Description:FIELD OF THE INVENTION

The present disclosure relates to development of a coating formulation. More specifically, the present invention relates to a coating formulation composition to enhance the hydrophobicity of polypropylene surface, and process of preparation of said coating formulation.

BACKGROUND OF THE INVENTION

Hydrophobic surface has repellency to water. The hydrophobicity of a material is determined by the contact angle of a water droplet on the surface. If the contact angle of the water droplet becomes more than 140°, precisely more than 150°, the surface is understood to have super hydrophobicity. Polyolefins have wide range of industrial applications from packaging to building materials as well as automotive parts where hydrophobicity and clean surfaces are some of the key requirements.

Currently, various methods are available to increase the hydrophobicity of a surface. However, in several existing technologies fluorine-based compounds like fluorinated siloxanes have been used to meet the desired hydrophobicity. This type of fluorine-based compound is found to have both environment and health hazard. Also, various expensive techniques have been used to obtain the needed hierarchal surface texture. To improve hydrophobicity of the polymer surface, lot of established methods are available, e.g. by using fluorinated polydimethyl siloxanes (PDMS) or nano-particles like titanium dioxides (TiO2), nano- silica (SiO2). Usage of fluorinated compound is not at all environmentally benign. Also, nano-particle usage is not a cost-effective approach. Therefore, a keen need is found to introduce a new solution for producing hydrophobic surfaces.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide a fluorine free hydrophobic coating composition to enhance the hydrophobicity of polypropylene surface and a process of preparation thereof.

In an embodiment, the coating formulation composition to enhance the hydrophobicity of polypropylene surface comprises a powder extract of a Maleic anhydride grafted polypropylene (PP-g-MA), from 30-120 grams; a powder extract of a crystalline solid of amine oxide, from 5-20 grams; and a liquid extract of an Ortho xylene, from 200-300 milliliter.

In another embodiment, a process of preparing the coating formulation is disclosed. The process includes mixing 30-120 grams of PP-g-MA with 200-300 milliliter in a 500 ml round bottomed flask. The process further includes attaching a reflux condenser to the flask with continuous water circulation provision. The process further includes heating the flask for 1 h at 130°C to completely dissolve the PP-g-MA in xylene and reducing the temperature of the solution to 110°C after 1 hour. The process further includes adding 5-20 grams of surfactant amine oxide to the PP-g-MA solution in presence of 2 ml of distilled water as a catalyst to open the anhydride ring and to promote the reaction. The process further includes stirring the solution continuously for 1 h at 110°C to prepare coating formulation. The process further includes casting the developed coating formulation on a PP-sheet at hot condition to form a uniform coating and drying the coated sheet at 90°C for 1 h and cooled to room temperature.

In one embodiment, the temperature of the condenser water is maintained at 25°C with the help of a chilling unit during the water circulation provision.

In one embodiment, a stirrer is attached with the flask and the speed of the stirrer is kept at 600 rpm for uniform mixing.

In one embodiment, the amine-oxide reacts with maleic anhydride functional group following ‘Polonovski Reaction’ type pathway during continuous stirring at 110°C.

In one embodiment, higher MFI PP-g-MA is selected for better flow ability during solvent casting, whereas the Hot condition casting is selected to soften the matrix PP sheet surface and promote easy binding with the PP phase of PP-g-MA in solution phase, wherein the selected PP-g-MA is a commercial grade, OPTIM P-425, and its melt flow index is 110 gm/10 min at 190°C, 2.16 kg load with a higher maleic anhydride grafting content, wherein the higher grafting content promotes reaction with the amine oxide functional group.

In one embodiment, the developed coating formulation is casted on a PP-sheet at hot condition to form a uniform coating over the polypropylene surface.

In one embodiment, the amine oxide is preferably selected from Amine, bis (hydrogenated alkyl) methyl N-oxide.

In one embodiment, the long chain hydrocarbons from the prepared coating formulation (PP-g-MA surfactant adduct) spreads over the PP-sheet surface to enhance hydrophobicity.

An object of the present disclosure is to enhance the hydrophobicity of polypropylene surface.

Another object of the present disclosure is to bind the polar amine oxide group to the non-polar polypropylene surface.

Another object of the present disclosure is to develop a fluorine free user-friendly hydrophobic coating to meet the desired requirements.

Yet another object of the present invention is to deliver an expeditious and cost-effective coating formulation process to enhance the hydrophobicity of polypropylene surface.

To further clarify advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a flow chart of preparation of a coating formulation to enhance the hydrophobicity of polypropylene surface in accordance with an embodiment of the present disclosure;
Figure 2 illustrates chemical structures of (a) PP-g-MA, (b) Amine, bis (hydrogenated alkyl) methyl N-oxide surfactant, (c) O-xylene;
Figure 3 illustrates a process flow of synthesis of the coating formulation in accordance with an embodiment of the present disclosure;
Figure 4 illustrates a coating deposition on substrate using solvent casting method in accordance with an embodiment of the present disclosure;
Figure 5 illustrates (a) Uncoated and (b) Coated Polypropylene surface in accordance with an embodiment of the present disclosure; and
Figure 6 illustrates a FTIR spectra (ATR mode) of developed hydrophobic coating in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION:

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Referring to Figure 1, a flow chart of a process for preparation of a coating formulation to enhance the hydrophobicity of polypropylene surface in accordance with an embodiment of the present disclosure is illustrated. At step 102, the process 100 includes mixing 30-120 grams of Maleic anhydride grafted polypropylene (PP-g-MA) with 200-300 milliliter o- Xylene in a 500 ml round bottomed flask, wherein preferably 50 grams of Maleic anhydride grafted polypropylene (PP-g-MA) with 250 milliliter of o-Xylene in a 500 ml round bottomed flask.

At step 104, the process 100 includes attaching a reflux condenser to the flask with continuous water circulation provision. The reflux condenser made of glass with 400 ml capacity consists of 24/40 glass joint to be attached with the round bottom flask of 500 ml capacity. The condenser has one inlet and one out let valve connected with the chiller to maintain cold water recirculation temperature at 25°C. Teflon seal sleeve was used around the glass joint.

At step 106, the process 100 includes heating the flask for 1 hour at 130°C to completely dissolve the PP-g-MA in xylene and reducing the temperature of the solution to 110°C after 1 hour. Xylene is a good solvent for PP-g-MA to conduct the reaction in solution phase. The solubility parameter of PP-g-MA is ~18.6 MPa1/2, whereas it is ~18 MPa1/2 for Xylene. Closer the solubility parameter, better is the solubility. However, toluene may also be used.

At step 108, the process 100 includes adding 5-20 grams of surfactant amine oxide to the PP-g-MA solution in presence of 2 ml of distilled water as a catalyst to open the anhydride ring and to promote the reaction. Preferably, 5 gm of surfactant amine oxide is added to the PP-g-MA solution. Long chain fatty acid amine like oleylamine etc. can be used. However, when it reacts with maleic anhydride, forms amide linkage which is moisture sensitive and can decrease the overall hydrophobicity of the developed coating. Therefore, amine oxide surfactant molecule is selected which has two long chain hydrocarbon (C14-C24) attached to amine oxide groups that helps in enhancing the hydrophobicity of the formulation. Considering pH neutrality and low cost, distilled water is used as a catalyst to open the maleic anhydride ring. Acid like diluted hydrochloric acid (HCl) can also be used in trace amount, but it will change the pH of the reaction medium which is not desirable. Water reacts with the anhydride group (-CO-O-CO-) to open up the ring forming free Carboxylic acid functional group (-COOH) which further reacts with amine oxide to form the adduct. The reaction schematics are shown in Figure 3.

At step 110, the process 100 includes stirring the solution continuously for 1 h at 110°C to prepare coating formulation.

At step 112, the process 100 includes casting the developed coating formulation on a PP-sheet at hot condition to form a uniform coating and drying the coated sheet at 90°C for 1 h and cooled to room temperature.

In one embodiment, temperature of the condenser water is maintained at 25°C with the help of a chilling unit during the water circulation provision.

In one embodiment, a stirrer is attached with the flask and the speed of the stirrer is kept at 600 rpm for uniform mixing.

In one embodiment, the amine-oxide reacts with maleic anhydride functional group following ‘Polonovski Reaction’ type pathway during continuous stirring at 110°C.

In one embodiment, higher MFI PP-g-MA is selected for better flow ability during solvent casting, whereas the Hot condition casting is selected to soften the matrix PP sheet surface and promote easy binding with the PP phase of PP-g-MA in solution phase, wherein the selected PP-g-MA is a commercial grade, OPTIM P-425, and its melt flow index is 110 gm/10 min at 190°C, 2.16 kg load with a higher maleic anhydride grafting content, wherein the higher grafting content promotes reaction with the amine oxide functional group.

In another embodiment, a coating formulation composition to enhance the hydrophobicity of polypropylene surface comprises a powder extract of a Maleic anhydride grafted polypropylene (PP-g-MA), from 30-120 grams; a powder extract of a crystalline solid of amine oxide, from 5-20 grams; and a liquid extract of an Ortho xylene, from 200-300 milliliter.

In one embodiment, the developed coating formulation is casted on a PP-sheet at a hot condition to form a uniform coating over the polypropylene surface, wherein a molded PP sheet of 2 mm is prepared to evaluate performance of the developed coating and the sheet is then coated with the developed coating solution at around 90°C which is known as solvent casting method, wherein the elevated temperature coating softened the PP surface so that the PP moiety present in dissolved PP-g-MA/amine oxide adduct got easily bonded to the PP surface thereby the coated sheet is dried at 90°C for 1 h to remove the solvent and cooled to room temperature.

In one embodiment, the average thickness of the coating found to be 600 µm.

In one embodiment, the amine oxide is preferably selected from Amine, bis (hydrogenated alkyl) methyl N-oxide.

In one embodiment, the long chain hydrocarbons from the prepared coating formulation (PP-g-MA surfactant adduct) spreads over the PP-sheet surface to enhance hydrophobicity.
Figure 2 illustrates a chemical structures of (a) PP-g-MA, (b) Amine, bis (hydrogenated alkyl) methyl N-oxide surfactant, (c) O-xylene in accordance with an embodiment of the present disclosure. The process is introduced based on secondary amine oxide-based surfactant molecule. The surfactant molecule chosen considering its’ two long chain tallow (hydrocarbon having C14 to C24 alkyl chain) attached to polar amine-oxide group. Being a non-polymer polymer, it is really a challenge to bind the polar amine oxide group to the non-polar polypropylene surface. Therefore, maleic anhydride grafted polypropylene (PP-g-MA) is used, so that it’s polypropylene segment gets adhered to the matrix Polypropylene surface and maleic anhydride group binds with amine-oxide group easily. The reaction is conducted in a specific set-up, temperature & reaction time to synthesize the hydrophobic coating and finally solvent casted on polypropylene sheet surface.
Chemical used:
(a) Maleic anhydride grafted polypropylene (PP-g-MA) (MFI of 110 g/10 min at 190°C, 2.16 kg load and high grafting content)
(b) Amine, bis (hydrogenated alkyl) methyl N-oxide surfactant (Melting point of 90°C)
(c) Ortho xylene as solvent (Purity: 99%)
In an exemplary embodiment, preferably 50 g of PP-g-MA is taken in a 500 ml round bottomed flask and 250 ml of ortho-xylene is preferably added to it. The flask is then attached to a reflux condenser with continuous water circulation provision. The temperature of the condenser water is maintained at 25°C with the help of a chilling unit. The flask is then heated for 1 h at 130°C to completely dissolve the PP-g-MA in xylene. Stirrer speed is kept at 600 rpm. After 1 h, the temperature of the solution is reduced to 110°C. An excess amount of surfactant amine oxide (5 g) is added to the PP-g-MA solution in presence of 2 ml of distilled water as a catalyst to open the anhydride ring and to promote the reaction. The solution is continuously stirred for 1 h at 110°C. At this temperature, the amine-oxide reacts with maleic anhydride functional group following ‘Polonovski Reaction’ type pathway.

Figure 3 illustrates a process flow of synthesis of the coating formulation in accordance with an embodiment of the present disclosure. The developed coating formulation is then solvent casted on PP-sheet at hot condition to form a uniform coating. Higher MFI PP-g-MA is chosen for better flow ability during solvent casting. Hot condition casting is chosen so that the matrix PP sheet surface gets softened and can bind easily with the PP phase of PP-g-MA in solution phase. The coated sheet is then dried at 90°C for 1 h and cooled to room temperature.

Figure 4 illustrates a coating deposition on substrate using solvent casting method in accordance with an embodiment of the present disclosure. The performance of the coated surface is evaluated by measuring the contact angle. A drop of deionized water (4 µL) is gently deposited on the substrate surface using a micro syringe. The images are captured using the “Angle Cam Analyzing” system and the contact angle is measured. The untreated PP-sheet found to have a contact angle of 102°, whereas the treated surface showed an enhanced contact angle of 134° as a result of increased hydrophobicity.

To identify if reaction happened between PP-g-MA and Amine-oxide, FTIR analysis is carried out. The amine-oxide is taken in excess ratio, so that maleic anhydride groups can react completely. In the FTIR spectra of developed coating formulation no characteristic peaks of maleic anhydride (carbonyl stretching: 1780 to 1850 cm-1 and C-O stretching at 1058 cm-1) is observed.
Figure 5 illustrates (a) Uncoated and (b) Coated Polypropylene surface in accordance with an embodiment of the present disclosure. Contact angle of the water droplet is a measure of hydrophobicity of the surface. Higher the contact angle, higher is the hydrophobicity of the surface. The method to measure contact angle is furnished below:
Contact Angle Measurement:
The uncoated and hydrophobic coated sample surface is cleaned by blowing compressed air to remove any dust particle. It is ensured that both the surfaces remain horizontal to avoid rolling of the water droplet during measurement. At the middle of each surfaces one deionized water droplet (~4 µL) is kept with the help of a micro-syringe. Addition of multiple water droplets (>5 µL) is avoided to ensure that overweight of the droplet shouldn’t impact the shape as well as contact angle of the droplet. The images are captured and analyzed using the “Angle Cam Analyzing System”. The contact angle of the un-coated and coated surface is measured, and tabulated below as an average of five measurements at different location.
Polypropylene Sheet Surface Measured Contact Angle
Uncoated 102°
Coated with the developed coating 134°

To ensure the reaction happened between PP-g-MA and Amine-oxide, FTIR analysis is carried out as per ASTM E1252.

Figure 6 illustrates a FTIR spectra (ATR mode) of developed hydrophobic coating in accordance with an embodiment of the present disclosure. First of all, the hydrophobic coating is dried at 100°C for 1 hr to evaporate the remaining solvent so that the coating becomes powdery in nature. The test is done in ATR mode. With ATR accessory, the sample is placed on holder aperture above crystal and pressure is applied. The sample is scanned between 400 cm-1 – 4000 cm-1 wavenumbers with an accuracy of ±0.01 cm-1. The interferogram is made using OMNIC software to get spectrograph of %Transmittance vs Wavenumber.

In case of PP-g-MA, the characteristics peaks are as follows: symmetric carbonyl stretching at 1819 cm-1, asymmetric stretching at 1752 cm-1 and C-O stretching at 1058 cm-1. However, in the developed coating spectra as mentioned above, all the characteristic peaks of PP-g-MA found missing which indicates that there is no unreacted PP-g-MA present in the coating, all reacted. The peaks between 2837 to 2953 cm-1 and below 1000 cm-1 come from different hydrocarbon C-H stretching and bending. The peaks at 1454 cm-1 comes from –CH3 and 1374 & 1168 cm-1 indicates presence of –CH2 groups.

The prepared coating formulation can be used to for several end applications like automotive, marine, shielding and solar cells where properties like self-cleaning, self-healing, anti-icing, anti-fouling, anti-adhesion are of prime importance.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. , Claims:1. A coating formulation composition to enhance the hydrophobicity of a polypropylene surface, said composition comprising:
30-120 grams of powder extract of a Maleic anhydride grafted polypropylene (PP-g-MA);
5-20 grams of powder extract of a crystalline solid of amine oxide; and
200-300 milliliter of a liquid extract of Ortho xylene.

2. The composition as claimed in claim 1, wherein said coating formulation is casted on a PP-sheet at a hot condition to form a uniform coating over the polypropylene surface.

3. The composition as claimed in claim 1, wherein said coating formulation composition comprises:

50 grams of the powder extract of Maleic anhydride grafted polypropylene (PP-g-MA);
5 grams of powder extract of the crystalline solid of amine oxide; and
250 milliliter of the liquid extract of Ortho xylene.

4. A process to prepare a coating formulation to enhance the hydrophobicity of polypropylene surface, said process comprising:

mixing 30-120 grams of PP-g-MA with 200-300 milliliter of a solvent comprising Ortho xylene in a 500 ml round bottomed flask;
attaching a reflux condenser to the flask with continuous water circulation provision;
heating the flask for 1 h at 130°C to completely dissolve the PP-g-MA in xylene and reducing the temperature of the solution to 110°C after 1 hour;
adding 5-20 grams of a surfactant comprising amine oxide to the PP-g-MA solution in presence of 2 ml of distilled water as a catalyst;
stirring the solution continuously for 1 hour at 110°C to prepare coating formulation; and
casting the developed coating formulation on a PP-sheet at hot condition to form a uniform coating and drying the coated sheet at 90°C for 1 hour and cooled to room temperature.

5. The process as claimed in claim 4, wherein said process comprises mixing 50 grams of Maleic anhydride grafted polypropylene (PP-g-MA) with 250 millilitre of o-Xylene in a 500 ml round bottomed flask, and maintain temperature of the condenser water at 25°C with a help of a chilling unit during water circulation.

6. The process as claimed in claim 4, wherein said method comprises adding 5 grams of surfactant amine oxide to the PP-g-MA solution.

7. The process as claimed in claim 4, wherein said reflux condenser is made of glass, and wherein an outlet valve of said reflux condenser is connected with a chiller to maintain cold water recirculation temperature at 25°C, and wherein a stirrer is attached with the flask and the speed of the stirrer is kept at 600 rpm for uniform mixing.

8. The process as claimed in claim 4, wherein a higher MFI PP-g-MA is selected for solvent casting, and wherein Hot condition casting is selected to soften the matrix PP sheet surface and promote easy binding with the PP phase of PP-g-MA in solution phase.

9. The process as claimed in claim 4, wherein the amine oxide is selected from Amine, bis (hydrogenated alkyl) methyl N-oxide.

10. The process as claimed in claim 4, wherein the amine-oxide reacts with maleic anhydride functional group following ‘Polonovski Reaction’ type pathway during continuous stirring at 110°C, and wherein the long chain hydrocarbons from the prepared coating formulation (PP-g-MA surfactant adduct) spreads over the PP-sheet surface to enhance hydrophobicity.