Segmental relaxation and partial crystallization of chain‐extended Poly(l‐lactic acid) reinforced with carboxylated carbon nanotube

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).where T α is the dynamic (calorimetric) T g , ΔC − 1 p is the difference in the inverse of the isobaric heat capacity between the liquid and the glass at T α , ρ is the density at T α , k B is the Boltzmann constant, N A is Avogadro's number, m 0 is the molar Additional Supporting Information may be found in the online version of this article.Omid Yousefzade and Sofia Valenti contributed equally to this work.

Drug-Biopolymer Dispersions: Morphology- and Temperature- Dependent (Anti)Plasticizer Effect of the Drug and Component-Specific Johari–Goldstein Relaxations

“…As will be shown in detail below, a fit procedure shows that the T g of the partially crystallized microfibres is only 1 K higher than that of as-deposited ones. The small impact of partial crystallization on the T g of PLLA fibres is consistent with previous results on PLLA films [ 29 ].…”

“…Such cross-over in the relaxation time provides direct spectroscopic evidence of the slow-down of the cooperative α relaxation of PLLA upon partial crystallization of the fibre. The same effect has been observed in PLLA films [ 29 ], and as mentioned it is due to the enhanced rigidity of the amorphous fraction in the proximity to crystalline domains, as compared to the fully amorphous polymer [ 28 ].…”

Interfacial stability of compatibilizers dictated by the thermodynamic interactions in an immiscible system and the effects of micelles on the crystallization of PLLA

“…During the heating process, the partially melted amorphous PLLA molecular chains recrystallize to form thicker, more perfect PLLA lamellae, which will melt at high temperature, because of the nucleation effect of micelles . The nucleation effect of micelles can be further proved by the slight increase of the Δ H m with the addition of RC polymers in the PLLA/ABS‐2 system, as shown in Table . The speculation about the effect of micelles on the crystallization of PLLA can also be partly verified by the T cc of PLLA shifting to higher temperature with the gradual addition of RC polymers, because of the interaction of micelles with the PLLA molecular chains.…”

Nose Temperature and Anticorrelation between Recrystallization Kinetics and Molecular Relaxation Dynamics in Amorphous Morniflumate at High Pressure

“…where n is the Avrami exponent and Z is a constant, from which a crystallization rate with units of s -1 can be obtained 49 as k = Z 1/n . Eq.…”