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Correlating the structure and properties of highly plastic segmented polyurethane nanocomposites containing low silicon dioxide filler weight fractions
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|Title: ||Correlating the structure and properties of highly plastic segmented polyurethane nanocomposites containing low silicon dioxide filler weight fractions|
|Authors: ||Hood, Matthew Allen|
|Keywords: ||Materials science|
|Issue Date: ||Mar-2012 |
|Abstract: ||Segmented polyurethanes (SPUs), as a class of elastomers, display a large degree of toughness and elasticity. To modify the mechanical properties of an SPU matrix, high elastic modulus fillers may be added. In this work we systematically correlated the relationship between silicon dioxide (silica) particles size and functionality on the resulting mechanical properties of the SPU-silica composites.
SPU was synthesized of poly(tetramethylene glycol) soft segments, which contribute to the extensibility of the SPU, and hexamethylene diisocyanate-butanediol hard segments (HS), which contribute to the SPUs modulus and toughness. Blends of SPU with 25 wt% HS and silica nanoparticles, micrometer-sized silica particles and methyl modified silica nanoparticles were prepared. SPU-silica particle composites were also evaluated when silica particles were covalently attached to the SPU matrix. The HS concentration of in situ SPU-silica particle composites was also increased to 35 wt% and 45 wt%.
Blended composites displayed poor mechanical properties due to a weak interaction of silica particles with the SPU matrix and poor control over silica particle location within the composite. Covalently attached silica particles were relegated to HS-rich domains, introduced an astonishing 10-fold increase in strain-at-break (from 200 % for the pristine SPU to >2100 % with addition of 0.5 wt% and 1.0 wt% silica nanoparticles concentrations). A decrease in elastic modulus was observed due to disruption of the HS crystallinity. In situ SPU-amine modified silica nanoparticle composites displayed the greatest increase in strain-at-break over the largest range of silica nanoparticle concentrations. The variation in properties for SPU-amine modified silica nanoparticles composites was due to a difference in reactivity and nature of the amine functional silica nanoparticles compared to that of the unmodified silica nanoparticles. Micrometer-sized silica particles and di- and octa-functional polyhedral oligomeric silsesquioxane (POSS) molecules were added to an SPU matrix in situ. Mechanical reinforcement was not observed for di-functional POSS, which did not act as a cross-linking agent.
We have established a correlation between silica particle placement within an SPU matrix and the structure-properties relationship of the final polymer composites. A molecular level representation of the SPU chains near the silica fillers was proposed for the SPU-silica filler composites. A cause for the extraordinary increase in strain-at-break with in situ addition of the silica fillers at low weight concentrations is proposed.|
|Description: ||Thesis (PhD, Materials engineering)--Drexel University, 2012.|
|Appears in Collections:||Drexel Theses and Dissertations|
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