International audiencePoly (lactic acid) is an industrially mature, bio-sourced and biodegradable polymer. However, current applications of this eco-friendly material are limited as a result of its brittleness and its poorly melt properties. One of the keys to extend its processing window is to melt strengthen the native material. This paper considers the chain extension as a valuable solution for reaching such an objective. An additive based on epoxy-functionalized PLA was employed during reactive extrusion. The reaction times as a function of chain extender ratios were determined by monitoring the melt pressure during recirculating micro-extrusions. Once residence times were optimized, reactive extrusion experiments were performed on a twin screw extruder. Size exclusion chromatography provided information about the molecular weight distributions (MWD) of the modified PLAs and revealed the creation of a high molecular weight shoulder. The rheological experiments highlighted the enhancement of the melt properties brought about by the chain extension. Shear rheology revealed some enlarged and bimodal relaxation time spectra for the extended materials which are in accordance with the MWD analysis. Such a modification directly amplified the shear sensitivity of modified PLAs. Regarding the rheological temperature sensitivity, it was found to be decreased when the chain extender content is raised as shown from the Arrhenius viscosity fit. The reduction of the polar interactions from neat to highly chain-extended PLAs is here proposed to explain this surprising result. Chain extension was also found to impact on the elongational melt properties where strain hardening occurred for modified PLAs. Investigation of the chain extension architecture was made from the rheological data and revealed a long-chain branched topology for the modified PLAs

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Pollution of nature by plastics is a major environmental problem and the challenge for the future is to manage the lifetime of polymers better. The aim of this study is to establish a baseline on degradation mechanism and degradation kinetics for lifetime prediction of polylactide (PLA) in a marine environment. The ageing of PLA was accelerated by raising temperature in distilled water, filtered and renewed seawater and natural seawater. Samples were immersed in distilled water for six months at different temperatures (25, 30, 40 and 50°C) in order to evaluate the influence of temperature on PLA degradation kinetics and to predict lifetime. Then, samples were immersed in seawater both in the laboratory and at sea, in order to compare the effects of environment, marine organisms and salt, on degradation. The different degradation steps were followed by gravimetry, tensile tests, scanning electron microscopy (SEM), steric exclusion chromatography (SEC) and differential scanning calorimetry (DSC). In distilled water, accelerated ageing of PLA is complex with deviation from Fickian behaviour at higher temperature. Moreover, immersion in distilled water induces morphological changes, in particular holes, which are absent in seawater at 40°C for the same immersion time. Indeed, seawater has little impact on the diffusion kinetics but affects M ∞ values, which are slightly lower compare to the distilled water uptake.

International audienc

International audienc

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactide (PLA) with different PHBV/PLA weight ratios (100/0, 75/25, 50/50, 25/75, 0/100) were prepared by melt compounding. Their mutual contributions in terms of thermal stability, flammability resistance, mechanical properties and rheological behavior were investigated. The study showed that the increase in PLA content in PHBV/PLA blends leads to enhanced properties. Consequently, thermal stability and flammability resistance were improved. Further, the rheological measurements indicated an increase in storage modulus and loss modulus of PHBV matrix by addition of PLA.

International audienceAccelerated ageing was performed in distilled water at different temperatures (25, 30, 40 and 50°C) on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which is a biodegradable biopolymer, in order to estimate its lifetime in aqueous environment. In a first part, degradation mechanisms were followed by gravimetry, tensile tests and steric exclusion chromatography. Both immersion and relative humidity have been examined. In a second part, the strain at break was used as an indicator for lifetime prediction with an Arrhenius extrapolation. The study revealed the presence of only one irreversible degradation mechanism, i.e. hydrolytic degradation, which is temperature dependant. So, within the approach assumptions, the lifetime in distilled water of PHBV following Arrhenius behaviour can be predicted