Description:FIELD
The present disclosure relates to a melt mixing process for partially cross linking butyl rubber.
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 indicate otherwise.
Mooney Viscosity: The Mooney Viscosity test is the most popular test method for characterizing polymers and uncured rubber materials. As defined by international standards, the sample material is preheated for a defined period in a closed die cavity, then sheared by the embedded rotor at a constant rate. The Mooney Viscosity is recorded and data is automatically calculated at predefined time and viscosity points.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Cross linking of butyl rubber is a challenging task as commercially available butyl rubber contains typically about less than 3% of olefinic part. It is the olefinic part of butyl rubber which allows cross linking. The challenge lies in cross linking butyl rubber having low amounts of olefins. Typically, cross linking of butyl rubber is performed through a vulcanization process. However, the process is slow and generally limits obtaining higher cross-linking density in the vulcanized product. Thus, vulcanization process is not suitable for obtaining a product where higher density of cross-linking is desirable. Vulcanization process generally uses sulfur-based compounds or ZnO which does not allow having a good control over the three-dimensional structure of the vulcanized product. Further, if it is desired to obtain a partially cross linked butyl rubber, vulcanization is not a suitable process.
Cross linking of butyl rubber at gum rubber stage requires higher alkene content which can be achieved by incorporating higher percentage of the isoprene content. However, incorporation of higher content of isoprene changes the basic properties of butyl rubber that is meant for specific applications.
There is, therefore, felt a need to provide a better process for partial cross-linking of butyl rubber.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for partial cross-linking of butyl rubber.
Another object of the present disclosure is to provide a melt mixing process for partial cross linking of butyl rubber.
Another object of the present disclosure is to provide a process which does not require a solvent.
Still another object of the present disclosure is to provide a process for obtaining a partially cross-linked butyl rubber with improved Mooney Viscosity.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a melt mixing process for partially cross linking butyl rubber. The process comprises treating butyl rubber with a pre-determined weight ratio of a cross-linker and an initiator for a pre-determined period of time at a pre-determined temperature, to obtain partially cross linked butyl rubber.
In accordance with an embodiment of the present disclosure the melt mixing process is selected from an internal melt mixing process, two-roll melt mixing process, extruder melt mixing process and kneader melt mixing process.
In accordance with the present disclosure the initiator is a radical initiator selected from an organic radical initiator and an inorganic radical initiator. In an embodiment of the present disclosure, the initiator is selected from n-bromo succinamade, succinamide derivatives, azobis-isobutyro-nitrile, hydrogen peroxide, benzoyl peroxide and t-butyl hydroperoxide.
In accordance with the present disclosure, cross linker is selected from a bis maleimide and a maleimide derivative.
In accordance with the present disclosure, the pre-determined weight ratio of the cross linker and the initiator is in the range of 0.1 to 5. In accordance with an embodiment of the present disclosure, the pre-determined weight ratio of the cross linker and the initiator is 1. In another embodiment, the pre-determined ratio of the cross-linker and the initiator is 3.
In accordance with the present disclosure, the pre-determined period of time is in the range of 1 minute to 120 minutes.
In accordance with the present disclosure, the pre-determined temperature is in the range of 0oC to 250oC.
In accordance with the present disclosure, weight % of the initiator with respect to the weight of butyl rubber is in the range of 0.05% to 50%.
In accordance with the present disclosure, wt% of the crosslinker with respect to butyl rubber is in the range of 0.05% to 50%.
In accordance with the present disclosure, Mooney viscosity of the cross-linked butyl rubber is enhanced by 0.1% to 60% with respect to butyl rubber.
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 effect on Mooney Viscosity by varying concentration of the cross-linking agent bis maleimide (BMI) and keeping concentration of the initiator n-bromo succinamide (NBS) constant.
Figure 2 illustrates the effect of varying concentration of the initiator (NBS) and keeping concentration of the cross-linking agent (BMI) constant on the Mooney viscosity.
DETAILED DESCRIPTION
The present disclosure relates to a melt mixing process for obtaining a partially cross-linked butyl rubber.
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.
Cross linking of butyl rubber is a challenging task as commercially available butyl rubber contains typically about less than 3% of olefinic part. It is the olefinic part of butyl rubber which allows cross linking. The challenge lies in cross linking butyl rubber having low amounts of olefins. Typically, cross linking of butyl rubber is performed through a vulcanization process. However, the process is slow and generally limits obtaining higher cross-linking density in the vulcanized product. Thus, vulcanization process is not suitable for obtaining a product where higher density of cross-linking is desirable. Vulcanization process generally uses sulfur-based compounds or ZnO which does not allow having a good control over the three-dimensional structure of the vulcanized product. Further, if it is desired to obtain a partially cross linked butyl rubber, vulcanization is not a suitable process.
Cross linking of butyl rubber at gum rubber stage requires higher alkene content which can be achieved by incorporating higher percentage of the isoprene content. However, incorporation of higher content of isoprene changes the basic properties of butyl rubber that is meant for specific applications. The present disclosure relates to a melt mixing process for partially cross-linked butyl rubber.
In an aspect, the present disclosure provides a melt mixing process for partially cross linking butyl rubber and the process comprises treating butyl rubber with a pre-determined weight ratio of a cross-linker and an initiator, for a pre-determined period of time at a pre-determined temperature, to obtain partially cross linked butyl rubber.
In an embodiment of the present disclosure, the melt mixing process is selected from an internal melt mixing process, two-roll melt mixing process, extruder melt mixing process and kneader melt mixing process.
In accordance with the present disclosure, the initiator is an organic or an inorganic radical initiator and is selected from n-bromo succinamide, succinamide derivatives, azobis-isobutyro-nitrile, hydrogen peroxide, benzoyl peroxide and t-butyl hydroperoxide. In an exemplary embodiment of the present disclosure, the initiator is n-bromo-succinamide (NBS). At an elevated temperature, the initiator generates free radical sites along the rubber chains. Such active radical sites and the cross-linking structures are independent of available double bonds along the length of butyl rubber chain. The generated free radical sites react with the cross linker, producing a three-dimensional structure.
In accordance with the present disclosure, the cross linker is selected from a bis maleimide (BMI) and a maleimide derivate. In an exemplary embodiment of the present disclosure, 1,1'-(Methylenedi-4,1-phenylene) bismaleimide is a cross linker.
In an embodiment of the present disclosure, the pre-determined weight ratio of the cross-linker and the radical initiator is in the range of 0.1 to 5. In an exemplary embodiment, weight ratio of the cross-linker and the radical initiator is 3. In another exemplary embodiment, weight ratio of the cross-linker and the radical initiator is 2.
In accordance with the present disclosure, weight % of the initiator with respect to the weight of butyl rubber is in the range of 0.05% to 50%. In a preferred embodiment of the present disclosure, weight % of the initiator with respect to the weight of butyl rubber is in the range of 0.1% to 10%. In an exemplary embodiment, weight% of the initiator is 1.25% with respect to the weight of butyl rubber. In another exemplary embodiment, wt% of the initiator with respect to the weight of butyl rubber is 3%.
In accordance with the present disclosure, wt% of the crosslinker with respect to butyl rubber is in the range of 0.05% to 50%. In a preferred embodiment, weight % of the cross linker with respect to butyl rubber is in the range of 0.2% to 5%. In an exemplary embodiment, wt% of the cross linker with respect to the weight of butyl rubber is 2%. In another exemplary embodiment, wt% of the cross linker is 3% with respect to the weight of butyl rubber.
In accordance with the present disclosure, melt mixing temperature is in the range of 0oC to 250oC. In a preferred embodiment, melt mixing temperature is in the range of 50oC to 190oC. In an exemplary embodiment of the present disclosure, melt mixing temperature is 160o.
In accordance with the present disclosure, the pre-determined time period is in the range of 1 minute to 120 minutes. In a preferred embodiment, the pre-determined time period is in the range of 2 minutes to 15 minutes. In an exemplary embodiment, melt mixing time is 8 minutes.
In accordance with the present disclosure, Mooney Viscosity of the partially cross-linked butyl rubber is enhanced in the range of 0.1% to 60% with respect to butyl rubber. In a preferred embodiment, Mooney Viscosity of the cross-linked butyl rubber is enhanced in the range of 1% to 30% with respect to butyl rubber.
In accordance with the present disclosure, Figure 1 illustrates the effect of varying concentration of the cross linker (BMI) with respect to butyl rubber and keeping the concentration of initiator (NBS) constant with respect to butyl rubber and monitoring effect on the Mooney Viscosity of the cross-linked butyl rubber. In the figure 1, NBS was kept constant at 1.25 parts per hundred with respect to butyl rubber and BMI was varied from 1 part per hundred to 3 parts per hundred with respect to butyl rubber. It is observed that the maximum Mooney viscosity of 71.8 was obtained when BMI is 2 parts per hundred with respect to butyl rubber. Mooney viscosity of the cross-linked butyl rubber decreases when the concentration of BMI increases to 2.5 parts per hundred and 3 parts per hundred with respect to the weight of butyl rubber, when it falls to 71.2 and 68.4 respectively.
In accordance with the present disclosure, figure 2 illustrates effect of varying the concentration of initiator (NBS) with respect to butyl rubber and keeping the concentration of BMI constant with respect to butyl rubber and monitoring effect on the Mooney Viscosity of the cross-linked butyl rubber. It is observed from the figure 2, BMI is kept constant at 3 parts per hundred and NBS is varied from 0.25 parts per hundred to 3 parts per hundred with respect to butyl rubber. It is observed from the figure 2 that the maximum Mooney Viscosity of 72 for the cross-linked butyl rubber is obtained when the NBS is 1 part per hundred with respect to butyl rubber and it falls to 68.4 as the concentration of NBS is increased to 1.25 parts per hundred with respect to butyl rubber. As the concentration of NBS increases further, Mooney Viscosity of the cross-linked butyl rubber fell further.
The foregoing description of the embodiments has been provided for purposes of illustration and is 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
Example 1: Melt Mixing process for partially cross linking of butyl rubber

Butyl rubber was cut into small pieces of approximately 5 cms. and fed to a Brabender internal mixer (300 mL or 1600 mL) at 170oC. Butyl rubber was allowed to achieve temperature of 160 to 170oC by mixing for 3 minutes. Bis maleimide (BMI) was added to the heated butyl rubber and mixed for a period of 3 minutes. The initiator, N-bromo succinamide (NBS), was added and mixed for five minutes. After complete mixing, product was removed, cooled to room temperature and milled to a sheet form in the two-roll mill for uniform mixing. Experiments were performed varying parameters like temperature, time of mixing, ratio between BMI to NBS to optimize the cross linking process.
Table 1: Melt mixing process using Brabender at 240 g scale
Experiment Butyl Rubber 44 MU Cross Linker BMI Initiator NBS Mooney Viscosity
Weight (g) PHR* PHR* MU
Expt 1 240 1 1.25 67.6
Expt 2 240 1.5 1.25 71
Expt 3 240 2 1.25 71.8
Expt 4 240 2.5 1.25 71.2
Expt 5 240 3 1.25 68.4
Expt 6 240 3 0.25 42
Expt 7 240 3 0.5 49.7
Expt 8 240 3 1 72
Expt 9 240 3 1.25 68.4
Expt 10 240 3 2 63.5
Expt 11 240 3 2.5 60.9
Expt 12 240 3 3 54.2
*PHR Parts per hundred
Table 1 illustrates that maximum Mooney Viscosity of 71.2 was obtained when the ratio of BMI to NBS was 3.
Example 2: Scaled up melt mixing process for partially cross-linking of butyl rubber
Similar conditions as in experiment 1 were maintained for scaled up process optimization using 1.6 litre internal mixer.
Table 2: Scale up process of cross linking using internal mixer at 1.2 Kg scale
Experiment Butyl Rubber 44 MU Cross Linker BMI Initiator NBS Mooney Viscosity
Weight (Kg) PHR PHR MU
Expt 1 1.2 0.2 0.8 76
Expt 2 1.2 0.3 0.6 57
Expt 3 1.2 0.5 0.5 67
Expt 4 1.2 0.7 1.5 80
Expt 5 1.2 0.5 0.5 64
Expt 6 1.2 0.3 0.6 72

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a melt mixing process for obtaining a partially cross-linked butyl rubber that:
• is simple and does not require any solvent;
• is completed in a very short duration of time of a few minutes;
• does not require further processing of the cross-linked butyl rubber;
• can be used for sealant applications;
• uses less amounts of reagents; and
• economical and efficient.

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. , C , Claims:WE CLAIM:

1. A melt mixing process for partially cross linking butyl rubber, wherein the melt mixing process comprises treating butyl rubber with a pre-determined weight ratio of a cross-linker and an initiator, for a pre-determined period of time at a pre-determined temperature, to obtain partially cross linked butyl rubber.

2. The process as claimed in claim 1, wherein the melt mixing process is selected from an internal melt mixing process, two-roll melt mixing process, extruder melt mixing process and kneader melt mixing process.

3. The process as claimed in claim 1, wherein the initiator is a radical initiator selected from an organic radical initiator and an inorganic radical initiator.

4. The process as claimed in claim 3, wherein the radical initiator is selected from n-bromo succinamide, succinamide derivatives, azobis-isobutyro-nitrile, hydrogen peroxide, benzoyl peroxide and t-butyl hydroperoxide.

5. The process as claimed in claim 3, wherein the radical initiator is n-bromo succinamide.

6. The process as claimed in claim 4 and 5 wherein the weight % of the radical initiator with respect to the weight of butyl rubber is in the range of 0.05% to 50%.

7. The process as claimed in claim 6 wherein the weight % of the radical initiator with respect to the weight of butyl rubber is in the range of 0.1% to 10%.

8. The process as claimed in claim 1, wherein the cross linker is selected from a bis maleimide and a maleimide derivative.

9. The process as claimed in claim 8, wherein the cross linker is 1,1'-(Methylenedi-4,1-phenylene) bismaleimide.
10. The process as claimed in claim 8 and 9, wherein the wt% of the crosslinker with respect to butyl rubber is in the range of 0.05% to 50%.

11. The process as claimed in claim 10 wherein the weight % of the cross linker with respect to butyl rubber is in the range of 0.2% to 5%.

12. The process as claimed in claim 1, wherein the pre-determined weight ratio of the cross-linker and the initiator is in the range of 0.1 to 5.

13. The process as claimed in claim 12, wherein the pre-determined weight ratio of the cross-linker and the initiator is in the range 1 to 3.

14. The process as claimed in claim 1 wherein Mooney viscosity of the partially cross-linked butyl rubber is enhanced by 0.1% to 60% with respect to butyl rubber.

15. The process as claimed in claim 1 wherein the pre-determined period of time is in the range of 1 minute to 120 minutes.

16. The process as claimed in claim 15, wherein the pre-determined period of time is in the range of 2 minutes to 15 minutes.

17. The process as claimed in claim 1, wherein the pre-determined temperature is in the range of 0oC to 250oC.

18. The process as claimed in claim 17, wherein the pre-determined temperature is in the range of 50oC to 190oC.
Dated this 2nd day of January, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R.K.DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT\