Développement et caractérisation d'un procédé de fabrication de composites et biocomposites à base de nanoparticules d'argile et de résine polyester insaturée destinés à l'industrie du transport.

RÉSUMÉ Depuis les dix dernières années, l’ajout de nanoparticules dans la fabrication de pièces en matériaux composites provoque un intérêt croissant grâce aux nombreuses améliorations des propriétés observées une fois combinées à une matrice polymère et à un renfort fibreux. Bien que récente, cette technologie est en plein développement et est promise à un brillant avenir. L’attrait principal des nanoparticules est que celles-ci n’agissent pas seulement comme des additifs conventionnels, mais aussi comme un renfort qui apporte une contribution importante au niveau des propriétés générales des matériaux composites. L’obtention de telles propriétés, une bonne compréhension de l’interaction entre les nanoparticules et le polymère est essentielle. Ce projet de maîtrise a pour objectif le développement d’un matériau composite aux propriétés améliorées par l’addition de nanoparticules d’argile dans une matrice de résine polyester insaturée. L’étude vise l’optimisation des propriétés mécaniques de la pièce ainsi que de ses propriétés ignifuges grâce aux nanoargiles et ces améliorations sont de première importance pour l’industrie du transport. Le premier défi a été la dispersion des nanoparticules d’argiles dans une matrice afin d’obtenir une structure homogène sans agglomérats. En effet, ces derniers agissent en tant que concentrateurs de contraintes qui pourraient fragiliser la pièce. Trois différentes techniques de mélange ont été expérimentées dont la sonication, le mélange à haut cisaillement (HSM) et le mélange manuel. Dépendamment du choix de la technique de dispersion, différentes structures peuvent être obtenues, l’idéal étant une exfoliation des nanoparticules. De plus, cette dispersion dépend grandement de la compatibilité nanoargile-polymère ainsi que du choix de la technique de dispersion. Des études rhéologiques ont été accomplies afin de caractériser la structure interne des nanocomposites obtenus. Dans un premier temps, des mesures en cisaillement simple ont illustré une augmentation de la viscosité de l’ordre de 3 décades. De plus, un fort comportement non-Newtonien rhéofluidifiant est observé pour le mélange obtenu par HSM après l’addition et la dispersion des nanoparticules. Ce comportement se définit par une structure initiale désorganisée des feuillets et est dû à la baisse de la mobilité des chaînes polymères. Des mesures en mode oscillatoire à faible amplitude dans le domaine linéaire ont illustré un comportement de type « gel faible » pour les mélanges HSM. Cet état est régit par de fortes interactions entre les nanoargiles et la matrice indiquant une probable exfoliation des----------ABSTRACT For the ten last years, the addition of nanoparticles in the manufacturing process of composite material has a growing interest due to the enhancement of many properties obtained once they are combined to a polymeric matrix and a fibrous reinforcement. Although this technology is recent, it has a brilliant future ahead. Nanoparticles are not just usual additives, they also act as a reinforcement that makes an important contribution to the composite performance and in order achieve those improvements, a good understanding of the interaction between nanoparticles and the polymer is essential. The purpose of this project is to develop a composite with improved properties by the addition of clay nanoparticles in the unsaturated resin polyester matrix. This study seeks the general improvement of composite mechanical properties as well as its fireproof properties with the addition of nanoclays. This aspect would be most useful for the transport’s industry. The first challenge was the dispersion of nanoclays in a polymeric matrix to obtain a homogeneous structure without agglomerates. Three techniques were compared: manual mixing, sonication and high shear mixing (HSM). Various structures can be obtained depending on the dispersion technique, the ideal being exfoliation, i.e. a homogenized distribution of polymer between silicate nano-layers in order to increase matrix properties. This dispersion mainly depends on compatibility between clay and polymer. Rheological studies were accomplished in order to characterize the internal structure of manufactured nanocomposites. First, simple shear measurements showed an increase in viscosity of about 3 decades for HSM blends. Moreover, strong non-Newtonian behavior was observed for the HSM mixtures after the addition of nanoparticles and dispersion into the unsaturated polyester matrix. This behavior is defined by an initially disorganized structure of clay layers due to the decrease of polymer chains mobility. Later on, small amplitude oscillatory shear measurements in the linear viscoelastic zone illustrated a solid-like behavior for HSM mixtures. This state is governed by strong interactions between the nanoclay particles and the polymer indicating a probably exfoliated structure. The scanning electron microscopy images showed a reduction of the agglomerate’s size for the type of dispersion compared to manual mixing and sonication

A Study of Nanoclay Reinforcement of Biocomposites Made by Liquid Composite Molding

Liquid composite molding (LCM) processes are widely used to manufacture composite parts for the automotive industry. An appropriate selection of the materials and proper optimization of the manufacturing parameters are keys to produce parts with improved mechanical properties. This paper reports on a study of biobased composites reinforced with nanoclay particles. A soy-based unsaturated polyester resin was used as synthetic matrix, and glass and flax fiber fabrics were used as reinforcement. This paper aims to improve mechanical and flammability properties of reinforced composites by introducing nanoclay particles in the unsaturated polyester resin. Four different mixing techniques were investigated to improve the dispersion of nanoclay particles in the bioresin in order to obtain intercalated or exfoliated structures. An experimental study was carried out to define the adequate parameter combinations between vacuum pressure, filling time, and resin viscosity. Two manufacturing methods were investigated and compared: RTM and SCRIMP. Mechanical properties, such as flexural modulus and ultimate strength, were evaluated and compared for conventional glass fiber composites (GFC) and flax fiber biocomposites (GFBiores-C). Finally, smoke density analysis was performed to demonstrate the effects and advantages of using an environment-friendly resin combined with nanoclay particles

A Comparative Study of Dispersion Techniques for Nanocomposite Made with Nanoclays and an Unsaturated Polyester Resin

Over the last few years, polymer/clay nanocomposites have been an area of intensive research due to their capacity to improve the properties of the polymer resin. These nanocharged polymers exhibit a complex rheological behavior due to their dispersed structure in the matrix. Thus, to gain fundamental understanding of nanocomposite dispersion, characterization of their internal structure and their rheological behavior is crucial. Such understanding is also key to determine the manufacturing conditions to produce these nanomaterials by liquid composite molding (LCM) process. This paper investigates the mix of nanoclays particles in an unsaturated polyester resin using three different dispersion techniques: manual mixing, sonication, and high shear mixing (HSM). This paper shows that the mixing method has a significant effect on the sample morphology. Rheology, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) characterization techniques were used to analyze the blends morphology and evaluate the nanoclays stacks/polymer matrix interaction. Several phenomena, such as shear thinning and premature polymer gelification, were notably observed

In-service Behaviour of Flax Fibre Reinforced Composites for High Performance Applications

The use of flax fibres in the composites industry has been steadily growing, thanks to their good mechanical properties, manufacturing effectiveness, acoustic and thermal insulation, good vibration damping, low density and renewability. Flax fibres are a good alternative to less sustainable fibres, such as glass fibres, and they are good candidates to be used for high performance composite applications. The performance of flax fibre composites is believed to be controlled by the intrinsic properties of the flax fibres and the polymer matrix as well as the textile architecture features (e.g. twist). To achieve a good understanding of these effects on the flax composite properties, the following methodology was are undertaken: 1 - Understanding the effect of textile architecture/matrix combinations on the quasi-static mechanical behaviour of flax composites; 2- Investigation of the internal geometry of the flax composite and their implementation in modelling tools to predict the quasi-static properties; 3- Evaluation of the effect of fibre architecture on the impact and fatigue behaviour of flax composites; 4- Environmental impact assessment of flax composites end-of-life technologies and a comparative life cycle assessment of the flax composites in comparison to standard materials for two automotive cases. These studies were carried on using commercially available textile architectures (random mat, plain weave, twill 2x2, quasi-UD and UD) and two types of matrices, a thermoset epoxy and a thermoplastic maleic anhydride polypropylene (MAPP). The internal geometry of textile reinforcements is known for having a significant influence on the mechanical properties of composites. The study of the quasi-static properties (tensile and flexural) showed that the matrix type intrinsic properties have an important effect of the stiffness and strength properties of the composite. No large difference between the different types of woven fabric was seen, although the effect of specific reinforcement geometry parameters (crimp, twist, weave style, wet or dry spun yarns) could be identified. With the quasi-static properties known, the second step of this work aimed to predict these data through modelling. The combination of the textile features with the effective mechanical properties of the fibre/yarn and the matrix properties would make an easy tool to assess the potential of each textile architecture combination, while saving time on the trial-and-error methodology. The internal geometry was analysed via micro-CT imaging. The effective properties of the fibre/yarn used in the textile were assessed using the impregnated fibre bundle test method (IFBT). These parameters were then inputted into the Wisetex-Lamtex-Texcomp trio of software to reconstruct the textile 3D model and predict its quasi-static properties. The results showed that the predicted moduli were comparable to the experimental results with a maximal variation of 10%. The investigation of the impact and fatigue properties of flax-based composites is key in order to understand which material parameters determine the safety and longevity of flax composite products. For impact, the matrix choice was found to greatly influence the absorbed energy as well as the damage area. The absorbed energy at perforation for the flax-MAPP composite was more than 50% higher than for the flax-epoxy one. Furthermore, the use of a MAPP instead of epoxy led to a decreased impact damage area by 38% to 59% with limited delaminations. The decrease of the flexural properties after impact of the flax-MAPP composite was marginal, which is related to the increased absorbed energy per area, while the flax-epoxy composites experienced a stronger decline in properties after impact. The hypothesis that the presence of delaminations has an important influence on the impact performance of the flax composites has been proved wrong, since a limited amount of small delaminations was seen after a non-perforation impact. This was due to the high interlaminar fracture toughness properties of flax composites, which increases by at least 2-3 times over that of the unreinforced brittle epoxy polymer. The tensile toughness was found to be a good indicator of the capacity of a material to sustain perforation or non-perforation impact. The characterization of the tension-tension fatigue properties of flax-epoxy composites showed that the fibre architecture has a strong effect on the fatigue behaviour, where higher quasi-static strength and modulus combinations present the best fatigue characteristics. They have a delayed damage initiation and increased fatigue life as well as a reduced damage propagation rate combined with higher energy dissipation in the early stages of fatigue loading. Furthermore, a comparison with a glass fibre benchmark showed that the behaviour of flax-epoxy composites is comparable to glass fibre reinforced composites, when expressed in terms of specific stress (stress/density) and thus, flax composites are suitable for many new or existing industrial applications. To close the life cycle loop of the flax composite product, three end-of-life (EOL) options were investigated for the flax-MAPP composites: chemical recycling, mechanical recycling and incineration. It was found that the chemical recycling technique is feasible based on the mechanical properties of the recycled composite. However, its processing time, chemicals needed and equipment have negative effects on the environment. The second method, the mechanical recycling, resulted in a recycled, injection moulded composite with discontinuous fibres and hence somewhat lower mechanical properties compared to those of fresh random mat composites. The main advantage of the mechanical recycling technique is the speed of the process. Very large quantities of waste can be shredded and processed into new components while reducing the environmental burden of producing fresh MAPP and flax fibre. The last EOL method studied was incineration with energy recovery and it has been found to be a good alternative as well since all the material can be fully combusted and embodies a relatively high calorific value. Finally, to justify the use of flax composites instead of standard materials, two cradle-to-grave comparative life cycle assessments (LCA) were carried on for two automotive cases, a car roof (flexural design) and a bumper (impact design). A mass factor methodology was used in order to fairly compare equivalent amounts of flax and glass fibre based on the mechanical performance that need to be achieved. For the impact design case, the results of the life cycle analysis showed that the replacement of glass composite by flax composite was beneficial in the 40% and 50% fibre volume fraction case. However, it was not the case for the 30% fibre volume fraction case since the mass factor was higher than 1. This means that, at 30% fibre volume fraction, a higher amount of flax (1.11 kg vs 1 kg of glass fibres) is needed to be used in a composite to fulfil the same impact resistance performance. For the flexural design case, it was found that the use of flax composite has lower environmental impact than their glass composites counterparts. Overall, the LCA results showed that flax fibre composites are an environmentally favourable choice in comparison to glass fibre composites. However, the trade-off between mechanical properties has to be evaluated for each design case specifically.status: publishe

Interlaminar fracture toughness of flax-epoxy composites

The purpose of this study was to determine the influence of fibre architectures on the interlaminar fracture toughness and tensile toughness of flax fibre epoxy composites. The fracture toughness was investigated for both Mode I (GIC) and Mode II (GIIC) for seven flax-epoxy architectures: one plain weave, two twill 2 2 weaves, a quasi-unidirectional and a unidirectional architecture, the UD’s being tested in both [0,90] and [90,0] composite lay-ups. The results of the Mode I and Mode II showed promising results of the flax-epoxy composite performance. The addition of flax fibre increases the GIC and GIIC of the composites over that of the unreinforced brittle polymer by at least two to three times. Further improvements are made with the use of woven textiles. The tensile toughness was found to be a good indicator of the capacity of a material to sustain perforation or non-perforation impact.status: publishe

Automatic transformation of 3D micro-CT images into finite element models with anisotropic local properties

Finite element models derived from micro-CT images can be used for modelling of the actual material geometry and prediction of mechanical properties. The primary direction of anisotropy in a composite material is determined by the orientation of fibres, which can be calculated by means of the structure tensor. This paper presents results on direct conversion of a 3D micro-CT image into the finite element model with anisotropic local mechanical properties of the reinforcement.status: publishe

Comportement en fatigue et impact des composites à base de lin

L’étude présentée s’intéresse à la caractérisation et à l’évaluation des propriétés mécaniques, ainsi que de la résistance à l’impact et le comportement en fatigue pour des composites lin/époxy ayant différentes architectures et fabriqué par moulage transfert de résine (RTM). Une meilleure compréhension de ces comportements permettront la prédiction des propriétés à long terme afin d'évaluer la viabilité et la durabilité à long terme de ces matériaux. Les essais mécaniques ont montré qu’à fraction volumique égale de 40%, la toile et le sergé de lin ont une rigidité similaire d’environ 12.5GPa. On trouve aussi des valeurs de 7.2GPa, 18GPa et de 22,2 GPa pour le mat, quasi-UD et UD respectivement. Ces résultats sont cohérents avec les valeurs trouvées dans la littérature [1, 2]. Lors des essais de fatigue, il a été observé que la durée de vie en fatigue de lin toile/époxy est plus élevé que dans le cas du composite verre toile/époxy [3] (voir Figure 2b). De plus, le Lin_mat et le Verre_toile ont un comportement à long terme comparable, mais le Verre_toile a une durée de vie moindre dans le Lin_toile, ce qui démontre la possibilité de remplacer la fibre de verre par du lin. Par la suite, les résultats des tests d’impact accomplis sur les même composites montrent une absorption d'énergie plus élevé de près de 25% dans le cas des architectures sergé 2x2 et du laminé quasi-UD comparativement à la toile et au laminé UD.status: publishe

Fatigue behaviour of Flax composites: Influence of fibre architecture

As of today, a major lack of data on natural fibre durability properties, such as fatigue behaviour and impact resistance, which limits the use of these fibres for structural applications. This study seeks to assess and compare the mechanical properties and fatigue behaviour of flax fibre reinforced composites for various architectures which is later on compared to glass fiber. Sample were processed using Resin Transfer Moulding (RTM) process to obtain high quality samples. Quasi-static tensile test were carried to obtain the stiffness and ultimate tensile strength (UTS) of flax/epoxy composites. This data is crucial to understand the effect of architecture on the intrinsic properties of a biocomposites part. UTS values vary from 248 MPa for the unidirectional composite (UD) to 85 MPa for the chopped strand mat (MAT) as well as 190 MPa for twill 2x2 weave (TW) and 120MPa for plain weave (PW), at an equivalent fibre volume fraction of 40%. These values (So) are later used to carry on the fatigue testing. Tension–tension fatigue tests with a ratio of R = 0.1 at a frequency of 5Hz as well as loading level (S/So) varying from 0.3 to 0.9 UTS, were conducted at 22oC room temperature. Results showed that at comparable normalised stresses, MAT flax composites has a comparable life as PW glass preforms and can resist more than 1x106 cycles at 0.3 load level. As well, flax PW has an enhanced fatigue performance compared to glass with the first being able to sustain around 100 000 thousand cycle and the second only 20 000 cycles at a 0.65 load level. This results may help widens the application domain of possible application with flax fibre in replacement of glass by flax.status: publishe

Impact resistance, damage and absorbed energy behaviour of flax-based composites

The present study focuses on the characterization and evaluation of mechanical properties and resistance to impact of composites reinforced with flax fibres combined to an epoxy or PPMA matrix. A better understanding of this behaviour allows the prediction of long-term properties to assess the viability and long-term durability of these materials. The effect of fibre architectures on the impact resistance of flax-based composite is studied. Composites were manufactured using Resin Transfer Moulding (RTM) and Compression Moulding. The assessment of the impact properties of natural fibres-based composites is essential in order to ensure their use through time. This study focuses on the evaluation of the impact properties for six preforms architectures. The absorbed energy after the composite perforation as well as damage characterization after impact are analysed.status: publishe

Impact properties characterization of flax fibre-reinforced composites

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