DESC:FIELD
The present disclosure relates to a process for production of carbon fibers.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Carbon fibers are known to be high performance fibers having ultra-high mechanical properties. Carbon fibers have several advantages including exceptionally high structural stability, high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. These properties have made carbon fibers very popular in the fields such as aerospace, civil engineering, defense applications, medical equipments and sporting goods.
Conventionally, the different types of precursors such as polyacrylonitrile (PAN), pitch precursors, and cellulosic precursors are used to manufacture carbon fibers. The process of manufacturing involves stabilization of precursor fibers and subsequent carbonization at very high temperatures. Alternatively, graphitization of precursor fibers is carried out at high temperature. However, these precursors are expensive, thereby prohibiting use of carbon fibers for large scale applications.
There is, therefore, felt a need to provide a low cost alternative precursor for the production of carbon fibers with enhanced mechanical properties.
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 provide a low cost precursor for the production of carbon fibers.
Another object of the present disclosure is to provide a simple, economical and environment-friendly process for the production of carbon fibers.
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 process for producing the carbon fibers.
The process of the present disclosure comprises pre-stretching disentangled ultrahigh molecular weight polyethylene (DPE) powder below it’s melt temperature to obtain pre-stretched DPE. Pre-stretched DPE is further hot stretched at a temperature in the range of 135 °C to 200 °C to obtain oriented DPE. Oriented DPE is modified in the presence of at least one oxidizing agent below it’s melt temperature to obtain a modified DPE, followed by carbonizing the modified DPE in a furnace under inert atmosphere by increasing the temperature of the furnace from room temperature to 1200 ºC to obtain carbon fibers.
The carbon fibers obtained by the process of the present disclosure have a tensile strength in the range of 2.5 to 3 GPa, and a tensile modulus in the range of 120 to 200 GPa.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1(A) is a representation of FTIR spectra of virgin disentangled polyethylene (DPE);
Figure 1(B) is a representation of FTIR spectra of stretched sulfonated disentangled polyethylene (DPE); and
Figure 1(C) is a representation of FTIR spectra of pre-stretched sulfonated disentangled polyethylene (DPE).
DETAILED DESCRIPTION
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.
Carbon fibers are known to have excellent mechanical properties and low density, which makes them useful in different fields such as aerospace, civil engineering, defense applications, medical equipments and sporting goods.
However, the conventional precursors used in the production of carbon fibers are very costly. This is a limiting factor for use of carbon fibers for large scale applications. On the other hand, carbon fibers produced so far from polyethylene precursors have low tensile strength.
The present disclosure envisages a simple and economical process for the production of carbon fibers from disentangled ultrahigh molecular weight polyethylene (DPE). According to the process of the present disclosure, carbon fibers obtained from disentangled ultrahigh molecular weight polyethylene (DPE) have enhanced mechanical properties.
The process of the present disclosure is described in detail herein below:
Initially, disentangled ultrahigh molecular weight polyethylene (DPE) powder is pre-stretched below it’s melt temperature to obtain pre-stretched DPE. Pre-stretched DPE is further hot stretched at a temperature in the range of 135 °C to 200 °C to obtain oriented DPE.
In accordance with the embodiments of the present disclosure, disentangled ultrahigh molecular weight polyethylene (DPE) powder is pre-stretched at a temperature in the range of 120oC to below 134oC.
In accordance with the embodiments of the present disclosure, the step of pre-stretching involves compacting the DPE powder in a roll mill to obtained pre-stretched DPE.
In accordance with the embodiments of the present disclosure, the step of hot stretching is carried out in plurality of stages by increasing the temperature sequentially from 135 °C to 160 °C.
In accordance with the embodiments of the present disclosure, the step of hot stretching includes reducing the stretching ratio in the range of 6.0 to 2.0.
The oriented DPE obtained by the process of the present disclosure are characterized with crystallinity greater than 90%. Moreover, the crystalline morphology and high surface area developed while converting DPE to the oriented form favors the conversion of oriented DPE into high strength carbon fibers.
In accordance with the embodiments of the present disclosure, the oriented DPE is at least one form selected from the group consisting of tape, film and fibers.
The so obtained oriented DPE is modified below it’s melt temperature and in the presence of at least one oxidizing agent to obtain a modified DPE. In accordance with the present disclosure, the so obtained modified DPE neither melts nor deforms at higher temperature used during carbonization process.
In accordance with the embodiments of the present disclosure, the oxidizing agent is at least one selected from the group consisting of sulphuric acid, chlorosulphuric acid, and fuming sulphuric acid.
In accordance with one embodiment of the present disclosure, the step of modification comprises sulfonation of the oriented DPE in the presence of at least one oxidizing agent selected from sulphuric acid, chlorosulphuric acid, and fuming sulphuric acid. In accordance with an exemplary embodiment of the present disclosure, the step of medication is carried out in the presence of chlorosulphuric acid.
In accordance with one embodiment of the present disclosure, the step of modifying the oriented DPE is carried out at a temperature in the range of 60 to 100 °C and further comprises washing the modified DPE with water till pH of the washings is neutral.
The modified DPE is further subjected to carbonization under an inert atmosphere in a furnace by increasing the temperature of the furnace from room temperature to 1200 ºC to obtain carbon fibers.
In accordance with the exemplary embodiment of the present disclosure, the modified DPE is subjected to carbonization in plurality of stages by increasing the temperature sequentially from room temperature to 1200 ºC. In the step of carbonization, the modified DPE achieves complete cyclization of DPE chains to achieve high strength and high modulus of carbon fibers.
The present disclosure further provides carbon fibers, which are prepared by pre-stretching disentangled ultrahigh molecular weight polyethylene (DPE) powder, hot stretching the pre-stretched DPE in the form of fibers or tapes, films, modifying the fibers or tapes, and carbonizing the modified fibers or tapes to obtain carbon fibers. The so obtained carbon fibers have a tensile strength in the range of 2.5 to 3 GPa, and a tensile modulus in the range of 120 to 200 GPa.
The present disclosure provides the simple and economical process for the production of carbon fibers from disentangled ultrahigh molecular weight polyethylene (DPE). Carbon fibers obtained by the process of the present disclosure are characterized by comparatively high tensile strength and tensile modulus.
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
Example 1: Preparation of carbon fibers in accordance with the present disclosure
Step 1: Preparation of pre-stretched disentangled ultrahigh molecular weight polyethylene (DPE)
Disentangled ultrahigh molecular weight polyethylene (DPE) powder (5.1 kg, MW:4.58 g/mole, MWD:6.86, BD- 0.071 g/cc, Heat of fusion (?Hf) >200 J/g) was taken and stabilized using primary antioxidant (Irganox®, 1010 – 4000 ppm) in the presence of 250 ml of acetone. The stabilized DPE powder was further dried in oven at 80 °C under vacuum for 3 hour to remove acetone dried stabilized DPE powder.
The dried & stabilized DPE powder was compacted on Two Roll Mill at 132oC of the stabilized DPE into a continuous pre-stretched DPE tape roll (L- 280 m, W- 110 mm, T- ~130µ).
Step 2: Hot stretching of the Pre-stretched DPE tape roll
Pre-stretched DPE tape roll obtained in step 1 was oriented in four stretching steps at temperatures 135°C, 149°C, 155°C and 156°C in a sequential way with the stretching ratio 6.0, 3.0, 2.25 and 2.0 respectively to obtain an oriented DPE tape having high strength (2.62 GPa) and high modulus (156 GPa) and a thickness of 15µ.
Step 3: Sulfonation of the stretched DPE tape
Stretched DPE tape obtained in step 2, was sulfonated in three different reaction conditions in a flask (A, B, and C) by varying reaction temperature as 70°C, 80°C, and 90°C and varying time as 4 hours, 3.5 hours, and 3 hours respectively under N2 atmosphere.
After completion of reaction, sulfonated DPE tapes were washed several times with distilled water till the washings has neutral pH. The so obtained sulfonated tapes were characterized by FTIR and elemental (CHNS) analysis.
The FTIR spectra (Figure 1) of three samples showed a peak at 1170 cm-1 due to asymmetric stretching and 1040 cm-1 due to symmetric stretching vibration of >S=O bond of sulfonic acid group, which confirmed the sulfonation of DPE film. The CHNS analysis is given below in Table 1:
Sr. No. Reaction conditions Sulfonating agent Temperature
(°C) Time
(hour) Sulphur Content
(%)
1 A Chlorosulfonic acid (CSA) (4.5 g) and dichloroethane (DCE) (12.5 g) 70 4 1.1
2 B 80 3.5 1.0
3 C 90 3 2.5
From FTIR analysis and CHNS analysis, sulfonation of the stretched DPE is confirmed.
Further, it is evident from the table 1 that sulphur content in the modified DPE increases as the reaction temperature increases. Further, the time required for modification of oriented DPE decreases as the reaction temperature increases.
Step 4: Carbonization of sulfonated DPE stretched tape
The sulfonated DPE stretched tape obtained in step 3 was kept under tension and the two ends of tape were fixed in a tubular furnace for carbonization. The temperature of furnace was increased in step wise from room temperature to 1000°C. A consistent supply of nitrogen was maintained through the tubular furnace to keep the environment inert during carbonization.
The yield of the carbon fibers obtained is 10%.
Further, the carbon fibers so obtained are characterized are having high tensile strength (2.6 GPa) and high modulus (150 GPa).
Example 2:
The pre-stretched DPE obtained in step 1 of example 1 as well as the stretched DPE obtained in step 2 of the example 1 were subjected to sulfonation using chlorosulfonic acid (1 L) and dichloroethane (2.5 L) for 5h at 83 ºC.
After completion of reaction, sulfonated DPE tapes were washed several times with distilled water till the washings has neutral pH. The so obtained sulfonated tapes were characterized by FTIR and CHNS analysis. The degree of sulfonation from CHNS analysis was found 25-29 %, ion-exchange capacity 1.5 m equivalent of Na+/g and water content of 5 wt.%.
The sulfonated pre-stretched DPE (230mg) and stretched DUHMWPE tapes (80mg) were carbonized under similar conditions as described in step 4 of the Example 1 given above. After completion of carbonization up to 1000°C, the yield of carbon fibers were found to be 6.5% (13 mg) & 2.5 % (2 mg) respectively with an average tensile strength of 2.5 GPa and Tensile modulus of 160 GPa for both the samples.
Comparative Example 1: Preparation of carbon fibers
Virgin stretched DPE tape was carbonized under similar conditions as described in step 4 of the Example 1 given above.
After completion of carbonization up to 1000°C, the residue of the carbonized sample was found to be ~1.5% indicating low carbon fiber yield compared to sulfonated DPE polymer tapes.
Comparative Example 2: Preparation of carbon fibers from DPE fibers
DPE fibers was made by gel spinning process by dissolving DPE powder (MW 3.9 million g/mole) in decaline to obtain initially a compact DPE gel at ~150°. The DPE compact gel was further melt spun and stretched into high strength & high modulus fibers.
The DPE fibers so obtained above were wrapped on the spacer and kept in concentrated H2SO4 at 120 °C for sulfonation under constant stirring for 4 h. The sulfonated fibers sample was washed with water until the neutral pH.
The presence of sulfonic acid functional group was confirmed by FTIR and CHNS method (S% = 6.5).
The carbonization of sulfonated DPE fibers was done under similar conditions as described in step 4 of the example 1 given above.
After completion of carbonization up to 1000°C under nitrogen atmosphere the yield of carbon fibers was found to be 10% with a tensile strength of 2.7 GPa & tensile modulus of 160 GPa.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of, a process for the production of carbon fibers which:
- uses a low cost polyolefin precursor;
- provides carbon fibers with enhanced yields; and
- is simple and economical as the precursor made by solid state processing without using any solvents
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal 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 herein 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.
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 or 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.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments 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 changes in the preferred embodiment as well as other embodiments 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. A process for producing carbon fibers, said process comprising:
a. pre-stretching disentangled ultrahigh molecular weight polyethylene (DPE) powder below it’s melt temperature to obtain pre-stretched DPE;
b. hot stretching said pre-stretched DPE at a temperature in the range of 135 °C to 200 °C to obtain oriented DPE;
c. modifying said oriented DPE below it’s melt temperature in the presence of at least one oxidizing agent to obtain a modified DPE; and
d. carbonizing said modified DPE under inert atmosphere in a furnace by increasing the temperature of the furnace from room temperature to 1200 ºC to obtain said carbon fibers.
2. The process as claimed in claim 1, wherein said disentangled ultrahigh molecular weight polyethylene (DPE) powder is stabilized with the help of at least one anti-oxidant before pre-stretching.
3. The process as claimed in claim 1, wherein the step of pre-stretching is carried out at a temperature in the range of 125 °C to below 134 °C.
4. The process as claimed in claim 1, wherein the step of pre-stretching involves compacting the DPE powder in a roll mill to obtain pre-stretched DPE.
5. The process as claimed in claim 1, wherein the step of hot stretching is carried out in plurality of stages by increasing the temperature sequentially from 135 °C to 160 °C.
6. The process as claimed in claim 5, wherein the step of hot stretching includes reducing the stretching ratio in the range of 6.0 to 2.0.
7. The process as claimed in claim 1, wherein the step of hot stretching is carried out to the extent that the hot stretched DPE is oriented and has crystallinity greater than 90%.
8. The process as claimed in claim 1, wherein said oriented DPE is in a form selected from the group consisting of tape, film and fibers.
9. The process as claimed in claim 1, wherein said oxidizing agent is at least one selected from the group consisting of sulphuric acid, chlorosulphuric acid, and fuming sulphuric acid.
10. The process as claimed in claim 1, wherein the step of modifying said oriented DPE is carried out at a temperature in the range of 60 to 100 °C and further comprises washing the modified DPE with water till pH of the washings is neutral.
11. Carbon fibers prepared by pre-stretching disentangled ultrahigh molecular weight polyethylene (DPE) powder, sequentially hot stretching the pre-stretched DPE to obtain oriented DPE in the form of tape, fibers and films, modifying the oriented DPE, and carbonizing the modified DPE to obtain carbon fibers in yields between 2% to 10%;
said carbon fibers having a tensile strength in the range of 2.5 to 3.0 GPa, and a tensile modulus in the range of 120 to 200 GPa.