MULTIFUNCTIONAL LIQUID-ABSORBING PRODUCT AND THE

MANUFACTURE AND USE THEREOF

Field of the invention

[0001] The present invention relates generally to a sponge-like, liquid-absorbing product and to the manufacture and use thereof.

Background of the invention

[0002] Any discussion of the prior art throughout this specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0003] Absorbent products in the form of logs, sand bags, silt socks, superabsorbent polymer bags and the like have been used in flood control, for cleaning up spillages and in erosion management and riverbank protection.

[0004] The present inventors have developed simple, efficient absorbent products which are highly effective under a range of conditions and may conveniently be prepared from waste materials.

Summary of the invention

[0005] In a first aspect the present invention provides a liquid-absorbing product comprising cellulosic fibres.

[0006] The cellulosic fibres may be randomly oriented, non-twisted fibres.

[0007] The cellulosic fibres may comprise bundles of fibrils with pores located between the bundles of fibrils.

[0008] The cellulosic fibres may be ribbon-shaped.

[0009] The cellulosic fibres may be ribbon-shaped, with bundles of fibrils running along the ribbons.

[0010] The cellulosic fibres may be delignified. [0011] The cellulosic fibres may have a dry cross-section that is oblong.

[0012] The cellulosic fibres may have a wet cross-section that is round.

[0013] The cellulosic fibres may have a nominal fibre length of about 0.5 mm to about 3 mm.

[0014] The cellulosic fibres may have a nominal fibre length of about 1 mm to about 2 mm.

[0015] The cellulosic fibres may have a nominal fibre length of about 2 mm.

[0016] The cellulosic fibres may have breadths ranging between about 0.1 mhi and about 200 mm .

[0017] The cellulosic fibres may have an average breadth between about 1 mhi and about 30 mm .

[0018] The cellulosic fibres may have an average breadth between about 10 mhi and about 15 mm .

[0019] The cellulosic fibres may have an average specific surface area between about 4000 m ² /kg and 5000 m ² /kg.

[0020] The cellulosic fibres may have an average specific surface area between about 4500 m ² /kg and 4600 m ² /kg.

[0021] The cellulosic fibres may have a density between about 1 g/cm ³ and about 2 g/cm ³ .

[0022] The cellulosic fibres may have a density between about 1.3 g/cm ³ and about 1.5 g/cm ³ .

[0023] The cellulosic fibres may have an aspect ratio of about 1 : 100.

[0024] The cellulosic fibres may have a tensile strength between about 100 MPa and about 1000 MPa.

[0025] The cellulosic fibres may have a tensile strength between about 200 MPa and about 770 MPa. [0026] The cellulosic fibres may have an elastic modulus between about 10 GPa and about 75 GPa.

[0027] The cellulosic fibres may have an elastic modulus between about 20 GPa and about 55 GPa.

[0028] Greater than 80% of the cellulosic fibres by mass may have a diameter of less than 100 mm .

[0029] Greater than 90% of the cellulosic fibres by mass may have a diameter of less than 100 mm .

[0030] The cellulosic fibres may be compacted.

[0031] The cellulosic fibres may be in the form of panels.

[0032] The cellulosic fibres may be in the form of panels prepared by hot pressing.

[0033] The cellulosic fibres may be free of resins.

[0034] The cellulosic fibres may be free of additives.

[0035] The cellulosic fibres may be jute, sisal, hemp, coir or bamboo.

[0036] The cellulosic fibres may be jute or sisal. In one embodiment, the cellulosic fibres are jute.

[0037] The cellulosic fibres may be obtained from jute hessian fabric.

[0038] The cellulosic fibres may be obtained from waste fabric.

[0039] The cellulosic fibres may be obtained by fibrillation of a fabric.

[0040] The liquid may be an aqueous liquid, such as for example water.

[0041] The liquid may be a non-aqueous liquid, such as for example a hydrocarbon or an oil. [0042] The liquid may be a water/oil mixture or a water/hydrocarbon mixture, such as for example, an emulsion.

[0043] The product may further comprise a liquid-permeable exterior lining.

[0044] The liquid-permeable exterior lining may encapsulate the fibres.

[0045] The liquid-permeable exterior lining may be a wear-resistant hydrophilic fabric, such as for example, felt, cotton, sisal, linen, non-woven jute or hemp.

[0046] The liquid-permeable exterior lining may be a non-woven hydrophilic geotextile.

[0047] The liquid-permeable exterior lining may be cotton canvas or non-woven jute.

[0048] The product may be non-drip.

[0049] The product may be non-drip when saturated.

[0050] The product may be modular.

[0051] The product may be in the form of a mat, log or block.

[0052] In an embodiment of the first aspect the present invention provides a liquid- absorbing product comprising, consisting of, or consisting essentially of: cellulosic fibres encapsulated within a liquid-permeable exterior lining, wherein the cellulosic fibres are randomly oriented, non-twisted jute fibres.

[0053] The fibres in this embodiment may have one or more of the properties recited in Table 1 and/or recited above.

[0054] The fibres in this embodiment may be obtained from jute hessian fabric.

[0055] The fibres in this embodiment may be obtained by fibrillation of jute hessian fabric.

[0056] In an embodiment of the first aspect the present invention provides a liquid- absorbing product comprising, consisting of, or consisting essentially of: cellulosic fibres encapsulated within a liquid-permeable exterior lining, wherein the cellulosic fibres are randomly oriented, non-twisted jute fibres having a nominal fibre length of about 1 mm to about 2 mm. [0057] The fibres in this embodiment may have one or more of the properties recited in Table 1 and/or recited above.

[0058] The fibres in this embodiment may be obtained from jute hessian fabric.

[0059] The fibres in this embodiment may be obtained by fibrillation of jute hessian fabric.

[0060] In a second aspect the present invention provides a method for preparing a liquid- absorbing product of the first aspect, the method comprising the following steps:

(a) subjecting a cellulosic fabric to a first size reduction so as to provide a first flock of fibres;

(b) subjecting the first flock of fibres to a second size reduction so as to provide a second flock of fibres; and,

(c) passing the second flock of fibres through a sieve mesh so as to provide the cellulosic fibres.

[0061] The sieve mesh may be a 1 mm sieve mesh.

[0062] The cellulosic fabric may be as defined in the first aspect.

[0063] The cellulosic fabric may comprise a spun yarn or a twisted yarn.

[0064] The cellulosic fabric may be jute hessian fabric.

[0065] The first size reduction may be performed by mechanical shredding or coarse milling.

[0066] The second size reduction may be performed by mechanical fibrillation.

[0067] The method may further comprise encapsulating the fibres obtained following step (c) in a liquid-permeable exterior lining.

[0068] The method may further comprise subjecting the cellulosic fibres to sterilisation.

[0069] Sterilisation may be performed by heating the fibres. [0070] Heating may be performed at a temperature of greater than 100 °C.

[0071] Heating may be performed at a temperature between about 100 °C and about 180 °C.

[0072] In a third aspect the present invention provides a method for preparing a liquid- absorbing product according to the first aspect, the method comprising subjecting a cellulosic fabric to size reduction by mechanical cutting and shredding.

[0073] In a fourth aspect the present invention provides a method for absorbing liquid, comprising contacting the liquid with the product of the first aspect.

[0074] The liquid may be an aqueous liquid, such as for example water.

[0075] The liquid may be a non-aqueous liquid, such as for example a hydrocarbon or an oil.

[0076] The liquid may be a water/oil mixture or a water/hydrocarbon mixture, such as for example, an emulsion.

[0077] In a fifth aspect the present invention provides use of a product of the first aspect for absorbing a liquid.

[0078] The liquid may be an aqueous liquid, such as for example water.

[0079] The liquid may be a non-aqueous liquid, such as for example a hydrocarbon or an oil.

[0080] The liquid may be a water/oil mixture or a water/hydrocarbon mixture, such as for example, an emulsion.

Definitions

[0081] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Thus, in the context of this specification, the term "comprising" means "including principally, but not necessarily solely".

[0082] In the context of this specification the terms "a" and "an" are used herein to refer to one or to more than one (i.e to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0083] The term "about" is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in the context of achieving the same function or result.

[0084] The term "non-twisted" is understood to mean that the fibres to which it refers are not twisted together, or otherwise interlocked such as they would be when in the form of a yarn.

Brief Description of Drawings

[0085] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 : Macroscopic difference between jute yarn and jute short fibres.

Figure 2: Scanning electron microscope (SEM) image of fibrillated cellulosic fibres (jute) (a) bulk loose fine fibres (b) cross-section of a single fibre showing cellulose fibril bundles and pores.

Figure 3: Schematic drawing of inter-fibre and intra-fibre water absorption mechanisms.

Figure 4: Modular units in which products in accordance with embodiments of the invention may be provided.

Figure 5: Use of modular units in accordance with embodiments of the invention.

Figure 6: (a) woven jute fabric having spun yarns (b) short, randomly oriented, non-twisted cellulosic fibre bulk obtained by fibrillation of the woven jute fabric in (a) (c) a hot pressed panel obtained from the fibres in (b).

Figure 7: Comparison of jute fibres with commercial silica gel desiccant pearls under two environmental moisture conditions. Figure 8: Graphic representation of a product in the form of a block prepared from 7 hot-pressed panels made of jute fibre.

Figure 9: A block comprising panels made from hot-pressed jute fibres and having a liquid-permeable exterior lining made of cotton canvas.

Figure 10: The block shown in Figure 9. a) 2 hours after being immersed in water b), c) and d) 24 hours after being immersed in water.

Figure 11 : a) Initial dimensions of panel b) Front and side views of the panel post-immersion.

Figure 12: SEM images of jute fibres indicating the microscopic characteristics of the raw fibres 24 hours post-immersion and following the 7 day freeze-thaw cycle.

Figure 13: PCR band luminosity as a surrogate measure of target DNA concentration, and therefore target microbial biomass.

Figure 14: Comparison of water absorption behaviour of various jute samples.

Figure 15: Comparison of oleophilic absorption behaviour of various jute samples.

Figure 16: Comparison of FTIR spectra of raw jute fibres and post-immersion jute fibres after 22 absorption cycles.

Figure 17: Water absorption curve showing percentage absorption rate for a block product comprising jute fibres.

Detailed description

[0086] In one aspect the present invention provides a liquid-absorbing product comprising cellulosic fibres. The product is sponge-like, lightweight, and able to efficiently absorb water and other liquids, including hydrocarbons and oils, without dripping and without losing its structural integrity. Advantageously, the cellulosic fibres may be conveniently prepared from waste cellulosic materials, such as for example waste hessian packaging.

[0087] In some embodiments the cellulosic fibres may be short, randomly oriented, non- twisted fibres. It has been found by the inventors that water diffusion and absorption performance of short, randomly oriented, non-twisted cellulosic fibres is improved as compared to fibrous materials based on ordered, twisted fibre bundles such as geotextiles, non-woven batts, nettings and yarns, as well as inorganic particles, fines and synthetic foams. In this context, the term "short" in relation to the cellulosic fibres may mean that the fibres have a nominal fibre length of about 0.25 mm to about 5 mm, or about 0.5 mm to about 3 mm, or about 1 mm to about 2 mm, or about 2 mm.

[0088] Figure 1 shows the macroscopic difference between a yarn made of twisted jute fibres (Figure 1(a)) and non-twisted, randomly oriented, short single fibres which can be obtained by fibrillation of the yarn (Figure 1(b)). As also shown in Figure 1(b), the non- twisted single fibres are composed of bundles of single fibrils.

[0089] Figure 2 shows SEM images of cellulosic jute fibres suitable for use as the cellulosic fibres in accordance with the present invention obtained by size reduction of food-grade hessian bi-axial woven packaging. In Figure 2(a) it is seen that the fibres are ribbon-shaped with parallel fibril bundles. The fibres appear to have unravelled longitudinally and lost the original torsion from the spun yarn. Table 1 below shows the physical characteristics of the jute fibres.

Table 1

[0090] The exposed cellulose fibril bundles at each end of the fibres are likely to be the main point for capillary action and intra-fibre water absorption. Without wishing to be bound by any particular theory, the inventors believe that the water absorption capability of the cellulosic fibres occurs via two mechanisms. The first mechanism involves inter- fibre capillary action through fluid-fibre contact surfaces, and the second involves intra- fibre water diffusion with spontaneous gelling within the porous fibre network. These mechanisms are depicted in Figure 3. As the cellulose molecules are aligned along the length of the fibres, the product tends to expand laterally rather than longitudinally on absorption of water. It has been found that the fibres have a water absorption rate of about 0.1 L/min and a water holding capacity of about 500% after 24 hours.

[0091] Cellulosic fibres suitable for use in the products include, but are not limited to, jute, sisal, hemp, coir, bamboo or any combination thereof. Those skilled in the art will appreciate that other cellulosic fibres may also be used. In some embodiments, the cellulosic fibres comprise a mixture of jute fibres and one or more other cellulosic fibres. Typically, the jute fibres are present in an amount of at least 80% by weight of the total amount of cellulosic fibres present.

[0092] The product may further comprise a liquid-permeable exterior lining. The liquid- permeable exterior lining may serve to contain the cellulosic fibres, as well as providing wear resistance. In some embodiments the liquid-permeable exterior lining encapsulates the fibres, such that the fibres act as an infill. The liquid-permeable exterior lining may be any material that permits the efficient passage of liquid such that the liquid is able to contact the cellulosic fibres. Preferably, the liquid-permeable exterior lining is a material that is hydrophilic, wear-resistant and UV-resistant. In some embodiments the liquid- permeable exterior lining is felt, cotton, sisal, linen, non-woven jute or hemp.

[0093] In order to provide additional structural integrity, in some embodiments the cellulosic fibres may be encased within a stretchable cording mesh, such as for example, a geotextile netting. When the liquid-permeable exterior lining is present, the wire mesh may be placed over the exterior lining.

[0094] In some embodiments the product is modular. Modularity offers the potential for customisation and design of structures so as to accommodate different operational and terrain requirements depending on the intended use of the product.

[0095] Figure 4 shows examples of modular units in which the product may be provided. Figure 4(a) is a flat mat which may be useful for water and oil spills as well as shallow water floods. Figure 4(b) is a custom length linear log shape which, in addition to water absorption, may find use in the control of sediment and erosion in contour areas. Figure 4(c) is a block which may find use as a retaining wall, in gabions or to protect riverbanks. [0096] Multiple modules may be stacked and/or placed next to one another so as to provide liquid absorption capability and also a retaining wall or dam structure. The products are light and easy to transport and handle which is advantageous in flood situations where it may be necessary to deploy multiple products rapidly in order to control rising flood waters.

[0097] Reference to Figure 5 shows examples of the use of modular products in accordance with the invention. Figure 5(a) shows two mats placed end-to-end on the ground in spilled water. Once the water is absorbed, the mat has sufficient load-bearing capability such that a board may be placed on top of the mats to provide a walking path. Figure 5 (b) shows a single block in flood water. Figure 5(c) shows three blocks placed one on top of the other in an offset pattern so as to provide a retaining wall to prevent ingress of flood water.

[0098] The product may find use in a wide range of areas in which it is desired to remove/control water or other liquids (such as oil or hydrocarbons), for example, civil engineering areas (such as work and construction sites), mining sites, agricultural areas, riparian areas, streets and flooded areas. In some embodiments, the product finds use in cleaning up water/oil spillages, controlling rain water and storm water runoff, soil stabilisation and protection of riverbanks. The product may also be used inside gabions.

[0099] In addition to water absorption, the products may also perform secondary functions such as for example, acting as a sediment barrier and/or a filter for silt, sediment and fine particle pollutants. The products may also find use in other moisture absorption applications, for example as a desiccant.

[00100] The inventors have found that the products are capable of performing at least 22 moisture/drying cycles and maintain their performance in adverse weather conditions, including frost temperatures of -18 °C. It has also been found that the products are not susceptible to melting in the presence of heat. It has further been found that when the product reaches saturation, it does not drip.

[00101] Typically the cellulosic fibres are free of additives and/or resins so that the environmental impact of the product is minimal during service life and non-hazardous when disposed of, or recycled at the end of its life. [00102] The cellulosic fibres may be prepared from cellulosic fabrics or textiles. In some embodiments the cellulosic fabrics or textiles may be waste fabrics or textiles. In one embodiment, the cellulosic fibres are prepared from waste hessian packaging. By utilising a waste material, the cellulosic fibres may be prepared cheaply and offer a use for a material that may otherwise be destined for landfill. As such, products in accordance with the invention may be conveniently prepared from sustainable resources.

[00103] The cellulosic fibres may be prepared by, for example, a process involving first, mechanical shredding and coarse milling of a cellulosic fabric, followed by mechanical fibrillation (using for example, a knife mill) and passage through 1 mm sieve mesh. In another embodiment the cellulosic fibres may be prepared by performing size reduction of a cellulosic fabric by mechanical cutting and shredding. Mechanical cutting and shredding may be carried out by, for example, a rotary shear shredder machine. Both of these processes provide a fine cellulosic fluff of short, randomly oriented, loose, non- twisted fibres.

[00104] The cellulosic fibres produced may be heat-treated for disinfection and sterilisation purposes. This minimises the potential for mould and fungal growth. Heat- treatment may be carried out at a temperature above 100 °C. The loose fibres may then be compacted prior to use, without the need for adhesives or thermal bonding. In some embodiments the fibres may be compacted by hot-pressing into panels. Figure 6 depicts the preparation of a panel comprising short, randomly oriented, non-twisted cellulosic fibres from woven jute fabric by fibrillation of the fabric followed by hot pressing of the bulk fibres. In alternative embodiments, the cellulosic fibres may be compacted by hand, for example by stuffing the fibres into the liquid-permeable exterior lining and hand- compacting until as much air as possible is forced from the lining.

Examples

[00105] The present invention is further described below by reference to the following non-limiting examples.

Example 1 - Moisture absorption - Desiccant use

[00106] The use of short, randomly oriented, non-twisted jute fibres as a desiccant was examined over a 144 hour (6 day) period compared to commercial silica gel beads. The jute fibres (about 2.78 g) and the beads (about 2.78 g) were placed in separate non- woven polypropylene tea bags and exposed to ambient conditions for 24 hours, followed by moist air conditions for 144 h. The results are shown in Table 2 below, and in Figure 7. It can be seen that the jute fibres are far superior desiccants compared to the silica gel beads in a moist environment.

Table 2

Example 2 - Water immersion test of a block product made from jute fibres

[00107] Short, randomly oriented, non-twisted jute fibres obtained from recycled woven jute hessian fibre by mechanical fibrillation with a knife mill having a metal screen aperture of about 1 mm were prepared. The fibres were hot-pressed in a steel die under the following conditions: 190 °C, 30 minutes, 50 bar pressure, so as to provide panels. A block was prepared from seven panels, the block having the following dimensions: 50 mm x 50 mm x 50 mm, and a weight of about 52 g (see Figure 8). The block was wrapped with a wire mesh (F = 0.05 mm) and subjected to a 5-minute water immersion test. The results are shown in Table 3.

Table 3

Example 3 - Water immersion test of a block product made from jute fibres with a liquid- permeable exterior lining made of cotton canvas

[00108] A block having the following dimensions: 100 mm x 100 mm x 100 mm, and a weight of about 61.5 g was prepared from seven hot-pressed panels prepared from short, randomly oriented, non-twisted jute fibres obtained from recycled jute hessian fabric prepared by mechanical fibrillation with a knife mill having a metal screen aperture of about 1 mm. The block was provided with a cotton canvas exterior lining together with meshed nylon on the outside of the lining (see Figure 9) and subjected to a 24-hour water immersion test. The results are shown in Table 4 and in Figure 10.

Table 4

[00109] Figure 10a shows the block 2 hours post-immersion and Figures 10b to 10d show the block 24 hours post-immersion. Note from figure 10c that no dripping occurs. In figure 10d, the cotton canvas exterior lining has been removed to reveal the water- soaked jute fibres.

Example 4 - Capillary test

[00110] A capillary test was conducted on a longitudinal section of a panel prepared from short, randomly oriented, non-twisted jute fibres and immersed into a glass jar for 2 hours in order to investigate water flow through the fibres in order to simulate a situation where the product is placed in shallow water. The results are shown in Table 5 and in Figure 11. Table 5

[00111] The initial dimension of the panel was 20 m x 100 mm x 5 mm. The results indicated that the water height rose 900% and that linear expansion occurred in all directions with an overall increase of 10% in length, 25% in width and 300% in thickness.

Example 5 - Freeze-thaw behaviour

[00112] The behaviour of short, randomly oriented, non-twisted jute fibres in frost conditions was examined using a freeze-thaw test which involved a low-temperature thermal stress cycle for 7 days under water saturation conditions. The experiment was performed in a domestic freezer.

[00113] A fibre sample was packed into a non-woven polypropylene tea bag having an initial mass of about 18 g. Dimensional and mass changes were measured. The results are shown below in Table 6. Table 6

[00114] SEM microstructural analysis of the fibre surface was also conducted so as to compare the frosted fibres with raw fibres, as well as the fibres obtained following the 24 hour immersion in Example 3 (see Figure 12).

[00115] The results indicate that the fibres are highly resilient with the original properties being preserved despite the stresses associated with the freeze-thaw cycles. The sample experienced a mass loss of 5.97% and a shrinkage of 6.7%.

Example 6 - Microbiology

[00116] The level of bacterial and fungal contamination was assessed using both culture-dependent and culture-independent methodology in a range of fibrillated jute samples as well as heat-treated panels made from the fibres. To assess bacterial contamination, PCR gel electrophoresis combined with image analysis of the PCR amplicon band was performed. The results obtained from both methods indicated that heat treatment reduced the initial number of viable microorganisms in the sample as well as their capacity for growth. See Table 7 below and Figure 13. Table 7

Example 1 - Water and oil absorption

[00117] The effect of fibre length, heat treatment/compression and bulk form on water absorption was assessed by comparing short, randomly oriented, non-twisted jute fibres, a hot-pressed pellet prepared from these fibres and a jute textile cutting. Three specimens per sample were prepared with similar initial weights of about 0.70 g. The samples were individually immersed in water for 24 hours (in 10 ml_ glass jars). An oil absorption test was also performed on three specimens of fine, raw and bulk fibres for a period of 4 hours. The samples were individually placed in petri dishes containing 5 ml_ of three different types of automotive oils and a water/oil emulsion under laboratory conditions.

[00118] The water absorption results indicated that the fibres outperform the hot pressed pellets and textile cutting by 84% and 63% respectively, with water absorption of 564% and an absorption rate of 0.28 mL/h confirming the superior behaviour of the fibres.

[00119] The oil absorption results indicated that the fibres absorbed all three substances indistinctively with a higher absorption percentage exhibited by the water/oil emulsion sample, thereby confirming the capacity of the fibres for simultaneous hydrophilic and oleophilic behaviour.

Example 8 - Assessment of water absorption service life using Fourier-transform infrared spectroscopy (FTIR)

[00120] FTIR analysis was performed on used short, randomly oriented, non-twisted jute fibres obtained from a block module that had undergone 22 absorption-desorption cycles with a view to comparing their water holding capacity with that of corresponding raw jute fibres. The FTIR spectra indicated only a minor decrease in -OH groups (which bind water molecules) for the used jute fibres as compared to the raw fibres, thereby confirming the ability of the used jute fibres to perform effectively in further water absorption cycles (see Figure 16).

Example 9 - Contamination and toxic element absorption

[00121] Inductively coupled plasma quantitative analysis revealed that jute fibres obtained from a block module that had undergone 22 absorption-desorption cycles in comparison to the corresponding raw fibres showed an increase in the concentration of elements such as Al, Ca, Fe, Si, and a decrease in the concentration of K, Na and Cl (see Table 8). These results confirm that the product may also be used to absorb pollutants.

Table 8

Example 10 - 72 hour water absorption jute pilot block

[00122] Water absorption behaviour was calculated for a product comprising short, randomly oriented, non-twisted jute fibres during a 72-hour immersion cycle. Most of the water was absorbed in the first 2 hours with an absorption rate of about 0.1 L/min (see Figure 17). [00123] Although the invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.