Modification of coconut fibers with polyaniline for manufacture of pressure‐sensitive devices

This article studies the modification of coconut fibers with polyaniline (PAni) with help of statistical experimental design techniques. The main factors studied here were the techniques used for particle dispersion (sonication vs. magnetic stirring) and the type of initiator (ammonium persulfate, APS, vs. ammonium cerium sulfate dihydrate, Ce(IV)). The obtained materials were characterized through low field nuclear magnetic resonance, small‐and wide‐angle X‐ray scattering, scanning electron microscopy, fourier transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Additionally, the electrical resistivities and respective sensitivities to variations of the applied pressure were evaluated for all obtained samples, with help of standard volume resistivity measurements and electro‐mechanical tests. The materials prepared through magnetic stirring with APS presented the best electrical and electromechanical properties, although materials prepared through sonication with Ce(IV) also presented good electrical and electromechanical properties and could be prepared much faster. As a consequence, modification of coconut fibers with PAni, using sonication as the particle dispersion technique and Ce(IV) as initiator, constitutes a very promising procedure for manufacture of pressure‐sensitive devices. POLYM. ENG. SCI., 54:2887–2895, 2014. © 2014 Society of Plastics Engineers     

Control of Microbial Adhesion as a Strategy for Food and Bioprocess Technology

Bacteria and other microorganisms have a natural tendency to adhere to surfaces as a survival mechanism. This can occur in many environments, including the living host, industrial systems, and natural waters. The general outcome of bacterial colonization of a surface is biofilm formation, which consists of microorganisms immobilized in a variety of polymeric compounds generally referred to as extracellular polymeric substances. Bacterial adhesion to a solid surface is a crucial step in the biofilm process. This step is dependent upon van der Waals, electrostatic, and acid–base interactions. These interactions are influenced by physicochemical properties of the substratum and the bacterial surface, such as hydrophobicity, surface charge, and electron donor–electron acceptor properties. In addition, the roughness of the substratum and the microbiological characteristics of the cell surface, such as cellular appendages and production of exopolysaccharides, can affect the adherence process. To date, many strategies have been developed to decrease the adherence of bacteria to surfaces. Surface modification with the addition of the suitable compounds makes surfaces less attractive for microorganisms and therefore prevents bacterial adherence and biofilm formation.     

Effect of active packaging incorporated with triclosan on bacteria adhesion

ABSTRACT: Antimicrobial polyethylene and cellulose based films incorporated with triclosan were studied. The antimicrobial efficacy, the hydrophobicity, microscopic and the mechanical characteristics of the films, as well free energy of adhesion between bacteria and antimicrobial films were evaluated. It was observed that both polyethylene and cellulose based films incorporated with the antimicrobial were homogeneous. Furthermore, the addition of triclosan did not affect mechanical characteristics of the films (P > 0.05). However, triclosan incorporated into polyethylene films reduced its hydrophobicity while antimicrobial cellulose based films became more hydrophobic. The adhesion was thermodynamically favorable between tested bacteria and polyethylene films. On the other hand, the adhesion to triclosan cellulose based film was thermodynamically unfavorable to Staphylococcus aureus and Escherichia coli and favorable to Listeria innocua and Pseudomonas aeruginosa. Polyethylene and cellulose based films showed inhibitory effect against S. aureus and E. coli, being the inhibition halo higher for polyethylene films. This study improves the knowledge about antimicrobial films.     

Antimicrobial effects of silver nanoparticles against bacterial cells adhered to stainless steel surfaces

Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antimicrobials, silver has attracted interest in the scientific community because of its recognized antimicrobial activity. This study aimed to evaluate the antimicrobial effects of silver nanoparticles (NP) obtained by a new method and tested at concentrations of 6 μg/ml and 60 μg/ml against the species Staphylococcus aureus, Listeria innocua, Salmonella Choleraesuis, Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus. The ability of these nanoparticles to remove or kill vegetative cells adhered to stainless steel surfaces was also evaluated. We observed that the NP obtained with the new method, concentrated silver nanoparticles (CNP), and silver nanoparticles with added sodium chloride (NPNaCl) had high antimicrobial activities (P < 0.05). We also verified that the most effective condition for the removal of P. aeruginosa cells on stainless steel coupons (10 by 10 mm) was immersion of the surfaces in CNP. The CNP treatment produced a 5-log reduction of the microbial population after 30 to 60 min of immersion. The CNP treatment also performed better than water and sodium carbonate, a compound commonly applied in clean-in-place procedures in the food industry, in removing adherent B. cereus cells from stainless steel cylinders. Therefore, these results suggest that NP synthesized by a new procedure may be used as antimicrobials in the food industry, for example, for the sanitization of utensils that come into contact with foods.     

Survival of Lactobacillus delbrueckii UFV H2b20 in ice cream produced with different fat levels and after submission to stress acid and bile salts

The survival of Lactobacillus delbrueckii UFV H2b20 in three ice cream formulations (low fat, fat free and high fat) was evaluated after the processing and storage at ?16 °C. The survival of L. delbrueckii UFV H2b20 was not significantly affected (P > 0.05) in three ice cream formulations after processing. The same result was observed during storage for 40 days at ?16 °C. Cells of L. delbrueckii UFV H2b20 incorporated in three ice cream formulation survived when exposed to acid stress and bile salts. The results demonstrate that L. delbrueckii UFV H2b20 has potential for being used in ice cream and capacity to resist acid stress and to grow in the presence of bile salts. This demonstrates that reduction of fat in ice cream does not compromise the viability of L. delbrueckii UFV H2B20.     

Effect of Cleaning Treatment on Adhesion of Streptococcus agalactiae to Milking Machine Surfaces

Streptococcus agalactiae is a common subclinical mastitis agent in dairy cattle. In this study, the influence of hygiene procedure time on the adhesion of S. agalactiae to rubber and silicone surfaces used in milking machines was evaluated. The effect of hygiene practices on the thermodynamic and microscopic features of both surfaces was also evaluated. The hydrophobicity of milking machines and bacterial surfaces was investigated by measuring the contact angle with a goniometer 0, 30, 90, and 180 days after a full hygiene procedure simulated using rubber and silicone coupons. As the time of cleaning procedures enhanced, there was a reduction in the adhesion of S. agalactiae to both surfaces. The rubber and silicone surfaces were hydrophobic in all treatments $ \left( {\Delta G_{\text{sws}}^{\text{TOT}}\; < \;0} \right) $ , while the bacterial surface presented hydrophilic behavior $ \left( {\Delta G_{\text{sws}}^{\text{TOT}}\; > \;0} \right) $ , which makes the adhesion process difficult. Photomicrographs showed rapid wear of both surfaces, pointing to damages caused by cleaning agents. However, the silicone was more resistant to cleaning and sanitizing treatments. Thus, this work shows that changes caused by hygiene procedures in the thermodynamic and in the morphology of milking surfaces have an enormous importance in the S. agalactiae adhesion and, consequently, in mastitis transmission between cattle herd.     

GIS insulation co-ordination: on-site tests and dielectricdiagnostic techniques. A utility point of view

This paper summarizes the Electricite de France experience with insulation coordination of gas-insulated substations (GIS). After a review of the insulation coordination practice, mainly dealing with fast front overvoltages and the one minute AC test, some results of the on-site test procedure applied for 30 years are presented and related to the insulation co-ordination practice. The in-service return of experience dealing with dielectric failures is analyzed. The dielectric diagnostic techniques now available are briefly presented with their possibilities and limitations. According to this survey, the expectations of EDF from these diagnostic techniques as well as the new on-site test and online monitoring tendencies at EDF are presented     

Development of a symbiotic cottage cheese added with Lactobacillus delbrueckii UFV H2b20 and inulin

The aim of the study was to develop a symbiotic cottage cheese containing Lactobacillus delbrueckii UFV H2b20 and inulin, and to evaluate the survival of this bacterium when the cheese was exposed to conditions simulating those found in the gastro-intestinal tract. Throughout the entire whole shelf-life period of the cheese, the probiotic cell counts were higher than those recommended for probiotic products containing 5% of inulin. The probiotic bacterium exhibited satisfactory resistance to low pH values and to high concentrations of bile salts. The addition of probiotic cells and inulin generated no alterations in the physicochemical characteristics of cheese.     

Ion Diffusion Study in the Oxide Layers Due to Oxidation of AISI 439 Ferritic Stainless Steel

Chromium diffusion coefficients were determined in thermally grown chromia layers on the AISI 439 ferritic stainless steel oxidized at 750, 800, 850 and 900 °C in synthetic air. The stable isotope ⁵⁴Cr was used as chromium tracer and the diffusion profiles were established by SIMS analysis. The chromium ion bulk diffusion coefficients evaluated numerically from experimentation were around five orders of magnitude smaller than the chromium ion diffusion coefficients at grain-boundary regions. The values of the chromium ion diffusivities in chromia grown on the AISI steel were lower than the corresponding oxygen ion diffusivities obtained in a previous study. Comparison of experimental and calculated parabolic oxidation constants, for the oxidation of the AISI 439 steel, showed that the chromia scale growth mechanism is controlled not only by inward oxygen ion diffusion from atmosphere, but also by outward chromium diffusion from the metallic substrate. However, the role of the oxygen ion diffusion appears to be more important than that of the chromium ion diffusion.