Process for the preparation of carbon fiber-carbon nanotubes reinforced hybrid polymer composites for high strength structural applications

Abstract

The present invention relates to the development of carbon fiber carbon nanotubes reinforced polymer composites for high strength structural applications. It is very difficult to incorporate higher amount of carbon fiber >60 vol % in any of the polymer matrix. Beyond this loading the mechanical properties of these composite starts deteriorate. Therefore, further improvement in the mechanical properties is not possible. Herein, a novel method is developed to fabricate the hybrid carbon fiber epoxy composites reinforced with multiwalled carbon nanotubes. The flexural strength of the hybrid composites (45 vol % CF+CNT) was achieved more than 600 MPa which is more than 35% over pure carbon fiber/epoxy composites (50 vol % CF). These high strength hybrid composites can be used in wind mill blades, turbine blades, sport industries, automobile and airframe.

Claims

1. A process for the preparation of carbon fiber carbon nanotubes (CNTs) reinforced polymer composites wherein the steps comprising: a) mixing 0.1 to 0.5% (w/w) of multi walled carbon nanotubes (MWCNTs) having a diameter in the range of 20 to 100 nm and a length in the range of 20 to 200 microns with 45 to 55 g of epoxy polymer pre heated at a temperature ranging from 40 to 60 degree C. and homogenizing for 5 to 30 min to obtain a mixture; b) adding a hardener at 23% by weight of epoxy to the mixture obtained in step [a] followed by stirring for 2 to 10 min using a magnetic stirrer; c) cutting six layers of Carbon fiber cloth (CF) of dimension 14 cm17 cm each from a carbon fiber cloth sheet; d) dispersing the MWCNTs having the diameter in the range of 20 to 100 nm and the length in the range of 20 to 200 microns in a solvent with a high energy homogenizer for 10 to 15 min; e) sonicating the MWCNTs obtained in step [d] for a period of 20 to 40 min and again homogenizing for 5 to 10 min to obtain homogenized MWCNTs; f) fabricating five MWCNT papers having a dimension of 20 cm20 cm using the homogenized MWCNTs obtained in step [e] by vacuum filtration; g) cutting the MWCNT papers obtained in step [f] to a dimension of 14 cm17 cm length; and h) applying the mixture obtained in step [b] on both sides of the six layers of the CF as obtained in step [c] and the MWCNT papers as obtained in step [g] and stacking them alternately and sandwiched between die steel plates, followed by pressing at 100 to 150 kg/cm.sup.2 first at a temperature ranging from 70 to 90 degree C. for a period of 1.5 to 2.5 h and then at a temperature ranging from 140 to 160 degree C. for a period of 3.5 to 4.5 h, followed by cooling at room temperature to obtain the desired CNTs reinforced polymer composites.

2. The process as claimed in claim 1, wherein the epoxy polymer is selected from a thermosetting resin.

3. The process as claimed in claim 2, wherein the thermosetting resin is epoxy resins or polyesters.

4. The process as claimed in claim 1, wherein the CNTs are MWCNTs.

5. The process as claimed in claim 1, wherein the CNTs are selected from the group consisting of arc discharged based and chemical vapor deposition (CVD) based CNTs.

6. The process as claimed in claim 1, wherein the vacuum filtration is carried out using a vacuum filtration unit comprising a top, filter paper/nylon cloth, metallic sieve, bottom tank, silicon sheet, nut and bolt, silicon O-ring, vacuum port and rotary pump.

7. The process as claimed in claim 1, wherein the pressing is done using a hydraulic press with heater.

8. The process as claimed in claim 1, wherein the solvent is selected from the group consisting of water, chloroform, toluene, N-methyl pyrolidone, ethanol, acetone and combinations thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention relates to a process for the preparation of carbon fiber-carbon nanotubes reinforced hybrid polymer composites useful for high strength structural applications. The developed CNT-CF reinforced hybrid epoxy composite containing up to 50 vol % CNT-CF is a light weight, high strength material exhibiting density in the range of 1.3 to 1.55 g/cc and flexural strength in the range of 474 to 720 MPa. The sandwiching of layers of multiwalled carbon nanotube papers between the carbon fiber fabric as done in the present invention improves the interlaminar shear strength which is very much helpful for further improvement in the mechanical properties of the developed carbon fiber based polymer composites.

(2) MWCNTs having diameter in the range of 20 to 100 nm and length in the range of 20 to 200 microns were mixed with pre heated epoxy polymer and homogenized to obtain a mixture. Hardener @ 23% by weight of epoxy was added to the mixture thus obtained followed by stirring using a magnetic stirrer. Six layers of Carbon fiber cloth (CF) of dimension 14 cm17 cm each were cut from the carbon fiber cloth sheet. MWCNTs having diameter in the range of 20 to 100 nm and length in the range of 20 to 200 microns were dispersed in a suitable solvent with the help of high energy homogenizer followed by sonication and again homogenization to obtain homogenized MWCNTs. MWCNT papers having dimension of 20 cm20 cm were fabricated using the homogenized MWCNTs by vacuum filtration and cut into dimension of 14 cm17 cm length. The mixture of MWCNTs and epoxy obtained above was applied on both sides of all layers of CF and MWCNT papers followed by stacking them alternately and sandwiching between the die steel plates followed by pressing under heat. The composite thus obtained was cooled at room temperature to obtain the desired carbon fiber carbon nanotubes reinforced hybrid polymer composites having high mechanical strength.

(3) In an aspect of the present invention, 55 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.2% MWCNTs were mixed with it using high energy Homogenizer for 10 min. 23% hardener was added in the heated epoxy and continued stirring for 10 min. 6 layers of CF cloth of dimension 14 cm17 cm were cut from the carbon cloth sheet. 3.75 g MWCNTs were mixed in 1.5 L acetone with the help of high energy Homogenizer for 10 min. followed by sonication for 30 min. and again homogenized for 10 min. from which 5 no of MWCNT flexible papers of dimension 20 cm20 cm were prepared by vacuum filtration technique. These MWCNT flexible papers were cut into dimension 14 cm17 cm. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF and MWCNT flexible paper. All CF layers and MWCNT papers were stacked alternately and sandwiched between die steel plates. These die steel plates were pressed @ 100-150 kg/cm.sup.2 in the hydraulic press with heater at 80 C. for 2 h followed by 150 C. for 4 h then cooled at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

(4) In another aspect of the present invention, to make the CF-CNTepoxy-CNT papers composite, 0.2% (w/w) MWCNTs (20-100 nm in diameter and 20-200 microns in length) were added in 55 g epoxy pre heated at 40-60 C., and homogenized for 5-15 min. 23% (w/w) hardener was added in mixture of MWCNTs and epoxy then stirred for 2-10 min by using magnetic stirrer. Six layers of Carbon fiber cloth (CF) were cut from the carbon fiber cloth sheet. The dimension of each cut sheet was 14 cm17 cm. The mixture of MWCNT, epoxy and hardener was applied by the glass rod on both sides of all layers of CF. All layers of CF were stacked and sandwiched between die steel plates. These die steel plates were pressed at 100 kg/cm in the hydraulic press (with heater) at 70-90 C. for 1.5-2.5 h and 140-160 C. for 3.5-4.5 h and then cooled at room temperature. Samples were cut according to the ASTM D 790 from the cured CF-CNT epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

(5) In another aspect of the present invention, in order to improve the mechanical strength property of the developed composite, 23% (w/w) hardener was added into 50 g epoxy preheated at 60 C., and stirred for 10-30 min. Again 6 layers of Carbon fiber cloth (CF) were cut from the carbon fiber cloth sheet of dimension 14 cm17 cm each. MWCNTs (20-100 nm in diameter and 20-200 microns in length) were dispersed into a suitable solvent (water, acetone, toluene, NMP, DMF, ethanol or combinations thereof) with the help of high energy Homogenizer for 10-30 min. After the homogenization, sonication was done for 10-30 min and again homogenized for 10-30 min. Then 5 no of MWCNT papers of dimension 20 cm20 cm were prepared by vacuum filtration technique. These MWCNT papers were cut into dimensions measuring 14 cm wide and 17 cm in length. The mixture of epoxy and hardener was applied by the glass rod on both sides of all layers of CF and MWCNT paper as well. All layers of CF and MWCNT papers were stacked alternately and sandwiched between die steel plates. These die steel plates were pressed (100-150 kg/cm.sup.2) in the hydraulic press (with heater) at 80 C. for 2 h and 150 C. for 4 h and allowed to cool down at room temperature. Samples were cut according to the ASTM D 790 from the cured CF-epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

(6) The density, CNT-CF content and three points bending testing of the prepared composites were measured. Three points bending testing was measured by Instron universal testing machine model 5967. The sample size for three-points bending testing was taken according to the ASTM D 790.

EXAMPLES

(7) The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention in any manner.

Example 1

(8) 45 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.1% MWCNTs were mixed with it using high energy Homogenizer for 10 min. 23% hardener was added in the heated epoxy mixture and continued stirring for 10 min. This homogeneous mixture was poured into a rectangular die. The die was placed into heating oven at 80 C. for 2 h followed by 160 C. for 4 h and then cooled at room temperature to obtain the desired composite. Samples were removed from the die. The three point bending strength was measured using Instron universal testing machine model 4411.

Example 2

(9) 45 g epoxy was heated at 60 C. on magnetic stirrer for 15 min and 0.2% MWCNTs were mixed with it using high energy Homogenizer for 10 min. Then 23% hardener was added in the heated epoxy mixture and continued the stirring for 10 min. This homogeneous mixture was poured into a rectangular die. The die was placed into heating oven at 85 C. for 2 h followed by 150 C. for 4 h and then cooled at room temperature to obtain the desired composite. Samples were removed from the die. The three point bending strength was measured using Instron universal testing machine model 4411.

Example 3

(10) 45 g epoxy was heated at 60 C. on magnetic stirrer for 20 min and 0.3% MWCNTs were mixed with it using high energy Homogenizer for 20 min. 23% hardener was added in the heated epoxy mixture and continued the stirring for 10 min. This homogeneous mixture was poured into a rectangular die. The die was placed into heating oven at 90 C. for 2 h followed by 145 C. for 4 h and then cooled at room temperature to obtain the desired composite. Samples were removed from the die. The three point bending strength was measured using Instron universal testing machine model 4411.

Example 4

(11) 45 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.5% MWCNTs were mixed with it using high energy Homogenizer for 30 min. 23% hardener was added in the heated epoxy mixture and continued the stirring for 10 min. This homogeneous mixture was poured into a rectangular die. The die was placed into heating oven at 75 C. for 2 h followed by 160 C. for 4 h and then cooled at room temperature to obtain the desired composite. Samples were removed from the die. The three point bending strength was measured using Instron universal testing machine model 4411.

Example 5

(12) 45 g epoxy was heated at 60 C. on magnetic stirrer for 10 min. 23% hardener was added in the heated epoxy and continued stirring for 10 min. 6 layers of carbon fiber (CF) cloth of dimension 14 cm17 cm were cut from the carbon cloth sheet. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF. All CF layers were stacked and sandwiched between die steel plates. These die steel plates were pressed (100 kg/cm.sup.2) in the hydraulic press (with heater) at 80 C. for 2 h and 150 C. for 4 h then cool at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied by using Instron universal testing machine model 5967.

Examples 6

(13) 50 g epoxy was heated at 60 C. on magnetic stirrer for 10 min. 23% hardener was added in the heated epoxy and continued stirring for 10 min. 6 layers of CF cloth of dimension 14 cm17 cm were cut from the carbon cloth sheet. 3.75 g MWCNTs were mixed in 1.5 L acetone with the help of high energy Homogenizer for 10 min. followed by sonication for 30 min. and again homogenized for 10 min. from which 5 no of MWCNT flexible papers of dimension 20 cm20 cm were prepared by vacuum filtration technique. These MWCNT flexible papers were cut into dimension 14 cm17 cm. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF and MWCNT flexible paper. All CF layers and MWCNT papers were stacked alternately and sandwiched between die steel plates. These die steel plates were pressed @ 10-100 kg/cm.sup.2 in the hydraulic press with heater at 80 C. for 2 h followed by 150 C. for 4 h then cooled at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

Example 7

(14) 55 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.2% MWCNTs were mixed with it using high energy Homogenizer for 10 min. 23% hardener was added in the heated epoxy and continued stirring for 10 min. 6 layers of CF cloth of dimension 14 cm17 cm were cut from the carbon cloth sheet. 3.75 g MWCNTs were mixed in 1.5 L acetone with the help of high energy Homogenizer for 10 min. followed by sonication for 30 min. and again homogenized for 10 min. from which 5 no of MWCNT flexible papers of dimension 20 cm20 cm were prepared by vacuum filtration technique. These MWCNT flexible papers were cut into dimension 14 cm17 cm. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF and MWCNT flexible paper. All CF layers and MWCNT papers were stacked alternately and sandwiched between die steel plates. These die steel plates were pressed @ 10-100 kg/cm.sup.2 in the hydraulic press with heater at 80 C. for 2 h followed by 150 C. for 4 h then cooled at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

Example 8

(15) 55 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.2% MWCNTs were mixed with it using high energy Homogenizer for 10 min. 23% hardener was added in the heated epoxy and continued the stirring for 10 min. 6 layers of CF of dimension 14 cm17 cm were cut from the carbon cloth sheet. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF. All CF layers were stacked and sandwiched between die steel plates. These die steel plates were pressed (100 kg/cm.sup.2) in the hydraulic press (with heater) at 80 C. for 2 h and 150 C. for 4 h then cool at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

Example 9

(16) 55 g epoxy was heated at 60 C. on magnetic stirrer for 10 min and 0.3% MWCNTs were mixed with it using high energy Homogenizer for 20 min. 23% hardener was added in the heated epoxy and continued stirring for 10 min. 6 layers of CF of dimension 14 cm17 cm were cut from the carbon cloth sheet. The mixture of epoxy and hardener was applied by glass rod on both sides of all layers of CF. All CF layers were stacked and sandwiched between die steel plates. These die steel plates were pressed (100 kg/cm.sup.2) in the hydraulic press (with heater) at 80 C. for 2 h and 150 C. for 4 h then cool at room temperature. Samples were cut according to the ASTM D 790 from the cured CF epoxy composite plate. The three point bending strength was studied according to the ASTM D 790 by using Instron universal testing machine model 5967.

(17) TABLE-US-00001 TABLE 1 Results obtained in examples 1 to 9 Carbon MWCNT Ex- Rein- Wt. % of Fiber paper Flexural ample forcement MWCNTs Type of Layers Layers strength No Type in epoxy samples (No.) (No.) (MPa) 1 MWCNTs 0.1 MWCNTs- 0 0 104-114 epoxy composites 2 MWCNTs 0.2 MWCNTs- 0 0 107-119 epoxy composites 3 MWCNTs 0.3 MWCNTs- 0 0 100-107 epoxy composites 4 MWCNTs 0.5 MWCNTs- 0 0 82-93 epoxy composites 5 Carbon CF-epoxy 6 0 444-496 Fiber composites Cloth 6 Carbon CF- 6 5 552-635 Fiber MWCNTs Cloth and Papers MWCNTs epoxy Papers composites 7 Carbon 0.2 CF- 6 5 587-720 Fiber MWCNTs Cloth, Papers- MWCNTs MWCNTs Papers dispersed and epoxy MWCNTs composites 8 Carbon 0.2 CF- 6 0 582-670 Fiber MWCNTs Cloth and dispersed MWCNTs epoxy composites 9 Carbon 0.3 CF- 6 0 441-570 Fiber MWCNTs Cloth and dispersed MWCNTs epoxy composites

ADVANTAGES OF THE INVENTION

(18) The present invention identifies the improvement of carbon fiber-carbon nanotubes strengthened polymer composites for high quality structural applications. These composites can be utilized as a part of structural applications in car, defense and space, airframe, wind mills, sports factory and so forth. The present invention demonstrates the procedure to develop the composites unlike the customary methods of dispersion, for example, surfactant-helped systems, arrangement blending, in situ polymerization, in-situ development of MWCNTs on the carbon fiber and melt-mixing strategies. The developed hybrid composites (45 vol % CF+CNT) have flexural strength of more than 600 MPa. The developed composites have more than 35% bending strength (45 vol % CF+CNT) over pure carbon fiber-epoxy composites (50 vol % CF). A higher content of carbon fiber increase the strength of composite. The utilization of a novel system not just gives a higher quality of the composites; furthermore the impregnated MWCNT paper is very adaptable and can be formed into different shapes before curing relying upon the application. The composite is consumption safe and light weight with a density of 1.3-1.55 g/cc. The composite arranged by this strategy is a mass isotropic composites and containing just CF, MWCNT and polymer. No other fixing has been included other than solvents. The system is straightforward and includes few simple processing steps.