Frontal polymerisation has the potential to bring unprecedented reductions in energy demand and process time to produce fibre reinforced polymer composites. Production of epoxy-based fibre reinforced polymer parts with high fibre volume content, commonly encountered in industry, is however hindered by the heat sink created by the fibres and the mould, overcoming the heat output of the chemical reaction, thus preventing front propagation. We propose a novel self-catalysed frontal polymerisation manufacturing method based on the integration of thin resin channels in thermal contact with the composite stack as a strategy for low-energy production of high fibre volume fraction polymer composites without the need for a continuous energy input. Frontal polymerisation inside the resin channel proceeds faster and preheats the fabric stack, thus catalysing the process. Parts with up to 60% fibre content are successfully produced independently of the sample thickness. Fillers added within the resin channels provide means to tailor the frontal polymerisation process kinetics. The parts have a significantly higher glass transition temperature than those produced in a conventional oven, and comparable mechanical properties while energy consumption is reduced by over 99.5%.

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Radical induced cationic frontal polymerisation (RICFP) is considered a promising low energy method for processing of fibre reinforced polymers (FRPs). Optimisation of the local heat balance between reinforcement, epoxy resin and the surrounding mould is required to pave the way for its adaptation to an industrial processing method for high volume fraction structural fibre reinforced composites. In this work, we investigate several methods to control the governing heat balance in RICFP-processing of FRPs. Heat generation was controlled by tuning the initiator concentration while limitation of heat losses using highly insulating moulds was found beneficial to the front characteristics and resulting curing degrees. An optimised mould configuration allowed for self-sustaining RICFP in FRPs with fibre volume fractions (V_fs) up to 45.8%, exceeding previously reported maxima of similar systems. A process window was moreover established relating the V_f and required heat generation to the potential formation of a self-sustaining or supported front.

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Capillarity plays a crucial role in many natural and engineered systems, ranging from nutrient delivery in plants to functional textiles for wear comfort or thermal heat pipes for heat dissipation. Unlike nano- or microfluidic systems with well-defined pore network geometries and well-understood capillary flow, fiber textiles or preforms used in composite structures exhibit highly anisotropic pore networks that span from micron scale pores between fibers to millimeter scale pores between fiber yarns that are woven or stitched into a textile preform. Owing to the nature of the composite manufacturing processes, capillary action taking place in the complex network is usually coupled with hydrodynamics as well as the (chemo) rheology of the polymer matrices; these phenomena are known to play a crucial role in producing high quality composites. Despite its importance, the role of capillary effects in composite processing largely remained overlooked. Their magnitude is indeed rather low as compared to hydrodynamic effects, and it is difficult to characterize them due to a lack of adequate monitoring techniques to capture the time and spatial scale on which the capillary effects take place. There is a renewed interest in this topic, due to a combination of increasing demand for high performance composites and recent advances in experimental techniques as well as numerical modeling methods. The present review covers the developments in the identification, measurement and exploitation of capillary effects in composite manufacturing. A special focus is placed on Liquid Composite Molding processes, where a dry stack is impregnated with a low viscosity thermoset resin mainly via in-plane flow, thus exacerbating the capillary effects within the anisotropic pore network of the reinforcements. Experimental techniques to investigate the capillary effects and their evolution from post-mortem analyses to in-situ/rapid techniques compatible with both translucent and non-translucent reinforcements are reviewed. Approaches to control and enhance the capillary effects for improving composite quality are then introduced. This is complemented by a survey of numerical techniques to incorporate capillary effects in process simulation, material characterization and by the remaining challenges in the study of capillary effects in composite manufacturing.

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Radical Induced Cationic Frontal Polymerisation (RICFP) has recently been proposed as a promising strategy for processing of epoxide carbon fibre reinforced polymers. Control of the local heat balance is crucial towards the production of industrial-quality composites, which is typically achieved via controlling the heat generation. In this work we present a comprehensive overview of RICFP processing of cycloaliphatic epoxide composites with enhance heat insulation. The thermal initiating compound was identified as the main component to control heat generation, which correlated well with the front velocity. A processing window was defined as function of the fibre and initiator contents and composites with to 45.8% Vf were successfully produced. Optimisation of resulting mechanical properties was made possible by optimisation of the heat balance, with matrix glass transition temperatures of up to 187°C achieved for the used cycloaliphatic system. Post-curing was found beneficial to overcome suggested inhomogeneous curing due to the dual-scale nature of fabrics. @en

Radical induced cationic frontal polymerization (RICFP) is considered as a promising method for processing of fiber reinforced polymers (FRPs). Optimization of the local heat flow is required to pave the way for its adaptation to an industrial processing method. In this work we present an overview on the role of the mold design on the frontal polymerization characteristics and resulting chemical properties. Mold properties were found of significant influence on the front characteristics. Highly insulating molds allowed for the highest front temperatures and velocities while consequent delayed cooling is suggested beneficial for the monomer conversion in neat polymer and FRP systems. An optimized mold configuration was subsequently used for FRP production, allowing for self-sustaining RICFP in FRPs with fiber volume fractions (Vfs) up to 45.8%. A processing window was moreover defined relating the Vf and required heat generation to the potential formation of a self-sustaining or supported front.

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In-plane permeability of small area (100 × 50 mm) alumina fiber woven fabrics grafted with aligned carbon nanotubes (CNT) was quantified by placing them in series with a glass mat of known permeability during a flow experiment. The methodology was first validated on a reference woven textile. Permeability values matched those obtained by a direct method within a margin of ±15%. Permeabilities of radial-aligned (short CNT, SCNT) and so-called ‘Mohawk’ (long CNT, LCNT) morphologies of the CNT-grafted samples were then measured and compared to the non-grafted alumina, showing a decrease attributed to a change in local textile structure as assessed in previous studies. Unsaturated permeability decreased by 77% after SCNT- and 88% after LCNT-grafting, while saturated permeability further decreased by 90% and 93%, respectively. The high ratio of unsaturated to saturated permeability (in the range of 1.14 – 2.89) implies that capillary wicking contributes largely to the impregnation of CNT-grafted fabrics.

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