Starch-containing adhesive compositions and uses thereof

Abstract

The invention relates to aqueous adhesive compositions comprising a starch, in particular to starch-based adhesives for bonding paper products. Provided is an aqueous adhesive composition comprising a starch derivative and a clay, wherein said starch derivative is a highly branched starch (HBS) obtained by treatment of starch or starch derivatives with a glycogen branching enzyme (EC 2.4.1.18), and wherein the weight ratio of said HBS to said clay is within the range of from about 1:1 to 1:4.

Claims

1. An aqueous adhesive composition comprising a starch derivative and a clay, wherein said starch derivative is a highly branched starch (HBS) obtained by treatment of starch or starch derivatives with a glycogen branching enzyme (EC 2.4.1.18), and wherein the weight ratio of said HBS to the clay in the composition is within the range of from about 1:1 to 1:4.

2. The adhesive composition according to claim 1, wherein said clay is a kaolin-type clay.

3. The adhesive composition according to claim 1, wherein said clay comprises particles and said clay particles have diameters at which 90% of a sample's mass is comprised of particles within the range of from about 1 to 20 ?m.

4. The adhesive composition according to claim 1, having a viscosity within the range of from about 300 to 10000 mPa.Math.s, wherein the viscosity is measured at a temperature of 25? C. and at 20 rpm.

5. The adhesive composition according to claim 1, wherein said HBS has a molecular branching degree of at least 6%, wherein the molecular branching degree is defined as the percentage of ?-1,6 glycosidic linkages of the total of ?-1,6 and ?-1,4 glycosidic linkages ((?-1,6/(?-1,6+?-1,4)*100%).

6. The adhesive composition according to claim 1, wherein the HBS has an average molecular weight (Mw) ranging between 0.5*10.sup.5 g/mol and 1*10.sup.6 g/mol.

7. The adhesive composition according to claim 1, wherein said HBS is obtained from starch or a starch derivative in a partially or completely gelatinized form.

8. The adhesive composition according to claim 1, wherein said HBS is obtained from a non-cereal starch.

9. The adhesive composition according to claim 1, wherein the pH of said composition is below 7.

10. The adhesive composition according to claim 1, wherein said adhesive composition contains 20-80 wt % dry matter.

11. The adhesive composition according to claim 1, wherein HBS is present in an amount of from 5 to 40% (w/w), by weight of the total weight of the composition and/or wherein the clay content is from about 10 to 60% (w/w), by weight of the total weight of the composition.

12. The adhesive composition according to claim 1, which contains 50-65 wt % dry matter and wherein the weight ratio of HBS to clay is within the range of from about 1:2 to 1:3.

13. The adhesive composition according to claim 1, comprising less than 0.1 wt % of borates.

14. A method for adhering a first substrate to a second substrate, comprising applying to at least said first or said second substrate a water-based adhesive composition according to claim 1.

15. The method according to claim 14, wherein said first or said second substrate is a paper substrate having at least one of the following properties: (i) grammage in the range of about 60 to about 250 g/m.sup.2; (ii) water absorbance expressed as Cobb30 in the range of 12 to 40 g/m.sup.2; and (iii) Dennison wax in the range of about Nr. 10 to Nr. 25.

16. A glued product obtainable by adhering a first substrate to a second substrate according to the method of claim 14.

17. The adhesive composition according to claim 1, wherein said starch or starch derivative is selected from native, unmodified and chemically modified starch derived from non-genetically modified as well as genetically modified plant variants, and modified starches including low DE maltodextrins and amylomaltase-treated starch.

18. The adhesive composition according to claim 1, wherein said HBS is obtained from a potato starch.

19. The adhesive composition according to claim 1, wherein the pH of said composition is within the range of pH 3-5.

20. The method according to claim 14, wherein at least one of said substrates is a paper or cardboard substrate.

Description

EXPERIMENTAL SECTION

(1) Methods: Brookfield viscosity The viscosity of the solution (25?1? C.) is determined with a digital Brookfield DV-I viscosimeter (mPa.Math.s) using the correct applicable spindle at 20 rpm during 15 seconds (or five revolutions) Dry solids 1.5 to 2.5 gram of adhesive is applied with a wire winded rod of 200 ?m on a predried glass fibre filter for an IR balance (material number: 6909640) and dried with IR of 80? C. to constant mass Refractive index The refractive index is determined with a Bellingham+Stanley RFM300+Refractometer. at 25?0.1? C. AdhesionSetting time The setting time of the adhesive is determined with a Fipago-Adhesion tester (PKL system) in a conditioned room (RH=50?2%, T=23?1? C.). A thin adhesive film (standard 60 ?m) of liquid adhesive (23?1? C.) is applied with a wire winded rod on the smooth side of a standard kraft paper stripe (Natural machine-glazed kraft paper (one smooth and shiny side, one matt side) Manufacterer: Sopal Doetinchem, The Netherlands; Gurley porosity: 72 s; PPS smoothness (smooth side): 3.42 ?m; Cobb 60: 24 g/m2; Grammage: 85 g/m2; Dennison wax test: 18; 30?200 mm). The open time is set on 0 s. The glued paper strip is placed on another piece of paper (kraftliner Pitea Royal Brown, Manufacterer: Kappa Smurfit, Sweden; Supplier: Fipago, The Netherlands (Fipago 2006 kraftline); Grammage: 200 g/m2; Cobb 1800: 86 g/m2; Dennison wax test: 18; 60?100 mm) by means of a metal pressure roller (standard 500 g). After the close time is exceeded (varied in the interval 0 . . . 20 seconds, but can be longer if fibre tear has not yet occurred) the two pieces of paper are separated from each other. Every adhesive is characterized by at least five different closed times, yielding a more or less sigmoid curve. This curve represents the work needed to overcome the bond strength as function of closed time. Results are given as work (cJ). The value for the setting time (s) is the time where the peel strength of 40 cJ is exceeded.
Preparation: HBS

(2) HBS was produced by jet cooking. A 17% dry solid potato starch slurry was jet cooked (149-153? C., 8 min residence time, pressure 4 bar). After cooling down to 70? C. and adjusting the pH to 6.1, 1000 units of branching enzyme (measured as the change in the absorbance of a iodine/iodide starch complex at 660 nm) were added per gram dry substance of starch. The branching enzyme used was the product NS28067 of Novozymes, a pilot plant product containing the branching enzyme of Rhodothermus obamensis.

(3) After 20 h of incubation, the enzyme was inactivated by lowering the pH to 2.5 with 4M HCl. After 35 min the pH was readjusted to 4.5. Then the solution was filtered over a filter with pore size of 2-4 micrometer, followed by ion-exchange (Aquadem E200, Kruger). Finally, the solution was dried by evaporation of the water first at 61? C. and then spray dried at 200? C. (temp out 82? C.). This yielded starch having a degree of branching of 10%.

(4) The activity of the branching enzyme is determined by monitoring changes in the iodine/iodide/amylose complex as a result of the branching enzyme activity. A substrate solution is prepared by adding 10 mg Amylose type III (Sigma) to 0.5 ml 2 M NaOH, subsequently adding 1 ml ultra pure water and then adjusting the pH by adding 0.5 ml 2 M HCl and 7.8 ml phosphate buffer (pH 7.2). An iodine/iodide stock solution is prepared by adding 0.26 g I2 and 2.6 g KI to 10 ml ultra pure water. To 100 microliter of this stock solution, 50 microliter 2 M HCl is added and 26 ml ultra pure water (stop reagent). The activity of the enzyme is determined by mixing 50 microliter of appropriately diluted enzyme to 50 microliter of amylose substrate solution and incubation this for 30 min at 60? C. Then, 2 ml of stop reagent is added and after mixing well the absorbance is measured at 660 nm (the absorbance should be between 0.15 and 0.3).

(5) The activity (U/mL) is calculated using the following formula:
U/ml=(ODreference?ODsample)?100%?dilution/(ODreference?ODblank)/30 min/0.05 ml HBS/clay adhesive

(6) HBS and clay were dry mixed in the appropriate weight ratio until homogenous. The resulting mixture was dissolved by adding the product in about 10 seconds (in a steady flow) to demineralised water (25?1? C.) in a plastic beaker (? 90 mm), while being stirred at 1000 rpm with a 3-propeller stirrer (? 60 mm) for 30 minutes.

Example 1: Influence Paper Type on Setting Speed of a HBS Adhesive and HBS/Clay Adhesive

(7) This example shows the influence of the paper type on the setting speed of a potato starch HBS adhesive and a potato starch HBS/clay adhesive. To rule out the possible effect of viscosity, both adhesives were tested at comparable viscosities.

(8) Potato Starch HBS/Clay Adhesive:

(9) 52.00 gram HBS

(10) 104.00 gram Speswhite (highly refined kaolin of ultrafine particle size from Imerys)

(11) 93.75 gram water

(12) Potato Starch HBS Adhesive:

(13) potato starch HBS is dissolved in a product to water ratio to result in a viscosity of 3000-3500 mPa.Math.s.

(14) The tested paper types are characterized by:

(15) TABLE-US-00001 Water absorbance Grammage [g/m.sup.2] Dennison Gurley Porosity Name [g/m.sup.2] Cobb30 Cobb60 Wax [Nr] [s/100 ml] Standard 85 24 18 72 PKL paper Reflex 70.7 15.1 20 142 Special Paper A 229.6 34.3 12 >1000* Paper B 72.3 13.4 20 461 Paper C 73.1 24.2 23 >1000* *too closed surface, could not be measured

(16) TABLE-US-00002 Experiment 1 2 Adhesive type HBS/Clay HBS Properties: Brookfield viscosity 3320 3250 [mPa .Math. s], 25? C., RVT, 20 rpm Directly after preparation Dry solids [%] 62.0 51.0 pH 4.2 4.2 Standard PKL paper Setting time [s] 8.5 10 Reflex Special Setting time [s] 9 19 Paper A Setting time [s] 12 17.5 Paper B Setting time [s] 12 15 Paper C Setting time [s] 11.5 17

(17) Example 1 shows that for the adhesive based solely on HBS the setting speed is strongly dependent on the type of paper adhered. In contrast, the setting speed of the HBS/clay adhesive is almost not influenced by the type of paper adhered. This demonstrates that clay is not only a filler but also a setting speed enhancer.

Example 2: Influence Amount of Clay on Adhesive Properties

(18) This example demonstrates the influence of the weight ratio HBS (potato starch):clay (Speswhite) on adhesive properties. The amount of water used for the preparation of the formulations was such that a viscosity of 2500-4500 mPa.Math.s was obtained.

(19) TABLE-US-00003 Experiment 3 4 1 5 6 7 8 9 10 Weight Ratio HBS:clay 1:0 1:0.5 1:1 1:2 1:3 1:4 1:5 1:6 1:10 Properties: Brookfield viscosity 3250 2730 3320 2700 3440 3310 2930 4300 4210 [mPa .Math. s], 25? C., RVT, 20 rpm Directly after preparation Dry solids [%] 51.0 57.5 62.0 60.2 62.6 62.1 61.3 63.0 61.9 pH 4.2 4.3 4.2 4.2 4.2 4.5 4.6 4.6 4.8 Standard PKL paper Setting time [s] 10 10 8.5 9.5 9.5 10 14 n.a.* n.a.* Reflex Special Setting time [s] 19 13 9 9 9.5 10 14 n.a.* n.a.* *The dried adhesive film has no internal strength; a force of 40 cJ is not reached

(20) Example 2 shows that the ratio of potato starch HBS:clay has an influence on the setting speed on different paper types. If the amount of clay is too low a difference in setting speed between the paper types is observed. On the other hand, if the amount of clay is too high the formulation acts like a coating and not as an adhesive, thus resulting in very poor internal strength. To obtain fast setting at various paper types the ratio of HBS:clay should be between 1:1 and 1:4

Example 3: Adhesive Properties of HBS with Various Types of Clay

(21) Recipe:

(22) 52.00 gram potato starch HBS

(23) 104.00 gram clay

(24) 93.75 gram water

(25) After preparation the products were, if applicable, diluted with water to a viscosity of 3000-5000 mPa.Math.s. Products with a viscosity below 2000 mPa.Math.s were prepared again with a lower amount of water to achieve a viscosity of 2700-3700 mPa.Math.s

(26) TABLE-US-00004 Experiment 11 1 12 13 14 15 16 Product B1 Speswhite Argirec Polwhite B KKA- KKA- HC B22 HB KA Type Clay Kaolin Kaolin Kaolin Kaolin Kaolin Clay D90 [?m] 1.0 3.0 4.5 8.6 10.1 22 102 Properties: Brookfield viscosity 27000 3320 14500 3500 3080 3530 2020 [mPa .Math. s], 25? C., RVT, 20 rpm Directly after preparation After diluting 4900 n.a. 3470 n.a. n.a. n.a. n.a. Dry solids [%] 55.9 62.0 58.3 63.1 66.8 65.6 62.4 pH 5.4 4.2 4.0 4.2 5.6 5.6 4.3 Standard PKL paper Setting time [s] 15 8.5 12 12 13 15 >45

(27) Example 3 shows that the D90 of the clay has an influence on the setting speed with an optimum at a D90 of around 3 ?m. In order to obtain a fast setting, the D90 of the clay is preferably in the range between 1 and 20 ?m.

Example 4: Adhesive Properties of HBS from Various Botanical Origins Combined with Clay

(28) Recipe:

(29) 52.00 gram HBS

(30) 104.00 gram Speswhite (highly refined kaolin of ultrafine particle size from Imerys)

(31) 93.75 gram water

(32) After preparation the products were, if applicable, diluted with water to a viscosity of 3000-5000 mPa.Math.s.

(33) TABLE-US-00005 Experiment 1 17 18 19 20 Botanical origin HBS Potato Waxy Tapioca Maize Waxy Potato Maize Properties: Brookfield viscosity 3320 1700 3000 49100 48500 [mPa .Math. s], 25? C., RVT, 20 rpm Directly after preparation After diluting n.a. n.a. n.a. 4050 4740 Dry solids [%] 62.0 61.6 61.3 40.6 40.6 pH 4.2 5.6 4.0 4.3 4.8 Standard PKL paper Setting time [s] 8.5 8.5 9.0 24.5 21.0 Experiment 21 22 23 24 Botanical origin HBS Wheat Pea Sago Mungbean Properties: Brookfield viscosity 49800 6840 1350 1520 [mPa .Math. s], 25? C., RVT, 20 rpm Directly after preparation After diluting 3800 3500 n.a. n.a. Dry solids [%] 42.1 60.3 61.5 62.2 pH 4.3 3.7 3.8 3.9 Standard PKL paper Setting time [s] 24.5 16.5 10.5 10.5

(34) Example 4 surprisingly shows that HBS combined with clay obtained from potato, waxy potato, tapioca, sago or mungbean starch results in a fast setting, shear thinning adhesive in the acidic pH range. In contrast, the use of maize, waxy maize or wheat HBS in combination with clay results in slow setting shear thinning adhesive. Pea HBS combined with clay shows borderline setting speed.

Example 5: Influence pH on Adhesive Properties of an Adhesive with a HBS:Clay Weight Ratio of 1:2

(35) In this example the impact of the pH on the wet tack and setting speed of an adhesive with HBS and clay (1:2 by weight) is shown for HBS originating from potato and waxy maize.

(36) Recipe:

(37) 52.00 gram HBS (from potato (P) or waxy maize (WM))

(38) 104.00 gram Speswhite

(39) 93.75 gram water

(40) After preparation the pH is brought to the desired level with either 6N HCl or 25% NaOH. The solutions were, if applicable, diluted with water to a viscosity of 3000-5000 mPa.Math.s.

(41) TABLE-US-00006 Experiment 25 26 27 28 29 30 31 32 33 Origin HBS.sup.1 P P P P P WM WM WM WM Properties: Brookfield viscosity 3410 3320 2730 3170 3120 4740 3300 2130 2230 [mPa .Math. s], 25? C., RVT, 20 rpm Dry solids [%] 56.0 62.0 62.0 60.1 61.5 40.6 59.7 62.7 62.2 pH 2.8 4.2 6.9 9.0 10.6 4.8 7.0 9.0 10.4 Standard PKL paper Setting time [s] 9 8.5 9.5 10 10 23.5 11 9 9.5 Paper C Setting time [s] 12.5 9.5 13 13.5 12.5 30 15 12 12.5 .sup.1P = Potato, WM = Waxy maize

(42) This experiment shows that at pH between 2.8 and 10.6 the adhesive based on potato HBS shows comparable setting speed at standard PKL paper. On Paper C the optimum pH is around 4. For the adhesive based on waxy maize HBS the pH needs to be at least 7, the optimum on both tested paper types is around 9. At pH 9 and higher, potato HBS and waxy maize HBS show comparable wet tack and setting times on both standard PKL paper and Paper C.

Example 6: Influence pH on Adhesive Properties of an Adhesive with a HBS:Clay Weight Ratio of 1:3

(43) In this example the impact of the pH on the wet tack and setting speed of an adhesive with HBS and clay (1:3 by weight) is shown for HBS originating from potato and waxy maize.

(44) Recipe:

(45) 50.0 gram HBS

(46) 150.0 gram Speswhite

(47) 110.0 gram water

(48) After preparation the pH was brought to the desired level with either 6N HCl or 25% NaOH. The solutions were, if applicable, diluted with water to a viscosity of 2200-4000 mPa.Math.s.

(49) TABLE-US-00007 Experiment 34 35 36 37 38 39 40 41 42 Origin HBS.sup.1 P P P P P WM WM WM WM Properties: Brookfield viscosity 3790 3440 2690 3340 3230 3470 2550 1500 2510 [mPa .Math. s], 25? C., RVT, 20 rpm Dry solids [%] 58.1 62.6 62.6 62.4 63.1 35.7 63.0 65.3 62.8 pH 3.1 4.2 7.0 8.8 10.2 4.9 7.0 9.1 10.2 Standard PKL paper Setting time [s] 11.0 9.5 10 9 8.5 50 10 9.5 10 Paper C Setting time [s] 12.5 10.5 13.5 12.5 12 >60 13.5 12 12.5 .sup.1P = Potato, WM = Waxy maize

(50) This experiment shows that at pH between 3.1 and 10.2 the adhesive based on potato HBS shows comparable setting speed at standard PKL paper. On Paper C the optimum pH is around 4.

(51) For the adhesive based on waxy maize HBS the pH needs to be at least 7, whereas the optimum on both tested paper types is around 9.

(52) At pH 7 and higher, potato HBS and waxy maize HBS show comparable wet tack and setting times on both standard PKL paper and Paper C.

Example 7: Influence Ratio HBS:Clay at about pH 10.5 on Adhesive Properties

(53) This example demonstrates the influence of the weight ratio potato starch HBS:clay at a pH of about 10.5 on adhesive properties. The amount of water used for the preparation of the formulations was such that a viscosity of 2200-4000 mPa.Math.s was obtained.

(54) TABLE-US-00008 Experiment 43 44 29 33 38 42 45 46 Ratio 1:1 1:1 1:2 1:2 1:3 1:3 1:4 1:4 HBS:Speswhite Origin HBS P WM P WM P WM P WM Properties: Brookfield viscosity 3290 2750 3120 2230 3230 2510 3510 2700 [mPa .Math. s], 25? C., RVT, 20 rpm Dry solids [%] 59.5 60.7 61.5 62.2 63.1 62.8 57.1 56.8 pH 10.0 10.5 10.6 10.4 10.2 10.2 10.4 10.7 Standard PKL paper Setting time [s] 11 10.5 10 9.5 8.5 10 11 11 Paper C Setting time [s] 13.5 12.5 12.5 12.5 12 12.5 14 15 .sup.1P = Potato, WM = Waxy maize

(55) This example shows that at a pH of about 10.5 HBS originating from potato and waxy maize show at each ratio comparable setting speed on both papers.