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Auteur(s): Bouhelal, Said
Date de publication: 15-avr-2018
Résumé: The present work deals with two parts . First part deals with reactive blending of isotactic polypropylene (iPP)/low density polyethylene (LDPE)/ ethylene propylene diene monomer(EPDM) and second part deals with the Reversibly crosslinked isotactic polypropylene (iPP) was prepared in the presence of dicumyl peroxide (DCP) and the investigation has been extended the iPP/LDPE blends to see the influence of the crosslinking process in the microstructure and the micro- and macromechanical properties of the modified blends. The reactive blending of iPP/LDPE/EPDM was used to study the effects of peroxide oxy-radicals on melt miscibility in relation to chemical modification, i.e network crosslinking. Blends were prepared in presence of dicumyl peroxide (DCP), using a plastograph at 30 rpm rotor speed and at 200°C. The crosslinking reaction was evaluated using the Monsanto method. The peroxide effect increases the torque value as residency time in the plastograph is increased, and consequently, the overall viscosity increases . This is shown by capillary rheometry. The overall cristalline degree, as estimated by differencial scanning calorimetry (DSC), decreases , meaning that the mode of cristallisation is affected too. This is illustrated by the decrease of cristallisation temperature and spherulite size dimensions of iPP and LDPE. Impact strength results show a ductile-brittle behavior transition appearing for the equilibrium weight fraction of (iPP/LDPE) matrix. Scanning electronic microscopy (SEM) analysis shows a ductile fracture for compositions where each component of the matrix is predominant or major. The complex interpenetrating networks formed are accompagnied by some islands regions of iPP and LDPE. Such a structure is evaluated by combining results of DSC and dynamical mechanical thermal analysis (DMTA). The binary blends based on LDPE/EPDM offer interesting materials (from the mechanical point of view); this is not the case for the reactive binary blends based on iPP/EPDM . Finally , the ternary reactive blends of iPP/LDPE and 20 phr EPDM overcome the problem of compatibility with an increase in the ductile behavior and a larger visco-elastic domain, particularly when LDPE is the major component. Concerning the second part of the reversibly crosslinked iPP, it was prepared in the presence of dicumyl peroxide (DCP). The effects of the peroxide oxy-radicals in the melt were investigated in relation to the modification of the polymer. The dynamic rheology analysis of the crosslinking process was carried out by using a plastograph. The crosslinking reaction was evaluated by the Monsanto method. The resulting structure of the modified samples was studied by means of Infra-red (FTIR) , differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), dynamical mechanical thermal analysis (DMTA), microhardness and mechanical properties. The degree of crystallinity of the modified iPP, derived from DSC and WAXS, remains almost unchanged, i.e., the crystalline structure is unaffected, though the lamellar thickness slightly decreases. Some mechanical properties of the crosslinked iPP, in particular, the impact strength, are greatly improved with reference to the properties of the unmodified material. The impact strength shows a brittle-ductile behavior transition appearing in the modified iPP for all the crosslinking agents studied. We have extended the investigation to analyse the generated ethylenic chains by means of DMTA, DSC, and FTIR. More than that, this crosslinking method was extended to the blends based on iPP/LDPE by using WAXS, DSC, microhadness and tensile experiments. The differents compulations shows an academic and industrial interest.
URI/URL: http://dspace.univ-setif.dz:8888/jspui/handle/123456789/1255
Collection(s) :Thèses de doctorat

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