Investigation of Transcrystalline Interphases in Polypropylene/Glass Fiber Composites Using Micromechanical Tests

Abstract

In composites, a strong interphase between the components is essential for mechanical properties. By using a suitable sizing (i.e., surface modification) of the fiber, the interphase may be varied, e.g., by suppressing or promoting heterogeneous nucleation of a thermoplastic matrix. In the latter case, three-dimensional transcrystallized interphases with properties differing from those of the bulk matrix are formed. Polypropylene-glass fiber composites are prepared as single-fiber model composites with (a) sizings either inducing or suppressing a transcrystalline interphase, (b) different amounts of modifier maleic acid anhydride grafted polypropylene, and (c) different molecular weights of the matrix polymer. These are studied in quasi-static or cyclic load tests. Static tests permit insights in the interfacial characteristics such as critical interface energy release rate, adhesion strength and frictional stress. Cyclic tests on these model composites can be used to study the nature of dissipative processes and the damage behavior. Atomic Force Microscopy (AFM) investigations of the fiber fracture surfaces provide supplementary information. The transcrystalline layer can indeed improve the mechanical parameters (a 70–100% increase of strength and a 25 or 125% increase in toughness, depending on the molecular weight (MW) of the matrix polymer at low modifier concentration). However, the effect is partially neutralized by an opposing effect: high nucleation in the bulk in samples with commonly used concentrations of modifier.

Utilization of Recycled Material Sources for Wood-Polypropylene Composites: Effect on Internal Composite Structure, Particle Characteristics and Physico-Mechanical Properties

“…However, other factors as coupling agent and particle/fibre agglomerations have to be considered. MAPP improves adhesion as the maleic moieties form bonds with the hydroxyl groups of the wood component [55], whereby the scarcity of noticed aggregates within the microstructure is in contrast to the improved mechanical properties after reprocessing. As indicated by Bledzki and Gassan [56], the tendency of wood to form aggregates, by means of a high intermolecular bonding among particles/fibres, is an important factor in processing wood-thermoplastic composites.…”

“…A strong interphase between the wood-polypropylene matrix can only be suggested. Studies on polypropylene-glass fibre composites with varied MAPP concentrations have shown that transcrystalline layers can improve mechanical properties [55]. Nevertheless, further opposing effects like a sufficient dispersion of wood particles/fibres seems to be crucial to the performance of composites.…”

A Finite Element Investigation into the Cohesive Properties of Glass-Fiber-Reinforced Polymers with Nanostructured Interphases

“…A proper characterization of the interphase is crucial to evaluate the adhesion energy and further the enhancement of the mechanical properties. Currently, this is achieved by micromechanical tests such as single and bundled fiber pull-out tests, which facilitate evaluation of the interfacial shear stress (IFSS) [13,14]. It is worth emphasizing that reported analyses of failure regions on laminated composites have shown fiber bundles pulled out from the specimen [15].…”

Enhanced Interfacial Shear Strength and Critical Energy Release Rate in Single Glass Fiber-Crosslinked Polypropylene Model Microcomposites

“…There are several approaches to enhancing the low interfacial adhesion between the GF and PP matrix. These are plasma treatment [5,6], the use of sizing [7], surface grafting [8,9], and the use of transcrystalline interphases [10]. In the case of continuous GF-reinforced PP composites, the simultaneous in situ commingling of glass and polypropylene filaments as well as the application of a water-based sizing containing aminosilane and maleic anhydride-grafted PP (MAH-g-PP) led to reduced fiber damage, a homogeneous mixing of both glass and PP filaments, good impregnation of glass filaments with the PP matrix, and the best performance of continuous GF-reinforced PP composites [11].…”