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Title: Studies of thermal, mechanical and fracture behaviors of rigid nanoparticulates filled polymeric composites
Other Titles: Gang xing na mi ke li tian chong ju he wu ji fu he cai liao zhi re xing neng, li xue xing neng ji duan lie xing neng de yan jiu
剛性納米顆粒填充聚合物基復合材料熱性能, 力學性能及斷裂性能的研究
Authors: Zhao, Hongxia (趙紅霞)
Department: Dept. of Physics and Materials Science
Degree: Doctor of Philosophy
Issue Date: 2005
Publisher: City University of Hong Kong
Subjects: Nanostructured materials
Polymeric composites
Notes: CityU Call Number: TA455.P58 Z45 2005
Includes bibliographical references.
Thesis (Ph.D.)--City University of Hong Kong, 2005
xviii, 180 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: In this research work, several types of nano-sized rigid particles (such as Al2O3 and ZnO) were introduced into polymer matrices, including polypropylene (PP), epoxy resin and poly (ethylene terephthalate) (PET). For the PP and PET systems, the nanocomposites were prepared by twin-screw melt compounding, while the epoxy based nanocomposites were prepared by casting. The main objective of this project is to gain a deep understanding on the mechanics of polymer matrix nanocomposites. The major work of study carried out includes: (1) thermal and crystallization behaviors of nanocomposites; (2) mechanical behavior and fracture mechanisms of nanocomposites; and (3) environmental effects such as ultraviolet (UV) exposure and water absorption on the performance of nanocomposites. Structural and morphological observations on the nanocomposites were carried out by means of microscopy techniques, such as optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Various other aspects of the nanocomposites were characterized by techniques such as differential scanning calirometry (DSC), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and wide angle x-ray diffraction (WAXD). The mechanical properties of the nanocomposites were evaluated through tensile, impact and bending tests. For the PP nanocomposites, it is found that both the Al2O3 and ZnO nanoparticles can lead to the formation of β-PP crystals. Additionally the nanoparticles also act as effective nucleating agents to facilitate the crystallization of PP, causing the reduction in PP spherulite size and increase in the PP crystallization temperature. Both tensile modulus and tensile yield strength of PP can be improved by the incorporation of nanoparticles. The study of the effect of particle surface treatment for the Al2O3/PP nanocompoistes shows that stronger interfacial interaction results in more pronounced mechanical property improvements, especially the tensile yield strength. Toughness enhancement is more significant at a relatively low particle loading. The fracture mechanisms were investigated using single-edge-double-notch four point bending (SEDN-4PB) specimens. It is observed that crazing and microcracking are the dominant deformation mechanisms, which can release the high stress state of the crack tip and facilitate the ensuing PP matrix plastic deformation. The study of the effect of UV radiation exposure on PP and the ZnO/PP nanocomposites, based on the chemical, thermal and mechanical measurements, indicates that the ZnO nanoparticles can greatly reduce the damage of UV radiation on the PP molecules of the nanocomposites. Mechanisms on the UV radiation damage on the PP molecules were given in this research. For the Al2O3 and ZnO filled diglycidyl ether of bisphenol A (DGEBA) based epoxy nanocomposites, DMA results show that the glass transition temperature (Tg) of the Al2O3/epoxy nanocomposites is not affected by the addition of nanoparticles. For the ZnO/epoxy nanocomposites, however, Tg decreases with increasing nanoparticle content. The storage modulus improvement for the Al2O3/epoxy nanocomposites is more prominent when the matrix is in the rubbery regime (i.e. when the temperature is over Tg). For the ZnO/epoxy nanocomposite system, the critical stress intensity factor KIC increases upon the addition of the ZnO nanoparticles and then maintains almost constant with increasing nanoparticle content. Microscopic observations of the SEDN-4PB ZnO/epoxy nanocomposite specimens indicate that no clear particle-matrix debonding takes place. Matrix microcracking around nanoparticles and particle bridging between cracks, as well as epoxy matrix shear yielding are the main fracture mechanisms. From water absorption experiments for the Al2O3/epoxy nanocomposites, it is found that water absorption has the effect of reducing the tensile modulus and tensile strength. This is rationalized by the water degradation on epoxy. The effect of water absorption on the coefficient of thermal expansion (CTE) behaves differently for measurements carried out below and above Tg. CTE of the Al2O3/epoxy nanocomposites increases upon water absorption when the measurement temperature is below Tg, and decreases for measurements carried out above Tg. Dielectric property tests of the Al2O3/epoxy nanocomposites indicate that both incorporation of the Al2O3 nanoparticles and water absorption can improve the dielectric constant and dielectric loss. Mechanical blending of a γ irradiation cross-linked acrylate-styrene rubber (UR) with PET was carried out. Due to the cross-linked morphology, agglomeration of the UR particles during the melt blending did not occur. This is favorable to maintain a fine dispersion of the UR particles in the PET matrix. Blends with up to 5.0 wt% of UR were prepared and their properties evaluated. The high degree of cross-link in UR helped to maintain its fine dispersion in the PET matrix. However, the high degree of cross-link also induced a high Tg in the rubber phase. Tensile and Charpy impact tests suggest that property improvements can only be achieved for the blend that contains 1.5 wt% of the UR particles. No deformation of the UR particles can be observed from the SEM micrographs taken from the tensile and impact fracture surfaces.
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