β-phase crystal formation in carbon nanotube filled PVDF fibre

Crystalline morphology in poly(vinylidene fluoride)(PVDF), in particular the presence of polar β phase crystals, is of importance for the material´s piezoelectricity. Recently, the influence of carbon nanotubes (CNT) on PVDF crystalline structure has been investigated by a few groups, but only for films. For fibres, marginally results have been reported (only for electrospinning). In this project, we find that by  employing a specific preparation, where de-agglomeration of CNT was much improved by adding a small amount of PVDF to the sonicated solvating medium, amino (NH2) functionalized double-wall carbon nanotubes (DWNT) can favourably influence the β to α polymorphic balance. We systematically studied the behaviour using the X-ray Diffraction (XRD) technique.  In the diffractograms [ref. 1, figure 5 therein,  X-ray diffractograms for three melt-spun fibres. The fibres are: unfilled PVDF, PVDF containing 0.01 wt% non-functionalized DWNT (NF-DWNT), and PVDF containing 0.01 wt% NH2-functionalized DWNT (NH2-DWNT)], the presence of polar β phase crystals is manifested by the β110/200  peak at ~31°, and is the highest for PVDF melt-spun fibre containing 0.01 wt% NH2-DWNT
Simultaneously, computational studies of PVDF system in order to better understand the interaction between the polymer and CNT is performed within this project at Borås University. Our results have been published in scientific journal and at conferences. The potential commercialization is pursued in collaboration with Swerea and Imego.

Project participants:

Prof. Rodney Rychwalski   Anja Lund (Phd. stud.)   

Collaborators:
Prof. Hans Bertilsson,  Cornelia Gustafsson (MSc. stud)

Dissemination:

1. Enhancement of β phase crystals formation with the use of nanofillers in PVDF films and fibres, Compos. Sci. Tech., 71(2) (2011) 222-229
    
2. Towards piezoelectric nanocarbon/PVDF fibres, A Nano Connect Scandinavia event NanoUpdate 2011, May 23-24, Helsingborg (Sweden), 2011
    
3. Nanotechnological enhancement in β phase crystals formation in PVDF fibres, Nordic Polymer Days (NPD 11), June 15-16, Stockholm, 2011

Solvent exfoliation of direct-graphite nanoplatelets

High quality incorporation of graphene fillers into polymeric matrices is of crucial importance. Graphene has triggered off huge expectations, and there is a possibility that this filler may impart higher quality to filled polymers. However, presently, only minute amounts of ideal single monolayer graphene from bottom-up production are available. For nanocomposites, massive amounts of graphene are needed. As a first step, we turn to direct-graphite nanoplatelets (GNP) now commercially available. This material is of lower cost compared to multi-wall carbon nanotubes (MWNT), and graphene layers are mainly undamaged (of importance among others towards electrical conductivity). However, the pristine GNP material requires refining and improved definition in order to prepare high quality electrically conductive composites, thus exfoliation of the nanoplatelets is important. In the present project we have found a practical method of solvent dispersion of GNP, where thin stacks consisting of 2-5 single graphene layers are produced [ref. 1, fig. 3 therein, TEM image of a thin graphene stack. Thin arrows indicate the edges of individual layers, and the bold arrow indicates a folded off-plane fragment of layer]

Project participants:                                    

Prof. Rodney Rychwalski       Henrik Persson (PhD. stud.)

Collaborators: 
Prof. Uta Klement,  Dr. Yiming Yao

Dissemination:

1. A simple way of improving graphite nanoplatelets (GNP) for their incorporation into a polymer matrix, in print in Express Polymer Letters, doi: 10.3144/expresspolymlett.2012

Break-up of GNP agglomerates in polymer melt

Direct-graphite nanoplatelets (GNP) may enable a new generation of electrically conductive polymers, as it was earlier explained. However, the pristine GNP material forms agglomerates which need to be broken up. From the industrial use point of view, the melt processing is more attractive compared to solvent processing.  In the present project, we are studying elongational flow dispersive mixing in melt, using a recently developed elsewhere mixer (RMX, Scamex). The device realizes flow between two opposite chambers through a small diameter die, and the material is alternately pushed from one chamber to the other through the die, and the flow in the present mixer is characterized by a high contribution from elongational flow. In the present project, we find that this type of mixing efficiently refines GNP microagglomerates, and the particle break-up is closely comparable to that in solvent processing. Using this type of mixing, the smallest amount of large microagglomerates, and simultaneously the largest amount of small microagglomerates are produced in the GNP filled polystyrene (PS) (shown in the histogram below). Both, elongational flow mixing and solvent processing yield higher microdispersibility compared to some other mixing processes established in the industrial reality and frequently used.

Histogram representing various manufacturing methods including elongational flow mixing, employed to prepare a composite containing 5 wt.% GNP in PS.

Collaborations in the project include industrial (Borealis), and academic partners (Strasburg University).

Project participants:                  

Prof. Mikael Rigdahl   Prof. Rodney Rychwalski     Henrik Persson (PhD. stud.)

Collaborators:

Dr. Takashi Uematsu (photo), Dr. Christer Svanberg (photo)
as well as:  Prof. René Müller, Dr. Michel Bouquey, and Jérôme Rondin (Ph.D stud.)

Dissemination:

1. Melt rheology as a tool to evaluate dispersion of expanded graphite in PS, Annual European Rheology Conference AERC 2010, April 7-9, Göteborg (Sweden), 2010
    
2. Influence of manufacturing on electrical performances of graphite nanoplatelet filled polystyrene, NT11 International Conference on Science and Applications of Nanotubes, University of Cambridge, July 11-16, Cambridge (UK), 2011
    
3. Influence of manufacturing on electrical performances of GNP/PS composites, Nordic Polymer Days (NPD 11), June 15-16, Stockholm, 2011

Imparting photoelectric and photorefractive (PR) properties in nanocarbon polymer composites in the near-infrared region

Efficiently imparting photoelectric and photorefractive sensitivity to polymers in the near-infrared (IR) region is of importance for the practical use of such materials for medical diagnostics and telecommunication applications. If this would be achieved, then presently used higher cost materials could be replaced with lower cost ones studied here. Thus, the behaviour at 1064 nm and 1550 nm, nonlinear optical (NLO) and electron-transport behaviour is being investigated by us in the present project.  This application requires not only the electroactive performance mentioned above, but also stability of the material at elevated temperatures. Thus we focus on polyvinylcarbazole (PVK) and aromatic polyimide (API) (high temperature polymers) and fill them with carbon nanoparticles. We find that the polymers containing 0.26 wt% single-wall carbon nanotubes (SWNT) show high 3rd order susceptibility (3) [ref. 2, see table 2 therein, 2nd order (2) and 3rd  order (3) susceptibilities at E0 = 12.5 V/m in the different polymer layers]; these being examples showing that stable unplasticized polymers can be used in a photorefractive cell, consequently paving the way towards applications mentioned above.

The work was carried out in collaboration with the International Science and Technology Center, Russian Foundation for Basic Research, and the Russian Academy of Sciences co-financing the project. The potential commercialization will be pursued.

Project participants: 

Prof. Anatoly V. Vannikov, Prof. Antonina D. Grishina, Prof. Rodney Rychwalski  

Dissemination:

1. Photoelectric, nonlinear optical, and photorefractive properties of polyvinylcarbozole composites with single-wall carbon nanotubes, High Energy Chemistry, 43/7 (2009) pp. 540-542
    
2. Photoelectric, nonlinear optical and photorefractive properties of polymer/carbon nanotube composites, Carbon, 49 (2011) 311-319
    
3. Third-order optical susceptibility of single-walled carbon nanotubes, High Energy Chemistry, 45/3 (2011) pp. 245-249
    
4. Photoelectric, Nonlinear Optical (NLO) and Photorefractive (PR) Properties of CNT/Polymer Composites: NT11 International Conference on Science and Applications of Nanotubes, University of Cambridge, July 11-16, Cambridge (UK), 2011

Validation of graphene based polymer nanocomposite in electrically conductive textile fibres

High performance fibre spinning of carbon nanoparticle filled polymers is particularly of importance when preparing electrically conductive fibres, as the formation of nanoparticle network is dependent on the process. Within the area of smart textiles there is a need for electrically conductive and lightweight high quality fibres, for example with heating ability. The case is particularly challenging, as spinning is associated with very large deformations. Thus, recently, we have undertaken a study on graphene nanoplatelet (GNP) and carbon black (CB) filled polypropylene (PP) fibres. To start with, supplies of GNP in massive amounts, incorporation of the carbon filler within the polymeric matrix, and various spinning strategies are being looked into. Towards this end, jointly Swerea IVF and Department of Materials and Manufacturing Technology, Chalmers, have started a collaboration to develop electroactive prototype fibres, with focus on processes. The work is supported by the Nanoscience and Nanotechnology Area of Advance, Chalmers.

As promising examples from early trials, fibre surface roughness has been reduced (lower fibre in figure 1 below), and simultaneously melt draw ratio at break (MDRb) was increased (not shown)  

Fig. 1  Towards higher quality nanocarbon filled fibres [E. Nilsson]


Project is in progress and results will be reported.

Participants:                                                                  

Prof. Rodney Rychwalski   Prof. Bengt Hagström    Erik Nilsson (PhD. stud)    Henrik Persson (PhD. stud.)

Further projects