Enthalpy of melting of α′- and α-crystals of poly(l-lactic acid)

Righetti, Maria Cristina; Gazzano, Massimo; Lorenzo, Maria Laura Di; Androsch, René

doi:10.1016/j.eurpolymj.2015.07.024

Cited by 155 publications

(138 citation statements)

References 37 publications

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“…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.…”

Section: Resultsmentioning

confidence: 99%

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

Coiai¹,

Cicogna²,

Santi³

et al. 2017

Express Polym. Lett.

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Abstract. Low molecular weight polyesters were end-functionalized with ammonium and carboxylate salts and used in ionic exchange reactions with respectively cationic (MMT) and anionic (LDH) clays. The hybrid organic-inorganic substrates were structurally analysed to determine the ester oligomers' modification degree and their thermal behaviour owing to confinement effects. The dispersion of such hybrids in polylactic acid (PLA) matrix was performed and the ultimate structural, morphological and thermal properties of the collected nanocomposites were investigated and correlated to the tailored interfacial properties with the different inorganic substrates. While the composites with MMT proved to be stable under thermo-oxidative conditions, the samples obtained by dispersing the LDH hybrid suffered from poor final thermostability owing to molecular weights decrease. Deeper insights about the effect of the interactions at interface (polymer chain-surfactant and polymer chain-inorganic surface) evidenced that by promoting an intimate contact between PLA chains and LDH surface (through oligoester used as inorganic substrate modifier) a certain extent of PLA hydrolysis triggered by both surfactant and inorganic surface (LDH) occurred and cannot completely avoided.

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Section: Resultsmentioning

confidence: 99%

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

Coiai¹,

Cicogna²,

Santi³

et al. 2017

Express Polym. Lett.

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“…From the partial areas of the average heat flow rate ( HF ), which is drawn superimposed on the experimental modulated HF mod signal at T c = 135 °C, the w C curve was derived according to Equation (2). For crystallization at T c = 90 °C, the

Δ h_{m}^{o} (T_{c})

of the α′-form was used, whereas for crystallization at T c = 130 °C, and 135 °C, the

Δ h_{m}^{o} (T_{c})

values referring to the α-form were applied [46]. Finally, the rigid amorphous weight fraction ( w RA ) evolution was determined by difference, being ( w C + w MA + w RA ) =1.…”

Section: Quasi-isothermal Crystallizationmentioning

confidence: 99%

“…The reduction in the MA fraction during non-isothermal crystallization was derived according to Equation (7), and the growth of the crystalline weight fraction from the integration of the crystallization peak, according to Equation (9), by using for

Δ h_{m}^{o} (T)

the average of the enthalpy of fusions of the 100% crystalline α′- and α-forms [46]. Finally, the RA fraction evolution upon non-isothermal crystallization was determined by difference.…”

Section: Non-isothermal Crystallization and Stepwise Quasi-isothermentioning

confidence: 99%

Crystallization of Polymers Investigated by Temperature-Modulated DSC

Righetti

2017

Materials

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The aim of this review is to summarize studies conducted by temperature-modulated differential scanning calorimetry (TMDSC) on polymer crystallization. This technique can provide several advantages for the analysis of polymers with respect to conventional differential scanning calorimetry. Crystallizations conducted by TMDSC in different experimental conditions are analysed and discussed, in order to illustrate the type of information that can be deduced. Isothermal and non-isothermal crystallizations upon heating and cooling are examined separately, together with the relevant mathematical treatments that allow the evolution of the crystalline, mobile amorphous and rigid amorphous fractions to be determined. The phenomena of ‘reversing’ and ‘reversible‘ melting are explicated through the analysis of the thermal response of various semi-crystalline polymers to temperature modulation.

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“…the totally crystalline polymer (93.1 J/g [28]). Due to the polymorphic nature of PLA leading to a melt recrystallization process and to its complex stereo-chemistry, this value may reasonably be debated [29]. The crystallization kinetics are plotted in Fig.…”

Section: Pla Crystallization Kineticsmentioning

confidence: 99%

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

Nassar

Guinault

Delpouve

et al. 2017

Polymer

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scale analysis of the impact of polylactide morphology on gas barrier properties. Polymer, Elsevier, 2017, 108, pp.163-172. 10.1016/j.polymer.2016 Multi-scale analysis of the impact of polylactide morphology on gas barrier properties Samira Fernandes Nassar t r a c tSemicrystalline polylactide (PLA) films with controlled morphology were produced by thermal crystallization to optimize the oxygen barrier properties. The crystalline morphology of PLA at the scales of the lamella and the spherulite was investigated and the mobile amorphous phase dynamics were studied. The crystalline morphology had a negligible impact on the oxygen diffusion coefficient. The occurrence of a rigid amorphous fraction (RAF) in the amorphous phase due to its insufficient decoupling from the crystalline phase provided an accelerated pathway for diffusion, though. As a conclusion, for reaching optimal barrier properties, semicrystalline PLA should be pre-nucleated and rapidly crystallized from the glass in the a-polymorph in the aim to reach a high crystallinity degree and decoupling of the amorphous and the crystalline phase. These recommendations can benefit to industry for the optimization of PLA annealing treatments.

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Enthalpy of melting of α′- and α-crystals of poly(l-lactic acid)

Cited by 155 publications

References 37 publications

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

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

Crystallization of Polymers Investigated by Temperature-Modulated DSC

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

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