Structure versus properties relationship of poly(lactic acid). I. Effect of crystallinity on barrier properties

Abstract

Poly(lactic acid) is at present the most promising and commercially available bio‐based and biocompostable (bio)plastic. The properties of PLA, however, are rather poor, notably its low glass transition temperature Tg of ∼55 °C, its intrinsic low crystallization rate and the limited barrier properties with respect to water, oxygen and carbon dioxide in comparison with to oil‐based counterparts, notably polyesters (PET). In this manuscript we address the question of what could ultimately be achieved in terms of barrier properties when PLA is crystallized fully. In fact, this question is rather academic in view of the long crystallization/annealing times needed to obtain maximum crystallinity but serves the purpose of better understanding current limits and notably a better understanding of the role of crystallinity on the barrier properties. A correlation is made between crystallization, various morphological parameters and the barrier properties of PLA. Crystallization of PLA causes a decrease of the oxygen permeability, but not in linear proportion with the decrease in amorphous volume. We explain this in terms of influence of the space filling and the inner crystalline structure on gas transport properties. Furthermore we suggest that the presence of a rigid amorphous fraction with lower density can have strong impact on PLA gas permeability, in particular on the gas solubility coefficient of PLA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2247–2258, 2009

Potential of Lignins as Antioxidant Additive in Active Biodegradable Packaging Materials

“…Neat PLA oxygen barrier properties are in accordance with published data [54,[60][61][62][63][64][65]. Interestingly, the inclusion of at least 10 wt% of lignin yielded a decrease in oxygen permeability of around 20 %.…”

Water vapour permeability of poly(lactic acid): Crystallinity and the tortuous path model

“…It is that the crystalline phase reduces the polymer chain mobility in the amorphous phase, giving rise to constrained or restricted regions, which have reduced water solubility and therefore reduced permeability. The concept of constrained amorphous regions has been mentioned by a number of authors in discussions of the effect of crystallinity on both gaseous and aqueous permeability in PLA 10,14 and generally in other polymers. 8,9 Finally, while discussing the linear model and the effects of solubility, it should be mentioned that Siparsky et al 12 have reported that the water solubility parameter for PLA at temperatures around 40 C is constant regardless of the degree of crystallinity of the polymer.…”

“…Drieskens et al 10 have investigated the effect of crystallinity on the oxygen permeability of poly(lactic acid). Crystallisation of PLA caused a reduction in oxygen permeability but this was not in linear proportion with the decrease in amorphous volume.…”

Composites of High-Temperature Thermomechanical Pulps and Polylactic Acid

“…The limited crystallization of PLA in injection molding can cause the impairment of mechanical properties (Harris and Lee 2008;Drieskens et al 2009;Sanchez-Garcia and Lagaron 2010), but our data indicate that the introduction of fibers speeds up the crystallization process in the used experimental setup. Transcrystallization, the formation of oriented crystals at the fiber-matrix interface, has been found to dominate in PLA/wood flour composites, where the fiber surface is rough (Mathew et al 2006).…”