Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003. / Includes bibliographical references (leaves 120-123). / Composites of polymer matrix and filler particles constitute an important class of materials. Filler particles are used to reduce overall cost and to improve the mechanical properties of the polymer matrix. Until recently, there exists a trade-off between stiffness and toughness in using filler particles in polymer composites. This thesis studies the mechanisms whereby both stiffness and toughness can be enhanced using rigid mineral filler particles. The mechanisms of deformation and fracture of isotactic polypropylene filled with CaCO3 particles were studied. In slow tension, addition of fillers increased the modulus and decreased the yield stress independent of filler type. An optimum size of particles was found to improve Izod impact energy up to four times that of the unfilled matrix. The toughening mechanisms at work were plastic deformation of interparticle ligaments following particle-matrix debonding with additional contribution coming from crack deflection toughening. The failure of too large or too small particles to toughen the matrix was attributed to poor dispersion. A study on the volume evolution of these composites during deformation revealed that measurement of volume strain can be used to identify the onset of debonding. It also provided a new evidence for the existence of an interphase layer between the filler particles and the polymer matrix. This layer is comprised of polypropylene chains strongly bound to the surface of the particles. The thickness of this layer was estimated to be 20 nm. The effect of particle-matrix interaction was investigated in a study of composites of isotactic polypropylene and glass spheres. / (cont.) Silane treatment was used to modify the surface energy of glass. A model study performed on bulk polypropylene and glass samples demonstrated that the use of mixtures of silanes - one with a perfluoro-alkane endgroup and one with an alkane endgroup - can be used to vary the surface energy of the glass and also the adhesion strength between the glass and polypropylene. The debonding process in composites of polypropylene and surface-treated glass particles was investigated by measuring the local volumetric strain during deformation. Weaker particle-matrix interaction was demonstrated to result in earlier debonding, which in turn produces higher fracture toughness. In a given mineral filler-polymer matrix system, the mechanical properties of the matrix polymer are expected to determine whether the mechanism outlined here is applicable. Based on this and previous studies, the most important parameter in the improvement in toughening is the plasticity of the matrix as indicated by the glass transition temperature and the yield stress. / by Yonathan Setioputra Thio. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/29605 |
| Date | January 2003 |
| Creators | Thio, Yonathan Setioputra, 1977- |
| Contributors | Robert E. Cohen and Ali S. Argon., Massachusetts Institute of Technology. Dept. of Chemical Engineering., Massachusetts Institute of Technology. Dept. of Chemical Engineering. |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 123 leaves, 6153081 bytes, 6152889 bytes, application/pdf, application/pdf, application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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