The effect of coatings on the interfacial strength of a hollow glass microsphere/polyester composite and their capacity to endure thermal stresses were studied by mechanical testing and an active Acoustic Emission (AE) method. AE was postulated to provide more local information at or near the glass/polyester interface due to the sensitivity of elastic waves to the rigidity of polymer chains at the glass sphere/polyester interface compared to mechanical testing. Three frequency ranges identified by multivariate statistics yet consolidated for the initial analysis into a band of 140-240 kHz, were found to be changing with the different coated glass filler for different glass content and heating state. Considering the acoustic behavior of the composites containing different levels of glass sphere content (1-10 vol%), a lower concentration (aminoethylamino)-propyl-trimethoxy silane coated glass (AS6), demonstrated the lowest attenuation after heating (associated with higher interfacial strength). As anticipated, the highest attenuation after heating was observed for uncoated glass (16K) due to expectedly weaker associations. Mechanical testing results after heating were consistent with the AE response for AS6 and 16K for this frequency range. Trends in amplitude for the three narrower, frequency ranges of 130-160 kHz, 180-220 kHz and 230-260 kHz were compared against that of 140-240 kHz and very small differences were observed. It was found that the frequency range of 130-60 kHz was more descriptive of the changes of interfacial strength in composites (at 10 vol%), being consistent with the mechanical test results. Considering the AE response at 130-160 kHz and mechanical data, higher concentration (aminoethylamino)-propyl-trimethoxy silane (AS12), better endured thermal stresses compared to other coatings. A smaller trial looked at the effect of moisture aging and subsequent thermal cycling on the glass/polymer interface strength as another method to perturb the interface. Attenuation for the band of 180-260 kHz was studied for aged versus non-aged composites. The commercial coating, L21 demonstrated a better moisture resistance before and after thermal cycling compared to uncoated glass spheres. An improved evaluation of interfacial strength in glass/polyester was expected using AE technique versus mechanical testing due to its higher sensitivity to changes in internal structure, however; no significant improvement compared to mechanical testing was observed, at least based on the analysis technique currently being used. / Thesis / Master of Applied Science (MASc) / Sheet molded compound (SMC) is a polymer material reinforced by fibers providing a combination of light weight and high mechanical properties and is used in automotive industry. Light weight fillers (hollow glass microspheres) are used to obtain further weight reduction; however, addition of these fillers leads to reduced mechanical properties and further problems during painting process known as ‘paint popping’. The former is due to uncertain interfacial state between polymer and fillers and the latter results from different thermal expansion behavior of the polymer and filler materials while the material is exposed to high temperatures for painting process. This research aims to devise a highly sensitive technique and evaluate its suitability compared to mechanical testing for investigation of the origin of aforementioned problems. Acoustic Emission (AE) is a method with high sensitivity to changes in internal structure of the material which is postulated to provide a better insight on material microstructure compared to more commonly used method i.e. mechanical testing. Use of interfacial controlling agents was examined to reduce the problems as a result of introduction of fillers. The effect of using surface modified fillers and the effect of thermal stresses on material was investigated using AE technique. Application of AE method in this study provided a good insight about the changes in material internal structure; however, it did not demonstrate a significant improvement in detecting the origins of studied problems compared to mechanical testing at least based on the analysis technique used in this study.

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L’objectif de ce travail est d’adapter une formulation dispersante mise au point par la société Mäder à la dispersion de carbonate de calcium (CaCO3) dans une résine polyester insaturée (UP). Le carbonate de calcium est utilisé en tant que charge dans les matériaux composites à matrice thermodurcissable et en particulier dans les SMC (Sheet Molding Compound). Le rôle de cette formulation est de diminuer les viscosités de résines UP fortement chargées tout en conservant voire en améliorant les propriétés mécaniques des composites formés par un renforcement de l’interface charge / matrice. Trois grands axes ont été développés au cours de ce travail : - le comportement rhéologique d’un mélange CaCO3/résine UP a été déterminé et la formulation dispersante a été optimisée ; - la nature des interactions entre les différents constituants de la formulation dispersante et la surface du CaCO3 a été mise en évidence ; - de nouveaux polymères permettant une dispersion plus efficace de la charge dans la résine ont été synthétisés. Le mélange CaCO3 / résine UP présente un comportement rhéologique complexe. L’optimisation de la formulation dispersante a permis d’augmenter de plusieurs pourcents le taux de charge tout en conservant des viscosités inférieures à celle autorisée par le procédé industriel. L’étude des interactions des constituants de la formulation avec le carbonate de calcium a permis de déterminer les fonctions les plus réactives et de comprendre leur interaction avec la surface de la charge. La synthèse de nouveaux dispersants a également été effectuée. Ces derniers ont ensuite été testés dans l’application et ont montré une efficacité à disperser le CaCO3 dans la résine UP. / The aim of this study is to adapt a dispersive formulation developed by the Mäder group to the dispersion of calcium carbonate (CaCO3) in an unsaturated polyester resin (UP). The CaCO3 is commonly used as filler in the domain of composites especially for Sheet Molding Compound (SMC). This dispersive formulation is able to decrease the viscosity of UP resin containing a high amount of filler. In addition, the mechanical properties of composites could be increased by reinforcing the filler / matrix interface. Three main ways have been studied: - characterization of the rheological behavior of CaCO3 / polyester blends and optimization of the dispersive formulation ; - determination of the interactions between the dispersive formulation components and the CaCO3 surface ; - synthesis of new polymers in order to improve the CaCO3 dispersion in an organic matrix. A complex rheological behavior has been observed for CaCO3 / polyester blends. The dispersive formulation improvement led to an increasing of the filler percentage by keeping the viscosity under the industrial limit. The most reactive functions with the CaCO3 surface have been identified by studying the interactions between the dispersive formulation components and the CaCO3 surface. New dispersing agents have been synthesized. Their efficiency has been demonstrated for the dispersion of CaCO3 in a UP resin.