Arnold Lustiger

Effect of water on the mechanical adhesion of the glass/epoxy interface

Abstract In recent years, the quality of the fibre/matrix bonding in polymer composites has been quantified by means of a single mechanical parameter, the interfacial shear strength, based on measurements made using micromechanical techniques. It has gradually appeared, however, that this parameter is both ambiguous in terms of its physical meaning and, at the same time, difficult to measure reliably in many cases. Moreover, different micromechanical techniques yield differing values of the interfacial shear strength. Finally, it has been suggested in a few studies that it may not be the critical factor governing fibre/matrix debonding. In this paper an energy balance approach is proposed, by which the degree of fibre/matrix bonding is now quantified by means of the interfacial energy, as a function of the fibre geometrical and mechanical characteristics, the stress transfer length and the debonding length. The validity of the approach is discussed in the case of the single-fibre composite test, in which progressive fragmentation of a single brittle fibre in a more ductile polymeric matrix takes place, using data for E-glass fibres embedded in epoxy, both in the dry state and in the presence of hot distilled water.

Interlamellar failure at transcrystalline interfaces in glass/polypropylene composites

Abstract Transcrystalline microstructures are normally not observed at the interface between E-glass fibers and an isotactic polypropylene matrix, unless mechanical translation is applied to the fiber while it is in the supercooled polymer melt. We demonstrate here that transcrystallinity can form at the surface of E-glass fibers if appropriate nucleating agents are used to coat the fibers. These agents can nucleate either the α (monoclinic) or β (hexagonal) crystal forms of polypropylene. Single-fiber composite experiments were performed to assess the effect of transcrystallinity on matrix deformation. The preliminary results presented here reveal the occurrence of a previously unreported damage mechanism by which interlamellar fractures form preferentially at the interface well before any bulk matrix damage occurs. The density of this damage zone is higher in transcrystallinity of the β crystal form than of the α form, although it was found that in the α form the damage can propagate into the matrix. The occurrence of this damage mechanism suggests that toughness increases may potentially be obtained by careful design of the interfacial transcrystalline region in E-glass/polypropylene composites.

Morphology and Damage Mechanisms of the Transcrystalline Interphase in Polypropylene

Abstract By coating glass fibers with the appropriate nucleating agent, transcrystallinity can be generated in polypropylene/glass composities. Transcrystallinity can consist either of the alpha (monoclinic) or beta (hexagonal) crystal structure. Through the use of directional solidification, the transcrystalline morphology can be duplicated in polypropylene films on a level large enough for mechanical and morphological study. Permanganic etching and subsequent electron microscopy reveals that lamellar orientation in alpha transcrystallinity differs significantly from the beta form. Alpha transcrystallinity consists of lamellae which are edge-on relative to the polypropylene film thickness, while beta transcrystallinity consists of lamellae which are primarily flat-on. This difference in morphology results in significant variations in mechanical properties and damage mechanisms.