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  • Open access
  • 21 Reads
Cavitation erosion and cavitation slurry erosion of AlTiN films deposited on bronzes and stainless steel substrates

The resistance to cavitation erosion in clean water and slurry of bronze and stainless steel can be improved by PVD coating deposition. This study aimed to investigate the cavitation erosion resistance of magnetron-sputtered AlTiN films deposited with different contents of chemical elements onto stainless steel and bronze substrates. The AlTiN films were deposited with different ranges of chemical elements. The surface morphology and structure of samples were examined by optical profilometry, light optical microscopy (LOM) and scanning electron microscopy (SEM-EDS). Mechanical properties (hardness, elastic modulus) were tested using a nanoindentation tester. The adhesion of the deposited coatings was determined by the scratch test. Cavitation erosion tests were performed according to ASTM G32 (vibratory apparatus), in compliance with the stationary specimen procedure. Two test mediums were used, i.e., distilled water and slurry composed of water and silica. The erosion curves indicate the higher wear resistance of bronze versus stainless steel. The results demonstrate that the cavitation erosion mechanism of the AlTiN coatings consists of the films' chemical composition and is strongly affected by the substrate properties. The slurry affects the wear mechanism and facilitates material degradation. Compared to the bare bronze and bare stainless steel reference samples, the deposition of PVD films exhibits superior resistance to cavitation erosion in pure water and slurry.

  • Open access
  • 19 Reads
Investigation of sputtered CaP coatings doped with Mg

The purpose of the current paper is to show the effect of Mg addition on the CaP sputtered coatings as possible resorbable material used for biomedical applications. The coatings were produced by RF magnetron sputtering method on silicon and Mg alloy substrates. Comparatively examinations were performed in terms of their elemental and phase composition, mechanical characteristics, and degradation rate in two acellular media (SBF and DMEM) at 37°C for a period ranged from 1 to 21 days. CaP coating without Mg addition was used as reference coating. The results showed that the Mg addition into CaP decreased the degradation rate of CaP coatings, being an advantage for the biomedical degradable products.

We acknowledge the support of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project ERANET-M-ISIDE-1, no. 171/2020 (INOE2000 partner) or 172/2020 (UPB partner), within PNCDI III, and no. 19PFE/2018 (PROINSTITUTIO) – institutional project.

  • Open access
  • 12 Reads
Hydrophobic Surface Modification of Sintered UHMWPE Ski Base Materials

Ultra-high-molecular-weight polyethylene (UHMWPE) is the material of choice for many tough applications, including high-strength fibers, biomaterials for hip and knee replacements, as a manufacturing material for other thermoplastics, and as the base material of choice for nearly all skis and snowboards in production. However, UHMWPE is highly susceptible to abrasion. In ski bases, abrasion produces UHMWPE “micro-hairs”, which drastically increase friction and have been partially responsible for producing the need for topical waxes, which are subsequently abraded from ski bases into the snow pack and watershed during use. Ski waxes contain many additives in an effort to enhance their performance in many environmental conditions, including air temperature, humidity, snow temperature, snow crystal structures, and many others. The best-performing waxes are fluorocarbon-based waxes, which are known sources of PFOA and have been linked to many health hazards due to the tendency of PFOA to bioaccumulate in both the human body during application and in the environment. This has resulted in a full ban of fluorocarbon-based waxes by all major ski bodies starting with the 2020–2021 competitive season, which has resulted in the need for new non-toxic, high-performance products in the snowsport industry. This project focuses on the development of a permanent surface modification of UHMWPE using non-toxic polymers that can improve the baseline toughness and wear resistance, thereby preventing the occurrence of micro-hairs that reduce long-term glide performance. We have determined both the porosity and diffusion kinetics of small monomers into sintered UHMWPE and how they affect the wear rate of the base polymer. We report on the scientific principles surrounding surface modification, on-snow friction, and the functional groups of polymers and organic molecules that result in broad-range, high-performance ski base treatments.

  • Open access
  • 14 Reads
Conductive epoxy/carbon nanofiber coatings for scale control
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Calcium carbonate (CaCO3) is one of the most common scaling minerals and has been a long-standing problem for many industries. Undesirable scale formation can clog wells and pipelines in the oil and gas industry, affect the efficiency in nuclear power plants, and is described as a major challenge in wastewater reclamation and in the development of geothermal energy. Since precipitation of CaCO3 is pH-dependent, scaling calcium carbonate on conductive surfaces can be prevented electrochemically by applying anodic polarization. However, anodic polarization is restricted to materials that do not undergo corrosion at anodic polarization conditions. Thus, in this study, we propose applying a conductive coating to a metal surface to allow anodic polarization and inhibit surface scaling without corrosion taking place. An epoxy/carbon nanofiber (CNF) conductive coating was developed and deposited onto steel (SS316) surfaces. The anti-scaling performance of the coating under anodic polarization was investigated upon exposure to a 1.5 wt% CaCl2 solution in contact with CO2. The coating was tested at different potentials to find optimal conditions for scale inhibition. Potentials greater than 3 VOCP (open circuit potential) caused a degradation of the coating due to the oxygen evolution at the anode. At 1.5 and 2 VOCP, the coating remained intact and the precipitation of CaCO3 was significantly reduced. The cathodic polarization of the coating was also investigated. Enhanced scaling and no coating degradation were observed during cathodic polarization, even at potentials as high as -5 VOCP. In this study, we show that the polarization of steel coated with epoxy/CNF composite material can be utilized to either prevent surfaces from scaling or enhance scaling of pH-sensitive scaling minerals.

  • Open access
  • 11 Reads
Physical property analysis of cellulose/pectin biocomposites for food packaging
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The European Plastics Strategy sets a target of 2030 to ensure that only plastic packaging that is reusable or easily recyclable is used in the EU. As a result, lately, the interest in environmentally friendly and biodegradable food packaging has increased. Researchers are looking for materials that would meet the requirements of changing world. The use of biocomposites could be one of the ways to develop bio-based food packaging. Biocomposites are made of two or more different materials from which at least one is natural. Usually its biopolymers such as proteins, lipids, polysaccharides, etc. Thus, cellulose and polysaccharide pectin could be a promising biocomposite materials due to its availability, low cost, and mechanical characteristics. So, the aim of the research was to produce cellulose/pectin biocomposites by laminating prepared cellulose fiber plates with 5.0%–20.0% concentration pectin containing glycerol as a plasticizer and evaluate their properties. The solubility in water, water vapor permeability (WVP), and surface hydrophobicity of prepared cellulose/pectin biocomposites were evaluated and compared. It was observed that increased amount of plasticizer glycerol increases solubility in water, as well as WVP, but decreases surface hydrophobicity of cellulose/pectin biocomposites. The highest result of WVP was in biocomposite with 5.0% of glycerol while lowest with 1.0% glycerol. All of the analyzed cellulose/pectin biocomposites had partly hydrophobic surface and highest surface hydrophobicity was achieved in biocomposite with 16.7% pectin without plasticizer (59 o). Overall results show, that cellulose/pectin biocomposites could be a promising material in developing food packaging for dry food products.

  • Open access
  • 20 Reads
Deposition of synthetic and bio-based polycations onto negatively charged solid surfaces: Effect of the polymer cationicity, ionic strength, and the addition of an anionic surfactant
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The deposition of layers of different polycations (synthetic or derived from natural, renewable resources) onto oppositely charged surfaces has been studied using ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D). Information about the thickness of the deposited layers and their water content was ascertained. The adsorption of the different polycations onto negatively charged surfaces was found to be a complex process, which is influenced by the chemical nature of the polymer chains, ionic strength, polymer concentration, and the addition of additives, such as surfactants. The experimental picture shows a good agreement with theoretical calculations performed using the self-consistent mean field (SCF) approach. The results show that the electrostatically-driven deposition can be tuned by modifying the physico-chemical properties of the solutions and the chemical nature of the adsorbed polymer. This versatile approach is a big step forward in aiding the design of new polymers for many industrial applications and, in particular, the design of sustainable washing formulations for cosmetic applications

  • Open access
  • 20 Reads
Assessment of copper alloy corrosion inhibitors 1H-Benzotriazole and 5-Phelyn-1H-tetrazole and their nanoencapsulation via one-step synthesis: a comparative study by spectroscopic methods and microscopy techniques
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Metals are fundamental materials for industrial applications, architectural buildings and Cultural Heritage artifacts. Thus, corrosion of metals and alloys is a major global issue, involving a great waste of economic resources and negative effects on the environment and on human health. For instance, organic molecules used as copper corrosion inhibitors, i.e., 1H-Benzotriazole (HBTA), and solvents needed for applications on the metal surface are often toxic and harmful for the operators. Moreover, these substances can easily spread into the environment, thus causing eco-sustainability issues and fast loss of efficacy.

For this reason, more and more efforts are being made to develop less toxic systems for the application of chemicals and to explore new inhibitors with very high efficiency at low concentrations. Currently, in the fight against corrosion, the trend is to combine both active/passive protection by dispersing the inhibitor molecules inside a polymeric matrix as an anticorrosion coating. However, the direct addition of corrosion inhibitors to a coating formulation can involve various disadvantages, such as the undesired interaction between the inhibitor molecules and the polymers of the coating, preventing proper function. More importantly, inhibitor protection against leaching is not guaranteed. The concept of “smart coatings” can be further improved by confining inhibitors in suitable inert nanocontainers able to release them on demand in order to overcome already discussed critical issues and minimize the amount of active chemical agents.

In this work, the effectiveness of two organic molecules against the corrosion of the copper-based alloy B14 is evaluated: commercial 1H-Benzotriazole (HBTA) and non-commercial 5-Phynil-1H-tetrazole (PhTA). The effectiveness assessment of the two organic molecules in a chloride environment on the B14 alloy is performed by electrochemical techniques (PP, EIS). Scanning Electron Microscopy (SEM-EDS), Atomic Force Microscopy (AFM), X-ray Photoemission Spectroscopy (XPS) and Raman Spectroscopy are performed in order to investigate the corrosion inhibition mechanism. Afterward, silica nanocapsules (SiNCs) have been prepared via one-stage synthesis, incorporating the corrosion inhibitors. The morphology and structure of the SiNCs are observed by Scanning Electron Microscopy (SEM-EDS) and Transmission Electron Microscopy (TEM), and their porosity is determined by N2 physisorption (BET/BJH). The loading capacity (L%) and the encapsulation efficiency (EE%), and the composition of composite SiNCs are evaluated by UV-Vis Spectroscopy and Raman Spectroscopy, respectively.

  • Open access
  • 11 Reads

Protective coating failure can lead to excessive substrate wear, thus increasing the need for maintenance. Self-healing systems can offer autonomous crack repair and increase a coating’s service lifetime. Polymeric microcapsules (MCs) containing healing agents can be used in that perspective and exhibit significant potential. In the case of micro-cracks, microcapsules are ruptured and the healing agent flows into the crack. The released agent comes into contact with the catalyst that is also embedded in the matrix and is polymerized, bonding the crack faces, increasing the coating service lifetime and protecting the substrate from corrosion with significant benefits for industrial applications, such as marine. Epoxy-loaded microcapsules with a poly(urea-formaldehyde) shell were successfully prepared within the current study using one-step in situ polymerization based on the work of Tzavidi et al. (Journal of Applied Polymer Science, 2020). Microcapsules were obtained as a colorless free-flowing powder with a diameter of 37 μm and 78 % encapsulation efficiency (ratio of encapsulated substance to microcapsule mass). In order to study the self-healing properties of the microcapsules, they were dispersed in a commercially available alkyd-based paint at a content of 5, 10, or 15 % wt. along with the catalyst. Steel specimens were coated using a paintbrush with either an MC-loaded paint or pure paint as reference. A scratch was manually made on the coating with a blade, and electrochemical impedance spectroscopy (EIS) was used to evaluate the self-healing properties of the coating before and after the scratch. Based on the EIS tests, the MC-containing coating was found to offer corrosion protection even in the case of the low 5 % wt. microcapsule content.

  • Open access
  • 15 Reads
Glass surface roughness correlation with adhesion in polymer-glass hybrid injection molding
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Polymer-glass components can be fabricated using different processes nowadays. These processes have disadvantages due to the necessary large number of fabrication steps and restrictions in productivity, as well as due to the achievable component complexity.

Hybrid injection molding technology is a new approach which will enhance the possible options to use glass assembly of very complex multi-component products in a single step. In addition, it allows excellent final tolerances, as well as the reduction of finishing requirements. These are further enhanced by cost benefits resulting from their relative ease of assembly. However, there is still a lack of information of the polymer-glass hybrid molding process, since glass presents a fragile behavior when subjected to bending stress, behavior that occurs often during the filling the mold cavity process. Therefore, it is necessary to evaluate the behavior of the glass insert to the overmolding process, and the adhesion between the two materials that guarantees the tightness and resistance of the hybrid structure.

This research work focuses on investigating the correlation between the surface topography of glass, injection overmolding process parameters and polymer-glass interface. The primary approaches to provide maximized interfacial adhesion are via surface modification to create greater surface roughness. To this end, acid etchings based on hydrofluoric acid and other formulations were studied. In order to strengthen the adhesion of polymer to glass, silanes were applied as adhesion promoter. The effectiveness of the surface treatment was experimentally evaluated using surface analytical tools including optical microscopy, scanning electron microscopy and water contact angle. Adhesion was measured using the shear test in order to find the optimal match between processing parameters and bonding strength. As an outcome, the mold temperature, injection pressure, and surface roughness were found to influence bonding at the interface.

  • Open access
  • 11 Reads
Bio-based versus fossil-based UV-curable acrylate coatings in mechanical abrasion
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The abrasion resistance for a series of UV-curable acrylates has been tested when applied as a protective coating on either hardwood (pine) or softwood (beech) substrates. In particular, the abrasive performance was systematically compared for acrylates originating from bio-based resources versus their traditional fossil-based equivalents. The acrylate systems are formulated by mixing a viscous oligomer with a monomer diluent in a given 50:50 ratio while incorporating monomers with different functionalities. Both the oligomer and monomers were synthesized from fossil-based (acrylic) or bio-based feedstock (wood, vegetable oil, lignocellulosic biomass), resulting in the same chemical composition. The effect of the bio-based content on coating performance was systematically investigated when either incorporated into the oligomer or the monomer fraction. Both the fossil-based and bio-based acrylates could be homogeneously applied through a bar-coating process and were characterized by comparable viscosities depending on the functionality rather than the resource origins. Interestingly, the abrasion under Taber testing conditions indicated systematically lower wear of the bio-based acrylate coatings, both when the bio-based content was augmented either in the oligomer or the monomer fraction. The ex situ evaluation of the wear track by profilometry indeed revealed that the bio-based acrylates were prone to a higher degree of ductility and recoverable elastic deformation, while the fossil-based acrylates showed more brittle cracks and permanent material loss. The different deformation behavior of the bio-based versus fossil-based grades was further confirmed by hardness and scratch resistance testing. The observations are in line with the development of a dual-phase microstructure inducing superior performance of bio-based grades.