Interfacial Polarization in Thermoplastic Basalt Fiber-Reinforced Composites.

Wojciech Ignaczak,Anne Ladegaard Skov,Miroslawa El Fray

doi:10.3390/polym12071486

Abstract

The aim of this work was to study the interfacial behavior of basalt-fiber-reinforced thermoplastic blends of polypropylene and poly(butylene terephthalate) (PP/PBT). We examined the effect of two compatibilizers and two basalt fiber (BF) sizings: commercial (REF) and experimental (EXP). Differential scanning calorimetry was used to assess the influence of BFs on the phase structure of obtained composites. Furthermore, dielectric relaxation spectroscopy was used for the first time to non-destructively study the interfacial adhesion within an entire volume of BF-reinforced composites by assessing the α relaxation, DC conductivity, and Maxwell–Wagner–Sillars (MWS) polarization. The fiber–matrix adhesion was further investigated using the Havriliak–Negami model. Using complex plane analysis, the dielectric strength, which is inversely related to the adhesion, was calculated. The composites reinforced with EXP fibers showed significantly lower values of dielectric strength compared to the REF fibers, indicating better adhesion between the reinforcement and blend matrix. Static bending tests also confirmed improved fiber adhesion with EXP fibers, while also suggesting a synergistic effect between compatibilizer and sizing in enhancing interfacial properties. Thus, we conclude that substantially improved adhesion of PP/PBT BF-reinforced composites is the result of mutual interactions of functional groups of blend matrix, mostly from blend compatibilizer, and fiber surface due to sizing.

Highlights

Over the last several decades, the modification of existing polymeric systems has arguably become even more important than the synthesis of new polymers
Thermoplastic basalt fiber (BF)-reinforced composites are a realistic answer to market demands for materials with lower environmental impact, increased recyclability, ease of processing, and lower
(provided by Isomatex, Gembloux (Isnes), Belgium) [27]. Both BFs used had a diameter of 11 μm and average fiber length of 5 mm, but differed in surface chemistry: (1) reference fibers (REF) was covered with a commercial sizing containing 1◦ and 2◦ amine groups, based on 3-(2-aminoethylaminopropyl)trimethoxysilane as coupling agent, which is commonly used in many formulations, especially in thermosetting composites; (2) EXP was covered with an experimental sizing enriched with maleic anhydride moieties (PP–g–MA)

Summary

Introduction

Over the last several decades, the modification of existing polymeric systems has arguably become even more important than the synthesis of new polymers. Polymer modification can be achieved in various ways, including copolymerization, blending, and/or by adding organic and inorganic compounds, fillers, or fibrous reinforcement. The most common technique of processing thermoplastic composites is injection molding, which enables the production of large quantities of parts with complex shapes within strict dimensional tolerances [10]. Over the last several decades, basalt fibers (BFs) have come into consideration as potential reinforcement of composite materials [11,12,13,14] due to their numerous attractive properties. Thermoplastic BF-reinforced composites are a realistic answer to market demands for materials with lower environmental impact, increased recyclability, ease of processing, and lower

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Conclusion