COMPOSITE MATERIALS

Abstract

The invention relates to a composite material comprising cellulose. The composite material comprises a first cellulose-based material, which may be a textile or fabric, and a second cellulose-based material, which may be a film or cellulose based material or powdered cellulose-based material. The second cellulose-based material may be a sheet material comprising cellulose, such as a paper or a regenerated cellulose film. In embodiments the material is a so called “all cellulose composite” where both of the materials that are brought together are different forms of material comprising or being cellulose. For example, the different materials originate from cellulose-based feedstocks. The invention also relates to a process for preparing the composite materials of the invention utilising ionic liquids.

Claims

1. A composite material, wherein the composite material is formed of a first cellulose-based material and a second cellulose-based material, wherein the first cellulose-based material and the second cellulose material are alternately layered with one another such that there are at least two layers of either the first or second cellulose-based material and at least one layer of the other cellulose-based material.

2. A composite material of claim 1, wherein the first cellulose-based material is a textile.

3. A composite material of claim 1 or claim 2, wherein the second cellulose-based material is a cellulose-based sheet, film or powder.

4. A composite material of any preceding claim, wherein the composite material further comprises an alloy region.

5. A composite material of any preceding claim, wherein the composite material has from 3 to 100 layers in total of the first cellulose-based material and the second cellulose-based material.

6. A composite material of any preceding claim, wherein the composite material comprises cellulose and the cellulose comprises: from about 40% to about 60% cellulose type 1; from about 25% to about 38% amorphous cellulose; and from about 2% to about 45% regenerated cellulose and/or cellulose II.

7. A composite material of any preceding claim, wherein the composite material has a peel strength of at least 50 N/m.

8. A composite material of any preceding claim, wherein the first cellulose-based material is selected from: cotton, flax, jute, hemp, ramie, sisal, bamboo, rayon, Tencel, Ioncell, and lyocell.

9. A composite material of any preceding claim, wherein the second cellulose-based material is selected from: cellulose powder, wood powder, filter paper and a regenerated cellulose film.

10. A cellulose-based composite material with a peel strength of from 50 N/m to 750 N/m.

11. A process for the preparation of a composite material, wherein the process comprises: a) providing a layered article comprising at least three layers, wherein the at least three layers are alternating layers of a first cellulose-based material layer and a second cellulose-based material layer; b) applying a solvent to the layered article; c) regenerating the layered article to form a composite material.

12. The process of claim 11, wherein the solvent is an aqueous solvent, an organic solvent or an ionic solvent.

13. The process of claim 12, wherein the solvent is an ionic solvent and is optionally selected from: N-Methylmorpholine N-oxide (NMMO); dimethyl sulfoxide (DMSO); dimethylformamide (DMF); N,N-dimethylacetamide; N,N-dimethylacetamide-lithium chloride; aqueous solution of NaOH; aqueous solution of NaOH-urea; poly(ethylene glycol) (PEG); poly(ethylene glycol) (PEG) and NaOH, aqueous zinc chloride; inorganic molten salt hydrates; ammonia/ammonium thiocyanate (NH3/NH4SCN); ethylene diamine (EDA)/KSCN; 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium dicyanoamide, 1-allyl-3-methylimidazolium chloride, and 1-hexyl-3-methylimidazolium chloride.

14. The process of any one of claims 11 to 13, wherein the solvent is applied in a weight ratio of cellulosic material:solvent of from 1:0.5 to 1:10.

15. The process of any one of claims 11 to 14, wherein the process further comprises the step of exposing the layered article to a pressure of up to 100 MPa.

16. The process of any one of claims 11 to 15, wherein the process further comprises the step of heating the layered article to a temperature of up to 120° C.

17. A composite material obtainable by a process of any one of claims 11 to 16.

18. An article comprising or consisting of the composite material of any one of claims 1 to 10.

19. A process for the preparation of a shaped article, wherein the process comprises: a. exposing a composite material of any one of claims 1 to 10 to water; and b. moulding the composite material to form a shaped article.

20. The process of claim 19, wherein the step of exposing the composite material to water further comprises heating the water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0140] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0141] FIG. 1A shows optical micrograph images of a material analogous to that of comparative example 1 that lacks an interleaf.

[0142] FIG. 1B shows a magnified view of the material shown in FIG. 1A.

[0143] FIGS. 2A and 2B show a composite material of the present invention with a filter paper interleaf.

[0144] FIGS. 3A and 3B show a composite material of the present invention with an interleaf layer made up of 2 regenerated cellulose films (Natureflex).

[0145] FIG. 4 shows a stress strain graph for the composite material of the invention and the comparative example without interleaf.

[0146] FIG. 5 shows a graph of peel strength against position defined as the distance from the edge of a piece of composite material.

[0147] FIG. 6 shows a graph of the average peel strength for a composite material made using the indicated ratio of solvent to the amount of cellulosic material.

[0148] FIG. 7 is a graph showing peel strength for a composite material made with different interleaf layers.

[0149] FIG. 8 shows the tensile properties for a composite material of the present invention with three levels of adsorbed water. 0%, 6% and 28%

EXAMPLES

Comparative Example 1

[0150] A composite material not forming part of the invention was prepared following the disclosure in Huber et al (Composites: Part A, 43 (2102) 1738-1421). Huber describes a process whereby layers of a woven cellulose material are impregnated with a weight of 1-butyl-3-methylimidazolium acetate (BMIMAc) equal to the average weight of each layer and arranged in a stack. The impregnated stack is then placed into a hot press (set to 110° C.) at a pressure of 1.5 MPa for 1 hour followed by an increased pressure of 2.5 MPa for a further 20 minutes. The assembly is then removed from the hot press and washed in water for 24 hours (the coagulation/regeneration step) then further washed in boiling water for 48 hours. Finally, the assembly is dried under a pressure of 0.5 MPa for 24 hours at 75° C.

[0151] FIG. 1A shows optical micrograph images of a material analogous to that of comparative example 1 that lacks an interleaf and FIG. 1B shows a close up version. The optical micrographs show that a thin layer of regenerated cellulose is formed around each fibre bundle due to the applied solvent, pressure and temperature. However, there is not enough to fill the gaps in the woven structure. The material that is visible in the gaps of the woven material is superglue that was used to hold the material in place during the optical micrographs.

Example 1a

[0152] A composite material of the invention was prepared by the following method. Layers of flax, a woven cellulose material, and interleaf layer are impregnated with 1-ethyl-3-methylimidazolium acetate (EMIMAc) in a ratio of weight of solvent to weight of cellulosic material of 2.5:1. The amount of solvent is reasonably equally shared across each of the layers. The flax was 2/2 twill and 100 g/m.sup.2. The impregnated woven cellulose fabric was stacked with an impregnated interleaf layer of filter paper placed in between each layer of woven cellulose material. The impregnated stack was then placed into a press at ambient temperature (around 20° C.) at a pressure of 1.4 MPa for 1 hour followed by an increased pressure of 2.5 MPa for a further 20 minutes at the same temperature. The assembly was then removed from the hot press and washed in water for 20 hours (the coagulation/regeneration step) there was no further washing step. Finally, the assembly is dried under a pressure of 2.5 MPa for 1 hour at 125° C. The parameters for the Huber et al process compared to the parameters of the process of the invention are provided in Table 1 below.

TABLE-US-00001 TABLE 1 Present Invention's Huber et al Process Process Woven cellulose material 4 layers of flax or rayon Flax Interleaf layer None Filter paper Solvent:cellulose ratio 1:1 2.5:1 Solvent BMIMAc EMIMAc First pressure stage 1.5 MPa for 1 hour 1.4 MPa for 1 hour Temperature for first 110° C. 20° C. pressure stage Second pressure stage 2.5 MPa for 20 mins 2.5 MPa for 20 mins Temperature for second 110° C. 20° C. stage Regeneration/coagulation 24 hours in water 20 hours in water Further washing 48 hours, 100° C. None Drying 48 hours, 75° C. 1 hour, 2.5 MPa, 125° C.

[0153] FIGS. 2 and 3 show optical micrograph images of a cross section of composite materials of the present invention. FIGS. 2A and 2B show a composite material of the present invention with a filter paper interleaf. It can be seen from the images that the filter paper interleaf layers fill in most of the gaps in the structure of the woven material and in turn regenerated cellulose fills any remaining gaps. The structure of the filter paper is still visible.

[0154] FIGS. 3A and 3B show a composite material of the present invention with an interleaf layer made up of 2 regenerated cellulose films (Natureflex). The interleaved films fill all of the gaps. The film is able to deform around the fibre bundles to bind the structure together. The individual films are still visible.

Example 1b

[0155] A composite material of the invention was prepared by forming an impregnated stack as described in Example 1a except the interleaf was cellophane. The impregnated stack was then placed into a press at ambient temperature (around 100° C.) at a pressure of 2 MPa for 2 hours. The assembly was then removed from the hot press and washed in water for 20 hours (the coagulation/regeneration step) there was no further washing step. Finally, the assembly is dried under a pressure of 2 MPa for 1 hour at 125° C. This process removes one of the pressure stages of Example 1a and increases the temperature and length of the pressure step.

Example 2

[0156] A comparison of the in-plane tensile properties of the composite materials of the invention was carried out. A composite material with a filter paper interleaf was prepared according to the process set out in Example 1a and a composite material using cellophane as the interleaf material was prepared as set out in Example 1b. A comparative material was also prepared without an interleaved layer but with the same procedure as Example 1a. It was demonstrated that the Young's modulus was significantly improved for Example 1a and 1b, while the tensile strength and failure strain remain unaffected. The properties of the materials prepared according to Example 1a and Example 1b demonstrated improved properties over the comparative example without the interleaf and the composite material described in Huber et al. The data is shown in Table 2 below for the composite material of Example 1a, Example 1b and the comparative example. The stress strain graph for the composite material of Example 1a, and the comparative example without interleaf is shown in FIG. 4

TABLE-US-00002 TABLE 2 Composite Comparative Results Material of Example Composite reported Example without Material of by Huber 1a Interleaf Example 1b et al Young's 5.4 2.8 7.1 0.9 Modulus (GPa) Tensile 75 75 120 45 Strength (MPa)

Example 3

[0157] A further experiment was carried out to compare the interlayer strength of the composite material of the present invention against a comparative example without an interleaf. This was conducted using a T peel test following the guidelines of ASTM D1876. The sample width was 10 mm, the length was 80 mm and the testing speed was 80 mm/min. The measured peel force was averaged between 20 mm and 70 mm on the sample, and the results are presented in terms of the average force for a 1 metre width (N/m). As can be seen from Table 3 below the peel strength was considerably higher for the composite material of the present invention.

TABLE-US-00003 TABLE 2 Comparative Composite Material Example without of the Invention Interleaf Peel Strength (N/m) 400 40

[0158] FIG. 5 shows a graph of peel strength against position defined as the distance from the edge of a piece of composite material. As is evident from FIG. 5 at all positions the composite of the material has a much higher peel strength.

[0159] It is clear from this data that the presence of an interleaf of a sheet-based cellulose material has a surprising beneficial effect of the peel strength of materials derived from cellulose based woven materials.

Example 4

[0160] The amount of solvent used in the process also has a surprising effect on the properties of the composite material of the present invention. A composite material was prepared according to Example 1; however, the solvent to cellulose material ratio was modified. Solvent to cellulose ratios of 1.73:1, 2.25:1, 2.63:1, 3.11:1 and 4.23:1 were tested with a pressure of 1.4 MPa applied to the stack of layers impregnated with the relevant amount of solvent. FIG. 6 shows that an increasing amount of solvent relative to the amount of cellulose material led to an increase in average peel strength.

[0161] However, at higher levels of solvent at around a 4:1 ratio of solvent to cellulose, a high amount of flashing was observed at the edges of the press as pressure and heat was being applied. Flashing is excess cellulose that is squeezed out of the press and therefore out of the composite material. Therefore, there is a preference to avoid ratios above 4.5:1.

Example 5

[0162] The type of textile also plays a role on the properties of the composite material. A composite material according to Example 1 was obtained with flax and Lyocell (a man-made cellulose-based fabric) as the woven cellulose material. The beneficial properties of composite materials of the invention were achieved. However, the flax based composite material performed significantly better than the Lyocell fabric. The results are shown in Table 3 below.

TABLE-US-00004 TABLE 3 Tensile Modulus Tensile Strength Peel (GPa) (MPa) Strength (N/m) Flax woven material 4.4 86 200-400 Lyocell woven 4.4 52 100 material

Example 6

[0163] As well as the type of textile playing a role on the peel strength. The material used as the interleaf layer also plays a role. A Flax composite material according to Example 1 was prepared with filter paper, Natureflex and cellulose powder as the interleaf. The results of peel tests with the different interleaf layers can be seen in FIG. 7.

Example 7

[0164] Wide angle X-ray measurements (WAXS) for a range of materials have been carried out. The WAXS measurements were carried out using a Huber goniometer employing Copper K.sub.α radiation using an accelerating Voltage of 40 kV and a current of 30 mA. 2θ scans were carried out between values of 5 and 30° C. at angle increments of 0.2° and a counting time of 120 s at each position. A background scan was carried out using the same conditions, but without the sample in position, to subtract any x-rays entering the detector by the air scattering, etc. After data collection, the resulting 20 scans are examined to assess what characteristic peaks are present (cellulose I, cellulose II and the amorphous phase) and then the data is fitted with these combinations of peaks (using Excel solver) to establish what phases are present and in what fraction. The materials that were tested are as follows:

[0165] (1) Pure linen cloth

[0166] (2) Flax cloth with no interleaf

[0167] (3) Flax cloth with a filter paper interleaf

[0168] (4) Flax cloth with a regenerated cellulose interleaf (Natureflex 23 NP film)

[0169] The X-ray measurements allow for the determination of the amount of different forms of cellulose. The percentage amounts of the different types of cellulose are indicated in Table 4 below.

TABLE-US-00005 TABLE 4 Amorphous Peel Cellulose 1 cellulose Regenerated Matrix Strength Material (%) (%) cellulose (%) Fraction (N/m) (1) 78 22 0 NA NA (2) 64 30 6 14 40 (3) 58 34 8 26 250 (4) 48 34 18 34 330

[0170] It is clear from Table 4 that incorporation of either a filter paper interleaf or a regenerated cellulose film interleaf gives an order of magnitude increase in the interlayer peel strength with only a 23% dilution of the original flax fibre content (86% fibres using no film and 66% with the Nature flex 23NP film). Accordingly, as shown in the Figures, the material properties of the flax fibre are maintained.

Example 8

[0171] A sheet of composite material of the present invention was formed into a shaped article by a hydroforming process. The apparatus utilised in the hydroforming process is based around that proposed by Hou in 1997 (Hou, M., Composites Part A28A (1997) 695-702q1997 Elsevier Science Limited) and consists of a matched hemispherical mould (or another desired shape) and a hold down (or gripper) plate. The gripper plate stops the composite material sheet from wrinkling as it is being deformed.

[0172] The composite material sheet to be hydroformed can be left to soak in water overnight or more preferably for 5 minutes before forming. It is then placed between the matched moulds ready for forming. The forming can be carried out at room temperature (and then the formed sheet is subsequently dried) or more preferably in a temperature controlled oven set at 120° C., where the sheet is both formed and dried in the same process. Forming is carried out at a closing speed of 80 mm/s and the forming process is stopped when the load reaches 5 kN. The mould is then opened and the formed sample is removed.

[0173] To aid understanding of the hydroforming process, tensile tests were carried out (under ASTM testing standard D638) at various levels of water absorption. Parallel strips were cut from a flat ACC sheet, and tested at room temperature after being conditioned at various water contents. FIG. 8 shows typical tensile stress-strain curves for three conditions. A dry ACC sheet, an ACC sheet with 6% adsorbed water (which is the normal equilibrium water uptake at standard room conditions of 20° C. and 50% RH) and a sample with 28% water.

[0174] The result show that while there is little effect on tensile properties of the ACC sheet at 6% content water, there is a significant difference for 28% water content. At this highest water content, the stiffness (as specified by the initial gradient of the stress-strain curve) is six times lower than for the other water contents. Also, the maximum strain before failure increases by 100% with 28% water content.

[0175] It is considered that during forming the sheet is subjected mainly to tensile stresses. Consequently, the high water content reduces the resistance to deformation (as determined by the modulus) by six times and also increases the amount the sheet can stretch before breaking (as measured by the failure strain) by a factor of 2. It is clear that these two features significantly improve the formability of the ACC sheet.

[0176] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0177] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0178] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.