Polysaccharide aerogel

Abstract

A polysaccharide based aerogel comprising a network of polysaccharide fibers with pores therebetween, wherein the sizes of the pores are in the micrometer range.

Claims

1. A polysaccharide based aerogel comprising a network of polysaccharide fibers with pores therebetween, wherein the polysaccharide fibers are obtained from recycled cellulose fibers, the sizes of the pores are in the-range of 20 to 1000 m and the diameters of the polysaccharide fibers are in the range of 5 to 100 m, wherein said aerogel, free of pure cellulose fibers, is formed from recycled cellulose fibers in the presence of a sonication power of 1500 to 2000 W and has an oil absorption capacity of 18.4-24.4 g/g.

2. The aerogel of claim 1, wherein the pore sizes are in the range of 20 to 50 m, 50 to 1000 m, 30 to 250 m, or 40 to 200 m.

3. The aerogel of claim 1, wherein the diameters of the polysaccharide fibers are in the range of 8 to 50 m.

4. The aerogel of claim 1, wherein said aerogel has a porosity in the range of 94% to 98%.

5. The aerogel of claim 1, wherein the thermal conductivity of said aerogel is in the range of 0.02 to 0.04 Wm.sup.1K.sup.1.

6. The aerogel of claim 1, wherein said aerogel is coated with a hydrophobic agent.

7. The aerogel of claim 1, wherein said polysaccharide fibers are functionalized with a silane compound.

8. The aerogel of claim 7, wherein said silane compound comprises at least one functional group selected from the group consisting of alkenyl, alkyl, alkoxy, benzyl, acryloxy, amino, ureide, sulfide, isocyanurate, mercapto and isocyanate.

9. The aerogel of claim 1, wherein said recycled cellulose fibers are selected from the group consisting of lignin, hemicellulose, chitin, arabinoxylan and pectin.

10. The aerogel of claim 1, wherein said polysaccharide fibers are bonded to each other via hydrogen bonding.

11. A reusable absorbent comprising the polysaccharide based aerogel of claim 1.

12. The absorbent of claim 11, wherein the absorbance capacity of said absorbent for a liquid is up to 25 times the weight of said absorbent.

13. A method for forming a polysaccharide based aerogel of claim 1, the method comprising the steps of: a) dissolving polysaccharide fibers from recycled cellulose fibers in a polysaccharide solvent in the presence of a sonication power of 1500 to 2000 W to form a polysaccharide dispersion; and b) forming said polysaccharide dispersion into said aerogel.

14. The method of claim 13, wherein step b) comprises the steps of: c) forming said polysaccharide dispersion into a gel; and d) drying said polysaccharide gel to form said aerogel.

15. The method of claim 14, wherein said drying step d) comprises freeze-drying or supercritical drying.

16. The method of claim 13, wherein said polysaccharide solvent is an aqueous solution of alkali with urea or thiourea.

17. The method of claim 13, further comprising the step of e) coating said aerogel with a hydrophobic agent to form a hydrophobic polysaccharide based aerogel.

18. The method of claim 17, wherein said coating step comprises spraying said hydrophobic agent.

19. The method of claim 17, wherein said coating step comprises the step of applying said hydrophobic agent by gas phase chemical vapour deposition.

20. The method of claim 17, further comprising the step of removing excess hydrophobic agent from said coated hydrophobic aerogel.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1(a) is a photographic image of recycled cellulose fibers obtained from waste paper. FIG. 1(b) is a photographic image of recycled cellulose aerogel made in accordance with Example 1. FIG. 1(c) is a field-emission scanning electron microscopic image at a scale bar of 500 m of the internal structure of the recycled cellulose aerogel.

(3) FIG. 2(a) is a photographic image showing the experimental set-up of the water absorption test. FIG. 2(b) is a photographic image of the dry aerogel sample before the test. FIG. 2(c) is a photographic image of the wet sample after the first absorption test. FIG. 2(d) is a photographic image of the squeezed sample after the first test. FIG. 2(e) is a photographic image of the squeezed sample in water after the first absorption test (that is, the second water absorption test). FIG. 2(f) is a photographic image of the wet sample after the second absorption test.

(4) FIG. 3(a) is a photographic image of a bent aerogel showing the flexibility of the aerogel. FIG. 3(b) is a photographic image of the experimental set-up of the mechanical strength test in which a load of 200 g was applied to the aerogel. FIG. 3(c) is the tensile curve of the aerogel. FIG. 3(d) is the compressive curve of the aerogel.

(5) FIG. 4(a) is a photographic image of the experimental set-up of the thermal conductivity test. FIG. 4(b) is a curve showing the thermogravimetric analysis of the recycled cellulose aerogel.

(6) FIG. 5(a) is a scanning electron microscopic (SEM) image at a scale bar of 500 m showing a cellulose aerogel coated with a commercial water repellent agent. FIG. 5(b) is a SEM image at a scale bar of 250 m showing a cellulose aerogel coated with methytrimethoxysilane (MTMS). FIG. 5(c) is an image showing the water contact angle measurement of the sample of FIG. 5(a). FIG. 5(d) is an image showing the water contact angle measurement of the sample of FIG. 5(b). FIG. 5(e) is an image showing the water contact angle measurement of the sample of FIG. 5(d), when cut open. FIG. 5(f) is a graph showing the effect of exposure time on the average water contact angle.

(7) FIG. 6(a) is a photographic image showing the experimental set-up of an oil absorption test using MTMS-coated recycled cellulose aerogel in Oil (1). FIG. 6(b) is a photographic image of the aerogel of FIG. 6(a) after the oil absorption test. FIG. 6(c) is a photographic image showing the experimental set-up of an oil absorption test using MTMS-coated recycled cellulose aerogel in Oil (2). FIG. 6(d) is a photographic image of the aerogel of FIG. 6(c) after the oil absorption test.

(8) FIG. 7(a) is a photographic image of the top view of a MTMS-coated recycled cellulose aerogel immediately upon contact with an oil (time=0). FIG. 7(b) is a photographic image showing the aerogel immersed in the oil of FIG. 7(a) at a time period of 1 minute. FIG. 7(c) is a photographic image showing the aerogel immersed in the oil of FIG. 7(a) at a time period of 3 minutes.

(9) FIG. 8 is a graph showing the absorption kinetics of the various oils on the coated aerogel.

(10) FIG. 9 is a graph showing the effect of temperature on oil absorption capability of a MTMS-coated recycled cellulose aerogel and on the viscosity of Oil (3).

(11) FIG. 10(a) is a photographic image showing a MTMS-coated recycled cellulose aerogel before the first oil absorption test. FIG. 10(b) is a photographic image of the cellulose aerogel of FIG. 10(a) but after the first absorption test. FIG. 10(c) is a photographic image showing the squeezing of the cellulose aerogel of FIG. 10(b). FIG. 10(d) is a photographic image of the squeezed cellulose aerogel of FIG. 10(c). FIG. 10(e) is a photographic image of the showing the flexibility of the squeezed cellulose aerogel of FIG. 10(c).

(12) FIG. 11(a) is a graph showing the effect of sorption cycles on the oil absorption capacity and sample volume of the aerogel. FIG. 11(b) is a graph showing the effect of sorption cycles on the squeezed ratio of absorbed oil.

(13) FIG. 12(a) is a photographic image of the top view of the water sample before the addition of Oil (3). FIG. 12(b) is a photographic image of the top view of the mixture of water and oil. FIG. 12(c) is a photographic image of the top view of the MTMS-coated cellulose aerogel when placed in the mixture of FIG. 12(b). FIG. 12(d) is a photographic image of the top view of the aerogel absorbing the oil from the mixture of water and oil at a time duration of 1 minute. FIG. 12(e) is a photographic image of the top view of the aerogel at a time duration of 3 minutes. FIG. 12(f) is a photographic image of the tope view of the aerogel at a time duration of 4 minutes.

EXAMPLES

(14) Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Synthesis of Cellulose Aerogels

(15) The raw material used for the synthesis of cellulose aerogels was recycled cellulose fibers (see FIG. 1(a)) from paper waste. Recycled cellulose fibers were obtained from Insul-Dek Engineering Pte. Ltd. of Singapore. Recycled cellulose fibers (1.2 to 4 wt %) was dispersed in sodium hydroxide/urea solutions (1.5 to 3 wt % of NaOH with 10 to 20 wt % of urea, both chemicals obtained from Sigma-Aldrich of Missouri of the United States of America) by sonicating for 6 minutes. A probe sonicator was used for sonicating the mixture at a frequency of 20 to 25 kHz and at a power of 1800 W.

(16) After sonication, the solution was placed in a refrigerator at a temperature of 14 C. for more than 24 hours to allow gelation of the solution. After the solution has formed a gel, it is then thawed at room temperature (of about 25 C.) and then followed by immersing into ethanol (99%) which functions as a coagulation solvent for coagulation. In order to control the thickness of the aerogel, a beaker was used as a mold to control the thickness at 1 cm and a diameter of 3.5 cm.

(17) After coagulation, solvent exchange was carried out by immersing the gel in de-ionised water for 2 days. To dry the sample without destroying the structure, freeze drying was carried out. In this technique, the sample was frozen and the surrounding pressure was reduced to allow the frozen water in the sample to sublimate directly from the solid phase to the gas phase, which creates minimal force on the pore walls of the aerogel, thereby preventing the porous structure from collapsing. Here, the sample was frozen in a freezer at 18 C. for 12 hours. After this, freeze drying was carried out for 2 days with a ScanVac CoolSafe 95-15 Pro freeze dryer (from LaboGene of Denmark) to obtain the desired cellulose aerogel, as shown in FIG. 1(b). Referring to FIG. 1(b), a light and porous aerogel was formed after the freeze drying step. The aerogel may also be termed hereinafter as cellulose aerogel or recycled cellulose aerogel.

(18) Field-emission scanning electron microscopy (FE-SEM) was used to investigate the morphology of the cellulose aerogel prepared from recycled cellulose fibers. Here, the sample was kept in a dry cabinet prior to FE-SEM. The sample was then coated with a thin gold layer using sputtering. A Hitachi 54300 scanning electron microscope (from Hitachi of Japan) operated at kV was used to capture structural images of the cellulose aerogel. As seen in FIG. 1(c), the cellulose aerogel has an open porous network structure of uniform fibers (about 8 m wide), indicating that the recycled cellulose fibers successfully self-assembled via hydrogen bonding to form a three-dimensional (3D) porous network. The width of the recycled cellulose fibers is much larger than that of nanocellulose fibers (2 to 100 nm). From FIG. 1(c), it can be observed that the pore size of the pores in the cellulose aerogel is in the range of 40 to 200 m, indicating the porous property of the cellulose aerogel. It is to be noted that aerogels formed using nanocellulose fibers are nanoporous, rather than having micron-sized pores.

(19) The cellulose aerogel has a density of 0.078 g/cm.sup.3 calculated from the weight (0.9690 g) and volume (12475 mm.sup.3) of the cellulose aerogel (please refer to Table 1 below). With a cellulose fiber density of 1.5 g/cm.sup.3, the porosity of the cellulose aerogel sample is 94.8%. This value is lower than that of cellulose aerogels made from nanocellulose fibers, probably due to the micron-sized porous structure of the recycled cellulose aerogel compared to the nanoporous network of the nanocellulose aerogel.

Example 2

Water Absorption Capability

(20) To investigate the water absorption capability of the recycled cellulose aerogel, a water absorption test was performed for a cellulose aerogel sample synthesized from 2% recycled cellulose and 1.9% NaOH/13.76% urea using a home-made dip coater (FIG. 2(a)). The water absorption capability of the aerogel sample was investigated in de-ionized (DI) water using a modified ASTM D570-98. The dry sample dimensions were 38 mm (diameter)11 mm (thickness). The dry sample was weighed and immersed in 800 ml of DI water for a certain period of time. After the immersion, the wet sample was lifted up at a rate of 200 mm/min with the dip coater of FIG. 2(a). Excess water on the surface of the sample was removed with filter paper.

(21) The wet sample was weighed, the dimensions measured, squeezed and weighed again. The test was repeated three times with an immersion time of 2 hours. The size and weight of the sample were measured before and after each test.

(22) FIG. 2(b) shows the dry cellulose aerogel sample before the test while FIG. 2(c) shows the wet sample after the first absorption test. After the first absorption test, it can be seen that there is only a small change in the size of the aerogel sample (comparing FIG. 2(b) and FIG. 2(c)). This is confirmed by the data in Table 1. The ratio of the volume of the sample before and after the first test is only 1.2. However, the sample can hold a large amount of water, up to 7.4 times of its dry weight. It can be seen that the shape of the sample is still preserved after being immersed in water for 2 hours although no cross-linkers were used in the synthesis of the aerogel, indicating that the material has a stable structure due to the cellulose-cellulose hydrogen bonding. The absorbed water remained very well inside the cellulose aerogel without dripping and if not squeezed, the water naturally evaporates from the aerogel under atmospheric conditions in 7 days. As compared to conventional superabsorbent polymers where absorbed water can only be removed by drying, it is easy to remove absorbed water from the recycled cellulose aerogel by squeezing (FIG. 2(d)). This advantage facilitates the reusability of the absorbent aerogel. Assuming that the squeezed sample has a spherical shape, it is observed that its volume is approximately that of the original sample. From the weights of the dry, wet and squeezed samples (Table 1), it is found that most of the absorbed water was removed (m.sub.r=0.998) after a simple squeezing of the wet sample.

(23) The squeezed aerogel sample was then placed back into water for a second water absorption test (FIG. 2(e)). After half a minute, the squeezed sample nearly recovered its original round shape. This fact demonstrates the fast shape recovery characteristic of the recycled cellulose aerogel. The wet sample was taken out after 2 hours, weighed and the dimensions measured. As shown in FIG. 2(f), the sample shrank compared to the original one (FIG. 2(b)). It is possible that there was a partial collapse of the micron-sized pores of the aerogel during squeezing. This is confirmed by the data in Table 1. The volume ratio of the wet sample after the second water absorption test and the original dry sample is only 0.42. The wet sample was then squeezed again. In the second test, the sample can only absorb a water amount of 3.8 times of its dry weight due to the shrinkage of the porous structure. It is also easy to remove most of the absorbed water this time with a m.sub.r value of 0.998 (Table 1).

(24) The third water absorption test was then carried out. The volume of the wet sample after the third test was similar to that of the wet sample after the second test (Table 1) indicating that no more shrinkage was created in the structure of the aerogel. As a result, the absorbed water amount in the third time was almost the same of that in the second time. A m.sub.r value of 0.999 of the third water absorption test again indicated that nearly all the absorbed water was eliminated after a simple squeezing.

(25) Similar water absorption tests were performed for other aerogel samples synthesized by changing synthesis parameter values as stated in Example 1. The highest water uptake content of 20 g/g was achieved with the cellulose aerogel produced from 2% cellulose and 1.9% NaOH/10% urea. This water absorption capability is comparable to those of commercial water sorbents.

(26) TABLE-US-00001 TABLE 1 Data obtained from the water absorption test of Example 2 d.sub.d, t.sub.d, d.sub.w, t.sub.w, d.sub.s, v.sub.d, v.sub.w, v.sub.s, m.sub.d, g m.sub.w, g m.sub.s, g m.sub.u m.sub.r mm mm mm mm mm mm.sup.3 mm.sup.3 mm.sup.3 r.sub.v1 r.sub.v2 1.sup.st 0.9690 8.1315 0.9840 7.4 0.998 38 11 40 12 23 12475 15080 4247 1.20 0.34 absorption 2.sup.nd 4.6447 0.9765 3.8 0.998 31 7 21 5283 3232 0.42 0.26 absorption 3.sup.rd 4.8530 0.9712 4.0 0.999 30.5 7 21 5114 3232 0.41 0.26 absorption m.sub.d: weight of dry sample; m.sub.w: weight of wet sample; m.sub.s: weight of squeezed sample; m.sub.u: water uptake content; m.sub.r: water content removed after squeezing; d.sub.d: diameter of dry sample; t.sub.d: thickness of dry sample; d.sub.w: diameter of wet sample; t.sub.w: thickness of wet sample; d.sub.s: diameter of squeezed sample; v.sub.d: volume of dry sample; v.sub.w: volume of wet sample; v.sub.s: volume of squeezed sample; r.sub.v1: volume ratio v.sub.w/v.sub.d; r.sub.v2: volume ratio v.sub.s/v.sub.d

Example 3

Flexibility of Cellulose Aerogel

(27) To investigate the flexibility of the recycled cellulose aerogel, a test was performed on a cellulose aerogel sample synthesized from 1.2 wt % recycled cellulose fibers and 1.5 wt % NaOH/10 wt % urea, sonicated for 6 minutes. As shown in FIG. 3(a), the cellulose aerogel can be easily and repeatedly bent 180 degrees without damaging the shape of the sample.

(28) A qualitative test was performed for the cellulose aerogel sample to investigate its mechanical strength by loading a 200 g weight on the sample (FIG. 3(b)). It can be seen that the aerogel did not change its shape under the heavy loading.

(29) For further understanding of the mechanical property of the cellulose aerogel, tensile and compression tests were performed with an Instron 5500 microtester (from Instron of Massachusetts of the United States of America) and the results are shown in FIG. 3(c) and FIG. 3(d). The size of the cellulose aerogel sample was 38 mm (diameter) by 11 mm (thickness). The sample was compressed at a rate of 1 mm/min.

(30) From FIG. 3(c), it can be seen that the yield strength and tensile strength of the aerogel are about 1080 N/m.sup.2 and 1470 N/m.sup.2, respectively, with a Young's modulus of 11 kPa.

Example 4

Thermal Studies

(31) To investigate the thermal insulation ability of the recycled cellulose aerogel, a thermal conductivity measurement was carried out at room temperature with a C-Therm TCi Thermal Conductivity Analyser System (FIG. 4(a)) (from C-Therm Technologies Ltd of Canada) on a cellulose aerogel sample synthesized from 1.2 wt % recycled cellulose fibers and 1.5 wt % NaOH/10 wt % urea, sonicated for 6 minutes. The sensor of the equipment was placed on a stable and flat table with the sensor head facing upwards. The sample was placed directly on the top of the sensor with a loaded weight to ensure a good surface contact between the sample and the sensor. The measured thermal conductivity of the cellulose aerogel sample was 0.032 Wm.sup.1K.sup.1, which is comparable to those of good insulation materials such as silica aerogel (0.026 Wm.sup.1K.sup.1) and wool (0.03 to 0.04 Wm.sup.1K.sup.1). This low thermal conductivity value and the low cost of paper waste make the recycled cellulose aerogel promising for thermal insulation applications.

(32) To evaluate the thermal stability of the cellulose aerogel, a thermogravimetric analysis (TGA) test was performed for the sample in air. A Shimadzu DTG60H (from Shimadzu Corporation of Japan) was used to determine the weight loss in relation to the temperature. The sample was heated up to 150 C. for 1 hour to ensure that the adsorbed water in specimen was removed. The specimen was then heated to 1000 C. at a rate of 5 C./min in air. Referring to FIG. 4(b), it can be seen that there was a weight loss of about 23% in the temperature range of 25 to 230 C. due to the removal of absorbed water and some traces of urea left in the sample. A weight loss of 42% can be seen in the range of 230 to 330 C. due to the degradation and burning of the cellulose aerogel structure. There was a small drop in the weight of the sample in the range of 550 to 630 C. possibly due to the oxidation of some stable local structures of the aerogel.

Example 5

Hydrophobic Cellulose Aerogel

(33) Cellulose aerogels synthesized from the method of Example 1 were used to develop hydrophobic recycled cellulose aerogels. Here, the cellulose aerogels were synthesized from 1.2 wt % recycled cellulose fibers and 1.5 wt % NaOH/10 wt % urea, sonicated for 6 minutes

(34) For water repellent coating, two different coating methodsphysical and chemical, were used. In the physical coating method, a commercial water repellent spray (ReviveX Nubuck, obtained from Gear Aid of McNett Corporation of Washington of the United States of America) was used to spray the dried aerogel from a. distance of 15 cm and then left to dry for one day at room temperature. As shown in FIG. 5(a), the surface of the aerogel was covered by the water repellent polymer and all the pores on the surface (but not within the structure) were fully covered.

(35) In the second methodthe chemical method (chemical vapor deposition method), a recycled cellulose aerogel sample was placed in a big glass bottle. A small open glass vial containing methyltrimethoxysilane (MTMS) was added into the glass bottle. The glass bottle was then capped and heated in an oven at 70 C. for 2 hours for the silanation reaction. After that, the coated sample was placed in a vacuum oven to remove the excess coating reagent until the pressure reaches 0.03 mbar. As shown in FIG. 5(b), in contrast to FIG. 5(a), the MTMS-functionalized sample still had a porous structure.

(36) After being coated with MTMS, the MTMS-coated aerogel shows a thermal conductivity value of 0.029 Wm.sup.1K.sup.1, which is lower than the thermal conductivity of the uncoated sample (0.032 Wm.sup.1K.sup.1), indicating an improvement in the thermal insulation property due to the MTMS coating.

(37) Water contact angle measurements were performed for the original uncoated sample and the coated samples. Here, a VCA Optima goniometer (from AST Products Inc. of Massachusetts of the United States of America) was used to investigate the water repellency of the uncoated and coated samples. Water was dispensed, drop by drop, using the syringe control of the machine. This was repeated at different positions of the sample and an average was taken. The test was also carried out for coated samples that were left in the atmosphere for several days. For the uncoated sample, water was easily absorbed by the aerogel due to the hydrophilic nature of cellulose. As can be seen in FIG. 5(c), the physically-coated sample had a water contact angle of 130.7, which was smaller than that of the chemically-coated sample, which had a water contact angle of 145 (FIG. 5(d)). This indicated that the MTMS coating was more water-repellent than the coating with the commercial agent. To ensure that the internal surface of the pores were fully coated with MTMS, the sample was cut into two pieces and a water contact angle of 143 was obtained on the cut surface of the sample (FIG. 5(e)), proving that substantially the entire porous structure was hydrophobic.

(38) The samples were then exposed in air and sunlight for several days and their water contact angles were measured during the exposure time (FIG. 5(f)). It can be seen that both samples showed little changes in water contact angle, indicating their excellent water-repellent durability.

Example 6

Oil Absorption Test

(39) The chemically-coated hydrophobic sample from Example 5 was used to test the affinity to oil. When the material was coated with MTMS, it will become hydrophobic and oleophilic and therefore, has a good affinity to oil. The MTMS-coated recycled cellulose aerogel was used for the oil absorption test based on a modified ASTM F726-06. The oil absorption test was similar to the water absorption test except that 300 ml of oil was used and that the excess oil was allowed to drain for 30 seconds to 1 minute after lifting up the wet sample. The wet sample was weighed, the dimensions measured, squeezed by hand and weighed again. The test was repeated several times for a total of 5 cycles.

(40) Five types of oils were used for the absorption test: (1) a motor oil, (2) cooking oil, (3) Ruby (RB), (4) Te Giac Trang (TGT) and (5) Rang Dong (RD). The specifications of these oils are shown in Table 2. Oils (1) and (2) were purchased commercially while oils (3) to (5) were supplied from Petrovietnam Research and Development Center for Petroleum Processing (PVPro).

(41) TABLE-US-00002 TABLE 2 Specifications of Oil Samples Density at 25 C., Viscosity, Pa .Math. s Oil g/cm.sup.3 10 C. 25 C. 40 C. 60 C. (1) n/a n/a 0.13 n/a n/a (2) n/a n/a 0.06 n/a n/a (3) 0.8236 42 0.0090 0.0049 0.0027 (4) 0.8264 n/a 0.0088 n/a n/a (5) 0.8153 n/a 0.0062 n/a n/a

(42) Crude oil absorption capacity was calculated using the following formula:

(43) $\begin{array}{cc}{Q}_t=\frac{m_{w-m_d}}{m_d}& \left(1\right)\end{array}$
where Q.sub.t (g/g) is the crude oil absorption capacity of the aerogel at a certain time t (min)

(44) m.sub.w (g) is the weight of the aerogel after absorption

(45) m.sub.d (g) is the weight of the aerogel before absorption

(46) The ratio of the sample volume before absorption test and its original volume (V.sub.n) was calculated as below:

(47) $\begin{array}{cc}{V}_n=\frac{V_d}{V_i}& \left(2\right)\end{array}$
where V.sub.d (mm.sup.3) is the volume the sample before absorption test

(48) V.sub.i (mm.sup.3) is the original volume of the sample

(49) The squeezed ratio of crude oil (Q.sub.s) was calculated using equation (3):

(50) $\begin{array}{cc}{Q}_s=\frac{\mathrm{Squeezed}\mathrm{amount}\mathrm{of}\mathrm{oil}}{\mathrm{Absorbed}\mathrm{amount}\mathrm{of}\mathrm{oil}}=\frac{m_w-m_s}{m_w-m_d}& \left(3\right)\end{array}$
where m.sub.s (g) is the weight of the aerogel after squeezing.

(51) The MTMS-coated aerogels were first investigated using Oils (1) and (2). Referring to FIG. 6(a) and FIG. 6(c), these figures show the aerogel samples being dipped into Oil (1) and Oil (2), respectively using a dip coater. FIG. 6(b) and FIG. 6(d) then show the aerogels after the oil absorption test using Oil (1) and Oil (2) respectively. It was determined that the MTMS-coated aerogels show strong affinities to both Oils (1) and (2) with high oil absorption capacities of 18 and 17.6 g/g, respectively.

(52) The MTMS-coated aerogels were then investigated using Oils (3) to (5). FIG. 7(a) to FIG. 7(c) is a succession of photographs showing the sorption process based on Oil (3) from the start (FIG. 7(a)) to 1 minute (FIG. 7(b)) to 3 minutes (FIG. 7(c)). It was seen that the aerogel easily absorbed crude oil and completely immersed into the oil after about 3 minutes indicating the high crude oil affinity of the aerogel as an oil absorbent.

(53) The sorption kinetics of the Oils (3) to (5) on the aerogel are shown in FIG. 8. The absorption rates are very high at the first stage and saturation is achieved after about 20 minutes. The maximum absorption capacities (calculated by Equation 1) of Oil (3), Oil (4) and Oil (5) on the aerogel are 18.4, 18.5 and 20.5 g/g, respectively. These values are nearly double those obtained with polypropylene fibrous mats which are widely used as absorbents for crude oil spill cleaning. The highest absorption capacity value is found for Oil (5) while the aerogel shows similar oil absorption behavior for Oil (3) and Oil (4). This is probably due to the fact that Oil (5) possesses the lowest viscosity while Oils (3) and (4) have comparable viscosity values (Table 2).

(54) It appears that the oil viscosity plays a main role in the absorption capacities of Oils (3) to (5). A lower viscosity may facilitate the penetration of the oil into the porous network of the aerogel and thus, results in a higher oil absorption capacity.

(55) An investigation into the effects of temperature on the crude oil absorption capability of the MTMS-coated recycled cellulose aerogel was examined with Oil (3) at 10, 25, 40 and 60 C. As shown in FIG. 9, the oil absorption capacity increases from 13.9 to 18.4 g/g when increasing temperature from 10 to 25 C., achieving the highest value of 24.4 g/g at 40 C., which decreases to 19.9 g/g when the temperature increases to 60 C. This can be explained based on the change of oil viscosity with temperature, as displayed in FIG. 9 and Table 2. At 10 C., the oil forms a gel with a high viscosity value of 42 Pa.Math.s. This high viscosity inhibits the diffusion of the oil into the pores of the aerogel, leading to a low absorption capacity. When the testing temperature was increased to 25, 40 and 60 C., the viscosity of the crude oil decreased from 42 to 0.0090, 0.0049 and 0.0027 Pa.Math.s. The reduction in the viscosity allowed the oil to diffuse into the porous matrix of the aerogel faster and more easily. However, the large decrease of the oil viscosity at 60 C. may have resulted in a low adherence of the oil to the pore walls and as a consequence, more oil was drained out during the drainage step. The maximum oil absorption capacity was achieved at 40 C., at which the low oil viscosity value facilitated the penetration of the crude oil into the pores and was also high enough for the retention of oil in the structure of the aerogel.

(56) The effect of test cycles of sorption on the oil absorption capacity of the aerogel was investigated. FIG. 10(a) and FIG. 10(b) show photographic images of the aerogel sample before and after the first oil absorption test cycle. From FIG. 10(a), it can be seen that the diameter of the aerogel sample was 45.0 mm before the oil absorption test while from FIG. 10(b), the diameter of the aerogel sample was 45.2 mm after the oil absorption test. It can be seen that the size of the sample was nearly unchanged after absorbing oil. This was confirmed by a volume ratio of 1.05 found for the aerogel. To remove the absorbed oil, a simple squeezing was performed (FIG. 10(c)). FIG. 10(d) and FIG. 10(e) show the aerogel after squeezing and the good flexibility of the aerogel, respectively. The squeezed aerogel was then used for the next absorption test cycle.

(57) The oil absorption capacities of the aerogel after five sorption cycles are displayed in FIG. 11(a). The sample achieved a high absorption capacity of 18.4 g/g in cycle 1. However, the capacity dropped to 0.96, 0.68, 0.59 and 0.63 g/g in cycles 2, 3, 4 and 5, respectively. This phenomenon can be explained based on the change of the aerogel volume (calculated by Equation 2), as shown in FIG. 11(a). After cycle 1, the aerogel was squeezed to remove the absorbed oil and the squeezed aerogel was used for cycle 2. After this squeezing, the ratio of the volume of the squeezed aerogel and its original volume was 0.32 indicating that the porous structure of the aerogel had largely collapsed. As a result, the oil absorption capacity of the aerogel sharply decreased to 0.96 g/g in cycle 2. In later cycles, the volume ratio values (0.27, 0.23 and 0.29) were similar to the value after the first cycle implying that the aerogel structure did not change anymore. Regarding the squeezed amount of the absorbed oil (calculated by Equation 3), as presented in FIG. 11(b), 81.5, 98.5, 95.9, 96.9 and 96.4% of the absorbed oil were released after cycles 1, 2, 3, 4, and 5, respectively, by using simple squeezing.

(58) FIG. 12(a) to FIG. 12(f) are a succession of photographs showing the crude oil absorption test of the aerogel in a mixture of Oil (3) and DI water (40 ml water/5 ml of Oil (3)). FIG. 12(a) is a photograph of the DI water used at the beginning. Oil (3) was then added to the water, which formed as a dark layer on the water surface (FIG. 12(b)). In FIG. 12(c), the aerogel was added to the mixture and it can be observed that the hydrophobic aerogel floated on the mixture and rapidly absorbed Oil (3). FIG. 12(d) and FIG. 12(e) show the absorption of the oil by the aerogel after 1 minute and 3 minutes respectively. After about 4 minutes, most of the oil (99.4%) was absorbed by the hydrophobic aerogel (FIG. 12(f)). The test indicated that the MTMS-coated aerogel is promising for crude oil spill cleaning application.

Comparative Example

Synthesis of Aerogel from Pure Cellulose Fibers

(59) Pure cellulose fibers (1.2 wt %, obtained from Sigma-Aldrich) were dispersed in sodium hydroxide/urea solutions (1.5 wt % of NaOH with 10 wt % of urea) by stirring for 15 minutes. The solution was placed in a refrigerator for more than 24 hours to allow gelation of the solution. The gel was then thawed at room temperature (of about 25 C.) and then followed by immersing into ethanol (99%) for coagulation. In order to control the thickness of the aerogel, a beaker was used as a mold to control the thickness at 1 cm and a diameter of 3.5 cm. After coagulation, solvent exchange was carried out by immersing the gel in de-ionised water for 2 days. To dry the sample without destroying the structure, freeze drying was carried out. The sample was frozen in a freezer at 18 C. for 12 hours. After this, freeze drying was carried out for 2 days with a ScanVac CoolSafe 95-15 Pro freeze dryer to obtain the desired cellulose aerogel.

(60) The cellulose aerogel synthesized from pure cellulose fibers had pores that were in the nanosized range. In addition, the diameter of the pure cellulose fibers was in the range of 5 to 20 nm, with length of up to several micrometer.

(61) The pure cellulose aerogel was subjected to a flexibility test and it was found that the aerogel was not flexible and was brittle. The sample broke easily after the test.

(62) In addition, the pure cellulose aerogel was subjected to the same oil absorption test as mentioned in Example 6 and it was found that the oil absorption capacity of this aerogel was 10 g/g.

(63) Hence, as compared to cellulose aerogels synthesized from recycled cellulose fibers, the pure cellulose aerogel had a lower oil absorption capacity (which is most probably due to the smaller pores in the aerogel) and was inflexible.

Applications

(64) The process to form the polysaccharide based aerogel from recycled polysaccharide fibers may be cost effective and simple.

(65) By using recycled polysaccharide fibers such as recycled cellulose fibers, conventional methods of synthesizing cellulose fibers from bioengineering processes or from wood powders are not required, which are usually complicated, expensive or requires the use of toxic and environmental-polluting chemicals such as benzene to remove wax or lignin from wood powders. Hence, the use of recycled cellulose fibers from recyclable material is environmental friendly and may reduce carbon footprint.

(66) Due to the thermal insulation properties of the polysaccharide based aerogel, it may be used in thermal and acoustic insulation industries. If the polysaccharide based aerogel is coated with a hydrophobic agent, the coated polysaccharide based aerogel may possess self-cleaning properties and may be used a surface to confer both insulating and cleaning effects. In addition, the hydrophobic property of the polysaccharide based aerogel may protect the surface from moisture attack. Hence, the polysaccharide based aerogel may be applied onto the exterior wall of a building or a vehicle, or as an insulating layer in a piece of clothing.

(67) The ability of the polysaccharide based aerogel to absorb a polar liquid such as water or an aqueous solution allows the polysaccharide based aerogel to be used in applications where high absorption capacities are required. For example, the polysaccharide based aerogel may be used as an absorbent in diapers, sanitary napkins, etc.

(68) The hydrophobic polysaccharide based aerogel may be used in oil remediation or in applications where hydrophobicity is required.

(69) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.