Method for production and use of nanocellulose and its precursors

Abstract

Objective of the method is a procedure for production of nanocellulose, where energy consumption and other costs of production are lower than in methods presented previously. It is based on separation of minute particles from cellulose or plant based ingredients by effects of light, thermal energy or water-soluble organic solvents. These particles act as precursors of nanocellulose. After separation they form in dry state aerosol, in liquid media a suspension, and combine to chains, microfibrils and secondarily formed fibrils, which form further networks with each other or with other fibers and fibrils. Applications are based on their action as reinforcing structure in composites, paper, cardboard, paints and other materials, on forming thin-layer films for electrical, electronic and medical applications, or on viscosity, surface and permeability properties.

Claims

1. A method for production of nanocellulose, its precursors and concentrates, characterized by, that nanometer-sized particles are separated from fibrils of cellulosic material which is in dry or air-dry state, in organic solvents or in other hydrophobic liquid media, by removal of water by means of light, controlled heating or by water-soluble organic solvent.

2. A method according to claim 1, characterized by, that heat treatment is performed at temperatures not exceeding 180 C.

3. A method according to claim 1, characterized by, that heating is performed by feeding heat producing electromagnetic energy.

4. A method according to claim 1, characterized by, that the material to be treated consists of parts or constituents of non-woody plants.

5. A method according to claim 1, characterized by, that the material to be treated is recirculated cellulosic fibre or cellulosic material containing it.

6. A method according to claim 1, characterized by, that the cellulosic material is pretreated with hemicellulose or pectin decomposing enzymes.

7. A method according to claim 1, characterized by, that nanometre-scaled particles are separated in dry state as aerosol, and in a liquid medium as a suspension.

8. A method according to claim 1, characterized by, that nanometer-scaled particles are combined to each other forming chains, elementary fibrils, microfibrils, secondarily formed fibrils and networks of these.

9. A method according to claim 8, characterized by, that microfibrils, secondary fibrils or their network crosslink cellulosic fibres or fibrils.

10. A method according to claim 7, characterized by, that separation of nano-scaled particles and subsequent stages are performed in dry or air-dry cellulose material.

11. A method according to claim 7, characterized by, that separation of nano-scaled particles from cellulosic material and subsequent stages are performed when it is suspended in a hydrophobic liquid medium.

12. A method according to claim 11, characterized by, that the hydrophobic liquid medium consists of ingredients of composite or paint materials.

13. A method according claim 12, characterized by, that nano-scaled particles are bound with a binding material without any separating crack or crevice.

14. A method according to claim 9, characterized by, that it causes development of microfibril network improving mechanical and surface properties of paper.

15. A method according to claim 1, characterized by, that nanocellulose or its precursors are produced in a dressing material for treating wounds or burns and are emitted to the wound or burn surface from this material as such or after activatiation by light, controlled heating or water-soluble organic solvent.

Description

EXAMPLES

Example 1

Enriching Nanocellulose and Precursors

(1) 8.8 g of paper produced from oat straw cellulose prepared according to U.S. Pat. No. 8,956,522 (Cerefi Ltd, 18 Apr. 2006) was pulped in 400 ml of demineralized water. 100 mg of citric acid was added for complexing potentially remaining divalent cations, whereby pH was lowered to 5.5. 0.5 ml of pectinase enzyme (Biotouch PL 300, AB Enzymes, Rajamki, Finland) was added. The mixture was incubated at 50 C. for 90 minutes, and homogenized with a blade mixer. Subsequently the mixture was subjected to two freezing-thawing cycles to disintegrate the cellular structure. 1 ml of household tenside mixture (Nopa A/S, Denmark) was added, the mixture foamed by stirring, and dried in microwave oven by 700 W effect in six subsequent 30 sec periods. In the enriched product, clusters of visible precursors were microscopically discernible. The product, as such or omitting some of the steps given, as sheets or ground, can be used as an ingredient or intermediate, to be activated to nanocellulose or microfibrils within the product of an application, by energy sources or solvents given in the description.

Example 2

Microfibril Thin Layers on Solid Surfaces

(2) A sample of the enriched nanoprecursor preparation according to Example 1 was illuminated with microscope lamp of 100 W, the light was focused to an area of 7 mm.sup.2 After ca 30 seconds, disintegration producing aerosol started emitting nano-scaled particles. Flow of aerosol was directed to a glass plate placed 2 or 3 mm above the illuminated material. Thin film developed on the glass plate 3 mm above the illuminated cellulose sample had a homogenous and oriented network of microfibrils and was substantially free from solid fragments of the starting material, whereas such fragments were occasionally found on the glass plate 2 mm above the sample. Covering the glass plate with polyethene foil resulted collection of a similar network on this flexible material. This principle can be scaled up to larger batch or continuous productions for purposes of electrical and electronic industries and for production of medical devices.

Example 3

Effect on Mechanical and Surface Properties of Paper

(3) From oat fibre cellulose prepared according to U.S. Pat. No. 8,956,502, paper sheets of 35 g/m.sup.2 were prepared. When treated, they were in equilibrium with 38% air humidity. Test sheets were subjected to ultraviolet light (Omnilux R 80 75 W, omnilux-lamps.com), infrared light (Sylvania Infra-red 100 W, havells-sylvania.com) or microwave (700 W) irradiation, or immersion in 100% ethanol. Each treatment lasted for 60 seconds. Energy transferred at ultraviolet light or microwave treatments corresponded to 1.57 kWh/kg, and in infrared light treatment 2.09 kWh/kg of the paper. Under these conditions, treatments other than ultraviolet light resulted a similar development of microfibril network, crosslinking cellulosic fibres and fibrils of the paper. The effect of ethanol was the most rapid. After microwave treatment, elastic modulus of the paper, equilibrated to 50% air humidity, was measured. After one hour from treatment, no significant change from the starting value was observed. During 24 hours from the treatment, the elastic modulus elevated from initial value of 2.24 GPa to 15.34 GPa. With ultraviolet light, a thick aerosol was developed on and above the glossy surface adjacent to the light source, and was sedimenting slowly. After ultraviolet light treatment, no change in elastic modulus was found in 10 days. The difference has most probably been due to concentrating the effect on the surface, due to the lower penetration of the ultraviolet light, and by absence of any thermal effect, which with the other treatments had effected removal of residual moisture and consequently higher release of nano-scaled particles. The treatments effected a more dense fibrillar network, and a more smooth surface.

Example 4

Effect on Mechanical Properties of a Composite

(4) From oat cellulose prepared according to U.S. Pat. No. 8,956,502, paper sheets of 102 g/m.sup.2 were prepared and wet laminated in four layers in a vacuum sack equipment with Ashland Envirez polyester. Weight percentage of cellulose in the composite was 65%, curing time 12 hours at 80 C. Thickness of the resulting composite sheet was 1.1 mm. Flexural strength of the composite was 102 MPa, and flexural modulus 5.1 GPa. Corresponding values for polycondensed resin without fibre were 33.8 MPa and 3.0 GPa, respectively. Microscopic evaluation indicated that a part of the cellulosic material was converted to microfibrils and secondary fibrils during curing.

Example 5

Preparations for Burn and Wound Healing

(5) Oat straw paper was prepared as described in U.S. Pat. No. 8,956,522, foam dried as described in Example 1, and activated by heating at 130 C. for 90 minutes. The product was tested for healing a bum wound of 70 mm in length, 5 mm broad, and 0.5 to 2 mm deep in an arm of a male patient. The product was placed on the wound when it started to exude liquid, and was removed after 12 hours. 24 days after the injury, microscopic study of surface samples of the healed skin revealed microfibrils mixed in the healed tissue indicating that aerosol from the product had integrated in it and supported the growth of the healing tissue. Within 6 months from the injury, no scar was formed, and also the surface pattern of the skin on the site of injury was similar to the skin nearby.