Rheology, mechanical properties, barrier properties of poly(lactic acid)

Sous presseVolume Title: Synthesis, Structure and Properties of Poly(lactic acid)Volume Editors: Maria Laura Di Lorenzo, René AndroschThe knowledge of the fundamental parameters of the poly(lactic acid) (PLA) molecular chain and the resulting macroscopic use properties are important for successful application of polymers in different domains. Rheological data show that PLA has the typical properties of a linear and semi-stiff polymer chain. The stereochemical composition of the atactic polymer chain does not impact the rheological, neither the mechanical and barrier properties of PLA. Most commercial PLA grades include a large majority of L-Lactic acid, the polymer is named in that case PLLA. PLLA is at room temperature a brittle glassy polymer and its main fracture mechanism is crazing. Above glass transition, the semicrystalline PLLA shows extensive cavitation. Uniaxial deformation above, but near the glass transition temperature leads to the formation of a mesophase, responsible for strain hardening. At higher temperatures, strain hardening is caused by induced crystallization. The PLLA oxygen barrier properties are comparable to polystyrene (PS). The water vapor barrier properties are higher than that of PS because of the higher polarity of the polymer chain. The increase of the barrier properties can be obtained by specific crystallization techniques, multilayer strategies or the addition of (nano)fillers