Nanofilled polypropylene fibres

SFILIGOJ SMOLE and K. STANA KLEINSCHEK, University of Maribor, Slovenia 

Polypropylene (PP) is, besides polyesters, one of the most widely used polymers for producing synthetic fibres, especially for technical applications. PP fibres are mostly used in different technical fields due to their excellent mechanical properties, high chemical stability and processability. However, because of low surface energy, lack of reactive sites and sensitivity to photo- or thermal oxidation the polymer properties are insufficient for some applications. Therefore, several techniques for fibre modification have been reported, e.g. plasma treatment, chemical modification and nanomodification, i.e. production of nanocoated and nanofilled materials. 

There is a wide variety of both synthetic and natural crystalline fillers that are able, under specific conditions, to influence the properties of PP. In PP nanocomposites, particles are dispersed on the nano-scale. The incorporation of one-, two- and three-dimensional nanoparticles, e.g. layered clays, nanotubes, nanofibres, metal-containing nanoparticles, carbon black, etc. is used to prepare nanocomposite fibres. However, the preparation of nanofilled fibres offers several possibilities, such as the creation of nanocomposite fibres by dispersing of nanoparticles into polymer solutions, the polymer melt blending of nanoparticles, in situ prepared nanoparticles within a polymeric substrate (e.g. PP/silica nanocomposites prepared in situ via sol-gel reaction), the intercalative polymerization of the monomer. 

Nanomodification creates improved fibre characteristics, e.g. mechanical strength, thermal stability, the enhancement of barrier properties, fire resistance, ion exchange capability, etc., for use in different application fields. In order to follow modification efficiency, various characterization techniques can be used, e.g. X-ray analysis to study composite structure, morphological observations by electron microscopy, mechanical tests, determination of electrokinehc properties, calorimetric measurements. The dispersion of particles within the hybrid system is of fundamental importance, and thus to observe particles a method based on selective etching of the polymer using a plasma 

Generally, polymer-clay nanocomposites use smectic-type clays as fillers, such as hectorite, MMT, kaolin or synthetic mica, aU minerals with a layered structure They are of great industrial value because of their high 

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Polymers generally have high thermal expansion coefficients and the addition of aligned graphene nanoplatelets to polypropylene has been shown to reduce the thermal expansion coefficient in two directions rather than one in the case of aligned fibres.A similar reduction in the thermal expansion coefficient of an epoxy resin is obtained with the use of graphene oxide. It is also found that the addition of graphene-based nanofillers to a polymer can... 

Nanofillers are increasingly being used as high-performance additives for plastics and Finegan et / [ 51 ] have used DMA to qualitatively and quantitatively study the fibre-matrix adhesion of various carbon nanofibres that had been subjected to several different types of surface treatments in a polypropylene matrix. Lee, Hsieh and McKinley [52] have characterised a nanocomposite of poly(methylmethacrylate) containing 1-7.5% of modified montmorillonite clay. They established a number of relationships, which included that the storage and loss moduli were strongly dependent upon the clay content, and that the presence of the clay increased the distortion temperature of the plastic. 

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