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Title: Understanding the effect of ultra-low nanofiller loadings on optically transparent polycarbonate
Author: Higlett, Sian L. C.
ISNI:       0000 0004 7971 0047
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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The use of fillers in materials engineering has long been used to improve material properties such as strength, stiffness and toughness. However, these enhancements tend to occur at the detriment to optical transparency in transparent polymeric materials. Nano-sized fillers or nanofillers are thought to maintain the transparency of such materials due to their small size. Moreover because of their smaller size, nanofillers have larger interfacial areas and can therefore provide increased interaction sites (providing fine dispersion in the medium). In this work, the nanofiller trisilanol-phenyl polyhedral oligomeric silsesquioxane (TSP-POSS) was added to polycarbonate (PC) to create a series of polymer nanocomposites for the intended use in transparent, lightweight armour. A variety of techniques were used to characterise the structural, morphological, viscoelastic, optical and mechanical properties of the polymer nanocomposites. A preliminary study into the effect of TSP-POSS on the physical aging behaviour of polycarbonate was also carried out. The effect of TSP-POSS on polycarbonate depended on its loading in the matrix and the type of strain it was subjected to. Increases in toughness were seen in the nanocomposites in comparison to the unmodified polymer and is thought to be due to the formation of a stretchy hydrogen bonded network between TSP-POSS and the polycarbonate chains. Spectroscopy and microscopy techniques suggest TSP-POSS is uniformly dispersed at the nano- or molecular-scale within the polymer matrix, and therefore indicative of high compatibility between the nanofiller and the polymer. Moreover, TSP-POSS can induce one of two toughening mechanisms in the polymer matrix; at low loadings (0.1-0.3wt%) ductility of the matrix increases to form stretched fibrils, at higher loadings (0.5-1wt%), potential nanoscale TSP-POSS aggregates are observed, which appear to be involved in plastic void growth. Both changes increase the energy absorbing capabilities of the polymer matrix. Crucially, it was found that the optical transparency was maintained at all nanofiller loadings. However, at higher strain rates the toughness enhancements of TSP-POSS disappear. This could be due to the higher impact energy which overcomes the interactions between TSP-POSS and the polymer chains, particularly if these involve weak bonds e.g. hydrogen. Therefore, the TSP-POSS/PC nanocomposite studied in this work would be more suitable for protective applications involving low velocity projectiles or even as lightweight, backing materials for energy absorbing applications.
Supervisor: Not available Sponsor: EPSRC ; DSTL
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Engineering not elsewhere classified ; POSS ; Polycarbonate ; Polymer nanocomposite