Description:FIELD
The present disclosure relates to an elastomeric blend and a process of its preparation.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Crosslink density refers to the density of chains or segments that connect two infinite parts of the polymer network, rather than the density of cross-link junctures.
Air permeability refers to the rate of airflow passing perpendicularly through a known area under a prescribed air pressure differential between the two surfaces of a material.
Partially cured rubber: The term “partially cured rubber” refers to incomplete vulcanization which may vary from 10% to 80 % of actual crosslinking and has lesser crosslink density.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Butyl rubber is a copolymer of isoprene and isobutylene rubber (IIR). Generally, the inner liner of a tire is a layer of synthetic (butyl, halobutyl) rubber that is designed to prevent airflow. This is equivalent to a tire tube in a modern tubeless car tire and serves the purpose of maintaining the high air pressure of the tire. The inner liner assures that the tire will hold high-pressure air inside, without an inner tube thus, minimizing diffusion through the rubber structure. The more effective the inner liner, the less air pressure of tire will reduce over time.
The use of butyl rubber in tire tubes is due to its excellent flexibility, fatigue resistance and improved air retention in comparison to natural rubber. Further, the butyl rubber is halogenated for improving the ability to co-cure with the unsaturated rubbers specifically for application in tire inner liner. Various grades of butyl and halobutyl are available which can be employed depending upon the application requirement. However, the conventional process relates to complete curing of butyl rubber and halobutyl rubber with covalent sulphur linkages, which are heat stable. These heat stable sulphur linkages are sometimes not desirable depending upon the application of elastomer/rubber as the movement of rubber molecules gets restricted in fully cured sample due to the increase in crosslink density. Therefore, there is a room to develop a new elastomeric blend having desired properties and to meet the market demand.
Therefore, there is, felt a need to provide a process for the preparation of a partially cured elastomeric blend that mitigates the drawbacks mentioned herein above or at least provides a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems given in the background or to at least provide a useful alternative.
An object of the present disclosure is to provide an elastomeric blend.
Another object of the present disclosure is to provide an elastomeric blend having improved air impermeability.
Still another object of the present disclosure is to provide an elastomeric blend that is partially cured.
Yet another object of the present disclosure is to provide an elastomeric blend having self-healing ability.
Still another object of the present disclosure is to provide a process for the preparation of a partially cured elastomeric blend.
Yet another object of the present disclosure is to provide a process for the preparation of a partially cured elastomeric blend which is cost-effective, simple and scalable.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to an elastomeric blend comprising a butyl rubber ionomer, an elastomer co-curable with the butyl rubber ionomer and additives selected from a filler, a plasticizer, a curing agent, a dispersing agent, an activator, a retarder and an antioxidant, wherein the blend is partially cured.
The present disclosure further relates to a process for the preparation of an elastomeric blend. The process comprises the step of homogenizing a butyl rubber ionomer and a halobutyl rubber in a predetermined mass ratio to obtain a homogeneous mixture. Predetermined amounts of additives selected from a plasticizer, a dispersing agent, an activator, an accelerator and an antioxidant are added to the homogeneous mixture to obtain a slurry. A predetermined amount of a filler is added to the slurry in an open two roll mill to obtain a blend. The blend is partially cured at a predetermined temperature to obtain the elastomeric blend.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates diagrammatic representation of (A) matrix with only ionic crosslinks; (B) trapped rubber molecules in ionic crosslinks; (C) matrix with ionic crosslink and sulphur linkages and (D) matrix with ionic crosslinks which are partially cured in accordance with the present disclosure.
DETAILED DESCRIPTION
The present disclosure relates to an elastomeric blend and a process of its preparation.
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Butyl rubber is a copolymer of isoprene and isobutylene rubber (IIR). Conventionally, butyl rubber is prepared by cationic polymerization through the random copolymerization of isobutylene with small amounts of isoprene. Further, the butyl rubber is halogenated for improving the ability to co-cure with the unsaturated rubbers specifically for application in tire inner liner. Various grades of butyl and halobutyl are available which can be employed depending upon the application requirement. However, the conventional process relates to complete curing of butyl rubber and halobutyl rubber with fillers with covalent sulphur linkages, which are heat stable. These heat stable sulphur linkages are sometimes not desirable depending upon the application of elastomer/rubber as the movement of rubber molecules gets restricted in fully cured sample due to the increase in crosslink density. Therefore, there is a room to develop a new elastomeric blend having desired properties and to meet the market demand.
The present disclosure provides an elastomeric blend and a process for the preparation of an elastomeric blend.
In an aspect, the present disclosure provides an elastomeric blend of a butyl rubber ionomer, a halobutyl rubber co-curable with the butyl rubber ionomer and additives selected from a filler, a plasticizer, a curing agent, a dispersing agent, an activator, an accelerator and an antioxidant, wherein the blend is partially cured.
In an embodiment of the present disclosure, the butyl rubber ionomer can be selected from phosphonium ionomer of butyl rubber and ammonium ionomer of butyl rubber. In an exemplary embodiment of the present disclosure, the butyl rubber ionomer is phosphonium ionomer of butyl rubber.
The halobutyl rubber can be selected from bromobutyl rubber and chlorobutylrubber. In an exemplary embodiment, the halobutyl rubber is bromobutyl rubber.
Halogenation of butyl rubber extends its usefulness by significantly increasing curing rates. This enables co-vulcanization with other general purpose rubbers used in the tire carcass without affecting the desirable impermeability and fatigue properties.
In an embodiment of the present disclosure, the mass ratio of the butyl rubber ionomer to the halobutyl rubber is in the range of 1:9 to 9:1. In an exemplary embodiment, the mass ratio of phosphonium ionomer of bromobutyl rubber to bromobutyl rubber is 1:1.
In an embodiment of the present disclosure, the filler can be at least one selected from carbon black (N-660), magnesium oxide (MgO), silica, clay, calcium carbonate, talc and zinc oxide. In an exemplary embodiment, the filler is a combination of carbon black (N-660) and MgO.
The plasticizer can be at least one selected from wood rosin, coumarone indene resin, dibutyl phthalate (DBP), dioctylphtalate (DOP), diisooctylphtalate (DIOP) and dibutylsebacate.
Plasticizers are a group of material which can help in processability of material during molding or extrusion of various goods. It improves the flow behaviour of the compounded material.
The curing agent can be at least one selected from sulfur, peroxides and metal oxide. In an exemplary embodiment, the curing agent is sulfur.
The peroxide is selected from dicumyl peroxide, zinc peroxide, benzoyl peroxide, 2,4-chlorobenzoyl peroxide and 2,5-bis(t-butylperoxy)-2,5-dimethylhexane.
In an embodiment of the present disclosure, when peroxide is used as the curing agent, the mechanism of crosslinking using peroxides takes place in a homolytical manner. At the beginning of the vulcanization process, the organic peroxide splits into 2 radicals, as represented below:
ROOR ? 2RO•
The free radicals formed as a consequence of the decomposition of the peroxide, abstract hydrogen atoms from the elastomer macromolecules, converting them into macro-radicals.
~CH2C(CH3)=CHCH2 + RO• ? ROH + ~CH2C(CH3)=CHHC•~
The resulting macro-radicals react with each other by forming carbon – carbon intermolecular bridges.
In an embodiment of the present disclosure, the metal oxide is zinc oxide.
In an embodiment of the present disclosure, when metal oxide is used as the curing agent, the mechanism of crosslinking using metal oxides is that the metal oxide reacts with halogen group and forms metal halides and its hydroxy derivative. Further, in the presence of the metal halides, pendent unsaturation gets activated and creates an active electron deficient centre by moving an electron to the backbone carbon which is connected to halogen group. This electron deficient carbon atom further gets connected to the available pendent unsaturated group from other halobutyl rubber group and generates a chemical crosslinked structure with another electron deficient center for further crosslinking. This active molecule having electron deficient center helps in creating another double bond by removing halogen group from backbone. This process gets repeated inside the backbone to create multiple crosslinking.
The dispersing agent can be at least one selected from naphthenic oil, phthalate esters, aromatic oil, paraffinic oil, bio – based vegetable oil, sebacates and adipates. In an exemplary embodiment, the dispersing agent is naphthenic oil.
The activator can be at least one selected from stearic acid and zinc oxide (ZnO). In an exemplary embodiment, the activator is a combination of stearic acid and ZnO.
The accelerator can be at least one selected from 2-2’-Dithiobis(benzothiazole) (MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-tert.-butyl-2-benzothiazyl sulphenamide (TBBS), Benzothiazyl-2-Dicyclohexyl Sulfenamide (DCBS), tetramethyl thiuram disulfide (TMTD) and tetramethylthiuram monosulfide (TMTM). In an exemplary embodiment, the retarder is MBTS.
The antioxidant can be at least one selected from phenolic based antioxidant and amine based antioxidant.
The amine based antioxidant is N- isopropyl- N'- phenyl- p- phenylenediamine.
In another aspect, the present disclosure provides a process for the preparation of an elastomeric blend.
The process comprises the step of homogenizing a butyl rubber ionomer and a halobutyl rubber in a predetermined mass ratio to obtain a homogeneous mixture. Predetermined amounts of additives selected from a plasticizer, a dispersing agent, an activator, an accelerator and an antioxidant are added to the homogeneous mixture to obtain a slurry. A predetermined amount of a filler is added to the slurry in an open two roll mill to obtain a blend. The blend is partially cured at a predetermined temperature to obtain the elastomeric blend.
In an embodiment of the present disclosure, the butyl rubber ionomer can be selected from phosphonium ionomer of butyl rubber and ammonium ionomer of butyl rubber. In an exemplary embodiment of the present disclosure, the butyl rubber ionomer is phosphonium ionomer of butyl rubber.
The halobutyl rubber can be selected from bromobutyl rubber and chlorobutylrubber. In an exemplary embodiment, the halobutyl rubber is bromobutyl rubber.
In an embodiment of the present disclosure, the mass ratio of the butyl rubber ionomer to the halobutyl ribber is in the range of 1:9 to 9:1. In an exemplary embodiment, the mass ratio of phosphonium ionomer of bromobutyl rubber to bromobutyl rubber is 1:1.
In an embodiment of the present disclosure, the filler can be at least one selected from carbon black (N-660), magnesium oxide (MgO), silica, clay, calcium carbonate, talc and zinc oxide. In an exemplary embodiment, the filler is a combination of carbon black (N-660) and MgO.
The plasticizer can be at least one selected from wood rosin, coumarone indene resin, dibutyl phthalate (DBP), dioctylphtalate (DOP), diisooctylphtalate (DIOP) and dibutylsebacate.
The curing agent can be at least one selected from sulfur, peroxides and metal oxide.
The peroxide is selected from dicumyl peroxide, zinc peroxide, benzoyl peroxide, 2,4-chlorobenzoyl peroxide and 2,5-bis(t-butylperoxy)-2,5-dimethylhexane.
The metal oxide is zinc oxide.
In an exemplary embodiment, the curing agent is sulfur.
The dispersing agent can be at least one selected from naphthenic oil, phthalate esters, aromatic oil, paraffinic oil, bio – based vegetable oil, sebacates and adipates. In an exemplary embodiment, the dispersing agent is naphthenic oil.
The activator can be at least one selected from stearic acid and zinc oxide (ZnO). In an exemplary embodiment, the activator is a combination of stearic acid and ZnO.
The accelerator can be at least one selected from 2-2’-Dithiobis(benzothiazole) (MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-tert.-butyl-2-benzothiazyl sulphenamide (TBBS), Benzothiazyl-2-Dicyclohexyl Sulfenamide (DCBS), tetramethyl thiuram disulfide (TMTD) and tetramethylthiuram monosulfide (TMTM). In an exemplary embodiment, the retarder is MBTS.
The antioxidant can be at least one selected from phenolic based antioxidant and amine based antioxidant.
The amine based antioxidant is N- isopropyl- N'- phenyl- p- phenylenediamine.
The predetermined temperature is in the range of 140 °C to 180 °C. In an exemplary embodiment of the present disclosure, the predetermined temperature is 150 °C.
The partial curing of the elastomeric blend is in the range of 20 % to 80 % of the complete curing.
In an embodiment of the present disclosure, the partial curing is done for a predetermined time period. The predetermined time period can be derived from a rheometric curve for 20 % to 80 % curing.
The present disclosure provides the process for preparation of an elastomeric blend which has applications in tire industry, especially in the inner liners of tubeless tires.
The present disclosure provides an elastomeric blend which is partially cured, having improved air impermeability and self-healing ability in case of minor pin holes or defects. The elastomeric blend also has combined low gas and moisture permeability, high heat and flux resistance and ability to co-vulcanize with highly unsaturated rubber.
The mechanism of partially cured elastomeric blend in accordance with the present disclosure is represented in Figure 1. The partially cured elastomeric blend containing ionomers has mechanical strength due to the presence of ionic clusters (Figure 1B). In case of fracture or formation of micro holes, the ionomers tend to melt and flow to fill up the space created due to rupture of the elastomer. This phenomenon does not take place evidently in case of fully cured elastomers due to the restricted molecular mobility because of the presence of high amount of sulfur crosslinks (Figure 1C). Rather, upon heating, possibly the material around the rupture gets hardened due to formation of additional crosslinks thereby creating a clear passage for the air and leading to an increase in air permeability.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experimental details:
Experiment 1: Process for the preparation of the elastomeric blend in accordance with the present disclosure
Example 1: Preparation of the elastomeric blend in accordance with the present disclosure
A butyl rubber ionomer and a halobutyl rubber in a predetermined mass ratio were homogenized to obtain a homogeneous mixture. Predetermined amounts of additives were added to the homogeneous mixture to obtain a slurry. A predetermined amount of a filler was added to the slurry in an open two roll mill to obtain a blend. The blend was cured by using a conventional molding set up at 150 °C to obtain the elastomeric blend.
Comparative Example: Preparation of the elastomeric blend without a butyl rubber ionomer
An elastomeric blend without a butyl rubber ionomer was prepared by using the same process of Example 1.
The mass% and the specific components of the elastomeric blend of Example 1 and comparative example are tabulated in Table 1 below.
The elastomeric blend was further tested for various mechanical properties and curing at different time period (T40, T60, T80 and T90).
Table 1: Ingredients (in mass %) of elastomeric blends
ingredients Example 1 Comparative Example
BIIR* 50 100
PIIR** 50 0
Carbon black (N-660) 60 60
Naphthenic Oil 8 8
Stearic Acid 1 1
MgO 0.15 0.15
ZnO 3 3
Sulfur 0.5 0.5
MBTS 1.5 1.5
*BIIR: Brominated butyl rubber, **PIIR: Phosphonium ionomer of brominated butyl rubber
Experiment 2: Study of curing properties of the elastomeric blends of Example 1 and comparative example
The curing properties of the elastomeric blends as prepared in Example 1 of the present disclosure and comparative example were studied by using a moving die rheometer MDR 3000 from Montech at 160 °C for 60 minutes as per ASTM D 1646 (standard test method for rubber properties). The Table 2 below enlists the results of lowest torque, highest torque, scorch time, curing time and CRI values for Example 1 and comparative example.
Table 2: Curing Properties
Parameter Example 1 Comparative Example
Lowest torque - ML (lb.in) 1.90 1.76
Highest torque- MH (lb.in) 6.77 4.67
Scorch time TS1 (mins) 3.62 5.98
Scorch time TS2 (mins) 5.25 10.33
Curing time T40(mins) 5.16 6.62
Curing time T60(mins) 6.99 9.02
Curing time T80(mins) 10.20 12.80
Curing time T90(mins) 14.35 17.47
Cure rate Index (CRI) 7.21 9.00
From Table 2, it is observed that the lowest torque (ML) and the highest torque (MH) values for elastomeric blend of Example 1 (which contains 50% of phosphonium ionomer) have increased as compared to the comparative example, indicating that the viscosity of the elastomeric blend of Example 1 increases upon incorporation of ionomers in the elastomeric blend. The scorch time (TS1, TS2) and optimum cure time (T90) are observed to decrease for elastomeric blend of Example 1 which indicates that the ionomers which already have ionic linkages, requires lesser time to achieve the final state of curing.
The cure rate index for Example 1 is observed to be slower in comparison to the comparative example as the elastomeric blend of Example 1 contains ionomers in which some of the reactive sites for curing are already engaged in the formation of ionic clusters whereas in case of comparative example which contains 100% BIIR the CRI is higher due to the availability of all the functionalities during curing. Therefore the pre-existence of ionic clusters impacts the rheometric properties.
Experiment 3: Study of mechanical properties of the elastomeric blends of Example 1 and Comparative example
A) Mechanical properties before aging of the elastomeric blend
The mechanical properties of the elastomeric blends of Example 1 and comparative example were measured by using a Universal Testing machine from Tinius Olsen at a speed of 500 mm/min as per ASTM D 412 (Tensile Set of Rubber and Thermoplastic Elastomers). Table 3 below enlists the results of tensile properties of the elastomeric blends for Example 1 and comparative example.
Table 3: Mechanical properties of elastomeric blend of Example 1 and Comparative example before aging
Property Comparative example Example 1
(fully cured) Partially Cured elastomeric blend
Example 1 t40 Example 1 t60 Example 1 t80
Hardness, Shore A 53 57 58 58 58
Tensile Strength, MPa 12.2 15.2 9.7 10.4 12.7
Elongation at break, % 460 550 350 310 500
100 % Modulus, MPa 1.86 4.2 3.6 2.78 3.8
200 % Modulus, MPa 4.28 8.36 5.44 6.44 7.36
300 % Modulus, MPa 7.33 8.86 9.01 8.62 9.18
Tear Strength, Kg/cm 47 67.7 61 60 58
From Table 3, it is observed that the elastomeric blend of Example 1 (containing butyl ionomer) exhibits superior mechanical properties as compared to the elastomeric blend of the comparative example (based on halobutyl rubber). Further, it is observed that the ionic crosslinks in the butyl ionomers (elastomeric blend of Example 1) provide additional reinforcing effect which can be attributed to the improvement in the mechanical properties of the elastomeric blend of Example 1. Under cured elastomeric blends i.e. at T40, T60, T80 exhibit slightly inferior mechanical properties compared to the fully cured elastomeric blend which is due to the reduction in crosslink density due to the partial curing. Therefore, the under cured elastomeric blends containing ionomers showed only slightly inferior tensile strength but, better modulus and tear strength in comparison to the fully cured blend. However, the 80% cured blend showed superior properties in comparison to comparative blend which is due to the presence of ionic clusters as depicted in Figure 1.
B) Mechanical properties after aging of the elastomeric blend
The elastomeric blends of Example 1 and comparative example were further subjected for accelerated aging at 120 °C for 72 hours, followed by cooling for 96 hours at room temperature to obtain cooled elastomeric blends. The so obtained cooled elastomeric blends were analyzed for mechanical properties such as hardness, tensile strength, elongation at break and modulus. Table 4 below enlists the change in the result values of mechanical properties of the elastomeric blends of Example 1 and Comparative example as compared to the result values of mechanical properties of elastomeric blends before aging conditions.
Table 4: Mechanical properties of the elastomeric blend of Example 1 and Comparative example after accelerated ageing test at 120 °C for 72 hours

Test Parameters Comparative Example Example 1 Partially Cured Sample
Example 1 t40 Example 1 t60 Example 1 t80
Change in Hardness, Shore A +4 +1 +3 +3 +1
Change in Tensile Strength, % -10.66 +3.31 -9.72 -2.44 -1.75
Change in Elongation at Break, % -23.91 0 -14.58 -4.55 -3.00
Change in 100 % Modulus, % +39.25 +24.89 +28.01 +13.46 +21.69
Change in 200 % Modulus, % +45.79 +20.0 +23.58 +8.25 +18.07
Change in 300 % Modulus, % +29.33 +9.93 +5.91 +2.99 +10.45
From Table 4, it is observed that at 60 % cured blend of Example 1 (t60) exhibits minimum change in 100, 200 and 300 % modulus properties after accelerated ageing study. However, Example 1 t80 showed better ageing resistance properties with respect to the fully cured blend of Example 1. Most of the mechanical properties of t60 and t80 exhibit minimum change in original properties.
Experiment 4: Study of properties of the elastomeric blends of Example 1 and Comparative example after curing
A) Study of Crosslink density of the elastomeric blends after curing
0.05 g of the elastomeric blend of Example 1 and comparative example were swollen to equilibrium in toluene for four days at room temperature (23 °C ± 1°C) to obtain swollen elastomeric blends. The so obtained swollen elastomeric blends were dried for four days at 60°C in an air oven till a constant weight is achieved. The crosslink density was calculated based on the Flory-Rehner equation
?=1/(2M_c )=- ( ln?(1-V_r )+V_r+??V_r?^2)/(2?_(rV_0 ) (V_r^(1/3)- V_r/2)) ……. (1)
? = crosslink density per unit volume in mol/g;
Vr = volume fraction of rubber in a swollen sample;
V0 = solvent molar volume (for toluene: V0 =106.9 in cm3 /mol);
f – functionality of crosslinks (f = 4, assuming the formation of tetra-functional crosslinks);
?r = is the density of the rubber sample (0.91 g/cm3),
? – Flory-Huggins rubber-solvent interaction parameter (for the SBR-toluene system: ? = 0.557)
Table 5 below enlists the results of the crosslink density of the cured elastomeric blends of Example 1 and comparative example.
Table 5: Crosslink density of the cured elastomeric blend
SAMPLE CROSSLINK DENSITY (mol/cm³) X10 ¯ 4

Comparative Example 2.6202
Example 1 7.7015
Example 1 t40 2.3104
Example 1 t60 3.8202
Example 1 t80 6.6202
From Table 5, it is observed that the crosslink density for the cured elastomeric blend of comparative example (containing only halobutyl rubber) is lower as compared to the elastomeric blend of Example 1 (containing butyl ionomers). Further, as compared to the comparative example even the partially cured ionomers (Example 1 t40, Example 1 t60 and Example 1 t80) exhibited comparable crosslink density or higher crosslink density.
B) Study of air permeability of the elastomeric blends
(i) Study of air permeability of the cured elastomeric blends
Air permeability of the cured elastomeric blends were measured as per the standard IS-3400 – Part 21, by using constant pressure method – Circular specimen – 100 mm diameter at a constant pressure of 4 Kg. The air permeability was calculated based on the following equation

A1 = Cross section of capillary tube in square meters.
A2 = Free area of the test piece in 'm2'
b = Thickness of the test piece in 'm'
?L = Change in length of meniscus in meters, obtained during time interval of t seconds.
P1 = Pressure (absolute) on the low-pressure side in pascals.
P2 = Pressure (absolute) on the high-pressure side in pascals.
?Q = Rubber permeability in meters squared per pascal second [ m2 / (Pa. S)]
T = Test temperature (absolute) in Kelvin.
? t = Time interval in seconds for a given change in length of displacement of the meniscus.
0.0027 = constant.
(ii) Study of air permeability of the pricked cured elastomeric blends
The cured elastomeric blends were pricked with the help of a sharp needle followed by measurement of air permeability in accordance with the formula of Experiment 4 (B) (i). The self- healing behaviour of the cured elastomeric blends was studied by keeping in a hot air oven operating at 120oC for duration of 72 hours. The cured elastomeric blends were cooled down to room temperature and conditioned at ambient temperature for 24 hours and further tested for air permeability. The values of air permeability are reported in Table 6.
Table 6: Air Permeability results
Sample Permeability Permeability Permeability
x 10-17(m²/Pa.s) x 10-17(m²/Pa.s) x 10-17(m²/Pa.s)
After Pricking with Needle After healing of the sample at 120oC, 72 hours
Comparative Example 1.2435 1.3827 91.053
Example 1 0.7006 1.4862 89.053
Example 1 t40 0.2528 0.6298 0.5048
Example 1 t60 0.3555 0.7203 21.4160
Example 1 t80 0.6104 2.0632 88.053
From Table 6, it is observed that the air permeability drastically increased for comparative example and fully cured Example 1 after pricking with needle whereas, when partially cured samples (Example 1- t40, t60 and t80) were pricked with needle, they showed lower air permeability
When all the samples were exposed to high temperature at 120 °C for 72 hours, there was no indication of self-healing in comparative example and fully cured Example 1 due to heat exposure as compared to partially cured samples. The partially cured sample of Example 1- t40 got healed and puncture was blocked and hence, permeability value reduced. However in other cases (Example 1- t60 and t80) permeability was increased drastically due to extension of the puncture at high temperature.
Thus, the ability to self-heal on exposure to heat is observed to reduce with an increase in curing index from 40% to 80% and fully cured.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
an elastomeric blend that;
has improved air impermeability; and
has self- healing ability in case of minor defects; and
a process for the preparation of an elastomeric blend that;
is simple and economic; and
is scalable.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, 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.
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
, Claims:WE CLAIM:
1. An elastomeric blend of
i) a butyl rubber ionomer;
ii) a halobutyl rubber co-curable with said butyl rubber ionomer; and
iii) additives selected from a filler, a plasticizer, a curing agent, a dispersing agent, an activator, an accelerator and an antioxidant,
wherein said blend is partially cured.
2. The elastomeric blend as claimed in claim 1, wherein said butyl rubber ionomer is selected from phosphonium ionomer of butyl rubber and ammonium ionomer of butyl rubber.
3. The elastomeric blend as claimed in claim 1, wherein said halobutyl rubber is selected from bromobutyl rubber and chlorobutyl rubber.
4. The elastomeric blend as claimed in claim 1, wherein a mass ratio of said butyl rubber ionomer to said halobutyl rubber is in the range of 1:9 to 9:1.
5. The elastomeric blend as claimed in claim 1, wherein said filler is at least one selected from carbon black, magnesium oxide (MgO), silica, clay, calcium carbonate, talc and zinc oxide.
6. The elastomeric blend as claimed in claim 1, wherein said plasticizer is at least one selected from wood rosin, coumarone indene resin, dibutyl phthalate (DBP), dioctylphtalate (DOP), diisooctylphtalate (DIOP), and dibutylsebacate.
7. The elastomeric blend as claimed in claim 1, wherein said curing agent is at least one selected from sulfur, peroxides and metal oxide.
8. The elastomeric blend as claimed in claim 7, wherein said peroxide is selected from dicumyl peroxide, zinc peroxide, benzoyl peroxide, 2,4-chlorobenzoyl peroxide and 2,5-bis(t-butylperoxy)-2,5-dimethylhexane; and said metal oxide is zinc oxide.
9. The elastomeric blend as claimed in claim 1, wherein said dispersing agent is at least one selected from naphthenic oil, phthalate esters, aromatic oil, paraffinic oil, sebacates and adipates.
10. The elastomeric blend as claimed in claim 1, wherein said activator is at least one selected from stearic acid and zinc oxide (ZnO).
11. The elastomeric blend as claimed in claim 1, wherein said accelerator is at least one selected from 2-2’-Dithiobis(benzothiazole) (MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-tert.-butyl-2-benzothiazyl sulphenamide (TBBS), Benzothiazyl-2-Dicyclohexyl Sulfenamide (DCBS), tetramethyl thiuram disulfide (TMTD) and tetramethylthiuram monosulfide (TMTM).
12. The elastomeric blend as claimed in claim 1, wherein said antioxidant is selected from a phenolic based antioxidant and an amine based antioxidant.
13. The elastomeric blend as claimed in claim 12, wherein said amine based antioxidant is N-isopropyl-N'- phenyl-p-phenylenediamine.
14. A process for the preparation of an elastomeric blend, said process comprising the following steps:
(a) homogenizing a butyl rubber ionomer and a halobutyl rubber in a predetermined mass ratio to obtain a homogeneous mixture;
(b) adding predetermined amounts of additives selected from a plasticizer, a dispersing agent, an activator, an accelerator and an antioxidant to said homogeneous mixture to obtain a slurry;
(c) adding a predetermined amount of a filler to said slurry in an open two roll mill to obtain a blend; and
(d) partially curing said blend at a predetermined temperature to obtain said elastomeric blend.
15. The process as claimed in claim 14, wherein said butyl rubber ionomer is selected from phosphonium ionomer of butyl rubber and ammonium ionomer of butyl rubber.
16. The process as claimed in claim 14, wherein said halobutyl rubber is selected from bromobutyl rubber and chlorobutyl rubber.
17. The process as claimed in claim 14, wherein said predetermined mass ratio of said butyl rubber ionomer to said halobutyl rubber is in the range of 1:9 to 9:1.
18. The process as claimed in claim 14, wherein said filler is at least one selected from carbon black, magnesium oxide (MgO), silica, clay, calcium carbonate, talc and zinc oxide.
19. The process as claimed in claim 14, wherein said plasticizer is at least one selected from wood rosin, coumarone indene resin, dibutyl phthalate (DBP), dioctylphtalate (DOP), diisooctylphtalate (DIOP), and dibutylsebacate.
20. The process as claimed in claim 14, wherein said curing agent is at least one selected from sulfur, peroxides and metal oxide.
21. The process as claimed in claim 20, wherein said peroxide is selected from dicumyl peroxide, zinc peroxide, benzoyl peroxide, 2,4-chlorobenzoyl peroxide and 2,5-bis(t-butylperoxy)-2,5-dimethylhexane; and said metal oxide is zinc oxide.
22. The process as claimed in claim 14, wherein said dispersing agent is at least one selected from naphthenic oil, phthalate esters, aromatic oil, paraffinic oil, sebacates and adipates.
23. The process as claimed in claim 14, wherein said activator is at least one selected from stearic acid and zinc oxide (ZnO).
24. The process as claimed in claim 14, wherein said accelerator is at least one selected from 2-2’-Dithiobis(benzothiazole) (MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-tert.-butyl-2-benzothiazyl sulphenamide (TBBS), Benzothiazyl-2-Dicyclohexyl Sulfenamide (DCBS), tetramethyl thiuram disulfide (TMTD), tetramethylthiuram monosulfide (TMTM).
25. The process as claimed in claim 14, wherein said antioxidant is selected from a phenolic based antioxidant and an amine based antioxidant.
26. The process as claimed in claim 25, wherein said amine based antioxidant is N-isopropyl-N'-phenyl-p-phenylenediamine.
27. The process as claimed in claim 14, wherein said predetermined temperature is in the range of 140 °C to 180 °C.
28. The process as claimed in claim 14, wherein said partial curing of said elastomeric blend is in the range of 20 % to 80 % of the complete curing.
Dated this 07th day of February, 2023

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K. DEWAN & CO.
Authorized Agent of Applicant