No abstract

No abstract

No abstract

ABSTRACT:Modification of chitosan by grafting of vinyl pyrrolidone (VP) was carried out in homogeneous phase using potassium persulfate as redox initiator. The effect of the reaction variables on the extent of grafting was studied systematically. Values for grafting percentages up to 290% were reached. It was observed that the solubility of chitosan was markedly reduced after grafting with vinyl pyrrolidone. The grafted product is insoluble in common organic solvents as well in dilute organic and inorganic acids. However, the solubility of the grafted chitosan after adsorption of copper ions changed substantially, becoming completely soluble in dilute hydrochloric acid. This was attributed to the effect of complex formation produced by coordination of amino groups of chitosan with copper ions.

No abstract

Hybrid layered aluminosilicate nanoparticles (HLNP) containing octadecylamine (ODA) as the organic part, and silica nanoparticles with spherical morphology containing ODA (HSNP) or without ODA (SNP) were prepared by the sol–gel method and used for the formation of nanocomposites with polypropylene. The polypropylene matrices, of different molecular weight and polydispersity, were prepared using polymers obtained via Ziegler–Natta or metallocene catalysts. A strong influence of the morphology and the presence of ODA on the surface of the nanoparticles was found on the formation and characteristics of the nanocomposites. The mechanical properties and thermal stability of these materials were determined and compared with those of nanocomposites prepared with 2:1 phylosilicate clays such as montmorillonite and hectorite in similar polymer matrices. X-ray diffraction, transmission electron microscopy, and the study of mechanical properties showed that the use of HLNP allows nanocomposites with considerably improved mechanical properties to be obtained, compared with nanocomposites prepared with exfoliated clays. In the case of nanocomposites prepared with spherical particles functionalized with ODA (HSNP), materials with high specific strength combined with high elongation before rupture were obtained. The thermal stabilization of polypropylene matrices containing the synthesized nanoparticles (HLNP, HSNP or SNP) occurs about 50 °C higher than that attained with clays.

In this paper, we report the preparation by the sol-gel technique of organic-inorganic hybrid composites containing the biopolymer chitosan incorporated in a siloxane-based inorganic network. The hybrid xerogels were transformed into porous silica particles by elimination of the organic phase. Surface characteristics of the silica samples can be easily tailored. In this way Brunauer-Emmett-Teller areas, pore volume, and pore diameter of the prepared silica can be predetermined within a wide range. Morphology of the particles at longer length scales can be designed to obtain either irregularly shaped particles with layered morphology or spherical particles. The results are explained on the basis of the cationic polyelectrolytic properties of chitosan, which allows easy association with siloxane oligomers, the precursors of silica in forming hybrid nanocomposites.

The feasibility of grafting poly( methyl acrylate) and poly[ 1-(methoxycarbonyl) ethylene] onto chitosan, poly-P( 1 +4)-2-amino-2-deoxy-D-glucose, was investigated. The grafting reaction was carried out in aqueous solution by using ferrous ammonium sulfate (FAS) in combination with H,O, as redox initiator. The effects of such reaction variables as chitosan, monomer and initiator concentrations, reaction time, and reaction temperature were determined. Through this study the grafting reaction could be optimized. The grafting yield reached its maximum 1037 Copyright 0 1995 by Marcel Dekker, Inc.Downloaded by [Michigan State University] at 23:07 27 December 2014 1038 YAZDANI-PEDRAM ET AL.value of 332% when 0.3 g chitosan was copolymerized with 3 mL monomer at 7OoC for 120 minutes with [FAS] = 6 x lo-' M, [H,O,] = 6 x 10 -3 M, and 8 mL water. The grafted chitosan was found to be insoluble in solvents for chitosan and solvents for poly(methy1 acrylate), but did show swelling in dilute acetic acid, methanol, acetone, and in an ethanol/2% acetic acid 1 : 1 mixture. The thermal stability of chitosan and grafted chitosan were studied by dynamic thermogravimetric analysis. The results show that the graft copolymer is thermally more stable than pure chitosan. The overall activation energy for graft copolymerization was estimated to be 32.8 kcal/mol.