  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.
