POLYSACCHARIDE COATINGS FOR PAPER

Abstract

Coating compositions that can provide grease and oil resistant coating for substrates, especially paper and textile substrates, are disclosed. The coating compositions comprise water insoluble -(1,3.fwdarw.glucan) polymer and/or dextran polymer and optionally other additives.

Claims

1. A substrate wherein at least a portion of the substrate is coated with a continuous layer of a coating composition, wherein the coating composition comprises A) water insoluble -(1,3.fwdarw.glucan) polymer having 90% or greater -1,3-glycosidic linkages, less than 1% by weight of -1,3,6-glycosidic branch points and a number average degree of polymerization in the range of from 55 to 10,000 and/or B) dextran comprising: (i) 87-93% -1,6 glycosidic linkages; (ii) 0.1-1.2% -1,3-glycosidic linkages; (iii) 0.1-0.7% -1,4-glycosidic linkages; (iv) 7.7-8.6% -1,3,6-glycosidic linkages; and (v) 0.4-1.7% -1,2,6-glycosidic or -1,4,6-glycosidic linkages; wherein the weight-average molecular weight (Mw) of the dextran is about 50-200 million Daltons, the z-average radius of gyration of the dextran is about 200-280 nm. 20

2. The substrate of claim 1, wherein the water insoluble -(1,3.fwdarw.glucan) polymer comprises greater than or equal to 95% -1,3-glycosidic linkages.

3. The substrate of claim 1, wherein the coating composition further comprises one or more additives.

4. The substrate of claim 1, wherein the coating composition is essentially free from starch or hydroxyalkyl starch.

5. The substrate of claim 1, wherein the water insoluble -(1,3.fwdarw.glucan) polymer is a linear polymer having greater than or equal to 99% of -1,3-glucosydic linkages and less than 1% -1,3,6-branching points.

6. The substrate of claim 1, wherein the substrate resists grease and/or oil.

7. The substrate of claim 1, wherein the dried layer of water insoluble -(1,3.fwdarw.glucan) polymer forms a layer having a thickness in the range of from 0.1 micrometers to 50 micrometers.

8. The substrate of claim 1, wherein the substrate is a cellulose substrate, a polymer, paper, a textile, paperboard, cardboard, or corrugated board.

9. A method comprising: 1) providing an aqueous coating composition comprising A) water insoluble -(1,3.fwdarw.glucan) polymer having 90% or greater -1,3-glycosidic linkages, less than 1% by weight of -1,3,6-glycosidic branch points and a number average degree of polymerization in the range of from 55 to 10,000 in aqueous alkali metal hydroxide and/or B) dextran in water wherein the dextran comprises: (i) 87-93% -1,6 glycosidic linkages; (ii) 0.1-1.2% -1,3-glycosidic linkages; (iii) 0.1-0.7% -1,4-glycosidic linkages; (iv) 7.7-8.6% -1,3,6-glycosidic linkages; and (v) 0.4-1.7% -1,2,6-glycosidic or -1,4,6-glycosidic linkages; wherein the weight-average molecular weight (Mw) of the dextran is about 50-200 million Daltons, the z-average radius of gyration of the dextran is about 200-280 nm; and 2) applying a layer of the aqueous coating composition to at least a portion of a substrate; and 3) removing at least a portion of the water from the applied layer; wherein the dried layer of coating composition forms a continuous layer on the substrate.

10. The method of claim 9, wherein the method further comprises washing the applied layer with water prior to or after step 3) removing at least a portion of the water.

11. The method of claim 9, wherein the method further comprises washing the applied layer with an aqueous acid prior to or after step 3) removing at least a portion of the water.

12. The method of claim 9, wherein the dried layer has a thickness in the range of from 0.1 micrometers to 50 micrometers.

13. The method of claim 9, wherein the removal of water step is performed by evaporation, heating or a combination thereof.

14. The substrate of claim 1, wherein the dextran comprises: (i) about 89.5-90.5 wt % glucose linked at positions 1 and 6; (ii) about 0.4-0.9 wt % glucose linked at positions 1 and 3; (iii) about 0.3-0.5 wt % glucose linked at positions 1 and 4; (iv) about 8.0-8.3 wt % glucose linked at positions 1, 3 and 6; and (v) about 0.7-1.4 wt % glucose linked at: (a) positions 1, 2 and 6, or (b) positions 1, 4 and 6.

15. The substrate of claim 1, wherein the dextran comprises chains linked together within a branching structure, wherein said chains are similar in length and comprise substantially alpha-1,6-glycosidic linkages.

16. The substrate of claim 15, wherein the average length of the chains is about 10-50 monomeric units.

17. The substrate of claim 1, wherein the weight average molecular weight of the dextran is 80-120 million Daltons.

18. The substrate of claim 1, wherein the z-average radius of gyration of the dextran is 230-250 nm.

Description

EXAMPLES

[0158] Unless otherwise stated, all ingredients are available from Sigma-Aldrich, St, Louis, Mo.

[0159] PENFORD Gum 270 starch is available from Ingredion, Inc., Westchester, Ill.

[0160] The water insoluble -(1,3.fwdarw.glucan) polymer was produced according to a method of U.S. Pat. No. 8,871,474. The polymer had a number average degree of polymerization of about 300 and >98% -1,3 glycosidic linkages.

[0161] Preparation of Coating Composition #1

[0162] 14.99 grams of glucan polymer #1 was mixed with 40.01 grams of water and stirred using a rotor stator until a homogeneous dispersion was obtained. 5.02 grams of 40% sodium hydroxide solution was then added to the dispersion and the stirring was continued until a solution formed.

[0163] Preparation of Comparative Coating Composition A

[0164] PENFORD gum 270 19.98 grams was mixed with 80.04 grams of water and stirred until a uniform slurry formed. The mixture was heated while mixing until the mixture thickened. The heat source was removed and the mixture was stirred by hand until it was cool enough to coat onto the substrate.

[0165] Grease and Oil Resistance Tests

[0166] All testing was performed using the Technical Association of the Pulp and Paper Industry (TAPPI) Test Method T-559.

[0167] Coating compositions were applied to food wrapper grade paper using a Myer bar with the gap set at 0.127 millimeter (mm) or 0.203 mm. The coated papers were then dried in a convection oven. When tested using the TAPPI test, Comparative Coating Composition A failed test #1 while Coating Composition #1 passed tests #1 and #5.

[0168] Preparation of Coating Composition #2

[0169] A 12% by weight solution of the water insoluble -(1,3.fwdarw.glucan) polymer in 4.5% by weight solution of aqueous NaOH was produced by stirring until a solution formed.

[0170] NK-40 type unbleached Kraft paper was used as the substrate.

[0171] Following procedures common in the paper industry, the glucan solution was hand coated onto NK-40 type unbleached kraft paper substrate. The weight difference between the freshly coated paper and the uncoated paper multiplied by the % solids (in this case 16.5%) and divided by the area of the coated paper to provide a measure of the coating weight. Coatings were done using a 0, a 10 and a 20 Mayer rod for the hand coating of the paper. The coatings were done in triplicate.

[0172] The average and relative standard error of the coating weight is shown in Table 1 below. The coated paper was dried at 105 C. for 5 min. The paper was then allowed to stand at room temperature for at least 24 hours.

TABLE-US-00001 TABLE 1 Gurley porosity (seconds/100 Average Relative ml of air to coat standard TAPPI pass through Rod weight error (3 Kit the coated Sheffield number (g/m.sup.2) replicates) value paper) roughness Control 0 0 0 11 +/ 0.3 407 +/ 0.7 0 4.2 4.7% 2 2464 +/ 1330 372 +/ 9 10 5.7 1.4% 3 3320 +/ 893 377 +/ 10 20 7.7 3.5% 5 Out of range >21000

[0173] The grease resistance was measured using the standard kit type test (TAPPI T559 standard). The Glucan coating imparted a dramatic improvement in the grease resistance of the Kraft paper for all coating weights. The Gurley porosity and Sheffield roughness of the coated paper was measured using a PROFILE Plus Roughness and Porosity tester manufactured by the Technidyne Corporation, New Albany, Ind., following TAPPI T-460 and TAPPI T536-88 standards. The results of these measurements are also shown in the table above. The porosity of the coated paper dropped dramatically as indicated by the higher Gurley numbers. At the highest coating weight the Gurley porosity value was too high to accurately measure. The coating imparted a smoother surface to the paper as indicated by the Sheffield roughness parameter.

[0174] Preparation of Dextran Polymer

Expression of a Glucosyltransferase (0768) in E. coli and Production of Active Crude Enzyme Lysate

[0175] This Example describes expression of a mature glucosyltransferase (gtf) enzyme in E. coll. Crude cell lysate of an E. coli expression strain was produced and showed gel product-forming activity in the presence of sucrose,

[0176] A putative YG repeat-containing hydrolase (categorized in GENBANK under GI number 339480768, but now having GI number 497964659) with 1484 amino acids was identified from Leuconostoc pseudomesenteroides strain KCTC3652 by whole genome shotgun sequencing. This putative glucosyltransferase (designated herein as gtf 0768) belongs to the GH70 family of glycosyl hydrolases containing a glucan-binding domain. The N-terminal 37 amino acid segment of gtf 0768 was deduced as the signal peptide of the enzyme by the SIGNALP 4.0 program (Petersen et al., Nature Methods 8:785-786).

[0177] To construct a plasmid for bacterial expression of gtf 0768, a DNA sequence encoding a mature form of the gtf without the signal peptide was synthesized by GenScript USA Inc. (Piscataway, N.J.). The synthesized sequence was subcloned into the Nhel and Hindlll sites of the pET23D+vector (NOVAGEN; Merck KGaA, Darmstadt, Germany). The 0768 gtf (SEQ ID NO:2) encoded by this construct included a start methionine and 3 additional amino acids (Ala-Ser-Ala) at the N-terminus, and 6 histidine residues at the C-terminus, compared to the wild type mature (predicted) form of gtf 0768. The plasmid construct was sequence-confirmed and transformed into E. coli BL21 DE3 host cells with ampicillin selection, resulting in expression strain EC0052.

[0178] Cells of EC0052 and a control strain containing only empty pET23D+ vector were grown in LB medium with 100 g/mL ampicillin to OD.sub.6000.5, and then induced with 1 mM IPTG at 37 C. for 3 hours or alternatively induced at 23 C. overnight. Following this induction period, cells were collected by centrifugation at 4000g for 10 min and resuspended in PBS buffer pH 6.8. The cells were then lysed by passing through a French Press at 14,000 psi (96.53 MPa) twice, after which cell debris was pelleted by centrifugation at 15,000g for 20 min. The supernatants of each crude cell lysate were aliquoted and frozen at 80 C.

[0179] The activity of crude cell lysate from EC0052 cells was checked by reaction with sucrose. A control reaction was set up similarly using cell lysate prepared from cells containing the empty vector. Each sucrose reaction was set up using 10% (v/v) of cell lysate with 100 g/L sucrose, 10 mM sodium citrate pH 5, and 1 mM CaCl.sub.2. After incubation of the reactions at 37 C. for a few hours, a gel-like product, believed to be a dextran, was formed in the tube in which EC0052 cell lysate had been added. No gel-like product was formed in the control reaction. HPLC analysis confirmed that sucrose was consumed in the reaction containing EC0052 cell lysate, and not in the control reaction, This result suggested that the EC0052 crude cell lysate expressed active gtf 0768 enzyme, and that this gtf produced a dextran product having high viscosity.

[0180] Preparation of Dextran Polymer #1

[0181] A 12 liter reaction was prepared containing 20 mM sodium phosphate buffer (buffer was diluted 50-fold with ddH2O from 1 M stock, pH 6.5), 100 g/L sucrose, and 25 units (2 milliliters/liter) of the gtf 0768 enzyme solution, produced above. The reaction was shaken at 100 rpm in an incubator shaker (lnnova, Model 4000) at 25 C. for 27 hours.

[0182] The gtf enzyme was deactivated by heating the reaction at 85 C. for 10 minutes. The deactivated viscous reaction was then mixed with methanol to precipitate the viscous product. A white precipitate was formed. After carefully decanting the supernatant, the white precipitate was washed twice with methanol. The solid product was dried at 45 C. under vacuum in an oven for 48 hours.

[0183] Samples (1 mL) of the reaction were taken at 0. 0,5, 1, 2, and 24 hours, respectively. The gtf enzyme was deactivated in each sample by heating at 80 C. for 10 minutes. Each sample was then diluted 10-fold with sterile water. 500 L of diluted sample was transferred into a centrifuge tube filter (SPIN-X, 0.45-m Nylon, 2.0 mL Polypropylene Tube, Costar # 8170) and centrifuged at 12,000 rpm in a table centrifuge for 60 minutes, after which 200 L of flowthrough was used for HPLC analysis to measure sucrose consumption during the reaction, The following HPLC conditions were applied for analyzing each sample: column (AMINEX HPX-87C carbohydrate column, 3007.8 mm, Bio-Rad, No. 125-0095), eluent (water), flow rate (0.6 mL/min), temperature (85 C.), refractive index detector. HPLC analysis of the samples indicated substantial sucrose consumption during the 0768 gtf reaction.

[0184] HPLC was also used to analyze other products of the reaction. Polymer yield was back-calculated by subtracting the amount of all other saccharides left in the reaction from the amount of the starting sucrose. The back-calculated number was consistent with the viscous product dry weight analysis. Sucrose, leucrose, glucose and fructose were quantified by HPLC with an HPX-87C column (HPLC conditions as described above). DP2-7 oligosaccharides were quantified by HPLC with the following conditions: column (AMINEX HPX-42A carbohydrate column, 3007.8 mm, Bio-Rad, No. 125-0097), eluent (water), flow rate (0.6 mL/min), temperature (85 C.), refractive index detector. These HPLC analyses indicated that the glucosyl-containing saccharide products of the 0768 gtf reaction consisted of 92.3% polymer product, 1.3% glucose, 5.0% leucrose, and 1.4% DP2-7 oligosaccharides.

[0185] A sample of dry dextran powder product (0.2 g) of the above reaction was used for molecular weight analysis. Molecular weight was determined by a flow injection chromatographic method using an ALLIANCE 2695 separation module from Waters Corporation (Milford, Mass.) coupled with three online detectors: a differential refractometer 2414 from Waters, a HELEOS-2 18-angle multiangle light scattering (MALS) photometer with quasielastic light scattering (QELS) detector from Wyatt Technologies (Santa Barbara, Calif.), and a VISCO START differential capillary viscometer from Wyatt. The dry dextran powder was dissolved at 0.5 mg/mL in aqueous Tris (Tris[hydroxymethyl]aminomethane) buffer (0.075 M) containing 200 ppm NaN3. The dissolution of dextran was achieved by shaking overnight at 50 C. Two AQUAGEL-OH GUARD columns from Agilent Technologies (Santa Clara, Calif.) were used to separate the dextran polymer peak from the injection peak. The mobile base for this procedure was the same as the dextran solvent, the flow rate was 0.2 mL/min, the injection volume was 0.1 mL, and the column temperature was 30 C. EMPOWER version 3 software from Waters was used for data acquisition, and ASTRA version 6 software from Wyatt was used for multidetector data reduction. It was determined that the dextran polymer product had a weight-average molecular weight (Mw) of 78.610.sup.6 g/mol (i.e., roughly 78 million Daltons) (from MALS analysis), a z-average radius of gyration of 213 nm (from MALS analysis), and a z-average hydrodynamic radius of 187 nm (from QELS analysis).

[0186] Paper Coating Comprising Dextran Polymer #1

[0187] 12 and 15 percent by weight aqueous solutions of dextran polymer #1 were prepared using deionized water. The mixtures were stirred until a solution formed. The aqueous coating composition was coated onto NK-40 type unbleached Kraft paper using a one or more Mayer rods. The coated paper was dried for 5 minutes at 105 C. and was then allowed to stand at room temperature overnight. The average coating weight for three replications was 6.4 grams/meter' with a relative standard error of 2.5%.

TABLE-US-00002 TABLE 2 Avg Coating Mayer weight Gurley Sheffield % dextran Rod (g/m.sup.2) Kit Value Porosity Roughness 0 (control) 0 0 11 0.3 407 0.7 12 0 3.4 <1 1539 229 380 11 12 10 5.1 3-4 10791 383 6 5844 12 20 6.7 7-8 >21000 na 15 20 8.1 10-11 na na na means data not measured.

[0188] The grease resistance was measured using the standard kit type test (TAPPI T559 standard), with three replications per test. Using the above dextran coated paper and the same type of paper with no coating as a control. The control paper failed at kit value 0, while the dextran coated paper failed at up to kits 3-4, 7-8 or 10-11, depending on the coating thickness, indicating a much improved resistance to grease compared to the untreated control. The Gurley porosity measures the amounts of seconds it takes for 100 milliliters of air to pass through the coated paper. Both Gurley porosity and Sheffield roughness of the coated paper was measured using a PROFILE Plus Roughness and Porosity tester manufactured by Technidyne following TAPPI T-460 and TAPPI T536-88 standards.

[0189] Several polysaccharides, including chemically modified ones, were used to assess the grease barrier properties of coating compositions comprising the polysaccharides on paper. All coating compositions were water based. Each coating composition was prepared with the desired solid concentration shown in Table 3. The polymer solutions were directly dissolved into water with mixing, as described below.

[0190] Preparation of Coating Composition #3

[0191] This coating composition comprised Dextran Polymer #2. Dextran was prepared as disclosed in US Patent Application Publication 2016/0122445 A1. A 10 percent by weight aqueous solution of dextran polymer #2 was prepared.

[0192] Preparation of Comparative Coating Composition B

[0193] A comparative coating composition containing 10 percent by weight of polyvinyl alcohol (Elvanol 80-18) in water was prepared. This comparative composition did not contain polysaccharide.

[0194] Preparation of Coating Composition #4

[0195] This coating composition comprised 75% polyvinyl alcohol and 25% -(1,3.fwdarw.glucan) polymer. The glucan polymer was dispersed in a PVOH solution so that the final composition had 75 parts by weight of PVOH and 25 parts by weight of glucan. The polyvinyl alcohol (PVOH) was heated to 70-90 C. to solubilize it,

[0196] Preparation of Coating Composition #5

[0197] This coating composition comprised quaternary ammonium poly alpha-1,3-glucan, specifically trimethylammonium hydroxypropyl poly alpha-1,3-glucan. Quaternary ammonium poly alpha-1,3-glucans and their preparation are described in published patent application WO 2015/195960. 10 g of poly alpha-1,3-glucan (M.sub.w [weight-average molecular weight]=168,000) was added to 100 mL of isopropanol in a 500-mL capacity round bottom flask fitted with a thermocouple for temperature monitoring and a condenser connected to a recirculating bath, and a magnetic stir bar. 30 mL of sodium hydroxide (17.5% solution) was added dropwise to this preparation, which was then heated to 25 C. on a hotplate. The preparation was stirred for 1 hour before the temperature was increased to 55 C. 3-chloro-2-hydroxypropyl-trimethylammonium chloride (31.25 g) was then added to provide a reaction, which was held at 55 C. for 1.5 hours before being neutralized with 90% acetic acid. The solid thus formed (trimethylammonium hydroxypropyl poly alpha-1,3-glucan) was collected by vacuum filtration and washed with ethanol (95%) four times, dried under vacuum at 20-25 C., and analyzed by NMR and SEC to determine molecular weight and DoS. The DoS was 0.8.

[0198] Each of the above coating compositions were hand-coated onto 175 or 176 g/m.sup.2 Kraft Cardstock (Recollections, 651b/176 gsm) substrate using a Mayer Rod. The uncoated cardstock is referred to as base paper in the Table below and in the following description of the coating procedure. The base paper to be used for hand drawdown coating was placed on a smooth surface and the edge taped to secure it to the surface. The desired coating rod (bar) on the top of the base paper, 3-5 cm to the top and the coating solution (2-5 ml) is applied evenly below the coating rod (bar) in a line. Two hands held each side of the rod (bar) and the rod was drawn down from the top to the end of the paper with a constant steady speed, applying evenly pressure on both sides. The rod should not be rotated during the drawdown process. The wet coated paper was placed on a flat surface with weight or tape on the edges to avoid curling while drying. To accelerate drying, a fan/hot gun can be used to dry the surface.

[0199] The coated substrates were dried for 5 minutes at 105 C. Coating weight was determined by the difference in mass between uncoated and coated paper, normalized by the area,

[0200] The grease barrier properties of the coating compositions were evaluated using the standard KIT type test following TAPPI T559 cm-02 test. The values are from 1 to 12 (1 being the poorest performance and 12 being the best), Results are presented in Table 3.

[0201] PVOH is known to have excellent grease barrier properties and many of the polysaccharide-based coating compositions showed comparable grease barrier performance at similar coating weights (see table below for details).

TABLE-US-00003 TABLE 3 Coating Base Coating Cal'd * Coating Grease Coating Solid Paper Thickness Coating Weight Weight Barrier Kit Composition (wt %) (GSM) (micron) (GSM) (GSM) (unfolded) .sup.# Base paper 0 175 0.0 0.0 0.0 0.0 #3 10 175 13.7 1.4 2.2 7.0 #3 10 175 45.7 4.6 3.6 8.5 #3 10 175 80.0 8.0 11.3 10.7 Comparative B 10 175 13.7 1.4 5.2 11.5 Comparative B 10 175 45.7 4.6 6.7 11.5 Comparative B 10 175 80.0 8.0 17.3 12.0 #4 10 176 13.7 1.4 1.4 9.8 #4 10 176 45.7 4.6 3.9 10.5 #4 10 176 80.0 8.0 13.3 12.0 #5 10 176 13.7 1.4 1.9 8.0 #5 10 176 45.7 4.6 4.6 10.8 #5 10 176 80.0 8.0 8.5 12.0 Notes: * Cal'd means calculated .sup.# The values are averages of four measurements

[0202] Barrier against mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbon (MOAN) are becoming increasingly important as the use of recycled paper (with increasing amounts of ink contamination) is increasing. Thus, barrier coatings are required to avoid migration of mineral oil, particularly in papers used for food packaging. The lower the MOSH and MOAH values the better the coating performance.

[0203] Three coating compositions were evaluated for MOSH and MOAH barrier protection. The coating compositions were as described herein above. Coating weights and results are reported in Table 4.

[0204] The MOSH and MOAH (10 day, 40 C.) barrier analysis was carried out according to the method detailed in Barriers Against the Migration from Recycled Paper Board into Food: Measuring Efficiency by Surrogate Components (Biedermann-Brem and Krob, Pack Techno. Sci, February/2014). A paper (donor) is spiked with mineral oil (Gravex 913) and the testing barrier are placed in a migration cell. Tenax (receptor) is used as an absorbent for the migrated mineral oil (no direct contact with the sample). The tightly capped migration cells were stored at 40 C. for 10 days. Following this, the Tenax was extracted with an organic solvent and the extract was measured with online-HPLC-GC-FID on mineral oil. In addition to duplicates of every sample, a positive control (instead of the permeable paper) and a negative control (aluminum foil used as a barrier) were also run. All coated substrate samples had dimensions of 10 cm10 cm.

[0205] The MOSH and MOAH results in Table 4 show that coating compositions containing water soluble cationic glucan as in Coating Composition #5 show exceptional barrier performance, comparable to that of PVOH.

TABLE-US-00004 TABLE 4 Spiked Coating amount on Coating weight the paper MOSH (ug MOAH (ug Composition (g/m.sup.2) (donor) absolute) absolute) Blank 0 610 ug 670 225 ~1000 mg/kg 650 225 #3 12 610 ug 560 175 ~1000 mg/kg 570 185 Comparative 13 610 ug 3.7 <2 B ~1000 mg/kg 4.9 <2 #5 12 610 ug 14 3 ~1000 mg/kg 13 3