Plastics in robots: a degradation study of a humanoid skin mask made of soft urethane elastomer

Understanding the degradation of plastic materials is a big challenge for curators, conservators and conservation scientists in museums worldwide aiming to preserve their collections due to the variety of formulations of synthetic polymers and pigments. The conservation of polyurethane (PUR) based objects is challenging because they can suffer from extensive degradation. Particularly PUR elastomers can degrade shortly after their production, as occurred to the mask of the Japanese robot SAYA, which within 8 years suffered from two large tears, discoloration and stickiness. This research aims at studying the degradation phenomena of the androids’ synthetic skin. Better knowledge of the chemical composition of the mask and the chemical and physical decay will contribute to planning a suitable stabilization treatment. Within a multi-analytical approach, colorimetric and microscopic investigations highlighted discolored areas, which showed further color changes within a five months monitoring campaign, confirming the instability of the material likely due to ongoing degradation. Raman microscopy allowed the identification of Pigment White 6 (titanium dioxide TiO2) in the anatase form, known to promote the photosensitivity of PUR substrates towards ultraviolet (UV) light. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy identified the PUR composition of the mask, the presence of phthalates as plasticizers and suggested the formation of quinone chromophores in the polymer structure as a result of photo-oxidation, possibly responsible for the mask yellowing. Evolved gas analysis-mass spectrometry (EGA-MS) and double-shot-gas chromatography/mass spectrometry (TD/Py–GC/MS) analyses support the characterization of the formulation of the mask as being made of methylene diphenyl diisocyanate (MDI) PUR ether elastomer. Plasticizers in high concentration, mainly diisononyl phthalate (DINP) and bis(2-ethylhexyl)phthalate (DEHP), and the UV stabilizer Tinuvin 328 were also detected. In addition, the presence of styrene-acrylonitrile (SAN) could also contribute to the mask’s chemical instability. More amount of UV stabilizer and phthalates were detected at the surface (contributing to its stickiness) than in the inner core. The degradation of the mask results from the light susceptibility of MDI PUR ether and SAN, as well as the higher photochemical activity of anatase. The mask was transferred on to a mannequin and placed in the storage area to prevent light exposure and photo-oxidation. As loose edges had to be stabilized, tests were conducted and adhesive stripes glued with a PUR dispersion were selected for keeping the head’s shape. The novelty of this study is the implementation of conservation science on the study of androids with PUR elastomeric components in robotic collections, which are becoming increasingly popular in technical museums, however still seldomly studied.

Influence of iron nanoparticles (Fe3O4 and Fe2O3) on the growth, photosynthesis and antioxidant balance of wheat plants (Triticum aestivum)

More and more attention is paid to the development of technologies using iron nanoparticles in agriculture. In this regard, the effect of treatment of wheat seeds with various concentrations of iron nanoparticles Fe3O4 and Fe2O3 on the accumulation of biomass, the rate of photosynthesis and respiration, as well as on photochemical activity and antioxidant balance was studied. The seeds were treated for 3 h, germinated for 2 days in Petri dishes, transplanted into sand and grown under light for 18 days without mineral nutrition until the third leaf appeared. At a Fe3O4 concentration of 200 mg L-1 a significant increase in the dry biomass of the second leaf by 45% and the rate of photosynthesis by 16% was observed. At a concentration of nanoparticles in the form of Fe2O3 of 200 and 500 mg L-1, an increase in the rate of photosynthesis in the second leaf was also observed, but not in the biomass of the leaves. The activity of photosystem 2, estimated from the Fv/Fm value, also increased in experiments with nanoiron. However, the activity of antioxidant enzymes, guaiacol-dependent peroxidase and superoxide dismutase, decreased. It is assumed that the acceleration of growth at an early stage of wheat development is associated with an increase in photosynthetic processes.

Zinc oxide hollow spheres decorated with cerium dioxide. The role of morphology in the photoactivity of semiconducting oxides

The photochemical activity of the recently proposed CeO2-ZnO photocatalytic material active under visible light has been improved by means of significant modifications of its morphology. A polymeric templating agent (Pluronic) has been used in the synthesis obtaining a particle morphology based on hollow spheres that is better defined in the case of high template concentration. The charge separation ability and the light-induced surface electron transfer under irradiation with visible polychromatic light in various ranges of frequency has been investigated by Electron Paramagnetic Resonance. The reactivity of the photogenerated holes has been monitored by the spin trapping technique in the presence of DMPO. The hollow spheres morphology achieved through the synthesis here reported leads to systems with a higher photoactivity under visible irradiation than the same system displaying the classic platelets morphology. A parallel increase of the photocatalytic activity of this novel system in pollution remediation reactions is therefore predictable.

Analyses of OJIP transients in leaves of two epiphytic orchids under drought stress

The tolerance to low water availability is a decisive factor for growth and survival of orchids in their natural environment. The objective of this study was to characterize the photochemical traits of two epiphytic orchids (Cattleya warneri and Miltonia spectabilis) under water deficit (WD). Chlorophyll a fluorescence signals were recorded from young and fully expanded leaves of 5 plants/species after dark-adaption for 60 minutes, between 6-9 a.m. after 0, 30, 60, and 90 days of WD, using a Handy-PEA fluorometer (Hansatech, UK). Increases of O-J and J-I phases and L and K-bands and decreases of I-P phase were observed after 30 days of WD, especially in C. warneri. Decreases in the capacity to photochemically reduce quinone A (QA) and the kinetic properties required for redox reactions of the plastoquinone pool, the loss of energetic connectivity between units of PSII, inactivation of the oxygen evolution complex, and decrease of the overall rate of reducing the electron acceptor pool of photosystem I were observed in M. spectabilis, a more tolerant species. The greater ability of this species to maintain higher relative water content (RWC) in photosynthetic tissues allows greater photochemical activity.

Synthesis and Characterisation of Photocatalyst Silver/Silver Halide Nanocomposites

<p>The photochemical activity of silver halides forms the basis of photography and latent image formation. More recently it has been used to create hybrid silver/silver halide nanoparticles. These are formed through partial reduction of Ag⁺ to Ag⁰ by a photochemical self-sensitisation when irradiated with light. This gives the silver/silver halide nanoparticles interesting photocatalytic properties. As such, these silver/silver halide nanoparticles have seen to be part of group of photocatalysts known as plasmonic photocatalysts. Where, the photocatalytic mechanism is enhanced by the surface plasmon resonance of noble metal nanodomains on the surface of the silver halide nanoparticle. The silver/silver halide nanoparticles of Cl⁻, Br⁻ and I⁻ were synthesised and characterised. Silver/silver halide nanoparticles were then incorporated into porous support materials creating silver/silver halide nanocomposite materials. This was through a straight forward aqueous synthesis method, where silver halide nanoparticles precipitated from solution, and nanoparticle size, shape and stabilisation was controlled by the porous support material. Silver/silver halide nanocomposite samples using Cl⁻, Br⁻ and I⁻ were synthesised using wool fibres, kraft paper fibres and nanostructured calcium silicate as supports. UV/Vis and XRD showed Ag⁰ nanodomains were formed during the self-sensitisation process. SEM showed the morphology of the nanocomposites and that the nanoparticles were distributed within the nanocomposite matrix, not deposited on the surface. Preliminary photocatalytic activity of Ag/AgCl nanoparticles and nanocomposites was evaluated through the degradation of methylene blue when irradiated with light. All samples showed increased photocatalytic activity with the Ag/AgCl nanoparticles.</p>

Synthesis and Characterisation of Photocatalyst Silver/Silver Halide Nanocomposites

<p>The photochemical activity of silver halides forms the basis of photography and latent image formation. More recently it has been used to create hybrid silver/silver halide nanoparticles. These are formed through partial reduction of Ag⁺ to Ag⁰ by a photochemical self-sensitisation when irradiated with light. This gives the silver/silver halide nanoparticles interesting photocatalytic properties. As such, these silver/silver halide nanoparticles have seen to be part of group of photocatalysts known as plasmonic photocatalysts. Where, the photocatalytic mechanism is enhanced by the surface plasmon resonance of noble metal nanodomains on the surface of the silver halide nanoparticle. The silver/silver halide nanoparticles of Cl⁻, Br⁻ and I⁻ were synthesised and characterised. Silver/silver halide nanoparticles were then incorporated into porous support materials creating silver/silver halide nanocomposite materials. This was through a straight forward aqueous synthesis method, where silver halide nanoparticles precipitated from solution, and nanoparticle size, shape and stabilisation was controlled by the porous support material. Silver/silver halide nanocomposite samples using Cl⁻, Br⁻ and I⁻ were synthesised using wool fibres, kraft paper fibres and nanostructured calcium silicate as supports. UV/Vis and XRD showed Ag⁰ nanodomains were formed during the self-sensitisation process. SEM showed the morphology of the nanocomposites and that the nanoparticles were distributed within the nanocomposite matrix, not deposited on the surface. Preliminary photocatalytic activity of Ag/AgCl nanoparticles and nanocomposites was evaluated through the degradation of methylene blue when irradiated with light. All samples showed increased photocatalytic activity with the Ag/AgCl nanoparticles.</p>

Growth and Physiological Performance of a Coastal Species Trifolium fragiferum as Affected by a Coexistence with Trifolium repens, NaCl Treatment and Inoculation with Rhizobia

The aim of the present study was to analyze the growth and physiological performance of two coexisting species, Trifolium fragiferum, and Trifolium repens, under the effect of NaCl and rhizobial symbiosis. Seeds of T. fragiferum and T. repens were collected from populations in the wild, and plants were cultivated in an automated greenhouse, two plants per container. Three basic types of planting were performed: (1) both plants were T. fragiferum (single species), (2) one T. fragiferum and one T. repens (species coexistence), (3) both plants were T. repens (single species). For every basic type, three subtypes were made: (1) non-inoculated, (2) inoculated with rhizobia taken from T. fargiferum, (3) inoculated with rhizobia taken from T. repens. For every subtype, half of the containers were used as control, and half were treated with NaCl. Shoot fresh mass of plants was significantly (p < 0.001) affected by species coexistence, inoculant, and NaCl. Three significant two-way interactions on plant shoot growth were found: between species coexistence and NaCl (p < 0.001), inoculant and species (p < 0.05), and NaCl and species (p < 0.001). A significant three-way interaction between inoculant, NaCl, and species (p < 0.001) indicated different responses of shoot growth of the two species to inoculant type and NaCl. NaCl treatment was an important factor for T. fragiferum, resulting in better growth in conditions of species coexistence, but the positive effect of bacterial inoculant was significantly more pronounced. A decrease in peroxidase activity in leaves was a good indicator of relative NaCl tolerance, while the absence/presence of rhizobial inoculation was reflected by changes in leaf chlorophyll concentration and photochemical activity of photosystem II. It can be concluded that interaction between biotic and abiotic factors affected the outcome of the coexistence of the two Trifolium species. Distribution of T. fragiferum in sea-affected habitats seems to be related to a higher competitive ability with allied species at increased substrate salinity, based on better physiological salinity tolerance.

Nighttime chemistry of biomass burning emissions in urban areas: A dual mobile chamber study

Residential biomass burning for heating purposes is an important source of air pollutants during winter. Here we test the hypothesis that significant secondary organic aerosol production can take place even during winter nights through oxidation of the emitted organic vapors by the nitrate (NO3) radical produced during the reaction of ozone and nitrogen oxides. We use a mobile dual smog chamber system which allows the study of chemical aging of ambient air against a control reference. Ambient urban air sampled during a wintertime campaign during nighttime periods with high concentrations of biomass burning emissions was used as the starting point for the aging experiments. Biomass burning organic aerosol (OA) was, on average, 70 % of the total OA at the beginning of our experiments. Ozone was added in the perturbed chamber to simulate mixing with background air (and subsequent NO3 radical production and aging), while the second chamber was used as a reference. Following the injection of ozone, rapid OA formation was observed in all experiments, leading to increases in the OA concentration by 20 %–70 %. The oxygen-to-carbon ratio of the OA increased on average by 50 %, and the mass spectra of the produced OA was quite similar to the oxidized OA mass spectra reported during winter in urban areas. Furthermore, good correlation was found for the OA mass spectra between the ambient-derived emissions in this study and the nocturnal aged laboratory-derived biomass burning emissions from previous work. Concentrations of NO3 radicals as high as 25 ppt (parts per trillion) were measured in the perturbed chamber, with an accompanying production of 0.1–3.2 µg m−3 of organic nitrate in the aerosol phase. Organic nitrate represented approximately 10 % of the mass of the secondary OA formed. These results strongly indicate that the OA in biomass burning plumes can chemically evolve rapidly even during wintertime periods with low photochemical activity.