Elsevier

Polymer

Volume 190, 2 March 2020, 122192
Polymer

Comparing the sorption kinetics of poly-tetrafluoroethylene processed either by extrusion or spark plasma sintering

https://doi.org/10.1016/j.polymer.2020.122192Get rights and content

Highlights

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    We compare the sorption kinetics properties of poly-tetrafluoroethylene (PTFE) processed either by spark plasma sintering (SPS-PTFE) or extrusion methods (Ext-PTFE).

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    Swelling of spark plasma sintering reduces slightly the crystallite thickness, the Young’s modulus and yield stress.

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    In contrast, the crystalline phase is less impacted by swelling for Ext-PTFE samples for witch Young's modulus is increased under the combined effect of swelling and tensile stress.

Abstract

The key goal of this study was to compare the sorption kinetics properties of poly-tetrafluoroethylene (PTFE) processed either by spark plasma sintering (SPS-PTFE) or extrusion methods (Ext-PTFE). A gravimetric-sorption technique was used to obtain kinetic and equilibrium adsorption data at room temperature in several liquids (toluene, n-hexane, tetrahydrofuran and chloroform). Sorption kinetics was quantified using the Berens-Hopfenberg empirical model. The results are discussed in terms of liquid diffusion and polymer relaxation. An attempt was made to correlate the crystallization rate, apparent diffusion coefficient and sorption rate for the series of samples. Additionally, the effect of sorption kinetics on the structure and mechanical properties of PTFE samples was investigated. Swelling of SPS-PTFE reduces slightly the crystallite thickness, the Young's modulus and yield stress. In contrast, the crystalline phase is less impacted by swelling for Ext-PTFE samples for witch Young's modulus is increased under the combined effect of swelling and tensile stress.

Section snippets

Introduction and overview

PTFE is a synthetic fluoropolymer used in numerous industrial applications (it is often referred by its trade name Teflon). The production of PTFE is forecast to continue to increase over the course of the next ten years [1]. The demand arises because PTFE combines various excellent properties: chemical resistance, high temperature stability, favorable mechanical properties and low permittivity [2]. Such unique characteristics made PTFE widely used in automotive, electrical, and electronic

Materials

Industrial grade PTFE was used to perform the experiments. On the one hand, Ext-PTFE samples were purchased from Guarniflon Society, of density 2.18 g/cm3. On the other hand, SPS samples were obtained by using PTFE powder provided by the Hoechst-Germany company (Hostaflon TF1620) and an HP 25/1 machine from FCT system GmbH (Germany). The size distribution of the PTFE particles was obtained from SEM observations by dispersing PTFE powder in a suitable solvent (2-propanol). The average value of

Modeling solvent sorption kinetics

The sorption kinetics of polymers in a low molecular weight liquid has been studied extensively. A standard model for mass diffusion kinetics is based on the second Fick's law. It is known in the archival literature as case I or Fickian diffusion and is represented by Eq. (2)∂C∂t=−D∂²C∂x²where C is the solvent concentration, x denotes the distance from the sample center, D is the diffusion coefficient, and t is time. If we assume that the surface concentration attains its equilibrium value C∝

Crystallinity of PTFE samples

The thermograms depicted in Fig. 3 show the transitions of Ext-PTFE and SPS-PTFE samples in the temperature range 30–400 °C. A summary of the melting, crystallization peaks temperatures and heats of fusion are given in Table 2. In the first cycle of heating-cooling, the Ext-PTFE exhibits a peak of melting at 333 °C and provides a total heat of fusion 45 J/g. In case of SPS-PTFE, double melting peaks are observed at 330 °C and 348 °C. The corresponding endothermal enthalpies of fusion are about

Concluding remarks

We reported on the effect of swelling on the structural and mechanical properties of Ext-PTFE and SPS-PTFE. The above results show that the sorption kinetics behavior of toluene, n-hexane, tetrahydrofuran and chloroform are pseudo-Fickian. To rationalize the sorption kinetics data the BH equation was used. Overall, we found that SPS-PTFE is characterized by property gradients from the surface to the bulk and that the equilibrium uptake is larger than for Ext-PTFE. An attempt was made to

CRediT authorship contribution statement

Ilham Elaboudi: Conceptualization, Methodology, Investigation, Supervision, Writing - original draft. Ahmed Mdarhri: Conceptualization, Methodology, Supervision, Writing - original draft, Writing - review & editing. Christian Brosseau: Conceptualization, Writing - original draft, Writing - review & editing. Ali Nourdine: Investigation, Supervision. Mourad Rzaizi: Investigation, Validation. Laurent Servant: Methodology, Writing - review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors thank the Center of Analysis of Cadi Ayyad University for FTIR and XRD characterizations. We gratefully acknowledge the assistance of G. Bonnefont for SPS experiments.

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