Piezoelectric Response of Spun Polyvinylidene Fluoride and High Density Polyethylene Bicomponent Fibers with Carbon Black

carbon black;piezoresponse force microscopy;piezoelectric;thermalproperties;composite fibers;high density polyethylene;polyvinylidenefluoride;percolation threshold.;crystallinity;x-ray diffraction

Sun, Moran Henry ; Martin W. King, Committee Chair,Sun, Moran Henry ; Martin W. King ; Committee Chair

University:North Carolina State University

关键词: carbon black;    piezoresponse force microscopy;    piezoelectric;    thermalproperties;    composite fibers;    high density polyethylene;    polyvinylidenefluoride;    percolation threshold.;    crystallinity;    x-ray diffraction;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/1933/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

Sensors and actuators featuring biomimetic properties, with linear andangular resolution, good compliance and long term biostability are in growingdemand for applications such as synthetic muscles, sensor equipped limps and otherbio-engineering designs.Recent research papers have demonstrated that insulatormaterials coated with polypyrrole or polyaniline and combined with various dopantscan achieve piezoresistive and dielectric properties, enabling the detection anddisplacement of local strains in polymer sheets, textile fibers and fabrics.It is known that composite films made from layers of carbon black (CB)filled polyvinylindene fluoride (PVDF) and high density polyethylene (HDPE) filmsprovide stable piezoelectric behavior in the temperature range from 20 to 140 oC andlow tensile loss on exposure to moisture and hydrolytic conditions. However, to datethe literature contains no references to the use of this particular polymer system infiber or textile form.Moreover, since the resistivity of such composites can bequantitatively specified by selectively localizing CB in one polymer phase or at theinterface of an immiscible polymer blend, it was hypothesized that bicomponent fiberspinning might lead to similar piezoelectric properties within individual fibers.This research study was therefore aimed first at determining whether a blendof PVDF and HDPE polymers filled with CB could be melt spun and drawn into aseries of composite or bicomponent fibers using a laboratory extruder and drawingmachine.This was accomplished successfully with loadings of CB varying fromzero to 27.7% by weight.The second goal was to determine the weight fraction ofCB that should be added to PVDF / HDPE composite fibers in order to optimize theirelectrical functionality and piezoelectric performance.Analysis of the deformationof the as-spun and drawn fibers in their longitudinal direction during charging and discharging was conducted in a novel piezoresponse force microscope (PFM).Itdemonstrated that increasing the CB content also increased the ferroelectric hysteresisand piezoelectric constant of the composite fiber up to the percolation threshold of20.7% of CB by weight.The CB was selectively located in the HDPE phase, resulting in a significantloss of crystallinity in the HDPE phase.At the same time, the PVDF phase wastransformed from a non-polar to a polar form.The optimum spun and drawncomposite piezoelectric fiber measuring 120 microns in diameter contained 56/32/12PVDF/HDPE/CB by weight.Under the electric stimulation of a few volts it waspredicted to be capable of producing a tensile force of about 2 x 10⁻² N for a 350 mmlong fiber with 1 mm 2 cross-sectional area.It is anticipated that a bundle of suchpiezoelectric fibers measuring 26 mm² in cross-section could generate the force of 0.5N required to complete flexion of a human distal interphalangeal (finger) joint.The incorporation of CB filled HDPE produces a conductive matrix phasewithin these bicomponent fibers, which acts as an electrode around the PVDF regions,facilitating a more uniform distribution of the piezoelectric charge within the PVDFphase.These encouraging results bode well for future piezoelectric fibers, whichhave both rapid electromechanical response and good biostability.Additional largerscale tests are recommended to evaluate the efficiency of these novel biomaterials foruse in biomedical and electrotextile end-uses.