Suédina M.L. Silva

Application of Infrared Spectroscopy to Analysis of Chitosan/Clay Nanocomposites

In recent years, polymer/clay nanocomposites have attracted considerable interest because they combine the structure and physical and chemical properties of inorganic and organic materials. Most work with polymer/clay nanocomposites has concentrated on synthetic polymers, including thermosets such as epoxy polymers, and thermoplastics, such as polyethylene, polypropylene, nylon and poly(ethylene terephthalate) (Pandey & Mishra, 2011). Comparatively little attention has been paid to natural polymer/clay nanocomposites. However, the opportunity to combine at nanometric level clays and natural polymers (biopolymers), such as chitosan, appears as an attractive way to modify some of the properties of this polysaccharide including its mechanical and thermal behavior, solubility and swelling properties, antimicrobial activity, bioadhesion, etc. (Han et al., 2010). Chitosan/clay nanocomposites are economically interesting because they are easy to prepare and involve inexpensive chemical reagents. Chitosan, obtained from chitin, is a relatively inexpensive material because chitin is the second most abundant polymer in nature, next to cellulose (Chang & Juang, 2004). In the same way, clays are abundant and low-cost natural materials. Although chitosan/clay nanocomposites are very attractive, they were not extensively investigated, with relatively small number of scientific publications. In addition, the successful preparation of the nanocomposites still encounters problems, mainly related to the proper dispersion of nano-fillers within the polymer matrix. In this chapter, in addition to discussing the synthesis and characterisation by infrared spectroscopy of chitosan/clay nanocomposites, data of x-ray diffraction and mechanical properties are also considered.

Influência da adição e da modificação química de uma carga mineral nanoparticulada nas propriedades mecânicas e no envelhecimento térmico de compósitos poliuretano/sisal

This work deals with filler hybridization effects, by the addition of a nanoparticulate mineral filler (bentonite), on the mechanical performance of compression molded Polyurethane/sisal composites with 25 wt % fiber content. Composite tensile and impact properties were evaluated as a function of mineral filler content (0-10 wt %) and chemical modifications. Thermal aging effects onf tensile (s, E, e) properties of selected composites were also ascertained. The mineral filler (Brasgel PA sodium bentonite) was employed in the following forms: a) as received; b) treated with a 0,6N HCl solution; c) chemically modified with dodecyl dimethyl benzyl ammonium chloride (Dodigen) and d) chemically modified with cetyl trimethyl ammonium bromide (Cetremide). Our results show that bentonite addition increases the mechanical properties of PU/sisal composites and that best overall mechanical performances was achieved with addition of the hydrochloric acid trated mineral filler. Thermal aging for short times (up to 4 days) led to small increases in composites elastic modulus na tensile strengths, which was attributed to post-curing of the matrix. Long thermal exposure (32 days) led to decreases in composite tensile properties (s, E, e), which was attributed to oxidative degradation of both: matrix and sisal fibers. The most thermally resistant composite was the hybrid (PU/sisal-bentonite) whose mineral filler was chemically modified with Cetremide. DRX and SEM data indicate the hybrids with organofilized bentonites to be composed of micro and nanocomposite structures.

Stress Cracking e Ataque Químico do PET em Diferentes Agentes Químicos

The investigation of stress cracking resistance (ESCR) of PET was done in injection-moulded tensile test bars using different fluids as active agents. These were methanol, ethanol, propanol, butanol and solutions based on sodium hydroxide. Both dynamic and static tensile experiments were conducted. During the tensile experiments, the samples were kept in contact with the fluids and the mechanical properties were monitored. The results showed that all sodium hydroxide solutions were aggressive stress cracking agents for PET, reducing mechanical properties and causing catastrophic failure. On the other hand, the other fluids did not cause much influence on the mechanical behaviour but changed drastically the surface appearance. Also observed was a chemical attack when NaOH solutions were used, causing a reduction in molar mass of PET molecules.

Efeitos de Diferentes Argilas Organofílicas nas Propriedades de Compósitos PET/Bentonita

This work has for purpose evaluate the effect of the utilization of two organoclays bentonites, one national, organophilizated with the salt cetyl trimethyl ammonium bromide, ASCM and other commercial, Cloisite 30B on the properties of the compounds PET/bentonite by melting intercalation. Initially, masterbatch (1:1) was added to PET so that PET/bentonita compounds with 1, 2 and 3 weight % of bentonite. These mixtures were extruded on a counter-rotating twin screw extruder coupled to the torque rheometer Haake operating at 275oC and 60 rpm and then injection molded on a Fluidmec injection machine. The compounds were coded as PET/ASCM and PET/CL and were characterized by X rays diffraction, XRD, thermogravimetric analysis, TGA and tensile properties and, the clays infrared spectroscopy, FTIR, XRD and TGA. The analysis of FTIR and XRD confirmed the clay organophilization. The thermal stability was more significative for the compound PET/ASCM and the best tensile properties was verificated for the compound PET/CL with 3 weight % of Cloisite 30B.

Uso de argila organofílica na compatibilização de misturas PP/EPDM

PP/EPDM blends with different PP:EPDM ratios, non-compatibilized and compatibilized with maleic anhydride grafted polypropylene (PP-g-MA) were prepared by melting. The influence of 1 phr bentonite clay addition on the morphology, mechanical and rheological properties of these blends was evaluated. The bentonite used as a filler, provided by Bentonit Uniao Nordeste/PB, was purified and organically modified with a technology developed by our research group, before being added to the blends. X-ray diffraction results showed that, for blends having different PP:EPDM ratios, 1 phr organoclay addition led to the formation of intercalated (20 or 40% EPDM) or intercalated/exfoliated (10 and 30% EPDM) nanocomposites. The morphological, mechanical and rheological properties of the blends were modified by organoclay addition, especially for those with 30 wt% of EPDM, where a compatibilizing effect of the organoclay was observed.

Falha por Stress Cracking em Híbridos PET/Argila

This study investigates stress-cracking failure of polymer/clay composites. Tensile and stress relaxation tests were conducted to evaluate the stress cracking resistance of PET and PET/clay in the presence of sodium hydroxide aqueous solution. The X-ray diffraction analyses showed that the clay formed a typical structure of a microcomposite, and not an exfoliated structure. The presence of clay causes stress concentration, with a strong consequence to the stress cracking behavior, but the effects depend on the lamellar ordering and the content of clay. When the clay lamellae are less ordered the rise in stress concentration is lower, but causes more surface cracks on the polymer, suggesting that the barrier effect was not very effective. Molar mass measurements showed that the clay accelerates the chemical attack of the matrix when higher concentrations of NaOH are used, but reduces the effect of mechanical stress on degradation.

Thermomechanical Behavior of High Performance Epoxy/Organoclay Nanocomposites

Nanocomposites of epoxy resin containing bentonite clay were fabricated to evaluate the thermomechanical behavior during heating. The epoxy resin system studied was prepared using bifunctional diglycidyl ether of bisphenol A (DGEBA), crosslinking agent diaminodiphenylsulfone (DDS), and diethylenetriamine (DETA). The purified bentonite organoclay (APOC) was used in all experiments. The formation of nanocomposite was confirmed by X-ray diffraction analysis. Specimens of the fabricated nanocomposites were characterized by dynamic mechanical analysis (DMA). According to the DMA results a significant increase in glass transition temperature and storage modulus was evidenced when 1 phr of clay is added to epoxy resin.

Comportamento termomecânico de compósitos ativos preparados com nanocompósitos epóxi/argila organofílica e fios de liga Ni-Ti com memória de forma

In this work, epoxy/organoclay nanocomposites were selected as matrix for presenting high enough glass transition temperature (Tg) and thermal stability values in order to be incorporated in shape memory alloys (SMA). Four volume fractions of SMA wires containing Ni-Ti (1.55, 2.56, 3.57 and 4.54%) were embedded in diglycidyl ether of bisphenol A (DGEBA), cured with the aromatic amine 4,4’-diamino diphenyl sulfone (DDS) and containing 1 phr of purified organobentonite (APOC). The formation of nanocomposite was confirmed by X ray diffraction analysis, while the phase transformation of Ni-Ti wires was determined by dynamic mechanical analysis (DMA). Samples of the active composites prepared from nanocomposite matrix and Ni-Ti wires were mainly characterized by DMA. A recovery of the storage modulus of the active composite was observed during heating in the range of phase transformation of Ni-Ti wires when the volume fraction was maintained at around 3.5%.

Ionically Crosslinked Chitosan Membranes Used as Drug Carriers for Cancer Therapy Application

The aim of this paper was to prepare, by the freeze-drying method, ionically crosslinked chitosan membranes with different contents of pentasodium tripolyphosphate (TPP) and loaded with 1,4-naphthoquinone (NQ14) drug, in order to evaluate how the physical crosslinking affects NQ14 release from chitosan membranes for cancer therapy application. The membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), swelling degree, and through in vitro drug release and cytotoxicity studies. According to the results, the molecular structure, porosity and hydrophilicity of the chitosan membranes were affected by TPP concentration and, consequently, the NQ14 drug release behavior from the membranes was also affected. The release of NQ14 from crosslinked chitosan membranes decreased when the cross-linker TPP quantity increased. Thus, depending on the TPP amount, the crosslinked chitosan membranes would be a potential delivery system to control the release of NQ14 for cancer therapy application. Lastly, the inhibitory potential of chitosan membranes ionically crosslinked with TPP and loaded with NQ14 against the B16F10 melanoma cell line was confirmed through in vitro cytotoxicity studies assessed via MTT assay. The anti-proliferative effect of prepared membranes was directly related to the amount of cross-linker and among all membranes prepared, such that one crosslinked with 0.3% of TPP may become a potential delivery system for releasing NQ14 drug for cancer therapy.

HDPE/Chitosan Blends Modified with Organobentonite Synthesized with Quaternary Ammonium Salt Impregnated Chitosan

In this study, blends based on a high density polyethylene (HDPE) and chitosan (CS) were successfully prepared by melt processing, in a laboratory internal mixer. The CS biopolymer content effect (up to maximum of 40%), and, the addition of bentonite clay modified with quaternary ammonium salt (CTAB) impregnated chitosan as a compatibilizing agent, on the properties of the blends was analyzed by Fourier transform-infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analyses (TG), tensile strength, and scanning electron microscopy (SEM). The use of clay modified with CTAB impregnated chitosan, employing a method developed here, improved the compatibility of HDPE with chitosan, and therefore the thermal and some of the mechanical properties were enhanced, making HDPE/chitosan blends suitable candidates for food packaging. It was possible to obtain products of synthetic polymer, HDPE, with natural polymer, chitosan, using a method very used industrially, with acceptable and more friendly properties to the environment, when compared to conventional synthetic polymers. In addition, due to the possibility of impregnated chitosan with quaternary ammonium salt exhibit higher antibacterial activity than neat chitosan, the HDPE/chitosan/organobentonite blends may be potentially applied in food containers to favor the preservation of food for a longer time in comparison to conventional materials.