Developing Post-Consumer Recycled Flexible Polypropylene and Fumed Silica-Based Nanocomposites with Improved Processability and Thermal Stability.

Collection and mechanical recycling of post-consumer flexible polypropylene packaging is limited, principally due to polypropylene being very light-weight. Moreover, service life and thermal-mechanical reprocessing degrade PP and change its thermal and rheological properties according to the structure and provenance of recycled PP. This work determined the effect of incorporating two fumed nanosilica (NS) types on processability improvement of post-consumer recycled flexible polypropylene (PCPP) through ATR-FTIR, TGA, DSC, MFI and rheological analysis. Presence of trace polyethylene in the collected PCPP increased the thermal stability of the PP and was significantly maximized by NS addition. The onset decomposition temperature raised around 15 °C when 4 and 2 wt% of a non-treated and organically modified NS were used, respectively. NS acted as a nucleating agent and increased the crystallinity of the polymer, but the crystallization and melting temperatures were not affected. The processability of the nanocomposites was improved, observed as an increase in viscosity, storage and loss moduli with respect to the control PCPP, which were deteriorated due to chain scission during recycling. The highest recovery in viscosity and reduction in MFI were found for the hydrophilic NS due to a greater impact of hydrogen bond interactions between the silanol groups of this NS and the oxidized groups of the PCPP.

Morphometric parameters of foodborne related-pathogens estimated by transmission electron microscopy and their relation to optical density and colony forming units.

The different morphological characteristics of five bacterial pathogen strains were analyzed through transmission electron microscopy for addressing the particular relationship between optical density and colony-forming units for each strain. Generated linear equations will allow a reliable calculation of bacterial concentrations through simple optical density measurements.

Fracture behavior of a commercial starch/polycaprolactone blend reinforced with different layered silicates.

In the present work, composites based on a commercial starch/PCL blend (MaterBi-Z) reinforced with three different nanoclays: natural montmorillonite (Cloisite Na(+) (MMT)) and two modified montmorillonites (Cloisite 30B (C30B) and Cloisite 10A (C10A)) were prepared in an intensive mixer. The aim of this investigation was to determine the effect of the different nanoclays on the quasi-static fracture behavior of MaterBi-Z nanocomposites. An improvement in the fracture behavior for the composite with low contents of C30B was obtained, probably due to the easy debonding of clay achieved from a relatively weak filler-matrix interaction. On the other hand, a strong interaction had a detrimental effect on the material fracture toughness for the MaterBi-Z/C10A composites as a result of the higher compatibility of this organo-modified clay with the hydrophobic matrix. Intermediate values of fracture toughness, determined using the J-integral approach (Jc), were found for the composites with MMT due to its intermediate interaction with the matrix. The different filler-matrix interactions observed were also confirmed from the application of Pukánszky and Maurer model. In addition, multifractal analysis was applied to describe the topography of fracture surfaces. Thus, the complex fracture process could be successfully described by both experimental and theoretical tools. The obtained results suggest that it is possible to tailor the mechanical properties of the studied composites taking into account their further application.

Assessment of insecticide resistance in five insect pests attacking field and vegetable crops in Nicaragua.

Field populations of Hypothenemus hampei (Ferrari), Plutella xylostella (L.), Spodoptera exigua (Hübner), Helicoverpa zea (Boddie) and Bemisia tabaci (Gennadius) were tested for resistance to several insecticides commonly used in Nicariagua. Assays were conducted to estimate the LD50s or LC50s and the corresponding resistance ratios. A diagnostic concentration was used to discriminate between susceptible and resistant strains of H. hampei. The tests with >6,000 H. hampei adults collected from six different sites indicate the absence of resistance to endosulfan. Resistance to cypermethrin, deltamethrin, chlorfluazuron, thiocyclam, and methamidophos was documented in six field populations of P. xylostella. High levels of resistance to cypermethrin and deltamethrin, but moderate levels of resistance to chlorpyriphos and methomyl, were also documented in two field populations of S. exigua. Moderate levels of resistance to cypermethrin, deltamethrin and chlorpyriphos were also documented in three field populations of H. zea. Moderate to high levels of resistance to bifenthrin, methamidophos and endosulfan were documented in four field populations of B. tabaci. The presence of significant correlations between LD50s or LC50s suggests the occurrence of cross-resistance or simultaneous selection for resistance by different insecticides with different modes of action. Our data could not differentiate between these two possibilities. Because insecticides will continue being used in Nicaragua, a resistance management program is urgently needed. The implementation of integrated pest management tactics must be accompanied by specific regulations for pesticide registration. In the future, pesticide registration regulations in Nicaragua should include periodic resistance monitoring. The mechanisms to cover the costs of resistance monitoring and resistance management should also be established.