27 research outputs found
Ascorbate assay as a measure of oxidative potential for ambient particles: Evidence for the importance of cell-free surrogate lung fluid composition
No full textIn this study, we investigated the cell-free ascorbic acid assay (OPAA response)to quantify the oxidative potential (OP)of particle matter (PM), as a promising metric for studying the association between the chemical properties and toxicological effects of PM. With the purpose of designing an experimental set-up mostly representative of the intracellular oxidation, the assay was performed in different media, representing an artificial respiratory tract lining fluid (RTLF), i.e., simple ascorbate (Asc)or mixtures of reduced glutathione (GSH), urate (UA)and citrate (Cit). The study was performed on real PM2.5 samples collected at an urban and rural site in the Po Valley (northern Italy). For comparison, standard solutions of redox-active species were investigated, i.e., Cu2+, Fe2+, 1,2-naphthoquinone, 1,4-naphthoquinone and 9,10-phenantrenequinone, that are known to give positive response to the AA assay. The composition of the synthetic RTLF strongly effected the OPAA responses, as they decreased with increasing the mixture complexity, following the order: Asc > Asc + Cit > Asc + UA > Asc + GSH > Asc + Cit + GSH ∼ Asc + Cit + GSH + UA. Based on comparison of the dependence of OPAA on RTLF composition, we could infer that Cu2+ and quinones were the redox active species most responsible of the OPAA response of the analysed PM2.5 samples
Proinflammatory and oxidative effects of some PM components on human keratinocytes
No full textNo abstract availabl
Scratch and wear characteristics of polyamide nanocomposites
No full text1. Introduction
Polymer nanocomposites have found wide application replacing metals in aerospace components, sporting goods and in the automotive industry; the advantages of polymers compared with metals are low cost, low density, vibration damping and ease of processing. Other research applications of nanocomposites include improving ballistic performance, high temperature applications, electronics, fire retardant coatings, reduction in flammability on coating systems and biodegradable polymers.
The objective of this study was to analyze the effect of nano and micro particles on the tribological and mechanical performance of several types of composites prepared by extrusion mixing of the same polyamide PA66 matrix with varying quantities of nanoclay (NC, 1.75 and 3.50 wt%), polyhedral sislesquioxanes (POSS, 0.5 and 5.0 wt%), fullerene (0.7 wt%) and also micro-sized glass spheres, both hollow (GB7, 7wt%) and solid (GB20, 20wt%).
2. Results and discussion
The inclusion of fillers did not change the matrix’s degree of crystallinity, as proved by differential scanning calorimetry. The particle dispersion was investigated by means of scanning electron microscopy and found to be quite uniform in all samples.
Tensile and compressive mechanical properties were determined. A moderate increase of the elastic modulus and yield stress was reported for the composites with respect to the unfilled matrix. Unfortunately, this reinforcing effect was counterbalanced by a severe loss of ductility for the inorganic fillers (i.e. all but fullerene).
Scratch tests were performed at constant load and sliding speed on a microscratch tester. Scratch resistance, was evaluated using a method already adopted on unfilled polymers. In this previous work a strong correlation between scratch hardness and the material’s compressive yield stress had been identified. In the present one, the same trend was observed.
The friction and wear characteristics (against steel) of the investigated materials were measured on a thrust washer machine, applying constant load and rotating speed. While the friction coefficient was almost unaffected by filler addition, different wear phenomenology and different wear rates were displayed by different filler types: the wear rate (normalized by pressure and speed to give the wear factor) decreased substantially in the case of NC and POSS.
3. Conclusions
The results confirm that, for these kinds of particles, the scratch hardness is directly linked to the effect their presence has on bulk mechanical properties (in particular on the compressive yield stress).
On the other hand, fillers influence wear phenomena in a complex way and specific interactions need to be taken into account in order to have an accurate description of the wear process
Proprietà tribologiche di nanocompositi in poliammide
No full textSi sono preparati nano- e micro- compositi a partire da una matrice PA66 con l’aggiunta di un contenuto variabile di nanoargille, fullerene, silsesquiossani oligomerici poliedrici (POSS) e microsfere di vetro (piene e cave). La resistenza al graffio dei materiali ottenuti è stata valutata in termini di durezza utilizzando il modello di Pelletier e i risultati sono stati correlati con proprietà meccaniche “di volume”, in particolare lo sforzo di snervamento. Inoltre si è effettuata una caratterizzazione tribologica volta a rilevare le proprietà di attrito e usura
Oxidative Potential Dependence on the Chemical Composition of PM2.5 and PM10 Samples
No full textEpidemiological and toxicological studies have shown that the exposure to ambient particulate matter (PM) leads to adverse health effects in humans. The most accredited pathophysiological mechanisms involve several oxidative mechanisms leading to high concentrations of reactive oxygen species (ROS) in vivo. Such an imbalance toward a ROS excess translates into numerous health outcomes. Two common acellular techniques based on low-cost spectrophotometric UV-Vis measurements were used in this study to assess the oxidative potential (OP) of PM10 and PM2.5 samples. One is the dithiothreitol (DTT) assay, where DTT acts as a surrogate for biological reducing agents owing to its two sulfhydryl groups. The other assay is based on the ascorbic acid (AA), that is a physiologically antioxidant found in lung fluid. In order to investigate the association of the measured oxidative responses with the PM chemical composition, inorganic and organic ions, metals, organic and elemental carbon were quantified in simultaneously collected PM2.5 and PM10 samples.
The DTT and AA assays provided DTT-OP and AA-OP responses very similar in mean values and variability range, but different in association with chemical species and seasonal variation. More specifically, the AA-OP was strongly positively correlated with the main tracers of traffic and/or combustion emissions in Autumn-Winter (AW). In Sprin-Summer (SS) AA-OP was mainly correlated with species related with secondary aerosol and resuspended soil from vehicular traffic and/or long-range transport of Sahara dust. The DTT-OP of AW samples was well correlated with tracers of the resuspended reacted dust source, vehicle-related metals, and EC and OC associated with combustion sources. Conversely, in SS the DTT-OP of SS was correlated only with NH4+,Cu, EC and POC.
In conclusion, our study has highlighted the differences between the responses of the two commonly utilized DTT and AA assays to assess aerosol OP in both PM10 and PM2.5. Moreover, paper’s results have confirmed that the toxicity of ambient PM is a multifaceted phenomenon caused by a multiplicity of redox-active species and depending on the activity and concentration level of the individual components as well as on possible interaction/synergic effects
Scratch properties of PA66 nanocomposites
No full textNano- and micro- composites were prepared from a PA66 matrix with the addition of varying content of nanoclay, fullerene, polyhedral oligomeric silsesquioxane (POSS) and glass spheres. The composites’ scratch hardness was evaluated by using Pelletier’s model and results were correlated with their bulk mechanical properties
Tribological properties of PA66 nanocomposites
No full textNano- and micro- composites were prepared from a PA66 matrix with the addition of varying content of nanoclay, fullerene, polyhedral oligomeric silsesquioxane (POSS) and glass spheres. The composites’ scratch hardness was evaluated by using Pelletier’s model and results were correlated with their bulk mechanical properties. Results were compared with measurements of other tribological properties such as friction coefficient and wear resistance
PM 10 oxidative potential at a Central Mediterranean Site: Association with chemical composition and meteorological parameters
No full textAn extended study on the oxidative potential (OP) of PM10particles collected from December 2014 to October 2015 at a peninsular site of the Central Mediterranean basin has been performed. PM10particles have been selected to better account for all different aged/fresh particle types. Two acellular assays, i.e., the dithiothreitol (DTT) and ascorbic acid (AA) methods, were used to measure the OP of PM10particles chemically speciated by more than 40 species. DTT and AA assays provide close mean values of volume normalized OPVresponses, with similar variability range, i.e., mean OPDTTV= 0.24 ± 0.12 nmolDTTmin−1m−3and mean OPAAV= 0.29 ± 0.18 nmolAAmin−1m−3. Also mass normalized OPmresponses are similar for both assays, with mean value close to 0.008 nmol min−1μg−1. The measured OPDTTVand OPAAVare correlated with several inorganic species, namely ions and metals, and with organic/elemental carbon. The discrimination of the data according seasonality, i.e., Autumn-Winter (AW, October–March) and Spring-Summer (SS, April–September) days, shows a clear seasonal trend of correlation coefficients. In AW, OPDTTVis strongly correlated with nss-K+and nss-Ca2+, in addition to Ba, Cd, Ce, Cr, Cu, Fe, and Mn (traffic-related metals) and with EC, OC, and POC associated with the traffic exhaust source and/or with the combustion including biomass-burning source. Otherwise, OPDTTVof SS samples is correlated only with NH4+, Cu, EC, OC, and POC. The OPAAVof AW samples is well correlated with Ba, Ce, Cr, Cu, Fe, Mn, nss-K+, EC, OC, and POC, which are related with traffic and/or combustion emissions. Conversely, in SS, OPAAVis mainly correlated with NH4+, nss-K+, nss-Mg2+, nss-Ca2+, nss-SO42−, Cu, Mn, P, Pb, and oxalate, that are species related to secondary aerosols and resuspended soil from vehicular traffic and/or transported Saharan dust. These findings point the importance of both organic components and transition metals to PM oxidative properties, and also suggest that synergistic/antagonistic interactions and cross-correlations between the PM redox-active components are likely responsible for the seasonal variation of the AA and DTT assay response. The inter-correlation among all analysed species has been investigated to explain contrasting results and the negative correlations between OP values and some chemical species. Cell-free methods assessed the oxidative potential of particulate matter collected at a Central Mediterranean Site and the results were correlated with PM10chemical composition
Source apportionment of PM2.5 and of its oxidative potential in an industrial suburban site in South Italy
No full textSome studies suggested a role of the atmospheric particulate matter (PM) and of its oxidative potential (OP) in determining adverse health effects. Several works have focused on characterisation of source contributions to PM OP, mainly using three approaches: correlation between OP and chemical markers of specific sources; use of OP as input variable in source apportionment with receptor models; and multi-linear regression (MLR) between OP and source contributions to PM obtained from receptor models. Up to now, comparison of results obtained with different approaches on the same dataset is scarce. This work aims to perform a OP study of PM2.5 collected in an industrial site, located near a biogas production and combustion plant (in southern Italy), comparing different approaches to investigate the contributions of the different sources to OP. The PM2.5 samples were analysed for determining ions, metals, carbonaceous components, and OP activity with the DTT (dithiotreitol) assay. Results showed that OP normalised in volume (DTTV) is correlated with carbonaceous components and some ions (NO3−, and Ca2+) indicating that PM of combustion, secondary, and crustal origin could contribute to the OP activity. The source apportionment, done with the Environmental Protection Agency (EPA)—Positive Matrix Factorization (PMF5.0) model, identified six sources: secondary sulphate; biomass burning; industrial emissions; crustal; vehicle traffic and secondary nitrate; and sea spray. A MLR analysis between the source’s daily contributions and the daily DTTV values showed a reasonable agreement of the two approaches (PMF and MLR), identifying the biomass burning and the vehicle traffic and secondary nitrate as the main sources contributing to DTTV activity
