Development of improved polypropylene adhesive bonding by abrasion and atmospheric plasma surface modifications

The present work deals with the problematic adhesive bonding of substrates with low surface energy. Different approaches have been explored with the aim of creating adequate adhesive joints based on polyolefinic substrate and polyurethane adhesive. The selected material under study was polypropylene (PP) as adherend, and a commercial Sikaflex®-252 polyurethane one component based structural adhesive (PU) as joint fluid. Among the diverse pre-treatments typically used to prepare surfaces prior to bonding, mechanical abrasion with emery paper of 80 grain size, the use of a chemical primer and atmospheric pressure air plasma torch (APPT) were the selected methods to facilitate the application of the PU by means of surface energy enhancement as well as to create a correct mechanical interlocking of the adherent-adhesive interface. Changes in the wettability of the polymer were evaluated by contact angle measurements following the UNE EN 828:2010. Surface energy was calculated both in terms of Owens approximation and acid-base considerations, leading to the possibility of determining a relationship between changes in surface energy and adhesion. Changes in the chemical composition of the surface were studied by X-ray photoelectron spectroscopy (XPS), electron diffraction X-Ray (EDX) probe and attenuated total multiple reflection mode infrared spectroscopy (ATR-FTIR). Morphological modifications were investigated with scanning electron microscopy (SEM). Variations in the strength of single-lap PP-PP joints with the treatments were evaluated by lap shear tests following the UNE-EN 1465:2008 standard. Experimental evidence supports the superiority of the APPT treatment to increase wettability and adhesion of polyolefinic surfaces, especially when combined with the use of a primer.Financial support from the Universidad Carlos III de Madrid Foundation and Chemistry and Materials Technological Institute ‘‘Álvaro Alonso Barba’’ is acknowledged. Also Sika S.A.U (Spain) is acknowledged

Approaches to poly(tetrafluoroethylene) adhesive bonding

Presented in part at the 4th International Conference on Advanced Computational Engineering and Experimenting (ACE X 2010), Special session on "Adhesive bonding", Paris, France, 8 9 July 2010In this work, we present an approach to achieve improved adhesive bonding with a poly(tetrafluoroethylene) (PTFE) substrate. Surfaces were modified by abrasion, atmospheric air plasma torch (APPT) treatment, and by immersion in basic (NaOH) and strongly acidic/oxidizing (HNO3/KMnO4) solutions. The wetting properties of the polymer were studied in terms of surface energy, and adhesion tests were carried out using polyurethane, acrylic, and epoxy adhesives. The surface characterisation included surface energy calculation through contact angle measurements, infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), and X-ray electron diffraction (EDX). Adhesion was evaluated by pull-off tests following the UNE EN-24624 standard. Experiments revealed that both oxidation and plasma treatment enhanced surface energy, defluorination, and the creation of a rougher PTFE surface, resulting in adhesion. Simple oxidation and its combination with plasma treatments yielded the higher tensile strength results, with epoxy as the most suitable adhesive among those studied. Samples presented adhesive or mixed type failure modes

Control of wettability of polymers by surface roughness modification

Most polymeric materials, particularly polyolefins and their derivatives, present a low surface energy which is the cause of their poor wettability and limits processes such as adhesive bonding, painting, or metalizing. Many methods have been developed and used to modify polymer surfaces for improved wetting, including mechanical treatments, wet-chemical treatments with strong acids or bases, and exposure to flames or corona discharge.In this paper the improvement of wetting properties of several polymeric materials widely used in the automotive industry, such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and silicone, is studied by means of surface mechanical abrasion using sandpapers of different grain sizes (1000, 180 and 80). Measurements of the surface roughness are performed using a Hommel Tester T8000 device equipped with a diamond stylus, which provides data on the arithmetic average roughness Ra parameter and Abbott-Firestone curve. Variations in the polymers surface energy (SE) are estimated through contact angle measurements using five test liquids of different polarities. Both components of the SE, dispersion (σD ) and polar (σP), as well as total (σT) at different conditions of treatment are analyzed using the Owens-Wendt-Rabel-Kaelble (OWRK) method. Morphological changes induced in the surface are analyzed by Scanning Electron Microscopy (SEM). Additionally, measurements of the static friction coefficient (μs) are carried out by the standard method ASTM D 1894-08. A slight enhancement in surface wettability is found with the mechanical abrasion pre-treatment from the SE increase. Finally, a higher value of μs is achieved for the abraded specimens as the normal force acting onto the system is increased.Financial support from the Fundación Universidad Carlos III de Madrid and Instituto Tecnológico de Química y Materiales “Álvaro Alonso Barba” is acknowledged

Extreme durability of wettability changes on polyolefin surfaces by atmospheric pressure plasma torch

In the present work three common polyolefins: high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) have been treated with an atmospheric pressure air plasma torch (APPT) in order to improve their wettability properties. The variations in surface energy (γs), as well as the durability of the treatment are determined by means of contact angle measurements for different aging times after plasma exposure (up to 270 days) using five test liquids which cover a wide range of polarities. The introduction of new polar moieties (carbonyl, amine or hydroxyl) is confirmed by Fourier transform infrared spectroscopy in attenuated total multiple reflection mode (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, scanning electron microscopy (SEM) provides information on the morphological changes and variation on surface roughness, revealing that smoother, lamellar and semispheric micrometric structures are created on the LDPE, HDPE and PP surfaces, respectively. Results show that APPT treatment enhances both the total and polar components of the gammas under study, with an unprecedent stability (> 8 months) in time.Financial support from the Fundación Universidad Carlos III de Madrid e Instituto Tecnológico de Química y Materiales “Álvaro Alonso Barba” is acknowledged. Authors also acknowledge MCI for the financial support to the project MAT2006 11614 C03 02

Recent progress in carbon fiber reinforced polymers recycling: a review of recycling methods and reuse of carbon fibers

The rapid increase in the application of carbon fiber reinforced polymer (CFRP) composite materials represents a challenge to waste recycling. The circular economy approach coupled with the possibility of recovering carbon fibers from CFRP waste with similar properties to virgin carbon fibers at a much lower cost and with lower energy consumption motivate the study of CFRP recycling. Mechanical recycling methods allow the obtention of chopped composite materials, while both thermal and chemical recycling methods aim towards recovering carbon fibers. This review examines the three main recycling methods, their processes, and particularities, as well as the reuse of recycled carbon fibers in the manufacture of new composite materials.This research received no external funding

Crack detection in concrete tunnels using a gabor filter invariant to rotation

Producción CientíficaIn this article, a system for the detection of cracks in concrete tunnel surfaces, based on image sensors, is presented. Both data acquisition and processing are covered. Linear cameras and proper lighting are used for data acquisition. The required resolution of the camera sensors and the number of cameras is discussed in terms of the crack size and the tunnel type. Data processing is done by applying a new method called Gabor filter invariant to rotation, allowing the detection of cracks in any direction. The parameter values of this filter are set by using a modified genetic algorithm based on the Differential Evolution optimization method. The detection of the pixels belonging to cracks is obtained to a balanced accuracy of 95.27%, thus improving the results of previous approaches.Ministerio de Economía y Competitividad under project Ref. IPT-2012-0980-370000Ministerio de Ciencia e Innovación, research project Ref. DPI2014-56500Junta de Castilla y León Ref. VA036U14

Can the craniocervical position modulate trunk muscle activation during a deadlift? A preliminary electromyographical analysis comparing conventional and sumo variations

To prevent back pain and injuries, it is essential to select appropriate strength training exercises and to ensure their correct technical execution. The deadlift exercise and its variations seem to be highly effective at activating the posterior body kinetic chain. This exercise is therefore recommended, when is properly performed, for injury and back pain prevention in both athletes and inactive people. Therefore, a more comprehensive understanding of the deadlift exercise is still necessary. The aim of this study was to compare trunk muscle activity in conventional and sumo deadlift variations performed in various craniocervical positions. Similar submaximal loads were used across all experimental conditions. Three participants with strength training experience (age: 21.67±1.15 years, height: 169±10 cm, body mass: 75.13 ± 7.00 kg and body fat percentage: 9.87±2.49 %) performed the conventional and sumo deadlift variations in different craniocervical positions: neutral, extension and flexion. Participants followed a familiarization session applying the same submaximal load, number of repetitions, lifting velocity and exercise variations than in the posterior testing session. Trunk muscle activation was quantified via surface electromyography (EMG). Participants presented greater latissimus dorsi activation in the neutral condition, and this activation level was higher during the conventional deadlift variation. The greatest EMG response was found in the erector spinae muscles in the extension position, especially in the conventional variation. Finally, the greatest trapezium musculature activation was found in the flexion condition. During the sumo performance, the highest trapezium activity was detected in the middle trapezium fibers whereas during the conventional performance, the highest value was recorded in the superior trapezium fibers. Deadlift variations and craniocervical positions thus did trigger different levels of myoelectric activation in the analyzed musculature, showing how the craniocervical position influences the activity of posterior trunk musculature.This research was funded by Consellería de Educación, Investigación, Cultura y Deporte de la Generalitat Valenciana, and the European Social Fund (European Union), research project number ACIF/2016/048

Novel thermoplastic composites strengthened with carbon fiber-reinforced epoxy composite waste rods: development and characterization

The increasing use of carbon fiber and epoxy resin composite materials yields an increase in the amount of waste. Therefore, we present a solution consisting of composites manufactured by hot pressing, employing polyamides (either PA11 or PA12) and a mechanically recycled carbon fiber-reinforced polymer (CFRP) as reinforcement. The main objectives are to study the manufacturing of those composites, to evaluate the fiber distribution, and to perform a mechanical, dynamical, and thermomechanical characterizations. The X-ray micro-computed tomography (muCT) shows that the fibers are well-distributed, maintaining a homogeneous fiber volume fraction across the material. The variability in the results is typical of discontinuous fiber composites in which the fibers, although oriented, are not as homogeneously distributed as in a continuous fiber composite. The mechanical and dynamic properties barely differ between the two sets of composites. A dynamic-mechanical analysis revealed that the glass transition temperature (Tg) increases slightly for both composites, compared to the polymers. These results illustrate the viability of the recycling and reuse route for preventing the deterioration of carbon fibers and promoting the subsequent reduction in the environmental impact by employing a thermoplastic matrix.This research was carried out with financial support from the University Carlos III Madrid and Álvaro Alonso Barba Institute of Chemistry and Materials Technology (IAAB)

Atmospheric pressure plasma hydrophilic modification of a silicone surface

Presented in part at the 1st International Conference on Structural Adhesive Bonding (AB2011), Porto, Portugal, 7-8 July 2011.The aim of this study was the creation of a silicone hydrophilic surface prior to bonding. Modifications in wettability and adhesion properties of silicone were performed with an atmospheric plasma torch (APPT). Surface energy variations of the substrate, both pristine and APPT-treated, were evaluated through contact angle measurements, studying the hydrophobic recovery of the samples up to 24 hours of aging. Compositional and topographical changes induced by APPT and aging were studied by attenuated total multiple reflection mode infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), mechanical profilometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Adhesion pull-off tests were performed on silicone-aluminium stud joints using three commercial adhesives, which were Sikaflex®-252, polyurethane-based, Loctite®-330, urethane methacrylate ester-based acrylic, and Terostat®-922, modified silicone. Although experimental data of all the bonding specimens led to an undesired adhesive failure, it was found that APPT-treated samples gave higher adhesive strength than the pristine ones, which was explained by the higher surface energy, thus more wettable material, after APPT. This effect remained stable for just 1 h, when the substrate began its hydrophobic recovery, reaching the original surface energy values after 24 h of aging.Financial support from the Universidad Carlos III de Madrid Foundation and Chemistry and Materials Technological Institute ‘‘Álvaro Alonso Barba’’ are acknowledged, as well as from the Universidad Pontificia Comillas (ICAI) (Spain)

Population Genomics in Rhamdia quelen (Heptapteridae, Siluriformes) Reveals Deep Divergence and Adaptation in the Neotropical Region

Rhamdia quelen, a Neotropical fish with hybridization between highly divergent mitochondrial DNA (mtDNA) lineages, represents an interesting evolutionary model. Previous studies suggested that there might be demographic differences between coastal lagoons and riverine environments, as well as divergent populations that could be reproductively isolated. Here, we investigated the genetic diversity pattern of this taxon in the Southern Neotropical Basin system that includes the La Plata Basin, Patos-Merin lagoon basin and the coastal lagoons draining to the SW Atlantic Ocean, through a population genomics approach using 2b-RAD-sequencing-derived single nucleotide polymorphisms (SNPs). The genomic scan identified selection footprints associated with divergence and suggested local adaptation environmental drivers. Two major genomic clusters latitudinally distributed in the Northern and Southern basins were identified, along with consistent signatures of divergent selection between them. Population structure based on the whole set of loci and on the presumptive neutral vs. adaptive loci showed deep genomic divergence between the two major clusters. Annotation of the most consistent SNPs under divergent selection revealed some interesting candidate genes for further functional studies. Moreover, signals of adaptation to a coastal lagoon environment mediated by purifying selection were found. These new insights provide a better understanding of the complex evolutionary history of R. quelen in the southernmost basin of the Neotropical regionThis research was funded by Agencia Nacional de Investigación e Innovación grant number FMV_2014_104718. We would like to thank Fondo María Viñas—Agencia Nacional de Investigación e Innovación (FMV_2014_104718) for financial support. The research of Néstor Ríos and Graciela García was also supported by Sistema Nacional de Investigadores—Agencia Nacional de Investigación e Innovación (SNI-ANII)S