METHODS FOR PROCESSING FIBROUS CELLULOSIC MATERIAL, PRODUCTS AND USES THEREOF

Abstract

A method for processing fibrous cellulosic material from algae comprising: (i) suspending the fibrous cellulosic material in water to form a suspension; and (ii) passing the suspension through at least one chamber having a large gap, at a high shear to produce cellulose nanofibrils. Also described are cellulose nanofibrils and cellulose nanocrystals, products, methods and uses of the same.

Claims

1. A method for processing fibrous cellulosic material from algae comprising: i) suspending the fibrous cellulosic material in water to form a suspension; and ii) passing the suspension through at least one chamber having a large gap, at a high shear to produce cellulose nanofibrils.

2. The method of claim 1 wherein the fibrous cellulosic material is suspended in water at a concentration of from 0.5 to 5% by weight.

3. The method of claim 1 wherein the fibrous cellulosic material is suspended in water at a concentration of from 1 to 3% by weight.

4. The method of claim 1 wherein the at least one chamber has a gap of 70 micron to 250 microns.

5. The method of claim 1 wherein the suspension undergoes a single pass through the at least one chamber having a large gap, at a high shear.

6. The method of claim 1 wherein the suspension undergoes up to 7 passes through the at least one chamber having a large gap at a high shear.

7. The method of claim 1 wherein the suspension undergoes up to 3 passes through the at least one chamber having a large gap at a high shear.

8. The method of claim 1 wherein the suspension is passed through the at least one chamber at a low pressure.

9. The method of claim 1 wherein the suspension is passed through the at least one chamber at a pressure up to 200 MPa.

10. The method of claim 1 wherein the water is removed from the suspension comprising the cellulose nanofibrils to produce cellulose nanofibrils in a dry form.

11. The method of claim 1 wherein the method is carried out in a high shear homogeniser.

12. The method of claim 1 further comprising the step of subjecting the cellulose nanofibrils to acid hydrolysis to form cellulose nanocrystals.

13. The method of claim 12 wherein the acid hydrolysis uses hydrochloric acid.

14. The method of claim 1 wherein the cellulose nanofibrils or cellulose nanocrystals undergo surface modification.

15. Cellulose nanofibrils having a width of from 40 to 100 nm and an aspect ratio of greater than 50.

16. The cellulose nanofibrils of claim 15 being a substantially homogeneous product.

17. The cellulose nanofirbrils of claim 15 having an aspect ratio of greater than 100.

18. The cellulose nanofibrils of claim 15 having a water retention of greater than 5000%.

19. Cellulose nanocrystals formed by the method of claim 12.

20. A rheological modifier comprising at least one of the cellulose nanofibrils of claim 15 and the cellulose nanocrystals of claim 19.

21. A medical composite comprising at least one of the cellulose nanofibrils of claim 15 and the cellulose nanocrystals of claim 19.

22. A single use plastic replacement product comprising at least one of the cellulose nanofibrils of claim 15 and the cellulose nanocrystals of claim 19.

23. A medical implant or a medical mesh comprising at least one of the cellulose nanofibrils of claim 15 and the cellulose nanocrystals of claim 19.

24. A method of producing a medical implant or a medical mesh comprising 3-D printing of at least one of the cellulose nanofibrils of claim 15 and the cellulose nanocrystals of claim 19.

25. Use of the cellulose nanofibrils of claim 15 in composites, oil and gas, paints, cosmetics, foods, coatings or films.

26. Use of the cellulose nanocrystals of claim 19 in composites, oil and gas, paints, cosmetics, foods, coatings or films.

Description

DETAILED DESCRIPTION

[0056] Embodiments of the present invention will now be described with reference to the following, non-limiting examples and figures.

[0057] FIG. 1A-1F illustrates SEM images of the different types of nanocellulose;

[0058] FIGS. 2a and 2b graphically depict the comparison of storage modulus of fibrous cellulosic material harvested from different origins, processed in accordance with an embodiment of the present invention;

[0059] FIGS. 3a-3c illustrate SEM images for the processed fibrous cellulosic material harvested from the different origins;

[0060] FIGS. 4a and 4b illustrate FTIR analysis of the processed fibrous cellulosic material harvested from the different origins;

[0061] FIGS. 5a and 5b illustrate SEM images of nanocellulose at the start and end of processing via a method in accordance with a first embodiment of the present invention;

[0062] FIG. 6 illustrates comparative SEM images of cellulose nanofibrils results from the method of the first embodiment and cellulose nanofibrils derived from wood pulp;

[0063] FIG. 7 illustrates an SEM image of cellulose nanocrystals formed by the method in accordance with a second embodiment of the present invention;

[0064] FIG. 8 illustrates SEM images of cellulose nanocrystals derived from sources of nanocellulose other than algae; and

[0065] FIG. 9 illustrates redispersible stable suspensions of cellulose nanocrystals.

[0066] In accordance with one embodiment of the first aspect of the present invention, the steps for the production of nanofibrillated cellulose (CNF) from coarse cellulose extracted from brown algae are described below. In particular, the fibrous cellulosic material processed in the method of this embodiment was derived from brown seaweed species Laminaria hyperborea.

Source of Fibrous Cellulosic Material

[0067] Fibrous cellulosic material was obtained from three sources of Laminaria hyperborea: the first two sources were by-products of alginate production obtained from Marine Biopolymers Ltd who extracted the fibrous cellulosic material with alginate from seaweed harvested from the Scotland (Ayr) and from Iceland and then separated the two products; and the third source was obtained by harvesting L. hyperborea directly from Ayr beach in Scotland by Edinburgh Napier University (ENU) and extracting the coarse cellulose in the laboratory as per the procedure below.

Seaweed Extraction Procedure

[0068] 1. Laminaria hyperborea stems cut into small pieces; [0069] 2. Soak overnight in 0.2M HCl; [0070] 3. Neutralise to pH 7 with NaOH and then water wash in centrifuge; [0071] 4. Soak the resultant material for 4 hours and 30 minutes in 2% sodium bicarbonate; and [0072] 5. Centrifuge to remove aliginate.

[0073] The extracted fibrous cellulosic material from each source was subjected to the method of the present invention in accordance with the embodiment described in further detail below to produce nanofibrillated cellulose (CNF).

[0074] A comparison of rheology (storage modulus) and scanning electron microscopy (SEM) analyses of the resulting CNF and Fourier Transform Infra-Red (FTIR) analysis of the extracted fibrous cellulosic material harvested from the above sources was undertaken. The various methods of analysis were intended to establish whether the source of the fibrous cellulosic material and method of extraction affect the nature of the starting material and the subsequent processing into CNF in accordance with the method of the present invention.

[0075] Storage modulus is a measure of the elastic response of a material and refers to the stored energy within it. The results for the resulting CNF from the different sources of fibrous cellulosic material are provided in Table 1 below and in FIG. 2a.

TABLE-US-00001 TABLE 1 Storage Storage Storage modulus modulus modulus @50 rad/s @50 rad/s @50 rad/s (Pa) (Pa) (Pa) Number of Icelandic Scottish Scottish Passes in LHCNF LHCNF LHCNF high shear Harvested Harvested Harvested homogeniser by MBL SD by MBL SD by ENU SD 1 330.7 4.9 343.7 25.6 337.3 12.4 2 341 10.4 347.7 2.1 341.7 6.2 3 370 8 356.7 4.2 362.2 9.6 4 417.5 0.7 410.3 10.1 409 1.7 5 439 7.1 427.3 9.5 425.3 16.3

[0076] From the results in Table 1 and FIG. 2a, it is evident that all three samples of seaweed derived CNF show similar profiles with no significant differences at each pass through the chamber having a large gap.

[0077] When compared to wood derived cellulose, processed after swelling in morpholine, the difference between seaweed derived CNF and wood derived CNF is evident, with a single pass of seaweed material two to three times the storage modulus of five passes with wood derived material, as illustrated in FIG. 2b.

[0078] The shape of the graphs is typical of processing cellulose in this embodiment of the present invention, with increase in storage modulus most evident after three passes and levelling off after five passes. Storage modulus increases with entanglement of fibres supported through hydrogen bonding between and within the fibres. The values are much higher with seaweed derived material since the fibres are much longer and therefore entanglement is greater. After five passes the hydrogen bonding between the fibres is more easily broken and so storage modulus does not increase further to any great extent. While the storage modulus increases with number of passes for seaweed CNF, the benefits of slightly higher storage modulus may not outweigh the energy costs in increasing number of passes.

[0079] Scanning electron images (SEMs) of CNF material after 1 pass are shown in FIG. 3, in which FIG. 3a shows Icelandic derived LHCNF from MBL extraction, FIG. 3b shows Scottish derived CNF from MBL extraction, and FIG. 3c shows Scottish derived CNF from ENU extraction described above. From these images it is clear that there is no discernible differences between the samples.

[0080] The FTIR (Fourier Transform Infra-Red) traces illustrated in FIG. 4a, and quantified in FIG. 4b, for the fibrous cellulosic material harvested from all three samples are very similar, showing a pattern expected from seaweed derived cellulose. The ENU and Icelandic samples appear to be the most similar, although no differences are significant between any of the samples i.e. known peaks are where they are expected, with no unexpected peaks. Accordingly, the fibrous cellulosic harvested from the different sources and extracted by different methods (as a by-product of alginate production or via the ENU method) is essentially identical.

[0081] Taken together, the results from rheological, SEM imaging, and FTIR analyses show no significant differences between any of the three CNF samples at each pass or three fibrous cellulosic material samples, i.e. in coarse pre-processed form. Therefore, it is apparent that the source of fibrous cellulosic material from algae and method of extraction are not significant to the subsequent CNF processing in accordance with the method of the present invention.

[0082] The fibrous cellulosic material starting material used in the subsequent examples is that obtained from MBL, harvested from Scotland and extracted as a by-product of alginate production.

Method of Production of Cellulose Nanofibers (CNF) and Cellulose Nanocrystals (CNC)

[0083] An SEM image of the fibrous cellulosic starting material is provided in FIG. 5a which shows cellulose particles in the millimetre size range, i.e. ×10.sup.6 order of magnitude greater than the target fibrils. A 500 g suspension of 1% w/w fibrous cellulosic material in deionised water was made up.

[0084] A high shear mixer with a 200 micron auxiliary chamber was used in this example. In particular, a M110EH-30 (Microfluidics) high shear mixer was employed in which the 100 micron interaction chamber had been removed.

[0085] The fibrous cellulosic material suspension was added to the reservoir of the high shear mixer and mixed to maintain a stable suspension. Mixing may be performed manually with a stirring rod or with a rotor stator mixer, for example an IKA T25 ultra-turrax high speed homogeniser.

[0086] The higher shear mixer was then turned on and the fibrous cellulosic material suspension was passed through the auxiliary chamber once and the product was collected. In this example, the flow rate was around 8 to 10 L/hr and so the product was collected in around 3 to 5 minutes. The default pressure in the chamber was 9 Kpsi (approx. 62 MPa).

[0087] The resulting product for a stable suspension of fibrous cellulosic material is high quality cellulosic nanofibrils, as detailed below. A SEM image of the resulting cellulose nanofibrils is provided in FIG. 5b which clearly show elongated fibrils having widths within the nano range.

[0088] The water retention value (%) of the resulting cellulose nanofibrils was investigated. The water retention value provides an indication of the ability of the fibrils to take up water and swell and therefore the ability to act as a rheology modifier. However, it is also reported to be an indication of the degree of fibrillation of a material (“Microemulsion Systems for Fiber Deconstruction into Cellulose Nanofibrils”, Carrillo et al., ACS Applied Materials and Interfaces 6, 22622-22627, 2014).

[0089] The water retention value was determined by the following procedure: [0090] 1. For dried CNF powders: [0091] 1.1. Weight 0.5 g of dried powder in disposable plastic bottle [0092] 1.2. Add 49.5 g of pure water in the bottle [0093] 1.3. Re-disperse the sample by any known methods, for example using a rotor stator mixer, sonication or a further pass through the high shear homogeniser. [0094] 1.4. Place the suspension in a 50 ml falcon tube [0095] 2. For never dried cellulosic material in solvent other than water, for example, CNF which has undergone surface modification: [0096] 2.1. Solvent exchange the sample into water via multiple, e.g. 4-7, centrifugation steps. [0097] 2.2. Homogenise the washed sample using the rotor-stator mixer to eliminate the flocculation or aggregation due to the washing process [0098] 2.3. Determine the solid content of the washed suspension by moisture balance and prepare 1% suspension in water. Moisture balance uses the loss on drying (LOD) method. In particular, a liquid or solid sample is placed in a sample pan and an integrated balance weighs the initial sample and then a heating element evaporates the water. The final reading is the percent solids in the initial sample, which indicates how much the sample should be diluted for the required concentration. [0099] 2.4. Place the suspension in a 50 ml falcon tube [0100] 3. The falcon tube was placed in the centrifuge. A Sorvall™ RC 6 Plus Centrifuge (Thermo Scientific) was used in this example. The sample was centrifuged at 900 g for 30 mins. [0101] 4. After the centrifugation, the falcon tube was removed and the top liquid phase was poured off without disrupting the bottom one to ensure there was no free flow liquid at the top of the tube [0102] 5. Three aluminium trays were prepared and their weight recorded as W.sub.empty pan [0103] 6. The remaining material in the falcon tube was split into the three trays and the trays weighed and recorded as W.sub.empty pan+wet sample [0104] 7. The trays were placed in the oven at 105° C. for overnight [0105] 8. The trays were weighed again and recorded as W.sub.empty pan+dry sample [0106] 9. The WRV (%) result was then calculated using the equation below:

[00001]$\mathrm{WRV}=\frac{W_{\mathrm{empty}\mathrm{pan}+\mathrm{wet}\mathrm{sample}}-W_{\mathrm{empty}\mathrm{pan}+\mathrm{dry}\mathrm{sample}}}{W_{\mathrm{empty}\mathrm{pan}+\mathrm{dry}\mathrm{sample}}-W_{\mathrm{empty}\mathrm{pan}}}\times 100$

[0107] A comparison of the cellulose nanofibrils formed by this method, together with cellulose nanofibrils derived from wood pulp from trees and engineered from bacteria is provided in Table 2 below.

TABLE-US-00002 TABLE 2 Tree/wood (pulp) Bacteria Seaweed Aspect ratio  10 >100 >100 Water Retention Value (%) 5000 1000 7000 Energy consumption (kwh/tonne) >2000  Very high Very low (>10,000?) <200 Time to CNF from source (days)   7+   21+  +/−1 Charged dispersible product Yes No Yes or No as required Biocompatibility No Yes Yes Value end product Low-medium Very high Very high Yield from raw material Low Low High (~100%)

[0108] As is shown, the resulting cellulose nanofibrils are more akin to CNF derived from high cost bacterial processes, thus providing a high quality product at a much lower production cost and in a much shorter time frame from source to end product. In addition, the seaweed derived CNF offers far greater water retention than is achieved for CNF derived from either wood pulp or bacterial processes.

[0109] Further, the yield of CNF from seaweed is significantly greater than that for wood pulp or bacteria, achieving close to 100%.

[0110] FIG. 6 shows SEM images comparing cellulose nanofibrils derived from seaweed (on the left) to cellulose nanofibrils derived from wood pulp (on the right). It is readily apparent from these images that the seaweed derived CNF has a much higher aspect ratio than the wood pulp derived CNF and so provides a much higher quality end product.

[0111] In a further embodiment of the present invention, the cellulose nanofibrils resulting from the above method may be further processed to produces cellulose nanocrystals.

[0112] The cellulose nanofibrils are subjected to acid hydrolysis using hydrochloric acid or a strong oxidising agent to produce cellulose nanocrystals, which are subsequently extracted from the acid solution by centrifugation and washing.

[0113] In particular, unmodified CNC, oxidised CNC and sulphated CNC were produced using hydrochloric acid, ammonium persulphate, and sulphuric acid, in accordance with methods known in the art. The reactions were left for sufficient time to obtain the modified or unmodified CNC but stopped before complete hydrolysis occurred.

[0114] The yield of the resulting material cellulose nanocrystals is approximately 70%, as compared to yields of less than 30% which are achieved for acid hydrolysis of wood pulp derived cellulose nanofibrils. The cellulose nanocrystals are a high quality end product comparable to cellulose nanocrystals derived from bacterial sources. As can be seen from FIGS. 7 and 8, the nanocrystals formed by the method of the present invention (FIG. 7) are large crystals similar in size and morphology to bacterial synthesised nanocellulose (FIG. 8d). The cellulose nanocrystals derived from wood (FIG. 8a), cotton (FIG. 8b) and bamboo (FIG. 8c) are much smaller crystals, which are of inferior quality, and the cellulose nanocrystals derived from Glaucophyte algae via microalgae synthesis (FIG. 8e) and tunicate (FIG. 8f) are larger crystals. While the high costs of the bacterial derived CNC synthesis and the high costs and difficulties in culturing Glaucophyte algae and tunicates render such processes suitable only for high value commercial end products, CNC derived from the method of the present invention is a more commercial viable product. The resulting CNC can therefore be used in a range of applications without any cost prohibition.

[0115] Due to the high yield and high quality of cellulose nanocrystals achieved via acid hydrolysis of cellulose nanofibrils derived from algae via the method of the present invention, further processing of the CNC is efficient and effective, making such processing an economically viable option. For example, as shown in Table 3 below and in FIG. 9, CNC derived from acid hydrolysis (using hydrochloric acid) of the cellulose nanofibrils derived from seaweed via the method of the present invention for a reaction time of 4 hours, namely unmodified CNC, has no surface modification and has a low zeta potential. Subsequent oxidisation of the CNC with ammonium persulphate provides an oxidised CNC which has a carboxyl group surface modification and a higher zeta potential. Alternatively, if the cellulose nanofibrils undergo acid hydrolysis using with sulphuric acid for a reaction time of 2 hours, a sulfated CNC is produced which has a sulfate ester group modification with a significantly higher zeta potential.

TABLE-US-00003 TABLE 3 Product Zeta potential mV Surface modification Unmodified CNC 26.2 None (native hydroxyl) Oxidised CNC 35.2 Carboxyl group Sulfated CNC 56.6 Sulfate ester group

[0116] The zeta potentials were derived directly from zeta potential measurements using electrophoretic light scattering and the surface charge moieties were confirmed by FTIR.

[0117] Therefore, the cellulose nanofibrils of the present invention are amenable to acid hydrolysis to form cellulose nanocrystals and subsequent surface modification by techniques known in the art. Further, such products are comparable with bacterial derived CNC, thus providing a high quality product at a much lower cost.

[0118] Nanocellulose (CNF and CNC) produced by the method of the present invention is naturally uncharged but can be easily modified to requirements, giving flexibility in applications for polar and non-polar environments. For example, a charge may be applied to CNF via a mild oxidation reaction, as is known in the art and discussed in further detail above. As with CNC, CNF derived from the method of the present invention is much more amenable to chemical modification than CNF derived from other sources (e.g. wood pulp) and so such modification reactions require less oxidant and much shorter reaction times to achieve comparable products, thus providing more economically viable methods.

[0119] The method of the present invention is faster, cleaner and much cheaper than existing higher plant or bacterial derived cellulose processes. In particular, the time frame from source to CNF may be as little as 3 days and less than a day when the method is scaled up. Further, the method may be a single step high-shear process which allows for ease of scale up via bolt-on modular technology to existing seaweed processing and alginate extraction facility. Further, no harsh chemicals are required and seaweed cellulose is currently a by-product from alginate production. As such the energy requirements for production are at least an order of magnitude lower than with any existing process.

[0120] The CNF produced is more homogeneous than with existing methodologies and exhibits certain desirable characteristics, namely, high aspect ratio, highly absorbent fibres. Initial characterisations show this product to be of a higher quality by all standard metrics than any other CNF product currently available.