•The maximum inlet velocity of the filament is determined according to the process parameters.•The velocity field, shear rate and viscosity in the nozzle were determined by analytical study and ...numerical simulation.•The shear rate is maximum for high inlet velocity near the internal wall.•The extrudate shape agrees with the numerical simulation: the extrudate undergoes severe deformation at high shear rate.
Fused filament fabrication (FFF) is one of the various types of additive manufacturing processes. Similar to other types, FFF enables free-form fabrication and optimised structures by using polymeric filaments as the raw material. This work aims to optimise the printing conditions of the FFF process based on reliable properties, such as printing parameters and physical properties of polymers. The selected polymer is poly(lactic) acid (PLA), which is a biodegradable thermoplastic polyester derived from corn starch and is one of the most common polymers in the FFF process. Firstly, the maximum inlet velocity of the filament in the liquefier was empirically determined according to process parameters, such as feed rate, nozzle diameter and dimensions of the deposited segment. Secondly, the rheological behaviour of the PLA, including the velocity field, shear rate and viscosity distribution in the nozzle, was determined via analytical study and numerical simulation. Our results indicated the variation in the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate attained its maximum value near the internal wall at high inlet velocities and smaller diameters. Finally, the distribution of the viscosity along the radius of the nozzle was obtained. At high inlet velocity, several defects appeared at the surface of the extrudates. At the highest shear rates, the extrudates underwent severe deformation. The defects predicted via numerical simulation were reasonably consistent with that observed from an optical microscope. Hence, these results are effective for selecting the printing parameters (i.e. nozzle diameter, feed rate and layer height) to improve the quality of the manufactured parts.
•Hygrothermal ageing causes various phenomena on the composite material surfaces, which can be problematic for achieving good bonding.•Atmospheric plasma treatment allows, despite slight thermal ...degradation, to chemically activate unaged and aged surfaces by oxygen grafting.•Desorption is found on the aged treated surfaces because of the thermal action of plasma.
In this paper, the effects of hygrothermal ageing and atmospheric plasma surface treatment on a 3D carbon/epoxy-amine woven composite material are studied. The goal is to study the surface evolution of the materials in terms of chemical composition and morphology. Plasma treatment is applied on new and hygrothermally aged samples in order to analyse its contribution to the surface modifications and degradations. It appears that hygrothermal ageing has irreversible absorption behaviour causing hydrolysis, oxidation and particle losses, which modifies the surface chemistry and topology. On the other hand, the atmospheric plasma causes oxidation of the matrix. Indeed, when a repair is necessary, the damaged part could evolve due to moisture absorption related to ageing. As the fibres are exposed, the topology and surface chemistry are modified. Nevertheless, it allows to desorb the humidity adsorbed on the surface and reach an oxidation level similar to unaged treated samples.
The hygrothermal ageing of epoxy resins and epoxy matrix composite materials has been studied many times in the literature. Models have been developed to represent the diffusion behaviour of the ...materials. For reversible diffusions, Fick, Dual–Fick and Carter and Kibler models are widely used. Many parameters, correlated or not, have been identified. The objectives of this review by statistical analysis are to confirm or infirm these correlations, to highlight other correlations if they exist, and to establish which are the most important to study. This study focuses on the parameters of the Fick, Dual–Fick and Carter and Kibler models. For this purpose, statistical analyses are performed on data extracted and calculated from individuals described in the literature. Box plot and PCA analyses were chosen. Differences are then noticeable according to the different qualitative parameters chosen in the study. Moreover, correlations, already observed in the literature for quantitative variables, are confirmed. On the other hand, differences appear which may suggest that the models used are inappropriate for certain materials.
•Identification of PT30 resin degradation products by TGA-IR and TGA-MS.•Proposal of a degradation mechanism for PT30 resin in a nitrogen atmosphere.•Identification of the initiation degradation ...reaction based on the results of Density Functional Theory (DFT) calculations which highlight the less energetic network bonds.•Description of each step in the chain scissions of the PT30 resin.•Description of each step in the creation of degradation products.
The non-isothermal thermal degradation of the cured phenolic triazine thermoset resin (PT30) was considered under nitrogen atmosphere. Thermogravimetric analyses (TGA) showed that the degradation mechanism was decomposed in three main steps occurring at 440°C, 550°C, and 720°C. To understand the chemical reactions that happen, TGA experiments were coupled with the analyses of the gaseous products by Fourier transform infrared detection (TGA/FTIR) and by mass spectrometry (TGA/MS). A degradation mechanism is proposed based on these experimental results and on Density Functional Theory (DFT) calculations. It was found that carbon dioxide is the main degradation product generated by the oxygen-carbon chain scissions. In the second step, triazine rings’ rupture led to the formation of cyanide hydrogen and probably cyanic/isocyanic acid. Then, various aromatic compounds are produced from chain scissions and molecules’ recombination. Analyses of these degradation products contributed to proposing assumptions of thermal degradation mechanisms of the PT30 resin.
Adhesives with a variation of properties along the bondline are appealing to the joining industry, yet few developments give easy, versatile implementations and at the same time a control over the ...toughness of the joints. We herein present an original methodology to control the variation of properties in functionally graded epoxy adhesives (FGAs). The FGAs are obtained by putting into contact two plots of compatible adhesives, where the two plots occupy each half of the aluminum substrates. Diffusion of thermoplastic, triblock copolymers in the epoxy-amine adhesive within the joint provokes a gradient of copolymers, inducing in turn a variation of properties along the overlap. We use a driven wedge test (DWT) to assess the variation of properties within the FGAs, by continuously inserting a wedge in the unbonded part of the sample. We discuss on the contribution of the ductility and resilience of the FGAs to the overall energy dissipated, which is found to be superior for FGAs, compared to homogenously filled adhesives. We infer this result to the heterogeneous spatial distribution of the copolymers in the FGAs, due to the diffusion.
Moisture content measurements are performed on scrapped Outlet Guide Vanes (OGV) that have operated in different climates. These measurements are made by three Karl Fischer titration methods. The ...results are separated into two parts. On one side, a comparison of these different techniques highlights their advantages and disadvantages. The methods for studying the samples and the duration of the tests differ. The standard method is not sufficient to extract all the water from the samples. The chemical extraction and grinding methods provide higher water content. On the other side, a mapping of the water content through three scrapped OGV blades is performed with the Karl Fischer titration. Differences are observed according to the service area climate. Concentration gradients are also visible within the part, with more water at the leading edges and less water in the foam. Parts that have flown in hot and humid regions have the lowest water contents by standard Karl Fischer titration. These measurements are compared with the analysis of the damage they have been subjected to. They allow to highlight the composite material degradation, manifested by resin erosion, which is more significant for parts that have operated in wet and humid areas. This erosion involves a lower resin percentage and could explain the lower water contents measured.
Several researchers have examined the interest in using a thermoplastic to increase thermoset polymers' shock resistance. However, fewer studies have examined the nature of the mechanisms involved ...between both kinds of polymers. This was the objective of our work, which was carried out using a gradual approach. First, we describe the synthesis of a poly(ether ether ketone) oligomer (oPEEK) with hydroxyl terminations from the reaction of hydroquinone and 4,4'-difluorobenzophenone in N-methyl-2-pyrrolidone. Then, the main physicochemical properties of this oligomer were determined using different thermal analyses (i.e., differential scanning calorimetry (DSC), thermogravimetric (ATG), and thermomechanical analyses) to isolate its response alone. The chemical characterisation of this compound using conventional analytical chemistry techniques was more complex due to its insolubility. To this end, it was sulfonated, according to a well-known process, to make it soluble and enable nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) experiments. Additional information about the structural and chemical characteristics of the oligomer and its average molecular weight could thus be obtained. The synthesis of an oligoPEEK with α,ω-hydroxyl end-groups and a molecular weight of around 5070 g/mol was thus confirmed by NMR. This value was in accordance with that determined by SEC analysis. Next, the reaction of oPEEK with an epoxy prepolymer was demonstrated using DSC and dynamic rheometry. To this end, uncured mixtures of epoxy prepolymer (DGEBA) with different proportions of oPEEK (3, 5, 10 and 25%) were prepared and characterised by both techniques. Ultimately, the epoxy-oPEEK mixture was cured with isophorone diamine. Finally, topological analyses were performed by atomic force microscopy (AFM) in tapping mode to investigate the interface quality between the epoxy matrix and the oPEEK particles indirectly. No defects, such as decohesion areas, microvoids, or cracks, were observed between both systems.
The manufacturing of composites based on reactive thermoplastic polyamide 6 (PA6), reinforced with glass particles or fibers for structural applications, is quite sensitive to the state of the ...interface. Surface hydroxyls present at the glass surface can completely inhibit both the PA6 polymerization and crystallization processes. Care must then be exerted when tuning the interfacial chemistry in this system. This work demonstrates how an adequate choice of silane coupling agent, combined with a precise surface grafting methodology and tight control of hydroxyl groups density on glass particulates, yields kinetics and degrees of polymerization and crystallization comparable to the pure PA6 resin. Various silanes were grafted onto the microparticles and their surfaces were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, confocal laser scanning microscopy and contact angle measurements. The activator was also grafted onto the glass surface to initiate polymerization directly from the surface. The results showed that all treated glass particles surfaces allowed obtaining a high degree of conversion but with varying polymerization and crystallization kinetics. The results provide fundamental information on the role of the surface chemistry of glass reinforcements on the polymerization and crystallization of PA6, which are essential for the proper control of composite manufacturing.
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Reactive thermoplastics matrices offer ease of processing using well-known molding techniques (such as Resin Transfer Molding) due to their initially low viscosity. For Polyamide 6 (PA6)/glass ...composites, the hydroxyl groups on the glass surface slow down the anionic ring-opening polymerization (AROP) reaction, and can ultimately inhibit it. This work aims to thoroughly control the hydroxyl groups and the surface chemistry of glass particulates to facilitate in situ AROP-an aspect that has been barely explored until now. A model system composed of a PA6 matrix synthesized by AROP is reinforced with calcinated and silanized glass microparticles. We systematically quantify, by TGA and FTIR, the complete particle surface modification sequence, from the dehydration, dehydroxylation and rehydroxylation processes, to the silanization step. Finally, the impact of the particle surface chemistry on the polymerization and crystallization of the PA6/glass composites was quantified by DSC. The results confirm that a careful balance is required between the dehydroxylation process, the simultaneous rehydroxylation and silane grafting, and the residual hydroxyl groups, in order to maintain fast polymerization and crystallization kinetics and to prevent reaction inhibition. Specifically, a hydroxyl concentration above 0.2 mmol OH·g−1 leads to a slowdown of the PA6 polymerization reaction. This reaction can be completely inhibited when the hydroxyl concentration reaches 0.77 mmol OH·g−1 as in the case of fully rehydroxylated particles or pristine raw particles. Furthermore, both the rehydroxylation and silanization processes can be realized simultaneously without any negative impact on the polymerization. This can be achieved with a silanization time of 2 h under the treatment conditions of the study. In this case, the silane agent gradually replaces the regenerated hydroxyls. This work provides a roadmap for the preparation of reinforced reactive thermoplastic materials.
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