Edward D. McCarthy

Revealing the interface in polymer nanocomposites.

The morphological characterization of polymer nanocomposites over multiple length scales is a fundamental challenge. Here, we report a technique for high-throughput monitoring of interface and dispersion in polymer nanocomposites based on Förster resonance energy transfer (FRET). Nanofibrillated cellulose (NFC), fluorescently labeled with 5-(4,6-dichlorotriazinyl)-aminofluorescein (FL) and dispersed into polyethylene (PE) doped with Coumarin 30 (C30), is used as a model system to assess the ability of FRET to evaluate the effect of processing on NFC dispersion in PE. The level of energy transfer and its standard deviation, measured by fluorescence spectroscopy and laser scanning confocal microscopy (LSCM), are exploited to monitor the extent of interface formation and composite homogeneity, respectively. FRET algorithms are used to generate color-coded images for a real-space observation of energy transfer efficiency. These images reveal interface formation at a nanoscale while probing a macroscale area that is large enough to be representative of the entire sample. The unique ability of this technique to simultaneously provide orientation/spatial information at a macroscale and nanoscale features, encoded in the FRET signal, provides a new powerful tool for structure-property-processing investigation in polymer nanocomposites.

Fiber-reinforced epoxy composites exposed to high temperature environments. Part II: Modeling mechanical property degradation

This article is part of a series on the thermo-mechanical responses of fiber-reinforced composites at elevated temperatures and it follows the first part containing experimental results. A flame-retardant system consisting of a cellulosic charring agent and an interactive intumescent additive (melamine phosphate) has been used in order to improve the post-fire mechanical performance of glass fiber-reinforced epoxy composites. The effect of one-sided radiant heat on the residual flexural stiffness of laminate coupons exposed to incident heat fluxes of 25 and 35 kW m-2 was investigated. The flame-retarded coupons retained a higher percentage of their original room temperature flexural modulus after heat exposure while the control specimens showed inferior material property retention over the same exposure periods. A heat transfer (thermal) model based on Henderson’s equation is used to predict the through thickness temperature profiles and subsequently the mass loss due to the resin matrix decomposition at elevated temperatures. The theoretical results from the heat transfer model are validated against experimentally obtained data and then coupled with a mechanics model that describes material property-temperature dependence in order to predict the residual flexural stiffness, after heat damage. The accuracy of the thermo-mechanical model was validated against the experimental data and a good agreement was observed.

Formation of extended ionomeric network by bulk polymerization of l,d-lactide with layered-double-hydroxide

Abstract We report the formation of an ionomeric network in a poly( l , d -lactide) hybrid nanocomposite, (PLDLA-HYB) during in-situ melt polymerization of l , d -lactide in the presence of magnesium/aluminum layered-double-hydroxide (LDH) without added catalyst. The effect of LDH mass loading and reaction time on molecular mass and yield of soluble poly( l , d -lactide) (PLDLA-SOL) present in the hybrid was investigated for a better understanding of the conflicting roles of LDH in polymerization and degradation of PLDLA-SOL. High molecular mass PLDLA-SOL is obtained through initiation of polymerization by LDH. However an additional insoluble organic–inorganic fraction, INSOL, is also observed within the product when PLDLA-SOL is extracted using methylene chloride as solvent. It is proposed that INSOL is an ionomeric network comprising hydrogen-bonded, or otherwise co-ordinated, lactic acid monomer salts of magnesium, together with PLDLA in a 24%–76% mass ratio.

Modelling flaming combustion in glass fibre-reinforced composite laminates:

A heat transfer model based on the well-known Henderson equation has been modified to allow for self-sustained ignition and the flaming combustion phenomena of E-glass fibre-reinforced epoxy composites to be predicted from first principles using known thermal-physical and thermodynamic data for their constituents. The modifications consider: (1) the assignment of thermodynamic conditions (e.g. ignition temperature and mass flux of volatiles) necessary and sufficient to trigger self-sustained ignition, and (2) the inclusion of an integrated loop allowing the heat energy generated from the flaming combustion process to be fed back into the burning laminate. The model compares moderately well with experimental results obtained from cone calorimetric measurements. The additional modelling capabilities considered in this study provide the basis for an analytical model that can more accurately predict the thermal response and flaming combustion of glass fibre-reinforced polymer composites exposed to a one-sided radiant heating environment in the presence of an ignition source.

Investigation of factors affecting the thermal expansion of perfluoroelastomer seal materials

The high thermal expansion coefficient of perfluoroelastomer materials can cause problems with the design of adequate seal grooves to cover both high and low temperature operation. Variations in filler shape and proportions have been shown to have a significant effect on thermal expansion over part of the temperature range. This feature describes an investigation of relevant literature that has been compared with experimental verification.