| dc.description.abstract | Isotropic polymers lack sufficient strength and stiffness for many engineering
applications. In order to improve these properties polymers can be filled with structural
reinforcements such as glass or natural fibres. However, current major trends focus on
simple monocomponent systems in an effort to reduce costs and increase recyclability.
Composite systems, by definition, must employ at least two phases with different
material properties. With the introduction of careful processing routes, it has been
proven possible to create a fibrous, two phase composite, in which both are
polypropylene.
Polypropylene can be melt spun and solid state drawn to give oriented tapes, and moduli
of -15GPa and tensile strengths of -550MPa can be achieved. These tapes can then be
oriented into sheets, either in the form of woven fabrics or unidirectional layers. These
sheets form the reinforcing phase of a single polymer composite material. Such single
polymer composites based on polyolefins can be produced by using a separate matrix
impregnation route, but these are limited by relatively low volume fractions of
reinforcement. Previous work executed at the University of Leeds showed that polymer
fibres can be welded together by selective melting of the fibre exterior, but this method is
limited by a small temperature processing window.
By using polypropylene tapes co-extruded with a copolymer skin, it has been shown that
such tapes can be welded together at temperatures far below the melting temperature of
the tapes, thus ensuring that thermal relaxation of the highly oriented polymer does not
occur. The temperature processing window can be widened further by constraining
fibres during heating. The optimisation of the drawing and structure of these tapes,
together with an investigation of the static and dynamic mechanical properties, impact
resistance and interfacial properties of composites formed from these tapes, are
investigated in this thesis | en_US |
