Effect of the pressure on the crystallization behavior of polyamide 66

Abstract

ABSTRACT:The crystallization behavior of polyamide 66 under high pressure up to 2500 bar was investigated by the use of dilatometric and calorimetric techniques in nonisothermal and isothermal conditions. The solid-solid Brill transition is detected from the evolution of the specific volume in the PVT diagram. The variation of supercooling was examined under different pressures and temperatures. In nonisothermal conditions, when the same cooling rate is applied, the crystallization supercooling is not changed for different pressures. In isothermal conditions, for a given temperature, a pressure increase extends the crystallization supercooling. By the analysis of melting peaks of samples crystallized in different conditions of pressure and temperature, we can conclude that the increasing of the crystallization supercooling leads to a decrease of the lamellae thickness. Finally, the evolution of the thermodynamic equilibrium melting temperature according to pressure was examined.

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

“…Another melt peak ( T m3 ) at about 251 °C appears, and it shifts to lower temperature with an increasing MMT content, which might result from the melt of imperfect crystals in the nylon‐66/MMTs. Multiple melting behavior in nylon‐66 has been observed and discussed previously,31, 32 and it is believed to be due to the melting of two different types of nylon‐66 spherulites, form I and form II, respectively. The organic MMT acts as a heterogeneous nucleating agent and induces the formation of form II spherulites.…”

“…In the WAXD patterns of nylon‐66/MMTs, two characteristic peaks of the triclinic α form approached each other, and the Brill transition occurred at 190 °C, which was 10 °C higher than that of neat nylon‐66. This transition was recorded by X‐ray diffraction, but was not as easy with DSC because the enthalpy difference between the two structures was very small 36…”

Evolution of the amorphous fraction of PEEK during annealing at atmospheric and high pressure above the glass transition temperature

“…[48][49][50] Following this scheme, DSC thermograms after annealings under pressure could be interpreted in terms of nucleation of small crystals which growth would be inhibited because of a weak molecular mobility. On the first hand, pressure is known to promote nucleation and to increase the crystallization temperature in primary crystallization (i.e., from the liquid to the solid state).…”

“…The crystalline morphology and the number of nuclei are mainly governed by the crystallization supercooling. [48][49][50] Following this scheme, DSC thermograms after annealings under pressure could be interpreted in terms of nucleation of small crystals which growth would be inhibited because of a weak molecular mobility. The number of nuclei would increase with time but the average size would be unchanged.…”

A new PvT device for high performance thermoplastics: Heat transfer analysis and crystallization kinetics identification

“…In this case, pressure is applied by the pistons but does not remain hydrostatic in the solid state. A well-known apparatus of this type is the PvT 100 manufactured by SWO Polymertechnick GmbH (Krefeld, Germany) [2] [3]. Drawbacks of these two technologies are linked to heat transfer that cannot be controlled accurately inside the sample.…”