Patent Application
20140248442
The present invention is related to a method for the functionalization of particulate and powdered products such as for example carbon black, glass fibres, carbon fibres and in particular carbon nanotubes. The present invention is also related to a plasma reactor able to functionalize these products.
Particulate and powdered substrates are often used as additives for reinforced polymer-based composites. In particular fibres, powders and nanoparticles are able to improve the physical properties of polymer-based composites.
Among the variety of particles, carbon nanotubes (CNTs) are particularly promising due to their unique mechanical and physical properties. However, the use of carbon nanotubes in polymer-based composites is now still limited due to the nonreactive nature of their surface and the agglomeration of CNTs into micron-size structures (as bundles, spheres etc.) during their growth. To overcome these problems, a functionalization (modification) of CNTs by changing their surface composition via the introduction of other elements or groups of elements (functional groups) has proved to be efficient.
Functionalization of carbon nanotubes can improve their solubility and processability and will allow to combine the unique properties of the carbon nanotubes with those of other types of materials. New chemical bonds created during the functionalization process might be used to tailor the interaction of the nanotubes with solvents or polymer matrices.
Functionalization of carbon nanotubes usually begins with the introduction of O-containing groups (mainly carboxylic groups), which further gives an access to a large number of functional exploitations by transformation of the carboxylic functions and provides anchor groups for further modification.
The introduction of O-containing groups in the structure of the CNTs can be realized via liquid-phase and gas-phase methods.
Liquid-phase oxidative treatment of carbon nanotubes is usually performed using boiling nitric acid, sulfuric acid, or a mixture of both. A so-called “piranha” solution (sulfuric acid-hydrogen peroxide mixture) can also be used. These methods have a low efficiency of functionalization, create defects in the structure of the CNTs, decrease their length, dramatically increase the density of the material and produce considerable amounts of toxic acidic waste.
Gas-phase oxidative processes are based on the treatment of the carbon nanotubes with oxygen, ozone or air at elevated temperatures. The main disadvantages of this type of functionalization are high-process temperatures leading to the creation of defects in the nanotube structure. Furthermore, this type of process requests a preliminary purification to remove the traces of metal catalysts which can catalyze the reaction of CNTs with O2 or O3.
Gas-phase functionalization can also be realized by using mechano-chemical treatment via ball milling of nanotubes under different reactive atmospheres such as H2O, NH3 and/or Cl2. Nevertheless mechano-chemical functionalization also results in the considerable densification of CNTs and the formation of structural defects.
In contradistinction to the methods mentioned above, the functionalization method based on plasma treatment is a low-temperature process which is very effective, non-polluting and which can provide a wide range of functional groups. Thus, for industrial applications a plasma functionalization process should be preferred to other methods mentioned previously.
A plasma is a partially or entirely ionized gas or vapour comprising elements in various excitation states. This includes all molecules which are not in a fundamental state. Such plasma can be created and maintained by electromagnetic fields. Due to the exposure of the electromagnetic field, active species of plasma such as ions and free radicals are formed by collisions between molecules from the gas phase and free electrons. The resulting plasma consists of ions, free electrons, free radicals, species in an excited state, photons and neutral stable species. Free radicals react with the surface of treated materials differently depending on the gas nature and the surface chemistry of the material.
Depending on gas pressure, the plasma can be atmospheric or low-pressure. The pressure range below approximately 103 Pa is designated as low-pressure plasma. One of the most important advantages of low-pressure plasma is that reactions requiring elevated temperatures at atmospheric pressure typically take place near ambient temperature under low-pressure plasma conditions. This phenomenon is due to the fact that despite low gas temperatures, high electron temperatures are realized in low-pressure plasma due to the increased free path length. Another advantage of low-pressure plasma is that treatment occurs under vacuum, i.e. in a precisely controlled environment. Due to this fact, the low-pressure plasma treatment has higher repeatability in comparison with atmospheric plasma process. Due to these advantages, low-pressure plasmas have found wide applications in materials processing (M. A. Lieberman, A. J. “Principles of plasma discharges and materials processing”, New York, Wiley, 1994). Low-pressure plasma can be formed by applying a direct current (DC), low frequency (50 Hz), radio frequency (RF) (40 kHz, 13.56 MHz) or microwave (GHz) electric field over a pair or a series of electrodes.
Radio frequency (RF) plasma devices generally use 13.56 MHz electromagnetic waves since this frequency band is dedicated to the research and does not affect telecommunications.
Plasma treatments can be achieved under various gas pressures in various reactors. In case of powders such as carbon black, graphite or carbon nanotubes, a uniform treatment of each particle is desirable but difficult to obtain. This is mainly due to particle size distributions and to the agglomeration of the particles.
In the prior art, vibrating and fluidized-bed reactors have been developed to functionalize carbon nanotubes (CNTs) with O-containing groups via plasma treatment by using high frequency electric fields. The disadvantage of a fluidized-bed reactor working continuously lies in the fact that the residence time of each particle treated in the reactor is in fact unknown and uncontrollable.
The document WO 2010/081747A discloses a fluidized-bed reactor of a particular shape, comprising a section enlargement in the reactor, where the plasma treatment of the powder occurs.
The present invention aims to provide a plasma reactor and a method which does not have the drawbacks of the prior art.
The present invention aims in particular to propose a method allowing the powder to fall by gravity through the reaction zone containing active species created by the plasma at low pressure, which guarantees a specific residence time and a controlled treatment.
Finally the present invention discloses polymer-based composites reinforced with carbon nanotubes functionalized according to the method of the invention and in the reactor of the invention.
The present invention discloses a continuous method for the functionalization of a pulverulent product in a plasma reactor comprising the steps of:
Preferred embodiments of the present invention disclose at least one or an appropriate combination of the following features:
amines such as alkylamines, for example methylamine (CH5N), heptylamine (C7H17N), butylamine (C4H11N), propylamine (C3H9N), 1,3-diaminopropane or allylamines such as allylamine (C3H7N); amides such as, for example, dimethylformamide (C3H7NO), alcohols such as methanol (CH3OH), ethanol (C2H5OH), allyl alcohol (C3H5OH), isopropyl alcohol (C3H7OH), 1-propanol (C3H7OH), propargyl alcohol (C3H3OH), furfuryl alcohol (C5HSO2H), isobutanol (C4H9OH); silanes and their derivatives; siloxanes and their derivatives such as hexamethyldisiloxane (C6H18OSi2); halogens and their derivatives, such as fluorocarbons, for example as tetrafluoromethane (CE); terpenes and terpenoids such as isoprene (C5H8) and its derivatives.
The present invention further discloses an installation for the functionalization of a pulverulent product by means of the method according to the invention comprising:
a second device in connection with the plasma reactor for charging the reactor with a pulverulent product;
Preferred embodiments of the installation according to the invention disclose at least one or an appropriate combination of the following features:
The present invention further discloses polymer-based composites comprising carbon nanotubes which are functionalized according to the method and the installation of the invention.
A large-scale method for the functionalization of powders, and in particular carbon nanotubes, together with a specific reactor type was developed.
The method is based on the treatment of the powders under plasma conditions and in particular under radio frequency (RF) plasma conditions in the presence of different gases.
Depending on the nature of the gas used, this method results in the particular case of carbon nanotubes in the replacement of a part of carbon atoms by other atoms or groups of atoms, and/or in the attachment of other atoms or groups of atoms to the carbon atoms of CNTs, or in the deposition of a layer of various substances on the surface of CNTs.
The variation of the process conditions allows to vary the nature and the concentration of elements or compounds introduced in or deposited on the structure of the CNT surface or other powders. The main advantages of the method according to the invention are:
Setup Description
The reactor is connected at the top with a powder insertion (feeding) system 5 with feeding means, for example an endless screw 6 and a gas inlet 7, and at the bottom with a product recovering system 8. The gas line consists in a gas inlet system 7, a flow mass controller 9 and a gas balloon (in the case of gaseous precursors) or container with a liquid (in the case of precursor in liquid state) 10. In a particular embodiment, both the gas inlet and the pumping system are situated on the top of the reactor.
The pressure inside the vertical reactor is controlled by one or more turbo pumping system(s) (11, 13) and a shielding system 12 avoids the propagation of electromagnetic waves outside the reactor zone.
The treated powder is delivered from the insertion system on the top of the reactor by a suitable feeding system, for example an endless screw, and is transferred through the reactor where it is submitted to the plasma treatment while falling by gravity forces to the bottom of the reactor where it is collected.
Since the reactor operates under specific low pressure conditions, the (vacuum) outlet 8 and the inlet 5 lock chambers are necessary for the introduction and the recovery of the plasma treated powders to maintain a low pressure inside the reactor. Double lock chambers in a parallel position (5, 8) such as represented in
Operating Conditions
The RF plasma is generated by a frequency of 13.56 MHz and the available power ranges between 100-1000 W. The process gas pressure in the reactor during the treatment is in the range of 10−2 and 10 Pa.
The functionalization can be performed in presence of various substances, for example inert gases such as argon (Ar), helium (He); nitrogen-containing gases such as molecular nitrogen (N2), ammonia (NH3); oxygen-containing gases such as oxygen (O2), ozone (O3), carbon monoxide (CO), carbon dioxide (CO2); alkanes such as, for example, ethane (C2H6), hexane (C6H14); alkenes such as, for example, ethylene (C2H4); alkynes such as, for example, acetylene (C2H2); monomers such as, for example, methyl methacrylate (C5H8O2); carboxylic acids with the formula R—COOH, where R is some monovalent functional group and R can be saturated, for example propanoic acid (C3H6O2), or unsaturated, for example acrylic acid (C3H4O2); amines such as alkylamines, for example methylamine (CH5N), heptylamine (C7H17N), butylamine (C4H11N), propylamine (C3H9N), 1,3-diaminopropane or allylamines such as allylamine (C3H7N); amides such as, for example dimethylformamide (C3H7NO); alcohols such as methanol (CH3OH), ethanol (C2H5OH), allyl alcohol (C3H5OH), isopropyl alcohol (C3H7OH), 1-propanol (C3H7OH), propargyl alcohol (C3H3OH), furfuryl alcohol (C5HSO2H), isobutanol (C4H9OH); silanes and their derivatives; siloxanes and their derivatives such as hexamethyldisiloxane (C6H180Si2); halogens and their derivatives, such as fluorocarbons, for example as tetrafluoromethane (CF4), terpenes and terpenoids such as isoprene (C5H8) and its derivatives.
The method and the installation are suitable for any pulverulent material. Non-limitative examples of powders submitted to functionalization can be single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs), carbon fibres, carbon black, graphite, glass fibres, metal oxides ex: ferrite, fumed silica, silicate glass, nanoclays.
Characterization Methods
The structure of the particles after functionalization was characterized by transmission electron microscopy (TEM). The concentration of inserted elements has been estimated by X-ray photoelectron spectroscopy (XPS).
In the particular case of carbon nanotubes, unique electrical and mechanical properties of polymer-based composites containing these nanotubes are obtained via the structure and the morphology of their aggregates. The preservation of the structure of CNTs and their aggregates during functionalization is therefore one of the important tasks. The structure of CNTs before and after plasma functionalization was investigated with TEM. Typical TEM images of pristine and plasma treated nanotubes presented in
XPS spectra of CNTs after plasma functionalization proved the introduction/attachment of the elements (Oor/and N) in the nanotubes. The estimation of atomic concentrations of carbon and introduced elements is based on the measurements of the area of their characteristic peaks. The changes in typical XPS spectra of CNTs after functionalization are presented in
The nature of the elements introduced during plasma functionalization can vary by using different gases. The concentration of elements can vary by changing the following parameters:
The results presented in
The increase of the number of passages through the plasma zone also results in the increase of the concentration of the introduced elements (
5.0 g of multi-wall carbon nanotubes were placed in the reservoir of the insertion system via an inlet lock chamber, the system was hermetically closed and the setup was pumped by a turbo pump up to a pressure of 5.10−3 Pa. An N2 gas was inserted into the system via the top of the vertical reactor tube with a pressure of about 0.99 Pa. The RF plasma was generated by a frequency of 13.56 MHz with a power of 300 W and an antenna with 4 solenoid coils on a quartz reactor. CNTs were transferred from the reservoir to the center of the reactor on the top using the insertion system with an endless screw with the speed 0.4 rotation/sec approximately. CNTs passed through the plasma zone driven by the gravity force.
After passing the plasma zone, CNTs were collected in the recovery system tank via an outlet lock chamber. The whole system is arranged to coordinate the closure and the opening of the lock chambers so that the low pressure can be maintained while a continuous supply and recovery of CNTs is possible. The concentration of N, O and C was estimated by XPS method. The structure of CNTs was investigated by transmission electron microscopy. The composition of the CNTs sample after functionalization is the following: 93.7 at. % of C, 2.9 at. % of N, 3.4 at. % of O. The composition of the CNTs sample before functionalization was: 99.1 at. % of C, 0.9 at. % of O.
The same operating conditions as in Example 1 were chosen, but an NH3 gas was used instead of N2, with the same pressure (0.99 Pa). The composition of CNT sample after functionalization based on XPS measurements was the following: 96.8 at. % of C, 1.0 at. % of N, 2.2 at. % of O.
The same operating conditions as in Example 1 were chosen, but an C3H5NH2 gas was used instead of N2, with the same pressure (0.99 Pa). The composition of CNT sample after functionalization based on XPS measurements was the following: 95.7 at. % of C, 1.8 at. % of N, 2.5 at. % of O.
The same operating conditions as in Example 1 were chosen, but an H2 gas was used instead of N2, with the same pressure (0.99 Pa). The composition of CNT sample after functionalization based on XPS measurements was the following: 98.5 at. % of C, and 1.5 at. % of O.
The same operating conditions as in Example 1 were chosen, but an H2O gas was used instead of N2, with the same pressure (0.99 Pa). The composition of the CNT sample after functionalization based on XPS measurements was the following: 97.2 at. % of C, and 2.8 at. % of O.
The same operating conditions as in Example 1 were chosen, but an 02 gas was used instead of N2, with the same pressure (0.99 Pa). The composition of the CNT sample after functionalization based on XPS measurements was the following: 96.5 at. % of C, and 3.5 at% of O.
The same operating conditions as in Example 1 were chosen, but a C3H4O2 gas was used instead of N2, with the same pressure (0.99 Pa). The composition of the CNT sample after functionalization based on XPS measurements was the following: 97.6 at. % of C, and 2.4 at. % of O.
The same operating conditions as in Example 1 were chosen, but the sample was passed through the plasma zone 5 times instead of one. The composition of the CNT sample after functionalization based on XPS measurements was the following: 87.4 at. % of C, 6.2 at. % of N, 6.4 at. % of O.
The same operating conditions as in Example 1 were chosen, but the antenna with 8 solenoid coils was used instead of a 4-coils antenna. The composition of the CNT sample after functionalization based on XPS measurements was the following: 91.2 at. % of C, 5.6 at. % of N, 3.2 at. % of O.
The same operating conditions as in Example 1 were chosen, but the antenna with 8 solenoid coils was used instead of a 4-coils antenna and the sample was passed through the plasma zone 5 times instead of one. The composition of the CNT sample after functionalization based on XPS measurements was the following: 81.3 at. % of C, 13.4 at. % of N, 5.3 at. % of O.
The same operating conditions as in Example 1 were chosen, but the power of 100 W was used instead of 300 W. The composition of the CNT sample after functionalization based on XPS measurements was the following: 94.7 at. % of C, 1.2 at. % of N, 4.1 at. % of O.
The same operating conditions as in Example 1 were chosen, but the power of 200 W was used instead of 300 W. The composition of the CNT sample after functionalization based on XPS measurements was the following: 89.8 at. % of C, 5.9 at. % of N, 4.3 at. % of O.
The same operating conditions as in Example 1 were chosen, but the N2 pressure of 0.48 Pa was used instead of 0.99 Pa. The composition of the CNT sample after functionalization based on XPS measurements was the following: 88.1 at. % of C, 8.7 at. % of N, 3.2 at. % of O.
The same operating conditions as in Example 1 were chosen, but the N2 pressure of 0.48 Pa was used instead of 0.99 Pa and the power of 100 W was used instead of 300 W. The composition of the CNT sample after functionalization based on XPS measurements was the following: 93.5 at. % of C, 3.1 at. % of N, 3.4 at. % of O.
The same operating conditions as in Example 1 were chosen, but the N2 pressure of 0.48 Pa was used instead of 0.99 Pa and the power of 200 W was used instead of 300 W. The composition of the CNT sample after functionalization based on XPS measurements was the following: 93.7 at. % of C, 3.7 at. % of N, 2.6 at. % of O.
The same operating conditions as in Example 1 were chosen, but 5.0 g of carbon black (KETJENBLACK EC600JD, AKZO NOBEL) were used instead of multi-wall carbon nanotubes. The composition of the sample after functionalization based on XPS measurements was the following: 93.5 at. % of C, 4.1 at. % of N, 2.4 at. % of O. The composition of the sample before the plasma treatment was: 97.4 at. % of C, 2.6 at. % of O.
The same operating conditions as in Example 1 were chosen, but 5.0 g of graphite (Expandable graphite GHL PX 98, HUNTSMAN) were used instead of multi-wall carbon nanotubes. The composition of the sample after functionalization based on XPS measurements was the following: 95.2 at. % of C, 1.6 at. % of N, 3.2 at. % of O. The composition of the sample before the treatment was: 99.1 at. % of C, 0.9 at. % of O.
The same operating conditions as in Example 1 were chosen, but 5.0 g of glass fibers were used instead of multi-wall carbon nanotubes. The composition of the sample after functionalization based on XPS measurements was the following: 44.2 at. % of C, 16.1 at. % of N, 39.7 at. % of O. The composition of the sample before the treatment was: 73.4 at. % of C, 26.6 at. % of O. No presence of Si was detected because of the presence of polymer sizing on the surface of glass fibers.
The same operating conditions as in Example 1 were chosen, but 5.0 g of ferrite powder (Fe2O3), consisting of irregular shape particles with size 0.2-50 μm (
The same operating conditions as in Example 1 were chosen, but 5.0 g of fumed silica powder (SiO2), consisting of agglomerates with size 1-20 μm of particles with size <100nm (
The same operating conditions as in Example 1 were chosen, but 5.0 g of silicate glass powder (with approximate formula Na2OCa0.6SiO2), consisting of spherical particles with size 0.1-50 μm (
The same operating conditions as in Example 1 were chosen, but 5.0 g of silicate glass powder (with approximate formula Na2OCa0.6SiO2) were used instead of multi-wall carbon nanotubes, the antenna with 8 solenoid coils was used instead of a 4-coils antenna, allylamine (C3H5NH2) with pressure of 2.0 Pa were used instead of nitrogen and the sample was passed through the plasma zone 5 times instead of one. The composition of the sample after functionalization based on XPS measurements was the following: 12.1 at. % of N, 56.2 at. % of O, 23.7 at. % of Si, 6.6 at. % of Na, 1.4 at. % of Ca. The composition of the sample before the treatment was: 63.2 at. % of O, 26.4 at. % of Si, 8.8 at. % of Na, 1.6 at. % of Ca.
The same operating conditions as in Example 1 were chosen, but 5.0 g of nanoclay Cloisite 20A powder (with approximate formula Mx(Al4-xMg)Si8O28(OH)4, where M can be Na+, Ca2+ or NH4+), consisting of irregular shape agglomerates of flakes-like /particles with aggregates size 1-20 μm (
Table 1 summarizes the correlation between the nature of the gas, the reaction parameters and the concentration of the elements which 1t0091/ZIOZ OM are introduced in the powder structure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11167044.4 | May 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/059437 | 5/22/2012 | WO | 00 | 5/8/2014 |
