Glass-fibre-reinforced composites with enhanced mechanical and electrical properties - Benefits and limitations of a nanoparticle modified matrix

Nanoparticles and especially carbon nanotubes (CNTs) provide a high potential for the modification of polymers. They are very effective fillers regarding mechanical properties, especially toughness. Furthermore, they allow the implication of functional properties, which are connected to their electrical conductivity, into polymeric matrices. In the present paper, different nanoparticles, as fumed silica and carbon black, were used to optimise the epoxy matrix system of a glass-fibre-reinforced composite. Their nanometre-size enables their application as particle-reinforcement in FRPs produced by the resin-transfer-moulding method (RTM), without being filtered by the glass-fibre bundles. Additionally, an electrical field was applied during curing, in order to enhance orientation of the nanofillers in z-direction. The interlaminar shear strengths of the nanoparticle modified composites were significantly improved (+16%) by adding only 0.3 wt.% of CNTs. The interlaminar toughness G_Ic and G_IIc was not affected in a comparable manner. The laminates containing carbon nanotubes exhibited a relatively high electrical conductivity at very low filler contents, which allows the implication of functional properties, such as stress-strain monitoring and damage detection.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

Über den Anbau von Pilinuß conorium ovatum und die Fettsäuren-und Triglycerid-Zusammensetzung des Öls

Cultivation of Pilinut conorium ovatum and the Composition of Fatty Acids and Triglycerides of the Oil It is reported on the cultivation of Pilinut conorium ovatum and the composition of the fatty acids and triglycerides of the pilinut oil. Characteristic for this oil is the high content in palmitic acid. Exceptional for nut oils is the content of the low fatty acids capryl-, caprin-, lauric- and myristic acid. Characteristic for the composition of the triglycerides of pilinut oil is the low content of triolein.     

Load and health monitoring in glass fibre reinforced composites with an electrically conductive nanocomposite epoxy matrix

Fibre reinforced polymers (FRPs) are an important group of materials in lightweight constructions. Most of the parts produced from FRPs, like aircraft wings or wind turbine rotor blades are designed for high load levels and a lifetime of 30 years or more, leading to an extremely high number of load cycles to sustain. Consequently, the fatigue life and the degradation of the mechanical properties are aspects to be considered. Therefore, in the last years condition monitoring of FRP-structures has gained importance and different types of sensors for load and damage sensing have been developed.

In this work a new approach for condition monitoring was investigated, which, unlike other attempts, does not require additional sensors, but instead is performed directly by the measurement of a material property of the FRP. An epoxy resin was modified with two different types of carbon nanotubes and with carbon black, in order to achieve an electrical conductivity. Glass fibre reinforced composites (GFRP) were produced with these modified epoxies by resin transfer moulding (RTM). Specimens were cut from the produced materials and tested by incremental tensile tests and fatigue tests and the interlaminar shear strength (ILSS) was measured. During the mechanical tests the electrical conductivity of all specimens was monitored simultaneously, to assess the potential for stress/strain and damage monitoring.

The results presented in this work, show a high potential for both, damage and load detection of FRP structures via electrical conductivity methods, involving a nanocomposite matrix.     

Age of entry to day nursery and allergy in later childhood

BACKGROUND: Infections in early childhood may prevent allergies in later life. If this hypothesis is true, early exposure to childcare outside the home would protect against atopy by promotion of cross infections. We investigated whether children who attend a nursery at a young age have a lower rate of atopy and fewer allergies than children who attend from an older age. METHODS: In a cross-sectional study carried out in 1992-93, we examined 2471 children in three age-groups (5-7, 8-10, and 11-14 years) from the towns of Bitterfeld, Hettstedt, and Zerbst in eastern Germany. The children's parents answered a questionnaire about allergies and symptoms, attendance at day care, and related factors. Sensitisation was assessed by skin-prick tests and measurement of allergen-specific IgE antibodies in serum. FINDINGS: In 669 children from small families (up to three people), the prevalence of atopy was higher among children who started to attend day nursery at an older age than in those who started to attend at a younger age (p<0.05). Compared with children who first attended at age 6-11 months, the adjusted odds ratios for a positive skin-prick test were 1.99 (95% CI 1.08-3.66) for children who attended at age 12-23 months and 2.72 (1.37-5.40) for those who attended at age 24 months and older. In 1761 children from large families (more than three people), age of entry to day nursery had no effect on atopy. INTERPRETATION: Our findings accord with the hypothesis that early infection may protect against allergies in later life.     

Review of the technological approaches for grey water treatment and reuses

Based on literature review, a non-potable urban grey water reuse standard is proposed and the treatment alternatives and reuse scheme for grey water reuses are evaluated according to grey water characteristics and the proposed standard. The literature review shows that all types of grey water have good biodegradability. The bathroom and the laundry grey water are deficient in both nitrogen and phosphors. The kitchen grey water has a balanced COD: N: P ratio. The review also reveals that physical processes alone are not sufficient to guarantee an adequate reduction of the organics, nutrients and surfactants. The chemical processes can efficiently remove the suspended solids, organic materials and surfactants in the low strength grey water. The combination of aerobic biological process with physical filtration and disinfection is considered to be the most economical and feasible solution for grey water recycling. The MBR appears to be a very attractive solution in collective urban residential buildings.