Comparison of rancimat evaluation modes to assess oxidative stability of fish oils

Two Rancimat evaluation modes, the induction period (IP), and the time needed to achieve a selected difference in conductivity (tΔK) were compared for assessing relative stability of anchovy, sardine, and hake liver oils. Mean coefficients of variation were 2.5 and 2.4% for IP and tΔK values, respectively, for oils oxidized in the range 55–90°C. Natural logarithms of IP and tΔK values varied linearly with temperature (P<0.001). A linear relationship (r=0.999) was established between the IP and tΔK values (P<0.001). Relative oxidative stability of fish oils was determined with the same degree of confidence by either IP or tΔK values.     

Physicochemical and structural effects of electrolyte‐induced delamination on polyethylene teraphthalate‐coated steel plates

This research evaluated the in situ physicochemical changes and alterations occurring in an electrolytic chromium coated steel (ECCS), surface protected by polyethylene teraphthalate (PET) copolymer, after inducing a fracture on the coating in an acid acetic‐acetate medium. The delamination was characterized in the front of the failure by means of anodic and cathodic electrochemical mechanisms, and the resistance and degradation of the metal‐polymer composite's substrates were analyzed by means of Raman vibrational spectroscopy. The application of an electrochemical cell to generate in situ delamination, simulating the formation of pores or artificial defects, provided information on the activity inside the substrates of the PET‐coated ECCS composite as a result of the effect of the acetic acid. The anodic delamination mechanism is based on the diffusion of the electrolyte through the metal‐polymer interface and the pre‐existence of pores on the polymer layer. The cathodic delamination mechanism is based on the mechanical action of the gaseous hydrogen as a result of the reduction of H⁺. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Incorporation of polyfluorenes into poly(lactic acid) films for sensor and optoelectronics applications

Films of neat and plasticized biodegradable poly(lactic acid) (PLA) matrices containing anionic conjugated polyelectrolytes, poly[9,9‐bis(4‐phenoxybutylsulfonate)]fluorene‐2,7‐diyl‐alt‐arylenes, with 1,4‐phenylene and 4,4″‐p‐terphenylene, respectively, as arylene groups or a neutral poly(9,9‐dialkylfluorene) for comparison were prepared by solution casting. These films were characterized using differential scanning calorimetry, thermogravimetry, scanning electron microscopy and fluorescence spectroscopy. In addition, the effects of plasticizer on the thermal properties and the oxygen permeability of the PLA films were measured through the oxygen transmission rate. Results show that it is possible to obtain thin, optically transparent and luminescent films with potential in oxygen sensing, exhibiting good thermal and photochemical stability. At high polyelectrolyte content, evidence is found for phase separation and aggregate formation and it is no longer possible to obtain completely homogeneous films. The possibility of incorporating the cationic metal complex tris(2,2′‐bipyridyl)ruthenium(II) into plasticized PLA films containing conjugated polyelectrolytes for dual‐wavelength ratiometric luminescence sensing is also discussed. Copyright © 2012 Society of Chemical Industry     

Rotational molding of polyethylene composites based on agave fibers

In this study, agave fiber/linear medium density polyethylene composites were manufactured by rotational molding. A laboratory scale biaxial machine was used, where the internal air temperature during the processing cycle was measured. Two sizes of agave fibers (50 and 100 mesh) were used separately and mixed together (50/50) at concentrations varying between 0 and 15 wt%. The initial mixtures were obtained by dry blending, rotomolded under different operation conditions (oven temperature, processing cycle time, and rotational speeds), and the final pieces were compared. For each process condition, a complete morphological analysis was performed to relate with mechanical properties in terms of tensile, impact, and flexural strength. The results show that there is an optimum fiber concentration around 10%, and blending fiber sizes gave better tensile properties than using each size alone. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Electrospun nanofibers of a degradable poly(ester amide). Scaffolds loaded with antimicrobial agents

Electrospinning conditions were evaluated to prepare micro/nanofibers of a biodegradable poly(ester amide) constituted by L-alanine, 1,12-dodecanediol and sebacic acid. 1,1,1,3,3,3-Hexafluroroisopropanol appeared as the most appropriate solvent to obtain fibers in a wide range of electrospinning conditions that allowed tuning the final diameter size. Fiber diameter increased with the flow, distance between the needle tip and the collector and decreasing voltage, which made it possible to obtain homogeneous fibers in the 1700–320 nm range. Fibers were loaded with antimicrobial agents like silver and chlorohexidine, and the influence of agent concentration in the electrospinning solutions on the fiber diameter size was determined. The polymer was able to crystallize during the electrospinning process, giving rise to a structure slightly different from that obtained by solution crystallization and related to that attained after crystallization from the melt state. Addition of antimicrobial agents had little effect on the degree of crystallinity, although it decreased slightly when chlorhexidine was employed. Scaffolds prepared from the silver and chlorhexidine loaded samples supported cell adhesion and proliferation. Furthermore, a clear and well differentiated antimicrobial effect against both Gram-positive (e.g. M. luteus) and Gram-negative (e.g. E. coli) bacteria was demonstrated.     

Effect of physical aging on the shape-memory behavior of amorphous networks

This paper presents an experimental and modeling study of the effects of physical aging on the shape-memory performance of (meth)acrylate-based networks composed of tert-butyl acrylate (tBA) crosslinked by various concentrations of poly(ethylene glycol dimethacrylate) (PEGDMA). The experiments measured the unconstrained recovery response of samples stored at 20 °C (T_g ? 36 °C) for zero to 180 days and evaluated the effects of storage on the strain fixity, activation temperature, and initial recovery rate. A thermoviscoelastic model recently developed for amorphous networks near the T_g was applied to study the influence of structural and viscoelastic relaxation and the aging time and temperature on the recovery response. Results showed that the activation temperature and the initial recovery rate increased with the aging time, producing a sharper initial recovery response. The thermoviscoelastic model predicted that the magnitude of these effects depended on the aging temperature. There was an optimum aging temperature that maximized the initial recovery rate. These results suggest that physical aging can be manipulated to accelerate the recovery performance of shape-memory polymer devices.     

Dendritic Nanotheranostic for the Delivery of Infliximab: A Potential Carrier in Rheumatoid Arthritis Therapy

Antibodies are macromolecules that specifically recognize their target, making them good candidates to be employed in various therapies. The possibility of attaching a drug to an immunoglobulin makes it possible to release it specifically into the affected tissue as long as it overexpresses the target. However, chemical coupling could affect the functionality (specificity and affinity) of the antibody. It has been observed that the use of intermediaries, such as dendrimers, could resolve this issue. Because carbosilane dendrimers have aroused great interest in the field of biomedicine, this report describes the synthesis of an anionic carbosilane dendrimer with a fluorochrome on its surface that then forms a conjugate with an antibody. It has been used as immunoglobulin and infliximab, whose target is TNF-α, which is a cytokine that is overexpressed in the inflamed area or even in the blood of patients with autoimmune diseases, such as rheumatoid arthritis. In addition, the integrity and functionality of the antibody has been studied to see if they have been affected after the chemical coupling process.     

Catalytic Reduction of 4-Nitrobenzoic Acid by cis-[Rh(CO)2(Amine)2](PF6) Complexes Under Water–Gas Shift Reaction Conditions: Kinetics Study

Rhodium(I) complexes of the type, cis-[Rh(CO)₂(amine)₂](PF₆) where (amine = 3-picoline, 2-picoline, pyridine, 2,6-lutidina or 3,5-lutidine) dissolved in 80% aqueous amine solutions catalyzed the selective reduction of 4-nitrobenzoic acid to 4-aminobenzoic acid under CO atmosphere. The importance of these catalytic systems is their high chemo selectivity for the aromatic nitro group of the 4-nitrobenzoic acid with respect to the carboxylic group, allowing the production of the desired aromatic amine in high yields. The 4-aminobenzoic acid production depends on the nature of the coordinated amine. The Rh/3,5-lutidine system, the most active catalyst among tested, displays turnover frequencies for 4-aminobenzoic acid production of about 173 moles per mole Rh per day for [Rh] = 1 × 10^?4 mol, [4-nitrobenzoic acid] = 3.82 × 10^?3mol, 10 mL of 80% aqueous 3,5-lutidine, P(CO) = 0.9 atm at 100 °C. Analyses of kinetic results for the Rh/3,5-lutidine system show a first order dependence on 4-nitrobenzoic acid concentration, a non-linear dependence on CO pressure, a segmented Arrhenius plot and dependence on the nature of the reducing gas agent. These data are discussed in terms of a possible mechanism.