Epoxy resin composites filled with ceramic particles are commonly applied in electrification devices as an electrical insulation. In order to maintain proper functionality of such apparatuses it is ...crucial to optimize a broad range of properties, such as thermal, mechanical and dielectric parameters. In an earlier paper, a novel core-shell filler was developed in order to enhance the thermal conductivity in the epoxy composite used as electrical insulation. The new filler was made of a standard material, which was covered by a thin layer of high thermally conductive shell, namely, alumina coated by aluminum nitride. It was previously shown that the epoxy resin filled with the core-shell Al2O3@AlN particles showed a significant increase in thermal conductivity with a 63% relative increase. In this paper, a set of complementary measurements was performed and analyzed, namely, rheology, tensile strength, dynamic mechanical analysis, and dilatometry. Moreover, the dielectric permittivity and strength, and electrical resistivity were investigated in order to check if the electrical insulation properties were maintained. The obtained results were compared with the epoxy composite filled with the standard filler. The rheological behavior of the core-shell filled system showed that the processability will not be hindered. The mechanical properties of the composite based on core-shell filler are better than those of the reference system. The coefficient of linear thermal expansion is lower for epoxy filled with core-shell filler, which can lead to better adhesion to internal parts in the electrification devices. The dielectric strength was enhanced by 16% for the core-shell filled epoxy. The investigation clearly demonstrates that the epoxy composite filled with the core-shell particles is an appropriate material for application as electrical insulation with enhanced thermal conductivity.
Ulva
species are characterised by the capacity to achieve rapid biomass increase, which results in the formation of “green tides”, particularly in nutrient-rich seawaters. Over the last decade, ...formation of large-scale
Ulva
mats has been increasingly observed in freshwater systems in Central Europe. Mass development of
Ulva
in freshwater ecosystems presents a growing burden in spite of its economic benefits. This study explores the formation dynamics of
Ulva flexuosa
mats with respect to habitat conditions, using the examples of a number of water systems located in Poland. Elevated water temperature, pH and high concentration of sulphates are among the most important factors affecting biometric parameters of
Ulva
blooms. An evident disparity was observed between lotic water ecosystems and lentic water ecosystems, which differed in terms of chemical characteristics of the habitat and mat structure properties. In flowing water,
U. flexuosa
displays a definitely higher potential for blooms. On the other hand, mass occurrence of
U. flexuosa
in freshwaters is caused by the inflow of fecund waters, especially following intense precipitation in summertime, as well as by periodic increases in salinity, pH and sulphate levels. The study suggests that potential
U. flexuosa
blooms in landlocked ecosystems may be controlled by means of reducing the inflow of particularly sulphate-rich waters.
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•Use of U. pilifera as an indicator is compatible with the WFD guidelines.•Freshwater U. pilifera occurs in eutrophic ponds.•U. pilifera can be easily identified even by ...non-expert.•U. pilifera can be used as trophic indicator for pond systems.•U. pilifera should be included into pond monitoring protocols.
Mass occurrence of green algae of the genus Ulva in the form of algal blooms (known as “green tides”) is often associated with high concentrations of biogens in the water. Therefore, Ulva species are most often used in monitoring seawater trophy and far less frequently freshwater trophy. In Europe, the biomonitoring of river ecosystems is based on aquatic plants. According to the River Macrophyte Index (RMI), river populations of Ulva macroalgae (only tubular Enteromorpha-like Ulva) are considered good indicators for eutrophic waters. This paper analyses the legitimacy of using U. pilifera as a trophy indicator in the case of ponds. It has been noted that freshwater populations of U. pilifera are much more common in lakes, dammed reservoirs, or ponds than in rivers. In this study, analysed populations of U. pilifera originated from 14 ponds located in central Poland. Data analysis relied on the Carlson Trophic State Index (CTSI), which was compared with other known trophic indices. According to CTSI values, U. pilifera was most common in eutrophic ponds, where the mean concentrations of ammonium nitrogen, nitrates, total phosphorus, and chlorophyll a reached 581, 241, 212, and 20 µg·L−1, respectively. The results indicate that U. pilifera can be considered a bioindicator for eutrophic waters (50–70 of CTSI). It would therefore be appropriate to introduce U. pilifera as part of biomonitoring conducted in small bodies of water. Major arguments in favour of practical application of U. pilifera are: (i) it is a large macroalga, the thalli of which can reach a length of > 1.0 m, (ii) it is an easy-to-identify species; even by non-experts (it is characterized by a distinctive tubular shape of the thallus), and (iii) it occurs in bulk in conditions of eutrophy, creating an easily observable bloom.
The evaluation of a possible application of functional shrinkable materials in thermally conductive electrical insulation elements was investigated. The effectiveness of an electron beam and gamma ...radiation on the crosslinking of a selected high density polyethylene grade was analyzed, both qualitatively and quantitatively. The crosslinked polymer composites filled with ceramic particles were successfully fabricated and tested. On the basis of the performed investigation, it was concluded that the selected filler, namely a boron nitride powder, is suitable for the preparation of the crosslinked polymer composites with enhanced thermal conductivity. The shape memory effect was fully observed in the crosslinked samples with a recovery factor reaching nearly 99%. There was no significant influence of the crosslinking, stretching, and recovery of the polymer composite during shape memory phenomenon on the value of thermal conductivity. The proposed boron nitride filled polyethylene composite subjected to crosslinking is a promising candidate for fabrication of thermally shrinkable material with enhanced heat dissipation functionality for application as electrically insulating components.
The influence of the structure and the temperature on the Conductive Polymer Composites (CPC) properties has been studied. The investigated CPC are based on homo- and heterogeneous polymer blends of ...high density polyethylene, polybutylene terephthalate and poly(m-xylene adipamide), filled with dispersed silver nanoparticles (Ag). It is shown that by the appropriate use of the immiscible polymers blends the percolation threshold can be decreased twice, what significantly reduces costs and keeps better mechanical properties. Additionally, it was found that depending on the choice of CPC structure the commutation temperature from a conducting state to an insulating state can be observed between 45 and 180
°C. The observed high intensity of Positive Temperature Coefficient (PTC) effect, i.e. a sharp (narrow temperature range) and strong (10 orders of magnitude) resistivity increase, makes such composites promising for current limiting devices and temperature sensors.
SUMMARY
Cosmopolitan species of the genus Ulva (Ulvaceae; Chlorophyta) that populate the littoral zone of marine habitats constitute a staple diet for a variety of organisms, particularly snails, ...shellfish, polychaetes, and birds. Occurrence of Ulva species (e.g., U. flexuosa and U
. prolifera) has also been observed in freshwater inland ecosystems that have no contact with saline water. However, the influence of the development of macroalgal mats of Ulva on indigenous organisms in limnic ecosystems has not been established. This study investigates the trophic relationships between Ulva flexuosa and one species of snail from freshwater habitats in central Europe. During the summer, the great pond snail (Lymnaea stagnalis) consumed Ulva as a source of nutrition even when other algae and plants were available. Lymnaea stagnalis consumed an average of 100 mg of Ulva thalli per day. This level of biomass exceeded the consumption of an alternative food source, the shoots of Elodea canadensis. Ulva thalli are more actively consumed by great pond snails than Elodea shoots, and this is expressed in terms of the differences of biomass consumption. It was also observed that the interior of the monostromatic tubular thalli of Ulva flexuosa serves as a protective shelter for juvenile great pond snails.
An effective model to calculate thermal conductivity of polymer composites using core-shell fillers is presented, wherein a core material of filler grains is covered by a layer of a ...high-thermal-conductivity (HTC) material. Such fillers can provide a significant increase of the composite thermal conductivity by an addition of a small amount of the HTC material. The model employs the Lewis-Nielsen formula describing filled systems. The effective thermal conductivity of the core-shell filler grains is calculated using the Russel model for porous materials. Modelling results are compared with recent measurements made on composites filled with cellulose microbeads coated with hexagonal boron nitride (h-BN) platelets and good agreement is demonstrated. Comparison with measurements made on epoxy composites, using silver-coated glass spheres as a filler, is also provided. It is demonstrated how the modelling procedure can improve understanding of properties of materials and structures used and mechanisms of thermal conduction within the composite.
This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by ...means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young's modulus and tensile strength are reached as the composites become more brittle.
Research on the diversity of thalli and mats built by freshwater
, as well as the impact of abiotic factors on the development and distribution of
mats, was conducted from May to August 2013. The ...study describes the dynamics of “green tides” formation by
. The study assessed abiotic factors that may influence the colonization and the growth of
populations in freshwater systems. The results are of major importance to the trade and industry sectors. In total, eleven environmental parameters were included in the analysis. The most important environmental parameters characterizing the
sites are sodium chloride levels and conductivity. High values of pH inhibited the development of
, leading to a lower percentage of mature thalli in the mats. The water depth was positively correlated with an increase in the density of thalli in the mats and the average thallus length. Significant differences were identified between the concentrations of nitrates under and outside the
mats. Concentrations of nitrate under the
thalli were always lower.
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