Liquid moulding strategies for challenging functional matrices: repair and energy storage applications
Topic(s) : Special Sessions
Co-authors :
Dominic R. PALUBISKI (UNITED KINGDOM), Shirshova NATASHA (UNITED KINGDOM), Emile GREENHALGH (UNITED KINGDOM), Milo S. P. SHAFFER (UNITED KINGDOM), Marco L. LONGANA , Janice M. DULIEU-BARTON (UNITED KINGDOM), Ian HAMERTON (UNITED KINGDOM), Dmitry S. Ivanov (UNITED KINGDOM)Abstract :
The drive for sustainability challenges researchers to enhance existing characteristics of composites to extend their service life, incorporate additional functions, and improve their efficiency. With the structural behaviour of composites primarily driven by the fibrous architecture, the matrix must provide any extra functionality. This is commonly done using multicomponent formulations and incorporating functional additives, which often affects manufacturability. The characteristics that the novel formulations typically exhibit are high viscosity, short processing windows, and greater tendency for runaway exotherms. In addition, novel matrices may require special treatment associated with peculiarities of phase separation, the need for better control of wettability, or requirements on pressure at curing.
All of the above characteristics present challenges for manufacturing. In particular, methods such as liquid moulding cannot be used as manufacturing costs are increased, as well as limiting available material forms. In the paper two very different material systems are studied that present a range of manufacturing challenges characteristic for functional materials: covalent adaptive networks (CANs, aka vitrimers) that permit material repair [1] and multi-functional resin for structural power applications (structural electrolyte, SE), which introduce a biphasic resin/ionic liquid matrix to allow for charge transport [2].
The reformable side-chains introduced to vitrimers greatly increases the viscosity of the material and reduce pot life. With viscosities well above 1000 Pa·s and pot life between 10-30 minutes, infusing these materials using typical resin infusion with flexible tooling (RIFT) conditions is not possible. SE resins, while possessing lower viscosity, typically have cure kinetics far different to the mono-functional resin on which they are based. The addition of the charge carrier alters the cure kinetics and can result in a pot life even shorter than vitrimers. More interestingly, the post-cure microarchitecture is dependent on temperature and pressure used during infusion and cure (Figure 1).
Summarising these challenges, we conclude that the conventional composites liquid moulding methods, such as resin transfer moulding (RTM) and RIFT, may not be practical for these multi-functional systems. Ideally, a system that allows independent control of resin and consolidation pressure, as well as fine temperature/pressure control able to react to small changes in material state, is required. To address these challenges, a hybrid manufacturing tooling that comprises features of flexible tooling, as in RIFT, resin pressure control, as in RTM, consolidation pressure control as in autoclave, and vacuum relaxation [3] is proposed. In a series of manufacturing trials, the potential and characteristic examples of pressure infusions with such flexible tooling systems are demonstrated.
All of the above characteristics present challenges for manufacturing. In particular, methods such as liquid moulding cannot be used as manufacturing costs are increased, as well as limiting available material forms. In the paper two very different material systems are studied that present a range of manufacturing challenges characteristic for functional materials: covalent adaptive networks (CANs, aka vitrimers) that permit material repair [1] and multi-functional resin for structural power applications (structural electrolyte, SE), which introduce a biphasic resin/ionic liquid matrix to allow for charge transport [2].
The reformable side-chains introduced to vitrimers greatly increases the viscosity of the material and reduce pot life. With viscosities well above 1000 Pa·s and pot life between 10-30 minutes, infusing these materials using typical resin infusion with flexible tooling (RIFT) conditions is not possible. SE resins, while possessing lower viscosity, typically have cure kinetics far different to the mono-functional resin on which they are based. The addition of the charge carrier alters the cure kinetics and can result in a pot life even shorter than vitrimers. More interestingly, the post-cure microarchitecture is dependent on temperature and pressure used during infusion and cure (Figure 1).
Summarising these challenges, we conclude that the conventional composites liquid moulding methods, such as resin transfer moulding (RTM) and RIFT, may not be practical for these multi-functional systems. Ideally, a system that allows independent control of resin and consolidation pressure, as well as fine temperature/pressure control able to react to small changes in material state, is required. To address these challenges, a hybrid manufacturing tooling that comprises features of flexible tooling, as in RIFT, resin pressure control, as in RTM, consolidation pressure control as in autoclave, and vacuum relaxation [3] is proposed. In a series of manufacturing trials, the potential and characteristic examples of pressure infusions with such flexible tooling systems are demonstrated.