Autor(es):
Martins, R. S. 
; Gonçalves, Renato Ferreira ; Azevedo, Tiago ; Nóbrega, J. M. ; Carvalho, Helder ; Lanceros-Méndez, S. ; Rocha, J. G.
Data: 2013
Identificador Persistente: http://hdl.handle.net/1822/25709
Origem: RepositóriUM - Universidade do Minho
Assunto(s): Piezoelectric; PVDF; Extrusion; Multilayer filament
Descrição
Poly(vinylidene fluoride) (PVDF) is extensively studied due to its piezo-, pyro- and ferroelectric properties. These properties enable the use of this polymer in a number of applications either as sensor or actuator.
PVDF is a semi-crystalline polymer and can crystallize in four different crystalline phases, called α, β, γ and δ. The β-phase presents the most interesting electroactive activity. These properties depend on the employed processing conditions and on the crystallinity degree, structure and orientation of polymer crystalline fraction.
A 3-layer piezoelectric filament appropriate for textile integration was produced by coextrusion and characterized. The filament samples were obtained in a prototype filament extrusion line, using commercially available polymers. An electrically conductive polymer composite, comprising a polypropylene matrix filled with carbon black, was used for the inner and outer layers, forming the sensor electrodes, whilst the middle layer, made of PVDF, formed the electroactive part. The desired coaxial geometry and layer arrangement were achieved with a special coextrusion die, designed for this purpose.
The drawing process, required to produce the β-phase PVDF, was performed on the above mentioned extrusion line, using draw ratios of 4 and temperatures of 180ºC and 210ºC.
After extrusion, a poling process allowed to induce a preferential orientation of the PVDF dipolar moments, which enhances its piezoelectric response. Poling was performed at a temperature of 80°C during 30 min.
Characterisation tests performed allowed verifying that a mechanical action applied to the filament produces a measurable electric signal, evidencing that the filament can be used for sensor applications. The characterisation performed to filaments produced under different conditions allowed to correlate the extrusion parameters with its piezoelectric response. Additionally, tests were performed to characterise the electrical response of the produced filaments as well as their mechanical behaviour.
It was concluded that the produced flexible multilayer sensors are suitable for applications in areas such as e-textile and structural health monitoring.
