High Density Polyethylene Composites Containing Alumina-Toughened Zirconia Particles: Mechanical and Tribological Behavior

Alumina-toughened Zirconia (ATZ) was used as filler to endow High Density Polyethylene (HDPE) with enhanced mechanical and wear properties, hence widening the application field of the polyolefin as biomaterial. Composites at different ATZ loadings were produced by melt extrusion followed by compression molding. A good filler dispersion was obtained for all the materials, despite the presence of few voids and agglomerates observed at high ATZ loadings. The combination of high crystallinity and, mainly, lack of voids and agglomerates, appeared responsible for the improvement of Young modulus and mechanical strength. Besides, the filler positively affected the wear resistance of the composites under lubricated conditions

Influence of Different Dry-Mixing Techniques on the Mechanical, Thermal and Electrical Behavior of Ultra High Molecular Weight Polyethylene/Exhausted Tire Carbon Composites

The mechanical, thermal and electrical behavior of ultra high molecular weight (UHMWPE) composites containing different amount of pyrolyzed exhausted tire carbon (ETC) is investigated. Composites were obtained by dry-mixing the powders with a homogenizer and an impact mill. The results clearly indicate that, by changing the mixing method, it is possible to tune the rheological and morphological characteristics of the composites and in turn their mechanical, thermal and electrical properties. Better performances were observed for the composites obtained with the impact mill, which showed improved Young modulus, reduced electrical and thermal resistance with respect to those of homogenized counterparts. All the composites exhibited a relevant decrease of electrical resistivity

Piezoelectricity measurements of hybrid films functionalized with ZnO nanostructures and cellulose nanocrystals

Piezoelectric energy scavengers for the conversion of mechanical energy (e.g., pressure, bending, stretching and vibrational motions) into electricity, have been manufactured using both polymeric and inorganic materials as well as a combination of those [1-3]. It is well known that inorganic materials possess larger piezoelectric coefficients than polymers, however they exhibit higher stiffness, which makes them less sensitive to small vibrations and more prone to stress failure. On the other hand, polymer-based generators represent a relatively small proportion of the total research due to the involvement of complicated material processing and device fabrication (using precise manipulators), which represent hurdles for scalability and cost. The aim of this work is to develop a novel coating of easy fabrication and low environmental impact that could lead to a real competition in the field of renewable/alternative energy technologies. In particular, we have utilized two different geometries of ZnO nanoparticles, synthesized on purpose and embedded into a UV-curable acrylic polymer matrix. The experimental set-up for assessing the piezoelectric behavior of the obtained UV-cured films has been assembled and preliminary results of this behavior are here presented

All Natural High-Density Fiber- and Particleboards from Hemp Fibers or Rice Husk Particles

In the present study, long hemp fibers and rice husk particles have been used for producing all natural-based boards for building, automotive and in-door furniture, employing a simple and economic transformation process (namely, compression molding). In order to have the required consistence and mechanical strength, cornstarch was employed as binder. By this way, fiber- and particleboards have been prepared and characterized in terms of morphology, mechanical properties (flexural modulus and strength). The influence of different relative humidity levels on composite storage modulus and heat deflection temperatures has been investigated, as well. Long fibers turned out to be capable of sustaining approximately three times the load with respect to particles in standard conditions. Thermal, hygro- and photo stability of the above materials have been investigated under three ageing conditions: namely, (i) high temperature (thermal ageing), (ii) humidity plus high temperature (hygro-thermal ageing) and (iii) UV radiations (photo ageing). Regardless of the experimental ageing conditions adopted, fiberboards have shown good mechanical stability with a modest decrease of storage modulus (<20%) with respect to the values before exposure

Reuse and Valorisation of Hemp Fibres and Rice Husk Particles for Fire Resistant Fibreboards and Particleboards

The present manuscript deals with the reuse and valorisation of agricultural wastes and by-products (namely, hemp fibres and rice husk particles) to produce fire retardant fibreboards and particleboards for applications in biobuilding. Since fire retardancy is one of the most important challenges, a detailed study on the thermal and flame retardant properties of the above materials assembled using starch as the binder and different ammonium dihydrogen phosphate contents as fire retardant agents, is proposed. The combustion properties have been investigated in developing fire conditions, employing a radiating heat flux of 35&nbsp;kW/m2generated by a cone calorimeter. An optimised formulation able to make both fibreboards and particleboards not ignitable has been found and is predicted to be \u201cA2/B\u201d class in the European fire classification for building products. The resultant materials have proven to undergo pyrolysis and not to burn, favouring the formation of a dense and consistent final residue

Polymerization in Magnetic Field. XIX. Thermal Behavior of the Copolymers of Methyl Methacrylate with Glycidyl Methacrylate Synthesized in the Magnetic Field Presence

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Enhancement of SSVEPs Classification in BCI-based Wearable Instrumentation Through Machine Learning Techniques

This work addresses the adoption of Machine Learning classifiers and Convolutional Neural Networks to improve the performance of highly wearable, single-channel instrumentation for Brain-Computer Interfaces. The proposed measurement system is based on the classification of Steady-State Visually Evoked Potentials (SSVEPs). In particular, Head-Mounted Displays for Augmented Reality are used to generate and display the flickering stimuli for the SSVEPs elicitation. Four experiments were conducted by employing, in turn, a different Head-Mounted Display. For each experiment, two different algorithms were applied and compared with the state-of-the-art-techniques. Furthermore, the impact of different Augmented Reality technologies in the elicitation and classification of SSVEPs was also explored. The experimental metrological characterization demonstrates (i) that the proposed Machine Learning-based processing strategies provide a significant enhancement of the SSVEP classification accuracy with respect to the state of the art, and (ii) that choosing an adequate Head-Mounted Display is crucial to obtain acceptable performance. Finally, it is also shown that the adoption of inter-subjective validation strategies such as the Leave-One-Subject-Out Cross Validation successfully leads to an increase in the inter-individual 1-σ reproducibility: this, in turn, anticipates an easier development of ready-to-use systems

Electron-Beam-Induced Grafting Of Chitosan Onto HDPE/ATZ Composites for Biomedical Applications

HDPE and HDPE/ATZ surfaces were functionalised with chitosan Via electron-beam irradiation technique in order to prepare materials suitable for biomedical purposes. ATR–FTIR and wettability measurements were employed for monitoring the surface changes after both irradiation and chitosan grafting reaction. The presence of ATZ influenced both the EB irradiation process and the surface functionalisation. Mechanical properties of irradiated materials were not remarkably affected by irradiation processing. Biological assays indicated that electrostatic interactions between the negative charges of the surface of cell membranes and the –NH3+ sites on chitosan chains promoted cell adhesion, while some oxidized species produced during the irradiation process were thought to cause a detrimental effect on the cell Viability

Influence of chitosan on the mechanical and biological properties of HDPE for biomedical applications

High density polyethylene (HDPE) is widely used in biomedical field, except when strong cell-material interactions and high mechanical properties are required. To address this pitfall, two kinds of chitosan in different amounts were used as filler in the present research. Composites were prepared by melt extrusion process and their microstructural, thermal and mechanical properties were widely investigated. Also roughness and wettability were studied, as features of paramount importance in dictating cell response. Both types of chitosan endowed HDPE with higher Young modulus and lower elongation at break. Interestingly, fibroblast adhesion and viability were enhanced when a low amount of filler was used. The interaction of HDPE/chitosan composites with biological environment was investigated for the first time in order to assess the feasibility of these composites as materials for biomedical application

Multimodal assessment of circadian sleep health in predicting mental health outcomes in adolescents

IntroductionAspects of circadian sleep health including circadian alignment, circadian phase, or chronotype may be related to mental health outcomes in adolescents. Using novel and robust data collection methods, this study explored the relationship between adolescents' circadian sleep health and traits related to depression, anxiety, stress, and emotional regulation.MethodsFifty-two healthy 14–18-year-olds (58% female; 94% European American) participated in this study. Across a 10-day period, participants completed wrist-worn actigraphy. Next, participants completed a dim-light melatonin onset (DLMO) protocol where 12 saliva samples were collected over a 6-h period to measure circadian phase. Circadian phase was calculated as the duration of time between DMLO to average sleep onset time across the monitoring period. Social jetlag was measured as the discrepancy between sleep times from weekday to weekend. Participants completed the Depression Anxiety Stress Scales (DASS-21), Emotion Regulation Questionnaire (ERQ), and the Morningness-Eveningness Questionnaire for Adolescents (MEQ). Following dichotomizing sleep outcomes into clinically relevant groups (late vs. early circadian phase, aligned vs. misaligned circadian rhythms, minimal social jetlag vs. presence of social jetlag, intermediate to morningness vs. eveningness chronotype), we conducted general linear models to determine circadian group differences in mental health outcomes (depression, anxiety, stress, expressive suppression, and cognitive reappraisal) while controlling for gender and pubertal development.ResultsCircadian phase had a large effect on depression symptoms in adolescents, with adolescents with later DLMO having significantly higher depression scores than those with earlier DLMO (p = 0.031). Chronotype had a medium but non-significant effect on anxiety and stress symptoms in adolescents, with adolescents with eveningness-tendencies having higher anxiety and stress symptoms than those with intermediate to morningness-tendencies (p's = 0.140 and 0.111, respectively).ConclusionsIn the first ever study using gold-standard methodologies to examine the relationship between mental health and circadian sleep health in healthy adolescents, we observed that adolescents with later circadian phase had increased depressive symptoms compared to earlier circadian phase. Furthermore, adolescents who endorsed behaviors that suggest eveningness tendencies may have heightened stress/anxiety. These conclusions encourage future experimental research regarding this topic and may help inform interventions aimed to decrease depression, anxiety, and stress in adolescents