Abstract Molecular dynamics simulations are valuable tools in enabling us to link molecular-level... more Abstract Molecular dynamics simulations are valuable tools in enabling us to link molecular-level structure to macroscopic properties of new polymer-based materials. However, molecular simulation of cyanate ester polymers presents specific challenges, as a few credible procedures that captures ring formation is available. Despite the presence of previous attempts to this end, an automated process, that is easy to reproduce and adaptable for modelling cyanate esters, is still lacking. Herein, a robust and reproducible triazine ring formation procedure to reliably model, test, and tune polymer structures for use in molecular simulations is reported. In addition to being entirely reproducible, this procedure provides sufficient details to be applied to model polymers generated via ring formation between cyanate groups. Amongst our developments, key features include a reliable process for generating and equilibrating liquid samples to be polymerised, a robust ring formation algorithm, and establishment of a clear protocol to predict macroscopic properties such as glass transition temperature and Young's modulus of the polymerised samples. Predicted macroscopic properties agreed well with experimentally available data. Our procedure provides a perfect platform for the process of modelling cyanate esters and can be easily adapted to generate porous polymers such as covalent organic frameworks.
Abstract: The aim of this chapter is to introduce the reader to the range of thermosetting polyme... more Abstract: The aim of this chapter is to introduce the reader to the range of thermosetting polymers (thermosets) that are currently used within the modern aerospace industry. Civil airliners, military aircraft (including unmanned drones), smaller executive and light aircraft all employ thermosets of one kind or another and, being subject to different performance demands or budgets, consequently have different materials selection criteria; each will be addressed here. The chapter examines the key requirements of materials used from the perspective of the resin, the reinforcement (in the form of prepreg or woven mat) and ultimately the composite. Finally, the authors give a view of the future development in this most dynamic area of polymer engineering.
Abstract Many fibre reinforced polymer (FRP) composite manufacturing processes benefit from the a... more Abstract Many fibre reinforced polymer (FRP) composite manufacturing processes benefit from the ability to monitor the polymerisation of the resin constituent, either for process control or quality assurance purposes. Whilst most available resin monitoring systems achieve this by measuring the percentage conversion of reactants, measurement of the corresponding glass transition temperature, Tg, is often more informative. The ability to measure Tg directly from spectra acquired by Raman spectroscopy, using principal components analysis, has been demonstrated here for an amine-cured epoxy resin system. A regression model was generated using principal components identified from spectra acquired of cured resin samples produced at a range of isothermal conditions, regressed against corresponding Tg values measured by dynamic scanning calorimetry (DSC). Spectra acquired during the cool-down period following completion of one trial were incorporated into the calibration dataset to ensure effects of sample temperature were accounted for in the principal components analysis (PCA). Measurements obtained with the resultant model, generated using 5 principal components accounting for 97% of the variance in the calibration dataset, were shown to agree well with final sample DSC measurements from in situ cure trials, differing by ≤ 0.6 °C, and exhibiting negligible sensitivity to sample temperature. The results demonstrate the potential of Raman spectroscopy coupled with PCA as a non-contact cure monitoring technique, able to directly measure Tg of a thermosetting epoxy resin system typical of those used in FRP composites manufacture, independent of sample temperature.
Abstract Fused filament fabrication (FFF), which is a thermoplastic layer-by-layer additive manuf... more Abstract Fused filament fabrication (FFF), which is a thermoplastic layer-by-layer additive manufacturing technique, called as 3D printing, can quickly build complex geometries, reducing design limitations and production costs of conventional manufacturing methods. Using a fibrous reinforcement strengthens the thermoplastic matrix, allowing FFF to be used in more structural complex-shape small-size applications in engineering. Aligned discontinuous fibre composites (ADFRC) incorporate a high-performance reinforcement architecture that, owing to a sufficient fibre length and high level of alignment, results in mechanical performance comparable to those of continuous fibre composites. Moreover, it can offer higher formability and, fewer manufacturing defects. In this paper, ADFRC preforms, produced with the High Performance Discontinuous Fibre (HiPerDiF) technology, were impregnated with poly(L-lactic acid) (PLA) and then reshaped to a circular-shaped 3D printing filament using a customised manual moulding and pultrusion method. Two different mould types were compared to maximise the filament quality and reduce the amount of trapped voids. The printability of the circular filaments was investigated by varying three parameters: deposition speed, processing temperature, and layer thickness. Finally, the tensile properties of samples from each manufacturing step: moulded, filament, single raster printed, and full height rectangular part, were investigated. Overall, the HiPerDiF-PLA filament can be printed using an 3D printer. Although the tensile properties of filament in each stage reduced as the result of the shape transformation process, the deposited layer of HiPerDiF-PLA part has greater stiffness and strength than other PLA composite materials. At this stage of technology development, the material has lower mechanical performance yet than the nylon continuous fibre composites printed with commercially available machines. However, there are clear routes forward for the improved performance of the HiPerDiF FFF printed filaments.
Abstract Molecular dynamics simulations are valuable tools in enabling us to link molecular-level... more Abstract Molecular dynamics simulations are valuable tools in enabling us to link molecular-level structure to macroscopic properties of new polymer-based materials. However, molecular simulation of cyanate ester polymers presents specific challenges, as a few credible procedures that captures ring formation is available. Despite the presence of previous attempts to this end, an automated process, that is easy to reproduce and adaptable for modelling cyanate esters, is still lacking. Herein, a robust and reproducible triazine ring formation procedure to reliably model, test, and tune polymer structures for use in molecular simulations is reported. In addition to being entirely reproducible, this procedure provides sufficient details to be applied to model polymers generated via ring formation between cyanate groups. Amongst our developments, key features include a reliable process for generating and equilibrating liquid samples to be polymerised, a robust ring formation algorithm, and establishment of a clear protocol to predict macroscopic properties such as glass transition temperature and Young's modulus of the polymerised samples. Predicted macroscopic properties agreed well with experimentally available data. Our procedure provides a perfect platform for the process of modelling cyanate esters and can be easily adapted to generate porous polymers such as covalent organic frameworks.
Abstract: The aim of this chapter is to introduce the reader to the range of thermosetting polyme... more Abstract: The aim of this chapter is to introduce the reader to the range of thermosetting polymers (thermosets) that are currently used within the modern aerospace industry. Civil airliners, military aircraft (including unmanned drones), smaller executive and light aircraft all employ thermosets of one kind or another and, being subject to different performance demands or budgets, consequently have different materials selection criteria; each will be addressed here. The chapter examines the key requirements of materials used from the perspective of the resin, the reinforcement (in the form of prepreg or woven mat) and ultimately the composite. Finally, the authors give a view of the future development in this most dynamic area of polymer engineering.
Abstract Many fibre reinforced polymer (FRP) composite manufacturing processes benefit from the a... more Abstract Many fibre reinforced polymer (FRP) composite manufacturing processes benefit from the ability to monitor the polymerisation of the resin constituent, either for process control or quality assurance purposes. Whilst most available resin monitoring systems achieve this by measuring the percentage conversion of reactants, measurement of the corresponding glass transition temperature, Tg, is often more informative. The ability to measure Tg directly from spectra acquired by Raman spectroscopy, using principal components analysis, has been demonstrated here for an amine-cured epoxy resin system. A regression model was generated using principal components identified from spectra acquired of cured resin samples produced at a range of isothermal conditions, regressed against corresponding Tg values measured by dynamic scanning calorimetry (DSC). Spectra acquired during the cool-down period following completion of one trial were incorporated into the calibration dataset to ensure effects of sample temperature were accounted for in the principal components analysis (PCA). Measurements obtained with the resultant model, generated using 5 principal components accounting for 97% of the variance in the calibration dataset, were shown to agree well with final sample DSC measurements from in situ cure trials, differing by ≤ 0.6 °C, and exhibiting negligible sensitivity to sample temperature. The results demonstrate the potential of Raman spectroscopy coupled with PCA as a non-contact cure monitoring technique, able to directly measure Tg of a thermosetting epoxy resin system typical of those used in FRP composites manufacture, independent of sample temperature.
Abstract Fused filament fabrication (FFF), which is a thermoplastic layer-by-layer additive manuf... more Abstract Fused filament fabrication (FFF), which is a thermoplastic layer-by-layer additive manufacturing technique, called as 3D printing, can quickly build complex geometries, reducing design limitations and production costs of conventional manufacturing methods. Using a fibrous reinforcement strengthens the thermoplastic matrix, allowing FFF to be used in more structural complex-shape small-size applications in engineering. Aligned discontinuous fibre composites (ADFRC) incorporate a high-performance reinforcement architecture that, owing to a sufficient fibre length and high level of alignment, results in mechanical performance comparable to those of continuous fibre composites. Moreover, it can offer higher formability and, fewer manufacturing defects. In this paper, ADFRC preforms, produced with the High Performance Discontinuous Fibre (HiPerDiF) technology, were impregnated with poly(L-lactic acid) (PLA) and then reshaped to a circular-shaped 3D printing filament using a customised manual moulding and pultrusion method. Two different mould types were compared to maximise the filament quality and reduce the amount of trapped voids. The printability of the circular filaments was investigated by varying three parameters: deposition speed, processing temperature, and layer thickness. Finally, the tensile properties of samples from each manufacturing step: moulded, filament, single raster printed, and full height rectangular part, were investigated. Overall, the HiPerDiF-PLA filament can be printed using an 3D printer. Although the tensile properties of filament in each stage reduced as the result of the shape transformation process, the deposited layer of HiPerDiF-PLA part has greater stiffness and strength than other PLA composite materials. At this stage of technology development, the material has lower mechanical performance yet than the nylon continuous fibre composites printed with commercially available machines. However, there are clear routes forward for the improved performance of the HiPerDiF FFF printed filaments.
A series of thermally stable dicyanate monomers was prepared containing different thermally stabl... more A series of thermally stable dicyanate monomers was prepared containing different thermally stable structural units, namely 2,2 ′-bis(4-cyanatophenyl)propane, bis-4-cyanato-biphenyl, bis-4-cyanato naphthalene, 3,3 ′-bis(4-cyanatophenyl)sulfide and 3,3 ′-bis(4-cyanatophenyl)sulfone, was prepared and the identity of the products was confirmed by Fourier transform infrared and NMR spectral methods. The corresponding cyanate homopolymers were prepared and their properties were evaluated and compared. The composites were analysed for their thermal stability and thermal degradation kinetics. The series of homopolymers exhibit excellent thermal characteristics, e.g. relatively high glass transition temperatures of at least 215 ∘ C, which were inversely proportional to the molecular weight between the crosslinks, high thermal decomposition temperature and high activation energies for the decomposition of cured resins. Determination of their limiting oxygen indices indicates that all the homopolymers are characterized as 'self-extinguishing' materials.
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