Numa J. Capiati

Polyethylene–polystyrene grafting reaction: effects of polyethylene molecular weight

Abstract Blending of different thermoplastic polymers usually results in segregated and low value materials for almost any mixing condition. Nevertheless, a synergetic combination of properties can be obtained by an adequate compatibilization via reactive blending. In this work a Friedel–Crafts alkylation reaction is used to graft polyethylene chains onto polystyrene. The relation between the initial PE molecular weight (MW) and the structure of the compatibilizer copolymer is studied by a combination of size exclusion chromatography and Fourier transform infrared spectroscopy. The amount of copolymer formed is estimated from the amount of polystyrene reacted. The relative lengths of the grafted polyethylene chains are assessed. It is found that lower MW PE produces, upon reaction, a greater amount of short chain length grafted PE onto PS than higher MW PE. The results are in agreement with theories relating the component MW to the reaction localization at the interface. The low cost Friedel–Crafts alkylation results in a convenient reaction for the in situ compatibilization of PE/PS blends. It produces enough graft copolymer to compatibilize the phases without causing PS crosslinking and PE chain scission.

Influence of talc morphology on the mechanical properties of talc filled polypropylene

Injected polypropylene (PP)/talc composites were studied to evaluate the influence of different talc morphologies on their final mechanical properties. Talc genesis is responsible for type and content of associated minerals, crystalline degree, particle size distribution, and specially, morphology. Consequently, when talc is incorporated into PP, differences in the genesis mean differences in particle morphology and may influence the composite properties. Two talc samples having predominant macro and microcrystalline morphologies were used to prepare two composite sets to be tested. Thermal and mechanical properties of each PP/talc composites set were measured, analyzed and discussed comparatively. The results reveal that the main influences of talc morphology are given on modulus, yield strength and elongation at break of PP/talc composites. Macrocrystalline morphology of talc induces better composite mechanical properties than microcrystalline one. This behavior could be explained by talc characteristics as lamellarity, crystalline character and crystallinity degree.

Impact Strength and Morphology of PP/LLDPE/EPDM Blends: Effect of Elastomer Viscosity and Content

This work presents results obtained for ternary blends of polypropylene (PP), a linear low density polyethylene (LLDPE) and two ethylene-propylene-norborene terpolymer (EPDM) of different viscosities. The effect of LLDPE added to the PP/elastomer blends is analyzed in terms of morphological features and impact properties. Press molded specimens were used throughout this work. The LLDPE dispersive effect is verified independently of the elastomer viscosity Ternary blends containing more than 50% EPDM in the disperse phase showed better impact strength than the corresponding binary PP/EPDM blend.

Viscoelastic Properties of Multiphase Polymeric Blends

Rheological analysis of multi-phase systems is very difficult because the morphology is strongly related to the flow history. The small amplitude oscillatory shear flow does not affect the morphology and is very useful to predict the viscoelastic behavior of immiscible blends. In this work we study the dynamic rheological properties of polypropylene based ternary blends with linear low density polyethylene and ethylene/propylene terpolymers of different viscosities taking into account the effects of changing the composition and concentration of the dispersed phase. The predictions of a constitutive equation for emulsions of viscoelastic fluids are also included.

Integrated Process for Purification of Low Grade Talc Ores

This study examines the development of an integrated process for separation and purification of low grade talc ores. This procedure involves leaching with HCl to dissolve gangue minerals and to purify a low purity talc ore containing up to 40% gangue minerals. Also, all cations from gangue minerals are recovered as hydroxides via selective precipitation. The effects of acid concentration, talc/acid solution ratio, time, and reaction temperature on talc purification were studied and the optimal conditions were determined. Laboratory-scale tests revealed that the resulting talc is free of gangue minerals, consisting of small particles with nanometric thicknesses. Reactants are fully consumed during dissolution and byproducts like ammonium chloride could be recirculated and reused. Resulting hydroxides can be used as a coagulation aid for water treatment.

Dispersed Particle Size Distribution in Impact Modified Polypropylene

In this work ternary polypropylene (PP) rich blends with ethylene propylene terpolymers (EPDM) and LLDPE are studied. Attention is focused on the effect of different viscosity ratios (β1/4 viscosity of dispersed phase/viscosity of PP matrix) on the particles sizes and particle size distribution of the dispersed phase. The incidence of the elastomer viscosity and dispersed phase content are also analyzed. A reduction in the viscosity ratio mainly affects the weight average particle diameter (Dw) rather than the number average particle diameter (Dn).

PP/LLDPE/EPDM Blends: Effect of the Elastomer Viscosity on Impact Properties

Publisher Summary Blending is an attractive method of creating materials with better performance than separate components. Such blends have already reached a massive application in the case of thermoplastics like polyethylene (PE) and polypropylene (PP), although their complex structure frequently hinders the prediction of the structure-properties relationship. Isotactic PP poor impact strength at room and low temperatures is well known. Blends of PP with elastomers as impact modifier have been studied extensively during the last decade. Some results on improvement of the rubber dispersability and blend stiffness by the addition of high density polyethylene (HDPE) have been reported. However, the effect of the third component is still a matter of discussion. In this chapter, PP/LLDPE/EPDM blends are prepared and focus is on the effect of the content and viscosity of the elastomer on the morphology of the disperse phase. Particle size distribution is obtained by transmission electron microscopy (TEM) and image analysis techniques. Izod Impact Strength (IS) properties were also determined at room and low temperature on press molded specimens. The morphology of the ternary blends studied, exhibits an increasing degree of LLDPE/EPDM interpenetration with the LLDPE content. The addition of LLDPE in both low and high viscosity elastomer improves its dispersability, affecting mainly the larger particles of the distribution. For a given composition, ternary blends with L-EPDM show higher impact strength. At low temperature, the dispersive effect of LLDPE is less significant on the impact properties.