US20200340182A1

US20200340182A1 - A cellulose paper composite and process for preparation thereof

Info

Publication number: US20200340182A1
Application number: US16/753,888
Authority: US
Inventors: Kadhiravan Shanmuganathan; Premnath Venugopalan; Tushar AMBONE
Original assignee: Council of Scientific and Industrial Research CSIR
Current assignee: Council of Scientific and Industrial Research CSIR
Priority date: 2017-10-06
Filing date: 2018-10-05
Publication date: 2020-10-29
Also published as: WO2019069325A1; EP3692206A4; EP3692206A1; JP2021508007A

Abstract

The present invention relates to a cellulose paper composite having enhanced ear propagation strength, ratio of tensile strength for cut and uncut paper, tensile strength and tensile modulus. The present invention further relates to a process for the preparation of cellulose paper composite having enhanced tensile strength and tensile modulus.

Description

FIELD OF THE INVENTION

The present invention relates to cellulose paper composite. More particularly, the present invention relates to a reinforced cellulose paper composite having enhanced tensile strength and tensile modulus and other parameters measured to determine strength of paper.

BACKGROUND AND PRIOR ART OF THE INVENTION

Printing of currency notes involves significant cost, time and administrative effort of Indian government. Soiling and tensile strength of currency note are major factors leading to early withdrawal and release of new currency notes. The circulation life of currency notes ranges from 1-5 years depending on denomination. Strategies to enhance tensile strength and durability of currency notes could have significant social and economic impact.
Current bank notes of India are made from 100% cotton rag paper. Strategies to enhance tensile strength of papers include adding various wet and dry strengthening resins, coating the paper with varnish, laminated paper containing synthetic polymer layer in between cellulosic layers. Nanocellulose reinforced paper could be processed in existing paper machinery, does not contain any synthetic polymer and can also provide additional advantages in smoothness and folding endurance apart from tensile strength. The increase in specific surface area arising from reduced fibre diameter is expected to enhance the hydrogen bonding between the fibres when water is drained out. Further colloidal interaction and mechanical interlocking is also expected to increase with increase in surface area of cellulosic fibres.
WO2017192476A1 discloses pulp product (e.g., paper) comprising cellulose and nanocellulose, wherein the nanocellulose is derived from the cellulose in a mechanical and/or chemical step that is separate from the main pulping process. The pulping process may be thermomechanical pulping or hydrothermal-mechanical pulping, for example. The pulp product is stronger and smoother with the presence of the nanocellulose. The nanocellulose improves the strength properties of the corrugated medium. The document further discloses that the addition of nanocellulose produced onsite gives a higher-strength corrugating medium product.
EP3228744A1 discloses a use of nano cellulose for increasing dog ear resistance of a paper product, a method of manufacturing a semi-finished paper product suitable for manufacturing a valuable document, a semi-finished paper product as well as a valuable document comprising the nano cellulose coated semi-finished paper product.
US20170072670A1 discloses a strong, light-weight composite laminates are made by impregnating layers of paper with a cellulose nanofiber (CNF) slurry, laying the coated papers up in a plurality of layers or stack, and subjecting the stack to pressure and heat for a period of time sufficient to cause the CNF to impregnate, reinforce, and bond the paper layers into a composite. The composite should have good strength to weight properties, and be recyclable or compostable, wherein the composite has a flexural strength of at least about 38 MPa and a flexural modulus of at least about 3.6 Gpa and wherein the composite has a tensile strength of at least about 52 MPa and tensile modulus of at least about 8.8 GPa.
WO2010142846A1 discloses a method for manufacturing nanostructured paper or board and a novel paper or board. The method comprises providing a liquid suspension of nanocellulose-containing material, forming a web from the suspension, and drying the web in order to form paper or board. According to the invention the water content of the suspension from which the web is formed is 50% or less by weight of liquids. By means of the invention, energy consumption of paper manufacturing can be significantly reduced.
WO2010142845A1 discloses a method for manufacturing nanostructured paper or board and a novel paper or board. The method comprises providing a liquid suspension of nanocellulose-containing material, forming a web from the suspension and drying the web in order to form paper or board. According to the invention, the water content of the suspension at the time of beginning of the drying is 50% or less by weight of liquids so as to form a paper or board having an average pore size between 200 and 400 nm.
WO2011113998A1 discloses a method for improving the properties of a paper product and to the corresponding paper product, wherein the paper product is formed from a fiber-based material. According to the invention the fines fraction is separated from chemical cellulose fiber -based pulp substantially after refining, and the cellulose fiber -based pulp from which the fines fraction has been separated is formed into the paper product in a papermaking apparatus. In addition, the invention relates to a method for manufacturing an additive component and to the corresponding additive component.
WO2013076372A1 discloses a method of preparing a composite material, comprising: preparing a mixture containing water and cellulose, and at least one of graphite and graphene as an additive; and removing water to form the composite, wherein at least a portion of the cellulose comprises nanocellulose fibrils and the portion of the nanocellulose fibrils from the cellulose is between 0.1-100%, such as 1-100%, for example 5-100% in weight.
US20100065236A1 discloses a method of producing cellulose based paper, the paper itself and the use thereof where the paper exhibits enhanced mechanical properties. The method involves providing a suspension of well dispersed modified cellulose at a low concentration. The properties and the chemical structure of the paper make it suitable for in vivo applications such as implant material, wherein the paper has a tensile strength of at least 250 MPa.
WO2012098296A2 discloses a method for improving strength and retention in the manufacture of paper. According to the invention, a composition containing microfibrillated cellulose is provided in a fiber suspension, and from 0.1 to 10 w-% of microfibrillated cellulose by mass of the fiber suspension is added to improve the strength and retention of the product to be formed. In addition, the invention relates to a corresponding paper product.
Article titled “The potential use of micro-and nanofibrillated cellulose as a reinforcing element in paper” by I kajanto et al. published in Journal of Science & Technology for Forest Products and Processes; 2012, vol. 2, no. 6, pp 42-48 reports the use of nanofibrillar cellulose as a reinforcement agent in paper has been evaluated on a high-speed pilot paper machine. Using mill pulp and mill process waters, two different grades of nanocellulose were tested at 1% and 2% addition levels together with 1% of cationic starch. The results indicate significant increase in tensile strength, enabling up to 8 g/m²grammage reduction.
Article titled “Effect of microfibrillated cellulose and fines on the drainage of kraft pulp suspension and paper strength” by T Taipale et al. published in Cellulose; October 2010, 17 (5), pp 1005-1020 reports different types of microfibrillated cellulose (MFC) and fines suspensions were produced, characterized, and then added to a papermaking pulp suspension. High and medium molar mass cationic polyelectrolytes were used as fixatives. The drainage behavior of the pulp suspensions with additives were evaluated against the strength properties of hand sheets made thereof. The effects of salt concentration, pH, fixative type, dosage and type of fibrillar material on drainage were examined.
Therefore, there is need to provide cellulose composite which shows better tensile strength and tensile modulus and accordingly the life of the cellulose composite can be enhanced. Accordingly, the present invention provides cellulose composite with enhanced tensile strength and tensile modulus.

OBJECTIVES OF THE INVENTION

The main objective of the present invention is to provide cellulose composite having enhanced tensile strength and tensile modulus.
Another objective of the present invention is to provide cellulose composite comprising 50 to 90% of micro-cellulose and 10 to 50% of nanocellulose having enhanced tensile strength and tensile modulus.
Still another objective of the present invention is to provide a reinforced cellulose paper composite comprising 50 to 90% of micro-cellulose and 10 to 50% of nanocellulose having enhanced tensile strength and tensile modulus and improve tear resistance of paper.
Yet another objective of the present invention is to provide a process for the preparation of said reinforced cellulose paper composite.

SUMMARY OF THE INVENTION

Accordingly, a cellulose paper composite comprising 80-85% of micro-cellulose and 15-20&of nanocellulose, wherein the tear propagation resistance of the composite is increased by 50-70% is provided.
In an embodiment, for the cellulose paper composite the ratio (R) of tensile strength of sample with a existing cut or tear to the tensile strength of the sample without a cut is 75-95%.
In another embodiment, in the cellulose paper composite an increase in tensile modulus is 15-40%, and tensile strength by 30-50%, when compared to micro cellulose paper composite is achieved.
In an embodiment, the present invention provides a process for the preparation of said cellulose paper composite wherein said process comprising the steps of:

- a) cutting the nanocellulose source material into small pieces;
- b) subjecting the pieces of step (a) to alkali treatment by washing with base for 4 to 5 hours under mechanical stirring to form fibres;
- c) subjecting the fibres of step (b) for bleaching treatment by using bleaching solution at temperature ranging from 70° C. to 80° C. for the time period ranging from 3 to 4 h; repeating process for 2 to 3 times to afford pulp;
- d) filtering and rinsing the pulp of step (c) followed by grinding the pulp in ultra-fine micro grinder and
- e) combining the nanocellulose pulp prepared as per above steps (a-d) with microcellulose pulp in different compositions to make a composite paper.

In preferred embodiment, the nanocellulose source material of step (a) is selected from cotton rag, sugarcane bagasse and sisal fibers.
The alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% base solution at 50 to 80° C. Preferably, the alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% sodium hydroxide solution at 50 to 80° C.
The bleaching solution of step (c) comprises 1:1 ratio of aqueous sodium hypochlorite (NaOCl in water) and an acetate buffer (NaOH and glacial acetic acid, diluted to 1 L using distilled water).
The fiber to liquor ratio is maintained 1:30 for both alkali and bleaching treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Paper making process

FIG. 2: With cut and without cut samples

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.
In view of the above, the present invention provides a reinforced cellulose paper composite comprising 50 to 90% of micro-cellulose and 10 to 50% of nanocellulose having enhanced tensile strength and tensile modulus. The higher surface area of nanocellulose fibrils, leads to more number of hydrogen bonds and more bonding area between the microcellulose and nanocellulose which linked with good mechanical interlocking provide necessary strength and stiffness to the composite paper.
In an embodiment, the present invention provides a reinforced cellulose paper composite comprising 50 to 90% of micro-cellulose and 10 to 50% of nanocellulose having enhanced tensile strength and tensile modulus.
In a preferred embodiment, the present invention provides a cellulose paper composite comprising 80 to 85% of micro-cellulose and 15 to 20% of nanocellulose having enhanced tensile strength and tensile modulus.
The tensile strength of reinforced cellulose paper composite is in the range of 20-50 MPa. In preferred embodiment, the tensile strength of with cut and without cut sample of cotton rag nanocellulose is in the range of 20-35 MPa and 25-40 MPa respectively.
The tensile modulus of reinforced cellulose paper composite is in the range of 3150 to 5050 MPa.
In another embodiment, the present invention provides a process for the preparation of said Reinforced Cellulose Paper composite comprising the steps of:

In a preferred embodiment, the nanocellulose source material of step (a) is selected from cotton rag, sugarcane bagasse or sisal fibers.
The alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% base solution at 50 to 80° C. Preferably, the alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% sodium hydroxide solution at 50 to 80° C.
The bleaching solution of step (c) comprises 1:1 ratio of aqueous sodium hypochlorite (NaOCl in water) and an acetate buffer (NaOH and glacial acetic acid, diluted to 1 L using distilled water).
The fiber to liquor ratio are maintained 1:30 for both alkali and bleaching treatment. The nanocellulose pulp of step (d) is combined with microcellulose pulp to afford composite paper.
In yet another embodiment, the present invention provides a paper making process comprising the steps of:

- a) preparing A4 printing paper pulp with the consistency of 1.2 to 1.57 wt %;
- b) beating the pulp in valley beater to get required Schopper-Riegler (SR) value, e.g. 40, 50, or 60 as per requirement and
- c) adding said A4 recycled pulp of step (b) to sheet former machine to form paper.

In a preferred embodiment, different source of nanocellulose/A4 recycled composites paper are made by varying nanocellulose content from 10 to 50%. In another preferred embodiment, the process is carried out at ambient temperature.
The present invention provides effect of with cut and without cut sample of nanocellulose source material on tensile strength and tensile modulus of A4 recycled paper.
Table 1 represent the effect of cotton rag (CR) nano cellulose on the mechanical properties of the composite paper. Values in bracket represent the standard deviation.

TABLE 1

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

A4	28.0	(0.7)	21.2	(0.8)	3156	(88)	3202	(107)
10CR	36.5	(1.7)	26.7	(1.5)	3689	(310)	3288	(177)
15CR	37.3	(1.2)	33.4	(0.9)	3896	(62.4)	3812	(337)
20CR	39.0	(0.5)	34.4	(2.9)	4328	(110)	4323	(207)

The tensile strength of with cut and without cut sample of cotton rag nanocellulose is in the range of 25-35 MPa and 35-40 MPa respectively.
The tensile modulus of with cut and without cut sample of cotton rag nanocellulose is in the range of 3250-4330 MPa and 3600-4400 MPa respectively.
Table 2 represent the effect of sugarcane (SC) nanocellulose on the mechanical properties of the composite paper. Values in bracket represent the standard deviation.

TABLE 2

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

A4	28.0	(0.7)	21.2	(0.8)	3156	(88)	3202	(107)
10 SC	35	(0.55)	27.6	(1.47)	3505	(205)	3950	(339)
20 SC	41	(0.45)	35	(0.6)	4090	(144)	5045	(217)
50 SC	48.41	(1.13)	26.9	(1.06)	3432	(381)	3519	(131)

The tensile strength of with cut and without cut sample of sugarcane nanocellulose is in the range of 25-40 MPa and 30-50 MPa respectively.
The tensile modulus of with cut and without cut sample of sugarcane nanocellulose is in the range of 3500-5100 MPa and 3400-4200 MPa.
Table 3 represent the effect of sugarcane nano cellulose from sisal on the mechanical properties of the composite paper. Bracket value represents the standard deviation.

TABLE 3

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

A4	28.0	(0.7)	21.2	(0.8)	3156	(88)	3202	(107)
10 Sisal	36.0	(0.55)	27.1	(1.44)	4009	(90)	4664	(94)
15 Sisal	38.0	(0.95)	32.6	(1.6)	4246	(225)	4646	(151)
20 Sisal	39.3	(0.46)	33.0	(0.6)	3946	(179)	3614	(147)

The tensile strength of with cut and without cut sample of sisal nanocellulose is in the range of 25-35 MPa and 30-40 MPa.
The tensile modulus of with cut sample of sisal nanocellulose is in the range of 3500-4800 MPa and 3700-4300 MPa respectively.
The ratio of tensile strength and tensile modulus for Cotton rag, sugarcane and sisal nano cellulose paper composites is listed in Table 4


	Tensile Strength (MPa)	Tensile Modulus (MPa)

Sample	Without	With		Without	With
Name	Cut	Cut	R*	Cut	Cut

A4	1.00	1.00	76%	1.00	1.00
10CR	1.30	1.26	73%	1.17	1.03
15CR	1.33	1.58	90%	1.23	1.19
20CR	1.39	1.62	88%	1.37	1.35

Tensile Strength (MPa)

Tensile Modulus (MPa)

Sample	Without	With		Without	With
Name	Cut	Cut	R	Cut	Cut

A4	1.00	1.00	76%	1.00	1.00
10 SC	1.25	1.30	79%	1.11	1.23
20 SC	1.46	1.65	85%	1.30	1.58
50 SC	1.73	1.27	56%	1.09	1.10
A4	1.00	1.00	76%	1.00	1.00
10 Sisal	1.29	1.28	75%	1.27	1.46
15 Sisal	1.36	1.54	86%	1.35	1.45
20 Sisal	1.40	1.56	84%	1.25	1.13

*R = ratio of tensile strength with cut to tensile strength without cut, R is a measure of tear propagation resistance to total tear resistance, Total tear resistance consists of tear initiation and tear propagation resistance

The tensile strength and tensile modulus in table 4 is expressed as a ratio of tensile strength or modulus of paper measured for each concentration of nano cellulose (with or without cut) to tensile strength or modulus of A4 paper(with or without cut respectively).
In an embodiment, referring to tables 1-4, an increase in tensile modulus by 15-40%, preferably 20-40%, is achieved by the addition of 15-20% nano cellulose for uncut paper.
In an embodiment, referring to tables 1-4, an increase in tensile strength by 30-50% is achieved by the addition of 15-20% nano cellulose for uncut paper.
In one more embodiment of the invention, the ratio (R) of tensile strength of sample with a existing cut or tear (which is a measure of only tear propagation resistance) to the tensile strength of the sample without a cut (a measure of both tear initiation and propagation resistance) is measured. Referring to table 4, a 75-95% enhancement is seen for an addition of 15-20 nano cellulose.
In a preferred embodiment, the ratio R is enhanced by 80-90% for an addition of 15-20 nano cellulose.
In yet another embodiment of the invention, tear propagation resistance is studied. Tear propagation resistance is the ratio of ratio of tensile strength of paper with cut measured for each concentration of nano cellulose to tensile strength or modulus of A4 paper with cut. The tear propagation resistance of cut paper is increased by 50-70% for an addition of 15-20% nano cellulose to micro cellulose. The tear propagation resistance is preferably enhanced by 50-65% by the addition of 15-20% nano cellulose to micro cellulose.
There is no suggestion in any prior art to add nano cellulose in the range of 15-20% to micro cellulose to accomplish enhancement of total tear resistance which consists of tear initiation and tear propagation resistance. It is surprisingly that the concentration range of 15-20% causes enhancement, while increasing the concentration greater than 20% or less than 15% does not cause an enhancement. The prior arts neither suggest nor teach that the specific range of nano cellulose causes enhancement of key parameters of measure of strength of paper.
The FIG. 1 is pictorial representation of nanocellulose preparation form the raw source material. A1, B1, C1 represent the raw material sugarcane bagasse, cotton rag and sisal respectively. A2, B2, C2 represent the bleached pulp of sugarcane bagasse, cotton rag and sisal respectively. A3, B3, C3 represent the final nanocellulose product of sugarcane bagasse, cotton rag and sisal respectively.
The FIG. 2 shows with cut and without cut samples. Without cut samples data gives information about tensile strength and modulus for the specimen which is not having any deformation in it. It is similar to Edge-tearing strength (TAPPI standard T-470) and is a measure of the force needed to initiate a tear. With cut samples data gives information about tensile strength and modulus of a specimen where a tear is already initiated. This is similar to commonly used tearing test (TAPPI T-414), also often called the Elmendorf tear test, which measures the internal tearing resistance of paper rather than the edge-tear strength of paper.
The paper composite prepared by the composition of the invention comprising 80-85% micro cellulose and 15-20% nano cellulose is useful in preparing security documents. The paper composition of the invention has enhanced folding resistance and is smooth and is versatile to be used for preparing paper for security applications. Security documents are documents made of paper that need to identified or authenticated as genuine using security features and are selected from, but not limited to currency notes, passports, bonds, certificates, agreements, stamp or stamp paper, share certificates and such like.
Examples Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

EXAMPLE

Preparation of Reinforced Cellulose Paper Composite

The nanocellulose source material was cut into small pieces. Alkali treatment was carried out by washing the pieces with base for 4 to 5 hours under mechanical stirring to form fibres. Bleaching treatment was carried out on fibres by bleaching solution at the temperature ranging from 70° C-80° C. for the time period ranging from 3 to 4 h; repeating process for 2 to 3 times to afford pulp. Then it was filtered and rinsed followed by grinding said pulp in ultra-fine micro grinder. Then the nano cellulose pulp was combined with micro cellulose pulp to form composite paper in ratios listed in the tables. After drying the paper are tested by tensile testing machine (INSTRON UTM) at rate lmm/min. The 13 mm×40 mm rectangular shape specimen are used. At least 6 specimens were tested for each composition listed below in the tables 1-3. Two types of mode were tested with cut and without cut.
A. Effect of Cotton Rag Nanocellulose on Tensile Strength and Tensile Modulus of A4 Recycled Paper. Figures in Bracket Indicates Std Deviation

TABLE 1

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

B: Effect of Sugarcane Nanocellulose on Tensile Strength and Tensile Modulus of A4 Recycled Paper.

TABLE 2

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

A4	28.0	(0.7)	21.2	(0.8)	3156	(179)	3202	(147)
10 SC	35	(0.55)	27.6	(1.47)	3505	(205)	3950	(339)
15 SC	39	(0.95)	29.5	(1.6)	3802	(175)	3762	(181)
20 SC	41	(0.45)	35	(0.6)	4090	(144)	5045	(217)
50 SC	48.41	(1.13)	26.9	(1.06)	3432	(381)	3519	(131)

C: Effect of Sisal Nanocellulose on Tensile Strength of and Tensile Modulus A4 Recycled Paper.

TABLE 3

Sample	Tensile Strength (MPa)	Tensile Modulus (MPa)

Name	Without Cut	With Cut	Without Cut	With Cut

A4	28.0	(0.7)	21.2	(0.8)	3156	(179)	3202	(147)
10 Sisal	36.0	(0.55)	27.1	(1.44)	4009	(90)	4664	(94)
15 Sisal	38.0	(0.95)	32.6	(1.6)	4246	(225)	4646	(151)
20 Sisal	39.3	(0.46)	33.0	(0.6)	3946	(179)	3614	(147)

Advantages of the Invention:

- 1) A Reinforced Cellulose Paper composite showing better tensile strength and tensile modulus is provided.
- 2) Reinforced Cellulose Paper composite shows smoothness and folding endurance.

Claims

1. A cellulose paper composite comprising 80-85% of micro-cellulose and 15-20% of nanocellulose, wherein the tear propagation resistance of the composite is increased by 50-70%.

2. The cellulose paper composite as claimed in claim 1, wherein the the ratio (R) of tensile strength of sample with an existing cut or tear to the tensile strength of the sample without a cut is 75-95%.

3. The cellulose paper composite as claimed in claim 1, wherein the increase in tensile modulus is 15-40%, and tensile strength by 30-50%, when compared to micro cellulose paper composite.

4. A process for the preparation of cellulose paper composite as claimed in claim 1, wherein said process comprising the steps of:

a) cutting the nanocellulose source material into small pieces;

b) subjecting the pieces of step (a) to alkali treatment by washing with base for 4 to 5 hours under mechanical stirring to form fibres;

c) subjecting the fibres of step (b) for bleaching treatment by using bleaching solution at temperature ranging from 70° C. to 80° C. for the time period ranging from 3 to 4 h; repeating process for 2 to 3 times to afford pulp;

d) filtering and rinsing the pulp of step (c) followed by grinding the pulp in ultra-fine micro grinder; and

e) combining the nanocellulose pulp prepared as per above steps (a-d) with microcellulose pulp in different compositions to make a composite paper.

5. The process as claimed in claim 4, wherein said nanocellulose source material of step (a) is selected from cotton rag, sugarcane bagasse and sisal fibers.

6. The process as claimed in claim 4, wherein said alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% base solution at 50 to 80° C.

7. The process as claimed in claim 4, wherein said alkali treatment of step (b) is carried out by washing small pieces of nanocellulose source material with 1-10% sodium hydroxide solution at 50 to 80° C.

8. The process as claimed in claim 4, wherein said bleaching solution of step (c) comprises 1:1 ratio of aqueous sodium hypochlorite (NaOCl in water) and an acetate buffer (NaOH and glacial acetic acid, diluted to 1 L using distilled water).

9. The process as claimed in claim 4, wherein the fiber to liquor ratio is maintained 1:30 for both alkali and bleaching treatment.