Luiz Claudio de Santa Maria

Preparation and antibacterial activity of silver nanoparticles impregnated in bacterial cellulose

A simple method was developed to load a large amount of silver nanoparticles into bacterial cellulose (BC) produced by Gluconacetobacter xylinus in a controlled manner. Due to the high electron-rich oxygen density in the BC macromolecules and the large surface area of the BC nanoporous structure as an effective nanoreactor, the in situ direct metallization technique was successfully used to synthesize Ag nanoparticles with an average diameter of 30 nm and a loading content of at least 5 wt. (%), approximately. This novel procedure provides an easy and economical way to manufacture Ag nanoparticles supported on a porous membrane for various biomedical applications. These composite fibers showed nearly 100% antibacterial activity (elimination of microorganisms) against Escherichia coli because of the presence of the silver nanoparticles.

Polietileno: principais tipos,propriedades e aplicações

The structure of each polymer has a direct influence on its density and mechanical properties. Long- chain branches, such as those present in low density polyethylene, for example, increase its impact strength, decrease density and improve processing. Short-chain branches present in linear low density polyethylene, on the other hand, increase crystallinity and tensile strength in comparison to low density polyethylene (produced by free radical initiators). The main applications and the type of processing used for each type of polyethylene are also presented in this work. A comparison between Ziegler-Natta and metallocene catalysts is carried out. The polyethylene produced by metallocene catalysts presents narrow molecular weight distribution and a uniform distribution of comonomer incorporated into the polymer chain. Those characteristics provide an enhancement on the tensile properties and impact strength of final products.

CHEMICAL MODIFICATION OF CROSS-LINKED RESIN BASED ON ACRYLONITRILE FOR ANCHORING METAL IONS

Abstract Network resin based on acrylonitrile has been chemically modified through different reactions to obtain different chelating groups. The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN) and divinylbenzene (DVB). The chemical modifications of these beads’ cyano groups were carried out by reaction with hydroxylamine, hydrazine and ethanolamine producing amidoxime, amidrazone and oxazoline groups, respectively. The copolymer and modified resins were characterized by apparent density, surface area, average pore diameter, elemental analysis (CHN), FTIR and optical and electronic microscopies. Qualitative experiments of adsorption were conducted to evaluate the resins (modified and unmodified) on fixing Hg(II), Cd(II), Cu(II), Zn(II), Cd(II), Co(II), Ni(II) and Pb(II) from aqueous solution using batch extractions. Based on the results obtained, it was concluded that it is possible to modify chemically a resin containing cyano groups by different routes and to use these resins as a very low cost effective sorbent for metal ions.

Thermal behaviour of modified wood fibers

Wood-fibers were modified by silanes treatments and/or by coating with polypropylene or polystyrene. Enhancement in thermal stability of wood fibers treated with γ-aminopropyl triethoxy silane and in fibers coated with polypropylene or polystyrene are discussed. Thermoanalytical data (TGA, TMA and DSC) of the samples may aid to predict the behaviour of these modified fibers in composites of polypropylene or polystyrene matrices.

Synthesis of crosslinked resin based on methacrylamide, styrene and divinylbenzene obtained from polymerization in aqueous suspension

Abstract A series of porous copolymer beads based on methacrylamide (MA), styrene and divinylbenzene (DVB) was prepared by aqueous suspension polymerization in the presence of diluents to act as precipitants. As MA is totally soluble into aqueous phase, the use of two types of phase transfer agent was investigated, namely: TritonX-100TM [polyoxyethylene-(10)-isooctylphenyl-ether] and tetrabutylammonium perchlorate. The effect of the diluents on the surface appearance and the porous structure of copolymer beads was studied. Suitable particle stabilisation was achieved by using a combination of two suspension agents, namely: gelatin and 2-hydroxy-ethyl-cellulose. The network resins were characterized by optical and scanning electron microscopy, IR spectroscopy, elemental analysis (CHN), apparent density, swelling in different solvents and specific area by BET method. It was observed that the MA incorporation was more effective when TritonTM was employed as phase transfer agent.

Synthesis and in vitro studies of gold nanoparticles loaded with docetaxel.

The aim of these studies was to synthesize, characterize and evaluate the efficacy of pegylated gold nanoparticles (AuNPs) that differed in their PEG molecular weight, using PEG 550 and PEG 2000. The synthesis of the gold nanoparticles was carried out by modified Brust method with a diameter of 4-15 nm. The targeting agent folic acid was introduced by the covalent linkage. Finally, the anti-cancer drug docetaxel was encapsulated by the AuNPs by non covalent adsorption. The nanoparticles were characterized by transmission electron microscopy and used for in vitro studies against a hormone-responsive prostate cancer cell line, LnCaP. The loaded nanoparticles reduced the cell viability in more than 50% at concentrations of 6 nM and above after 144 h of treatment. Moreover, observation of prostate cancer cells by optical microscopy showed damage to the cells after exposure to drug-loaded AuNPs while unloaded AuNPs had much less effect.

Preparation of composite materials containing iron in a cross-linked resin host based on styrene and divinylbenzene

Iron composite materials based on styrene/divinylbenzene network hosts were produced using aqueous suspension polymerization. The effects of different kinds of porogen agent, toluene, toluene/n-heptane mixture or a toluene solution of polyphenyleneoxide on the bulk density, swelling in toluene and ferromagnetic properties of these materials were evaluated. The specific area and average porous diameter of network resins were characterized by BET and BJH methods, while the iron content was determined by atomic absorption spectrometry. The morphology of the composites was studied by both optical microscopy and scanning electron microscopy with energy dispersive X-ray analysis. All the spherical beads, irrespective of their sizes, have agglomerated iron particles located only on their surface. The particles have exhibited ferromagnetic behavior, with a coercivity of 328.69 Oe. The porogen agents used affect the iron particle distribution on the bead surfaces.

Microscopic analysis of porosity of 2-vinylpyridine copolymer networks. 1. Influence of diluent

The porous structure of copolymer networks based on 2-vinylpyridine, styrene and divinylbenzene at varied proportions prepared by suspension polymerization was varied by using different kinds of porogen agent, namely toluene, n-heptane, ethyl acetate. The materials were characterized by determination of surface area, average pore diameter and pore volume by BET/BJH, apparent density, elemental analysis (CHN) and swelling degree. Their morphologic characteristics were evaluated by microscopic analyses and correlations among porous structures and reaction parameters were found. It was noted that all synthesized resins have presented narrow particle size distributions; their porosities and visual appearances were dependent on the type and dilution of solvent employed in their syntheses.

Polimerização 1,4-cis de butadieno com sistemas catalíticos Ziegler-Natta à base de neodímio

Nowadays the catalyst systems based on neodymium are the ones most used in the high cis polybutadiene production. These systems contain a neodymium compound (catalyst), an alkylaluminium compound (cocatalyst) and a halogen compound (halogenating agent). The microstructure, molecular weight characteristics and the reaction activity are influenced by the nature and concentration of catalyst system components. Those characteristics are also affected by the polymerization conditions. This paper presents a brief review on 1,4-cis-butadiene polymerization on neodymium catalysts.

Comparative study of homogeneous and heterogeneous styrene polymerizations with Ni(acac)2/MAO catalytic system

Abstract Styrene polymerization was carried out with Ni(acac) 2 /MAO and Ni(acac) 2 /SiO 2 /MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type.