result of using said additives, starch derivatives allow pigments to be held onto the paper more efficiently. US 5, 122,231 disclosed the usage of cationic starch in the wet-end stage of the production process, pH of the system in the range of 6-9, in order to improve properties of paper associating with degree of drainage and retention. Adding said cationic starch to the paper, which normally is negatively charged, equilibrates degree of charge in the paper, resulting in the Zeta potential approaching zero. Used cationic starch with the degree of substitution in the range of 0.03-0.04 has been cross-linked with polyepoxide compounds such polyaminepolyepoxide resin, phosphorousoxychloride, 1 ,4-butanediol diglycidyl ether, etc.

EP 0833007 Al disclosed the method of production of paper by using modified cationic starch. According to this prior art, using modified cationic starch with DS in a range of 0.01 - 0.05 has been structurally modified with organic compounds containing oxy functional group, i.e., propylene oxide or organic compound containing alkoxycarbonyl group, i.e., acetic anhydride. Measurement of the retention after using said modified cationic starch with DS in a range of 0.02-0.25 at the amount of 0.1 -5% by weight of dry pulp in the production process of paper shows that modified cationic starch of this prior art is able to increase the retention efficiency of precipitated calcium carbonate (PCC) on the pulp.

US 6,413,372 B l disclosed the usage of cationic starch together with anionic starch, i.e., anionic starch phosphate with Zeta potential in the range of +15 to -5 mV in the process of both acidic and basic paper producing system. According to this invention, by the usage of cationic starch together with anionic starch, the retention efficiency of filler is improved.

US 2004/0025744 Al disclosed the starch composition and the usage of said starch composition in the wet-end stage of preparation of paper. Starch compositions of this prior art includes anionic starch and cationic starch, at least one of which is waxy starch. Said starches are not agglomerated when they are mixed. Also, when they are boiled before added in the wet-end stage in order to produce paper and paperboard, they appear as clear and viscous solution. Moreover, starch composition of this prior art can also used in the size press stage. In this case, produced paper has better properties than those produced by adding anionic starch and cationic starch separately. Proportion of starch mixture is preferably 60%(w/w) of anionic waxy starch modified with maleic anhydride and 40%(w/w) of cationic maize starch. The starch composition is used in the range of 4-6% by weight of dry pulp.

US 2009/0188640 Al disclosed the production process of paper with the improved retention and drainage of pulp by adding cationic polysaccharide or amphoteric polysaccharide or polysaccharide modified with a metal silicate. According to this prior art, used a metal silicate is sodium silicate; and can be potassium silicate, or sodium metasilicate. Said cationic polysaccharide is cationic starch with DS in the range of 0.02-0.04, and said amphoteric polysaccharide has 0.07-0.18 mole of anionic groups per mole of cationic groups. Moreover, ratio of starch to metal silicate is from 1 : 10 to 50: 1.

Utilizing of starch and modified starch as mentioned hereinbefore in order to improve properties of paper proves to be beneficial, i.e., their abundance and economical price result in decrease of production budget and improvement of machine performance. However, to achieve the desired properties of pulp and paper, for example, improved strength of pulp and paper, high amount of starch or modified starch is required.

Summary of Invention

The present invention relates to paper products produced from pulp including cellulose fibres, namely unbleached chemical pulp, semi-chemical pulp, pulp from waste paper, recycled pulp, etc. that are improved for higher strength using modified polymer and the method for producing said paper product.

The present invention relates, especially, to high-strength paper containing modified polymer characterized in that said paper comprises fibres and modified polymer. Said modified polymer is obtained from a reaction between polymer with active hydroxyl group and cyclic dicarbonyl organic compound. Said polymer with active hydroxyl group can be selected from the group consisting of non-chemically modified synthetic polymer and non-genetically modified natural polymer.

Apart from that, the present invention relates, especially, to the method for producing high-strength paper containing modified polymer, comprising the steps of : preparing the pulp slurry, preparing the modified polymer, mixing the pulp slurry with the modified polymer; diluting said pulp slurry which has been mixed with modified polymer; and forming paper, characterized in that said modified polymer is obtained from a reaction between polymer with active hydroxyl group and cyclic dicarbonyl organic compound, wherein said polymer with active hydroxyl group can be selected from the group consisting of non-chemically modified synthetic polymer and non-genetically modified natural polymer.

The objective of the present invention is to provide high-strength paper containing modified polymer and the method for producing said paper product which is technically advantageous, i.e., paper products having modified polymer of the present invention have high- strength due to the fact that the modified polymer of the present invention is able to form partially covalent bonds to the cellulose in paper pulp. During the wet-end stage of the production process, cellulose in paper pulp and modified polymer are binding to each other with intermolecular hydrogen bond. Then, when water removal from molecules at high-temperature has occurred, some of the molecules may form covalent bonds, which is more stable than ionic bonds. As a result, the paper products of the present invention have higher strength, as well as flexibility, and not too much rigidity that may cause fracture. Therefore, only small amount of said modified polymer can be sufficiently used to make paper with higher strength. On the other hand, too much amount of starch may cause the paper to be inflexible, and the hard and fragile film may form when the starch is dried. The properties of the paper containing modified polymer of the present invention, i.e., has high strength, flexibility, and not too much rigidity that may cause fracture, are key characteristics in production of packaging paper which has high strength, due to that fact, it provides higher short span compression, ring crush resistance, and resistance of corrugating medium. Moreover, modified polymer of the present invention also increases strength of paper causing higher burst index, tensile index, and tensile energy absorption.

Apart from that, the production of paper using modified polymer of the present invention does not require additives or other modified polymers, for example, cationic starch, in the conventional production processes of paper since the modified polymers of the present invention can form partially covalent bonds as mentioned hereinbefore. In contrast, conventional production processes require additives, such as cationic starch, or cationic colloid etc, for hydrogen and ionic bonding mechanism in wet-end stage, or cationic colloid etc, for hydrogen and ionic bonding mechanism in wet-end stage. As a result, said forming ionic bonds causes decreasing in gaps between celluloses, therefore increasing in strength of paper.

Brief Description of the Drawings

Figure 1 : The graph represents burst index based on the standard test method ISO 2758,2759:2001

Figure 2 : The graph represents tensile index based on the standard test method ISO

1924-2:2008

Figure 3 : The graph represents stretch index of paper based on the standard test method ISO 1924-2:2008

Figure 4 : The graph represents ply bond between layers of papers based on the standard test method T 569 pm-09

Figure 5 : The graph represents Tensile Energy Absorption (TEA) from paper based on the standard test method ISO 1924-2:2008 Figure 6 : The graph represents Short Span Compression Test (SCT) based on the standard test method ISO 9895: 1989

Figure 7 : The graph represents Ring Crush Test (RCT) based on the standard test method ISO 12192:2002

Figure 8 : The graph represents corrugating medium test (CMT) based on the standard test method T 824 om-02

Figure 9 : The graph represents tear index based on the standard test method ISO 1974: 1990 of the paper produced from recycled pulp.

Figure 10 : The graph represents Tensile Energy Absorption (TEA) based on the standard test method ISO 1924-2:2008 of the paper produced from recycled pulp.

Figure 1 1 : The graph represents Tensile Energy Absorption (TEA) based on the standard test method ISO 1924-2:2008 of the paper produced from recycled pulp.

Figure 12 : The graph represents burst index based on the standard test method ISO 2758,2759:2001 of the paper produced from recycled pulp.

Figure 13 : The graph represents short span compression based on the standard test method ISO 9895: 1989 of the paper produced from recycled pulp.

Figure 14 : The graph represents corrugating medium test (CMT) based on the standard test method T 824 om-02 of the paper produced from recycled pulp.

Detailed Description The detailed description of the present invention will be further described.

According to the present invention, high-strength paper containing modified polymer characterized in that said paper comprises fibre and modified polymer, wherein said modified polymer is the modified polymer obtained from a reaction between polymer with active hydroxyl group and cyclic dicarbonyl organic compound; where said polymer containing active hydroxyl group can be selected from the group consisting of non-chemically modified synthetic polymer and non-genetically modified natural polymer.

Non-chemically modified synthetic polymer of the present invention is polyvinyl alcohol

(PVA).

Non-genetically modified natural polymer of the present invention is starch, which can be selected from the group consisting of corn starch, cassava starch, and sweet potato starch, preferably, cassava starch. Moreover, the starch used in the present invention has an amylose to amylopectin ratio in the range of 15-30 to 70-85. Cyclic dicarbonyl organic compound of the present invention is a saturated or unsaturated cyclic dicarbonyl organic compound in which structure of said compound comprises at least one heteroatom. Said heteroatom is nitrogen (N), oxygen (O), or sulfur (S).

Modification of the structure of natural or synthetic polymer having active hydroxyl group with cyclic dicarbonyl organic compound of the present invention is illustrated as follows:

polymer with active

Modified polymer of the

hydroxyl group

present invention

Wherein M is heteroatom selected from nigtrogen (N), oxygen (O) and sulfur (S).

(C _x H _y )n is an alkyl chain of saturated or unsaturated hydrocarbon compound.

Using of modified polymer of the present invention in paper production alters binding mechanism of modified polymer (i.e. cyclic dicarbonyl starch or synthetic polymer) to cellulose. Modification with said cyclic dicarbonyl organic compound results in high flexibility in obtained modified polymers, some of which are able to form covalent bonds with cellulose in paper pulp when treated with sufficient high heat, providing the paper with higher strength. The binding mechanism is shown as below:

Hydrogen bond

Binding mechanism between celluloses in paper pulp and modified polymer of the present invention is different from one that occurred in the production process of conventional wet-end stage, i.e., generally in wet-end system, cationic starch or amphoteric starch is required for hydrogen and ionic bondin as shown below:

Hydrogen bond

Thus, paper containing modified polymer of the present invention does not require additive such as cationic starch or amphoteric starch in the method of production in order to increase strength of paper.

Modified polymer of the present invention has degree of substitution (DS) in the range of 0.01-0.2, preferably having degree of substitution in the range of 0.04-0.10. Paper of the present invention is produced from pulp including cellulose fibres which can be selected from the group consisting of unbleached chemical pulp, bleached chemical pulp, pulp from waste paper, and recycled pulp.

According to the present invention, the method for producing high-strength paper containing modified polymer comprises the steps of : preparing the pulp slurry, preparing the modified polymer, mixing the pulp slurry with the modified polymer; diluting said pulp slurry which has been mixed with modified polymer; and forming paper, characterized in that said modified polymer is obtained from a reaction between polymer with active hydroxyl group and cyclic dicarbonyl organic compound, wherein said polymer with active hydroxyl group can be selected from the group consisting of non-chemically modified synthetic polymer and non- genetically modified natural polymer.

Non-chemically modified synthetic polymer used according to the method of the present invention is polyvinyl alcohol

Non-genetically modified natural polymer used according to the method of the present invention is starch, which can be selected from the group consisting of corn starch, cassava starch, and sweet potato starch, preferably, cassava starch. Moreover, the starch used according to the method of the present invention has an amylose to amylopectin ratio in the range of 15-30 to 70-85.

Cyclic dicarbonyl organic compound used according to the method of the present invention comprise of at least one heteroatom. Said heteroatom is nitrogen (N), oxygen (O), or sulfur (S). Said cyclic dicarbonyl organic compound is a saturated or unsaturated cyclic dicarbonyl organic compound.

Modified polymer used according to the method of the present invention has degree of substitution in the range of 0.01-0.2, preferably having degree of substitution in the range of 0.04-0.10.

The amount of modified polymer used according to the method of the present invention is in the range of 0.1-2.0% by weight of dry pulp. Preferably, the amount is in the range of 0.2- 0.6% by weight of dry pulp.

The present invention will be further described by means of examples. However, it is recognized that these examples are not intended to limit scope of the present invention. Example

Example 1: Method for producing paper

Method for producing paper of the present invention comprises the steps of:

1. Preparing of pulp slurry: Cellulose fibre or pulp is dispersed in water for 20-30 minutes. Consistency of prepared pulp slurry is 1.6% (w/w). In this case, prepared pulp slurry can be further refined to enhance water retention on pulp;

2. Preparing of modified polymer: Modified polymer is dispersed in water and treated with heat at the temperature of 80 ^° C for 30 minutes;

3. Mixing of the pulp slurry with the modified polymer: Heat treated modified polymer is added to the prepared pulp slurry and stirring is performed for at least 1 minute;

4. Diluting said pulp slurry which has been mixed with modified polymer until consistency of 0.3% (w/w) is reached; and

5. Forming of paper: Pulp slurry which has been mixed with modified polymer and diluted is passed through wire mesh screens, then pressed and dried.

Example 2: Method for cyclic dicarbonyl starch preparation

Method for modified starch preparation of the present invention comprises the steps of: 1. Conducting a reaction between starch and cyclic dicarbonyl organic compound in water, pH in the range of 8-9, under stirring for 2 hours at room temperature.

2. Terminating a reaction with hydrochloric acid solution.

3. Separating the product by filtration and dried at the temperature of 60 ^° C for at least 4 hours.

Example 3: Method for cyclic dicarbonyl polyvinyl alcohol preparation

Method for modified polyvinyl alcohol preparation of the present invention comprises the steps of:

1 . Conducting a reaction between polyvinyl alcohol and cyclic dicarbonyl organic compound in solvent consisting of water, ethanol, and acetic acid (ratio is 1 : 1 : 1), having sodium acetate, approximately at pH of 6.

2. Precipitating the product in alcohol.

3. Separating the product by filtration, washed with alcohol, and dried at the temperature of 60 ^° C. Example 4: The result of physical properties testing for paper containing modified polymer of the present invention.

The result of physical properties testing for paper products containing the cyclic dicarbonyl starch (Nat-A) and the cyclic dicarbonyl polyvinyl alcohol (Syn-B) of the present invention using modified polymer at 0-4 kg/T of dry pulp is shown in Figure 1-8.

According to said test results, it showed significantly that the paper containing modified polymer of the present invention has higher strength. Also, it can be used in lower amount comparing to the paper produced by using native starch (Nat) or cationic starch (Nat-C), which is generally available in market as strengthening enhancer.

The increased values (%) obtained from physical properties testing of paper when the strengthening enhancer with the amount of 4 kg T of dry pulp is used. The result is shown in the table below:

Table showed results of physical properties test of paper products of the present invention

Physical Properties Increased values (%) comparing with the paper containing Nat and Nat-C

Paper containing Nat-A Paper containing Syn-B

Burst index based on standard test 22 4-12

method

ISO 2758,2759:2001

Tensile index based on standard test 1 1 5-1 1

method

ISO 1924-2:2008

Stretch based on standard test 19 2-14

method

ISO 1924-2:2008

Ply bond based on standard test 27 24-30

method T 569 pm-09

Tensile Energy Absorption (TEA) 19 13-23

based on standard test method ISO

1924-2:2008

Short Span Compression Test (SCT) 14 9-15

based on standard test method ISO 9895:1989

Ring Crush Test (RCT) based on 13 2-12

standard test method ISO

12192:2002

Corrugating Medium Test (CMT) 12 2-6

based on standard test method T 824

om-02

Example 5: The result of physical properties testing for the paper produced from recycled pulp containing modified polymer of the present invention.

The result showed that the paper produced from recycled pulp containing modified polymer of the present invention has higher strength comparing to the paper produced by using amphoteric starch (Nat-Am) or cationic starch (Nat-C) which is shown in Figures 9-14

Comparing strength increasing efficiency at the same amount of agent, cyclic dicarbonyl starch at the amount of 2 kg/T of dry pulp increases tear index based on the standard test method ISO 1974-2: 1990 up to 10-15% and 3-9% (Figure 9); and increases tensile energy absorption of paper based on the standard test method ISO 1924-2:2008 up to 22-30% and 12-30% (Figure

10), comparing to amphoteric starch or cationic starch at the amount of 4 kg/T and 10 kg/T of dry pulp, respectively.

Moreover, increasing of the amount of cyclic dicarbonly starch to 4 kg/T of dry pulp results in the increase of tensile index based on the standard test method ISO 1924-2:2008 up to 4-1 1% (Figure 1 1), the increase of burst index based on the standard test method ISO

2758,2759:2001 up to 10-17% (Figurel2), the increase of Short Span Compression based on the standard test method ISO 9895: 1989 up to 3-6% (Figurel3), and the increase of Corrugating Medium based on the standard test method T 824 om-02 up to 9-18% (Figure 14), comparing to amphoteric starch or cationic starch at the amount of 10 kg/T of dry pulp.

According to the details described hereinbefore, high- strength paper containing modified polymer and method for producing high-strength paper of the present invention consists of components, amounts of components, steps, and details providing the advantages as described hereinbefore. However, the high-strength paper containing modified polymer and method for producing the high-strength paper of the present invention are not only limited to components, amounts of components, steps, and details as described hereinbefore. Variations or modifications those aforementioned are also within concept and scope of the present invention.