Claims:WE CLAIM:
1. A process for the synthesis of a superhydrophobic polyolefin surface, the process comprising:
a. wrapping a polyolefin substrate on a rotating roller positioned in a reactor;
b. outside the reactor, mixing at least one carbon source and at least one catalyst to prepare a mixture,
c. atomizing the mixture in a nebulizer and charging the atomized mixture into the reactor with the help of a carrier gas;
d. decomposing the charged atomized mixture at a temperature in the range of 800 to 1200 °C to produce multi-walled carbon nanotubes (MWCNT);
e. allowing the multi-walled carbon nanotubes (MWCNT) to deposit on the surface of the wrapped polyolefin substrate to obtain surface coated polyolefin; and
f. removing the surface coated polyolefin from the reactor; and treating with mineral acid to obtain the superhydrophobic polyolefin surface.
2. The process as claimed in claim 1, wherein the carbon source is at least one selected from the group consisting of C1 to C7 hydrocarbons and C1 to C7 alcohols.
3. The process as claimed in claims 1 or 2, wherein the carbon source is at least one selected from methanol, ethanol and propanol.
4. The process as claimed in claim 1, wherein the catalyst is an iron based catalyst.
5. The process as claimed in claims 1 or 4, wherein the catalyst is ferrocene.
6. The process as claimed in claim 1, wherein the amount of the catalyst is in the range of 0.1 to 5 wt% of the carbon source.
7. The process as claimed in claim 1, wherein the carrier gas is at least one selected from nitrogen and argon.
8. The process as claimed in claim 1, wherein the polyolefin substrate is at least one selected from the group consisting of polyethylene, polypropylene and polyethylene terephthalate.
9. The process as claimed in claim 1; wherein the polyolefin substrate is subjected to corona treatment before the step of depositing MWCNT.
10. The process as claimed in claim 1; wherein the thickness of MWCNT layer deposited on the polyolefin substrate is in the range of 2 to 12 microns.
11. The process as claimed in claim 1, wherein the mineral acid is at least one selected from hydrochloric acid, sulphuric acid and nitric acid.
12. The process as claimed in claim 1, wherein the MWCNT coated polyolefin substrate is MWCNT coated disentangled polyethylene having:
• contact angle in the range of 151 o 158°;
• electrical conductivity in the range of 4000 to 4500 S/m;
• tensile strength in the range of 2.0 to 2.5 GPa; and
• tensile modulus in the range of 60 to 100 GPa.
, Description:FIELD
The present disclosure relates to a process for the synthesis of superhydrophobic polyolefin surfaces. The present disclosure particularly relates to a process the synthesis of high strength and high modulus superhydrophobic polyolefin surfaces.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.
Superhydrophobicity refers to the inherent characteristic of a surface to repel water completely.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Surface hydrophobicity of solids is an important factor for various applications, e.g. products having self-cleaning properties, electronic systems, non-sticky, anti-reflecting and display devices. Highly hydrophobic surfaces are needed in many important applications, such as in manufacturing water-repellant textile, in constructing fuel cells, in batteries for membranes non-wetted under storage, desalination membranes, antenna coatings, etc.
Superhydrophobicity is the inherent characteristic of a surface to repel water completely. The main criterion for these characteristics is the contact angle (CA) between the surface and the water droplets. When the CA is ? < 5°, the surface is superhydrophilic, ? < 90°, surface is hydrophilic, ? = 90°-150°, the surface is hydrophobic and when ? = 150°, the surface is called superhydrophobic also it should have a roll off angle or contact angle hysteresis less than 10° [1]. The rolls off angle is the difference between forward and backward contact angles when droplet is about to move.
Numerous research activities have been done focused on achieving the state-of-the-art superhydrophobic surfaces by mimicking the phenomena of lotus leaf. However, practical needs of hydrophobic surfaces are not satisfied. In spite of significant experimental and theoretical efforts, a reproducible inexpensive manufacture of superhydrophobic surfaces is not available.
There is, therefore, felt a need to develop a process for producing super-hydrophobic polyolefin surfaces.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for preparation of the superhydrophobic polyolefin surfaces.
Still another object of the present disclosure is to provide a process for preparation of high strength and high modulus superhydrophobic polyolefin surfaces.
Yet another object of the present disclosure is to provide a superhydrophobic high strength high modulus poly-olefin surface.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for the synthesis of superhydrophobic polyolefin surfaces. The process of the present disclosure comprises following steps:
Initially, a polyolefin substrate is wrapped on a roller positioned at the exit of the reactor. Outside a reactor, at least one carbon source and at least one catalyst are mixed together to prepare a mixture. The mixture is atomized in a nebulizer and charged in a reactor with the help of a carrier gas.
The reactor is maintained at a temperature in the range of 800 to 1200 °C by gradual heating. The atomized mixture is decomposed in a quartz tube reactor to produce multi-walled carbon nano-tubes (MWCNT).
The multi-walled carbon nano-tubes (MWCNTs) are then allowed to deposit uniformly on the surface of the wrapped polyolefin substrate to achieve a thickness of 2 to 12 microns. The MWCNT coated polyolefin is removed from the reactor and is further treated with a mineral acid to remove amorphous carbon and residual metal catalyst impurities.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates the schematic representation of the apparatus used for the synthesis of superhydrophobic polyolefin surfaces.
Figure 2 illustrates water drop images for contact angle measurement of virgin DPE tape (A), multi-walled carbon nano-tubes (MWCNT) film (B), MWCNT coated on virgin DPE tape (C) and MWCNT coated on corona treated DPE tape (D).

DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
Superhydrophobicity is the inherent characteristic of a surface to repel water completely. Surface hydrophobicity of solids is an important factor for various applications, e.g. products having self-cleaning properties, electronic systems, non-sticky, anti-reflecting and display devices. The main criteria for these characteristics is the contact angle (CA) between the surface and the water droplets. When the CA is ? = 90°-150°, the surface is hydrophobic and when ? = 150°, the surface is called superhydrophobic.
Surface topology and surface energy are the two important factors which contribute more towards superhydrophobicity. Surface energy is inversely proportional to the contact angle of the surface i.e. lower the surface energy higher will be the contact angle. Accordingly, superhydrophobicity could be achieved either by modifying the surface morphology e.g. creating nano or microstructures or by incorporating or coating with materials which reduces the surface energy thereby increasing the surface hydrophobicity.
Numerous research activities have been done focused on achieving the state-of-the-art superhydrophobic surfaces by mimicking the phenomena of lotus leaf. The most commonly used method is the incorporation of nano-fillers having wide size distributions into the polymer matrices such as silica (SiO2), titanium dioxide (TiO2) and carbon nano-materials or by coating the polymer films on the surfaces of these materials.
However, practical needs of hydrophobic surfaces are not satisfied. In spite of significant experimental and theoretical efforts, a reproducible inexpensive manufacture of superhydrophobic surfaces is not available.
The present disclosure, therefore, provides an alternate process for synthesis of superhydrophobic polyolefin surfaces.
The process for the synthesis of superhydrophobic polyolefin surface comprises following steps:
Initially, a polyolefin substrate is wrapped on a rotating roller positioned at the exit of the reactor. Outside a reactor, at least one carbon source and at least one catalyst are mixed together to prepare a mixture. The mixture is atomized in a nebulizer and charged in a reactor with the help of a carrier gas.
The reactor is maintained at a temperature in the range of 800 to 1200 °C by gradual heating. In accordance with the exemplary embodiment of the present disclosure, the reactor is maintained at 1000 °C.
The atomized mixture is decomposed in a reactor to produce multi-walled carbon nano-tubes (MWCNT). The multi-walled carbon nano-tubes (MWCNTs) are then allowed to deposit uniformly on the surface of the wrapped polyolefin substrate to achieve a thickness of 2 to 12 microns. The MWCNT coated polyolefin is removed from the reactor and is further treated with mineral acid to obtain superhydrophobic polyolefin surface.
The carbon source is selected from the group consisting of C1 to C7 hydrocarbons and C1 to C7 alcohols. Preferably the carbon source is at least one selected from methanol, ethanol and propanol.
The catalyst is used for synthesis of the carbon nano-tubes (MWCNTs) is an iron based catalyst. Preferably, the catalyst is ferrocene. The amount of the catalyst is in the range of 0.1 to 5 wt% of the carbon source.
The polyolefin substrate is at least one selected from the group consisting of polyethylene, polypropylene and polyethylene terephthalate. Preferably, the polyolefin substrate is disentangled polyethylene (DPE). More preferably, the polyolefin substrate is corona treated disentangled polyethylene (DPE).
The corona treatment of DPE creates oxygen functionalities on the surface of DPE tape which in turn make the surface hydrophilic as compared to the virgin DPE resulting in the decreased contact angle values. However, the corona treatment helps in the uniform deposition of MWCNT on the DPE surface and shows very good adhesion properties as compared to the virgin DPE surface, which leads to enhanced superhydrophobicity of the corona treated DPE as compared to the virgin DPE.
Typically, the polyolefin substrate is wrapped on a rotating roller dynamically positioned in the reactor at a location distant from the furnace for easy recovery of the carbon nanotubes. In accordance with the embodiments of the present disclosure, polyolefin substrate wrapped on a rotating roller is positioned in a reactor, wherein the temperature is in the range of 50 to 70 °C, preferably 60 °C.
The carrier gas is at least one selected from nitrogen and argon. The carrier gas used in the process of the present disclosure facilitates removal of the atmospheric gases present in the reactor and also carries the vapors of carbon source into the high temperature zone of the reactor.
The mineral acid is at least one selected from hydrochloric acid, sulphuric acid and nitric acid. Preferably the mineral acid is nitric acid. The MWCNT coated polyolefin surface is treated with mineral acid to remove amorphous carbon and residual metal catalyst impurities.
In accordance with the exemplary embodiment of the present disclosure, the MWCNT coated polyolefin substrate is MWCNT coated disentangled polyethylene having contact angle in the range of 151 o 158°; electrical conductivity in the range of 4000 to 4500 S/m; tensile strength in the range of 2.0 to 2.5 GPa; and tensile modulus in the range of 60 to 100 GPa.
The apparatus used for the synthesis of superhydrophobic polyolefin surfaces is shown in Figure 1.
The apparatus comprises a reactor ‘4’ provided with inlet for introducing a mixture of the carbon source and a carrier gas. The mixture of the carbon source and the carrier gas is introduced in the quartz tube reactor ‘4’ through an inlet ‘1’. The carrier gas used in the process of the present disclosure facilitates removal of the atmospheric gases present in the reactor ‘4’ and also carries the vapors of precursors into the high temperature zone for the synthesis of the MWCNTs. Further, the carrier gas facilitates in moving forward the formed MWCNTs. The reactor ‘4’ is heated to a temperature in the range of 800 °C to 1200 °C, using the furnace ‘2’ for synthesizing the MWCNTs. The furnace ‘2’ has high temperature zone ‘3’, which is further divided into zones ‘3a’, ‘3b’, ‘3c’ and ‘3d’. On heating, the carbon source decomposes to form MWCNTs. The MWCNTs are continuously produced and carried forward through zone ‘5’ with the help of carrier gas to deposit on the polyolefin substrate ‘6’ placed on the roller positioned in a wooden box equipped with motor ‘7’.
Thereafter, the surface coated polyolefin is removed from the roller and treated with mineral acid to obtain the superhydrophobic polyolefin surface.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

EXPERIMENTAL DETAILS
Experiment 1: Preparation of disentangled ultra-high molecular polyethylene (DPE) substrate
The disentangled ultra-high molecular polyethylene (DPE) powder was formed into tape (L x W x T = 100 m x 138 mm x 150 µ) below the melt temperature of the polymer using a two roll mill by compaction. The tape obtained was further hot stretched in an oven at a temperature profile of 130 to 151°C. The final tape has width 40 mm, thickness 16 µ, tensile strength (TS) of 2.32 GPa and tensile modulus (TM) of 114 GPa.
The high strength and high modulus tape produced above was subjected to corona treatment for 1 to 5 cycles and were designated as
(1) DPE-CT-0: Virgin DPE tape;
(2) DPE-CT-1: Corona treated DPE surface for 1st cycle;
(3) DPE-CT-2: Corona treated DPE surface for 2nd cycle;
(4) DPE-CT-3: Corona treated DPE surface for 3rd cycle; and
(5) DPE-CT-4: Corona treated DPE surface for 4th cycle.
Where CT stands for corona treatment and number stands for corona treatment cycle.
Experiment 2: Synthesis of superhydrophobic polyolefin surface in accordance with the present disclosure
High strength and high modulus ultrahigh molecular weight polyethylene (DPE) substrate was made into superhydrophobic surfaces by the following procedure.
Initially, DPE-CT-1 tape obtained experiment 1 was wrapped on a rotating roller positioned in a reactor furnace.
Outside the reactor, 1 g of ferrocene catalyst was mixed with 100 mL ethanol (carbon source) to obtain a mixture. The reactor furnace was heated up to 1000oC by gradual heating. The mixture was atomized in a nebulizer positioned at the other end of the reactor furnace to obtain an atomized mixture. The atomized mixture was further charged in the reactor with the help of nitrogen gas, wherein the atomized mixture was decomposed to generate multi-walled carbon nanotubes (MWCNTs). These carbon nanotubes were allowed to deposit uniformly on to the DPE tapes wrapped on a roller to achieve thickness of 10 microns.
The MWCNT coated polyethylene (DPE) tape was removed from the reactor and further cleaned by using conc. nitric acid (HNO3) to remove amorphous carbon and residual metal catalyst impurities to obtain superhydrophobic DPE surface.
Experiments 3-7: Synthesis of superhydrophobic polyolefin surfaces
Similar experimental procedure was followed as described herein above to synthesize superhydrophobic polyolefin surfaces, except DPE tapes used. Corona treated DPE tapes and untreated DPE tape samples were coated with MWCNTs. The analysis for the MWCNT coated DPE substrates is given below:
1. Thickness:
Thickness of the MWCNT layer deposited on the DPE tape are given in Table 1 below:
Table 1: Thicknesses of Virgin and MWCNT coated DPE tapes
Ex. No. DPE Polymeric substrates Thickness (µm)
Before MWCNT coating After MWCNT coating MWCNT layer
1 DPE-CT-1 22 25 3
2 DPE-CT-2 22 24 2
3 DPE-CT-3 22 27 5
4 DPE-CT-4 22 28 6
5 DPE-CT-0
(Comparative example) 22 25 3

From table 1, it is evident that the thickness of the MWCNT layer deposited on the DPE tape is higher for corona treated DPE as compared to the virgin DPE.
2. Contact angle:
The contact angle for the virgin DPE tape and MWCNT coated DPE tape was measured on drop shape analyser (M/s KRUSS) using 33 µL volume of water to make drops on the surface. Contact angles measured with reference to water and their images are given in Figure 2 and Table 2 given below:
Table 2: Contact Angle values of DPE and MWCNT coated DPE tapes
Sr. No. DPE Polymeric surfaces Contact angle (deg)
Without MWCNT With MWCNT
1 Pure MWCNT film NA 138
2 DPE-CT-0 93 151
3 DPE-CT-0 + acid treatment 93 151
4 DPE-CT-4 58 147
5 DPE-CT-4 + acid treatment 58 158

From table 2, it is evident that the MWCNT coated DPE tape has the contact angle of 151 to 158° and therefore exhibit superhydrophobicity. Further, it is evident the contact angle of the corona treated DPE tape increases after acid treatment. However, acid treatment has no effect on virgin DPE tape.
Furthermore, the contact angle for DPE-CT-4 with MWCNT (~147 deg.) is slightly less as compared but the DPE-CT-0 with MWCNT (151 deg). The slight reduction in contact angle is attributed to the corona treatment of the surface of DPE tape. The corona treatment of DPE creates oxygen functionalities on the surface of DPE tape which in turn make the surface hydrophilic as compared to the virgin DPE resulting in the decreased contact angle values. However, the corona treatment helps in the uniform deposition of MWCNT on the DPE surface and shows very good adhesion properties as compared to the virgin DPE surface, which leads to enhanced superhydrophobicity of the corona treated DPE as compared to the virgin DPE.
3. Mechanical Properties
Mechanical properties of virgin DPE and MWCNT coated DPE tapes are given in Table 3.
Table 3: Tensile properties of DPE and MWCNT coated DPE tapes
DPE Substrates TS (GPa) TM (GPa) Load at Break (N) % Elongation
DPE-CT-0 without MWCNT 2.08 105 237 3.05
DPE-CT-0 with MWCNT 2.48 63 282 3.5
DPE-CT-4 without MWCNT 2.06 129 264 2.3
DPE-CT-4 with MWCNT 2.18 102 458 2.4
TS: Tensile Strength, TM: Tensile Modulus, CT: Corona Treated
From table 3, it is evident that MWCNT coated DPE tapes exhibit enhanced tensile strength along with enhanced elongation.
Further, it is observed that the tensile strength for DPE-CT-4 with MWCNT (~2.2 GPa) is slightly less as compared to the DPE-CT-0 with MWCNT (2.48 GPa). The tensile strength always decreases as DPE polymer is subjected to corona treatment, which results in formation of oxygen functionalities on the DPE surface However, the corona treatment helps in the uniform deposition of MWCNT on the DPE surface and shows very good adhesion properties as compared to the virgin DPE surface, which leads to enhanced superhydrophobicity of the corona treated DPE as compared to the virgin DPE.
Measurement of Electrical conductivity
Direct current (DC) electrical conductivity of MWCNT coated DPE tape was measured on a Source-meter (measure up to 106 O), a resistance meter by Keithley, Germany by two-point probe method and the results are given in Table 4.
Table 4: Electrical conductivity of DPE and MWCNT coated DPE tapes
DPE with MWCNT Deposition time (h) Thickness of MWCNT (µm) Conductivity (S/m)
DPE-CT-0 12 2 3158
DPE-CT-2 16 2 4116
DPE-CT-4 25 4 4363
From table 4, it is evident that the thickness of the MWCNT layer increases with time, which further leads to enhanced conductivity of the MWCNT coated DPE tapes.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, a process for preparation of superhydrophobic polyolefin surface, which provides polyolefin surface with:
- contact angle in the range of 151 to 158°; and
- enhanced tensile strength, tensile modulus and electrical conductivity.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.