Structure-property relationships of polypropylene nanocomposite fibres

Structure-property relationships of polypropylene nanocomposite fibres 

University of Oxford, UK and G. M. McN ALLY, Queen s University Belfast, UK 

Montecatini (Roder, 1999) first commercialised polypropylene as a synthetic fibre-forming material in 1957, nearly two decades later than the production of polyamide fibre by E. I. du Pont de Nemours Co. in 1939 (Carraher, 2003) and polyester fibre by ICI in 1941 (Whinfield, 1946). This was because the stereochemistry required to develop the spinnability properties for polypropylene was not achieved until 1954 with the independent discovery of stereospecific titanium halide-based coordination catalysts by Edwin Vandenberg (Vandenberg and Salamone, 1992) and Giulio Natta (Natta et al, 1955). 

Studies of propylene random copolymers have recently gained importance over isotactic polypropylene in applications requiring high clarity, flexibility and low-temperature performance (Maier and Calafut, 1998). Traditionally, the enhancement in mechanical performance of melt-spun fibres relies primarily on the control of molecular chain orientation and crystalline structure development through take-up speed, drawing ratio and quenching conditions. Heterogeneous particulate reinforcement of polymers often leads to phase separation, increases the melt viscosity and creates hydrodynamic instabilities. 

Several reinforcement techniques have been introduced for the fabrication of composite fibres, such as (i) the introduction of thermotropic liquid crystalline polymers (TLCP) to produce a matrix-fibril stmcture, (ii) use of multiphase polymer blends and hard/soft segmented thermoplastics, and (iii) bicomponent extrusion, where different polymers are brought in contact as separate streams just before the spinnerette to produce a sheath-core structure (Salem, 2000). However, the inapplicability of these techniques to high-commodity commercial polymers and other serious drawbacks has limited the appeal. For instance, fabrication of TLCP is very expensive and postprocessing may destroy its unique matrix-fibril structure. Incomplete microphase separation in some polymer blends often leads to a less desirable morphology in multiphase fibres and bicomponent spirming is sensitive to differences in viscosity between the polymers. 

---