Surface Free Energy Measurements Research Articles

Atmospheric Pressure Plasma Treatment of Glass Surface and Its Influence on the Reliability of Adhesive Bonding

Glass load-bearing structural elements are currently used more often in civil engineering. However, due to the brittle fracture of glass, it is necessary to design these structures with sufficient reliability. Adhesive joints have a number of advantages over mechanical connectors of glass commonly used in construction. Adhesives can eliminate thermal bridges and provide a more uniform stress distribution along the connection without weakening the bonded material.A variety of chemical methods have been developed for cleaning and activating glass surfaces prior to adhesive bonding. Recently, these methods have been substituted by glass surface cleaning and activation using ambient (humid) air plasma. Such an approach is considered much faster, technically simpler, and more environmentally friendly than the traditional chemical methods. For example, it eliminates the need for the so-called primer interlayer, where the primer is usually considered a heavy chemical with significant environmental impact.The presented work is focused on the surface activation of glass by atmospheric pressure plasma to improve adhesion using specially selected transparent adhesives. We studied Diffuse Coplanar Surface Barrier Discharge (DCSBD) plasma treatment of different float-glass, heat-treated and tempered glass surfaces in ambient air. The DCSBD plasma effect was evaluated by surface free energy and peel-test adhesion measurements. The morphological changes on the glass surface were investigated by scanning electron and atomic force microscopy. The glass-to-glass adhesion at elevated temperatures was tested with respect to the artificial ageing of adhesive bonding due to the environment. Acknowledgement: This research was supported by project LM2023039, funded by the Ministry of Education, Youth and Sports of the Czech Republic and supported by project No. GA23-06016S, funded by the Czech Science Foundation (GAČR).

Substrate controlled hydrophobicity of the Y2O3 films

The development of hydrophobic surfaces is an important factor for clean energy production from solar arrays, enabling their operation at the highest possible efficiencies for the longest possible time, without the need for physical intervention. This work reports the development of hydrophobic Y2O3 thin films on a range of transparent glass substrates. The growth of the Y2O3 films from the mono-hydrate yttrium (III) complex of 1,3-diphenyl-1,3-propanedione [Y(dbm)3(H2O)] is studied using the aerosol-assisted chemical vapor deposition (AACVD) technique. The qualitative evaluation of the deposited films and their hydrophobicity is assessed using several materials characterization techniques, such as scanning electron microscopy, grazing incident X-ray diffraction, Fourier-transform infrared, X-Ray photoelectron spectroscopy, in addition to a surface free energy and water contact angle measurements. This work demonstrates experimentally a relationship between the Y2O3 wettability and its physico-chemical characteristics in terms of surface energy, chemical composition, and morphology which is controlled by the type of glass support used. The water contact angle of the hydrophobic Y2O3 coating grown on the F-doped tin oxide glass reached 128°; currently the first deposited on transparent glass. This film exhibits the highest WCA reported up to date without the need for performing post-reaction surface treatment processes. The hydrophobic nature of the transparent Y2O3 films marks a significant leap forward in the field of anti-soiling coatings suitable for photovoltaic technology.

Towards the icephobicity evolution of metallic surfaces affected by transitional wettability

In light of the escalating demands for ice protection related applications in diverse fields, including wind energy, power lines and aerospace, there is a notable surge in interest and attention toward the icephobic materials. The increased focus reflects a growing recognition of the crucial role of materials that demonstrate superior resistance to icing phenomenon. However, the intricate correlation between material wettability and icephobicity remains inadequately elucidated. This study aimed to investigate the factors that influence the relationship between icephobicity and different wetting states. The impact of varying surface topographies was examined within the scope of this investigation. A comprehensive analysis was conducted to evaluate the anti-icing and de-icing performances of the surfaces, encompassing anti-frost, ice shear adhesion strength and electro-thermal heating de-icing aspects. Furthermore, the static and dynamic wettability, along with surface free energy measurements, were also performed to enhance the comprehension of icephobicity variation. The detailed water condensation on various surfaces was meticulously observed using environmental scanning electron microscopy (ESEM). The findings elucidated a strong correlation between the icing behaviour and surface topography. It was observed that the surface topography acted as an amplifier, intensifying the deteriorating effect in icephobicity: the formed glaze per unit area exhibited a significant increase with rough asperities; the ice adhesion strength suffered an obvious increase with rough surface and lower hydrophobicity as well as the prolonged ice detachment and overall energy consumption. Therefore, careful consideration should be devoted to the tailoring of surface morphology and wettability when designing and fabricating icephobic surfaces.

Plasma Treatment of Large-Area Polymer Substrates for the Enhanced Adhesion of UV-Digital Printing.

UV-digital printing belongs to the commonly used method for custom large-area substrate decoration. Despite low surface energy and adhesion, transparent polymer materials, such as polymethylmethacrylate (PMMA) and polycarbonate (PC), represent an ideal substrate for such purposes. The diffuse coplanar surface barrier discharge (DCSBD) in a novel compact configuration was used for substrate activation to improve ink adhesion to the polymer surface. This industrially applicable version of DCSBD was prepared, tested, and successfully implemented for the UV-digital printing process. Furthermore, wettability and surface free energy measurement, X-ray photoelectron spectroscopy, atomic force, and scanning electron microscopy evaluated the surface chemistry and morphology changes. The changes in the adhesion of the surface and of ink were analyzed by a peel-force and a crosscut test, respectively. A short plasma treatment (1-5 s) enhanced the substrate's properties of PMMA and PC while providing the pre-treatment suitable for further in-line UV-digital printing. Furthermore, we did not observe damage of or significant change in roughness affecting the substrate's initial transparency.

Bacterial adhesion and surface properties of computer-aided design-computer-aided manufacturing restorative materials.

This study aimed to evaluate the surface properties and bacterial adhesion of computer-aided design-computer-aided manufacturing (CAD-CAM) restorative materials. Four CAD-CAM resin-based blocks (Vita Enamic, Shofu block HC, Cerasmart [CS] and Lava Ultimate [LU]) and a leucite-reinforced glass ceramic block (IPS Empress CAD) were used in the present study. Specimens prepared with dimensions of 10 × 10 × 1 mm were polished. Surface characteristics were assessed with hydrophobicity and surface free energy (SFE) analysis. Surface roughness was measured using a profilometer, and elemental and topographic evaluations were performed with SEM-EDX analysis. After being kept in artificial saliva for 1 h, Streptococcus mutans (S. mutans) and Streptococcus mitis (S. mitis) were incubated separately in 5% CO2 atmosphere at 37°C for 24 h. The adhered bacteria were counted as ×108 CFU/mL. Surface roughness, contact angle and SFE measurement values were found to be in the range of 0.144-0.264 Ra, 28.362°-70.074° and 39.65-63.62 mN/m, respectively. The highest adhered amount of S. mutans was found in CS and the lowest in LU, while there was no significant difference between the amounts of adhered S. mitis. Despite differences in the surface properties of the materials used for the study, the materials exhibited identical properties with respect to bacterial adhesion.

Phospholipid-functionalized gold electrode for cellular membrane interface studies - interactions between DMPC bilayer and human cystatin C

This work describes the electrochemical studies on the interactions between V57G mutant of human cystatin C (hCC V57G) and membrane bilayer immobilized on the surface of a gold electrode. The electrode was modified with 6-mercaptohexan-1-ol (MCH) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). DMPC was used as a membrane mimetic for monitoring electrochemical changes resulting from the interactions between the functionalized electrode surface and human cystatin C. The interactions between the modified electrode and hCC V57G were investigated by cyclic voltammetry and electrochemical impedance spectroscopy in a phosphate buffered saline (PBS) containing Fe(CN)63−/4- as a redox probe. The electrochemical measurements confirm that fabricated electrode is sensitive to hCC V57G at the concentration of 1 × 10−14 M. The incubation studies carried out at higher concentrations resulted in insignificant changes observed in cyclic voltammetry and electrochemical impedance spectroscopy measurements. The calculated values of surface coverage θR confirm that the electrode is equally covered at higher concentrations of hCC V57G. Measurements of wettability and surface free energy made it possible to determine the influence of individual structural elements of the modified gold electrode on its properties, and thus allowed to understand the nature of the interactions. Contact angle values confirmed the results obtained during electrochemical measurements, indicating the sensitivity of the electrode towards hCC V57G at the concentration of 1 × 10−14 M. In addition, the XPS spectra confirmed the successful anchoring of hCC V57G to the DMPC-functionalized surface.

Epoxy Resin-Based Materials Containing Natural Additives of Plant Origin Dedicated to Rail Transport.

The presented study is focused on the modification of commercially available epoxy resin with flame retardants by means of using natural substances, including quercetin hydrate and potato starch. The main aim was to obtain environmentally friendly material dedicated to rail transport that is resistant to the aging process during exploitation but also more prone to biodegradation in environmental conditions after usage. Starch is a natural biopolymer that can be applied as a pro-ecological filler, which may contribute to degradation in environmental conditions, while quercetin hydrate is able to prevent a composite from premature degradation during exploitation. To determine the aging resistance of the prepared materials, the measurements of hardness, color, mechanical properties and surface free energy were performed before and after solar aging. To assess the mechanical properties of the composite material, one-directional tensile tests were performed for three directions (0, 90, 45 degrees referred to the plate edges). Moreover, the FT-IR spectra of pristine and aged materials were obtained to observe the changes in chemical structure. Furthermore, thermogravimetric analysis was conducted to achieve information about the impact of natural substances on the thermal resistance of the achieved composites.

A multi-parameter approach to predicting adhesive bond strength in carbon fiber reinforced composites through surface and dielectric characterization

Accurate assessment of composite adhesive bonds is one of the most crucial challenges in replacing metals with composites for structural materials. In this study, carbon fiber composite bonded lap-shear specimens with bond strengths varying from strong bonds to kissing bonds were manufactured using surface modifications and controlled chemical contaminations. The adherend surfaces were characterized by profilometry, Surface Free Energy (SFE) measurement, Fourier Transform Infrared (FTIR) spectroscopy, and Energy Dispersion Spectroscopy (EDS). The bonded specimens were characterized using Broadband Dielectric Spectroscopy (BbDS). Upon destructive testing, the strength and failure modes of the bonds were studied, and strong correlations were observed with the surface properties of the bonds. The observed trends of dielectric relaxation strength with lap-shear strength confirm the potential of BbDS as an effective non-destructive assessment tool.

Design optimization and performance evaluation of metakaolin-based geopolymer filled porous (semi-flexible) asphalt mixture

This study was conducted to enhance the mixture design proportions and performance of metakaolin based geopolymer (MKG) filled porous asphalt concrete (MKGAC) mixture. The optimum dosage contents of various admixtures, namely fly ash, fine sand, expansion agent, and coupling agent, were determined based on the laboratory evaluation of the mechanical, shrinkage, and fluidity properties of the modified MKG. Additionally, scanning electron microscope (SEM), energy spectra, X-ray diffraction (XRD), and surface free energy measurements were also conducted to characterize the morphological structure and interfacial bonding of the basic (unmodified) and modified MKGAC. In the study, the solid content of the basic MKG was varied within a range of 26%–32%, with 30% determined as the optimum content for maximizing workability and performance characteristics, namely fluidity, shrinkage resistance, low-temperature cracking resistance, moisture resistance, high-temperature stability, and fatigue-crack resistance potential. Based on the high-temperature stability, fatigue, low-temperature cracking, and moisture resistance evaluations, 30% fly ash, 40% fine sand, 6% HCSA expansive agent, and 1.25% KH550 coupling agent were recommended as the optimum admixture contents for modifying and maximizing the performance of MKGAC. The SEM, energy spectra, and XRD analyses, on the other hand, showed that the microstructure and morphological compositions of the geopolymer (MKG) were uniformly consistent after modification with the admixtures. Lastly, it was also quantitatively observed that the interfacial energy between the geopolymer and asphalt-binder matrix increased after adding the admixtures, indicating an enhancement in the adhesive bond strength between the geopolymer (MKG) and the asphalt-binder matrix.

Efficacy Comparison of Three Atmospheric Pressure Plasma Sources for Soybean Seed Treatment: Plasma Characteristics, Seed Properties, Germination

Plasma seed treatment has proven to be a useful technique for improving germination, growth dynamics, as well as plant resistance. In this paper, we studied the efficacy of soybean seeds treatment using various sources of cold atmospheric pressure plasma generated in air. We compared three types of plasma treatments: direct treatment with plasma generated by a diffuse coplanar surface barrier discharge (DCSBD), direct treatment with plasma generated by a multi-hollow surface dielectric barrier discharge, and indirect treatment using the gaseous products of plasma generated by an air plasma jet. The composition of plasma generated by each of the sources was analysed using optical emission spectroscopy and Fourier Transform Infrared spectroscopy (FTIR). Parameters of the plasma treatments have been optimized to improve soybean germination. Plasma-treated seeds were examined by the means of water contact angle, surface free energy and imbibition measurements, attenuated total reflectance FTIR (ATR-FTIR), x-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) analyses. Surface analysis by ATR-FTIR and XPS showed changes in the chemical bonds on the surface of the plasma-treated seeds, which led to an increase in wettability and imbibition. SEM analysis confirmed that the plasma treatment is non-invasive and does not cause changes in seed surface morphology. Among the studied sources, DCSBD proved to be the best suited for soybean seed treatment in terms of germination improvement as well as treatment time and energy efficiency.

Green synthesis of chitin/lignin based-polyurethane composites

Polyurethanes (PU) are still among the most promising high-performance materials in industrial applications. Nevertheless, the development of sustainable and efficient materials is an ongoing challenge for the plastics industry. In recent years there has been growing interest in utilizing natural materials such as chitin and lignin as additives in polyurethane foam production. This study focuses on the utilization of sustainable chitin–lignin filler for polyurethanes with the aim of producing sustainable, cost-effective, and efficient foam materials. A chitin–lignin filler was prepared using a mechanochemical approach, and flexible polyurethane foams (FPUFs) were synthesized with varying amounts of chitin–lignin additive. The resulting foams were characterized using various analytical techniques, including scanning electron microscopy, compression testing, tensile strength analysis, and measurements of surface free energy and contact angle. Possible interactions between the filler and PU were analyzed by means of FTIR spectroscopy. The results show that the addition of chitin–lignin filler improved the mechanical properties (in comparison to pristine chitin and lignin as filler), with a significant reduction in the compression set of the polyurethane foams, a crucial property in the production of seat foams. Synergy was observed between chitin–lignin filler in PU foam. Overall, the study demonstrates the potential of chitin–lignin as a sustainable and efficient natural filler that can be effectively applied on the industrial scale. The combination of these two biopolymers led to a polyurethane composite with better mechanical properties. Additionally, the use of biopolymers (chitin and lignin) as a filler for FPUFs is one of the options for the management of waste materials, which is in line with the idea of sustainable production.

YÜKSEK FREKANSLI RF PLAZMALAR İLE PMMA FİLMLERİNİN ISILABİLİRLİĞİNİN İYİLEŞTİRİLMESİ

Poly(methyl methacrylate) (PMMA) has a wide variety of applications due to its attractive physical and optical properties. Due to its hydrophobic (water-repellent) character, the surface of PMMA should be modified before being used in applications. In this study, the surface of PMMA films were modified by 40.68 MHz high frequency CCP (capacitive-coupled plasma) RF system with nitrogen (N) and argon (Ar) gases. The experiments carried out under various plasma powers while the pressure and treatment time were kept constant. The wettability of the plasma treated surfaces was analyzed with contact angle and surface free energy (SFE) measurements. Also, the change in the chemical structure of the surfaces was investigated with X-ray photoelectron spectroscopy (XPS). The results showed that all plasma treatments enhanced the hydrophilicity of the surfaces and the lowest contact angle values obtained at high plasma power. The total SFE of the treated surfaces increased with power and the main contribution to total SFE came from polar components. The polar groups formation on the surface after plasma treatment was proved with XPS results. Hence, it was found that high frequency CCP RF plasmas can be used effectively to obtain hydrophilic polymer surfaces.

The stain resistant effect of an ultraviolet curable coating material on denture base resin.

This study aimed to evaluate the effects of an ultraviolet (UV) curable coating material on denture base resin. The results of the three-point bending test showed no significant difference between treated and untreated specimens, suggesting that the UV curable coating material did not compromise the physical strength of denture base resin. The surface free energy measurement and the surface analysis with atomic force microscopy revealed superhydrophilicity and a regularly arranged structure on the coating surface, improving wettability. Moreover, untreated specimens were significantly discolored in the staining test. However, specimens treated with the UV curable coating material showed no significant difference in color with slight staining, suggesting excellent antifouling ability. Therefore, the UV curable coating material used in this study could contribute to simplifying hygiene without altering the physical properties of denture base resins.

Study on the Interaction of Plasma-Polymerized Hydrogel Coatings with Aqueous Solutions of Different pH.

Amphiphilic hydrogels from mixtures of 2-hydroxyethyl methacrylate and 2-(diethylamino)ethyl methacrylate p(HEMA-co-DEAEMA) with specific pH sensitivity and hydrophilic/hydrophobic structures were designed and polymerized via plasma polymerization. The behavior of plasma-polymerized (pp) hydrogels containing different ratios of pH-sensitive DEAEMA segments was investigated concerning possible applications in bioanalytics. In this regard, the morphological changes, permeability, and stability of the hydrogels immersed in solutions of different pHs were studied. The physico-chemical properties of the pp hydrogel coatings were analyzed using X-ray photoelectron spectroscopy, surface free energy measurements, and atomic force microscopy. Wettability measurements showed an increased hydrophilicity of the pp hydrogels when stored in acidic buffers and a slightly hydrophobic behavior after immersion in alkaline solutions, indicating a pH-dependent behavior. Furthermore, the pp (p(HEMA-co-DEAEMA) (ppHD) hydrogels were deposited on gold electrodes and studied electrochemically to investigate the pH sensitivity of the hydrogels. The hydrogel coatings with a higher ratio of DEAEMA segments showed excellent pH responsiveness at the studied pHs (pH 4, 7, and 10), demonstrating the importance of the DEAEMA ratio in the functionality of pp hydrogel films. Due to their stability and pH-responsive properties, pp (p(HEMA-co-DEAEMA) hydrogels are conceivable candidates for functional and immobilization layers for biosensors.

Functionalization of a chemically treated Ti6Al4V-ELI alloy with nisin for antibacterial purposes

This research aims to define a protocol for nisin adsorption onto Ti6Al4V- Extra Low Interstitial content (ELI) alloy to reduce the risk of peri-implant infections. The substrate is, first, etched to get a nanotextured surface with a high density of acidic hydroxyl groups and then functionalized with the antimicrobial peptide nisin. Nisin adsorption is performed at different pH values, in the range of 5–7. The nisin release in inorganic solutions mimicking physiological or pro-inflammatory conditions is tested. The surfaces are characterized by profilometry, SEM/EDS, contact angle and surface free energy measurements, zeta potential titrations, DLS, XPS, and UV–visible spectroscopy. Effective surface adsorption was achieved and maximized at pH 6. The coated surface has high surface energy suitable for tissue integration and it releases nisin in a time longer than 1 day. As a confirmation of the antibacterial properties due to the nisin adsorption, specimens were incubated with Staphylococcus aureus, whose metabolic activity was reduced by ≈ 70% in comparison to the untreated control, and the number of viable adhered colonies was ≈ 6 times reduced. In conclusion, coupling of nisin to a chemically treated titanium surface is promising for a bioactive and antibacterial surface for tissue integration.

Assessment of methods to select optimum doses of rejuvenators for asphalt mixtures with high RAP content

ABSTRACT This study explores different methodologies to select proper doses of three palm-oil-based rejuvenators to restore the properties of the effective binder present in asphalt mixtures with high Reclaimed Asphalt Pavement (RAP) content. Two commercial vegetable-based rejuvenators were also used as reference for comparison. The dose selection methods are based on penetration and softening point in unaged, short- and long-term aged states, and High Temperature Superpave Performance Grade (PGH) verified with Fatigue Low-Temperature Superpave Performance Grade (PGFL). In addition, a novel approach based on the thermodynamic properties of the recycled binder blends (i.e. mix of virgin binder, RAP binder and rejuvenator) quantified through the Surface Free Energy (SFE) measurements was also explored. In all cases, the optimum dose selection was determined by the amount of rejuvenator required to provide equivalent or better properties than the virgin binder in its unaged and aged conditions. The results suggest that the PGH approach verified with PGFL is the most appropriate method to determine the optimum rejuvenator dose. This methodology was initially validated by means of rheological and chemical testing conducted on the recycled binder blends at the selected dose in different ageing states.

Optimizing the Dose of Warm-Mix Asphalt Additives by Maximizing the Asphalt-Aggregate Adhesion Measured via Surface-Free Energy

Warm-mix asphalt (WMA) is a group of technologies focused on reducing the viscosity of the asphalt binder (or binder) to produce asphalt mixtures at a reduced temperature compared with that specified for conventional hot-mix asphalt mixtures. The WMA technologies include two main groups: foaming and additives. The additives can be classified as synthetic-chemical or natural-based. This study aims at assessing the feasibility of optimizing the WMA additives dose by maximizing the adhesion between the asphalt binder and the aggregate at their interface in WMA mixtures. Adhesion is quantified using energy parameters derived from surface-free energy measurements (SFE), including three WMA additives (Carnauba wax, a natural-based warm-mix additive, Sasobit, and Evotherm). Accomplishing this objective required measurements of SFE for four different asphalt binders, and corresponding WMA-modified asphalt binders were performed. The results suggest the possibility of identifying a WMA-additive dose that maximizes adhesion at the binder–aggregate interface in terms of resistance to fracture (i.e., adhesive failure) and moisture damage, and the wettability of the binder. In addition, the results showed that the inclusion of Carnauba wax as a warm-mix additive yielded equivalent adhesion at the binder–aggregate interface compared with the response of the other commercially available WMA additives evaluated (i.e., Sasobit and Evotherm). Additional studies at the mixture level are recommended to validate further the conclusions obtained in this study.

Characterization of Arboblend V2 Nature Textured Surfaces Obtained by Injection Molding

Surface texturing is an engineering technology used in order to improve the surface characteristic of plastic parts obtained by injection molding. Applying this process not only changes the part surface properties, but also its topography. The novel functionalities of plastic products become useful when other materials make contact with the textured surface. Of course, these characteristics may vary depending on the laser positioning, dimensions, and geometry of the texture. The present paper presents the surface characteristics obtained after the laser texturing of the Arboblend V2 Nature biodegradable polymer. Three distinct geometries were studied: hexagonal, square, and triangular, and different behaviors of them were highlighted during surface free energy (SFE) and contact angle (WCA) measurements: a hydrophobic character for square and hexagonal geometry with distilled water as the measure liquid, and a hydrophilic character with diiodomethane as the measure liquid; for triangle geometry, the contact angle measurements were impossible to extract because the drop turns into a flat puddle. Additionally, the friction coefficient varied depending on the geometry texture, with the lowest value being recorded by the sample with hexagonal geometry. The micro-indentation tests highlighted increased surface micro-hardness compared to the basic material. The possibility of use in the practice of textured surfaces is viable; thus, based on the obtained results, there is even the possibility to replace non-biodegradable polymers from different sectors of activity.

Chemical and thermodynamic properties of palm oil-based materials and their impact on recycled binder blends

• We characterised chemical and thermodynamic properties of palm oil-based materials. • We assessed the impact of adding these agents to binder blends of an HMA with high RAP. • Surface free energy was used to assess the adhesion quality and durability of the bonds between aggregates and recycled binder blends with these agents. • Key chemical compounds present in the palm oil materials contributed to the rejuvenation effectiveness. • Palm oil-based materials are promising candidates to be used as rejuvenators in HMA with high RAP. Rejuvenators are agents added during the production of hot mix asphalts with high contents of reclaimed asphalt pavement (RAP) to restore some properties of the aged RAP binder. These materials can be obtained from numerous sources; hence, their chemical composition and physical properties vary greatly, which can have an impact on the final mixtures’ properties. This work assesses key chemical properties of crude palm oil and two of its solid by-products to understand their rejuvenation effect on a blend of a virgin and an aged RAP asphalt binder. The evaluation included thermogravimetry analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and chromatography analysis. Besides, surface free energy measurements (SFE) on the recycled binder blends (i.e., virgin asphalt binder, RAP asphalt binder and rejuvenator) and of two aggregate sources were used to evaluate the impact of the palm oils in the adhesive bonds’ quality and moisture sensitivity of the recycled binder blends-aggregates systems. Results indicate that the palm oil materials have good thermal stability and contain several large molecular size (LMS) compounds that contribute to the rejuvenation effect. Besides, recycled binder blends produced with the palm oil materials developed strong adhesive bonds in dry and wet conditions. Overall, results highlight the potential of palm oil and its solid by-products as rejuvenators for high RAP content asphalt mixtures.

Robotised atmospheric plasma treatment to improve the adhesion of vulcanised and thermoplastic rubber materials for a more sustainable footwear

Surface treatment is essential to ensure the resistance and durability of adhesive upper-to-sole joints for footwear. This study investigates robotised atmospheric pressure plasma technology to increase adhesion on styrene-butadiene vulcanised (SBR) and styrene-butadiene-styrene thermoplastic (SBS) rubbers, which constitutes a more sustainable surface treatment as an alternative to solvent-based chemical treatments (i.e., halogenation). In this work, the different parameters such as application speed and distance of the nozzle of the atmospheric plasma system have been optimised and the effects of the plasma treatment on the physicochemical properties in the materials’ surface, roughness, wettability, as well as the adhesion properties have been evaluated by means of different experimental techniques: Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron (FESEM), Contact Angles (CA) and Surface Free Energy (SFE) measurements and T-peel strength tests. The results show that the values obtained for the T-peel strength of the reactive hot melt polyurethane adhesive (HMPUR) joints studied exceed the minimum quality requirements for footwear according to standardised tests. In consequence, the optimisation and validation of operating plasma conditions and adhesion properties of rubbers could consolidate atmospheric plasma as a solvent-free alternative for the preparation of footwear soling materials. The great advantage of this technology is its introduction into the production line by fully automating the bonding process with the use of robots.