TWI769089B - Modified cotton fabric used for oil-water separation and manufacturing method thereof - Google Patents

Abstract

The wettability of the surface of hydrophilic cotton fabrics were modified using one-step protocol with tannic acid (TA) to provide its excess catechol groups to be grafted with 1-eicosanamine. The grafting reactions were performed at pH 8.5 and room temperature with catalysts CuSO₄/H₂O₂. The chemical analysis highlighted the success of modification over the synthesis conditions while the contact angles of water and diiodomethane droplets ranged 132.68±0.49° to 143.95±0.80° and 100.08°±1.42° to 82.96±1.38°, respectivelv. The corresponding dispersive of the so-yielded cotton surface ranged 8.6 to 16.0 mJ/m², and the polar components ranged 0.08 to 2.7 mJ/m², much lower than the fluoroalkane, such as polytetrafluoroethylene. Restated, the modified cotton fabrics are omniphobic that can repel both water and commercial oil products. The absorption tests revealed that the modified cotton fabrics absorbed 1.10 g hexane/g cotton by contacting hexane (top)-water (bottom) layers and absorbed 1.26 g hexane/g cotton by contacting water first for 30 s then hexane for another 30 s. The modified fabrics reveal satisfactory absorption reusability as hexane absorbent. Parametric study revealed that the hydrophobicity of the surface would be enhanced by the added catalysts and prolonged reaction time.

Description

Modified cotton fabric for oil-water separation and its manufacturing method

The invention relates to a surface modification technology, in particular to a method for improving the surface hydrophobicity of cotton fabrics to be applied to oil-water separation and a product thereof.

Surface modification protocols have been widely used to convert hydrophilic surfaces to hydrophobic surfaces, for example, coating _TiO2 onto melamine sponges or grafting fluoroalkylsilanes onto balsa sponges. The modified surface has a high affinity for oil compounds and is therefore proposed for oil/water separation. Cellulose is the most abundant natural biopolymer with surface modification for adsorption applications. Excessive hydroxyl groups exist on the cellulose surface, which is the origin of the surface hydrophilicity. Modification schemes including dip coating, spray coating, and reactions involving complex chemical networks have been proposed in the past.

In the past, there have been precedents for the preparation of highly stable superhydrophobic cotton fabrics by in-situ cross-linking reactions. The triggering step therein requires high energy input, such as the application of UV light, creating a cost-limiting step for modification. In addition to cost concerns, there are requirements for the use of environmentally sound chemicals and modification processes, including post-use treatment. For example, fluorine-containing chemicals should be avoided during modification because the halogen-rich residues of cotton after use can adversely affect environmental quality.

Cotton fabrics can be converted into hydrophobic fabrics by doping nanoparticles or grafted polymers, fluoroalkylsilanes and alkylsilanes. 3,4-Dihydroxyphenethylamine is a hormone with multiple functional groups that can be attached to various surfaces. It is worth noting that if the cotton surface is coated with 3,4-dihydroxyphenylethyl An amine, octadecylamine (ODA), can be easily grafted onto it, resulting in a superhydrophobic surface. The disadvantages of using this modification process are high raw material costs and relatively long polymerization times (up to several days). Tannic acid (TA) is an inexpensive natural polyphenol that can replace the use of 3,4-dihydroxyphenethylamine as a linker. However, the reaction time required for TA grafting is not short: 25 hours for TA/Fe/ODA composites and 36 hours for TA/APTES/ODA composites.

Therefore, in order to improve the shortcomings of the above-mentioned conventional technologies, the present invention provides a superhydrophobic surface modification solution for cotton fabrics that can reduce cost and environmental burden.

The main purpose of the present invention is to provide a method for producing novel cotton surfaces with TA dip coating and 1-eicosylamine grafting by Michael addition/Schiff base reaction. The catalyst CuSO ₄ /H ₂ O ₂ was used to accelerate the grafting reaction. Cotton fabrics modified by this one-pot modification scheme, called TA-ESA, can possess superhydrophobic surfaces with extremely strong oil absorption capacity.

The method for manufacturing a modified cotton fabric for oil-water separation provided by the present invention may specifically include the following steps: washing a cotton fabric and drying it; preparing a tannic acid solution; dissolving a specific concentration of 1-eicosylamine In ethanol and at room temperature, it is mixed with the pre-prepared tannic acid solution to form a mixed solution; and the cotton fabric is immersed in the mixed solution at room temperature, and the Michael addition/Schiff base reaction is carried out according to the prescribed reaction time.

In one embodiment, before the Michael addition/Schiff base reaction is performed, the pH of the mixed solution is adjusted to 8.5.

In one embodiment, the step of preparing the tannic acid solution further includes selectively adding a catalyst to accelerate the grafting reaction of 1-eicosylamine. _The step of adding the catalyst includes adding a tannic _acid solution containing _CuSO4 and H2O2 to a stirred water bath.

In one embodiment, the tannic acid solution contains 5 mM CuSO ₄ , 19.6 mM H ₂ O ₂ and 2 mg/L tannic acid.

In one embodiment, the reaction time for the Michael addition/Schiff base reaction is 10-60 minutes.

In one embodiment, the specific concentration of 1-eicosylamine is between 1-5 mg/ml.

In one embodiment, the method of washing cotton fabric includes immersing the cotton fabric in an ultrasonic water bath after washing with water and ethanol.

In one example, after the Michael addition/Schiff base reaction, the cotton fabric is washed with water and ethanol and then dried at 60°C.

The above description is only an overview of the technical solution of this creation, in order to be able to understand the technical means of this creation more clearly, it can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of this creation more clearly understandable , the following specific preferred embodiments are described in detail as follows.

Specific structural and functional details disclosed herein are merely representative and for purposes of describing exemplary embodiments of the present invention. However, the present invention may be embodied in many alternative forms and should not be construed as limited only to the embodiments set forth herein.

In the description of the present invention, it should be understood that the terms "center", "lateral", "top", "bottom", "left", "right", "vertical", "horizontal", "top", The orientations or positions indicated by "bottom", "inside", "outside", etc. are based on the orientations or positions shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that The device or component must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more. Additionally, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

In the description of the present invention, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the exemplary embodiments. As used herein, the singular forms "a", "an" and "an" are intended to include the plural unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and/or "comprising" as used herein specify the presence of stated features, integers, steps, operations, units and/or components, but do not preclude the presence or addition of one or more Other features, integers, steps, operations, units, components and/or combinations thereof.

The present invention provides a treatment method for fabricating a novel cotton surface with TA dip coating and 1-eicosylamine grafting by Michael addition/Schiff base reaction, with catalyst CuSO ₄ /H ₂ O ₂ for accelerating grafting reaction. Cotton fabrics modified by this one-pot modification scheme, called TA-ESA, can possess superhydrophobic surfaces with extremely strong oil absorption capacity.

Experimental Materials

Cotton fabrics used in the experiments were obtained from a local store in Taipei, Taiwan. 1-Eicosylamine, n-hexane, diiodomethane, copper sulfate and ethanol, tannic acid and DMSO, tris(base peak), and hydrogen peroxide in ethanol were obtained from Angene Chemical (Hong Kong), Fisher Scientific (Pittsburgh) , PA, USA), MilliporeSigma (Burlington, MA, USA), J.T. Baker (Radnor, PA, USA), and Honeywell (Charlotte, NC, USA).

After washing the cotton fabric several times with water and ethanol, it was immersed in an ultrasonic water bath for 30 minutes. The washed cotton fabric was dried at 60°C for 24 hours. _{2 mg} /L tannic acid with/without ₅ mM CuSO4/19.6 mM H2O2 was then added to the stirred water bath. Specific concentrations of 1-eicosylamine (1.035, 2.07 or 4.14 mg/ml) were dissolved in ethanol and mixed with a pre-prepared solution of tannin at room temperature, the pH of the solution was adjusted to 8.5 with Tris and HCl. Then, the cotton fabric was immersed in the above mixed solution at room temperature, and the reaction was carried out according to the prescribed reaction time (for example: 60 minutes). After the reaction, the cotton fabric was washed with water and ethanol, and then dried at 60°C.

Oil absorption test

Two testing protocols were used to characterize the ability to use modified cotton fabrics. It is worth noting that Test One was performed by placing the cotton fabric horizontally on the hexane layer above the bottom 5 cm water layer for 30 seconds.

Test two was to place the cotton fabric horizontally in the pool for 30 seconds; the fabric was then moved to the hexane pool for another 30 seconds.

The absorbent capacity of cotton fabrics is calculated as follows: absorbent capacity=(weight gain of absorbed fabric)/(weight of original fabric). The amount of water or hexane absorbed by the fabric is calculated based on the mass balance Yes, concentrations are measured using UV-Vis spectroscopy.

To check if the fabric could be reused, the adsorbed samples were manually squeezed to remove the water and oil involved and reused for adsorption testing.

The characteristics of cotton fabrics were investigated by electron microscope, and it was found that the surface of cotton fabrics before modification looked smooth, and the surface mainly had carbon and oxygen atoms. In contrast, TA-ESA modified cotton fabrics with 5 mM CuSO ₄ and 19.6 mM H ₂ O ₂ as catalysts with a reaction time of 60 min had rough surfaces. It can be found from the SEM images that the modified cotton fabric incorporates nitrogen atoms, corresponding to the amide groups grafted to the modified surface.

After comparing the sample FTIR spectra of virgin cotton fabric and TA-ESA, it can be found that the functional groups recognized by virgin cotton fabric correlate with FTIR peaks at 3250-3600/cm (-OH stretch), 2967/cm (-CH ₃ stretch) ), 2902/cm (-CH ₂ stretching), and 1704/cm (C=O stretching vibration). After modification, the peaks at 2967/cm and 2905/cm are enhanced, helping to demonstrate the presence of long-chain alkylamines in _-CH3 and _-CH2 . The increased intensity of the 1705/cm peak is attributed to the quinone structure of the tannins. The enhanced intensity of 1505/cm is attributed to the appearance of the Michael addition reaction.

The ¹ H NMR signal at 1.22 ppm was observed from the ¹ H NMR spectrum of the TA-ESA cotton fabric, which was attributed to the long chain alkyl compound of 1-eicosylamine. The signal at 1.43 ppm was assigned to hydrogen atoms after the Schiff base reaction. In addition, the signal at 3.24 ppm is the hydrogen atom on the following Michael addition reaction. The ¹ H NMR spectrum of the modified cotton fabric support shows the grafting reaction of two Schiff base reactions and Michael addition reactions.

In the XPS spectra of the solid samples, the area ratios of the C1s peaks are listed in Table 1.

The surface of the original cotton fabric has C1s peaks of CC, CO and C=O bonds, the first two are the main bond atoms of C. The cotton surface with the TA-ESA grafted layer has excess C-O and C=O bonds, which are characteristic of TA. The enriched C=N and C-N indicated the presence of amide groups in the modified surface.

On the N1s peaks at 399.1 eV and 401.3 eV corresponding to the C-N and C=N bonds, the area ratio between these two bonds is 76:24; it is particularly emphasized that the Schiff base reaction and the Michael addition reaction to TA Contribution is close to 3:1.

Table 2 shows the static contact angles of water droplets or CH2I2 on the surface of cotton fabrics.

The contact angles of water droplets on the surface of TA-ESA were 132.68±0.49°, 138.53±1.33° and 143.95±0.80°, respectively, and the initial concentrations of 1-eicosylamine were 1.035, 2.07 and 4.14 mg/mL, respectively. The corresponding contact angles of CH ₂ I ₂ droplets on the TA-ESA surface are 100.08±1.42°, 84.67±3.07° and 82.96±1.38°, respectively. Note that both the water and diiodomethane contact angles of the modified surface are larger than those obtained by the PTFE predecessor, which strongly repels water with negligible affinity for CH ₂ I ₂ .

In the oil absorption test, the test protocol described in the previous literature was performed to simulate different field conditions of oil absorption from the spill site. The test results are shown in Table 3. Water absorption and n-hexane in Test I were 0.17 ± 0.06 grams per gram cotton and 1.10 ± 0.12 grams per gram cotton, respectively. Note that when both water and oil are in contact with the TA-ESA cotton fabric, the oil competes with the water to invade the substrate.

Test II results shown in Table 3 show that the TA-ESA cotton fabric absorbs 0.63 ± 0.07 grams of water per gram of cotton when immersed in a water bath for 30 seconds. After that, the cotton fabric was able to absorb excess oil (1.26±0.06 grams per gram of cotton). These observations suggest that (1) the modified cotton fabric, although fully hydrophobic at the pore surface, can absorb water and oil into the matrix, which may be attributed to the capillary suction of the macropores in the matrix; (2) accommodate water and oil The macropores of the oil are located differently in the matrix (probably also reticulated), preferentially accommodating oil over water. To reiterate, in Test I, when the pores were occupied by hexane, no further water intrusion occurred. In contrast, in Test II, even though part of the matrix has been occupied by water, further oil intrusion, bypassing the water-filled pores, still occurs.

Pour test using a 50/50 water/diiodomethane mixture in a reusability test examining TA-ESA fabrics of 2.07 mg/ml ₁ - _eicosylamine and ₅ mM CuSO4/19.6 mM H2O2 , the initial separation efficiency and flux were 95±2% and 3029.2±456.5 (L/m ² -h), respectively. However, the flux for cycle 2 dropped rapidly to 543.9 ± 164.6 (L/m ² -h), which was due to irreversible clogging of the pores by invading water, corresponding to the breakdown of hydrophobicity. From cycle 3, the filtration flux is close to zero. In contrast, the modified fabrics had satisfactory oil/water separation reusability under Test II. After completing each absorption test cycle, the absorbed fabric was dried at 60°C for 10 minutes. Therefore, it is suggested that the modified fabrics of the present invention can be used as filter media for oil/water separation in place of absorbents used in the prior art.

The modified surface has long-chain alkylamines grafted with TA, corresponding to the low polarity components listed in Table 2. Considering the large tail presented by the amine groups, the corresponding surface energy dispersive components are relatively low. Due to the hydrophobic interaction, the stacking of adjacent alkyl groups may occur in the grafted 1-eicosylamine layer, which reduces the effective volume of the grafted layer and thus the dispersion contribution.

Catalysts can be used to accelerate the grafting reaction to effectively modify cotton fabrics. When observing the contact angle of cotton fabrics with and without catalyst in the experiments, it was found that in all cases, the addition of catalyst increased the contact angle by about 6°, but the catalytic activity was not significant. It is worth noting that CuSO ₄ /H ₂ O ₂ participates in the grafting reaction as a reactant rather than a reaction catalyst. Experiments show that the reaction of 0 by the method of the present invention is almost completed within 10 minutes, therefore, the TA-ESA system of the present invention exhibits an ultrafast reaction compared to the long reaction times reported in the literature. For the synthesis of hydrophobic surfaces, the current _synthesis protocol without _CuSO4 / _H2O2 is sufficient. If a surface with a water droplet contact angle >140° is required, CuSO ₄ /H ₂ O ₂ can be added.

_The experiments also show the time evolution of the contact angle for ₁₀ or 60 min of the TA _- ESA reaction with/without modification with CuSO4/H2O2. All surfaces exhibited a kind of surface relaxation, with the water contact angle decreasing over time. However, the catalysts containing _CuSO4 / _H2O2 had higher stability _than those without added catalysts. When 5 mM CiSO ₄ and 19.6 mM H ₂ O ₂ were reacted for 60 min, the TA-ESA surface consistently had a contact angle greater than 140° for waterproofing applications.

To sum up, using the TA-ESA cotton fabric provided by the present invention, its surface is modified by dip-coating TA, and 1-eicosylamine is grafted onto the cotton fabric through Michael addition/Schiff base reaction . Analysis including FTIR, ¹ H NMR and XPS spectroscopy confirmed the success of the surface modification. The fractions of surface energy were γ S ^d = 8.6 mJ/m ² and γ S ^p = 0.08 mJ/m ² at 1-eicosylamine at a concentration of 1.035 mg/mL, and γ S p = 0.08 mJ/m 2 at a concentration of 4.14 mg/mL of 1- The increase to γ S ^d = 16.0 mJ/m2 and γ S ^p = 2.7 mJ/m2 under eicosylamine, both lower than PTFE, indicating that the current modified surface is a fully hydrophobic surface. Due to the capillary suction of the macropores in the matrix, TA-ESA cotton fabric is a very effective oil absorbent for oil/water mixtures. Furthermore, the additives CuSO ₄ /H ₂ O ₂ in the present invention are not catalysts proposed in the literature to accelerate the grafting reaction; instead, they are involved in promoting the hydrophobicity of the surface and the stability of surface relaxation under water droplet swelling.

The above detailed description of the preferred embodiments is intended to describe the features and spirit of the present invention more clearly, rather than limiting the scope of the present invention by the preferred embodiments disclosed above. On the contrary, the intention is to cover various modifications and equivalent arrangements within the scope of the claimed scope of the present invention.

Claims (8)

A method for manufacturing a modified cotton fabric for oil-water separation, comprising the following steps: washing a cotton fabric and drying; preparing a tannic acid solution, wherein the step of preparing the tannic acid solution further comprises selectively adding a catalyst to accelerate the grafting reaction of the 1-eicosylamine, and the step of adding the catalyst comprises adding the tannic acid solution containing CuSO ₄ and H ₂ O ₂ into a stirred water bath; adding a specific concentration of 1-dimethicone Tendecylamine is dissolved in ethanol, and is mixed with the pre-prepared tannic acid solution at room temperature to form a mixed solution; and the cotton fabric is immersed in the mixed solution at room temperature, and the reaction is carried out according to a prescribed reaction time. Michael addition/Schiff base reaction. The production method according to claim 1, wherein the pH of the mixed solution is adjusted to 8.5 before the Michael addition/Schiff base reaction is performed. The manufacturing method of claim 1, wherein the tannic acid solution contains 5 mM CuSO ₄ , 19.6 mM H ₂ O ₂ and 2 mg/L tannic acid. The manufacturing method according to claim 1, wherein the prescribed reaction time is 10-60 minutes. The manufacturing method of claim 1, wherein the specific concentration of the 1-eicosylamine is between 1-5 mg/ml. The manufacturing method of claim 1, wherein the method of washing the cotton fabric comprises washing the cotton fabric with water and ethanol, and then immersing the cotton fabric in an ultrasonic water bath. The production method of claim 1, wherein after the Michael addition/Schiff base reaction is performed, the cotton fabric is washed with water and ethanol, and then dried at 60°C. A modified cotton fabric for oil-water separation, which is manufactured by the manufacturing method as described in any one of claims 1-9, wherein the surface of the modified cotton fabric has a tannic acid-impregnated coating and 1- Eicosanylamine grafting.