Vulcanization degree influence on the mechanical properties of Fiber Reinforced Elastomeric Isolators made with reactivated EPDM

Rubber is well known as the basic material for some structural devices, such as seaport fenders and seismic isolators. In practice, to seismically isolate a structure it is necessary to interpose between the foundation and the superstructure a rubber device that increases the period of the superstructure, a feature that allows the structure to be “transparent” to the seismic excitation. A seismic isolator is constituted typically by a package of several rubber pads 1–2 cm thick vertically interspersed with either steel laminas or FRP dry textiles suitably treated. In this latter case the isolator is called FREI (Fiber Reinforced Elastomeric Isolator). FREIs exhibit light weight, easy installation and low cost. In this study, recycled rubber in the form of reactivated EPDM has been used to produce very low cost FREIs, combined with glass fiber reinforcement. To be ready for structural application, the rubber used must be vulcanized correctly to properly create the polymer crosslinking. However, all rubber mechanical properties are strongly affected by curing temperature and curing time. Here, the mechanical properties of a typology of FREI conceived and produced by the authors in prototypes are evaluated through a series of experimental tests and numerical computations, taking into account the different levels of vulcanization degree. Shore A hardness test, uniaxial tensile test, and relaxation test have been conducted and verified through Finite Element (FE) modeling. All collected data allow to precisely determine the curing time and temperature to use in the industrial production to obtain optimal output mechanical properties for FREIs

Dynamic stiffness and damping prediction on rubber material parts, FEA and experimental correlation

The final objective of the present work is the accurate prediction of the dynamic stiffness behaviour of complex rubber parts using finite element simulation tools. For this purpose, it becomes necessary to perform a complex rubber compound material characterisation and modelling work; this needs two important previous steps. These steps are detailed in the present document together with a theoretical review of viscoelastic visco-elasto-plastic models for elastomers. Firstly, a new characterisation method is proposed to determine the degree of cure of rubber parts. It is known that the degree of cure of rubbers bears heavily on their mechanical properties. This method consists of the correlation of swelling results to rheometer data achieving a good agreement. Secondly, the influence of the strain rate used in static characterisation tests is studied. In this step, a new characterisation method is proposed. The latter characterisation method will be used to fit extended hyperelastic models in Finite Element Analysis (FEA) software like ANSYS. The proposed method improves the correlation of experimental data to simulation results obtained by the use of standard methods. Finally, the overlay method proposed by Austrell concerning frequency dependence of the dynamic modulus and loss angle that is known to increase more with frequency for small amplitudes than for large amplitudes is developed. The original version of the overlay method yields no difference in frequency dependence with respect to different load amplitudes. However, if the element in the viscoelastic layer of the finite element model are given different stiffness and loss properties depending on the loading amplitude level, frequency dependence is shown to be more accurate compared to experiments. The commercial finite element program Ansys is used to model an industrial metal rubber part using two layers of elements. One layer is a hyper viscoelastic layer and the other layer uses an elasto-plastic model with a multi-linear kinematic hardening rule. The model, being intended for stationary cyclic loading, shows good agreement with measurements on the harmonically loaded industrial rubber part

Development of rubber–thermoplastic blends from ground tyre rubber and waste polypropylene

The aim of this thesis was to develop and process viable rubber–thermoplastics blends from ground tyre rubber (GTR) and waste polypropylene (WPP). The use of WPP with waste rubber in blends is novel, although limited studies have been carried out on virgin polypropylene (PP)–waste rubber blends. The Delink pretreatment for the GTR is also a novel technique used for property enhancement. To achieve the aim, a number of GTR/WPP blends were prepared, in different blend compositions (from 0 to 100 wt% of each polymer), at different processing parameters, and with two compatibilizing systems. One system called dimaleimide contained N-N' meta-phenylene dimaleimide (HVA-2) as the compatibilizer and either di(tert-butylperoxyisopropyl) benzene (DTBPIB) or 2-2'-dithiobenzothiazole (MBTS) as an activator. The other system contained phenolic resin compatibilizer (SP 1045H resin) and stannous chloride (SnCl2) activator in two forms: anhydrous and dihydrated. The compatibilizer level varied from 0 to 5 pphp, while the activator level varied from 0 to 1 pphp. [Continues.

Thermoplastic Vulcanizate Nanocomposites Based on Polypropylene/Ethylene Propylene Diene Terpolymer (PP/EPDM) Prepared by Reactive Extrusion

Les élastomères thermoplastiques (TPEs) représentent un groupe important de matériaux polymères, plus précisément des mélanges de polymères, qui possèdent un comportement élastique similaire aux matériaux caoutchouteux mais contiennent des liens thermoréversibles les rendant faciles à manipuler via des procédés de traitement des thermoplastiques. Une catégorie importante de TPEs consiste en des matériaux à base de polyoléfine, dont de polypropylène (PP) et de terpolymère éthylène-propylène-diène (EPDM) qui sont connus dans le marché pour leurs propriétés physique et mécanique intéressantes obtenues grâce à leur faible tension interfaciale (~0.3 mN/m) et à leur compatibilité de phase. Durant les dernières décennies les mélanges d’EPDM/PP ont, en raison de l’importance commerciale, attiré l’attention des milieux industriels et académiques afin d’améliorer leur comportement élastique et /ou leurs propriétés techniques, et étendre leurs champs d’application. Cette thèse s’intéresse principalement à l’usage des nanotechnologies par l’incorporation de la nano-argile dans la phase thermoplastique de ces matériaux. Elle étudie l’effet de différents niveaux de dispersion de la nano-argile sur la co-continuité des mélanges réactifs et la liaison interfaciale des mélanges préparés par l’extrusion réactive. De plus, la recherche portée dans ce travail a aussi pour but de déterminer le comportement élastique de ces mélanges en présence de la nano-argile et cela en relation avec le niveau de dispersion de ces particules dans les mélanges. Par conséquent, le développement morphologique et les propriétés fonctionnelles et techniques des nanocomposites thermoplastiques vulcanisées (TPV) ont été investigués. Pour ce travail, différentes sortes de polymères polypropylène-g-maléique anhydride ont été utilisées afin d’élucider l’effet de l’agent de comptabilisation sur le niveau de dispersion de la nano-argile dans la phase thermoplastique. Les analyses par diffractométrie de rayons X (XRD), la microscopie électronique à transmission (TEM), et la microscopie électronique à balayage (SEM) des mélanges préparés confirment que les nanocomposites PP se modifient d’une structure intercalée vers une coexistence des tactoïdes intercalés et des couches exfoliées nommées des nanocomposites ‘partiellement exfoliées’. Parmi les différents paramètres de performance de l’agent de comptabilisation, sa relaxation se corrèle directement avec les résultats de la caractérisation des nanocomposites; un temps de relaxation plus long de l’agent de comptabilisation est associé avec une meilleure dispersion de la nano-argile dans les mélanges. Pour étudier la co-continuité du développement des mélanges non-réactifs, l’EPDM et les nanocomposites PP ont été mélangés à l’état fondu avec différentes compositions en utilisant un mélangeur interne. Basé sur le mesure de continuité des TPEs et de leurs nanocomposites associées pour la phase thermoplastique et élastique, il est déduit que la présence de nano-argile réduit la plage de composition de la co-continuité et altère ses caractéristiques symétriques. Toutefois, cet effet est plus prononcé plus chez les nanocomposites intercalées que chez les nanocomposites partiellement exfoliées. Une meilleure dispersion de la nano-argile limite la réduction de la continuité de la phase thermoplastique de sorte que l’indice de continuité de la phase thermoplastique des nanocomposites TPE partiellement exfoliées préparées avec un contenu plus élevé d’EPDM (i.e. à 70 wt%) devient plus importante que celle des TPEs sans nano-argile. Ces résultats montrent qu’il est possible d’utiliser plus d’EPDM dans les mélanges en utilisant des nanocomposites partiellement exfoliées avant la formation de la matrice de dispersion de structure qui limite la production du TPV. Néanmoins, il s’avère important de mentionner que les radiations gamma ont été utilisées pour stabiliser la morphologie d’EPDM et estimer la continuité du PP en utilisant des extractions solubles et des techniques de gravimétrie. De plus, l’effet de la continuité sur le comportement rhéologique des nanocomposites TPE a été étudié. La viscosité transitoire s’est montrée plus sensible à l’indice de continuité que les autres fonctions matérielles obtenues en utilisant un balayage en fréquence, des essais de relaxation de contrainte, et les essais de fluage. Il a été montré qu’un indice de continuité d’EPDM plus élevé amène à une baisse de viscosité transitoire normalisée quand la phase thermoplastique est continue; car la déformation des domaines d’EPDM est plus facile que l’altération dans une matrice continue. D’un autre côté, basé sur les expérimence d’extraction et des micrographes SEM, il existe des preuves qui démontrent que l’argile reste principalement dans la phase PP. Les résultats de balayage par la calorimétrie différentielle (DSC) montrent que la présence de nano-argile dans la phase thermoplastique augmente la température de la cristallisation (jusqu’à ~20 °C), ce qui peut s’avérer bénéfique pour les applications de moulage par injection grâce à une solidification plus rapide et un temps de cycle plus court. L’objectif ultime de ce travail est de maximiser le comportement élastique en contrôlant la morphologie du mélange et son niveau de réticulation. Par conséquent, cette étude couvre aussi les effets de la présence de nano-argile et son niveau de dispersion sur la réaction de réticulation des nanocomposites TPV préparées par une extrusion réactive. Ici, la phase élastique a été vulcanisée d’une manière dynamique en utilisant une résine phénolique de diméthylol ou une résine d’octylphénol-formaldéhyde avec du chlorure d'étain déshydraté comme catalyseur. Dans cette étude, la vulcanisation dynamique des TPVs préparés et ses nanocomposites correspondant a été caractérisée en utilisant différents critères tels que : le contenu en fraction soluble, la viscosité et le module élastique G' en déformation dynamique, , la largeur du signal de résonance magnétique nucléaire (RMN), le contenu d’agent de réticulation et la concentration en diène résiduelle. La combinaison de ces paramètres a été jugée suffisante pour décrire le système. Contrairement aux mélanges préparés dans un mélangeur interne dans lequel le niveau de réticulation des nanocomposites TPV est toujours plus bas que celui des TPVs, l’effet de la présence de nano-argile dans les échantillons préparés par extrusion réactive s’avère plus compliqué. Il appert que la différence entre la taille de la réaction de réticulation entre les TPVs et les nanocomposites TPV est plus prononcée pour les échantillons préparés avec une vitesse de vis plus élevée (400 tour par minute (rpm), temps de résidence ~ 65 s). Néanmoins, il n’existe pas de différence significative pour les échantillons préparés avec une vitesse de vis plus basse (200 rpm, temps de résidence ~ 45 s). Pour ces mélanges réactifs, l’analyse de la courbe du couple de mélange en fonction du temps, ainsi que l’analyse des mesures sur la fraction soluble et des micrographes SEM à différentes positions dans l'extrudeuse confirment que la structure co-continue existe au moins avant la deuxième zone de mélange dans une extrudeuse bi-vis en fonctionnement co-rotatif. Autrement dit, la co-continuité des mélanges avant la deuxième zone de mélange n’est pas seulement contrôlée par la vulcanisation dynamique, mais aussi par la présence de nano-argile. Considérant ce fait et basé aussi sur le calcul de la conversion chimique par la mesure des valeurs de concentration de la diène résiduelle obtenu par RMN, il est suggéré que la présence de nano-argile affecte la réaction de réticulation principalement par son influence sur la continuité de la phase d’EPDM dans la structure co-continue qui se forme lors de l’étape initiale du processus de mélange. Il a été démontré qu’une plage de réticulation plus élevée est associée avec un indice de continuité d’EPDM plus haut. À son tour, le niveau de la co-continuité dépend aussi du degré de dispersion de nano-argiles. Aussi, quand la continuité de la phase d’EDPM des deux mélanges est similaire, l’effet de barrière des nano-argiles intensifie la réaction de réticulation par l’augmentation de la concentration de l’agent curatif local. Nos travaux montrent que si l’EPDM dans le système correspondant non-réactif est une phase continue, le niveau de la réaction de réticulation devient plus dépendant de la vitesse de rotation des vis. En autres mots, plus le temps de résidence est long, plus élevé est l’étendue de réticulation. De plus, il est important de mentionner que la valeur de la largeur de base du pic principal en spectroscopie RMN peut seulement être utilisée pour comparer l’étendue de réticulation dans des TPVs dû à l’influence du nano-argile sur la mobilité de la chaîne principale de l’EPDM dans les nanocomposites TPV. L’analyse des mélanges du point de vue de structure des nanocomposites révèle que l’interaction des chaînes de polymères dans les galeries inter-couches des nano-argiles est plus prononcée pour les nanocomposites TPV comparé aux nanocomposites TPE dû à une contrainte de cisaillement plus élevée exercée sur les couches nano-argiles durant la vulcanisation dynamique. Aussi, en augmentant le contenu d’EPDM, l’intercalation du polymère n’a pas été significativement améliorée. Pour les nanocomposites TPV préparés à une vitesse de vis plus élevée (400 rpm), le premier pic de la caractéristique du nano-argile en diffraction rayon X (2 =2.85 , l'espace-d correspondant est 3.1 nm) s’est déplacé à un angle plus bas (2 =0.94 , l’espace-d correspondant est 9.3 nm), tandis que celui des nanocomposites TPV basés sur une compositition partiellement exfoliée a complètement disparu. La dernière partie de cette thèse se penche sur la question de l’influence du niveau de dispersion des nano-argiles, et conséquemment l’étendue de réticulation, sur le comportement élastique et la morphologie des TPVs. Une méthode récemment développée, s’appelant le balayage de la température de relaxation de contrainte (TSSR), a été utilisée pour estimer l’indice d’élasticité des TPVs et des nanocomposites TPV. Cette méthode donne de l’information satisfaisante sur l’étendue de réaction de réticulation. Le comportement élastique des mélanges contenant 50 p/p % et 60 p/p% d’EPDM- dans lesquelles les études morphologiques suggèrent la présence des gouttes élastiques dans le voisinage des particules élastiques de formes irrégulières avec un niveau d’inter-connectivité bas- corrèle avec la taille de la gouttelette élastique. Par conséquent, la présence de nano-argile influence la valeur de l’indice d’élasticité par son effet sur la taille des gouttelettes élastiques qui contrôle le nombre des points de rétraction dans le mécanisme de fluage proposé durant l’essai TSSR. Il faut prendre note que l’augmentation du contenu d’EPDM abaisse le nombre des gouttes et augmente aussi la formation des particules élastiques avec des formes irrégulières. D’un autre côté, la relation directe entre les valeurs de l’indice élastique et la densité de réticulation est seulement observée pour des séries de TPVs qui montrent un réseau extensif bien développé entre les gouttes de forme irrégulière (mélanges contenant 70wt% d’EPDM). Finalement, l’effet de la présence de nano-argile et son niveau de dispersion sur le comportement élastique se démontre par son influence sur la densité de réticulation. ---------- Thermoplastic elastomeric materials (TPEs) are an important class of copolymers or polymer blends that exhibit the typical advantages of conventional rubbers but can be processed with the thermoplastic processing methods. Among different kind of thermoplastic elastomer , those based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) are known to have more interesting properties due to the relatively low interfacial tension between PP and EPDM (~0.3 mN/m). Considering the commercial significance of the mentioned blends, different approaches have been used during the last few decades to improve their rubber like behaviour and/or their engineering properties to expand their fields of applications. In this regard, in the present dissertation, the use of nanotechnology by incorporating the nanoclay in the thermoplastic phase is the major interest subject. The effects of different nanoclay dispersion levels on the co-continuity of non reactive blends and the extent of crosslinking in the blends prepared by reactive extrusion are studied. This research intends to tailor the rubber like behaviour by the nanoclay presence and its dispersion level. Therefore the morphology development along the screw axis and the functional and engineering properties of the prepared thermoplastic vulcanizates nanocomposites are also investigated. For this work, different grades of polypropylene-g-maleic anhydride polymers were chosen to elucidate the effect of compatibilizer on the nanoclay dispersion level in thermoplastic phase. X-ray diffraction (XRD) patterns along with transmission electron microscopy (TEM) and scanning electron microscope (SEM) micrographs confirmed that prepared PP nanocomposites ranged from intercalated structure to a coexistence of intercalated tactoids and exfoliated layers namely "partially exfoliated" nanocomposite. Among various factors affecting the compatibilizer performance, it is shown that only the relaxation behaviour of compatibilizer correlates directly with the nanocomposites characterization results; higher relaxation times of the compatibilizer are associated with better dispersion of nanoclay. To study the co-continuity development of the nonreactive blends, EPDM and the mentioned PP nanocomposites at various compositions were melt blended using an internal mixer. Based on continuity measurements of TPEs and TPE nanocomposites for both thermoplastic and rubber phase, it is shown that the presence of nanoclay decreases the co-continuity composition range and alters its symmetrical feature. However, this effect is more pronounced in the intercalated nanocomposites than in partially exfoliated nanocomposites. It seems that better nanoclay dispersion limits the reduction of the thermoplastic phase continuity in a manner that the continuity index of the thermoplastic phase for partially exfoliated TPE nanocomposite prepared at high EPDM content (i.e. at 70 wt%) is greater than that of corresponding TPE without nanoclay. According to these results, it is possible to shift to higher EPDM content using partially exfoliated system before formation of matrix-dispersed particle structure which limits thermoplastic vulcanizate production. This should be mentioned that gamma irradiation was carried out in order to fix the EPDM morphology to estimate the continuity of PP using the solvent extraction and gravimetry technique. Additionally, the effect of continuity on rheological behaviour of TPE nanocomposites was investigated. The stress growth viscosity was found to be more sensitive to the continuity index than other material functions obtained using frequency sweep, stress relaxation and creep experiments. It seems that a higher EPDM continuity index leads a lower overshoot of normalized stress growth viscosity when thermoplastic phase is continuous because deformation of the separated domains of EPDM is easier than alteration in a continuous network structure. On the other hand, based on extraction tests and SEM micrographs, there are some evidences that clay remain mainly in the PP phase. According to differential scanning calorimetry (DSC) results, the presence of nanoclay in the thermoplastic phase increases the crystallization temperature (up to ~20 °C) that could be beneficial for molding applications, because of the faster solidification and shorter cycle time. The ultimate goal in this field is to maximize the rubber like behaviour by controlling the blend morphology and the level of crosslinking. Therefore, this study also covers the effects of nanoclay presence and its dispersion level on the crosslinking reaction of thermoplastic vulcanizate nanocomposites prepared by reactive extrusion. Here, the rubber phase was dynamically vulcanized using dimethylol phenolic resin or octylphenol-formaldehyde resin along with stannous chloride dihydrate as the catalyst. In the present study, the dynamic vulcanization of the prepared TPVs and corresponding nanocomposites are characterized using different criteria, such as gel content, viscosity and normalized storage modulus in the time sweep tests, nuclear magnetic resonance (NMR) signal line width, bound curative content and residual diene concentration. The combination of the above parameters appears to be sufficient to provide a clear description of the systems. Contrary to the blends prepared in internal batch mixer in which the extent of crosslinking in TPV nanocomposites is always lower than that of TPVs, however, the effect of nanoclay presence in the samples prepared by reactive extrusion is more complicated. It seems that the difference in the extent of crosslinking reaction between TPVs and TPV nanocomposites is more pronounced for the samples prepared at higher screw speed (400 rpm, residence time of ~ 45 s). Whereas, there is no significant difference was found for the samples prepared at lower screw speed (200 rpm, residence time of ~ 65 s). The torque-time curve analysing obtained from internal batch mixer, gel content experiments and SEM micrographs along the extruder axis for the reactive blends confirm that the co-continuous structure exists at least before the second mixing zone of the twin screw extruder. In other words, the co-continuity of the blends before the second mixing zone is not only controlled by dynamic vulcanization but also by the presence of nanoclay. Considering this fact and based on the bound curative content and residual diene concentration values obtained by solid state NMR, it is suggested that nanoclay presence affects the extent of crosslinking reaction mainly through its effect on the continuity of the EPDM phase in the co-continuous structure forming in the initial stage of the mixing process. It is shown that the higher extent of crosslinking is associated with higher continuity index of EPDM. In turn, the level of co-continuity, as mentioned earlier, depends on the degree of dispersion of nanoclay. On the other hand, when the continuity of EPDM phase of two blends is similar, the barrier effect of nanoclays intensifies the crosslinking reaction by increasing the local concentration of curing agent. In our experimental window, if EPDM in the corresponding non-reactive system is a continuous phase, the extent of crosslinking reaction appears to be more dependent on the screw speed. Otherwise, higher residence time would increase the extent of crosslinking. Moreover, it should be mentioned that the backbone peak base width values may be used only to compare the extent of crosslinking in the TPVs due to the influence of nanoclay on the mobility of the backbone of EPDM in TPV nanocomposites. The investigation of the blends, from nanocomposite structure point of view, reveals that intercalation of polymer chains into the interlayer galleries of the nanoclays is more pronounced for the TPV nanocomposites compared to TPE nanocomposites due to the higher shear stress which is exerted on the nanoclay layers during dynamic vulcanization. It should be mentioned that by increasing EPDM content, polymer intercalation was not enhanced significantly. For the TPV nanocomposites based on intercalated system prepared at higher screw speed (400 rpm), the first characteristic peak of nanoclay (2 =2.85 , corresponding d-spacing is 3.1 nm) shifted to the lower angle (2 =0.94 , corresponding d-spacing is about 9.3 nm) while that of TPV nanocomposites based on partially exfoliated system disappeared. The last part of the present study is devoted to find how the dispersion level of nanoclay and consequently the extent of crosslinking change the rubber like behaviour and the morphology of the prepared TPVs. Therefore, recently developed method named temperature scanning stress relaxation (TSSR) was used to estimate the rubber indices of TPVs and TPV nanocomposites. The mentioned method also successfully provided information about the extent of crosslinking reaction. It is shown that the rubber like behaviour of the blends containing 50wt% and 60wt% of EPDM in which morphological studies suggest the presence of the rubber droplets in vicinity of irregular shape rubber particles with a low level of interconnectivity, correlates with the rubber droplet size. Therefore, the nanoclay presence affects the rubber index values mainly through its effect on the size of the rubber droplets that controls the number of retraction points in the proposed buckling mechanism during the TSSR test. It should be mentioned that by increasing the EPDM content, the number of the droplet like domains decreases and more irregular shape rubber particles is formed. On the other hand, the direct relation between rubber index values and the crosslink density is observed only for those series of TPVs showing the fully developed extensive network between irregular shape rubber domains (blends containing 70wt% of EPDM). Hence, the nanoclay dispersion level influences the rubber like behaviour through its effect on the crosslink density

Thermal insulation by heat resistant polymers

Internal insulation in a solid rocket motor is a layer of heat-barrier material placed between the internal surface of the case and the propellant. The primary function of internal insulation is to prevent the rocket motor case from reaching temperatures that may endanger its structural integrity. An extensive experimental and theoretical work in the development and characterization of asbestos-free rubbers for use as rocket motor insulators has been performed. The insulation is based on chopped carbon fiber and/or aramid fiber in the pulp form as fillers for Ethylene Propylene Diene Monomer (EPDM). The first aim of the research is to provide an understanding of the mechanism, the principle, and the process for making polymeric thermal insulants. The second aim is to produce thermal insulants based on polymers with different fillers having different compositions which are capable of working under extreme thermal conditions of 2760 °C (5000 °F). This is through an investigation on the processing, installation, physical, mechanical, thermal and ablative properties of these materials. A hybrid of chopped carbon fiber and Kevlar pulp filled EPDM has been shown to exhibit better thermal, mechanical, physical and ablative properties than its asbestos containing counterpart. Also the prediction of thermal conduction of multiphase thermal insulation composite materials was done using series, parallel, Maxwell Euken and effective medium theory models. Comparison with the measured values allows determining which model estimates best the thermal conductivity of composite insulation material. Development of a suitable optimization technique to reach the best parameters of the selected material was done by doing transient dynamic analysis to determine the response of these materials under a time-varying thermal load. A new type of insulation material using prepregs was developed for the first time. This consists of the development of the prepregs and their assembly to make insulant laminates. This laminate has been shown to exhibit better physical, mechanical, thermal and ablative properties than a hybrid of chopped carbon fiber and Kevlar pulp filled EPDM

Mécanisme de salissage et de nettoyage en surface de matériaux polymères

Résumé: Le développement de l’industrie des polymères fourni de plus en plus de choix pour la formulation de matériaux pour les couvre-planchers. Les caoutchoucs, le PVC et le linoleum sont les polymères habituellement utilisés dans l’industrie des couvre-planchers. Ce projet répond à un problème de facilité de nettoyage des couvre-planchers de caoutchouc qui sont reconnus pour être mous, collants et ayant une surface rugueuse. L’INTRODUCTION couvrira l’état actuel de la recherche sur les couvre-planchers, surtout en regard au problème de la «nettoyabilité». La théorie pertinente et les informations générales sur les polymères, les composites polymériques et la science des surfaces seront introduites au CHAPITRE 1. Ensuite, le CHAPITRE 2 couvrira la méthode utilisée pour déterminer la nettoyabilité, l’évaluation des résultats ainsi que l’équipement utilise. Le CHAPITRE 3, discutera des premières expériences sur l’effet de la mouillabilité, la rugosité et la dureté sur la facilité de nettoyage des polymères purs. Plusieurs polymères ayant des surfaces plus ou moins hydrophobes seront investigués afin d’observer leur effet sur la nettoyabilité. L’effet de la rugosité sur la nettoyabilité sera investigué en imprimant une rugosité définie lors du moulage des échantillons; l’influence de la dureté sera également étudiée. Ensuite, un modèle de salissage/nettoyage sera établi à partir de nos résultats et observations afin de rationaliser les facteurs, ou « règles », qui détrminent la facilité de nettoyage des surfaces. Finalement, la réticulation au peroxyde sera étudiée comme une méthode de modification des polymères dans le but d’améliorer leur nettoyabilité; un mécanisme découlant des résultats de ces études sera présenté. Le CHAPITRE 4 étendra cette recherche aux mélanges de polymères; ces derniers servent habituellement à optimiser la performance des polymères purs. Dans ce chapitre, les mêmes tests discutés dans le CHAPITRE 3 seront utilisés pour vérifier le modèle de nettoyabilité établi ci-haut. De plus, l’influence de la non-miscibilité des mélanges de polymères sera discutée du point de vue de la thermodynamique (DSC) et de la morphologie (MEB). L’utilisation de la réticulation par peroxyde sera étudié dans les mélanges EPDM/ (E-ran-MAA(Zn)-ran-BuMA) afin d’améliorer la compatibilité de ces polymères. Les effets du dosage en agent de réticulation et du temps de cuisson seront également examinés. Finalement, un compatibilisant pré-réticulé a été développé pour les mélanges ternaires EPDM/ (E-ran-MAA(Zn)-ran-BuMA)/ HSR; son effet sur la nettoyabilité et sur la morphologie du mélange sera exposé.Abstract: The development of industrial polymers provides more choices to the design of flooring materials. Rubbers, PVC and linoeleum are the most used polymers in the flooring industry. This project stems from the problem of cleanability (ease of cleaning) of the surface of rubber tile flooring which is known as a soft, sticky and rough surface. In the introduction, the current situation of research on the polymer flooring industry, especially the study on the cleaning problem will be introduced. The relevant theory and general information on polymers, polymer composites and surface science will be introduced in CHAPTER 1. In CHAPTER 2 different approaches, protocols and equipment to evaluate cleanability will be presented. The initial experiments and results (CHAPTER 3) will involve various fundamental concepts on surface wettability, roughness and hardness, as these properties can all influence the surface soiling and cleanability. In single-polymer systems, dozens of polymer materials with a hydrophobic or hydrophilic surface were investigated to observe their soiling and cleaning properties. The effect of roughness was also studied by surface printing method which is used to control the surface topography. Likewise, the influence of surface hardness on cleanability was also investigated with different polymer materials. From the above results and observations, a surface soiling/cleaning model is proposed in attempt to simplify the ― rules ‖ which determine the surface cleanability. Finally, peroxide crosslinking was investigated as a matrix modification method to improve the surface cleanability. The second part of the experiments and results (CHAPTER 4) extends to investigations of polymer blends, in attempt to optimize the performance of single-polymer materials. In this chapter, the surface cleaning model and its relevant rules are examined by the wettability, roughness and hardness tests discussed in CHAPTER 3. The influence of immiscibility on cleaning performance will be discussed in polymer blends from the point of view of thermodynamics (DSC) and morphology (SEM). In order to improve the compatibility in polymer blends, peroxide crosslinking was performed in EPDM/ (E-ran-MAA(Zn)-ran-BuMA) blends. The dosage of curing (cross-linking) agent and curing time were investigated to observe the influence of these experimental conditions on cleanability. Finally, a blend compatibilizer was designed to improve the compatibility of the EPDM/ (E-ran-MAA(Zn)-ran-BuMA)/HSR blends.The compatibilizer prepared by partial pre-crosslinking of EPDM (Nordel) and E-ran-MAA(Zn)-ran-BuMA (Surlyn) was incorpo rated in polymer composites and its influence on cleanability was studied and explained on the basis of changes in morphology of the blend polymer matrix

Polymer Electrolyte Membrane (PEM) fuel cell seals durability

Polymer electrolyte membrane fuel cell (PEMFC) stacks require sealing around the perimeter of the cells to prevent the gases inside the cell from leaking. Elastomeric materials are commonly used for this purpose. The overall performance and durability of the fuel cell is heavily dependent on the long-term stability of the gasket. In this study, the degradation of three elastomeric gasket materials (silicone rubber, commercial EPDM and a developed EPDM 2 compound) in an accelerated ageing environment was investigated. The change in properties and structure of a silicone rubber gasket caused by use in a real fuel cell was studied and compared to the changes in the same silicone rubber gasket material brought about by accelerated aging. The accelerated aging conditions were chosen to relate to the PEM fuel cell environment, but with more extreme conditions of elevated temperature (140°C) and greater acidity. Three accelerated ageing media were used. The first one was dilute sulphuric acid solution with the pH values of 1, 2 and 4. Secondly, Nafion ® membrane suspended in water was used for accelerated ageing at a pH 3 to 4. Finally, diluted trifluoroacetic acid (TFA) solution of pH 3.3 was chosen. Weight change and the tensile properties of the aged gasket samples were measured. In addition, compression set behaviour of the elastomeric seal materials was investigated in order to evaluate their potential sealing performance in PEM fuel cells. The results showed that acid hydrolysis was the most likely mechanism of silicone rubber degradation and that similar degradation occurred under both real fuel cell and accelerated aging conditions. The effect of TFA solution on silicone rubber was more aggressive than sulphuric acid and Nafion® solutions with the same acidity (pH value) suggesting that TFA accelerated the acid hydrolysis of silicone rubber. In addition, acid ageing in all three acidic solutions caused visible surface damage and a significant decrease in tensile strength of the silicone rubber material, but did not significantly affect the EPDM materials. EPDM 2 compound had a desirable (low) compression set value which was similar to silicone rubber and much better than the commercial EPDM. It also showed a very good performance in the fuel cell test rig conforming that it a potential replacement for silicone rubber in PEMFCs

Ground tyre rubber and post-consumer polyethylene reactive injection moulded composite

Post consumer tyres continue to present the community with challenges for their safe and sustainable disposal. They also present an opportunity to divert a significant waste stream in to a valuable resource. This thesis looks into one possible method to recycle post consumer tyres and high density polyethylene won from curb side collection of milk packaging. The study investigates the use of a bromomethyl phenol resin as the basis of a compatibilization chemistry enabling a bond to be formed between the ground tyre rubber particle and the polyethylene matrix. It builds upon the seminal work of Coran & Patel in developing thermoplastic vulcanites and the more recent work of Liu and colleagues. Unlike previous investigators, this work employed a single process to both compound the composite component materials and to form the end product. This single process was carried out using an injection moulding machine that was modified by the addition of a number of automated hoppers that delivered the composite component materials and compatibilization chemistry to the moulder’s screw. Through this system of reactive injection moulding it was demonstrated that both the composite material and product could be formed in a single process. Investigation of the mechanical properties of ground tyre rubber and polyethylene composites using tensile testing techniques was undertaken. The results of tensile testing indicated that the particle matrix bond was formed only when dicumyl peroxide was included in the compatibilization chemistry. This was established from the observation of dense arrays of fibrils joining the rubber particles to the HDPE matrix in samples that had been tested to ultimate failure. The particle matrix bond was not formed when dicumyl peroxide was not present. An investigation was undertaken using X-ray photo spectrometry to examine the bonding chemistry. This revealed the presence of the carbon oxygen carbon sequence at the particle surface when dicumyl peroxide was a component of the compatibilization chemistry. The presence of this sequence of atoms is a necessary, but not sufficient, condition for the Chroman Ring structure to be present in the bond. The presence of this structure would give rise to a more tenacious bonding between particle and matrix than would normally be achieved through either carbon carbon or carbon sulphur cross linking mechanisms. The identification of the Chroman Ring structure in ground tyre rubber and polyolefin composites has not previously been reported in the literature. The contribution made by the particle matrix bond to the overall performance of the composite was investigated using non linear explicit finite element analysis. Two models for the composite were developed, a simplified single particle model which was used to verify the interaction between particle and matrix and also to provide a development environment for a model of the particle matrix bond. Subsequently, a more complex multi particle model was developed which was of higher fidelity to the formed composites. Through the use of these models it has been deduced that the bond achieved between particle and matrix had a strength of approximately 1MPa and that, for the properties of the particle and the matrix materials, the bond was likely to fail significantly before the composite attained peak loading conditions. The use of these models also revealed the probability that the matrix material may have been significantly modified through cross linking during the forming process and that this may have accounted for some of the perceived improvement in the materials’ performance

Thermomechanical properties of elastomeric-filled composites

The aim of this research project was to modify the matrix polymer’s relaxation processes by the inclusion of filler and to characterise the interfacial interaction in between matrix polymer and filler. Three types of elastomers were selected for this research: a purely amorphous elastomer (poly(ethylene-co-propylene) diene monomer) (EPDM), a semi-crystalline elastomer (poly(ethylene-co-methyl acrylate)) (EMA) and a thermoplastic elastomer (thermoplastic polyurethane) (TPU). These elastomers possessed reinforcement via chemical crosslinking, crystalline molecular segments and hydrogen bonding. Fillers in the form of aluminas (with EPDM) and fumed silicas (with EMAs and TPUs) were added to the elastomers to form composites. Materials were prepared via a solvent casting method. Elastomers were dissolved in an appropriate solvent and fillers were added. A crosslinking agent was also added to the dissolved EPDM. Fillers were dispersed with ultrasonication after which dissolved elastomerfiller compositions were dried then pressed into films. EPDM composites underwent thermally-induced crosslinking. Characterizing techniques including environmental scanning electron microscopy (ESEM), thermogravimetry and analytical techniques including dynamic force thermomechanometry (df-TM), static force thermomechanometry (sf-TM) and modulated force thermomechanometry (mf-TM) were used to examine the interaction between filler and elastomer. Analysis was performed on data from sf-TM (4-element model for creep analysis data, Kohlrausch-Williams-Watts model for recovery analysis data) and mf-TM (Debye, Cole-Cole, Cole-Davidson and Havriliak-Negami relaxation equations). Mastercurves were created from multi-frequency mf-TM data. Sinusoidal frequency mode was determined to be the best method for obtaining multi-frequency data and the HN-based mastercurve method was the best method for constructing mastercurves. The accuracy of three different shift factor models (Williams-Landel-Ferry, Vogel-Fulcher-Tammann-Hesse and arctan based V’ant model) was compared. Super-mastercurves were constructed from mastercurves. ESEM micrographs of EPDM materials revealed that greater compatibility between elastomer and filler resulted in better dispersion of filler. All elastomers were observed to have thermal reinforcement provided by the presence of fillers. Greater compatibility between elastomer and filler resulted in increased thermal stability, as seen in EPDM composites. Thermal reinforcement was observed to increase with increasing silica volume fraction with the Abstract xxiii temperature of 50 %.w/w loss increasing by approximately 20 °C for the EMA-based materials and by 70 °C for the TPU-based materials at the highest filler volume fraction. Stress-strain analysis data indicated that composites were tougher with greater compatibility between filler and elastomer matrix. The Young’s moduli and strength of all elastomer based systems were observed to increase, but toughness decreased with increasing filler volume fraction. Creep and recovery analysis showed that greater compatibility between filler and elastomer, and increased filler volume fraction resulted in more resistance to elastic and viscoelastic deformation, and viscous flow. Modelling of creep analysis data revealed that the presence of any filler resulted in increased resistance to instantaneous and time dependant uncoiling and extension of molecules. Increasing filler volume fraction resulted in greater resistance to instantaneous and time dependant uncoiling of molecules, and irreversible flow. Materials analysed with a reduced force had greater resistance to all modes of deformation as indicated by their parameter values being greater than those obtained at a higher force. Modelling of recovery analysis data revealed greater compatibility between filler and elastomer resulted in less resistance to recovery and less constraints to the operation of relaxation modes. Resistance to recovery decreased with increasing filler volume fraction. Relaxation times decreased with increasing filler volume fraction. Parameter values obtained from analyses conducted with reduced analysis force indicated that a lower analysis force resulted in less resistance to viscoelastic recovery, longer relaxation times and fewer constraints to the operation of relaxation modes. Modulated force thermomechanometry characterised the elasticity and damping properties of materials. The storage modulus was observed to increase with increasing filler volume fraction; however increased compatibility between filler and elastomer resulted in reduced E′ values. The temperature of failure increased with compatibility and increasing filler volume fraction. The loss modulus was observed to increase with increasing filler volume fraction; however increased compatibility between filler and elastomer resulted in lower loss of energy. The tan d values decreased with the addition of any filler and increasing filler volume fraction; however increased compatibility between filler and elastomer reduced the tan d by a lesser amount. Mastercurves were constructed from the isothermal multi-frequency mf-TM data for the EMA and TPU series of materials. They possessed frequency ranges of approximately 10-9 – 1017 Hz. The storage modulus mastercurve data values were observed to increase with increasing filler volume fraction for all materials. The storage modulus values plateaued at Abstract xxiv 10 %.v/v filler. The loss modulus mastercurves of both EMA and TPU-based materials possessed a peak in the loss modulus data corresponding to Tg. The materials plateaued at approximately the same modulus values at the highest transposed frequencies. The modulus data obtained at the highest analysis frequencies exhibited constructive interference with the effects most pronounced in the highest filled composites. The WLF model most accurately modelled shift factor values with respect to temperature. The Wicket error function was used to determine the accuracy of modelling with the relaxation equations. The HN equation modelled the mastercurve data most accurately. The zero and infinite modulus HN parameter values increased with increasing silica volume fraction. The infinite modulus values plateaued at 10 %.v/v filler at the highest transposed frequencies. The relaxation time parameter values increased with increasing filler volume fraction while the a and b shape parameters were observed to overall decrease. Mastercurves could not be constructed for EPDM-based materials as they could not be analysed at sufficiently high frequencies, so single frequency mf-TM data was used with the HN relaxation equation. The addition of compatibilized filler resulted in an increase in E∞ modulus values while the uncompatabilzed filler caused a reduction. The a shape parameter was observed to decrease with the addition of all fillers with the untreated filler resulting in the greatest reduction. The b shape parameter was observed to slightly decrease with the addition of the compatibilized fillers but increase with the addition of the uncompatabilzed filler. The calculated relaxation times were observed to decrease with decreasing compatibility between filler and elastomer.