Impact of hydrothermal ageing on the thermal stability, morphology and viscoelastic performance of PLA/sisal biocomposites

Abstract

The influence of the combined exposure to water and temperature on the behaviour of polylactide/sisal biocomposites coupled with maleic acid anhydride was assessed through accelerated hydrothermal ageing. The biocomposites were immersed in water at temperatures from 65 to 85 ºC, between the glass transition and cold crystallisation of the PLA matrix. The results showed that the most influent factor for water absorption was the percentage of fibres, followed by the presence of coupling agent, whereas the effect of the temperature was not significant. Deep assessment was devoted to biocomposites subjected to hydrothermal ageing at 85 ºC, since it represents the extreme degrading condition. The morphology and crystallinity of the biocomposites were evaluated by means of X-Ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The viscoelastic and thermal performance were assessed by means of dynamic-mechanical-thermal analysis (DMTA) and thermogravimetry (TGA). The presence of sisal generally diminished the thermal stability of the biocomposites, which was mitigated by the addition of the coupling agent. After composite preparation, the effectiveness of the sisal fibre was improved by the crystallisation of PLA around sisal, which increased the storage modulus and reduced the dampening factor. The presence of the coupling agent strengthened this effect. After hydrothermal ageing, crystallisation was promoted in all biocomposites therefore showing more fragile behaviour evidencing pores and cracks. However, the addition of coupling agent in the formulation of biocomposites contributed in all cases to minimise the effects of hydrothermal ageing.

Relevant factors for the eco-design of polylactide/sisal biocomposites to control biodegradation in soil in an end-of-life scenario

“…The evolution of XC is given in Figure 7 for all biocomposites subjected to biodegradation in soil. Neat PLA showed very low XC, due to its amorphous character, in agreement with previous studies [6], [7].…”

Investigation on the Durability of PLA Bionanocomposite Fibers Under Hygrothermal Conditions

“…Table 5 summarizes the values of degradation temperature at 5 wt% loss (T 5% ) and 50 wt% loss (T 50% ) with exposure time. It is observed that T 5% of PLA fibers decreased significantly at 60 • C, while T 50% was almost unchanged, particularly at 45 • C. This is in a good agreement with the data published by Gil-Castell et al (2016) who reported that the temperature at maximum degradation rate of PLA and PLA/sisal biocomposites remains constant after hydrolysis in water at 85 • C, while the onset degradation temperature decreases significantly. Table 5 shows also that after 14 days at 60 • C, T 5% decreased considerably by 22, 52, and 56 • C for neat PLA, PLA/PLA-g-MA/MCC1, and PLA/PLA-g-MA/CNW1, respectively.…”

Poly(lactic acid) biocomposites with mango waste and organo‐montmorillonite for packaging

“…The PLA–tegument sample fracture surface, in Figure (c), displays a homogeneous PLA matrix, as also fiber bundles and tails randomly distributed over the surface. In addition, there is no distinguishable interface between the tegument's fibers and PLA, since the PLA's polarity contributes to the affinity between PLA and cellulose fibers . The PLA–almond–tegument samples [Figure (d)] show, as expected and mentioned before, the noncompatibility between the starch and PLA phases and the adhesiveness between PLA and cellulose fibers.…”