Cellulose platelet compositions, methods of preparing cellulose platelet compositions and products comprising same

Abstract

A composition and method of preparing a composition is presented wherein the composition comprises cellulose platelets and the cellulose platelets comprise at least 60% cellulose by dry weight, less than 10% pectin by dry weight and at least 5% hemicellulose by dry weight. The composition can be concentrated to at least 25% by weight solids content by pressing under low pressure, whilst retaining the ability to be re suspended within an aqueous medium. The resulting aqueous medium obtains the desired properties of the composition, such as increased viscosity or increased dispersion of pigment particles, for example, to the same extent as the composition before pressing.

Claims

1. A method of preparing a composition comprising cellulose platelets wherein the cellulose platelets comprise at least 60% cellulose by dry weight, less than 10% pectin by dry weight, and at least 5% hemicellulose by dry weight, said method comprising the steps of; providing a vegetable material pulp; treating the vegetable material pulp with at least 0.1 M alkaline metal hydroxide; heating the vegetable material pulp to a temperature less than 100° C. and homogenizing the vegetable material pulp at low shear; filtering, then reducing the water content of the resultant composition; and pressing the composition, while allowing the composition to expand laterally, to reduce the water content of the composition.

2. The method of claim 1, comprising pressing the composition, while allowing the composition to expand laterally, at a first pressure for a period of at least ten minutes; and then pressing the composition at a second, higher pressure.

3. The method of claim 1, wherein the water content of the composition is reduced by wicking.

4. The method of claim 1, wherein the first pressure the composition is pressed under is less than 2 kg/cm.sup.2.

5. The method of claim 1, wherein the cellulose platelets of the composition are generally planar and the pressure is sufficiently low that the platelets align themselves during pressing such that the direction of pressing is normal to the plane of the cellulose platelets.

6. The method of claim 1, wherein the alkaline metal hydroxide is sodium hydroxide.

7. The method of claim 1, wherein the vegetable material pulp is heated to at least 80° C.

8. The method of claim 1, wherein following the step of pressing, the composition is added to an aqueous medium and the cellulose platelets within the composition are rehydrated and uniformly suspended within the aqueous medium under low shear mixing.

Description

DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

(2) FIG. 1 is a flow diagram of the method of producing a composition of cellulose platelets;

(3) FIG. 2 is a side view of the step of pressing the composition to reduce the water content whilst allowing the composition to spread laterally (2b);

(4) FIG. 3 is a schematic diagram showing the cellulose platelets oriented randomly before pressing (3a) and that during pressing the cellulose platelets reorient themselves (3b);

(5) FIG. 4 is a scanned electron micrograph of the surface of multiple cellulose platelets; and

(6) FIG. 5 is a plot of viscosity versus sheer.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

(7) With reference to FIGS. 1 to 4, a composition of cellulose platelets according to the invention is produced in the following manner.

(8) Root vegetable waste, such as carrot or sugar beet from existing industrial processes, is processed to form a mixture having a concentration of between 0.1% and 10% solids content by weight (2) in water. 0.5M sodium hydroxide (NaOH) is added to the solution, raising and maintaining the pH of the solution at pH 14 (4). The addition of the NaOH extracts a significant proportion of hemicellulose and the majority of pectin from the cellulose of the cells within the mixture.

(9) The mixture is then heated to 90° C. for five hours and homogenised for periodically during the heating period for a total of one hour with a mixer blade rotating at a rate of 11 m/s (6), followed by homogenisation for a period of five minutes, at the end of the heating period, with a mixer blade rotating at a rate of 30 m/s (8). Homogenisation separates the cells along the line of the middle lamella, then breaks the separated cells into platelets. The resultant cellulose platelets are approximately 10 times smaller than the original separated cells.

(10) The resultant mixture is then filtered to remove the dissolved materials to a solids content of less than 8% by weight (10).

(11) Span 20 (“Span” is a registered trade mark of Croda International PLC, Goole UK), a dispersant, is then added to the mixture (12) and coats the surface of the cellulose platelets and prevents the cellulose platelets aggregating, allowing them to be more readily re-dispersed in aqueous media.

(12) The composition so-formed has a solids content by weight of around 4 to 8% and forms a thick paste. To reduce the water content further, it is necessary to press the composition (16).

(13) A small volume of the composition (18) is placed between two absorbent sheets (20) covering the interior surface of two spaced-apart metal plates (22). The absorbent sheets are able to remove water from the material by a wicking action as the material is compressed. The upper metal plate then exerts a low pressure onto the top surface of the material (24). The material is allowed to expand laterally (26) between the absorbent sheets as the pressure is applied to form a thin sheet of material approximately 2 mm or less thick. As the composition is compressed, water is wicked out by the absorbent sheets, thereby reducing the water content of the composition.

(14) This has been found to allow the cellulose platelets (28) within the material to be reoriented normal to the direction of the applied force within the composition (see FIG. 3b) and thereby preserving their shape and structure, reducing aggregation and thereby allowing the composition to be readily redispersed within aqueous media.

(15) The resulting sheets of material are then cut into suitable sized small pieces whilst ensuring that the material is not compressed, sheared or rolled during cutting otherwise the porosity of the platelets along with their flat shape can be compromised.

(16) Compositions made using the above method typically comprise up to 25 to 35% solids of cellulose platelets by weight.

(17) The surface of some multiple cellulose platelets made by the above method are shown in FIG. 4. In an example composition, the cellulose platelets are on average 50 μm in diameter and 0.25 μm thick. A 3% solids suspension in water of these cellulose platelets results in an aqueous medium exhibiting extreme shear-thinning behaviour characterised by very low power-law indexes of 0.067 to 0.107. The cellulose platelets comprise pores of up to 0.2 μm in diameter that allow water to enter into the interior of the cellulose platelets and results in the cellulose platelets swelling when fully hydrated. The cellulose platelets comprise 79% cellulose by dry weight, the remaining 21% predominantly comprising hemicellulose and a small amount (less than 5%) of pectin.

(18) Previous cellulose sections or fragments used as additives in the art typically have less than 0.5 H atoms available per glucose residue due to hydrogen bonds forming between OH groups from adjacent glucose residues, or glucose residues of opposing portions of the cellulose fragment/section. The resultant hydrogen bonds prevent the cellulose fragments/sections from being fully rehydrated after concentration.

(19) The glucose residues of the cellulose within the cellulose platelets have been found to have a high number of OH groups that may be available. The cellulose platelets atoms available in the above example composition is 1.5 H atoms available per glucose residue.

(20) Such high numbers of available OH groups allows the cellulose platelets to be highly hydrated and allows a high degree of functionalization, as desired.

(21) An example of use of the described composition will now be described.

(22) The composition may be used as an additive to a material or formulation to alter existing properties of the material or formulation, or to provide additional properties to them.

(23) For example, the composition may be added to a paint, such as a water based epoxy primer paint, to increase the rheology of the formulation. An example of such a formulation is given below.

(24) A red iron oxide anti-corrosive water-based epoxy primer is made by mixing two components (an epoxy resin and a curing agent). The first component, which contains the composition of the present invention, is made using the following method (quantities are given in the following table):

(25) The first part of the primer is made from an epoxy resin dispersion (Beckopox EP 2384w/57WA Epoxy Resin Dispersion, from Cytec Industries Inc. of New Jersey, USA) is initially well mixed with de-ionised water, pigment dispersant (Disperbyk 190 pigment dispersant, from BYK-Chemie of Wessel, Germany) and a defoaming agent (additol VXW-6393 defoamer, from Cytec Industries).

(26) Then pigments (RO-4097 red iron oxide and Halox SZP-391 anti-corrosive pigment, from Halox Pigments of Indiana, USA), and further additives (barium sulphate, from Gammaco, Inc. of Bangkok Thailand, 10ES wollastocoat treated wollastonite, from Nyco Minerals of New York, USA, Zeeosphere 400 ceramic microspheres, from Zeeosphere Ceramics of Los Angeles, USA, and 325 mesh water ground mica, from Zemex Minerals) are added and dispersed to a texture of 4 to 5 North Score on the higman grind gauge (equivalent to 38.1 to 50.8 μm).

(27) The formulation is then mixed well at 2200 rpm for approximately 30 minutes with further epoxy resin dispersion (of the same type as before), defoamer and the composition of the present invention.

(28) Further additives and de-ionised water are then added to the formulation (BYK 348 substrate wetting agent, from BYK-Chemie, and 10% Cotrol AMB ammonium benzoate, from Vertellus, Inc. of Indianapolis, USA).

(29) The second component is made by diluting an epoxy curing agent (Beckopox VEH 2188x/55WA Epoxy Curing Agent, from Cytec Industries) in deionised water.

(30) The first and second components are then mixed to allow the formulation to be applied to a substrate and cured to form a hardened material, suitable for protective coatings, for example.

(31) TABLE-US-00001 Imperial Metric weight volume weight volume Component (lbs) (G) (kg) (I) Part A Beckopox EP 2384w/57WA Epoxy 152.40 16.78 69.13 76.28 Resin Dispersion De-ionised water 52.70 6.33 23.90 28.78 Disperbyk 190 Pigment Dispersant 11.50 1.31 5.22 5.96 Additol VXW-6393 Defoamer 4.00 0.50 1.81 2.27 RO-4097 Red Iron Oxide 75.00 1.84 34.02 8.36 Halox SZP-391 Anti-Corrosive 50.00 2.14 22.68 9.73 Pigment Barium Sulphate 100.00 2.73 45.36 12.41 10ES Wollastocoat Treated 150.00 6.20 68.04 28.19 Wollastonite Zeeosphere 400 Ceramic 101.00 5.05 45.81 22.96 Microspheres 325 mesh Water Ground Mica 7.50 0.32 3.40 1.45 Beckopox EP 2384w/57WA Epoxy 286.20 31.52 129.82 143.29 Resin Dispersion Additol VXW-6393 Defoamer 4.00 0.52 1.81 2.36 Curran(R) thixC70 Rheology 2.50 0.27 1.13 1.23 Modifier De-Ionized Water 40.00 4.80 18.14 21.82 BYK 348 Substrate Wetting Agent 5.00 0.57 2.27 2.59 10% Cotrol AMB Ammonium Benzoate 40.00 4.70 18.14 21.37 Total 1081.80 85.58 490.70 389.05 Part B Beckopox VEH 2188w/55WA 160.8 17.87 72.94 81.24 Epoxy Curing Agent De-Ionised Water 27.7 3.33 12.56 15.14 De-Ionised Water 53 6.36 24.04 28.91 Reduction to 80 Krebs Units Total 241.5 27.56 109.54 125.29

(32) The dry fiber level of the composition of the present invention within the final formulation comprises only 0.047% and yet, with reference to FIG. 5, the resultant viscosity of the formulation with the composition of the invention is approximately a third greater than for a formulation without, at 10 rpm.

(33) A paint formulation with a higher loading of the cellulose platelets (greater than that given in the above example) has been made which gives the paint its required rheology while at the same time imparting improved hardness and increased crack resistance during drying of the paint.

(34) Further variations and modifications may be made within the scope of the invention herein disclosed.