Description:FIELD OF THE INVENTION
The invention relates to a polypropylene based formulation. More particularly, the present invention relates to a polypropylene based formulation and process of preparation of the same. The present invention also pertains to a safety cap molded from the polypropylene based formulation for liquefied petroleum gas (LPG) storage containers.

BACKGROUND OF THE INVENTION
Liquefied petroleum gas (LPG) is an admixture of propane and butane used in 50 /19 Kg industrial and 14.2 domestic cylinders in India. This mixture of gas is heavier than air and tends to settle down at the floor level and takes time to clear the area. The mixture or the gases are pressurized & pumped into cylinders and hence gases expand as much as 250 times when it leaks. A 14.2 kg cylinder will last only a day at home if not pressurized.

LPG was traditionally marketed in cylinders made up of stainless steels (Type-I) in India for domestic/household and commercial use. Recently new Type-IV cylinders have been introduced in Indian market by the marketing companies. Both Type-I and Type-IV cylinders currently sold in India are equipped with a safety cap covering the mouth of the cylinder. The safety cap serves following main purposes:
i. Prevents sudden release of pressure.
ii. Prevents leakage.
iii. Prevents deposition of foreign particulate material on the discharge valve.

Today, LPG is sold and marketed in different pack sizes. For domestic use, 5 kg and 14.2 kg cylinders are predominantly used, whereas 19 kg, 47.5 kg and 425 kg Jumbo cylinders are marketed for industrial and commercial consumption. These cylinders are made up of stainless steel fitted with a safety cap with a nylon/polypropylene cord. Recently, fiber composite cylinders of 5 kg and 10 kg are sold for domestic use fitted with similar safety caps.

Generally, LPG cylinder safety cap is mounted on the valve of the cylinder and is held in place by means of springs as shown in Figure 1. To remove the safety cap the spring needs to be pulled to release the spring grip on the valve neck. A nylon/PP cord is connected to the spring. By pulling, the spring loses the grip on the valve neck and the cap can be removed. The nylon cord prevents generation of static charge.

In WO 82/01580 application titled “A protection cap for gas bottles”, the inventor describes the use of polycarbonate based or similar material preferably transparent and/or colored to be used as the protective cap of LPG cylinder or bottle. Certain advantages of the material were listed such as economical to manufacture, mountable on the cylinder neck portion by simple axial displacement etc. However, polycarbonate is one of the complicated materials for injection molding. Due to its high viscosity, it makes thin wall injection molding difficult. Further, polycarbonate also easily absorbs moisture prior to injection and can cause splaying in the final part and undesirable streaking on the surface. Polycarbonate also tends to adhere to injection mold materials and machine equipment made from high iron-content alloys. There are several other drawbacks such as inconsistent resin temperature, excessive requirement of release agents during molding.

Indian Patent Application no. 1689/MUM/2009 relates to safety devices used for the LPG cylinders. The objective of the invention was to provide safety cap that requires less force to be removed from LPG cylinder valve, safety cap that can withstand high pressure, safety cap that can withstand clamp load during vibration/fatigue etc. The invention discloses use of synthetic polymeric materials such as Dopont Delrin 500 (manufactured by Dupont), Tenac 5010 (Polyacetal homopolymer grade produced by Asahi Kasei) or Celcon M90/M140 (polyacetal copolymer grade produced by Celanese Corporation). However, major drawback of the design was the limitation to reuse the safety cap. Once the nylon thread is pulled, the seal breaks along with the weak link. The seal break creates an opening along one side of the safety cap, post which the safety cap can’t be reused again.

Indian Patent no. 244036 describes the use of tamper proof seal for an LPG cylinder valve that breaks or visibly deforms on tampering and cannot be reused. The invention discloses a tamper proof seal having a hollow cylindrical shape having one end open and the other end with a small concentric hole. The opening of the seal has a first locking ring provided on the inner surface of the hollow cylindrical body. The tamper proof seal is made up of plastic material.

Conventionally, poly acetal is the first choice of material used for making safety caps for the LPG cylinder through injection molding process. However, polyacetal is being 100% imported and for making safety caps, which makes the process expensive and import dependent. Also, polyacetal requires pre-drying because of hygroscopic nature.

Furthermore, high amounts of inorganic fillers such as talc, mica, calcium carbonate etc. are added in various polyolefins formulations comprising of polymers such as polypropylene, polyethylene etc., due to certain advantages such as increase in stiffness, lower formulation costs, increases modulus of elasticity, better flexural strength etc. However, there are certain disadvantages associated with use of inorganic fillers in polyolefins such as reduced impact strength, higher directional warpage, increased abrasion, difficulty in recycling etc.

Therefore, there is a requirement for providing molding material to produce low weight reusable safety caps for LPG storage containers to achieve cost saving in raw material with better yield and reduced per piece cost of the safety caps. Further, there is requirement for molding material that has easy and timely availability and can cater to supply-demand issues.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a formulation for molding safety caps comprising a blend of:
i. polypropylene (PP) impact copolymer in a range of about 50% to 95% by weight;
ii. glass fiber in a range of about 10% to 30% by weight;
iii. maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
iv. polyolefin elastomer in a range of about 2% to 20% by weight; and
v. additives.

The present invention also provides a process for the preparation of a formulation for molding safety caps, comprising step of mixing:
- polypropylene (PP) impact copolymer in a range of about 50% to 95% by weight;
- glass fiber in a range of about 10% to 30% by weight;
- maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
- polyolefin elastomer in a range of about 2% to 20% by weight; and
- additives,
in a mixer.

The present invention further provides a safety cap for liquefied petroleum gas (LPG) storage container from the formulation as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS:
These and other features, aspects, and advantages of the present invention 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 depicts a typical layout of an LPG cylinder showing the placement of a safety cap.
Figure 2 depicts images of LPG cap molded using Delrin 500P and Formulation F-8.
Figure 3 depicts weight comparison between LPG cap molded using Delrin 500P and Formulation F-8.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a polypropylene (PP) based composition for molding safety caps for LPG cylinders. The safety caps prepared from the polypropylene based composition of the present invention has less raw material cost and due to easy availability of raw materials and higher yield due to density advantage in the PP.

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the 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 process, 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. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, formulation, methods, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

The term “about” in the context of the present invention denotes an interval of accuracy that the person skilled in the art will understand to still ensure the technical effect of the feature in question. The term typically indicates deviation from the indicated numerical value of ±20%, preferably ±15%, more preferably ±10%, and even more preferably ±5%.

Unless defined otherwise, 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 disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The polypropylene impact copolymers are thermoplastic resins made by copolymerizing propylene with one or more comonomers, typically ethylene. The structure of polypropylene impact copolymers is a combination of linear polypropylene chains with irregularities introduced by the comonomers. This complex structure is responsible for the copolymer's improved impact resistance and flexibility compared to pure polypropylene.

The present invention provides a formulation for molding safety caps comprising a blend of:
i. polypropylene impact copolymer in a range of 50% to 95% by weight, and preferably in the range of about 60% to 90% by weight;
ii. glass fiber in a range of about 10% to 30% by weight;
iii. maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
iv. polyolefin elastomer in a range of about 2% to 20% by weight; and
v. additives.

In some of the embodiments of the present invention, the polypropylene impact copolymer is preferably in the range of about 60% to 90% by weight and particularly in the range of about 70% to 80% by weight.

In some of the embodiments of the present invention, the polyolefin elastomer is in the range of about 5% to 10% by weight.

Polyolefin elastomers (POE) are a range of copolymers based on metallocene catalyst utilizing butene or octene as comonomers. Key characteristics of polyolefin elastomers are their low density & hardness, imparts high impact/toughness. These materials are commonly used in compounding applications with objective of improving impact strength, flexibility of thermoplastic based compounds. Companies like Dow, ExxonMobil, LG Chem etc. market polyolefin elastomers (POE) under the brand name like Engage, Vistamaxx, Lucene etc.

In an exemplary embodiment of the present invention, the polyolefin elastomer is ethylene-octene copolymer.

In an embodiment of the present invention, the glass fiber has a length ranging from about 2 mm to 10 mm.

In another embodiment of the present invention, the additives are selected from a group comprising an anti-static agent, a nucleating agent, an acid scavenger, a polymer stabilizer comprising an antioxidant additive or any combination thereof.

In yet another embodiment of the present invention, the antioxidant additive is a primary antioxidant additive, a secondary antioxidant additive or a combination thereof. The primary antioxidant additive is present in a range of about 0.010 to 0.350 % by weight and the secondary antioxidant additive is present in a range of about 0.010 to 0.750 % by weight.

In still another embodiment of the present invention, the anti-static agent is present in a range of about 0.05 to 0.40 % by weight, the nucleating agent is present in a range of about 0.010 to 0.50 % by weight and the acid scavenger is present in a range of about .025 to 0.50 % by weight.

In some embodiments, the primary antioxidant is selected from the family but not limited to sterically hindered phenols and amines; the secondary antioxidant is selected from the family not limited to phosphites and thioesters; the anti-static agent is based on but not limited to long-chain aliphatic amines, optionally ethoxylated and amides, quaternary ammonium salts selected from a group comprising behentrimonium chloride or cocamidopropyl betaine, esters of phosphoric acid, polyethylene glycol esters, or polyols; the acid scavengers is selected from a group comprising calcium stearate (CaSt), zinc stearate, DHT-4A, and zinc oxide; the nucleating agent is selected from family but not limited to phosphate ester compounds and sorbitol.

In another embodiment of the present invention, the nucleating agent is selected form a group comprising NA-27 and HPN-20E.

In a preferred embodiment of the present invention, the primary antioxidant additive is pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate), the secondary antioxidant additive is tris(2,4-di-t-butyl-phenyl) phosphate, the antistatic agent is glycerol monostearate-90 (GSM-90), the acid scavenger is calcium stearate, and the nucleating agent is NA-27.

In some embodiments of the present invention, the polypropylene impact copolymer has a melt flow index (MFI) ranging from about 5g/10min to 50g/10min, and preferably from about 7g/10min to 40g/10min.

In some embodiments of the present invention, the polypropylene impact copolymer has the melt flow index (MFI) ranging from about 10g/10min to 30g/10min.

In some embodiments of the present invention, the polypropylene impact copolymer has ethylene content ranging from about 5% to 30%, and preferably from about 7% to 25%.

In some embodiments of the present invention, the polypropylene impact copolymer has ethylene content ranging from about 9% to 20%.

In some embodiments of the present invention, the formulation is injection molded into safety caps for liquefied petroleum gas (LPG) cylinder or bottle or vessel.

The present invention also provides a process for the preparation of a formulation for molding safety caps comprising steps of mixing a polypropylene impact copolymer, glass fiber, maleic anhydride grafted polypropylene, polyolefin elastomer, and additives in a high speed mixer.

In an embodiment, the present invention provides a process for the preparation of a formulation for molding safety caps, comprising step of mixing:
- polypropylene (PP) impact copolymer in a range of about 50% to 95% by weight;
- glass fiber in a range of about 10% to 30% by weight;
- maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
- polyolefin elastomer in a range of about 2% to 20% by weight; and
- additives,
in a mixer.

In an embodiment of the present invention, the mixing is performed at a temperature ranging from about 10 ? to 40 ? for about 10 to 40 minutes in the presence of air or nitrogen.

In another embodiment of the present invention, the temperature should not exceed the degradation temperature of the individual components of the molding formulation.

In another embodiment of the present invention, the time for mixing is about 10 minutes or longer, preferably about 15 minutes or longer, and in particular about 30 minutes or longer.

In yet another embodiment of the present invention, the mixing is carried out at ambient pressure.

In an embodiment of the present invention, the safety cap is prepared from the molding formulation through injection molding on the injection molding machines.

The present invention also provides a safety cap for liquefied petroleum gas (LPG) storage container from the formulation as defined above.

In some embodiments, the advantages of the formulation and method of the present invention include but are not limited to:
• Product weight is reduced by about 25% (2 gm less).
• The LPG safety cap product achieves about 25% reduction in weight, resulting in a 2-gram reduction, and a 25% cost savings in raw materials. This improved yield leads to material savings, reducing the per-piece cost due to the density advantage of the PP material. This makes it a more cost-effective option.
• PP compound does not require any pre drying, making the process of the present invention quicker and more efficient. However, conventionally employed polyacetal requires pre drying because of hygroscopic nature.
• The present invention employs indigenous material for safety cap production and does not depend on acetal polymer which has to be imported with transit time of about 30-60 days. Thus, raw materials are timely available in the present invention, and the production cost is significantly lowered and more economical than processes employing polyacetal for manufacture of safety cap moulding formulations.

The present disclosure with reference to the accompanying examples below describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

PP: Polypropylene
MaPP: maleic anhydride grafted polypropylene
I-1010: pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate
I-168: tris(2,4-di-t-butyl-phenyl) phosphate
L-101: Luprox-101 (2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane)
POE: Polyolefin elastomer
CaSt: Calcium stearate
GMS-90: Glycerol monostearate-90

EXAMPLES:
Example 1: Formulations based upon 8 MFI (g/10min)
Formulations F1, F2 and F3 are prepared by mixing the components of molding formulation according to the weight % as given below in Table 1.

Table 1. Formulation F1, F2 and F3
Formulation F1 (wt%) F2 (wt%) F3 (wt%)
PP 99.79 77.72 79.74
I-1010 0.055 0.080 0.080
I-168 0.110 0.135 0.135
L-101 0.0 0.020 0.0
CaSt 0.045 0.045 0.045
MaPP 0.0 2.0 0
Glass Fiber 0.0 20.0 20.0

For formulation F1-F3, polypropylene (impact copolymer) having Melt Flow Index (MFI) of 8 g/10 min was used. For formulations F2-F3, polypropylene (impact copolymer) was mixed with 0.080% pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate (supplied as Irganox® I-1010 by BASF) and 0.1350% tris(2,4-ditert-butylphenyl) phosphite (supplied as Irgafos® I-168 by BASF). Formulations F2 and F3 were mixed with 20% short glass fibers having length of 4 mm as part of the formulation by weight. 0.020% of organic peroxide (2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, supplied as Luprox-101 by Arkema) was mixed as part of formulation F2 by weight. Additionally, formulation F2 has 2.0% maleic anhydride grafted polypropylene of the total formulation by weight.

Example 2: Formulations based upon 12MFI (g/10min)
Molding formulation F4, F5, F6 and F7 are prepared by mixing the components of molding formulation according to the weight % as given below in Table 2.

Table 2. Formulation F4, F5, F6 and F7
Formulation F4 (wt%) F5 (wt%) F6 (wt%) F7 (wt%)
PP 99.95 74.95 79.95 72.95
I-1010 0.0475 0.0725 0.0725 0.0725
I-168 0.0475 0.0725 0.0725 0.0725
CaSt 0.035 0.035 0.035 0.03540
GMS-90 0.180 0.180 0.180 0.180
MaPP 0 0 0 2.0
Glass Fiber 0 20.0 15.0 20.0
POE 0 5.0 5.0 5.0

For formulations F5-F7, polypropylene (impact copolymer) having MFI (12 g/10min) was used. Formulations F5-F7 were mixed with 0.0725% pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate) (supplied as Irganox 1010, by BASF) and 0.0725% tris(2,4-di-t-butyl-phenyl) phosphate (supplied as Irgafos 168, by BASF), 0.0725% of antistatic agent such as glycerol monostearate-90 and 0.0350% of acid scavenger such as calcium stearate. Formulations F5 and F7 were mixed with 20% glass fibers having length of 4 mm as part of the formulation by weight whereas formulation F6 was mixed with 15% glass fiber having length of 4 mm. Additionally formulation F7 have 2.0% of maleic anhydride grafted polypropylene as part of the formulation by weight.

Formulations F5-F7 had 5.0% of polyolefin elastomer having MFI (5 g/10min), supplied as Engage 8200 by Dow.

Example 3: Formulations based upon 25MFI (g/10min)
The molding formulation F8 is prepared by mixing the components of molding formulation according to the weight % as given below in Table 3.

Table 3. Formulation F8
Formulation F8 (wt%)
PP 72.687
I-1010 0.085
I-168 0.145
CaSt 0.035
NA-27 0.030
GMS-90 0.018
MaPP 2.0
Glass Fiber 20.0
POE 5.0

For formulations F8, polypropylene (impact copolymer) having MFI (25 g/10min) was mixed with 0.0850% pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate) (supplied as Irganox 1010, by BASF), 0.1450% tris(2,4-di-t-butyl-phenyl) phosphate (supplied as Irgafos 168, by BASF) and 0.035% of acid scavenger such as calcium stearate. Formulations F8 had 20% glass fibers having length of 4 mm, 0.030% of nucleating agent (supplied as NA-27 by Adeka Corporation), 0.0180% of antistatic agent such as glycerol monostearate-90 and 2.0% maleic anhydride grafted polypropylene and 5% ethylene-octene copolymer as part of the formulation by weight.

Example 4: Process for preparation of the formulation F, F2, F3, F4, F5, F6, F7, and F8
Polypropylene impact copolymer in 50-95 % by weight of the formulation, glass fiber in 10-30 % by weight of the formulation, maleic anhydride grafted polypropylene in 1-10 % by weight of the formulation, polyolefin elastomer in range from 2-20 % by weight of the formulation, and additive which includes primary & secondary antioxidants, antistatic agent and nucleating agent were mixed in a high speed mixer at a temperature ranging from 10 ? to 40 ? for 10 to 40 minutes in the presence of air or nitrogen to obtain the formulation F1, F2, F3, F4, F5, F6, F7, and F8.

Example 5: Physiochemical properties of the formulation F, F2, F3, F4, F5, F6, F7, and F8
The physiochemical properties of the formulation F1, F2, F3, F4, F5, F6, F7, and F8 are assessed for the parameters including MFI, Tensile Modulus (TS), Elongation, Notched Izod Impact Strength, Flexural Modulus, Heat Deflection Temperature HDT, Shrinkage in machine and transverse direction (MD/TD), Ash content, and Specific Gravity, and the results are provided in Table 4. The physiochemical properties of the molding formulations F1, F2, F3, f4, F5, F6, F7, and F8 are compared with the Delrin 500P (Technical data sheet (TDS) Value) and Lupital F20-03. Both Delrin 500P (supplied by Dupont) and Lupital F20-03 (supplied by Mitsbishi Engg.) are general purpose medium viscosity acetal homopolymer used for injection molding applications. These acetal grades are imported in India for Automotive, appliances and general purpose applications.

The formulations of the present invention have the similar or better mechanical properties with better flow and lower density as compared to Lupital F20-03.

The formulation has excellent process-ability, flexural modulus, impact strength, minimal shrinkage in machine and transverse direction (MD & TD).

Formulation F-8 had higher impact strength by 273% and 106% as compared to Delrin 500P and Lupitol 520-03. Flexural modulus was found to be 9% and 31% higher than Delrin 500P and Lupitol 520-03. Similarly, elongation and HDT of the inventive formulation was comparable to Delrin 500P and Lupitol 520-03. Shrinkage was significantly lower as compared to Delrin 500P and Lupitol 520-03.

Table 4. The physiochemical properties of the molding formulation F1, F2, F3, F4, F5, F6, F7, and F8

Parameters
Standard Delrin 500P (TDS VALUE) Delrin 500P
(test Result) Lupital F20-03

F1
F2
F3
F4
F5
F6
F7
F8
MFI
@230°C/ 2.16Kg load
ASTM D1238 7 (1.05kg @190°C) 33.51
(2.16 kg @230°C) 9.0
9.6
9.6
4.6
11.9
5.2
6.3
5.8
11.0
TS @ Yield/Break ASTM D 638 68/68 - 64 20.6/17.5 56.8/56.0 48.9/48.9 28.0/20.7 57.0/57.0 43.1/43.1 62.7/62.0 66.0/65.7
Elongation @ Yield/Break ASTM D 638
15/40
- 8.5/30
6.4/555.0
4.7/5.8
3.6/3.6
5.3/231.2
3.1/3.1
3.0/3.0
6.0/6.9
5.8/5.9
Notched Izod Impact Strength (23°C) ASTM D 256
75
38.6 70
898.2
199
97
68.4
78
70.4
169
144
Flexural Modulus (1% secant) ASTM D 790
3100
2576 2600
616.8
3168
3056.5
1378.9
3775.4
2784.3
3286
3388
HDT @0.455MPa ASTM D 648
167
159.2 156
80.93
155.67
155
108.2
159.27
156.87
160.43
160.2
Shrinkage (MD/TD) ASTM D 955 2/1.9 1.86/0.92 2.19/0.71 1.40/0.87 0/0.45 0.03/0.5 1.28/0.87 0.02/0.58 0.08/0.68 0.04/0.47 0.04/0.42
Ash Content (%) ASTM D 5630B - - 751 ppm 20.62 19.34 368 ppm 20.95 14.08 20.59 20.39
Specific Gravity ASTM D 792 1.42 1.4 1.41 0.8934 1.0338 1.0324 0.9002 1.0466 0.9937 - 1.0

Example 6: Process for preparation of the safety cap for LPG cylinder from the formulation

Raw materials including polypropylene impact copolymer, maleic anhydride grafted polypropylene, antistatic agent, nucleating agent and additives were mixed using a high speed mixer. Extrusion of material was done using an extruder to have a homogeneous compounded material. Then the homogeneous compounded material wass injection molded into the injection molding machine to prepare the safety cap for LPG cylinders or vessel.

Images of LPG cap molded using Delrin 500P and Formulation F8 are shown in Figure 2. Weight comparison between LPG cap molded using Delrin 500P and Formulation F8 is depicted in Figure 3. , Claims:1. A formulation for molding safety caps comprising a blend of:
i. polypropylene (PP) impact copolymer in a range of about 50% to 95% by weight;
ii. glass fiber in a range of about 10% to 30% by weight;
iii. maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
iv. polyolefin elastomer in a range of about 2% to 20% by weight; and
v. additives.

2. The formulation as claimed in claim 1, wherein the polypropylene impact copolymer is preferably in the range of about 60% to 90% by weight and particularly in the range of about 70% to 80% by weight; the polyolefin elastomer is in the range of about 5% to 10% by weight.

3. The formulation as claimed in claim 1, wherein the polyolefin elastomer is ethylene-octene based copolymer, the glass fiber has a length ranging from about 2 mm to 10 mm, the additives are selected from a group comprising an anti-static agent, a nucleating agent, an acid scavenger, a polymer stabilizer comprising an antioxidant additive or any combination thereof.

4. The formulation as claimed in claim 3, wherein the antistatic agent is glycerol monostearate-90, the acid scavenger is calcium stearate, and the nucleating agent is NA-27, the antioxidant additive is selected from pentaerthrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)-propionate), and tris(2,4-di-t-butyl-phenyl) phosphate or a combination thereof.

5. The formulation as claimed in claim 1, wherein the polypropylene impact copolymer has a melt flow index (MFI) ranging from about 5g/10min to 50g/10min, and preferably from about 7g/10min to 40g/10min, the polypropylene impact copolymer has ethylene content ranging from about 5% to 30%, and preferably from about 7% to 25%.

6. The formulation as claimed in claim 5, wherein the polypropylene impact copolymer has the melt flow index (MFI) ranging from about 10g/10min to 30g/10min, the polypropylene impact copolymer has ethylene content ranging from about 9% to 20%.

7. The formulation as claimed in any of claims 1 to 6, wherein the formulation is injection molded into safety caps for liquefied petroleum gas (LPG) cylinder or bottle.

8. A process for the preparation of a formulation for molding safety caps, comprising step of mixing:
- Polypropylene (PP) impact copolymer in a range of about 50% to 95% by weight;
- glass fiber in a range of about 10% to 30% by weight;
- maleic anhydride grafted polypropylene in a range of about 1% to 10% by weight;
- polyolefin elastomer in a range of about 2% to 20% by weight; and
- additives,
in a mixer.

9. The process as claimed in claim 8, wherein the mixing is performed at a temperature ranging from about 10 ? to 40 ? for about 10 to 40 minutes in the presence of air or nitrogen.

10. A safety cap for liquefied petroleum gas (LPG) storage container molded from the formulation as claimed in any of claims 1 to 7.