Accelerated ageing of polylactide in aqueous environments: Comparative study between distilled water and seawater

TLDR: In this article, a baseline on degradation mechanism and degradation kinetics for lifetime prediction of polylactide (PLA) in a marine environment was established, where samples were immersed in distilled water for six months at different temperatures (25, 30, 40 and 50°C).

About: This article is published in Polymer Degradation and Stability.The article was published on 2014-10-01 and is currently open access. It has received 178 citations till now. The article focuses on the topics: Distilled water & Seawater.

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Table 4. Evolution of thermal transitions of PLA samples aged in distilled water.

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Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Accelerated ageing of polylactide in aqueous environments: comparative study between distilled water and seawater" ?

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 different degradation steps were followed by gravimetry, tensile tests, scanning electron microscopy ( SEM ), steric exclusion chromatography ( SEC ) and differential scanning calorimetry ( DSC ). 

Q2. What are the future works mentioned in the paper "Accelerated ageing of polylactide in aqueous environments: comparative study between distilled water and seawater" ?

Further work is underway to extend the study, in particular by the use of thin film specimens which should enable more rapid saturation to be attained and core/surface differences to be limited. 

Q3. What is the effect of the presence of water on the polymer?

The presence of this water leads to a plasticization of the polymer, a decrease in Tg is observed indicating an increase in molecular mobility. 

Q4. What is the effect of the melting enthalpy on PLA?

The remaining PLA chains then have higher mobility and they can reorganize themselves more easily which leads to an increase of the melting enthalpy and degree of crystallinity [16,40]. 

Q5. What is the role of the mineral salts in the degradation of PLA?

Possible reasons are the role of mineral salts which facilitate the diffusion of seawater within the polymer and/or a lower pH of distilled water, ≈6against ≈8 for seawater, which can promote hydrolytic degradation [35]. 

Q6. How is the plasticization of PLA reversible?

the plasticization of the PLA by water is reversible [7] and the loss of properties is quite small after 6 months at 25°C. 

Q7. What is the evolution of the global crystallinity of PLA?

The evolution of the global crystallinity (χc) of the PLA chains during hydrolysis can be deduced from the evolutions of both ΔHcc and ΔHm. 

Q8. What is the average Fickian coefficient for water uptake?

An initial linear relationship between water uptake and square root of time is observed at 25 and 30°C, followed by plateau saturation, indicating a typical Fickian behaviour. 

Q9. What is the effect of the temperature on the degradation of PLA?

In this section, the authors have shown that hydrolytic degradation of PLA even in distilled water is a complex mechanism, due to the polymer morphology and its temperature sensitivity. 

Q10. What is the relationship between the intermediary plateau and the temperature?

Using the intermediary plateau to determine diffusion coefficients, a linear relation appears between log D and the inverse of temperature. 

Q11. What is the evolution of global dry mechanical properties?

The evolutions of global dry mechanical properties as a function of the temperature and immersion time are presented in Fig. 4 and property percentage losses are shown in Table 2.