Papers by Author: Marcos Lopes Dias

Abstract: This paper shows the importance of the clay surface chemistry in the preparation of nanocomposite materials. An Argentinean montmorillonite was used for preparing two modified clays. The filosilicate was intercalated with a quaternary ammonium salt derived from ε- caprolactam to obtain an organofilic material. The other modification was introduced by mixing the clay with hexadecyl trimethyl ammonium chloride. Thus, the polyamide 6 ability in dispersing clays was applied to prepare composites with the intercalated clays. The polyamide 6/clay dry composites with 3 wt % of filler were prepared by melt processing in a mixer chamber. Composites of polyamide 6/organoclay were characterized by X-ray diffraction, transmission and scanning electron microscopy and thermogravimetry. The barrier properties were determined by cyclohexane pervaporation. The results show that the dispersion and degree of delamination depend on a proper chemical treatment and the clay content influences the polyamide 6 nanocomposites solvent pervaporation resistance.

Abstract: Copolymerization of silicon alkoxides in alcoholic basic medium using trialkyl- or triarylchlorosilanes as terminator was investigated. Tetraethoxysilane (TEOS), phenyltriethoxysilane (PTEOS) and vinyltriethoxysilane (VTEOS) were used as monomers and triphenylchlorosilane (TPCS) and trimethylchlorosilane (TMCS) as terminator. The copolymerization of TEOS with PTEOS and VTEOS produces core-shell silica-silicone nanospherical hybrids containing large amounts of functional groups in the structure of their external layer. The structure is the result of the fast hopolymerization of TEOS in a first stage of the reaction, forming the core, followed by copolymerization of TEOS and the alkyl- or vinyl-trialkoxysilane comonomer in its last stage. The structure was confirmed by Raman and FTIR spectroscopy, wide angle X-ray scattering (WAXS) and thermogravimetry. The control of particle size is effectively made by the termination reaction and particles with average diameter between 20 and 100 nm were obtained. Introduction of other chemical functions on the surface of these nanoparticles can be carried out by common reactions with the functional surface groups. As an example, sulfonation of particles containing phenyl groups on the surface by direct sulfuric acid and chlorosulfonic acid was investigated and the results discussed.

Abstract: In this paper, we report the preparation of polyethylene composites with organically modified montmorillonite. Three different Na+-montmorillonites were modified in order to obtain organoclays and two grades of high-density polyethylene were used as composite matrices. All composites were prepared by melt blending, and their physical and mechanical properties were thoroughly characterized. The extent of clay platelet exfoliation in the composites was confirmed by X-ray diffraction (XRD). Mechanical properties under static and impact conditions were evaluated to assess the influence of the reinforcement on the properties of polyethylene.