Longitudinal acoustic properties of poly(lactic acid) and poly(lactic-co-glycolic acid)

TL;DR

This study investigates the acoustic properties of biodegradable polymers poly(lactic acid) and poly(lactic-co-glycolic acid) using a pulse-echo technique, revealing how temperature, ethanol, and material characteristics affect their acoustic behavior.

Contribution

It introduces a pulse-echo method to measure acoustic properties of these polymers and analyzes how additives and temperature influence their acoustic and glass transition behaviors.

Findings

Glass transition causes discontinuity in sound speed and increased attenuation.

Ethanol significantly alters acoustic properties and lowers glass transition temperature.

Acoustic properties are sensitive to visco-elasticity, molecular weight, and crystallinity.

Abstract

Acoustics offers rich possibilities for characterising and monitoring the biopolymer structures being employed in the field of biomedical engineering. Here we explore the rudimentary acoustic properties of two common biodegradable polymers poly(lactic acid) and poly(lactic-co-glycolic acid). A pulse-echo technique is developed to reveal the bulk speed of sound, acoustic impedance and acoustic attenuation of small samples of the polymer across a pertinent temperature range of 0- 70oC. The glass transition appears markedly as both a discontinuity in the first derivative of the speed of sound and a sharp increase in the acoustic attenuation. We further extend our analysis to consider the role of ethanol whose presence is observed to dramatically modify the acoustic properties and reduce the glass transition temperature of the polymers. Our results highlight the sensitivity of acoustic properties to a range of bulk properties, including visco-elasticity, molecular weight, co-polymer ratio, crystallinity and the presence of plasticizers.