Valdir Mano

Preparation and thermal study of polymers derived from acrylamide

Abstract Polyacrylamide (PAA) and some of its N -alkyl substituted derivatives have been synthesised and characterised using thermal analysis. Thermal stability was studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) was used to determine the glass transition temperatures ( T g ). The results showed an increase in degradation temperature ( T d ) as the hydrogens of the amide nitrogen were replaced by alkyl groups. An opposite tendency was verified for T g values. The observed increase in T d values is discussed in terms of the formation of an intermediate ion in the degradation, while the decrease in T g values is discussed in terms of polymer–polymer interactions such as hydrogen bonds.

Bioartificial polymeric materials based on collagen and poly(N-isopropylacrylamide)

Films of collagen (CLG) and poly(N-isopropylacrylamide), PNIPAAm, were prepared by casting from water solutions. These bioartificial polymeric materials were studied to examine the influence of PNIPAAm content and glutaraldehyde vapor cross-linking on the thermal and biological stability of CLG. Mixtures, ranging from 20-80 wt% CLG composition, were cross-linked through exposure to glutaraldehyde vapors. Thermal and morphological properties of the films, cross-linked or not, were investigated by differential scanning calorimetry, thermogravimetry, and scanning electron microscopy, with the aim of evaluating miscibility, thermal stability, and interactions among the constituents. The experimental results indicated that the homopolymers are not thermodynamically compatible. However, there is good evidence that effective interactions, probably due to hydrogen bond formation, takes place between the constituents. These interactions are more evident on the samples that were not cross-linked. DSC studies revealed that PNIPAAm exerts a thermal stabilizing effect on uncross-linked CLG, while the cross-linking with glutaraldehyde affects only the biological polymer, preventing the interactions with PNIPAAm. SEM micrographs of the uncross-linked mixtures showed that the morphology, in all compositions studied, remains similar to the pure collagen. In the corresponding cross-linked samples, a more compact aggregation is observed although no appreciably changes can be seen.

Development of pipette tip-based on molecularly imprinted polymer micro-solid phase extraction for selective enantioselective determination of (−)-(2S,4R) and (+)-(2R,4S) ketoconazole in human urine samples prior to HPLC-DAD

In this work a simple and selective sample preparation technique employing pipette tip-based on molecularly imprinted polymer micro-solid phase extraction (PT-MIP-μ-SPE) coupled to HPLC/DAD was developed for the determination of the cis-enantiomers of ketoconazole (KTZ) in human urine samples. Several parameters affecting the proposed PT-MIP-μ-SPE technique were investigated, namely the washing solvent, type and volume of the eluent, amount of material (molecularly imprinted polymer, MIP), sample volume, pH and salt addition. The recoveries were around 100% using 5 μg mL−1 for the (−)-(2S,4R) and (+)-(2R,4S) KTZ enantiomers. Optimum chromatographic conditions for determination of the (−)-(2S,4R) and (+)-(2R,4S)-KTZ enantiomers were found using the chiral stationary phase polysaccharide derived of amylose tris(3,5-dimethylphenylcarbamate). The mobile phase consisted of ethanol:water (95:5, v/v) at a flow rate of 1 mL min−1 and the detection was performed at 250 nm. The performance criteria for linearity, sensitivity, precision, accuracy, recovery, robustness and stability were assessed and they were within the recommended guidelines. The method showed to be linear over the concentration range from 6.25 to 650.00 ng mL−1 for each enantiomer, with the correlation coefficients of 0.9962 and 0.9952 for (+)-(2R,4S)-KTZ and (−)-(2S,4R)-KTZ, respectively. Within-day and between-day precision and accuracy assays for these analytes were studied at three concentration levels and were lower than 15%. The results for the application of the method in preliminary urinary excretion showed that there are not significant differences in the analyzed concentrations of KTZ cis-enantiomers in urine samples.

Preparation and characterization of a composite based on polyaniline, polypyrrole and cigarette filters: adsorption studies and kinetics of phenylbutazone in aqueous media

Understanding the adsorption mechanisms of drugs on the surfaces of solid materials is important for determining the fate of these compounds in aqueous samples during water or wastewater treatment. A composite based on polyaniline (PAni), polypyrrole (PPy) and cigarette filters (CFs), PAni–PPy–CFs, was prepared, characterized by FTIR, TGA and SEM and applied in the investigation of the adsorption of a non-steroidal anti-inflammatory, phenylbutazone (PBZ), from aqueous solution. A group of experiments were conducted, and four kinetic models and five isotherm models were used to describe the adsorption process. The experimental kinetic data fitted very well with the second-order kinetic model, indicating that PBZ adsorption involves chemical adsorption at different binding sites, which could control the reaction rate. The equilibrium adsorption data were best fitted with the dual-site Langmuir–Freundlich isotherm, with a maximum adsorption capacity of 100.22 mg g−1; this indicates the existence of two kinds of adsorption sites on the polymer composite surface. Finally, this composite may act as a excellent adsorbent for environmental and analytical processes, such as a stationary phase in separation processes.

Síntese e caracterização do copolímero poli(3-hidroxibutirato-co-E-caprolactona) a partir de poli (3-hidroxibutirato) e poli(E-caprolactona)

In the present work, the copolymer poly(3-hydroxybutyrate-co-e-caprolactone), P(HB-co-CL), was prepared by transesterification reaction from PHB and PCL. Zirconium (IV) acetylacetonate was used as catalyst and the copolymers were obtained in a wide range of compositions of PHB/PCL (20/80, 50/50, 80/20). These copolymers were characterized by GPC, FT-IR, 1H-NMR, 13C-NMR, TG, and DSC. The copolymers had weight average molecular weight less than 24.000 Daltons. All the systems were thermally more stable than PHB, showing lower crystallinity than the homopolymers. These materials are good candidates to be used as biomaterials, in drug release matrices, or even as PHB/PCL blends compatibilizers.

Bionanocompósitos preparados por incorporação de nanocristais de celulose em polímeros biodegradáveis por meio de evaporação de solvente, automontagem ou eletrofiação

This review reports the preparation and characterization of bionanocomposites based on biodegradable polymers reinforced with cellulose nanocrystals (CNC) described in the literature. The outstanding potential of cellulose nanocrystals as reinforcement fillers of biodegradable polymers is presented with an emphasis on the solution casting process, which is an appropriate method to investigate the physico-chemical effects of the incorporation of CNC into the polymeric matrices. Besides solution casting, other small scale methods such as electrospinning and layer-by-layer are also covered.

Polyaniline-deposited cellulose fiber composite prepared via in situ polymerization: enhancing adsorption properties for removal of meloxicam from aqueous media

Polyaniline (PAni), cellulose fiber (CF) and a PAni–CF composite, which were characterized by infrared spectroscopy, scanning electron microscopy and thermogravimetry, were investigated in adsorption studies of meloxicam (MLX) from aqueous media. PAni-deposited CF composites were prepared via in situ polymerization. These materials were assessed with varying pH, contact time between the adsorbent and adsorbate, and concentration. Kinetic data were evaluated by pseudo first- and second-order, Elovich and intraparticle diffusion models, and the concentration data were evaluated by Langmuir, Freundlich, Sips, single-site Langmuir–Freundlich and dual-site Langmuir–Freundlich models. MLX adsorption was better at pH 2, and the pseudo-second-order (R2 ≥ 0.999) kinetic model and the Langmuir–Freundlich (R2 ≥ 0.9901) isotherm model showed the best fit. PAni–CF composite was found to be the best adsorbent material compared to PAni and CF, because of the greater adsorption capacity (Q = 169.5 mg g−1), which can be explained by the combination of the adsorptive properties of the two materials.

HYDROLYTIC DEGRADATION BEHAVIOR OF PLLA NANOCOMPOSITES REINFORCED WITH MODIFIED CELLULOSE NANOCRYSTALS

Bionanocomposites derived from poly(L-Lactide) (PLLA) were reinforced with chemically modified cellulose nanocrystals (m-CNCs). The effects of these modified cellulose nanoparticles on the mechanical and hydrolytic degradation behavior of polylactide were studied. The m-CNCs were prepared by a method in which hydrolysis of cellulose chains is performed simultaneously with the esterification of hydroxyl groups to produce modified nanocrystals with ester groups. FTIR, elemental analysis, TEM, XRD and contact angle measurements were used to confirm and characterize the chemical modifications of the m-CNCs. These bionanocomposites gave considerably better mechanical properties than neat PLLA based on an approximately 100% increase in tensile strength. Due to the hydrophobic properties of the esterified nanocrystals incorporated into a polymer matrix, it was also demonstrated that a small amount of m-CNCs could lead to a remarkable decrease in the hydrolytic degradation rate of the biopolymer. In addition, the m-CNCs considerably delay the degradation of the nanocomposite by providing a physical barrier that prevents the permeation of water, which thus hinders the overall absorption of water into the matrix. The results obtained in this study show the nanocrystals can be used to reinforce polylactides and fine-tune their degradation rates in moist or physiological environments.

Preparação, caracterização e estudos de biodegradação de blendas à base de PDLLA e PVP

Poly(D,L-lactide), PDLLA, is a polymer with potential applications in medical, environmental, and pharmaceutical areas. Despite its versatility, the hydrophobicity limits its applications. To overcome this problem, one strategy is the preparation of blends with hydrophilic polymers such as poly(vinylpyrrolidone), PVP. In this study, we report the preparation and characterization of blends based on PDLLA and PVP and the biodegradation studies by the Sturm test. It was observed that the components of the blends PDLLA/PVP are thermodynamically immiscible, however the biodegradation is faster than that of pure PDLLA.

Glicólise do poli(3-hidroxibutirato) por via enzimática

to catalyze reactions in both aqueous and organic media. Thus, in this study, we performed the enzymatic glycolysis of PHB using the lipase Amano PS (Pseudomonas cepacia) with ethane-1,2-diol (ethylene glycol) as the functionalizing agent. The results indicated that the glycolysis was successful and afforded hydroxyl-terminated oligomeric PHB polyols. Nuclear magnetic resonance spectra of the products showed characteristic signals for the terminal hydroxyl groups of the polyols, while thermogravimetric and differential scanning calorimetry analyses confirmed an increase in the thermal stability and a decrease in the crystallinity of the polyols compared with the starting PHB polymer, which were both attributed to the reduction in the molecular weight due to glycolysis.