Chloroform desorption from poly(lactic acid) nanocomposites: A thermal desorption spectroscopy study

Abstract

Biopolymer nanocomposites were prepared by solvent casting dispersing lauryl-functionalized cellulose nano-fibrils (CNF) in a poly(lactic acid) matrix (PLA). The release of residual chloroform (CHCl3) solvent molecules was studied by Thermal Desorption Spectroscopy (TDS) analysis. TDS spectra of the PLA matrix show a single desorption peak at TP = 393 K with FWHM ~10 K, compatible with a zero-order desorption kinetics. This narrow TDS peak was accurately reproduced assuming that: (i) the rate limiting step is given by the CHCl3 de-trapping from sites in the PLA matrix where residual solvent molecules form small aggregates and (ii) the activation energy for desorption linearly decreases from 1.19 eV for saturated traps to 1.11 eV when the traps occupancy by solvent molecules approaches zero. The balance energy term Ïμ D =-0.08 eV is due to the attractive interactions between trapped CHCl3 molecules. Adding CNF particles to the PLA matrix the zero-order peak shifts to lower temperatures and a second peak with FWHM ~60 K appears at higher temperatures. This second peak is compatible with a first-order desorption kinetics and is attributed to the release of dispersed CHCl3 molecules from trapping sites in PLA-CNF interface region. The obtained information are of interest for applications in food and electronic packaging and for the development of medical materials.