Use of statistical design of experiments in the optimization of Ar–O2 low-pressure plasma treatment conditions of polydimethylsiloxane (PDMS) for increasing polarity and adhesion, and inhibiting hydrophobic recovery

Polydimethylsiloxane (PDMS) film was treated with RF low-pressure plasmas (LPPs) made of mixtures of oxygen and argon for increasing surface polarity, minimizing hydrophobic recovery (i.e. retard ageing) and increasing adhesion to acrylic adhesive tape for medical use. Statistical design of experiments has been used for determining the most influencing experimental parameters of the LPP treatment of PDMS. Water contact angle values (measured 24 h after treatment) and the O/C ratio obtained from XPS experiments were used as response variables. Working pressure was the most influencing parameter in LPP treatment of PDMS, and the duration of the treatment, the power and the oxygen–argon mixture composition determined noticeably its effectiveness. The optimal surface properties in PDMS and inhibited hydrophobic recovery were achieved by treatment with 93 vol% oxygen + 7 vol% argon LLP at low working pressure (300 mTorr), low power (25 W) and long duration of treatment (120 s).This study was carried out in the framework of COST MP1101project

Characterization of the chemical structure of vinyl ester resin in a climate chamber under different conditions of degradation

Due to the good strength and similar toughness of epoxy resins, vinyl ester resins are widely used as thermoset adhesives in structural adhesive joints and as composites for different industrial applications. However, vinyl ester adhesives are difficult to cure completely under environmental conditions, even after long periods of time because of gel formation slows the necessary diffusion of the catalyst across the polymer network. Several studies have used weathering chambers to investigate the degradation mechanisms of vinyl ester adhesives. However, a review of the scientific literature revealed both a wide variety of aging processes and several ambiguities between the recorded experimental results. In this work, post-cured vinyl ester resins at different aging cycles were aged under high temperature and relative humidity, and the changes in their structure, mechanical and adhesion properties were studied. Chemical and structural changes were observed in the vinyl ester resins after aging in a climatic chamber

Structure and adhesion properties before and after hydrolytic ageing of polyurethane urea adhesives made with mixtures of waterborne polyurethane dispersions

Several waterborne polyurethane urea dispersions (WPUUs) were prepared by mixing different amounts of two waterborne polyurethane urea dispersions made with polyester (WPUU-Polyester) and polycarbonate diol (WPUU-PCD). Their crystallinity, thermal, rheological, viscoelastic and adhesion properties depended on the segmented structure and degree of phase separation which were determined by the different content of the parent dispersions. The PUU films made with WPUU-Polyester+WPUU-PCD mixtures containing more than 50 wt% of WPUU-PCD showed higher hard segments content and lower degree of phase separation, and the addition of 25 wt% of WPUU-Polyester imparted crystallinity to the polyurethane urea due to the interactions between the carbonate groups in the soft segments. The differences in the degree of phase separation and crystallinity of the PUU films made with WPUU-Polyester+WPUU-PCD mixtures were evidenced by the increase in the glass transition temperature associated to the alpha relaxation of the soft segments, and the higher modulus at the cross-over between the storage and loss moduli. Excellent adhesion was obtained in plasticized PVC/WPUU/plasticized PVC joints, and a cohesive failure of PVC was always obtained, irrespective of the composition of WPUU-Polyester+WPUU-PCD mixtures. Furthermore, the adhesion of surface-chlorinated vulcanized styrene-butadiene (SBR) rubber/WPUU+5 wt% hardener/roughened leather joints were high and similar in all joints and a dominant cohesive failure in the rubber substrate was produced. The accelerated ageing by immersion in water at 70 °C during different times showed that the polyurethane urea film and the surface-chlorinated vulcanized SBR rubber/WPUU+5 wt% hardener/roughened leather joint made with WPUU-PCD dispersion were not affected, but noticeable hydrolytic degradation of the ester units in the soft segments was produced in PUU-Polyester and, to a less extent, in PUU-50Polyester/50PCD films and adhesive joints.Financial support by UBE CHEMICAL EUROPE (Grant no. UBE1-15ID) is acknowledged

Thermal, mechanical, and viscoelastic properties of recycled poly(ethylene terephthalate) fiber‐reinforced unsaturated polyester composites

Recycled polyethylene terephthalate (PET) fiber has been used as reinforcing filler for unsaturated polyester resin (UPR) in order to obtain UPR/PET fiber composites. Different loadings of PET fibers (5–18 phr—parts per hundred parts of resin) of different average lengths (2–3 to 20 mm) were added to the UPR. The mechanical properties of the UPR/PET fiber composites increased up to 8 phr PET fiber loading with a length lower than 5 mm, because of the high affinity between the UPR and the PET fiber surface and the good dispersion of the fiber into the matrix. However, higher PET fiber loading caused a decrease in the mechanical properties of the composites because of the agglomeration of the fibers. The UPR/PET fiber composites presented higher storage moduli than the UPR, and an increase of the glass transition temperature in the composites reinforced with 5–8 phr of short PET fiber was found; further, higher degree of crosslinking was reached. The addition of 5–8 phr PET fiber of short length improved the thermal stability of the composites and the post‐curing was produced at higher temperature with much reduced enthalpy

Effect of adding different amounts of graphite nanoplatelets on structural, thermal, mechanical and viscoelastic properties of vinylester based composites cured at 25°C

Different amounts (0.1–5wt%) of graphite nanoplatelets (GNs) were added to vinylester (VE) for improving the properties of the composites cured at 25°C. The addition of 0.1wt% GN only increased the Tg and the thermal stability of the composite cured at 25°C. Furthermore, the addition of GN increased both the tensile strength and elongation‐at‐break of the composites cured at 25°C, but the effect of adding GN was less important when cured at 100°C. The improved properties of the composites were ascribed to the interactions between the oxygen species on the GN edges and the C==O and OH groups in the VE monomer, and to the higher fraction of the partially crosslinked polymer within the matrix

Optimization of the surface properties of polydimethylsiloxane by plasma treatment for adhesion improvement and durability to acrylic adhesive for medical applications

El polidimetilsiloxano (PDMS) es un polímero amorfo en base inorgánica con grupos pendientes que le imparten hidrofobicidad que es ampliamente utilidado en aplicaciones biomédicas. Debido a la baja energía superficial del PDMS, su adhesión es pobre. En algunas aplicaciones biomédicas (catéteres, prótesis) se requiere adhesión para lo cual se modifica superficialmente. Los plasmas generados en condiciones de no-equilibrio, también llamados plasmas fríos, han sido utilizados en el tratamiento superficial de PDMS para aumentar su energía superficial, pero las modificaciones producidas son poco estables, produciéndose una rápida recuperación de la hidrofobicidad (hydrophobic recovery). La estabilidad de las modificaciones superficiales del PDMS depende de las características del plasma utilizado para su tratamiento, por lo que el objetivo de la tesis doctoral se centra en la utilización de diferentes tipos de plasmas fríos para modificar las propiedades superficiales de PDMS de manera que simultáneamente se aumente su estabilidad y se mejore su adhesión. Otro aspecto innovador en el estudio consiste en la discriminación y optimización de las condiciones de tratamiento con plasma utilizando un diseño estadístico de experimentos, lo que he permitido modelar el efecto del tratamiento con plasma de superficies de PDMS empleando los ángulos de contacto y la química superficial como variables respuesta. Se ha estudiado el efecto de los diferentes tipos de plasma en la hidrofobicidad y la energía superficial del PDMS mediante medidas de ángulo de contacto. Las modificaciones en la química superficial han sido evaluadas usando espectroscopia infrarroja en modo de reflectancia total atenuada (FTIR-ATR) y espectroscopia fotoelectrónica de rayos X (XPS), mientras que los cambios en la morfología y nanorugosidad superficial se monitorizaron usando microscopía electrónica de barrido (SEM) y microscopía de fuerza atómica (AFM). Las propiedades de adhesión del PDMS se evaluaron mediante ensayos de adhesión en pelado en T y de cizalla a solape simple, utilizando un adhesivo sensible a la presión (PSA) en base acrílica para uso médico. Estas propiedades fueron además monitorizadas en función del tiempo tras el tratamiento con plasma para determinar la estabilidad de las modificaciones producidas. En general, el tratamiento superficial de PDMS con plasma produce oxidación de las cadenas de polisiloxano por sustitución de los grupos metilo por grupos hidroxilo, lo que aumenta la polaridad y la energía superficial, incrementando las propiedades de adhesión. Se produce el entrecruzamiento de cadenas mediante condensación de los grupos hidroxilo, formando una delgada capa superficial con estructura de sílice. Cuando las características del plasma son demasiado agresivas aparecen grietas superficiales favoreciendo la recuperación hidrofóbica por difusión de especies apolares desde el seno del PDMS hacia la superficie, así como por la reorientación de los nuevos grupos polares en la superficie hacia el seno del material. Este fenómeno se minimiza optimizando las condiciones de tratamiento empelando un diseño estadístico de experimentos. En sistemas de generación de plasma a baja presión, tratamientos con baja potencia durante largos tiempos mejoran la funcionalización de la superficie del PDMS, y el uso de mezclas de argón y oxígeno como gas plasmógeno resulta más efectivo que el empleo de los gases puros; la presión de trabajo tiene un papel fundamental en la estabilidad de las modificaciones producidas. En sistemas de antorcha de plasma atmosférico el tiempo de tratamiento y la distancia de la boquilla a la superficie son los parámetros más relevantes en la oxidación superficial del PDMS, mientras que en sistemas de plasma atmosférico de doble barrera dieléctrica, el voltaje, el tiempo de tratamiento y la distancia entre electrodos son las variables críticas en la efectividad del tratamiento superficial. Finalmente, la deposición de monómeros mediante antorcha de plasma permite generar nanoestructuras superficiales en el PDMS aportándole características de superhidrofobicidad

Caracterización y optimización del tratamiento superficial mediante radiación UV y ozono de una mezcla de copolímero Eva y polietileno para mejorar sus propiedades de adhesión

Jofre Reche, JA. (2015). Caracterización y optimización del tratamiento superficial mediante radiación UV y ozono de una mezcla de copolímero Eva y polietileno para mejorar sus propiedades de adhesión. http://hdl.handle.net/10251/61877.Archivo delegad

Selective surface modification of ethylene-vinyl acetate and ethylene polymer blend by UV–ozone treatment

Ethylene-vinyl acetate (EVA) copolymers intended for sport sole manufacturing may contain noticeable amounts of polyethylene (LDPE) for improving abrasion resistance and decrease cost; however, this blend (EVA–PE) had low polarity and showed poor adhesion. In this study an effective environmentally friendly and fast surface treatment based on UV–ozone has been used to increase the wettability, polarity and roughness of EVA–PE material. Both the length of the UV–ozone treatment and the distance between the material surface and the UV-radiation source were tested. The UV–ozone treated EVA–PE material was characterized by ATR-IR spectroscopy using Ge prism, water contact angle measurements, X-Ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adhesion properties were obtained from T peel tests of as-received and UV–ozone treated EVA–PE/polyurethane adhesive/leather joints. The more extended length of treatment and the shorter UV source–substrate distance increased the wettability of the EVA–PE material. Oxidation of the EVA–PE surface was produced by UV–ozone treatment creating new carbonyl groups mainly, and the amounts of hydroxyl and carboxylic groups were increased. The UV–ozone treatment produced ablation and etching of the EVA–PE material surface, mainly in the vinyl acetate, creating a particular roughness consisting on ruffles with deep crevices; this topography was also produced by heating produced during UV–ozone treatment. For low length of UV treatment or high UV source–material distance, the modifications of the EVA–PE material were mainly produced in the ethylene causing the selective removal of vinyl acetate, whereas more aggressive conditions produced strong oxidation in the EVA–PE material. Finally, adhesive strength was noticeably increased in the UV–ozone treated EVA–PE/polyurethane adhesive joints, and a cohesive failure in the leather was obtained.Financial support by CELTECNIA S.L. (Monóvar, Spain)

Different compatibility approaches to improve the thermal and mechanical properties of EVA/starch composites

Biocompostable composites based of ethylene‐co‐vinyl acetate (EVA) copolymer were prepared by using a twin‐screw extruder. The compatibility between EVA/starch composites were improved either by addition of polyethylene‐grafted maleic anhydride (PE‐g‐MA), or by reactive extrusion with maleic anhydride (MA) and benzoyl peroxide. The crystallinity of the non‐compatibilized composites increased with the starch content. The addition of PE‐g‐MA increased the crystallinity of the composites made with up to 20 wt% of starch. The thermal stability of EVA/starch composites decreased with increasing the starch content, and the addition of PE‐g‐MA compatibilizer enhanced the thermal stability of the composite. The in‐situ grafting with MA and PBO led to an increase in the thermal stability of the composites containing higher amounts of starch. Further, the mechanical properties of the compatibilized EVA/starch composites were improved with increasing the starch content and this was ascribed to the improved interfacial interactions between starch and EVA

Increased adhesion of polydimethylsiloxane (PDMS) to acrylic adhesive tape for medical use by surface treatment with an atmospheric pressure rotating plasma jet

The surface properties of polydimethylsiloxane (PDMS) were modified by treatment with an atmospheric pressure rotating plasma jet (APPJ) and the surface modifications were studied to assess its hydrophilicity and adhesion to acrylic adhesive tape intended for medical applications. Furthermore, the extent of hydrophobic recovery under different storage conditions was studied. The surface treatment of PDMS with the APPJ under optimal conditions noticeably increased the oxygen content and most of the surface silicon species were fully oxidized. A brittle silica-like layer on the outermost surface was created showing changes in topography due to the formation of grooves and cracks. A huge improvement in T-peel and the shear adhesive strength of the APPJ-treated PDMS surface/acrylic tape joints was obtained. On the other hand, the hydrophilicity of the PDMS surface increased noticeably after the APPJ treatment, but 24 h after treatment almost 80% hydrophobicity was recovered and the adhesive strength was markedly reduced with time after the APPJ treatment. However, the application of an acrylic adhesive layer on the just-APPJ-treated PDMS surface retained the adhesive strength, limiting the extent of hydrophobic recovery.The STSM Grant by COST ACTION MP1101 ‘Biomedical Applications of Atmospheric Pressure Plasma Technology’ and financial support from the Innovaciones DisRas S L Company is gratefully acknowledged