Strength additive system and method for manufacturing a web comprising cellulosic fibres

Abstract

A strength additive system for manufacturing paper, board, tissue or the like includes preferably as separate components, a cationic strength agent, such as a cationic polymer with aldehyde functional groups, and an anionic copolymer obtained by polymerization of a reaction mixture including (meth)acrylamide and anionic monomers, the standard viscosity of the obtained copolymer being in a range of 1.5-5.0 mPas. A method for manufacturing of a paper, board, tissue or the like is further disclosed.

Claims

1. A strength additive composition for manufacturing paper, board or tissue, the composition comprising as separate components: a cationic strength agent being a cationic polymer with aldehyde functional groups and having a charge density of 0.1-5.5 meq/g; and an anionic copolymer obtained by polymerization of a reaction mixture comprising (meth)acrylamide and anionic monomers, the standard viscosity of the obtained copolymer being in a range of 1.8-3.0 mPas.

2. The strength additive composition according to claim 1, wherein the reaction mixture for the anionic copolymer comprises 1-90 mol % of anionic monomers.

3. The strength additive composition according to claim 1, wherein the anionic copolymer has an anionic charge density in a range of 0.1-10 meq/g, at pH 8.0.

4. The strength additive composition according to claim 1, wherein the anionic copolymer is obtained by polymerization of a reaction mixture comprising (meth)acrylamide and anionic monomers selected from group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid, tiglic acid, vinylsulphonic acid, allyl sulphonic acid, methallylsulphonic acid, styrenesulphonic acid, 2-acrylamido-2-phenylpropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, their salts and any combinations thereof.

5. The strength additive composition according to claim 1, wherein the anionic copolymer is obtained by inverse emulsion polymerization, gel polymerization or precipitation polymerization.

6. The strength additive composition according to claim 1, wherein the composition comprises at least one cationic strength agent, which is selected from alum, polyaluminium chloride, polyvinylamine (PVAm), polyethylene imine (PEI), homopolymers or copolymers of diallyldimethylammonium chloride (DADMAC), polyamine, cationic polyacrylamide-based solution polymers, cationic starches, or any combinations thereof.

7. The strength additive composition according to claim 1, wherein the cationic strength agent comprises a cationic reactive strength polymer, which is selected polyamidoamine-epichlorohydrin resins, cationic polymers with aldehyde functional groups, urea formaldehyde resins, and melamine formaldehyde resins, or any combinations thereof.

8. The strength additive composition according to claim 1, wherein the composition comprises at least one cationic reactive strength agent, which is a cationic polymer with aldehyde functional groups.

9. The strength additive composition according to claim 8, wherein the cationic reactive strength polymer is a glyoxalated cationic polyacrylamide, which is obtained by polymerization of polymerization mixture of acrylamide monomers and cationic monomers.

10. The strength additive composition according to claim 1, wherein the cationic strength agent has a charge density of 0.3-4.5 meq/g.

11. The strength additive composition according to claim 1, wherein the composition comprises 5-95 weight-%, of the cationic strength agent and 5-95 weight-% of the anionic copolymer.

12. The strength additive composition according to claim 1, wherein the composition has net cationic charge.

13. A method for manufacturing of a paper, board or tissue, the method comprising: obtaining a stock comprising cellulosic fibers; adding to the stock the strength additive composition of claim 1; and forming a web from the stock and drying the web.

14. The method according to claim 13, wherein at least part of the cationic strength agent and/or at least part of the anionic copolymer of the strength additive composition is added after a fan pump.

15. The method according to claim 14, wherein at least part of the cationic strength agent and/or at least part of the anionic copolymer of the strength additive composition is added after a screen.

16. The method according to claim 13, wherein the cationic strength agent and the anionic copolymer of the strength additive composition are added separately.

17. The method according to claim 13, wherein the cationic strength agent and the anionic copolymer of the strength additive composition are added simultaneously.

18. The method according to claim 13, wherein the cationic strength agent of the strength additive composition is added in amount of 0.5-40 lb/ton, and the anionic copolymer of the strength additive composition is added in amount of 0.1- 20 lb/ton.

Description

EXPERIMENTAL

(1) Determination of Polymer Molecular Weight by Standard Viscosity (SV)

(2) The molecular weight of a polymer may be determined by viscometric methods such as Standard Viscosity (“SV”, also known as “Solution Viscosity”), or Intrinsic Viscosity (“IV”). Both of these processes are well-known to persons of ordinary skill in the art.

(3) It is also well known in the art that the intrinsic viscosity of a polymer correlates to the molecular weight of that polymer using the Formula (1):
IV=0.000373×molecular weight 0.66  (1)

(4) Intrinsic viscosity is a cumbersome and time consuming property to measure, however. IV measurement is commonly taken with a Cannon-Ubbelohde capillary viscometer at various concentrations of, for instance, 100, 250, 500 and 1,000 ppm in 1 molar sodium chloride at 30° C. and at shear rates ranging between 50-1000 sec.sup.−1. The data thus obtained is subjected to linear regression to extrapolate it to zero shear rate and zero polymer concentration. The value obtained with this calculation is the intrinsic viscosity of the polymer.

(5) Standard (i.e. solution) viscosity SV values are relatively easier, i.e., less cumbersome and time consuming, to obtain than intrinsic viscosity values. Moreover, SV values can be correlated to IV values for a particular polymer. Thus, polymeric molecular weights can be approximated by reference to the solution viscosity of the polymer. That is, the higher the SV value for a particular polymer, the higher its molecular weight. For example (the following values are approximate):

(6) SV 4 mPas=IV 15 dl/g.=MW 10,000,000

(7) SV 5 mPas=IV 25 dl/g.=MW 20,000,000

(8) SV 6 mPas=1V 30 dl/g.=MW 26,000,000

(9) SV 7 mPas=IV 32 dl/g.=MW 30,000,000

(10) For purposes of the present invention, SV values are determined using a 0.1 weight-% polymer solution in 1 molar NaCl at 25° C. The measurement is taken using a Brookfield viscometer with a UL adapter at 60 rpm when the SV is 10 or less.

(11) Thus although one can calculate with a high degree of exactitude the molecular weight of a polymer within a solution using the IV value of the subject polymer with the Formula 1 provided above, the difficulty in obtaining these IV values, in terms of time and attention to detail required, is outweighed by the relative ease of using SV values for this purpose. This is because such SV values are relatively simple to obtain and may be mathematically correlated to corresponding IV values, thus permitting one to obtain a rough determination of the polymer's molecular weight based upon the SV value of the solution alone. IV and polymer's approximate molecular weight can be estimated from SV by assuming a linear relationship of two extremes and then using Formula 1 hereinabove.

(12) Materials

(13) GPAM1 was a cationic glyoxalated polyacrylamide sample having charge density of about 1.8 meq/g dry polymer, prepared by the crosslinking reaction between a poly(acrylamide-co-dimethyldiallylammonium chloride) base polymer and glyoxal as discussed e.g. in U.S. Pat. No. 4,605,702. Anionic polyacrylamide (APAM) samples A through D were copolymers of acrylamide and sodium acrylate prepared by inverse emulsion polymerization as discussed in U.S. Pat. Nos. 3,284,393; 4,650,827; 4,739,008 and 5,548,020. Anionic polyacrylamide E was a copolymer of acrylamide and sodium acrylate prepared by standard aqueous solution polymerization as well known by the persons of ordinary skills in the art. One example of such polymerization was discussed in U.S. Pat. No. 6,939,443. Sample E had a final polymer content of 20% and viscosity of 9000 mPas at room temperature. All APAM samples from A through E had an anionic charge density of 20 mol-%. The SV values of all APAM samples are shown in Table 1.

(14) Handsheet Preparation

(15) Handsheets were prepared using a pulp mixture (2.5 weight-%) of virgin bleached hardwood (50%) and virgin bleached softwood (50%). The Canadian Standard Freeness of the mixture was 450 ml. Pulp dilutions during handsheet preparation were carried out using a specially formulated water to simulate papermaking mill white water. This formulated water contained 150 ppm of sodium sulfate, 35 ppm of calcium chloride, and 100 ppm alkalinity (adjusted by sodium bicarbonate). The final pH was adjusted to 7.8 using dilute hydrochloric acid and sodium hydroxide. The pulp suspension was first diluted to 0.4 weight-%. While mixing with an overhead agitator, GPAM1 and APAM samples were added to the pulp suspension consecutively with a time interval of 30 seconds. After additional two minutes of mixing, the treated pulp suspension were added a standard (8″×8″) Nobel & Woods handsheet mold to produce 3 g sheets of paper to target a basis weight of 52 lbs/3470 ft.sup.2. Next, the handsheets were pressed between felts in the nip of a pneumatic roll press at about 15 psig and dried on a rotary dryer at 110° C. The paper samples were oven cured for 10 minutes at the temperature of 110° C., then conditioned in the standard TAPPI control room for overnight.

(16) Dry Tensile Strength Test

(17) Tensile strength is measured by applying a constant-rate-of-elongation to a sample and recording the force per unit width required to break a specimen. This procedure references TAPPI Test Method T494 (2001), and modified as described.

(18) Initial Wet Tensile Strength Test

(19) Initial wet tensile strength test method is used to determine the initial wet tensile strength of paper or paperboard that has been in contact with water for 2 seconds. A 1-inch wide paper strip sample is placed in the tensile testing machine and wetted on both strip sides with deionized water by a paint brush. After the contact time of 2 seconds, the strip is elongated as set forth in 6.8-6.10 TAPPI test method 494 (2001). The initial wet tensile is useful in the evaluation of the performance characteristics of tissue product, paper towels and other papers subjected to stress during processing or use while instantly wet. This method references U.S. Pat. No. 4,233,411, and modified as described.

(20) Drainage Test

(21) Pulp furnishes containing about 3.5% dry mass were obtained from a packaging paperboard machine and diluted with white water from the same machine to a final 1.0% dry mass. pH was adjusted to 7.5 using 0.5 N of sodium hydroxide or hydrochloric acid. The addition dosages of glyoxalated polyacrylamide and anionic polyacrylamide were based on dry chemical mass and dry fiber mass. A dynamic drainage analyzer (DDA) (AB Akribi Kemikonsulter) was used for the evaluation. 800 mL of diluted pulp furnish was first placed into DDA. Then, chemicals were added under mixing. Detailed contact time and chemical addition sequence are shown as follow:

(22) TABLE-US-00001  0 seconds started the stirrer at 950 rpm 10 seconds added GPAM1 and adjusted to 1400 rpm 20 seconds added APAM 28 seconds adjusted to 950 rpm 35 seconds stopped the stirrer

(23) After the stirrer stops, the treated pulp was filter through a 50-mesh screen under 165 mbar vacuum. The amount of time required to break the vacuum was recorded as an indication of drainage rate. A shorter time suggested a faster drainage rate.

(24) TABLE-US-00002 TABLE 1 SV values of APAM samples Sample SV (mPas) A 3.4 B 2.3 C 1.9 D 1.7 E (ref.) 1.2

(25) TABLE-US-00003 TABLE 2 Paper tensile properties GPAM (8 lb/ APAM Initial wet Example ton) (4 lb/ton) Dry tensile tensile 1 GPAM1 None 21.7 1.2 2 GPAM1 A 30.4 3.5 3 GPAM1 B 33.2 3.8 4 GPAM1 C 33.2 3.9 5 GPAM1 D 31 4.2 6 GPAM1 E 28.5 3.2

(26) TABLE-US-00004 TABLE 3 Drainage test GPAM APAM Drainage time Examples (8 lb/ton) (1 lb/ton) (s) 7 GPAM1 None 26 8 GPAM1 A 18.9 9 GPAM1 B 19.2 10 GPAM1 D 25.3 11 GPAM1 E 30.8
Results and Discussion

(27) The combination of a cationic GPAM and an anionic APAM was reported in U.S. Pat. Nos. 9,347,181 and 9,328,462 to increase paper strength and also improve papermaking retention/drainage process. The APAM samples applied were either very high molecular weight flocculants with a SV of at least 5.5 mPas or low molecular weight strength products with a SV of 1.2 mPas. The HMW flocculants can only be applied at low dosages to improve retention/drainage. Higher HMW flocculant dosages could lead to over-flocculation, poor paper formation, and lower tensile strength. In contrast, low molecular weight strength APAM can be applied at considerable higher dosages to enhance paper strength. However, those low molecular weight strength APAM samples can negatively impact retention/drainage.

(28) In this work we developed new APAM samples with medium SV values to enhance paper strength and improve retention/drainage simultaneously. Table 1 listed five APAM samples with a SV range from 1.2 to 3.4 mPas. Table 2 demonstrates the effect of those APAM samples on paper dry and initial wet strength when used in combination with a cationic GPAM. Surprisingly the two-component program of GPAM and APAM having intermediate SV provided a dry strength local maximum and an initial wet strength local maximum, by slightly different SV values. The best dry and initial wet strength performance combination can be seen in the partially overlapping SV values of 1.7-3.4 mPas, especially around SV 2 mPas. Too high or too low SV values led to the decrease of strength properties. The drainage rate was a function of APAM SV value. Table 4 shows that higher APAM SV value resulted in faster drainage rate. The APAM sample with a SV value of 1.2 led to lower drainage rate than the control test without APAM. Increasing SV value to 2.3 mPas resulted in significant drainage rate increase.

(29) Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.