Polymeric foams as the matrix of voltammetric sensors for the detection of catechol, hydroquinone, and their mixtures

Producción CientíficaPorous electrodes based on polymethylmethacrylate and graphite foams (PMMA_G_F) have been developed and characterized. Such devices have been successfully used as voltammetric sensors to analyze catechol, hydroquinone, and their mixtures. The presence of pores induces important changes in the oxidation/reduction mechanism of catechol and hydroquinone with respect to the sensing properties observed in nonfoamed PMMA_graphite electrodes (PMMA_G). The electropolymerization processes of catechol or hydroquinone at the electrode surface observed using PMMA_G do not occur at the surface of the foamed PMM_G_F. In addition, the limits of detection observed in foamed electrodes are one order of magnitude lower than the observed in the nonfoamed electrodes. Moreover, foamed electrodes can be used to detect simultaneously both isomers and a remarkable increase in the electrocatalytic properties shown by the foamed samples, produces a decrease in the oxidation potential peak of catechol in presence of hydroquinone, from +0.7 V to +0.3 V. Peak currents increased linearly with concentration of catechol in presence of hydroquinone over the range of 0.37·10−3 M to 1.69·10−3 M with a limit of detection (LOD) of 0.27 mM. These effects demonstrate the advantages obtained by increasing the active surface by means of porous structures.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AGL2015-67482-R)Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA-011U16

Testing and simulation of extruded polystyrene foam at low to moderate strain rates

This paper presents a study into the behaviour of extruded polystyrene foam at low strain rates. The foam is being studied in order assess its potential for use as part of a new innovative design of portable road safety barrier the aim to consume less water and reduce rates of serious injury. The foam was tested at a range of low strain rates, with the stress and strain behaviour of the foam specimens being recorded. The energy absorption capabilities of the foam were assessed as well as the response of the foam to multiple loadings. The experimental data was then used to create a material model of the foam for use in the explicit finite element solver LS-DYNA. Simulations were carried out using the material model which showed excellent correlation between the numerical material model and the experimental data

Polymeric Foams

Postprint (published version

Catalysts for polyimide foams from aromatic isocyanates and aromatic dianhydrides

Polyimide foam products having greatly improved burn-through and flame-spread resistance are prepared by the reaction of aromatic polyisocyanates with aromatic dianhydrides in the presence of metallic salts of octoic acid. The salts, for example stannous octoate, ferric octoate and aluminum octoate, favor the formation of imide linkages at the expense of other possible reactions

A flexible and highly sensitive pressure sensor based on a PDMS foam coated with graphene nanoplatelets

The demand for high performance multifunctional wearable devices is more and more pushing towards the development of novel low-cost, soft and flexible sensors with high sensitivity. In the present work, we describe the fabrication process and the properties of new polydimethylsiloxane (PDMS) foams loaded with multilayer graphene nanoplatelets (MLGs) for application as high sensitive piezoresistive pressure sensors. The effective DC conductivity of the produced foams is measured as a function of MLG loading. The piezoresistive response of the MLG-PDMS foam-based sensor at different strain rates is assessed through quasi-static pressure tests. The results of the experimental investigations demonstrated that sensor loaded with 0.96 wt.% of MLGs is characterized by a highly repeatable pressure-dependent conductance after a few stabilization cycles and it is suitable for detecting compressive stresses as low as 10 kPa, with a sensitivity of 0.23 kPa−1, corresponding to an applied pressure of 70 kPa. Moreover, it is estimated that the sensor is able to detect pressure variations of ~1 Pa. Therefore, the new graphene-PDMS composite foam is a lightweight cost-effective material, suitable for sensing applications in the subtle or low and medium pressure ranges

Low density polyethylene/silica nanocomposite foams. Relationship between chemical composition, particle dispersion, cellular structure and physical properties

Postprint (author's final draft

Polymeric foams from cross-linkable poly-N-ary lenebenzimidazoles

Foamed cross-linked poly-N-arylenebinzimidazoles are prepared by mixing an organic tetraamine and an ortho substituted aromatic dicarboxylic acid anhydride in the presence of a blowing agent, and then heating the prepolymer to a temperature sufficient to complete polymerization and foaming of the reactants. In another embodiment of the process, the reactants are heated to form a prepolymer. The prepolymer is then cured at higher temperatures to complete foaming and polymerization

Characterization of cork and cork agglomerates under compressive loads by means of energy absorption diagrams

Cork and cork agglomerates could be suitable replacements for petroleum-based polymeric foams due to their similar internal structure of cells and grains. Additionally, cork products have a renewable origin and are recyclable. Despite these notable properties, few studies have analysed the mechanical properties, especially the specific properties, of these materials under compressive loads. Moreover, although efficiency, ideality, and energy-normalized stress diagrams are commonly used for polymeric foams and 3D-printed lattice structures, these types of diagrams are not yet applied to cork products. It must be highlighted that efficiency diagrams are plotted only against nonspecific properties so, this article proposes additionally the use of nonspecific properties to compare materials not only in terms of properties per unit volume instead but also in terms of properties per unit mass that is more suitable for certain applications in which the weight is crucial. The materials studied herein include three different white cork agglomerates, a brown cork agglomerate, a black cork agglomerate, natural cork, and expanded polystyrene foam, which are subjected to quasi-static compressive loads

Impact testing of polymeric foam using Hopkinson bars and digital image analysis

International audienceThis paper has investigated the impact testing method on the polymeric foams using digital image correlation. Accurate average stress-strain relations can be obtained when soft large diameter polymeric pressure bars and appropriate data processing are used. However, as there is generally no homogeneous strain and stress fields for polymeric foam, an optical displacement field observation is essential. In contrast with quasi-static tests where the digital image correlation (DIC) measurement is commonly used, technical difficulties still remain for an use under impact conditions such as synchronization and measuring accuracy due to rather poor quality images obtained from high speed camera. In the present paper, an accurate synchronization method based on direct displacement measurement from DIC is proposed and the feasibility of a calibration method using DIC on pressure bar ends is discussed. The relevance of the present method for establishing mechanical response of polymeric foam is also demonstrated

Anisotropic Compressive Behavior of Rigid PVC and PES Foams at Elevated Strain Rates Up to 200 s-1

In this study, closed cell polyvinyl chloride (PVC) foam with five different densities ranging from 45 to 200 kg/m3, and polyethersulfone (PES) foam with three different densities ranging from 50 to 130 kg/m3, were subjected to compressive loading under quasi static and elevated strain rates for mechanical material assessment. Three orthogonal loading directions, (i.e., parallel and perpendicular to foam rise directions) were considered to investigate structural anisotropy. The elevated strain rate tests were performed using a customized drop tower device at three different strain rates of 50, 100, and 200 s-1. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Experimental results indicated that elastic modulus, compressive strength, plateau stress, and energy absorbing capacity of both PVC and PES foams were highly dependent on foam density. Except for the PVC foam with the lowest density of 45 kg/m3, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction for both PVC and PES foams. The strain rate effect was more evident at higher densities. When loading perpendicular to the foam rise direction, no significant strain rate effect was observed for PVC foam. However, a slight strain rate effect was observed for PES foam at the highest density of 130 kg/m3 in one of the perpendicular to foam rise directions. Scanning electron microscopy (SEM) analysis showed that the cell wall thickness of both PVC and PES foams continuously increased with the increase of foam density. However, cell sizes were not simply dependent on foam density. For both quasi static and elevated strain rate tests, plastic hinges were the primary deformation mechanism for both PVC and PES foam cells