The essential oil of Thymbra capitata and its application as a biocide on stone and derived surfaces

Many chemicals used nowadays for the preservation of cultural heritage pose a risk to both human health and the environment. Thus, it is desirable to find new and eco-friendly biocides that can replace the synthetic ones. In this regard, plant essential oils represent effective alternatives to synthetic substances for the preservation of historical monuments. Thymbra capitata (syn. Thymus capitatus) is a medicinal and aromatic plant growing in the Mediterranean area and endowed with important pharmacological properties related to its essential oil. Among them, the antimicrobial ones make the T. capitata essential oil an ideal candidate for industrial applications; for instance, as biocide for the inhibition and elimination of biological patinas of cyanobacteria and green algae on historical monuments. In the present work, we studied the chemical composition of the essential oil from T. capitata growing in Malta by gas chromatography-mass spectrometry (GC/MS). The major volatile component is the phenolic monoterpene carvacrol (73.2%), which is capable of damaging the cytoplasmic membrane and to interfere both in the growth curve and in the invasive capacity, though the contribution of minor components γ-terpinene and p-cymene cannot be disregarded. For the oil application on the stone surface, Pickering emulsions systems were prepared with an essential oil/water 1:3 mass ratio stabilized with kaolinite at 4 mass% in the presence of Laponite®; this allowed to limit the fast volatility of the oil and guaranteed a better application and an easier removal from the artefacts attacked by biodeteriogens both indoor and outdoor. This formulation caused the elimination of biodeteriogens from treated surfaces without residuals or films on artworks surface, and the effect was retained up to four months

New tool for sustainable treatments: agar spray—research and practice

In the last decades, the research in the field of cultural heritage has shifted its attention to the development of green methods, focusing on the use of renewable and biodegradable materials. Within this scenario, Agar has been one of the most innovative materials available to the conservator. However, sometimes its physical characteristics such as rigidity and gelation temperature are not always an advantage in the treatment of artwork. The atomization of hydrocolloid, a procedure presented in 2019 under the name of Agar spray, has enhanced the performance of this extraordinary material. This work aims to explore the new physical and mechanical characteristics imparted to the gel by the new spray procedure, compared to agar gel that forms under normal environmental conditions. Mechanical resistance and film transparency of both soft materials have been characterized, and the speed of water release has been detected on porous material, lateral solvent flow evaluated for confined cleaning. The new residues, potentially left by the gel after the spray application, were analyzed comparing them with the residues of the gel, which gels at room temperature. The dry Agar films were studied in terms of hydrophobicity of the dry film, agar towards water and water vapor permeability. The data that emerged from the study confirm the new features imparted to the gel by the new procedure, suggesting new measures to be taken to optimize its application

Thermal and mechanical properties of polycaprolactone-based composites with diatomaceous earth and halloysite nanotubes

1. Introduction The biodegradable polymers have been attracted interest for the design of green composites in recent decades to face the urgent environmental issues. Polycaprolactone (PCL) is one of the most promising environmentally friendly polymers. Recent studies have reported that blending PCL with different types of fillers may affect its physic-chemical properties and crystallization rate. Halloysite nanotubes (HNT) and diatomaceous earth (DE) have been recently investigated for the preparation of PCL-based composites with appealing performances1,2. Both are naturally occurring materials with nanoscale dimensions and a structure that lend them also absorbent properties. Potentialities of such materials in polymer composites need to be further developed for environmental remediation applications3. For the study, binary blends of PCL with HNT and DE were prepared by melt mixing, starting from 5 w/t% of filler to the maximum miscible concentration to the polymer. The thermal and mechanical properties of the obtained composites were investigated. Thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis were employed for the research purposes. 2. Results and Discussion Thermogravimetric analysis (TGA): The measurements were carried out by using the Q5000 IR instrument (TA Instruments) under nitrogen flow of 25 cm3/min by heating the samples from 20° to 800 °C. with a rate of 1°C/min. The degradation temperature of the pristine materials and their composites were taken at the maximum of the first order derivative curves of mass percentage vs. temperature. It was observed that concentration of HNTs up to 15 w/t% did not affect the thermal stability of PCL. The recorded Tmax values show no significant variations compared to pristine PCL. Higher content of HNT, beyond these levels, leads to a significative decrease in the thermal stability of the PCL matrix, resulted in a lower onset decomposition temperature. The addition of DE did not significatively affect the thermal stability of the composites, with a similar onset temperature for all of composites as the DE content increased. Graphs of the residue vs filler concentration showed a good dispersion degree of the filler particles throughout the polymeric matrix. Differential scanning calorimetry (DSC): The melting and crystallization behaviour testing of the composites and of pristine materials were carried out by using the differential scanning calorimeter TA Instrument DSC (2920 CE). Samples of approximately 5 mg were heated from 25°C to 80°C at a rate of 1 °C/min, under nitrogen atmosphere. The melting temperatures at the onset (Tmi), at the peak (Tmp) and the enthalpy of melting (ΔHm) per gram of PCL in the composites were calculated. The heating thermograms showed melting temperatures values constant for both PCL-based composites as compared to the neat PCL. The crystallinity degree (ꭓc) of PCL did not change for blends with DE while significant variations were observed in PCL/HNT nanocomposites. The results showed that, up to the filler concentration of 15 wt%, ꭓc increase, indicating that the well-dispersed HNT acted as nucleating agents in the PCL matrix. At higher concentrations, the crystallinity degree decreased, affected by the achievement of the percolation threshold of HNT and by the consequent decrease in molecular mobility of the PCL chains in the nanocomposites. Dynamic mechanical analysis (DMA): Dynamic mechanical measurements were performed by using the DMA Q800 (TA Instruments). The temperature range was 30° to 80°C with a scan rate of 2°C/min, at an applied oscillation frequency of 1 Hz and strain of 0.5%. The shear gear method with samples of a surface of 100 mm2 were employed to measure the elastic (storage modulus) and the viscous (loss modulus) components and tan delta parameters. For the study, the peak maximum of the loss modulus curves was considered. It was observed that these values reduced in the filled system as compared to the pristine counter parts, which is due to the reduction of viscous component of the polymer matrix by the presence of HNT and DE. 3. Conclusions Well-dispersed binary blends of PCL with HNT and DE were prepared by melt mixing. Composites with the maximum miscible concentration to the polymer were obtained since there is a lack of information in the literature on the evolution of crystallization rate in PCL composites containing high percentages of fillers. TGA and DSC analysis evidenced that the thermal properties of the polymer are mostly affected by the HNT addition and that the HNT concentration of 15 w/t% represents a sort of critical threshold after which a change in the behaviour of the composites occurs. Viscoelastic measurements showed that both fillers increase the capacity of PCL to store energy during mechanical stress as their content percentage increases. The reported data are the result of a preliminary characterization of sustainable composites whose potential for environmental remediation applications is currently being studied. References 1. Kassa, A.,et al. Effects of montmorillonite, sepiolite, and halloysite clays on the morphology and properties of polycaprolactone bionanocomposites. Polym.Compos. 28(2020) 2. Oun, A. A.,et al. Comparative study of oregano essential oil encapsulated in halloysite nanotubes and diatomaceous earth as antimicrobial and antioxidant composites. Appl. Clay Sci. 224(2022) 3. Cavallaro, G.,et al. Organic-nanoclay composite materials as removal agents for environmental decontamination. RSC Adv. 9(2019

Covalently modified halloysite clay nanotubes: synthesis, properties, biological and medical applications

Halloysite (HNT) is a promising natural nanosized tubular clay mineral that has many important uses in different industrial fields. It is naturally occurring, biocompatible, and available in thousands of tons at low cost. As a consequence of a hollow cavity, HNT is mainly used as nanocontainer for the controlled release of several chemicals. Chemical modification of both surfaces (inner lumen and outer surface) is a strategy to tune the nanotube's properties. Specifically, chemical modification of HNT surfaces generates a nanoarchitecture with targeted affinity through outer surface functionalization and drug transport ability from functionalization of the nanotube lumen. The primary focus of this review is the research of modified halloysite nanotubes and their applications in biological and medical fields

Generation of optimal trajectories for Earth hybrid pole sitters

A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles, by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion (SEP) on the same spacecraft, to enable such a pole-sitter orbit. Locally-optimal control laws are found with a semi-analytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the Sun-Earth circular restricted three-body problem. These solutions are subsequently used as first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, it is shown that for sufficiently long missions, a hybrid pole-sitter, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft

A review on biopolymer-based treatments for consolidation and surface protection of cultural heritage materials

Nowadays, the scientific community emphasizes the use of reversible and non-toxic materials in the field of cultural heritage. Biopolymers are one of the alternative materials to synthetic polymers and solvents that are dangerous for human health and for the environment, applied in consolidation and coating treatment. Natural biopolymers may be divided into polysaccharide, protein, and polyester: All of them are low cost, eco-friendly, and biocompatible, besides many physicochemical characteristics such as being transparent, soluble in water, hydrogel, and film-forming, and can be easily functionalized. The addition of nanoclay, essential oil, and active molecules improves the physicochemical properties of biopolymers and proposes smart response abilities to the new composite material. This work is intended to provide an overview of the development of biopolymers by considering the most general aspects and scanning the diverse substrates of application for the conservation and protection of cultural heritage. Graphical abstract: [Figure not available: see fulltext.

Sonication-induced modification of carbon nanotubes: Effect on the rheological and thermo-oxidative behaviour of polymer-based nanocomposites

The aim of this work is the investigation of the effect of ultrasound treatment on the structural characteristics of carbon nanotubes (CNTs) and the consequent influence that the shortening induced by sonication exerts on the morphology, rheological behaviour and thermo-oxidative resistance of ultra-high molecular weight polyethylene (UHMWPE)-based nanocomposites. First, CNTs have been subjected to sonication for different time intervals and the performed spectroscopic and morphological analyses reveal that a dramatic decrease of the CNT's original length occurs with increased sonication time. The reduction of the initial length of CNTs strongly affects the nanocomposite rheological behaviour, which progressively changes from solid-like to liquid-like as the CNT sonication time increases. The study of the thermo-oxidative behaviour of the investigated nanocomposites reveals that the CNT sonication has a detrimental effect on the thermo-oxidative stability of nanocomposites, especially for long exposure times. The worsening of the thermo-oxidative resistance of sonicated CNT-containing nanocomposites could be attributed to the lower thermal conductivity of low-aspect-ratio CNTs, which causes the increase of the local temperature at the polymer/nanofillers interphase, with the consequent acceleration of the degradative phenomena

Human Factors Applied to Perioperative Process Improvement

Human factors/ergonomics (HF/E) is its own scientific discipline that can be applied to understanding performance in perioperative medicine. Humans are not perfect decision makers and are affected by a variety of factors that can greatly harm their ability to perform, including attention, bias, stress, and fatigue. HF/E has a unique perspective on human error, and HF/E can illustrate how moving away from blame can enhance safety. HF/E offers strategies for undertaking a systematic approach to assessment of work processes in perioperative medicine that can be used to increase safety and wellbeing of patients and providers

Novel mission concepts for polar coverage : An overview of recent developments and possible future applications

The paper provides a survey of novel mission concepts for continuous, hemispheric polar observation and direct-link polar telecommunications. It is well known that these services cannot be provided by traditional platforms: geostationary satellites do not cover high-latitude regions, while low- and medium-orbit Sun-synchronous spacecraft only cover a narrow swath of the Earth at each passage. Concepts that are proposed in the literature are described, including the pole-sitter concept (in which a spacecraft is stationary above the pole), spacecraft in artificial equilibrium points in the Sun-Earth system and non-Keplerian polar Molniya orbits. Additionally, novel displaced eight-shaped orbits at Lagrangian points are presented. For many of these concepts, a continuous acceleration is required and propulsion systems include solar electric propulsion, solar sail and a hybridisation of the two. Advantages and drawbacks of each mission concept are assessed, and a comparison in terms of high-latitude coverage and distance, spacecraft mass, payload and lifetime is presented. Finally, the paper will describe a number of potential applications enabled by these concepts, focusing on polar Earth observation and telecommunications

Synthesis and Characterization of Halloysite-Cyclodextrin Nanosponges for Enhanced Dyes Adsorption

Inorganic-organic nanosponge hybrids based on halloysite clay and organic cyclodextrin derivatives (HNT-CDs) were developed by means of microwave irradiations in solvent-free conditions. The HNT-CDs nanomaterials characterized by FT-IR, TGA, BET, TEM, SEM, DLS, and zeta-potential have showed a hyper-reticulated network which possesses both HNT and cyclodextrin peculiarities. The new HNT-CDs nanosponge hybrids were employed as nanoadsorbents, first choosing Rhodamine B as the dye model, and furthermore for the removal of some cationic and anionic dyes, under different pH values (1.0, 4.54, and 7.4). The collected results showed that the pH solution as well as the electrostatic interactions affect the adsorption process. Factors controlling the adsorption process were discussed. The experimental adsorption equilibrium and kinetic data were best described by the Freundlich isotherm model. Excellent adsorption efficiency for cationic dyes were observed with respect to anionic ones. The results suggest that HNT-CDs nanosponge hybrids are a good nanoadsorbent for selective adsorption of cationic dyes with respect to the anionic ones from aqueous solutions