Segmental relaxation and partial crystallization of chain‐extended Poly(l‐lactic acid) reinforced with carboxylated carbon nanotube. Issue 4 (19th December 2018)

• Record Type: Journal Article
• Authors: Yousefzade, Omid; Valenti, Sofia; Puiggalí, Jordi; Garmabi, Hamid; Macovez, Roberto
• Is Part Of: Journal of polymer science. Volume 57:Issue 4(2019)
• Page Start: 222
• Page End: 233
• Publication Date: 2018-12-19
• Subjects: chain dynamics -- constrained polymer chains -- cooperative rearranging region -- heterogeneity -- PLLA nanocomposites; 547
• DOI: 10.1002/polb.24774
• Languages: English
• ISSNs: 0887-6266

Abstract

ABSTRACT: Temperature‐modulated differential scanning calorimetry (TMDSC) and broadband dielectric spectroscopy (BDS) were employed to study the glass transition, size of the cooperative rearranging regions (CRRs), crystallization kinetics, and dielectric relaxation response of nanocomposites constituted by chain‐extended poly(L‐lactide) (PLLA) and carboxylated carbon nanotubes (f‐CNTs). The CRR size and the number of relaxing structural units decreased in the presence of crystals during isothermal crystallization. All samples displayed both a primary (α) and secondary (β) relaxation in BDS spectra. The relaxation dynamics of PLLA chains was barely affected by the presence of the f‐CNT. Constrained polymer chains and thickness of interphase ( t i ) were measured using dielectric spectra in tan δ representation. t i values were found to be 46 and 24 nm for sample containing 0.2 and 0.5% weight fraction of f‐CNT, respectively. All samples underwent partial crystallization (with roughly 30% of final crystalline fraction) some 15 or 20° above their glass‐transition temperature ( T g ). Crystallization leads to a fragile‐to‐strong transition in the temperature dependence of the cooperative α relaxation and to the increased visibility of a Maxwell–Wagner–Sillars (MWS) interfacial relaxation, which appears to be present in all samples. The heterogeneity of the polymeric samples was quantified in terms of a new parameter, the heterogeneity index ( H ). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019, 57, 222–233 Abstract : Polymer nanocomposites are obtained by dispersing functionalized carbon nanotubes in chain‐extended polylactic acid, a biodegradable polymer. The glassy samples obtained by fast cooling the melt recrystallize just above their glass‐transition temperature. The glass transition, size of the cooperative rearranging regions, thickness of the constrained polymer‐nanotube interface layer, and dielectric relaxation response are studied experimentally in both the fully amorphous and semicrystalline nanocomposites by calorimetry and dielectric spectroscopy techniques.