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  • Open access
  • 109 Reads

Low-Cost Solar Heating Reservoir Manufactured by Double-Coating a Water Tank with Polymeric Materials

Published: 03 April 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Hybrid Surface Coatings & Process

One of the main needs of the modern society is the availability of low-cost energy sources, and the solar energy arises as an interesting alternative for both the generation of heat and electricity. In this work, a low-cost solar energy reservoir is proposed for domestic water heating. It is comprised of a thermoplastic (polyethylene) water tank thermally insulated by means of two different polymeric coatings, an acrylonitrile butadiene rubber foam, NBR, and a metalized polyester layer. The solar system also contains a flat collector based on a ceiling panel made of poly(vinyl chloride), PVC, coated with carbon black-filled glaze. The system design is cost-effective because of all the parts involved in the solar heating are made from commodity plastic materials. These plastic components present wide commercial availability and are easily handled, so that they can be rapidly assembled to build the entire system. Therefore, the solar heating system is simple, modular and easy-scalable, and may be even self-manufactured by the final user. It is an affordable option to the traditional high-cost copper, aluminum and glass solar panels and boilers or tanks used for heat storage.

  • Open access
  • 35 Reads
Compression Molding of Polyhydroxybutyrate Nano-composite Films as Coating on Paper Substrates

After successful preparation of master batch formulations including polyhydroxybutyrate (PHB) and fibrillated cellulose additives, the compositions with different types and concentrations of fillers were used for the deposition of a coating on packaging paper grades, by using compression moulding in a hydraulic press. The resulting paper coatings are considered to provide a green solution for the production of protective barrier layer films with tunable hydrophobicity and oxygen barrier resistance. The processing of the nanocomposites into flat and homogeneous coatings was optimized for different conditions of moulding temperature and times, in particular, the flow conditions of the coating under pressing in contact with the substrate strongly depends on the presence of fillers. The effects of filler types on adhesion of the coating at the paper/polymer interface were investigated and the poor adhesion of native PHB coatings was tremendously improved after hydrophobic surface modification of the nanocellulose fillers. The inclusion of a wax and nanoparticles attached to the nanocellulose fiber surface enhanced the flowing properties of the coating by eliminating fiber agglomeration in contact with the paper substrate and reducing the effects of fiber pull outs. Therefore, hydrophobic fiber modification is necessary to obtain a homogenous dispersion during compressing moulding of coating materials for paper applications. Furthermore, the effect of processing on the final crystallinity of the master batches, films and paper coatings is presented by considering the reduction in degree of crystallinity for coatings in contact with a paper substrate owing to the surface confinement of crystallization processes. On the other hand, also the time-effects of secondary crystallization of the coatings as a function of aging time were lower for the coatings as compared to the free-standing films, in relation with the reduction of molecular mobility of the polymer chains under confined conditions.

  • Open access
  • 43 Reads
Electrical Investigation of the Mechanism of Water Adsorption/Desorption by Natural Clinoptilolite Desiccant Used in Food Preservation

Zeolites are used as desiccant in the preservation of many type of vegetable foods (e.g., corns, onions, etc.). Natural clinoptilolite is a very abundant, inexpensive, nontoxic, regenerable, and environmentally friendly type of zeolite with good desiccant properties. Here, the water adsorption/desorption properties of natural clinoptilolite have been investigated by a novel technique based on a.c. electrical measurements. In particular, owing to the presence of extra-framework cations, zeolites are ionic conductors. The presence of water in the cationic site significantly changes the cation mobility, in fact owing to the strong electrostatic interaction acting between cations and the nucleophilic area in the 3D-framework, non-hydrated cations have a nearly zero mobility, while hydrated cations have a good mobility value at room temperature. Therefore, in a zeolite sample the carrier density (that can be simply determined by measuring the temporal evolution of the current intensity, I) increases during the isothermal process of water physical adsorption and such an increase is exactly corresponding to the adsorbed water increase. The type of law controlling the adsorption/desorption process can be established by monitoring the real time behavior of the relative current intensity (I/I0) moving in the sample surface biased by a sinusoidal voltage signal of 5kHz and exposed to a constant moisture atmosphere. This approach has been applied to a natural clinoptilolite slab exposed to a 75% humidity atmosphere at 25°C. An intergranular diffusion control was active at beginning of hydration because of the natural clinoptilolite fine-grained microstructure of lamellar texture, then a Lagergren pseudo-first-order kinetics took place. To confirm a reversible adsorption process and the possibility of re-using clinoptilolite as desiccant, the slab dehydration (by silicagel) was electrically monitored and an exponential kinetic law found.

  • Open access
  • 24 Reads
Wood Protective Coatings Prepared with Silanes Based on Fatty Acids
Published: 26 April 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

Wood is one of the most important materials in construction industry. Because of its organic constitution, it is slowly destroyed by the long-term impact of water, oxygen and light under atmospheric conditions and hence, needs to be sufficiently protected. Appropriate protection of wood leads to its longer life and hence, huge reduction in maintenance costs. There are several methods to protect wood, either by its chemical modification or by its surface treatment [1,2].

Unfortunately, many of the wood preservatives that have been used so far are highly toxic to humans and hence, much attention has been paid to development of nontoxic materials/methods for the protection of wood [3]. Recently, several reports have been published on the use of inorganic-organic hybrid coating for protection of wood substrates. The sol-gel process to generate hybrid coatings is quite versatile and even allows room temperature deposition of hybrid inorganic-organic films on a wide range of substrates, including wood [4].

Wood surfaces modification with multifunctional alkoxysilanes by sol–gel process is one of promising method to improve and provide new properties for wood materials. The advantage of the sol–gel process is that it allows deposition of thin inorganic–organic layer on various substrates as a result of controlled hydrolysis and polycondensation of alkoxysilanes [5]. The sol-gel coatings created on the wood surface provide barrier properties, moisture control and repellency properties.

In this communication we present a new trialkoxysilanes synthesised from fatty acid derivatives and their application in wood protective coatings.

References:

  • Lambourne, R. Strivens, T.A. (Eds), Paint and Surface Coatings. Theory and Practice, (1999) Woodhead Publishing
  • Hill, C, Wood Modification Chemical, Thermal and Other Processes, (2006) Wiley
  • Materne, T., de Buyl, F., Witucki,G.L., Organosilane Technology in Coating Applications: Review and Perspectives, (2012) Dow Corning Corporation
  • Mai, C., Militz H., Modification of wood with silicon compounds. Treatment systems based on organic silicon compounds – a review, Wood Sci Technol., 37, 453–461, (2004)
  • Arkles, B., Silane Coupling Agents, (2014) Gelest, Inc.
  • Open access
  • 40 Reads
Structure and Properties of Coatings Made of High-Entropy Alloy with Martensitic Transformations Obtained by HVOF Method in a Protective Atmosphere
Petr Rusinov, Zhesfina Blednova

The article is devoted to the comprehensive studies of high-entropy CoCuTiZrHf coating obtained by HVOF in a protective atmosphere. We have examined metallophysical properties of the coating (using electron microscopy and X-ray diffraction analysis) in order to obtain new information about its structure, mechanical properties and phase composition. Functional properties were also determined. We studied the effect of mechanical activation of highly entropic material powder on the structural phase state and coating quality. The optimal technological parameters of HVOF in a protective atmosphere were determined for the formation of a highly entropic CoCuTiZrHf coating, which provides the highest adhesion and low porosity. We have developed statistical process models with parameter optimization. Based on complex metallophysical studies, the structure formation in highly entropic coatings was researched after HVOF in a protective atmosphere and subsequent heat treatment. Calorimetric tests of the CoCuTiZrHf alloy were performed to identify the exo-effect corresponding to the manifestation of phase transformation. We determined the mechanical properties of coated steel are.

  • Open access
  • 42 Reads
Flexible, biodegradable LL37-anchored poly(vinyl alcohol)/cellulose acetate films for enhanced infection control
Published: 29 April 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

Wound care is a growing industry that lately has been facing multiple challenges due to the increasing health care costs, aging of population, appearance of antibiotic-resistant pathogens, and rise in the incidence of chronic diseases. Unlike acute wounds which heal in a predictable amount of time following the stages of healing, chronic wounds (CW) often fail to progress past the inflammatory phase, increasing costs and healing time. Bioactive dressings that incorporate drugs/antibiotics or bioactive molecules in their formulation have been suggested as alternatives to the conventional gauzes and foams. Here, we propose the combination of poly(vinyl alcohol) (PVA) and cellulose acetate (CA), both biodegradable and biocompatible polymers, for the production of films processed via a new method that combines principles from solvent casting and phase inversion, and modified with the antimicrobial peptide (AMP) LL37, as a new active solution.

To guarantee some degree of flexibility, films were produced with a higher percentage of PVA compared to CA, from 90/10 to 50/50. LL37 was then anchored using dopamine as a binding agent. Films were characterized in terms of functional groups, thermal stability, tensile strength, porosity, swelling and degradation rate. The antimicrobial performance of LL37 surface-modified films was tested against Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli in dynamic environment. LL37-modified films demonstrated great antibacterial efficacy against the three bacteria, ≈ 75% inhibition for S. aureus, ≈ 85% for S. epidermidis and ≈ 60% for E. coli, regardless of PVA/CA ratio. Films treated with LL37 accelerated clotting time (≈ 10 min) above vancomycin and bare surfaces, demonstrating great capacity to activate the intrinsic coagulation cascade. In the end, the potential of LL37 functionalized PVA/CA films for prospective wound-healing applications was demonstrated.

  • Open access
  • 45 Reads
Essential Oils Loading onto Cellulose Acetate/Polycaprolactone Fibers via Coagulation Bath for an Improved Antimicrobial Action
Published: 30 April 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

Essential oils (EOs) have been considered as a potential alternative to antibiotics in the treatment of several diseases, due to its antimicrobial properties. For instance, the tea tree essential oil (TTO), extracted from the Melaleuca alternifolia, has been reported to exhibit analgesic, antiviral, antibacterial, antifungal, antiprotozoal and anti-inflammatory properties. Likewise, the cinnamon leaf essential oil (CLO), has exhibited excellent antioxidant and antibacterial properties. However, one of the major drawbacks associated with the use of EOs in biomedical applications is their toxicity and the difficult control of EOs degradation and loss during manufacturing of the substrate. For this reason, recently, alternatives for the controlled release of EOs have been proposed, being the manufacturing of polymeric films loaded with nanocapsules highlighted. In this work, we report the nanoencapsulation of TTO and CLO using chitosan (CS), which is a polysaccharide that exhibits exceptional antibacterial features and is sensitive to the environment pH, for the subsequent functionalization of polymeric films. Cellulose acetate (CA) and polycaprolactone (PCL) at different ratios were processed in the form of wet-spun fibers, using acetone/acetic acid as solvent and ethanol as coagulation bath. TTO and CLO were diluted in etanol and presented to the fibers during production at the coagulation baths. The EOs presence in the fibers was detected visually by changes in the fibers’ coloration. EO-loaded and unloaded fibers were characterized according to their chemical, mechanical and thermal properties and their degradation profile was followed in physiological media. The minimum inhibitory concentration of EOs and the antimicrobial action of the CA/PCL films were determined against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. Data reported the EOs-modified fibers to be successfully prepared and that the addition of the TTO and CLO to increase significantly the antimicrobial action of the polymers.

  • Open access
  • 28 Reads
Impact Test Applications Supported by Fea-Models in Surface Engineering for Coatings Characterization
Georgios Skordaris, Antonios Bouzakis, Konstantinos-Dionysios Bouzakis

The impact test is used since several years, among others, for characterizing the fatigue strength, creep, adhesion and residual stresses of coatings at ambient and elevated temperatures under dry or lubricated conditions. In recent time, the impact test has also been applied to determine stress, strain, strain rate data of coatings and their substrates. A main advantage of this test method is that in many cases, it can be employed directly on the coated parts and not on specimens. The obtained experimental results are evaluated by convenient FEM supported algorithms. Based on these algorithms, critical data for predicting the life span of coated parts such cutting tools, bearing etc. and for planning appropriate replacements can be determined. The paper renders an overview about the development of impact test devices, experimental techniques and results evaluation methods. Characteristic examples highlighting the quantification of the fatigue strength of PVD coatings and its adhesion via a critical equivalent and shear stress respectively as well as of the temperature-dependent interfacial fatigue strength of diamond coatings via a critical shear stress are shown. The residual stresses in the diamond film structure play a dominant role on the interfacial fatigue stress and are calculated by appropriate FEM-evaluation of the inclined impact imprints.

  • Open access
  • 25 Reads
Surface and Morphological Features of ZrO2 Sol-Gel Coatings Obtained by Polymer Modified Solution
Ognian Dimitrov, Irina Stambolova, Sasho Vassilev, Katerina Lazarova, Tsvetanka Babeva, Ralitsa Mladenova

Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2.8H2O solution, modified with polyethylene glycol (PEG, Mw = 400). The films have thickness of 80 nm and refractive index of about 1.45, which varied with the amount of added PEG. The thermal behaviour of the precursor was studied with thermogravimetry and differential thermal analysis (TG-DTA). The X-ray diffraction (XRD) analysis revealed the presence of a mixture of monoclinic and tetragonal ZrO2 polycrystalline phases with nanosized crystallites. The formation of hydrogen bonds among the organic and inorganic components was proved by means of fourier transform infrared spectroscopy (FT-IR) analysis, while the different defect centers were investigated with electron paramagnetic resonance (EPR) spectroscopy. The scanning electron microscopy (SEM) images showed that the samples are dense, crack free with ganglia-like nanostructure. It was established that the addition of polymer resulted in the introduction of free volume in the films, which also varied with the content of PEG in the precursor solution.

  • Open access
  • 13 Reads
Study of Lead-Free Ferroelectric Composite Coatings by Impedance Spectroscopy
Mariya Aleksandrova, Tsvetozar Tsanev, Ivailo Pandiev, Georgi Dobrikov

The aim of the study is preparation and electrical characterization of lead-free ferroelectric oxide BaSrTiO3 in composition with piezoelectric polymer. The properties of the deposited films were compared with pure oxide. Scanning electron microscopy showed regular distribution of particles and homogeneous composition of both components. The dielectric properties (electric permittivity and dielectric loss) were investigated at different temperatures ranged from 5 oC to 130 oC. Impedance spectroscopy was applied in the frequency range 100 Hz-100 kHz. It was demonstrated that the dielectric constant increase with addition of piezoelectric polymer to the ceramic phase. Based on the equivalent electrical circuit parameters extraction (contact resistance and capacitance comparisons), it can be seen that the interface conditions at the electrodes are improved after inserting piezoelectric polymer. As well, interpretation of the plots of the complex impedance vs. frequency and real part of the impedance vs. imaginary part, gives information about the polarization process, revealing in the structures.

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