Semi-Crystalline Polypropylene Matrix

When the nanocomposite matrix is semi-ciystalline, incorporation of [nano)particles such as CNTs frequently aims at modifying the crystallization behavior of the polymer in order to improve its properties like, for example, its mechanical performance, and/or to shorten processing cycle times. This way, high levels of mechanical reinforcement can be achieved at low CNT loadings due to the formation of a highly crystalline layer in the immediate vicinity of the CNT walls, ensuring effective interfacial stress transfer. In addition, dispersion of electrically conductive particles into a semi-crystalline [as well as amorphous) polymer matrix also leads to the production of conductive materials. 

Nevertheless, synthesis of polyolefin latexes is certainly not straightforward and requires the use of water-resistant catalysts in 

A benchmarking, with regard to the achieved electrical properties in these semi-crystalline materials, is performed against a well-described fully amorphous model system, i.e., latex-based polystyrene nanocomposites also prepared by latex technology, which were extensively reported in previous chapters of this book, as well as elsewhere. 

SWCNT/ and MWCNT/iPP-g-MA nanocomposites were prepared by latex technology and a thermal and morphological evaluation of their properties was subsequently carried out.  

Based on both these morphological and thermal evaluations, it was possible to get a better representation of the overall structure of the nanocomposite. The latter is a multiphase system in which filler particles are covered by a trans-crystalline interphase in which polymer chains display a reduced segmental mobility [confinement]. These coated filler fibers proved to be dispersed in an unaffected bulk-like continuous iPP phase in which the polymer crystal perfection is lower than the one of the lamellae grown perpendicularly to the filler surface. 

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Therefore, the results of the present paper showed interrelation of elasticity modulus and amorphous chains tightness characterized by fiactal dimension of chain part between its fixation points for nanocomposites based on the semi-crystalline polypropylene. This assumes the polymeric matrix structure change in comparison with initial polymer the role of densely-packed regions for it is played by interfacial areas. An offered fractal model allows estimation of elasticity modulus limiting values. 

In general, the influences of the additives in a composite on the expression of the semi-crystalline morphology of the matrix polymer are rarely taken into account. In situ monitoring by means of small-angle X-ray scattering has shown that additives may vary the nanostructure at least of polypropylene considerably. Thus re-optimization of commercial recipes might be required in order to tune the crystallization kinetics of the polymer in the presence of nanoparticles. 

The crystallization of isotactic polypropylene (iPP) is affected by many factors, such as macromolecular characteristics [82], crystallization conditions (temperature, cooling rate), and stress (shear, elongational fields) [83-85]. In fiber reinforced iPP matrix composites, the crystalline morphology of the polymer is influenced by the fibers that can act as nucleating agents affecting the crystallization process [86-88]. TranscrystaUinity is a well-known structural feature in pol rmers, which occurs as the result of dense nucleation of the semi-... 

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