FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
“VISIBLE-INFRARED TRANSMITTING POLYSULFIDE MATERIAL AND ITS
METHOD OF PREPARATION”
Name: Reliance Industries Limited
Address: 3rd Floor, Maker Chamber-IV, 222, Nariman Point, Mumbai-400 021,
Maharashtra, India. Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
The present disclosure generally relates to the field of polymer engineering, advanced materials and applied industrial technology. Particularly, the present disclosure relates to a polysulfide material made of elemental sulfur and Ethylene Propylene Diene Monomer (EPDM) having transmittance in the Visible and Infrared region. A solid-state process for preparing the said sulfur-EPDM film and the material is also provided. The present disclosure also provides articles comprising the sulfur-EPDM polysulfide material and corresponding methods for preparing said article useful for example in infrared device applications for imaging and optical filtering purposes.
BACKGROUND OF THE INVENTION
The production of elemental sulfur from petroleum refining has created a technological opportunity to increase the valorization of elemental sulfur by the synthesis of high-performance sulfur-based plastics with improved optical, electrochemical, and mechanical properties aimed at applications in thermal imaging, energy storage, self-healable materials, and separation science.
Commercially available dienes such as diisopropenylbenzene (DIB), dicyclopentadiene (DCPD), Limonene etc. have been used for producing polymer with elemental sulfur. However, the commercially employed dienes are expensive and not readily available. Further, optical transparent materials obtained from such materials are brittle, expensive and require sophisticated synthetic and purification processes, involving complicated machinery and expensive purification processes, to modify such reactants into useful materials. Expensive components such as DIB (a commercial cross-linking agent monomer), Selenium and organically modified chalcogenide (ORMOCHALC) have been used for reacting with sulfur to produce copolymer from an organic material which exhibits transmittance in the NIR-Mid IR region.
Visible transparency along with infrared transparency is one of the essential criteria of optic material used in night vision camera gesture recognition in gaming, surveillance applications including both civilian and military purposes and other related applications. The quality of object image and vision clarity primarily depend upon visible light transparency of optical

material. Currently used IR transmitting materials including inorganic semiconductors, halides and chalcogenide glasses are toxic (e.g., BaF2, CdTe, GaAs, ZnSe), expensive (e.g., BaF2, CdTe, Ge, LiF, ZnSe, MgF2), water soluble (e.g., CsBr, CsI, KBr, KCl, NaCl) and difficult to process. The major problem associated with the currently available IR transmitting materials is their processing cost in addition to the cost of raw materials.
Furthermore, methods of the art employ solvent for solubilizing the source of diene monomers, additional reagent/catalyst, toxic agents, or multiple steps making the process expensive, environmentally hazardous and difficult to expand at an industrial level. Thus, there is a need for providing alternate means and methods for overcoming the constraints of the prior art, and providing simple, efficient, economic and environmentally friendly methods and products for obtaining stable infrared transparent co-polymer by employing elemental sulfur.
The inventors of the present invention have developed a sulfur-EPDM polysulfide material and method for preparation of the sulfur-EPDM polysulfide material which can overcome the problems faced by the commercial IR transparent materials making these materials non-toxic, non-hygroscopic, water insoluble or hydrophobic and non-expensive. These materials are soft and can be easily processed, and scaled up, and are thermally (up to 220 ˚C) and mechanically stable. Hence, a new family of inexpensive, functional materials obtained by practical methods is desirable.
Moreover, several commercial materials which are known to transmit in the NIR and Mid-IR regions are prepared through sophisticated processing conditions, toxic substrates are often used, and the optical products are brittle, nonflexible and water soluble to some extent. The present invention involves a simple and scalable process for the preparation of sulfur-EPDM material.
OBJECTS OF THE INVENTION
The principal objective of the present invention is to provide a polysulfide material made of elemental sulfur and Ethylene Propylene Diene Monomer (EPDM).
Another objective of the present invention is to provide polysulfide material having transmittance in the Visible and Infrared region.

Yet another objective of the present invention is to provide polysulfide material having sulfur content <40 % and having > 80% Visible and >75% IR transparency.
Another important objective of the present invention is to provide a solid-state process for preparing sulfur-EPDM film.
Yet another objective of the present invention is to provide articles comprising the sulfur-EPDM polysulfide material and corresponding methods for preparing said article useful for example in infrared device applications for imaging and optical filtering purposes.
SUMMARY OF THE INVENTION
Technical Problem
The technical problem to be solved in this invention is to provide thermally stable, physically
and chemically stable, flexible, non-toxic visible-infrared transparent optical materials at
commercial scale using EPDM as rubber polymer and elemental sulfur.
Solution to the problem
The problem has been solved by employing a simple process comprising (a) mixing elemental
sulfur with EPDM rubber to obtain a pre-mix; (b) subjecting the pre-mix obtained in step (a)
to two-roll milling at room temperature to obtain a uniform film/sheet like material; and (c)
compression molding the material obtained in step (b) to obtain the sulfur-EPDM polysulfide
material.
Overview of the invention
The present invention provides a stable polysulfide material made of elemental sulfur and
elastomer having higher transmittance in the infrared region and visible range. More
particularly, the present disclosure provides sulfur-EPDM rubber polysulfide material which is
sensitive towards visible-infrared transmittance and simple methods for preparing the same.
The disclosure also provides articles comprising the sulfur-EPDM polysulfide material and
corresponding methods for preparing said article useful for example in infrared device
applications for imaging and optical filtering purposes. A solid-state process for preparing the
said sulfur-EPDM film and the material is also provided.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are

incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:
Figure 1 depicts reactive polymeric sulfur di-radicals formation.
Figure 2 depicts the schematic process of preparing Visible and IR transparent films.
Figure 3 depicts conversion of EPDM-S powder lumps into physical homogeneous sheet by two roll milling.
Figure 4 depicts EPDM-S compression molded polysulfide films at temperature range of 165 – 185 ˚C.
Figure 5 depicts transmittance spectra of EPDM-S polysulfide films compression molded at temperature range of 165 ˚C – 185 ˚C
Figure 6 depicts FT-IR spectra of EPDM, EPDM-S compression molded films prepared at temperature range of 165 ˚C – 185 ˚C.
Figure 7 depicts TGA of EPDM-S polysulfide film compression molded at 165 ˚C.
Figure 8 depicts TGA of EPDM-S polysulfide film compression molded at 175 ˚C.
Figure 9 depicts TGA of EPDM-S polysulfide film compression molded at 185 ˚C.
Figure 10 depicts solvent resistance of the EPDM-S polysulfide film.
Figure 11 depicts visible transparency of EPDM-S polysulfide film.
Figure 12 depicts thermography study done to demonstrate IR transmittance.
DETAILED DESCRIPTION OF THE INVENTION
At the very outset, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment, without intending to imply any limitation on the scope of this invention. Accordingly, the description and examples are to be understood as exemplary embodiments for teaching the invention and not intended to be taken restrictively. The details of one or more embodiments of the invention are set forth in the accompanying description below including specific details of the best mode contemplated by the inventors for carrying out the invention, by way of

example. It will be apparent to one skilled in the art that the present invention may be practiced
without limitation to these specific details.
Abbreviations
DIB – 1,3‐diisopropenylbenzene
DVB – divinylbenzene
EPDM – Ethylene Propylene Diene Monomer
EPDM-S – Ethylene Propylene Diene Monomer-sulfur polymer film
ORMOCHALC – organically modified chalocogenides
IR – Infrared
VIS – Visible
Definitions:
Unless contraindicated or noted otherwise, throughout this specification, the terms “a” and “an”
mean one or more, and the term “or” means and/or. The use of “comprise”, “comprises”,
“comprising”, “contain”, “contains”, “containing”, “include”, “includes”, and “including” are
not intended to be limiting. It is to be understood that both the foregoing general description
and this detailed description are exemplary and explanatory only and are not restrictive.
Wherever there is an indefinite article used, the specification is to be understood as
contemplating plurality as well as singularity, unless the context requires otherwise. Unless
otherwise defined, scientific and technical terms used herein shall have meanings that are
commonly understood by those of ordinary skill in the art. Further, unless otherwise required
by context, singular terms shall include pluralities and plural terms shall include the singular.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
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 and 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
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base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications 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 modifications in the nature of the disclosure or the preferred embodiments 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.
However, before describing the elastomer-based material and process of the present disclosure in greater detail, it is important to take note of the common terms and phrases that are employed throughout the instant disclosure for better understanding of the technology provided herein. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
As used herein, the expression “sulfur-EPDM rubber polysulfide material” refers to a polysulfide material obtained on subjecting a homogenous mixture of elemental sulfur and elastomer such as but not limiting to polybutadiene rubber (PBR), ethylene propylene diene terpolymer (EPDM), natural rubber, synthetic butadiene rubber, butyl rubber, styrene butadiene rubber etc., to temperature ranging from about 165˚C to about 185˚C.
As used herein, the expression ‘elemental sulfur’ refers to octamer stable allotrope monomer molecule existing in nature. The present disclosure allows use of elemental sulfur from solid waste material obtained from the petrochemical industry, derived after the desulfurisation process in the industry.
As used herein, the expression ‘infrared transparent material’ refers to materials which transmit infrared radiation of different wavelengths through it.
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As used herein, the expression ‘infrared transmittance’ is employed for property quantification of the infrared transmitting material.
Unless otherwise defined, scientific and technical terms used herein shall have meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
The foregoing broadly outlines the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying the disclosed methods or for carrying out the same purposes of the present disclosure.
In view of the drawbacks associated and to remedy the need created by the art, the present disclosure aims to provide stable polysulfide material made of elemental sulfur and elastomer having higher transmittance in the infrared region and visible range. More particularly, the present disclosure provides sulfur-EPDM rubber polysulfide material which is sensitive towards visible-infrared transmittance and simple methods for preparing the same. The disclosure also provides articles comprising the sulfur-EPDM rubber polysulfide material and corresponding methods for preparing said article. In the present invention the inventors are able to achieve <40% elemental sulfur loading in the polysulfide material. As less cross-linked or low sulfur loaded polysulfide films/materials are obtained resulting in the retention of the elastomeric structure of the polysulfide material obtained.
Elemental sulfur at about 175°C forms a linear polymeric sulfur (polysulfide) diradical which can be trapped by reacting with olefinic moiety and thereby restricts sulfur from getting back into cyclic form. The present invention works on the principle of inverse vulcanisation of sulfur which happens above 165˚C where diradical of sulfur starts propagating to form linear polymeric structures which are ready to be cross-linked with unsaturated bonds.
In an embodiment, the present disclosure provides a simple method for making thermally stable, physically and chemically stable, flexible, non-toxic visible-infrared transparent optical materials at commercial scale using EPDM as rubber polymer and elemental sulfur.
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In embodiments of the present disclosure, elemental sulfur is known to form di-radical above 165°C. The activation of elemental sulfur at 175°C for certain amount of time leads to the formation of linear polymeric diradical chains (Figure 1). These diradicals react with the double bonds present in the EPDM to form internally cross-linked products (process is called inverse vulcanization). EPDM is a copolymer of ethylene, propylene and a small amount of non-conjugated diene monomers (2 – 3 mol%) which provide cross-linking sites for vulcanization. The sulfur-EPDM rubber polysulfide material was produced by creating more C-S and S-S bonds while reducing some of the C=C bonds.
The embodiment of the present disclosure employs a solvent less mixing (such as a solid-state mixing) using Brabender and two-roll milling to create a homogeneous mixture of the EPDM and sulfur, which allows for higher sulfur loading on the films and yields films of superior quality.
In an embodiment, the method of the present disclosure provides for sulfur-EPDM polysulfide material which is selective towards visible and infra-red transmittance. The developed methodology is also a green synthesis, as no solvent is used. Thus, the methods of the present disclosure do not employ a catalyst or a solvent.
The methods of the present disclosure for producing the sulfur-EPDM polysulfide material, such as but not limiting to films, employ a solid-state reaction wherein the polysulfide materials are obtained from a mixture of solid starting materials.
Usually, rubbers/elastomers do not form a stable film because it wrinkles and will not hold the shape. However, the present disclosure provides for solid-state methods which results in physically stable and self-standing EPDM-based polysulfide film.
In an embodiment, present invention provides a (solid-state) method of producing a sulfur-EPDM (Ethylene-Propylene-Diene-Monomer) polysulfide material, the method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature to
obtain a uniform film/sheet like material; and
c. compression molding the material obtained in step (b) to obtain the sulfur-EPDM
polysulfide material.
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In an embodiment, present invention provides a (solid-state) method of producing a sulfur-EPDM (Ethylene-Propylene-Diene-Monomer) polysulfide material, the method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature to
obtain a uniform film/sheet like material; and
c. compression molding the material obtained in step (b) at temperature ranging from
about 165°C to about 185°C, preferably about 175°C, optionally followed by cooling,
to obtain the sulfur-EPDM polysulfide material.
In an embodiment, the present invention provides a method, wherein the EPDM comprises one or more olefinic bonds; wherein the elemental sulfur is in amount ranging from 10 to 40 wt% and the EPDM is in amount ranging from 60 to 90 wt%.
In an embodiment, the present invention provides a method, wherein the mixing is carried out in a mixer at room temperature for time in the range of 5 to 10 minutes and rpm in the range of 25 rpm to 40 rpm.
In still another embodiment of the present disclosure, the mixing is carried out in a mixer (such as but not limited to Brabender).
In an embodiment, the present invention provides a method, wherein in the two-roll milling of step (c) is performed at room temperature for time in the range of 5 to 15 minutes.
In an embodiment, present invention provides a method, wherein the method does not employ a solvent or catalyst.
In still another embodiment of the present disclosure, the mixture of step b) is subjected to compression molding at temperature ranging from about 165°C to about 185°C, preferably 175°C, and pressure ranging from about 0.2 to about 2.6 ton per square inch and about 25 minutes to about 2 hours, preferably about 2 ton per square inch /30 minutes. The pressure applied during compression molding may be varied as desired, such as between 0.2 to about 2.6 ton per square inch, preferably about 1 to about 2 ton per square inch or more preferably about 1.4 to about 2 ton per square inch or about 1.8 to about 2 ton per square inch. In an exemplary and non-limiting embodiment, for large scale preparations, the pressure may be varied in the range of about 0.2 to 2.6 ton per square inch depending on the pressing conditions in a suitable press, such as but not limiting to an automated carver press.

In embodiments of the present disclosure, the cooling may be carried out by any means known in the art. In an exemplary and non-limiting embodiment, the cooling step is carried out as fast cooling by rapidly keeping in open air or by purging air/water within the compression molding instrument while maintaining the pressure.
In an embodiment, the present disclosure provides for process of making self-standing and stable EPDM-based polysulfide film by compression molding.
In an embodiment, present invention provides a (solid-state) method of producing a sulfur-EPDM (Ethylene-Propylene-Diene-Monomer) polysulfide film, the method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature to
obtain a uniform film/sheet like material; and
c. compression molding the material obtained in step (b) to obtain the sulfur-EPDM
polysulfide film.
In an embodiment, present invention provides a (solid-state) method of producing a sulfur-EPDM (Ethylene-Propylene-Diene-Monomer) polysulfide film, the method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature to
obtain a uniform film/sheet like material; and
c. compression molding the material obtained in step (b) at temperature ranging from
about 165°C to about 185°C, preferably about 175°C, optionally followed by cooling,
to obtain the sulfur-EPDM polysulfide film.
In an exemplary embodiment, the present disclosure provides for a two-step process for the production of stable infrared (IR) transparent material such as but not limiting to films from elemental sulfur (industrial by-products) and EPDM.
In another exemplary embodiment, elemental sulfur and EDPM are directly mixed at a ratio of about 1:2 in the absence of any catalyst or solvent. This mix is subjected to compression molding at about 175˚C to make optical thin films. It is also possible to tune the IR transmittance behavior by changing the temperature in the compression molding step. The present disclosure also maximizes the cost reduction of optical materials. The films obtained are mechanically stable, flexible and can be molded into any desired shapes.

In embodiments of the present disclosure, elemental sulfur and EPDM are directly mixed in a mixer such as but not limiting to Brabender internal mixer at a ratio of about 1:9 to about 7:3, preferably about 1:2, without the addition of any catalyst or solvent or reagent. This pre-mix was subjected to compression molding at temperature ranging from about 165-185°C, and pressure ranging from about 0.2 to about 2.6 ton per square inch for about 25-45 minutes to make thin films.
In embodiments of the present disclosure, the unique transparency feature of sulfur-EPDM polysulfide film is that it can transmit increased amount of visible light and infrared light and less amount of UV light. This contrasting behavior in light transmittance is ideally useful for infrared device applications for imaging and filtering purposes. For instance, applications include making lens/filters of thermal imaging night vision cameras or any FLIR systems.
In embodiments of the present disclosure, the polysulfide material has higher transmittance in the infrared range, i.e., at least about 80% or more transmittance in the infrared range and the visible range.
In embodiments of the present disclosure, the polysulfide material or the article thereof has about 70% to about 90%, preferably about 73% to about 88% transmittance in the infrared range.
In embodiments of the present disclosure, the infrared (IR) transparency of the film is measured using Vis-NIR spectrophotometer for a wide range of about 0.75 µm to about 2.6 µm.
In another embodiment, the polysulfide material of the present disclosure transmits in the VIS range of about 0.4 µm to about 0.8 µm, NIR range of about 0.75 µm to about 2.6 µm and mid-IR range of about 2.6 µm to about 22.2 µm), preferably higher transmittance in the NIR and mid-IR range of about 0.75 µm to about 22.2 µm.
In embodiments of the present disclosure, the IR transparency of the film is measured using FT-IR spectrometer is to verify the IR transparency of the material in both mid-IR and NIR range.
In embodiments of the present disclosure, Thermogravimetric analysis of the film (in air) confirmed its thermal stability where it decomposes step-wisely like 200-300°C (15.08% weight loss), 300-500°C (75.40%) and 500-700°C (9.09%). In TGA, sulfur alone decomposes at 200-300°C range whereas EPDM decomposition range is starting from 400-500°C. The third

transition in the TGA of sulfur-PBR polysulfide material film is attributed to the oxidation of the residual carbon left during heating in air.
In embodiments of the present disclosure, the films also exhibited thermal resistance up to 240°C as evident from the TGA analysis.
The polysulfide material of the present disclosure can be processed into any desired shape, such as but not limiting to by moulding for ease of processability.
In an embodiment, the present invention provides a polysulfide material, wherein the polysulfide material is in a form selected from a group comprising film, sheet, block, tape, fibre, tube, pipe, solid lump and rod or any combination thereof.
In non-limiting embodiments of the present disclosure, the said films include thin films, thick films, thin/thick multi-layered films, etc.
In another non-limiting embodiments of the present disclosure, the said films include thin sheets, thick sheets, thin/thick multi-layered sheets, etc.
In an embodiment, the polysulfide film of the present disclosure has thickness ranging from about 100 µm to about 160 µm.
In an embodiment, the present invention provides an article comprising the sulfur-EPDM polysulfide material.
In an embodiment, present invention provides a method of manufacturing an article comprising sulfur-EPDM polysulfide material, said method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature
to obtain a uniform films/sheet like material; and
c. compression molding the material obtained in step (b) to obtain the article of desired
shape.
In an embodiment, present invention provides a method, wherein in step (d) the polysulfide material is subjected to compression molding at temperature ranging from about 165°C to about 185°C, preferably about 175°C, and pressure ranging from 0.2 to 2.6 ton per square inch for 25 to 120 minutes, preferably about 2 ton per square inch for 30 minutes.

In an embodiment, present invention provides an article, wherein the article has thickness ranging from about 100 µm to about 160 µm; and/or wherein the article has high transmittance in the infrared range and visible range.
In an embodiment, the present invention provides an article, wherein the article is selected from a group comprising optic material, infrared transmitting material, sensing material, imaging material, or any combination thereof.
In an embodiment, the present invention provides an article, wherein the article is selected from but not limited to surveillance camera, advanced driver assistance, infrared photography, thermal imaging/vision, night vision, optical filters (long pass and band pass), LIDAR, dichroic mirrors, optical gas sensing, solar dryers.
In an embodiment, present invention provides a EPDM-S polysulfide material, the article or the methods, wherein the polysulfide material or article transmits the infrared in the range of 800 nm to about 2600 nm, and wherein the polysulfide material or the article has characteristics selected from a group comprising non-hygroscopicity, hydrophobicity, physical stability, mechanical stability, thermal stability, self-standing, flexibility, resistance to solvents or resistance to chemicals, ease of scalability, non-toxicity, moisture stability or any combination thereof.
The present disclosure also provides for sulfur-EPDM compression molded polysulfide material comprising elemental sulfur and EPDM. The EPDM based polysulfide films of the present disclosure are stable and self-standing.
EXAMPLES
The following examples particularly describe the manner in which the invention is to be performed. But the embodiments disclosed herein do not limit the scope of the invention in any manner.
Example 1: Preparation of homogenous mixture of EPDM and elemental sulfur
1.1 Brabender Premixing
This was the first step involved in preparing visible-infrared transparent sulfur-EPDM polymers. The premix was prepared in a batch process and the amount used for making one batch was 30 grams. The required amount of EPDM (18 grams) and sulfur (12 grams) were fed

into the Brabender Plasticoder at 25 rpm initially. After pre-determine time, the rpm was raised to 40 rpm and mixing continued for a time period of 5-6 minutes. All the mixing was performed at room temperature. In the output inventors got a highly homogeneous mixture of EPDM-sulfur in the form of lumps. The process is repeated for different batches in order to make the pre-mix ready for our future processes.
1.2 Two-roll milling
The crude lump obtained from the brabender premix (30 grams) was subjected to two-roll milling at room temperature to make it into homogeneous uniform sheet. The distance between the two rolls (nip gap) was maintained at 0.1 mm and the rotation of rolls maintained at 15 rpm. The two-roll milling was executed for a period of 10 minutes which ensured a uniform sheet which could be further processed in the next stage. Figure 3 illustrates conversion of EPDM-S powder lumps into physical homogeneous sheet by two roll milling.
Example 2: Preparation of visible-infrared films through compression molding
2.1 General experimental conditions under which the compression molding was carried out:
Temperature – 165 ˚C; Load – 13500 kg; Time – 1.5 hours; Mold used – 16 cm x 16 cm x 0.025 cm (250 µm), Premix amount – 5 g (two-roll milled).
The premix obtained after brabender mixing and two-roll milling were sandwiched between two transparent sheets along with the mold and kept into the platens of the automated carver press once the required temperature was reached.
2.2 There is a four-step program used in the automated carver press.
Step 1: In the first step, the load of 454 kilograms is applied for 5 minutes at 165 ˚C.
Step 2: In the second step the load was increased to 8000 kilograms for 5 minutes at 165 ˚C.
Further, when the load just reached 8000 kilograms one bumping was provided for 40 seconds.
The purpose of this process was to remove any entrapped gaseous molecules inside the material
so that the films will be defect free.
Step 3: In the third step, the load was raised to 13500 kilograms for 1.5 hours maintaining the
temperature of 165 ˚C

Step 4: Last step was that of cooling, where air and water purging was given for 20 minutes
without releasing the load of 13500 kilograms. The purpose of maintaining load while cooling
is to avoid any structural collapse during the rapid cooling process.
After the cooling process, the film was removed between the two transparent sheets by simple
peeling.
The above processing conditions were also used to make films at different temperatures such
as at 175 ˚C, 185 ˚C and at loads of 18000 kilograms, 22500 kilograms for different
compression molding time durations such as 2 hours, 2.5 hours.
Example 3: Temperature controlled Visible-IR transparency
The experiment was conducted at 22500 kg load for a time of 2 hours at three different temperatures such as 165 °C, 175 °C and 185 °C. Sulfur-EPDM rubber composites prepared at three different temperatures appeared in three different colors. Figure 4 illustrates EPDM-S compression molded films prepared at different temperatures. Transmittance spectra of EPDM-S films prepared at different temperatures is depicted in Figure 5.
It can be clearly inferred from the table as well as from Figure 5 that, the transparency of the three different films (prepared at different temperatures) measured for the range of 800-2600 nm appeared to be nearly same in all the cases. However, there is a slight gradual decrease in transparency in the region of 400 nm – 800 nm (visible range) for the films prepared at 165 °C to 185 °C. This is also supported by the color of the films obtained at three different temperatures (Figure 4) and also the corresponding spectral profiles mentioned in Figure 5. Further, Figure 11 demonstrates visible transparency of the EPDM-S compression molded polymer film.
Without any further processing or coating, the films prepared at different temperature conditions exhibited the unique transmittance behavior as described in the Table below:
a. Film prepared after two roll milling

Film Substrate Thickness (μm) Average VIS Trans (%) (400-800nm) Average IR Trans (%) 800-2600nm)
EPDM-S-1 (165˚C) 160 88 74
EPDM-S-2 (175˚C) 160 81 77
EPDM-S-3 (185˚C) 160 73 79

b. Film prepared without two roll milling

Film Substrate Thickness (μm) Average VIS Trans (%) (400-800nm) Average IR Trans (%) 800-2600nm)
EPDM-S-1 (165˚C) 160 31 40
EPDM-S-2 (175˚C) 160 31 43
EPDM-S-3 (185˚C) 160 23 41
Example 4: FT-IR Analysis
Fourier Transform Infrared Spectroscopy (FT-IR Analysis) of the compression molded polymer film having the thickness range (100 µm -160 µm) is carried out in transmission mode in Mid-IR range to characterize the extent of reaction happened between the double bond present in diene monomer and elemental sulfur.
The analysis results depicted in Figure 6 confirms the disappearance of alkene stretching vibrations (from the monomer present in EPDM) at 1540cm-1 especially for the films prepared at 175 ºC (EPDM-S-2) and 185 ºC (EPDM-S-3). Similarly, the alkene out of plane bending vibration at 869 cm-1 present in the EPDM monomer is also disappeared for the films as mentioned above. Also, the decrease in the intensity of the sharp absorption bands of CH2 (comes at 1450 cm-1) and other relevant vibrations in the polymer films when compared with the initial EPDM indicates the increased infrared transparency capability of the final polymer film.
Example 5: Thermogravimetric analysis
Thermogravimetric analysis of the compression molded polymer film (in air) having thickness of 100 µm - 160 µm is performed up to 800˚C with about 10-30 mg of sample in presence of air and a rate of heating of about 20˚C per minute, to understand the pattern of decomposition. The instrument used is TA instruments TGA Q500. TGA thermogram of the sulfur-EPDM polysulfide material film is depicted in Figure 7 – 9. In Figure 7, TGA of the film prepared at 165 ºC (EPDM-S-1) having thickness 140 µm and weighing 14.27 mg confirmed its thermal stability where it decomposes step-wisely like 200-300°C (15.08% weight loss), 300-500°C (75.04%) and 500-700°C (9.09%). In Figure 8, TGA of the film films prepared at 175 ºC (EPDM-S-2) having thickness 100 µm and weighing 15.63 mg confirmed its thermal stability

where it decomposes step-wisely like 200-300°C (15.56% weight loss), 300-500°C (9.65%) and 500-700°C (74.47%). In Figure 9, TGA of the film films prepared at 185 ºC (EPDM-S-3) having thickness 160 µm and weighing 29.77 mg confirmed its thermal stability where it decomposes stepwise like 200-300°C (28.12% weight loss), 300-500°C (%) and 500-700°C (71.65%).
In TGA, sulfur alone decomposes at 200-300°C range whereas EPDM decomposition range starts from 400-500°C. The third transition in the TGA of sulfur-EPDM polysulfide material film is attributed to the oxidation of the residual carbon left during heating in air.
Example 6: Moisture stability analysis
The compression molded S-EPDM polymer film is hydrophobic in nature; thus, it is stable to moisture and air as well.
When it comes to sulfur, the polysulfide linkages are not polar in nature and hence there is no possible interaction with water. The electronegativity of sulfur (2.5) is same as that of carbon and is not sufficient to make any hydrogen bonding interaction with water. Further, EPDM also does not contain polar group in its molecular skeleton and only hydrophobic hydrocarbon chains are embedded in structure. Thus, in the absence of electronegative atoms there is no possibility of hydrogen bonding interaction with water. As a result, when a drop of water is placed over the EPDM polysulfide, the water droplet assumes its spherical shape over the surface, no flattening of droplet observed confirming the hydrophobic nature of the EPDM polysulfide.
Example 7: Solvent resistance analysis
Solvent resistance of the compression molded polysulfide film prepared was tested for toluene solvent above its boiling point. A small piece of the film having thickness of about 160 µm is dipped in toluene solvent (Boiling condition at 120˚C) for 48 hours. The solvent remained colorless after boiling with the film and the film also remained intact. As illustrated in Figure 10, no dissolution or leaching of the film was observed in the solvent establishing that the film is insoluble in the said solvent even at boiling temperature.
Example 8: Thermography studies
IR transmittance of the material is further proved by using thermal/IR imaging camera depicted in Figure 12. Thermal imaging camera, also known as infrared imaging camera, works on the principle of thermal radiation emitted from a body which covers mostly mid-IR and NIR. The

thickness of the PBR-S compression molded film of the present disclosure tested herein is about 160 µm. The thermal and visible image obtained using the camera is depicted in Figure 12. It shows the infrared thermal images of a human hand when it is covered with the EPDM-S compression molded polymer film. Further, in the infrared thermal imaging mode, the fingers of the hand are clearly visible when the hand is covered with the EPDM-S compression molded film. This demonstrates the IR transmitting capacity of the EPDM-S compression molded film of the present disclosure.
Example 9: Transparency analysis
Visible transparency of the films having thickness ranging from 100 µm to 160 µm can be
analyzed through naked eyes or can be is measured using Visible Spectrophotometer.
Figure 11 depicts the EPDM-S compression molded polymer film having thickness 140 µm to be visibly transparent.
ADVANTAGES
In an exemplary embodiment, advantages of the present disclosure include but are not limited
to:
1. The EPDM-S polysulfide films having VIS & IR transparency prepared by a simple three stage solid state process.
2. The present disclosure provides for broad and high IR transmitting material (i.e., having a wide transparency range covering both NIR to mid-IR ranges) and is free from anti-reflective coating and which is photochemically stable.
3. The polysulfide material or articles thereof of the present disclosure are thermally stable.
4. It is also not sensitive towards moisture(hydrophobic) and insoluble in water.
5. The polysulfide material or articles thereof of the present disclosure is also chemically inert as it is not soluble or does not swell in organic solvents such as toluene, benzene, acetone, DMSO, DMF etc. even at boiling conditions of the respective solvents.
6. The polysulfide material of the present disclosure has mechanical stability and flexibility which offers tremendous opportunities to mold it into any desired shape. While most commercially available optic materials are brittle (mechanically unstable), not flexible and involve difficult synthetic conditions and sophisticated purification processes, the material of the present disclosure overcomes these limitations.

7. The material of the present disclosure can be prepared in a single step through a greener approach (no solvent, low temperature, less carbon footprint as it does not employ high power energy source); does not need any high-end purification processes, sophisticated machineries, or a polymer matrix for making a stable film; and employs waste (sulfur, PBR) generated from the petrochemical industry. Thus, the method of the present disclosure is simple, cost effective, environment friendly and is an excellent example of waste into value generation.
8. No utilization of external reagent to enhance the visible transparency.
9. Fine tuning of visible transparency by controlling the temperature during compression molding.
10. Since, night vision optical device works by amplifying the visible light in the immediate vicinity, it is required to have dual transparency. The dual transparency in night vision and surveillance cameras is also manipulated by using optical filters corresponding to which range of wavelength is required for applications.
Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.
The foregoing description of the specific embodiments fully reveals 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 in this disclosure 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.
Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” wherever used, will be understood to imply the inclusion of a stated element,

integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Similarly, terms such as “include” or “have” or “contain” and all their variations are inclusive and will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
As used herein, the term ‘comprising’ when placed before the recitation of steps in a method means that the method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps. For example, a method comprising steps a, b, and c encompasses a method of steps a, b, x, and c, a method of steps a, b, c, and x, as well as a method of steps x, a, b, and c. Furthermore, the term “comprising” when placed before the recitation of steps in a method does not (although it may) require sequential performance of the listed steps, unless the content clearly dictates otherwise. For example, a method comprising steps a, b, and c encompasses, for example, a method of performing steps in the order of steps a, c, and b, the order of steps c, b, and a, and the order of steps c, a, and b, etc. The terms “about” or “approximately” are used herein to mean approximately, in the region of, roughly, or around. When the term “about” is used in conjunction with a numerical value/range, it modifies that value/range by extending the boundaries above and below the numerical value(s) set forth. In general, the term “about” is used herein to modify a numerical value(s) or a measurable value(s) such as a parameter, an amount, a temporal duration, and the like, above and below the stated value(s) by a variance of +/-20% or less, +/-10% or less, +/-5% or less, +/-1% or less, and +/-0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention, and achieves the desired results and/or advantages as disclosed in the present disclosure. It is to be understood that the value to which the modifier “about” or “approximately” refers is itself also specifically, and preferably, disclosed.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The suffix ‘(s)’ at the end of any term in the present disclosure envisages in scope both the singular and plural forms of said term.

As used in this specification and the appended claims, the singular forms “a,” “an” and “the” includes both singular and plural references unless the content clearly dictates otherwise. 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. As such, the terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein.
Numerical ranges stated in the form ‘from x to y’ include the values mentioned and those values that lie within the range of the respective measurement accuracy as known to the skilled person. If several preferred numerical ranges are stated in this form, of course, all the ranges formed by a combination of the different end points are also included.
As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I;
B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H;
C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned
otherwise.
Throughout this specification, the term ‘a combination thereof’, ‘combinations thereof’ or ‘any combination thereof’ or ‘any combinations thereof’ are used interchangeably and are intended to have the same meaning, as regularly known in the field of patent disclosures.
Any discussion of documents, acts, materials, devices, articles and 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.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications 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 modifications in the nature of the disclosure or the preferred embodiments 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.
All references, articles, publications, general disclosures etc. cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication etc. cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

We claim:
1. A solid-state method of producing a sulfur-EPDM (Ethylene-Propylene-Diene-
Monomer) polysulfide material, the method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature
to obtain a uniform film/sheet like material; and
c. compression molding the material obtained in step (b) to obtain the sulfur-EPDM
polysulfide material.
2. The method as claimed in claim 1, wherein the EPDM comprises one or more olefinic bonds; wherein the elemental sulfur is in amount ranging from 10 to 40 wt% and the EPDM is in amount ranging from 60 to 90 wt%.
3. The method as claimed in claim 1, wherein the mixing is carried out in a mixer at room temperature for time in the range of 5 to 10 minutes and rpm in the range of 25 rpm to 40 rpm.
4. The method as claimed in claim 1, wherein in the two-roll milling of step (c) is performed at room temperature for time in the range of 5 to 15 minutes.
5. The method as claimed in claim 1, wherein the method does not employ a solvent or catalyst.
6. The method or the polysulfide material of any of the preceding claims, wherein the polysulfide material is in a form selected from a group comprising film, sheet, block, tape, fibre, tube, solid lump and rod or any combination thereof.
7. An article comprising the sulfur-EPDM polysulfide material as claimed in any of claims 6-7.
8. A method of manufacturing an article comprising sulfur-EPDM polysulfide material, said method comprising:
a. mixing elemental sulfur with EPDM rubber to obtain a pre-mix;
b. subjecting the pre-mix obtained in step (a) to two-roll milling at room temperature
to obtain a uniform films/sheet like material; and

c. compression molding the material obtained in step (b) to obtain the article of desired shape.
9. The method as claimed in claim 8, wherein in step (c) the polysulfide material is subjected to compression molding at temperature ranging from about 165°C to about 185°C, preferably about 175°C, and pressure ranging from 0.2 to 2.6 ton per square inch and 25 to 120 minutes, preferably about 2 ton per square inch for 30 minutes.
10. The article or the method as claimed in claim 8 or 9, wherein the article has thickness ranging from about 100 µm to about 160 µm; and/or wherein the article has high transmittance in the infrared range and visible range.
11. The article or the method as claimed in any of claims 8-10, wherein the article is selected from a group comprising optic material, infrared transmitting material, sensing material, imaging material, or any combination thereof.
12. The polysulfide material, the article or the methods as claimed in any of the preceding claims, wherein the polysulfide material or article transmits the visible-infrared in the range of 800 nm to about 2600 nm, and wherein the polysulfide material or the article has characteristics selected from a group comprising non-hygroscopicity, hydrophobicity, physical stability, mechanical stability, thermal stability, self-standing, flexibility, resistance to solvents or resistance to chemicals, ease of scalability, moisture stability, non-toxicity, or any combination thereof.