The effect of polyethylene crystallinity and polarity on thermal stability and controlled release of essential oils in antimicrobial films

Antimicrobial packaging can preserve and increase shelf life of free preservatives food products. Active materials present in the packaging material can migrate, in a controlled manner, to the food surface, avoiding bacterial and fungal proliferation and keeping the food product edible for longer periods of time. Essential oils (EO) are natural antimicrobial agents that can be released to the headspace with no direct contact between the package and the food. To minimize loses of EO during high heat melt processing, a three stages process was implemented and tested. Antimicrobial films were prepared by melt mixing a variety of polyethylene copolymers in the presence of organo‐modified montmorillonite nano clay (NC) and thymol, an EO present in oregano and thyme. A controlled EO desorption from films can be achieved by changing the polymer crystallinity and polarity. As the crystallinity increased, the thermal stability of the EO during the extrusion process improved. The addition of NC affects the structure and homogeneity of the crystals. The combination of high polymer crystallinity and chemical affinity between EO and NC increased the thermal stability of the EO during film processing, enabling to control the desorption rate. The effect of multilayer structure based on varied densities and polarities was also studied. Increasing the polarity of the outer layers in multilayered film reduced the EO desorption rate as a result of chemical interactions between the polymer and the EO. The final antimicrobial activity of the films was also found to be dependent on the EO partitioning. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40309.     

Chemical surface modification of wheat straw fibers for polypropylene reinforcement

The use of natural materials has grown in the last years in the plastics industry. Natural lignocellulose fibers derived from agricultural waste present potential to be used as a replacement for glass fibers for polymer reinforcement, leading to lower CO₂ footprint products. However, cellulose fibers are hydrophilic and polar and as a result of that, incompatible with hydrophobic polymers such as polypropylene. For this reason, a surface modification on the cellulose fiber is required. This work focuses on the modification of the cellulose fibers to improve the compatibility with polypropylene. Wheat straw fibers derived from agricultural waste were scoured with the purpose to remove lignin, hemicellulose and pectin to facilitate the defibrillation. The fibers were then esterified using acetic anhydride. Thermal gravimetric tests have shown an increase in the thermal stability of the scoured and esterified cellulose fibers, from 246°C for untreated fibers to 292°C and 316°C, respectively. From mechanical tests results it could be seen that the tensile modulus of the composites with esterified cellulose fibers increased 57% compared with the neat PP. Flexural strength increased by 31% and flexural modulus by 70%. The use of esterified fibers led to an improvement of 79% in the impact strength compared with the neat PP. A better compatibilization between fibers and matrix could be seen using maleic anhydride modified polypropylene copolymer as compatibilizer, even with esterified fibers, probably due to residual hydroxyl groups still available on modified cellulose. POLYM. COMPOS., 37:2133–2141, 2016. © 2015 Society of Plastics Engineers     

Multimodality exploration by an unsupervised projection pursuitneural network

Graphical inspection of multimodality is demonstrated using unsupervised lateral-inhibition neural networks. Three projection pursuit indexes are compared on low-dimensional simulated and real-world data: principal components, Legendre polynomial, and projection pursuit network.     

Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back‐Reflectors

Optical interference is used to enhance light–matter interaction and harvest broadband light in ultrathin semiconductor absorber films on specular back‐reflectors. However, the high‐temperature processing in oxygen atmosphere required for oxide absorbers often degrades metallic back‐reflectors and their specular reflectance. In order to overcome this problem, a newly developed film flip and transfer process is presented that enables high‐temperature processing without degradation of the metallic back‐reflector and without the need of passivation interlayers. The film flip and transfer process improves the performance of photoanodes for photoelectrochemical water splitting comprising ultrathin (<20 nm) hematite (α‐Fe₂O₃) films on silver–gold alloy (90 at% Ag–10 at% Au) back‐reflectors. Specular back‐reflectors are obtained with high reflectance below hematite films, which is necessary for maximizing the productive light absorption in the hematite film and minimizing nonproductive absorption in the back‐reflector. Furthermore, the film flip and transfer process opens up a new route to attach thin film stacks onto a wide range of substrates including flexible or temperature sensitive materials.     

High Performance Core/Shell Ni/Ni(OH)2 Electrospun Nanofiber Anodes for Decoupled Water Splitting

Decoupled water splitting is a promising new path for renewable hydrogen production, offering many potential advantages such as stable operation under partial-load conditions, high-pressure hydrogen production, overall system robustness, and higher safety levels. Here, the performance of electrospun core/shell nickel/nickel hydroxide anodes is demonstrated in an electrochemical-thermally activated chemical decoupled water splitting process. The high surface area of the hierarchical porous electrode structure improves the utilization efficiency, charge capacity, and current density of the redox anode while maintaining high process efficiency. The anodes reach average current densities as high as 113 mA cm⁻² at a working potential of 1.48 V_RHE and 64 mA cm⁻² at 1.43 V_RHE, with a Faradaic efficiency of nearly 100% and no H₂/O₂ intermixing in a membrane-free cell.     

Rates of experimental microbiological contamination of fish exposed to polluted water

Fish inhabiting fecally polluted bodies of water are often used for human consumption. Such fish can be contaminated by enteric human pathogens and may pose a potential risk to public health. Controlled experiments with 132 fish of 100 g average weight were conducted to evaluate the rate of contamination of various tissues of fish (tilapia hybrids). The fish were exposed to E. coli introduced into the ambient water at concentrations of up to 10⁶ cfu/ml. Additional experiments were conducted with diluted wastewater containing Aeromonas, enterococci, fecal coliform and F+ coliphages. In another experiment poliovirus I was also added. The highest bacterial concentrations were recovered from the digestive tract (DT), some 5–24 h following exposure, with DT levels essentially similar to those in the inoculated water. In the E. coli experiments, geometric mean levels of about 10² cfu/cm² were recovered from the skin, 26 cfu/g in the spleen and 10² cfu/g in the liver. Most of the muscle samples were not contaminated. Greater contamination was not found under conditions of stress such as high organic load, a water temperature of 37°C or low levels of dissolved oxygen.     

Effect of Doping and Excitation Wavelength on Charge Carrier Dynamics in Hematite by Time‐Resolved Microwave and Terahertz Photoconductivity

The charge carrier dynamics of epitaxial hematite films is studied by time‐resolved microwave (TRMC) and time‐resolved terahertz conductivity (TRTC). After excitation with above bandgap illumination, the TRTC signal decays within 3 ps, consistent with previous reports of charge carrier localization times in hematite. The TRMC measurements probe charge carrier dynamics at longer timescales, exhibiting biexponential decay with characteristic time constants of ≈20–50 ns and 1–2 μs. From the change in photoconductance, the effective carrier mobility is extracted, defined as the product of the charge carrier mobility and photogeneration yield, of differently doped (undoped, Ti, Sn, Zn) hematite films for excitation wavelengths of 355 and 532 nm. It is shown that, unlike in conventional semiconductors, donor doping of hematite dramatically increases the effective mobility of the photogenerated carriers. Furthermore, it is shown that all hematite films possess higher effective mobility for 355 nm excitation than for 532 nm excitation, although the time dependence of the photoconductance decay, or charge carrier lifetime, remains the same. These results provide an explanation for the wavelength dependent photoelectrochemical behavior of hematite photoelectrodes and suggest that an increase in photogeneration yield or charge carrier mobility is responsible for the improved performance at higher excitation energies.     

Thermally oxidized iron oxide nanoarchitectures for hydrogen production by solar-induced water splitting

Thermally oxidized iron oxide (α-Fe₂O₃, Hematite) nanostructures are investigated as photoanodes that convert solar energy into hydrogen by splitting water. α-Fe₂O₃ is stable for water photo-oxidation, it has a favorable band gap energy and is a non-toxic common material. However, α-Fe₂O₃ photoanodes suffer from high loss due to electron-hole recombination; therefore nanoarchitectures with high aspect ratio that allows photons to be absorbed close to the photoanode/electrolyte interface are preferred. The thermal oxidation of iron is a simple way to produce nanostructured iron oxide electrodes. Different morphologies, aspect ratios, and oxide thicknesses result depending on the process parameters. Nanorod structures were obtained by annealing iron foils in oxygen rich atmosphere, whereas annealing in oxygen lean atmosphere resulted in nanocoral-like morphology. The nanorod-structured photoanodes achieved moderate photocurrent density of 0.9 mA/cm² while the nanocoral morphology achieved 2.6 mA/cm² (both at 1.8 V vs. the reversible hydrogen electrode). The effect of the oxidation process and oxide layer on performance is discussed.     

Prospective materials for biodegradable and/or biobased pressure-sensitive adhesives: a review

A pressure-sensitive adhesive (PSA) is an adhesive system that is permanently tacky and adheres to a variety of surfaces with light pressure without phase changes. These adhesives are most commonly found in adhesive tapes such as the Scotch® tape or Post-it® notes. The majority of PSAs are petroleum-based products and usually not biodegradable. The amount of waste generated from these products is quite large as these products are considered disposable. The present review focuses on biodegradable elastomers and how they can be useful in PSAs. This review also covers some novel PSA systems that are biobased or biodegradable.