Electromechanical Properties of Poly-L-Lactic Acid

Abstract

The electromechanical coupling coefficient, the piezoelectric constant, the elastic compliance constant and the mechanical quality factor for a poly-L-lactic acid (PLLA) plate elongated to 4 times the original length were determined by a self-resonant method. k 14=0.064, d 14=9.82×10-12 C/N, s 44 E =9.28×10-10 m2/N and Q m =30.3 were obtained at room temperature for a 0° X-cut square plate. It is noted that elongated PLLA films have no spontaneous polarization, unlike poled polymers such as poly(vinylidene fluoride) (PVDF), but still have a large shear piezoelectric constant.

Direct Piezoelectric Coefficient Measurements of PVDF and PLLA under Controlled Strain and Stress

“…From the calculated coefficients (Table 1), the PLLA working in d14 mode is comparable to the PVDF in d31 mode for the actuation. The tested PLLA film presents piezoelectric d14 values below those of literature (10 × 10 −12 C.N −1 [1] and 18.9 × 10 −12 C.N −1 [2]) as it is still under development. …”

“…The method consists in measuring the open-circuit direct piezoelectric voltage by means of a contactless electrostatic voltmeter Trek 370 concurrently to the strain-stress curve of the polymer sample [1]. A switch is used to periodically reset the voltage to zero by discharging the sample into a resistance load, leading to a saw-tooth recorded voltage during the tensile cycle (Figure 2b).…”

“…According to [1], PLLA only has one shear constant (g14) that can be measured as a "g31" (strain perpendicular to electric field) by cutting the sample at 45° from the stretching axis. According to [1], the measured "g31" is at this point equal to 1/2 g14. …”

“…They develop natural piezoelectricity after mechanical stretching. For the PLA, the stretching creates a nonchiral film poly-L-lactic acid (PLLA) presenting only one shear piezoelectric constant d14 between 10 × 10 −12 C.N −1 [1] and 18.9 × 10 −12 C.N −1 [2]. This biodegradable polymer presents the advantage of not being pyroelectric, ensuring an absence of drift with the temperature.…”

Nanostructured polymer-based piezoelectric and triboelectric materials and devices for energy harvesting applications

“…Among polymers that possess piezoelectric properties, poly-L-lactic acid (PLLA) is special due to its helical conformation of the polymer chain leading to an inherent shear piezoelectricity [81][82][83] (figure 3), which is the coupling between a uniaxial polarisation and a shear stress or strain. PLLA is biocompatible and bio-degradable [84][85][86], making it a potential functional material for in vivo energy harvesting or biomedical sensing.…”