Preparation and properties of polypropylene nanocomposites reinforced with exfoliated graphene

We have prepared a series of polypropylene/exfoliated graphene (PP/EG) nanocomposite films via efficient meltcompounding and compression, and investigated their morphology, structures, thermal transition behavior, thermal stability, electrical and mechanical properties as a function of EG content. For the purpose, EG, which is composed of disordered graphene platelets as reinforcing nanoscale fillers, is prepared by the oxidation/exfoliation process of natural graphite flakes. SEM images and X-ray diffraction data confirm that the graphene platelets of EG are well dispersed in PP matrix for the nanocomposites with EG contents less than 1.0 wt%. It is found that thermo-oxidative degradation of PP/EG nanocomposites is noticeably retarded with the increasing of EG content. Electrical resistivity of the nanocomposite films was dramatically changed from ∼10¹⁶ to ∼10⁶ Ω·cm by forming electrical percolation threshold at an certain EG content between 1 and 3 wt%. Tensile drawing experiments demonstrate that yielding strength and initial modulus of PP/EG nanocomposite films are highly improved with the increment of EG content.     

Preparation and crystallization behavior of polylactide nanocomposites reinforced with POSS-modified montmorillonite

We herein report the preparation and crystallization behavior of polylactide (PLA) nanocomposites reinforced with polyhedral oligomeric silsesquioxane-modified montmorillonite (POSS-MMT), which is prepared by exchanging sodium cations of pristine sodium montmorillonite (Na-MMT) with protonated aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS-NH₃ ⁺). PLA nanocomposites with 1–10 wt% POSS-MMT contents are manufactured via melt-compounding, and their structures and melt-crystallization behavior are investigated. It is characterized that POSS-MMT nanoparticles in the nanocomposites have an exfoliated structure of MMT silicates with POSS-NH₃ ⁺ and partial POSS-NH₂ crystals. DSC cooling thermograms suggest that the overall melt-crystallization rates of the nanocomposite with only 3 wt% POSS-MMT are remarkably enhanced in comparison with the neat PLA. From the isothermal crystallization analysis based on the Avrami model, the overall melt-crystallization of PLA/POSS-MMT nanocomposites is found to be dominated by the heterogeneous nucleation and three-dimensional spherulite growth. Isothermal melt-crystallization experiments using a polarized optical microscope show that the spherulite nucleation density of PLA/POSS-MMT nanocomposites is much higher than that of the neat PLA, whereas the spherulite growth rates of all the nanocomposites are almost identical with the rate of the neat PLA. It is concluded that the highly enhanced melt-crystallization rates of PLA/POSS-MMT nanocomposites stem from the dominant nucleation effect of POSS-MMT nanoparticles for PLA crystals.     

Mechanical properties and crystallization behavior of polypropylene non-woven fabrics reinforced with POSS and SiO2 nanoparticles

PP/POSS and PP/SiO₂ composite non-woven fabrics filled with polyhedral oligomeric silsesquioxanes (POSS) and SiO₂ respectively using a convenient blending method were prepared through melt-blown process with corona charging. The morphology of the composite fibers and the distribution of POSS and SiO₂ nanoparticles in PP matrix were investigated by field-emission scanning electron microscope (FSEM) and transmission electron microscope (TEM), respectively. POSS and SiO₂ can act as nucleating agent and accelerate the crystallization process during nonisothermal cooling. The shear storage modulus G??, loss modulus G??, and complex viscosity ??* of non-woven fabric reduce when 1 wt % POSS was added and increase for PP5/POSS composite non-woven fabric compared with pure PP non-woven fabrics. However, all G??, G?? and ??* of PP/SiO₂ non-woven fabric decrease with increasing SiO₂ content owing to plasticization by SiO₂. Both stress and elongation at break of the PP/POSS melt-blown non-woven fabrics are improved compared with PP non-woven fabrics, however decrease when SiO₂ was added, as compared to the neat PP non-woven fabric. The onset temperature of decomposition for both the PP/POSS and PP/SiO₂ composite non-woven fabrics is higher (5?C10 °C) than pure PP and char content is increased with increasing POSS and SiO₂.     

Mechanical and thermal degradation behavior of sisal fiber (SF) reinforced recycled polypropylene (RPP) composites

The present investigation focuses on the effect of fiber surface treatment on the mechanical, thermal and morphological properties of sisal fiber (SF) reinforced recycled polypropylene (RPP) composites. The surface of sisal fiber was modified using different chemicals such as silane, glycidyl methacrylate (GMA) and O-hydroxybenzene diazonium chloride (OBDC) to improve the compatibility between fiber surface and polymer matrix. The experimental results revealed an improvement in the tensile strength to 11 %, 20 % and 31.36 % and impact strength to 78.72 %, 77 % and 81 % for silane, GMA and OBDC treated sisal fiber reinforced recycled polypropylene (RPP/SF) composites respectively as compared to RPP. The thermo gravimetric analysis (TGA), Differential scanning calorimeter (DSC) and heat deflection temperature (HDT) results revealed improved thermal stability as compared with RPP. The morphological analysis through scanning electron micrograph (SEM) supports improves surface interaction between fiber surface and polymer matrix.     

Functionalized graphene nanoplatelets/poly(ethylene oxide) nanocomposites: Correlation between crystallization behavior and mechanical performance

Poly(ethylene oxide) (PEO) nanocomposites containing pristine or functionalized graphene nanoplatelets (FGnP) prepared via solution blending and thermal and mechanical properties of nanocomposites were investigated. Chemical functionalization of graphene nanoplatelets was conducted through an amidation reaction between carboxylic acid groups of acidified graphene and hydroxyl groups of polyethylene glycol (PEG). An interfacial linkage and a good dispersion of FGnP was observed via scanning electron microscope (SEM). Differential scanning calorimetry (DSC) analysis revealed that the degree of crystallinity of samples decreased by addition of graphene nanoplatelets, while the size of spherulites increased as indicated by polarized optical microscope (POM). A lower degree of crystallinity and larger spherulites were detected in the case of FGnP. Filler/matrix interfacial adhesion was also remarkably influenced the mechanical properties of PEO as an effective reinforcement of matrix obtained upon the addition of FGnP nanosheets compared to untreated graphene.     

Balancing pest management and forest biodiversity: Vole populations and habitat in clearcut vs. variable retention harvested sites

Voles of the genus Microtus are long-standing pests in temperate and boreal forests of North America, Europe, and Asia where they feed on newly planted trees on cutover forest land. Clearcutting (CC) dominates forest harvesting and produces homogeneous habitats for voles. Variable retention (VR) harvests involve various partial cutting practices that produce heterogeneous habitat patterns compared with CC. This study tested the hypotheses (H) that compared to CC, VR harvesting will (H₁) limit population size of Microtus and feeding damage to tree seedlings; (H₂) provide some mature forest habitat for red-backed voles (Myodes gapperi); and (H₃) enhance abundance and species diversity of the terrestrial small mammal community. Microtus, red-backed voles, and other forest-floor small mammals were live-trapped for three years (2007-2009) on “young” and “older” CC and VR sites near Golden, British Columbia, Canada. Mean basal area (BA) and density of overstory coniferous trees were significantly (P ≤ 0.03) higher in the young VR than CC sites. Abundance of herbaceous vegetation and grasses was similar in both harvesting systems at 3- and 5-years post-harvest. Although not statistically significant, the relatively higher numbers (2.3-2.9 times) of Microtus on CC than VR sites at 3-4 years post-harvest is suggestive that VR may reduce Microtus population size. However, the mean abundance of 35 Microtus/ha in VR sites at 3 years post-harvest was at the border-line of moderate to high risk of feeding damage. Based on equivocal levels of vole damage to plantation trees on CC and VR sites, the damage part of H₁ was refuted. With respect to H₂, VR harvesting did provide some forest habitat for red-backed voles, at least initially in the third year, and then again at 10-20 years, after VR cutting. Total abundance and species diversity of the terrestrial small mammal community were similar in CC and VR sites, and hence H₃ was rejected. The mean BA (14.7 m²/ha) and density (73-127 trees/ha) of overstory (>10-20 m height) trees of our VR sites were insufficient to alter development of understory herbaceous vegetation and abundance of Microtus. Higher levels of VR should be investigated as a means of reducing this pest problem in young plantations.     

Beauveria bassiana characterization and efficacy vs. Sunn pest, Eurygaster integriceps Puton (Hemiptera:Scutelleridae)

The objectives of this study were to evaluate the efficacy of Sunn pest entomopathogenic fungi collected from wheat fields and overwintering sites in Syria and characterize them under different temperature regimes. Eleven isolates of Beauveria bassiana (Bals.) Vuil. were included in this study: five were isolated from overwintered adults of Sunn Pest, Eurygaster integriceps Puton and six from nymphs and new adults in wheat fields. Growth rate and conidial production were tested at 15, 20, 25, 30 and 35 degrees C. Results showed that highest growth rate of tested fungal isolates was at 25 degrees C, except for the two isolates SPDR-1 and SPDR-2 which exhibited highest growth rate at 20 degrees C. The highest production of conidia of tested fungal isolates was at 20 degrees C, except for isolates SPSR-1, SPSQ and SPSS which exhibited higher production at 25 degrees C. Virulence test of the tested fungal isolates on overwintered adults Sunn Pest showed that percent mortality after 14 days ranged between 86-100%.     

Genetic shifts in smooth bromegrass under grazing: changes in nutritional value and preference for surviving vs. original genotypes

Genetic shifts in plant morphology and reproductive characters under grazing may potentially affect nutritive value and preference. This research was conducted to determine the response of smooth bromegrass ( Bromus inermis Leyss.) populations to long-term grazing. Genotypes from five populations of smooth bromegrass that survived 9 years of grazing were compared with genotypes of each population grown from original seed. Plant height was measured and biomass estimated for each genotype, before and after grazing by sheep, in order to assess preference. Genotypes were also tested for nutritive value. The selective effect of competition during establishment and maintenance under grazing was accompanied by genetic shifts in smooth bromegrass plants in these pastures. Survivors had greater plant biomass despite having a decrease in plant height of up to 5%. Preference for survivors, quantified as percentage consumption by sheep, was up to 3% units less than for original populations. The nutritive value of survivors was similar to that of original populations, except for one population, which had a lower neutral-detergent fibre among the survivors after grazing.     

On the Health Benefits vs. Risks of Seaweeds and Their Constituents: The Curious Case of the Polymer Paradigm

To exploit the nutraceutical and biomedical potential of selected seaweed-derived polymers in an economically viable way, it is necessary to analyze and understand their quality and yield fluctuations throughout the seasons. In this study, the seasonal polysaccharide yield and respective quality were evaluated in three selected seaweeds, namely the agarophyte Gracilaria gracilis, the carrageenophyte Calliblepharis jubata (both red seaweeds) and the alginophyte Sargassum muticum (brown seaweed). It was found that the agar synthesis of G. gracilis did not significantly differ with the seasons (27.04% seaweed dry weight (DW)). In contrast, the carrageenan content in C. jubata varied seasonally, being synthesized in higher concentrations during the summer (18.73% DW). Meanwhile, the alginate synthesis of S. muticum exhibited a higher concentration (36.88% DW) during the winter. Therefore, there is a need to assess the threshold at which seaweed-derived polymers may have positive effects or negative impacts on human nutrition. Furthermore, this study highlights the three polymers, along with their known thresholds, at which they can have positive and/or negative health impacts. Such knowledge is key to recognizing the paradigm governing their successful deployment and related beneficial applications in humans.     

High-yield irrigated maize in the Western U.S. Corn Belt: I. On-farm yield,yield potential,and impact of agronomic practices

Quantifying the exploitable gap between average farmer yields and yield potential (Y_P) is essential to prioritize research and formulate policies for food security at national and international levels. While irrigated maize accounts for 58% of total annual maize production in the Western U.S. Corn Belt, current yield gap in these systems has not been quantified. Our objectives were to quantify Y_P, yield gaps, and the impact of agronomic practices on both parameters in irrigated maize systems of central Nebraska. The analysis was based on a 3-y database with field-specific values for yield, applied irrigation, and N fertilizer rate (n = 777). Y_P was estimated using a maize simulation model in combination with actual and interpolated weather records and detailed data on crop management collected from a subset of fields (n = 123). Yield gaps were estimated as the difference between actual yields and simulated Y_P for each field-year observation. Long-term simulation analysis was performed to evaluate the sensitivity of Y_P to changes in selected management practices. Results showed that current irrigated maize systems are operating near the Y_P ceiling. Average actual yield ranged from 12.5 to 13.6 Mg ha⁻¹ across years. Mean N fertilizer efficiency (kg grain per kg applied N) was 23% greater than average efficiency in the USA. Rotation, tillage system, sowing date, and plant population density were the most sensitive factors affecting actual yields. Average yield gap was 11% of simulated Y_P (14.9 Mg ha⁻¹). Time trends in average farm yields from 1970 to 2008 show that yields have not increased during the past 8 years. Average yield during this period represented ∼80% of Y_P ceiling estimated for this region based on current crop management practices. Simulation analysis showed that Y_P can be increased by higher plant population densities and by hybrids with longer maturity. Adoption of these practices, however, may be constrained by other factors such as difficulty in planting and harvest operations due to wet weather and snow, additional seed and grain drying costs, and greater risk of frost and lodging. Two key points can be made: (i) irrigated maize producers in this region are operating close to the Y_P ceiling and achieve high levels of N use efficiency and (ii) small increases in yield (<13%) can be achieved through fine tuning current management practices that require increased production costs and higher risk.     

Optimal harvest timing vs. harvesting for animal forage supply: Impacts on production and quality of lucerne on the Loess Plateau,China

The current promotion of larger areas of lucerne (Medicago sativa) production on the Loess Plateau in China prompted this study, which investigated lucerne harvesting practices by farmers and the scope for improved harvest yield and quality by optimizing harvest date, interval and height above ground. On-farm surveys were conducted to document the dominant harvesting practices used by farmers and their perceptions of barriers to adoption of alternative harvesting practices. In districts with less emphasis on livestock, less labour and inadequate facilities to store conserved lucerne, smaller areas of lucerne are grown and it is often harvested daily to meet demand from penned livestock. The consequence is that much of the lucerne is harvested either before or after flowering, resulting in suboptimal yield of biomass and crude protein. Field experiments conducted at low and high rainfall locations on the Loess Plateau over three seasons showed that delaying the start to harvest until after mid-June (the date of first flowering), while not affecting total biomass harvested for the season, does reduce leaf biomass harvested and hence crude protein concentration and yield. Lower crude protein is a consequence of a decline in both leaf percentage in harvested biomass and stem nitrogen concentration. Commencing harvests well before flowering with short (3 week) harvest intervals also penalized total and leaf biomass harvested. Raising cutting height from ground level (current farmer practice) to 50 mm (likely with the advent of mechanized harvesting) did not penalize harvested total or leaf biomass.     

RSK1 vs. RSK2 Inhibitory Activity of the Marine β-Carboline Alkaloid Manzamine A: A Biochemical,Cervical Cancer Protein Expression,and Computational Study

Manzamines are complex polycyclic marine-derived β-carboline alkaloids with reported anticancer, immunostimulatory, anti-inflammatory, antibacterial, antiviral, antimalarial, neuritogenic, hyperlipidemia, and atherosclerosis suppression bioactivities, putatively associated with inhibition of glycogen synthase kinase-3, cyclin-dependent kinase 5, SIX1, and vacuolar ATPases. We hypothesized that additional, yet undiscovered molecular targets might be associated with Manzamine A’s (MZA) reported pharmacological properties. We report here, for the first time, that MZA selectively inhibited a 90 kDa ribosomal protein kinase S6 (RSK1) when screened against a panel of 30 protein kinases, while in vitro RSK kinase assays demonstrated a 10-fold selectivity in the potency of MZA against RSK1 versus RSK2. The effect of MZA on inhibiting cellular RSK1 and RSK2 protein expression was validated in SiHa and CaSki human cervical carcinoma cell lines. MZA’s differential binding and selectivity toward the two isoforms was also supported by computational docking experiments. Specifically, the RSK1-MZA (N- and C-termini) complexes appear to have stronger interactions and preferable energetics contrary to the RSK2–MZA ones. In addition, our computational strategy suggests that MZA binds to the N-terminal kinase domain of RSK1 rather than the C-terminal domain. RSK is a vertebrate family of cytosolic serine-threonine kinases that act downstream of the ras-ERK1/2 (extracellular-signal-regulated kinase 1/2) pathway, which phosphorylates substrates shown to regulate several cellular processes, including growth, survival, and proliferation. Consequently, our findings have led us to hypothesize that MZA and the currently known manzamine-type alkaloids isolated from several sponge genera may have novel pharmacological properties with unique molecular targets, and MZA provides a new tool for chemical-biology studies involving RSK1.