Study On Structure-Property Relationships In Ethylene-Propylene Random Copolymer/SEBS/OMMT Nanocomposites

Polymer/clay nanocomposites (PNCs) have a potential application prospect in the food and medicine packaging field due to their good gas barrier and mechanical properties. The dispersion status of clay has an evident effect on the PNCs properties. The paper chose organic montmorillonite (OMMT) and ethylene-propylene random copolymer (PPR) to prepare nanocomposites via melt blending and explored the methods of regulating and controlling PNCs properties by investigating the effects of compatibilizers and toughening agent on the dispersion and distribution of OMMT and the PNCs properties.PPR/OMMT nanocomposites (PPRMNCs) were prepared with different compatibilizers via twice-screw extrusion processing and found that the types of compatibilizers affect significantly the dispersion and distribution of OMMT. Polypropylene (PP) grafting with maleic anhydride (MA)(PP-g-MA) has the strong intercalation ability into OMMT and causes OMMT to distribute directly in PPR phase. Ethylene-octylene block copolymer (POE) grafting with MA (POE-g-MA) and styrene-ethylene-butylene-styrene block copolymer (SEBS) have so strong adhesion ability to OMMT that OMMT is intercalated, partly exfoliated and surrounded by them to form a soft core-shell encapsulation structure and distribute in PPR phase. The dispersion status and loadings of OMMT have little effect on the melting temperature (Tm) but evidently effect on the crystallinity (Xc) of PPRMNCs. The dispersion status of OMMT affects significantly tensile modulus and properties at break. The optimal OMMT loadings induced the optimal comprehensive properties of PNCs at a certain ratio of compatibilizer to OMMT.The introduction of SEBS using as a toughening agent causes the more uniform and the smaller size of OMMT dispersion. OMMT is preferentially intercalated and partly exfoliated by SEBS and elastomeric compatibilizers to form a soft core-shell encapsulation structure and distribute in SEBS domains. When PP-g-MA is used as compatibilizer, OMMT is intercalated by the compatibilizer, PPR and SEBS to distribute in SEBS domains. Better the compatibility of compatibilizer with the matrix is, stronger the changes of dynamic mechanical behaviors are. Higher exfoliated extent of OMMT dispersion is, weaker the changes of dynamic mechanical behaviors are, better the thermal stability and Izod impact properties are. more evidently storage modulus G’and complex viscosity η*are improved, more the critical shear rate γ decreases and more evidently the shear thinning behavior is. SEBS hardly affects Tm and the crystallizing temperature (Tc) of PPR/SEBS/OMMT nanocomposites (PPRSMNCs) and slightly affects the crystal structure of PP. The intercalated OMMT distributing in PPR phase or PPR-SEBS interface markedly increases the thermal stability and the rigid and decreases the impact strength. The incorporation of SEBS and POE-g-MA induces the exfoliated OMMT dispersion thus the PPRSMNCs has the balance of rigidity and toughness, excellent ductility and impact properties.To investigate the dispersion and distribution mechanisms of OMMT, the effects of the screw extrusion temperatures, the intercalate agents of OMMT, the ratios of compatibilizer to OMMT, the OMMT loadings, the types of compatibilizer and the processing methods on the OMMT dispersion status, crystallization behaviors, thermal stability, mechanical properties and rheological behaviors were studied and found that the lower processing temperature induces the more uniform and exfoliated dispersion of OMMT and the type of compatibilizer and the compatibility of compatibilizer with PPR are the key factors on the dispersion and distribution of OMMT. The thermal stability and melt like-solid behavior of the PPRSMNCs prepared with SEBS-g-MA as compatibilizer via double-screw extrusion processing increase with the increase of OMMT loadings. Xc increases with the increase of OMMT loadings and decreases with the increase of compatibilizer loadings. The high loadings OMMT in the PPRMNCs via once-screw extrusion processing is mainly exfoliated dispersion but would be aggregated again after the second screw extrusion.iPP-PPRSMNCs alternating multilayered nanocomposites were prepared by a microlayered coextrusion system. Differential scanning calorimetry (DSC) and dynamic tensile results showed that with increase of layer number and decrease of layer thickness, storage modulus E’ and loss modulus E" all increase, crystallization of PPRSMNCs becomes weaker but that of iPP becomes stronger. When layer number is16. the crystallization of PPRSMNCs disappears and that of iPP displays the strongest one. In compared with lateral stretching, vertical stretching improves evidently E’ and E" of the nanocomposites but has the same effect on a and β relaxations.