Investigation of the Reaction Kinetics of Poly(butylene terephthalate) and Epoxide Chain Extender

Abstract

Polyesters, such as poly (butylene terephthalate) (PBT), owe a rather low melt strength, which is considered as not beneficial for foaming. To overcome this issue, a typical attempt is the incorporation of chemical modifications—so‐called chain extenders (CE)—in the reactive extrusion process. In this study, the reaction kinetic variables are investigated depending on the material and process parameters. For this purpose, different series of experiments are performed with varying PBT with different molecular weights and the commonly used CE, Joncryl ADR4468, on a micro compounder. The screw force is recorded and analyzed using an Avrami and an Arrhenius plot. First, the amount of CE is systematically varied. To study the course of the reaction in more detail, the reaction is stopped in a series of measurements (10, 30, 60, and 90 s after complete filling). Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectra are recorded. In the second series, the effect of processing temperatures between 250 and 270 °C is investigated, and finally, in the third series, the average molecular weight of PBT is varied. It could be shown that the activation energy seems to be dependent on the initial molecular weight; lower molecular weights result in lower activation energy.

Reaction Kinetics of Recycled Polyethylene Terephthalate with PMDA Chain Extender Analyzed by a Microcompounder

“…An Avrami-like eq (eq 1) was used to calculate the reaction rate constant. 34,35 n t n k ln ln( ) ln( ) ln( )…”

“…34−37 In this context, kinetic analyses are aiming to determine the reaction rate constant of the corresponding chain extension. 34,35 In reactive extrusion, the reaction rate, expressed by the rate constant "k", can be determined by the increasing viscosity, which is reflected in the increasing torque during processing. The temperature-dependent analysis of k is of particular interest in calculating the activation energy (EA), which is required to initiate the reaction.…”

“…FT-IR can be used to detect the transformation of a chain extender on the basis of changes in characteristic bands. 2,35 To detect the increase in molecular weight and changes in polydispersity, often occurring in chain extension reactions, size exclusion chromatography (SEC) may be a suitable method. 22,30,36,38 In addition to these chemical analysis methods, rheological investigations are particularly suitable for understanding reaction-induced changes in materials.…”

“…The temperature-dependent analysis of k is of particular interest in calculating the activation energy (EA), which is required to initiate the reaction . It is important to note that the reaction rate constant or activation energy always pertains to the entire process and not exclusively to the chemical reaction itself . Initial changes in the substance, which can already be observed during processing and allow conclusions to be drawn about the occurrence of a reaction, can also be verified with the aid of Fourier transform infrared spectroscopy (FT-IR).…”

“…Initial changes in the substance, which can already be observed during processing and allow conclusions to be drawn about the occurrence of a reaction, can also be verified with the aid of Fourier transform infrared spectroscopy (FT-IR). FT-IR can be used to detect the transformation of a chain extender on the basis of changes in characteristic bands. , To detect the increase in molecular weight and changes in polydispersity, often occurring in chain extension reactions, size exclusion chromatography (SEC) may be a suitable method. ,,, In addition to these chemical analysis methods, rheological investigations are particularly suitable for understanding reaction-induced changes in materials. Appropriate rheokinetic experiments can provide significant insights into chemical and structural transformations. , …”