Memory effect in melting behaviour, crystallization kinetics and morphology of poly(propylene terephthalate)

Abstract

Crystallization kinetics and melting behaviour of poly(propylene terephthalate) (PPT) were investigated by means of differential scanning calorimetry and hot-stage optical microscopy. Isothermal crystallization kinetics was analysed according to the Avrami treatment. The effects of temperature and duration of melting on the overall rate of isothermal crystallization were studied: the rate was found to decrease with increasing melting temperature and melting time. This result was discussed on the basis of the gradual destruction of predetermined athermal nuclei. Values of the Avrami exponent close to 3 were obtained, regardless of the adopted thermal treatment and the crystallization temperature, T c , in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, spacefilling spherulites were observed by optical microscopy at all T c 's, independent of the applied thermal treatments. For each of them, the rate of crystallization became lower as T c increased, as usual at low undercooling where the crystallization process is controlled by nucleation. The observed multiple endotherms, which are commonly displayed by polyesters, were influenced by T c and ascribed to melting and recrystallization processes. Linear and non-linear treatments were applied in order to estimate the equilibrium melting temperature for PPT, by using the corrected melting temperatures. The non-linear estimation yielded an about 33°C higher value with respect to the one obtained by means of the linear approach. Through the analysis of secondary nucleation theory, the classical II→III transition was found to occur at a temperature of 194°C. The average work of chain folding for nucleation was determined to be c. 5.2 kcal/mol. The heat of fusion was correlated to the specific heat increment for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend on the thermal treatment the polymer was subjected to.

The effect of aliphatic chain length on thermal properties of poly(alkylene dicarboxylate)s

“…All the samples present n data around 2.5-3.5 which are typical of heterogeneous nucleation and three-dimensional growth. Similar values are reported in literature for aromatic polyesters [32,39], aliphatic polyesters [26,29] and PE homopolymer [34].…”

Self-Nucleation of Crystalline Phases Within Homopolymers, Polymer Blends, Copolymers, and Nanocomposites

“…(b) Isothermal DSC curves recorded after applying the procedure indicated in (a). Reproduced from Müller et al [96] with permission of The Royal Society of Chemistry terephthalate)/SiO 2 nanocomposites [146], poly(propylene azelate) [147], poly(propylene sebacate) [147], poly(ethylene azelate) [148], sindiotactic poly(propylene) (sPP) [69,123], poly(propylene terephthalate) [149], poly(trimethylene terephthalate) [76], and poly(lactic acid) [150].…”

Poly(propylene terephthalate) Modified with 2,2‐Bis[4‐(ethylenoxy)‐1,4‐phenylene]propane terephthalate) Units: Thermal Behaviour, Crystallisation Kinetics and Morphology

“…[5,9] On the other hand, PPT films show good barrier properties in O 2 and H 2 O. [5] Accordingly, several studies on the synthesis, [10,11] molecular and crystalline structure, [12,13] spinning technology [14,15] and the crystallisation behaviour [16,17] of PPT have been published. In particular, some of us recently investigated the melting behaviour, crystallisation kinetics and morphology of PPT, focusing our attention on the influence of the crystalline memory effect.…”

“…In particular, some of us recently investigated the melting behaviour, crystallisation kinetics and morphology of PPT, focusing our attention on the influence of the crystalline memory effect. [17] In that same paper, the results of a study on the effect of thermal treatments on the rigid-amorphous phase (RAP) present in PPT were also published. [17] It must be emphasised that copolymerisation continues to attract great attention both academically and industrially due to the feasibility of tailor-made properties.…”

“…[17] In that same paper, the results of a study on the effect of thermal treatments on the rigid-amorphous phase (RAP) present in PPT were also published. [17] It must be emphasised that copolymerisation continues to attract great attention both academically and industrially due to the feasibility of tailor-made properties. Most commercial copolymers are designed to present synergistic improvements compared to their parent homopolymers, including better processability, higher mechanical properties and better chemical resistance, to mention but a few.…”