Final Report Summary - HARCANA (High Aspect Ratio Carbon-based Nanocomposites)
Executive summary:
High aspect ratio Carbon-based nanoparticles (mainly nanotubes (CNT), and to a less extent nanofibres (CNF), as well as nanosheets or exfoliated graphite (CNS)) will be introduced into bulk polymers, into polymeric foams and into membranes. It is expected that such nanofillers will tremendously improve and modify the properties of these families of materials, allowing them to reach new markets. However, a common and fundamental problem in polymer-based nanocomposites is the large extent of agglomeration of the nanoparticles due to their high surface to volume ratio. Therefore, techniques to control deagglomeration and possibly further organisation of these high aspect ratio nanoparticles in polymeric materials remain a challenge.
This project under industrial leadership will therefore aim at mastering, at the nanometric and mesoscale level, the spatial organisation of carbon-based nanoparticles (CNP) with various surface functionalities, sizes and shapes having large aspect ratios in bulk, foamed and thin film (membranes) polymers by using industrially viable processes. More precisely, the aim of HARCANA consists in generating polymer based nanocomposites with a percolating nanoparticle structure that is reinforcing the material and imparts it with improved electrical and thermal conductivity at a minimum of nanoparticle loading. To reach such radically improved properties, it is important to take into account that a complete dispersion is not useful and will lead to lower properties.
In order to control this CNP organisation within the polymer matrix, a large set of techniques will be used. They range from synthetic approaches ('grafting from', 'grafting to', 'grafting through', emulsion polymerisation) to (reactive) melt or solution blending processes, and the preparation in supercritical Carbon dioxide (CO2). The aim is to generate new classes of engineering materials for various applications like Electromagnetic interference (EMI) shielding, antistatic fuel systems parts and packaging materials and membranes, as well as biocompatible materials with brain cells that could be used to prepare scaffolds for tissue engineering in the future.
Organisation of HARCANA
The consortium of the project consists of seven academic and five industrial partners from five countries under the coordination of Helmholtz-Zentrum Geesthacht. The project is spanning a bridge between research and development of the nanocomposites on one side to the demonstration of the developed results on the other side. Life cycle assessment will be performed on selected examples. The achievements will be disseminated by publications in scientific and technical journals, oral and poster contributions at conferences and fairs, as well as by this homepage. These activities are distributed in several, inter-linked work packages.
Project context and objectives:
Plastics are generally cheap and light-weight materials in comparison to metals and ceramics. However, they often show worse properties compared to metals (mechanical properties, electric and thermal conductivity) or compared to most metals and ceramics (thermal stability, fire resistance), to mention just a few examples. A well-known way to improve mechanical properties of polymers is to add high aspect ratio particles like glass, carbon or polyaramide short fibres, which increase the tensile strength of the polymer matrix. A lot of work has been carried out in this field and has lead to numerous everyday life application in cars, household, sport equipments, but, in order to reach high mechanical properties, large quantities of those fillers have to be added, making the resulting materials more heavy, more brittle and with a poor surface finish in comparison with the initial polymer matrix.
Another way to enhance the mechanical and other properties of polymers consists in adding so-called nanofillers. Nanofillers differ from the aforementioned fillers by the fact that at least one of their dimensions is in the range of up to several nanometers. Exfoliated clays (layered silicates) and nanofibres are examples for such nanofillers. With these nanofillers, much lower filling level is usually required to obtain polymer-based materials with mechanical and thermal properties comparable to the composites based on larger amounts of microfillers. Due to their characteristic small dimension(s), nanofillers have much larger surface-to-volume ratios as compared to other fillers. These small dimensions may further lead to significantly different properties and have initiated research and development activities called 'Nanoscience' and 'Nanotechnology'.
A lot of work has been addressed to some nanofillers such as layered silicates, especially with respect to the separation of the layers (exfoliation) in order to get well dispersed plate-like filler nanoparticles in the matrix. Less work has been done so far in the area of another upcoming class of nanofillers, which are CNT. These cylindrical graphite-like carbon structures are characterised by diameters in the nanometre range and lengths of up to several micrometers (so a tremendous aspect ratio). In addition they are predicted to have a tensile modulus in the range of several TPa making them not only very interesting candidates for futuristic ideas (e.g. space elevators), but also for reinforcement of polymer matrices for light weight applications. Moreover, they show electric conductivity what is useful for many applications where electrostatic discharges may cause damage, and they are characterised by high thermal conductivity. Other carbon-based nanoparticles (CNF, CNS) are thought to display similar properties. Besides bulk polymer, the introduction of these nanofillers in polymeric foams and membranes can tremendously improve and modify the properties of these families of materials, allowing them to reach new markets. However, a common and fundamental problem in polymer-based nanocomposites is the large extent of agglomeration of the nanoparticles due to their high surface to volume ratio. Therefore, techniques to control deagglomeration and possibly further organisation of these high aspect ratio nanoparticles in polymeric materials remain a challenge.
HARCANA will therefore aim at mastering, at the nanometric and mesoscale level, the spatial organisation of CNPs with various surface functionalities, sizes and shapes having large aspect ratios (CNT, CNF, CNS) in bulk, foamed and thin film (membranes) polymers by using industrially viable processes. More precisely, the aim of this proposal consists in generating polymer-based nanocomposites with a percolating nanoparticle structure that is reinforcing the material and imparts it with improved electrical and thermal conductivity at a minimum of nanoparticle loading. To reach such radically improved properties, it is important to take into account that a complete dispersion (disappearance of contact points) is not useful and will lead to lower properties.
Within the frame of this proposal, dispersion of CNT or other high aspect ratio carbon-based nanoparticles will find applications in:
- Bulk nanocomposites, for injection moulded or extruded parts. The expected reinforcement of mechanical properties at low nanofiller loading, coupled to antistatic properties will advantageously replace common short fibre-based fillers in automotive, aeronautic or building materials, with improvement in materials weight and surface finish. Besides, mechanical and electrical properties, these carbon-based nanoparticles may also impart fire resistance to the processed parts.
- Nanocomposites foamed either by chemical or physical processes. These new polymeric foams will be tested for various applications such as new electronics packaging, where Electrostatic discharge (ESD) can damage a sensitive component, new lightweight and efficient EMI shielding materials or thin Radar absorbing materials (RAM). Such foams, based on biocompatible matrices, will also allow preparing new tissue scaffolds exploiting the three-dimensional (3D) structure of the foam and the conductive properties of the embedded CNP for neuronal growth.
- Thin film and membrane nanocomposites containing carbon-based nanofillers. They will have a potential in applications, where chemicals have to be separated by membrane processes and electrostatic discharges have to be avoided. They will also show enhanced mechanical and thermal stability which makes their operation under high pressure differences safer. The enhancement of their barrier properties may become important as well and may open new application areas.
Project objectives
The control of CNP structuration at the nano and meso scale in polymeric materials constitutes one typical pathway for mastering nano-scale complexity in materials. This proposal has as objectives to study all the parameters like the nature of CNPs and surface functionalisation, the nature of deagglomeration process, the influence of the materials preparation process in order to determine the optimised conditions to industrially produced bulk, foamed and thin film nanocomposites with dedicated properties. By doing so, we will gain more insight into the fundamental mechanisms of the filler-matrix interactions of these nanomaterials.
To achieve these goals, specific attention will be paid to the choice of CNP since intrinsic characteristics such as, in case of CNT, the number of walls (single, double or multi walled) and purity can have an effect on the modification of the CNP surface and intrinsic properties and their ability to interact with polymers. Due to the increasing number of companies producing different grades of CNP, it is necessary to understand and prioritise how these characteristics affect their possible surface modification and their incorporation into polymers. Thus it is a big advantage of this consortium to have included a company which is willing to produce specially designed nanofillers for these purposes. Related to the nanosize of the CNP, possible health issues are also to be considered when dealing with these materials. It is therefore an aim of the project to design preparation routes for these nanocomposites which enable the industrial user to safely deal with them at a minimum risk level. This can be achieved by embedding the CNP (or surface modified CNP) in matrices, what makes them macroscopic materials without the size specific risks of the nanoparticles.
Although, a number of studies on the cytotoxicity of CNTs are underway, there are as yet no firm conclusions . Research so far has mainly focused on lung and skin studies and there are no published studies on cultured neural cells regarding the cytotoxicity of CNP, nor is any data available from studies carried out in vivo for CNP-polymer nanocomposites. However, initial studies on biocompatibility of polyurethane and CNF and CNT films for neural applications have been reported. Neural stem cells (NSC) and neurons isolated from several brain regions have been shown to grow on carbon nanotubes. These studies provide the proof of concept for future applications of carbon nanotubes in neurobiology.
Accordingly, another objective of this proposal will be to test the biocompatibility of these nanocomposites with brain cells. If biocompatible materials are obtained within the framework of the HARCANA project, new tissue scaffolds could be prepared in a future project, then exploiting the 3D structure of the foam and the conductive properties of the embedded CNP for neuronal growth. The results obtained in the HARCANA project in terms of biocompatibility of CNPs with neuronal cells, could be the base for a future investigation of the potential application of these materials in the field of regenerative medicine.
Another objective of this proposal aims at determining what are the optimised methods for de-agglomerate CNPs in relation with the chemical nature of the polymer matrix in which the nanofillers will be ultimately dispersed, with the form of the final materials (bulk, foamed or thin film) and with the possibility to upscale the chosen process(es).
In the case of CNT both experimental preparation and modelling of CNT-polymer interaction will be used to achieve this goal. Modelling of polymer/carbon-based nanoparticle interaction will allow understanding the fundamental parameters that will favour CNT deagglomeration and possible structuration.
Life cycle analysis (LCA) was carried out within the project and the cost effectiveness of the various processing strategies leading to these designed materials in comparison to presently used technologies was analysed.
Potential impact:
The research carried out within HARCANA lead to a number of new methods to generate nanocomposites containing anisotropic carbon nanomaterials with a good level of dispersion. Although none of the developed systems led to a breakthrough in the specific applications envisioned by the industrial partners of this consortium, the obtained results are of potential interest for the scientific community. Besides a number of publications also two patents were submitted, underlying the technological potential of some of the results obtained in HARCANA.
High aspect ratio Carbon-based nanoparticles (mainly nanotubes (CNT), and to a less extent nanofibres (CNF), as well as nanosheets or exfoliated graphite (CNS)) will be introduced into bulk polymers, into polymeric foams and into membranes. It is expected that such nanofillers will tremendously improve and modify the properties of these families of materials, allowing them to reach new markets. However, a common and fundamental problem in polymer-based nanocomposites is the large extent of agglomeration of the nanoparticles due to their high surface to volume ratio. Therefore, techniques to control deagglomeration and possibly further organisation of these high aspect ratio nanoparticles in polymeric materials remain a challenge.
This project under industrial leadership will therefore aim at mastering, at the nanometric and mesoscale level, the spatial organisation of carbon-based nanoparticles (CNP) with various surface functionalities, sizes and shapes having large aspect ratios in bulk, foamed and thin film (membranes) polymers by using industrially viable processes. More precisely, the aim of HARCANA consists in generating polymer based nanocomposites with a percolating nanoparticle structure that is reinforcing the material and imparts it with improved electrical and thermal conductivity at a minimum of nanoparticle loading. To reach such radically improved properties, it is important to take into account that a complete dispersion is not useful and will lead to lower properties.
In order to control this CNP organisation within the polymer matrix, a large set of techniques will be used. They range from synthetic approaches ('grafting from', 'grafting to', 'grafting through', emulsion polymerisation) to (reactive) melt or solution blending processes, and the preparation in supercritical Carbon dioxide (CO2). The aim is to generate new classes of engineering materials for various applications like Electromagnetic interference (EMI) shielding, antistatic fuel systems parts and packaging materials and membranes, as well as biocompatible materials with brain cells that could be used to prepare scaffolds for tissue engineering in the future.
Organisation of HARCANA
The consortium of the project consists of seven academic and five industrial partners from five countries under the coordination of Helmholtz-Zentrum Geesthacht. The project is spanning a bridge between research and development of the nanocomposites on one side to the demonstration of the developed results on the other side. Life cycle assessment will be performed on selected examples. The achievements will be disseminated by publications in scientific and technical journals, oral and poster contributions at conferences and fairs, as well as by this homepage. These activities are distributed in several, inter-linked work packages.
Project context and objectives:
Plastics are generally cheap and light-weight materials in comparison to metals and ceramics. However, they often show worse properties compared to metals (mechanical properties, electric and thermal conductivity) or compared to most metals and ceramics (thermal stability, fire resistance), to mention just a few examples. A well-known way to improve mechanical properties of polymers is to add high aspect ratio particles like glass, carbon or polyaramide short fibres, which increase the tensile strength of the polymer matrix. A lot of work has been carried out in this field and has lead to numerous everyday life application in cars, household, sport equipments, but, in order to reach high mechanical properties, large quantities of those fillers have to be added, making the resulting materials more heavy, more brittle and with a poor surface finish in comparison with the initial polymer matrix.
Another way to enhance the mechanical and other properties of polymers consists in adding so-called nanofillers. Nanofillers differ from the aforementioned fillers by the fact that at least one of their dimensions is in the range of up to several nanometers. Exfoliated clays (layered silicates) and nanofibres are examples for such nanofillers. With these nanofillers, much lower filling level is usually required to obtain polymer-based materials with mechanical and thermal properties comparable to the composites based on larger amounts of microfillers. Due to their characteristic small dimension(s), nanofillers have much larger surface-to-volume ratios as compared to other fillers. These small dimensions may further lead to significantly different properties and have initiated research and development activities called 'Nanoscience' and 'Nanotechnology'.
A lot of work has been addressed to some nanofillers such as layered silicates, especially with respect to the separation of the layers (exfoliation) in order to get well dispersed plate-like filler nanoparticles in the matrix. Less work has been done so far in the area of another upcoming class of nanofillers, which are CNT. These cylindrical graphite-like carbon structures are characterised by diameters in the nanometre range and lengths of up to several micrometers (so a tremendous aspect ratio). In addition they are predicted to have a tensile modulus in the range of several TPa making them not only very interesting candidates for futuristic ideas (e.g. space elevators), but also for reinforcement of polymer matrices for light weight applications. Moreover, they show electric conductivity what is useful for many applications where electrostatic discharges may cause damage, and they are characterised by high thermal conductivity. Other carbon-based nanoparticles (CNF, CNS) are thought to display similar properties. Besides bulk polymer, the introduction of these nanofillers in polymeric foams and membranes can tremendously improve and modify the properties of these families of materials, allowing them to reach new markets. However, a common and fundamental problem in polymer-based nanocomposites is the large extent of agglomeration of the nanoparticles due to their high surface to volume ratio. Therefore, techniques to control deagglomeration and possibly further organisation of these high aspect ratio nanoparticles in polymeric materials remain a challenge.
HARCANA will therefore aim at mastering, at the nanometric and mesoscale level, the spatial organisation of CNPs with various surface functionalities, sizes and shapes having large aspect ratios (CNT, CNF, CNS) in bulk, foamed and thin film (membranes) polymers by using industrially viable processes. More precisely, the aim of this proposal consists in generating polymer-based nanocomposites with a percolating nanoparticle structure that is reinforcing the material and imparts it with improved electrical and thermal conductivity at a minimum of nanoparticle loading. To reach such radically improved properties, it is important to take into account that a complete dispersion (disappearance of contact points) is not useful and will lead to lower properties.
Within the frame of this proposal, dispersion of CNT or other high aspect ratio carbon-based nanoparticles will find applications in:
- Bulk nanocomposites, for injection moulded or extruded parts. The expected reinforcement of mechanical properties at low nanofiller loading, coupled to antistatic properties will advantageously replace common short fibre-based fillers in automotive, aeronautic or building materials, with improvement in materials weight and surface finish. Besides, mechanical and electrical properties, these carbon-based nanoparticles may also impart fire resistance to the processed parts.
- Nanocomposites foamed either by chemical or physical processes. These new polymeric foams will be tested for various applications such as new electronics packaging, where Electrostatic discharge (ESD) can damage a sensitive component, new lightweight and efficient EMI shielding materials or thin Radar absorbing materials (RAM). Such foams, based on biocompatible matrices, will also allow preparing new tissue scaffolds exploiting the three-dimensional (3D) structure of the foam and the conductive properties of the embedded CNP for neuronal growth.
- Thin film and membrane nanocomposites containing carbon-based nanofillers. They will have a potential in applications, where chemicals have to be separated by membrane processes and electrostatic discharges have to be avoided. They will also show enhanced mechanical and thermal stability which makes their operation under high pressure differences safer. The enhancement of their barrier properties may become important as well and may open new application areas.
Project objectives
The control of CNP structuration at the nano and meso scale in polymeric materials constitutes one typical pathway for mastering nano-scale complexity in materials. This proposal has as objectives to study all the parameters like the nature of CNPs and surface functionalisation, the nature of deagglomeration process, the influence of the materials preparation process in order to determine the optimised conditions to industrially produced bulk, foamed and thin film nanocomposites with dedicated properties. By doing so, we will gain more insight into the fundamental mechanisms of the filler-matrix interactions of these nanomaterials.
To achieve these goals, specific attention will be paid to the choice of CNP since intrinsic characteristics such as, in case of CNT, the number of walls (single, double or multi walled) and purity can have an effect on the modification of the CNP surface and intrinsic properties and their ability to interact with polymers. Due to the increasing number of companies producing different grades of CNP, it is necessary to understand and prioritise how these characteristics affect their possible surface modification and their incorporation into polymers. Thus it is a big advantage of this consortium to have included a company which is willing to produce specially designed nanofillers for these purposes. Related to the nanosize of the CNP, possible health issues are also to be considered when dealing with these materials. It is therefore an aim of the project to design preparation routes for these nanocomposites which enable the industrial user to safely deal with them at a minimum risk level. This can be achieved by embedding the CNP (or surface modified CNP) in matrices, what makes them macroscopic materials without the size specific risks of the nanoparticles.
Although, a number of studies on the cytotoxicity of CNTs are underway, there are as yet no firm conclusions . Research so far has mainly focused on lung and skin studies and there are no published studies on cultured neural cells regarding the cytotoxicity of CNP, nor is any data available from studies carried out in vivo for CNP-polymer nanocomposites. However, initial studies on biocompatibility of polyurethane and CNF and CNT films for neural applications have been reported. Neural stem cells (NSC) and neurons isolated from several brain regions have been shown to grow on carbon nanotubes. These studies provide the proof of concept for future applications of carbon nanotubes in neurobiology.
Accordingly, another objective of this proposal will be to test the biocompatibility of these nanocomposites with brain cells. If biocompatible materials are obtained within the framework of the HARCANA project, new tissue scaffolds could be prepared in a future project, then exploiting the 3D structure of the foam and the conductive properties of the embedded CNP for neuronal growth. The results obtained in the HARCANA project in terms of biocompatibility of CNPs with neuronal cells, could be the base for a future investigation of the potential application of these materials in the field of regenerative medicine.
Another objective of this proposal aims at determining what are the optimised methods for de-agglomerate CNPs in relation with the chemical nature of the polymer matrix in which the nanofillers will be ultimately dispersed, with the form of the final materials (bulk, foamed or thin film) and with the possibility to upscale the chosen process(es).
In the case of CNT both experimental preparation and modelling of CNT-polymer interaction will be used to achieve this goal. Modelling of polymer/carbon-based nanoparticle interaction will allow understanding the fundamental parameters that will favour CNT deagglomeration and possible structuration.
Life cycle analysis (LCA) was carried out within the project and the cost effectiveness of the various processing strategies leading to these designed materials in comparison to presently used technologies was analysed.
Potential impact:
The research carried out within HARCANA lead to a number of new methods to generate nanocomposites containing anisotropic carbon nanomaterials with a good level of dispersion. Although none of the developed systems led to a breakthrough in the specific applications envisioned by the industrial partners of this consortium, the obtained results are of potential interest for the scientific community. Besides a number of publications also two patents were submitted, underlying the technological potential of some of the results obtained in HARCANA.
