Suchergebnisse

The high versatility of polyurethanes (PU's) is encouraging the development of new formulations for new appli cations, like their use as a matrix for structural composites. PU's based technology offers some advantages, such as fatigue resistance and fast curing cycles. However, their high reactivity hinders some manufacturing processes like Resin Transfer Moulding (RTM). This work aimed to achieve a PU resin (PUR) formulation with the required latency and reactivity for the RTM. For this purpose, different catalytic systems based on an epoxide and LiCl were investigated. The reactivity of the systems was evaluated through Differential Scanning Calorimetry (DSC) and rheology tests, and the curing reaction and viscosity were modelled. Furthermore, the RTM process of a representative composite part was simulated. Results demon strated the processability improvements when the LiCl was incorporated into the isocyanate component of the formulation combined with a monool or a diol. It was observed that these combinations contribute to the encapsulation of the LiCl between the as formed urethane groups by hydrogen bonding, providing the desired latency and acting as a delayed action catalyst. Once the reaction started and the encapsulation was deactivated, an alkoxide was formed to act as a catalyst. En capsulation was more effective with the diol, providing a higher latency. ; We gratefully acknowledge the Basque Government for the fi nancial support through the ELKARTEK 2020 (ProjectAVAN SITE New generation of sustainable composites for advanced manufacturing KK2020/00019) program. The authors also ac knowledge the University of the Basque Country (UPV/EHU) in the frame of GIU18/216 Research Group and the Macrobe havior-Mesostructure-Nanotechnology SGIker unit.

ABSTRACTMany concrete structures, such as buildings, civil structures, or transport facilities, have an enormous need for rehabilitation. The defects have a critical influence on the resistance and durability of these structures. This study evaluates the effectiveness of strengthening reinforced concrete structures by bonding natural fiber composite materials (hemp fiber fabrics [HFF]) mixed with synthetic fibers (carbon fiber reinforced polymer [CFRP] or Glasse fiber reinforced polymer (GFRP) composites) using epoxy‐based adhesives to increase their mechanical strength and extend the lifespan of the structures. This strengthening consists of bonding a composite sheet based on natural fiber fabric to the judiciously targeted outer surface of the reinforced concrete structure. From a sustainable development perspective, replacing synthetic fibers as reinforcement with vegetal fiber plants is the first step in respecting environmental issues. This paper focuses on experimental investigations on reinforced concrete specimens (33 in all) considered strengthened by different composite mixes between natural and synthetic composite fibers. The crack propagation behavior and the influence of adhesive thickness were investigated. Considering that the adhesively bonded composite materials reduce the stress intensity at the crack tip and, therefore, increase the remaining lifetime of the concrete structure. In fact, the experimental results showed an increase in ultimate load in flexural strength from 65% to 104% of strengthened concrete specimens with hybrid (hemp and glass fiber fabrics) composite plate and from 117% to 163% of strengthened concrete specimens with hybrid (hemp and carbon fiber fabrics) composite plate, compared to the control concrete specimen without strengthening.

Bisphenol A (BPA) and its substitutes, bisphenol F (BPF) and S (BPS), have previously shown in vitro obesogenic activity. This study was designed to investigate their combined effect on the adipogenic differentiation of human adipose-derived stem cells (hASCs). Cells were exposed for 14 days to an equimolar mixture of bisphenols (MIX) (range 10 nM-10 mu M). Oil Red staining was used to measure intracellular lipid accumulation, quantitative real-time polymerase chain reaction (qRT-PCR) to study gene expression of adipogenic markers (PPAR gamma, C/EBP alpha, LPL, and FABP4), and Western Blot to determine their corresponding proteins. The MIX promoted intracellular lipid accumulation in a dose-dependent manner with a maximal response at 10 mu M. Co-incubation with pure antiestrogen (ICI 182,780) inhibited lipid accumulation, suggesting that the effect was mediated by the estrogen receptor. The MIX also significantly altered the expression of PPAR gamma, C/EBP alpha, LPL, and FABP4 markers, observing a non-monotonic (U-shaped) dose-response, with maximal gene expression at 10 nM and 10 mu M and lesser expression at 1 mu M. This pattern was not observed when bisphenols were tested individually. Exposure to MIX (1-10 mu M) also increased all encoded proteins except for FABP4, which showed no changes. Evaluation of the combined effect of relevant chemical mixtures is needed rather than single chemical testing. ; European Commission 733032 ; Biomedical Research Networking CenterCIBER de Epidemiologia y Salud Publica (CIBERESP) of the Institute of Health Carlos III European Commission FIS-PI16/01820 FIS-PI16/01812 FIS-PI16/01858 ; Spanish Government FPU 17/01848

Bisphenol A (BPA) is an organic compound used primarily as a monomer in production of polycarbonate plastics, epoxy resins and as a non-polymer additive to other plastics. Because of the extensive use of BPA in the manufacture of consumer products, such as polycarbonate baby bottles, epoxy-resin can liners, food containers and utensils, dental sealants, protective coatings, flame-retardants, and water supply pipes, there is a widespread human exposure to BPA. BPA has been shown to have weak binding affinity to oestrogen receptors. Concerning the results from human health effect assessments, while there is general consensus concerning data on acute and local effects and genotoxicity of BPA, there is not yet agreement as regards reproductive and developmental toxicity (specifically neurodevelopment) and carcinogenicity. There is also some debate on the toxicokinetics of BPA which is still not fully resolved. Some recent studies reported the detection of free BPA in blood and urine in animals and humans, leading to speculation on whether BPA might accumulate in the body and/or whether other, non-food sources may contribute to human exposure. There are also indications that transfer of BPA may take place from the mother to the foetus, which in turn may imply an exposure in pre-natal life following the mother's intake of BPA. However, the reliability of these findings should be confirmed by both sound analytical data on the amount of free BPA in human plasma and urine, and a better understanding of toxicokinetics in animals and humans. ; BG; bg; EFSAfocalpoint@mzh.government.bg