12 research outputs found
Particulate Fillers in Thermoplastics
The characteristics of particulate filled thermoplastics are determined by four factors: component properties, composition, structure and interfacial interactions. The most important filler characteristics are particle size, size distribution, specific surface area and particle shape, while the main matrix property is stiffness. Segregation, aggregation and the orientation of anisotropic particles determine structure. Interfacial interactions lead to the formation of a stiff interphase considerably influencing properties. Interactions are changed by surface modification, which must be always system specific and selected according to its goal. Under the effect of external load inhomogeneous stress distribution develops around heterogeneities, which initiate local micromechanical deformation processes determining the macroscopic properties of the composites
Comparing the use of leaf and soil analysis as N and P availability indices in a wildfire chronosequence
Two types of measures have traditionally been
used to monitor changes after disturbances in the nutrient
availability of forest ecosystems: (1) soil nutrient pools and
transformation rates and (2) foliar nutrient content. We
used a wildfire chronosequence in natural and unmanaged
Pinus canariensis forests to determine which kind of
measure is more effective in discriminating between disturbed
and undisturbed plots and to determine whether the
different availability indices provide comparable and consistent
results within the chronosequence and between
different sampling dates. The results showed that (1) foliar
N and P concentrations were the variables that best discriminated
between the plots of the chronosequence, (2) the
various soil N availability indices neither showed steady
relationships nor predicted the plant nutrient availability,
and (3) P availability indices showed steady relationships
and predicted plant nutrient availability. Due to the
changing nature of the soil N pools, repeated sampling over
a long period of time could yield results different from
those presented here. However, the large sampling effort
required would favor the use of foliar nutrient
concentrations as the most desirable first approach to the
community’s nutritional status, especially when time or
budget constraints are relevant
Increasing CO2 threatens human nutrition
Dietary deficiencies of zinc and iron are a substantial global public health problem. An estimated two billion people suffer these deficiencies, causing a loss of 63 million life-years annually. Most of these people depend on C3 grains and legumes as their primary dietary source of zinc and iron. Here we report that C3 grains and legumes have lower concentrations of zinc and iron when grown under field conditions at the elevated atmospheric CO2 concentration predicted for the middle of this century. C3 crops other than legumes also have lower concentrations of protein, whereas C4 crops seem to be less affected. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partly address these new challenges to global health
Particulate filled polypropylene: Structure and properties
The characteristics of all heterogeneous polymer systems including composites containing either micro or nano fillers are determined by four factors: component properties, composition, structure and interfacial interactions. The most important filler characteristics are particle size, size distribution, specific surface area and particle shape, while the main matrix property is stiffness. Segregation, aggregation and the orientation of anisotropic particles determine structure. Interfacial interactions lead to the formation of a stiff interphase considerably influencing properties. Interactions are changed by surface modification, which must be always system specific and selected according to its goal. Under the effect of external load inhomogeneous stress distribution develops around heterogeneities, which initiate local deformation processes determining the macroscopic properties of the composites. In filled polymers, the dominating deformation mechanism is usually debonding. Particulate filled polypropylene is used in many areas, but development never stops. Natural fiber and wood reinforced polymers, layered silicate nanocomposites and hybrid composites are in the focus of attention in recent times