Editorial, Preface of Special Issue devoted to 10th Brazilian Polymer Congress

Alginate-chitosan (ALG-CHI) microspheres obtained by polyelectrolyte complexation are pH-sensitive, biocompatible and adhesive, and are excellent candidates for the delivery of drugs, proteins and peptides in the human body. A wide variety of methods for the production of these polymeric complexes has been provided. The water-in-oil emulsion is a complex production method, but generally enhances the control of particle size and particle size distribution of the microspheres, extremely necessary for obtaining repeatable controlled release behavior. In this work, a novel and facile water-in-oil emulsion method for the ALG-CHI polyelectrolyte complexes is discussed. The method proposed produced ALG-CHI microspheres with improved morphology and enhanced drug loading in comparison with the aqueous medium method. The drug loading in the water-in-oil emulsion was over 30% higher than in the aqueous medium, an indication that the new method proposed the common drug leaching during the microspheres’ preparation is avoided, being an interesting alternative to encapsulate drugs of hydrophilic nature.

Natural fibers are widely used as plastic composite material reinforcements. In this work, composites of postconsumer high-density polyethylene (HDPE) reinforced with sisal fibers were prepared. PE and sisal fibers were chemically modified to improve their compatibilities, try to increase the hydrophobic character of the sisal fiber and hydrophilic character HDPE. Sisal was mercerized with a NaOH solution and acetylated and the PE was oxidized with KMnO₄ solution. The chemically modified fibers were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) and ¹³C Nuclear Magnetic Resonance Spectroscopy (¹³C NMR). The composites were prepared by extrusion of modified and unmodified materials containing either 5 or 10 wt% fibers. The morphology of the obtained materials was evaluated by SEM. The fiber chemical modification improves it adhesion with matrix, but not benefit were obtained with HDPE oxidation. Flexural and impact tests demonstrated that the composites prepared with modified sisal fibers and unmodified PE present improved mechanical performance compared to pure PE.

Aphrons fluids are being studied for application in oil well drilling operation. These fluids consist, basically, of polymer and surfactant, which act as thickening agent and microbubbles producer, respectively. The specific function of aphrons is to act in the filtrate reduction of oil reservoirs presenting low pressure and depleted zones. The aphrons characteristics were evaluated as a function of type and concentration of polymer (xanthan gum-XG and partially hydrolyzed polyacrylamide-PHPA) and surfactant: anionic (Blue Streak^®, sodium dodecyl sulfate-SDS) and nonionic (polyoxidebased copolymer). Through characterization results (size/size distribution of microbubbles, density and air content) and performance evaluation in the invasion controlling, it was possible to conclude that aphrons fluids prepared with SDS, at an optimal concentration but independent of the polymer type, showed better performance, and such result is related to relatively higher average diameter and broader size distribution of microbubbles, besides the low density and high air content, in the range evaluated in this study.

Poly(vinyl alcohol) (PVA) hydrogels have been used for numerous biomedical and pharmaceutical applications, as a consequence of their non-toxic, non-carcinogenic and bioadhesive properties. In this communication the effect of different factors, such as type of electrolyte, ionic strength, temperature (ranging from 20 to 40°C) and cationic surfactants on the distribution coefficients (α) and release rate constants (k_R) of deoxyribonucleic acid (DNA) from PVA-DNA blend gel matrices (of a sheet shape), will be presented and discussed. The release kinetic constant and the distribution coefficient of DNA are quite sensitive to the surrounding matrix media (e.g., k_R ranges from 1.5•10^–8 to 4.7•10^–7 s^–1). The analysis of the temperature dependence on k_R shows that the activation energy for the DNA desorption to an aqueous solution is equal to 21.2 kJ/mol. These results constitute a step forward towards the design of controlled DNA release PVA-based devices.

The main purposes were evaluating the influence of different starches on the miscibility with Poly(ethylene oxide) (PEO) and their effects on the spherulite growth rate. Polymer-polymer miscibility in PEO/cationic starch and PEO/hydrophobic starch blends consisting of different w/w ratios (100/0, 95/05, 90/10, 80/20, 70/30, 65/35 and 60/40) was investigated. This analysis was based on the depression in the equilibrium melting temperature (T_m⁰). By treating the data of thermal analysis (Differential Scanning Calorimetry – DSC) with Nishi-Wang equation, a positive value (0.68) was found for the interaction parameter of PEO/cationic starch. For PEO/hydrophobic starch blends, a negative value (–0.63) was obtained for the interaction parameter. The results suggested that PEO/cationic starch system should be immiscible. However, the system PEO/hydrophobic starch was considered to be miscible in the whole range of studied compositions. Through optical microscopy analysis, it was concluded that the spherulite growth rate is significantly affected by changing the amount and the type of starch as well.

In this work the effect of the compatibility between organoclays and styrene on the flammability of polystyrene/clay nanocomposites obtained through in situ incorporation was investigated. The reactions were carried out by bulk polymerization. The compatibility between organoclays and styrene was inferred from swelling of the organoclay in styrene. The nanocomposites were characterized by X-ray diffraction and Transmission Electron Microscopy. The heat release rate was obtained by Cone Calorimeter and the nanocomposites were tested by UL94 horizontal burn test. Results showed that intercalated and partially exfoliated polystyrene/clay nanocomposites were obtained depending on the swelling behavior of the organoclay in styrene. The nanocomposites submitted to UL94 burning test presented a burning rate faster than the virgin polystyrene (PS), however an increase of the decomposition temperature and an accentuated decrease on the peak of heat release of the nanocomposites were also observed compared to virgin PS. These results indicate that PS/clay nanocomposites, either intercalated or partially exfoliated, reduced the flammability approximately by the same extent, although reduced the ignition resistance of the PS.

The use of slow release fertilizer has become a new trend to save fertilizer consumption and to minimize environmental pollution. Due to its polymeric cationic, biodegradable, bioabsorbable, and bactericidal characteristics, chitosan (CS) nanoparticle is an interesting material for use in controlled release systems. However, there are no attempts to explore the potential of chitosan nanoparticles as controlled release for NPK fertilizers. In this work chitosan nanoparticles were obtained by polymerizing methacrylic acid for the incorporation of NPK fertilizers. The interaction and stability of chitosan nanoparticle suspensions containing nitrogen (N), phosphorus (P) and potassium (K) were evaluated by FTIR spectroscopy, particle size analysis and zeta-potential. The FTIR results indicated the existence of electrostatic interactions between chitosan nanoparticles and the elements N, P and K. The stability of the CS-PMAA colloidal suspension was higher with the addition of nitrogen and potassium than with the addition of phosphorus, due to the higher anion charge from the calcium phosphate than the anion charges from the potassium chloride and urea. The mean diameter increase of the CS-PMAA nanoparticles in suspension with the addition of different compounds indicated that the elements are being aggregated on the surface of the chitosan nanoparticles.