Mechanical properties and fracture behavior of polypropylene reinforced with polyaniline‐grafted short glass fibers

Abstract

This research was focused on the mechanical properties of electrically conducting composites based on polyaniline (PAn)-coated short glass fibers (SGFs) immersed in an isotactic polypropylene (iPP) matrix. In these composites, PAn was actually grafted onto the SGF surface, and so it was denoted PAn-g-SGF. The tensile, flexural, and interlaminar fracture toughness was investigated. To study the influence of PAn-g-SGF, three different concentrations (10, 20, and 30 wt %) were melt-mixed in the iPP resin with a batch mixer. X-ray patterns of the asmolded plaques of iPP and its composites showed an isotropic orientation. Uniaxial tensile deformation revealed that the Young's modulus and tensile stress increased as the concentration of PAn-g-SGF increased; on the other hand, the strain at failure was significantly reduced (by 2 orders of magnitude) with respect to the neat iPP. Scanning electron microscopy studies on the failure specimens indicated that the significant reduction of the strain at failure was due to the low interfacial bonding between the fibers and the surrounding matrix. Moreover, X-ray scattering analyses of the fractured regions showed that the uniaxial deformation enabled significant molecular orientation in the iPP, whereas the fractured composites remained isotropic. Detailed scanning electron microscopy analyses showed that the fracture mechanism arose from the fracture of the PAn-g-SGFs; the percolated PAn-g-SGFs formed a path for the stress transfer. Because the failure was dominated by both filler decohesion and polymeric chain rupture, the strength was not influenced significantly by the amount of PAn-g-SGFs.

Polymers in 2D confinement: A nanoscale mechanism for thermo‐mechanical reinforcement

“…Increase of modulus by a factor of approximately 2 is usually achieved for polymer composites at significantly higher filler concentrations, approximately 30 wt%. Figure illustrates clearly this point for PA6/glass fiber composites and polypropylene/glass fiber composites …”

“…Continuous upward curves correspond to Halpin‐Tsai‐Nielsen model for E ′ ∞ and E ′ 90°C , respectively, with parameter X indicated. Young modulus data of Romo‐Uribe et al and data of PA6‐MMT and PA6‐glass fiber adapted from Paul and Robeson, and of polypropylene‐glass fiber adapted from Flores et al [Colour figure can be viewed at wileyonlinelibrary.com]…”

Electrically conducting polypropylene/polyaniline‐grafted‐short glass fiber composites: Microstructure and dynamic mechanical analysis

“…The results showed that there is a percolation threshold above 20 wt% PAn‐ g ‐SGFs, producing an anisotropic electrically conductive composite. Furthermore, in our group, the linear viscoelastic properties of molten iPP/PAn‐ g ‐SGF as well as the mechanical properties and fracture behavior of these composites have been studied [26, 27]. Those results showed that the microfillers promote a significant increase in melt viscosity and eventually give rise to a yield stress.…”

“…On the other hand, mechanical measurements showed that the Young's modulus and yield stress were found to be an increasing function of microfiller concentration. However, the strain at failure was significantly reduced, microfiller dewetting (loss of adhesion between the microfiller and polymer matrix) was found to be largely responsible for this behavior [27]. In addition, the incorporation of a small amount of PP‐maleic anhydride copolymer (PP‐gMA) to the composites increased the melt viscosity and elasticity, and improved the mechanical properties, but affected negatively the electrical conductivity of the composites σ, dropping dramatically from ca.…”

“…In addition, the incorporation of a small amount of PP‐maleic anhydride copolymer (PP‐gMA) to the composites increased the melt viscosity and elasticity, and improved the mechanical properties, but affected negatively the electrical conductivity of the composites σ, dropping dramatically from ca. 2 × 10 −9 to about 10 −12 S/cm, due, apparently, to fiber encapsulation [16, 26, 27].…”