Probing the chain segment mobility at the interface of semi-crystalline polylactide/clay nanocomposites

MMT and LDH organo-modification with surfactants tailored for PLA nanocomposites

“…Accordingly, the OIt measurements did not show any benefit stemming from LDH (PLA_LDH) and its dispersion (PLA_(LDH-PLACOO)_1 and PLA_(LDH-PLA-COO)_2) (see Table 2). Instead, the addition of MMT-PLANH 3 , even if seemingly does not improve the thermal performance of the PLA matrix, as already reported in literature for PLA-based composites with MMT clays having similar morphologies [18,22,31], preserved the thermal stability of the PLA and showed a significant effect onto the OIT results. In particular, with reference to nanocomposites obtained by commercial organophilic MMT, Wu et al [32] reported even a decrease in the stability and Nieddu et al [33] fluctuating results depending on the content of inorganic clay and presumably on the morphology.…”

“…After intercalation in MMT-Na a remarkable increase of T g value was noticed presumably due to oligochains confinement between the silicate platelets; the same effect is likewise responsible for the delay in the cold crystallization whose peak temperature resulted shifted more than 10 degrees towards higher temperature values. The strong interactions of PLA chains with surface layers, granted by cationic exchange reaction of ammonium end groups, presumably hindered the packing of chains into the crystal lattice providing even broader crystallization and melting peaks (see Figure 3); this latter showed a split peak ascribable to melting phenomenon of α homocrystals developed in PLLA during heating [20] and induced by the platelets interaction, [18] here observed even for PLA oligomers. Likewise, the ATR spectrum of LDH-PLACOO (Figure 4a) showed absorptions due to the PLACOONa moiety thus confirming the hybrid nature of the collected LDH system.…”

“…The lowering and the enlargement of this diffraction peak suggested, moreover, a greater disorder degree in the stacking of the layers. At higher (2θ) angles, diffraction peaks ascribable to crystallized PLA chains were observed: the signals due to (200/100) and (203) at 16.65 and 19.05° were recognized and, on the basis of the attributions reported in the literature [18], referred the α form of PLA crystals. To better investigate the effect of intercalation/immobilization within the MMT layers on the thermal features (especially onto the crystallization behaviour) of PLA oligomer, the PLA-NH 3 Cl and its corresponding MMT hybrid were analysed by DSC analysis (Figure 3).…”

“…Accordingly, the increased crystallinity of sample PLA(MMT-PLANH 3 )_1 and PLA(MMT-PLANH 3 )_2 could be due to the exfoliated morphologies better allowing the growing of crystal domains. However, at the chosen annealing temperature, the crystalline domains exist in both forms α and α′ with prevalence of the form α′, the metastable crystalline phase having different associated enthalpy value with respect to more ordered α form [26]; by taking into account that the transition of the α′ to the α-form depends only on the temperature and annealing time, the differences observed for the composites, all treated in the same experimental conditions, could be attributed to the presence of the hybrid and its dispersion degree in the polymer matrix [18]. By highlighting the XRD curves of the composites in region of PLA diffraction peaks (focusing on (200) and (203)/ (113)) it appeared evident that both the clays favoured the formation of α′ with respect to PLA matrix, as proved by the peaks shifting to lower angle ( Figure 8) [20], whose amount, being difficult to be quantified, can certainly affect the final crystallinity data.…”

Multi-scale analysis of the impact of polylactide morphology on gas barrier properties

“…[26]. For the analysis of thermal transitions, a minimum of five modulation steps during the transition is required.…”