Models for the compressibility of layered polymeric sponges

A Highly Sensitive Piezoresistive Pressure Sensor Based on Graphene Oxide/Polypyrrole@Polyurethane Sponge

In this work, polyurethane sponge is employed as the structural substrate of the sensor. Graphene oxide (GO) and polypyrrole (PPy) are alternately coated on the sponge fiber skeleton by charge layer-by-layer assembly (LBL) to form a multilayer composite conductive layer to prepare the piezoresistive sensors. The 2D GO sheet is helpful for the formation of the GO layers, and separating the PPy layer. The prepared GO/PPy@PU (polyurethane) conductive sponges still had high compressibility. The unique fragmental microstructure and synergistic effect made the sensor reach a high sensitivity of 0.79 kPa⁻¹. The sensor could detect as low as 75 Pa, exhibited response time less than 70 ms and reproducibility over 10,000 cycles, and could be used for different types of motion detection. This work opens up new opportunities for high-performance piezoresistive sensors and other electronic devices for GO/PPy composites.

Solvent Effects on Tuning Pore Structures in Polyimide Aerogels

This work evaluates the effects of solvents and a block copolymer surfactant on pore structures in polyimide aerogels synthesized via sol-gel reaction process. Specifically, cross-linked polyimide gel networks are synthesized in single or mixed solvents from a combination of dimethylformamide, N-methylpyrrolidone, and dimethylacetamide and supercritically dried to obtain aerogels. The bulk density, pore size, and mechanical properties of aerogels are determined. The results show that gel times are strongly dependent on the electron acceptance ability of the solvent system and concentration of the surfactant. At longer gel times, the polyimide strands coarsen and the pores in aerogel shift from predominantly mesoporous to macroporous state with corresponding reduction in compressive modulus. The block copolymer surfactant also slows down gelation and coarsens the polyimide strands but only weakly affects the compressive modulus of the aerogels.

Review: Mechanical properties of dry cellular solid foods / Revisión: Propiedades mecánicas de alimentos celulares sólidos

The compressive stress-strain relationships of most cellular materials and solid foams have a char acteristic sigmoid shape that reflects three deformation mechanisms: primarily elastic distortion under small strains; collapse and/or fracture of cell walls; and densification. The exact shape of the relationship is mainly determined by the materials' composition including: moisture contents; the cells and cell wall size and geometry; and whether the cells are open or closed. Upon repeated compression the nature of the relationship may change as a result of irreversible changes in the solid matrix (especially rupture). When the cell wall material is very brittle the force-displacement curve can be extremely irregular and jagged, often concealing its underlying sigmoid shape. Characterization of such brittle products requires methods of jaggedness evaluation and smoothing procedures. These are now readily available and have been successfully applied to extruded puffed foods. Food particulates tested in bulk can show similar compressibility patterns even if they themselves do not have a cellular structure. Although tensile properties of spongy baked foods, like bread crumbs, can be determined experimentally they have not yet been proven useful as indicators of textural quality, primarily as it appears, because of structural non-uniformity.

The Effect of Padding Foam on the Compression Characteristics of Some Agglomerated Food Powders

Selected padding foam was used to reduce attrition in agglomerated food powders. This is a widely used strategy in fruits and vegetables during harvesting and processing to minimize impact damage. The objective of this research was to determine the padding effect on some agglomerated food powders when plastic foams of different thicknesses were added in the powder bed at different positions while conducting confined uniaxial compression tests. The padding effect was evaluated by two proposed indices: padding index and padding efficiency. The former index was based on the force-deformation behavior of the compression process, while the latter was based on weight comparisons of agglomerates retaining their original particle size with or without the use of padding foams. The padding thickness and positions significantly affect the force-deformation relationships for both agglomerates: instant coffee and instant milk. The padding effect, in terms of padding efficiency and padding index, was more obvious when the padding material was put at the top of the powder bed. The padding efficient index is more useful, in the cases under consideration, than the other index, because it should be more sensitive in depicting attrition.

Advanced Finite Element 3D Injection Molding

In this paper, we present aspects and examples relating to Rem3D, a 3D finite element software dedicated to the computation of the entire injection molding cycle (filling, packing and cooling). Recent developments are presented, namely mesh generation and adaptation driven by a local natural metric, compressible Stokes and temperature solvers, as well as a multidomain approach. As an example of the application of Rem3D, computations have been compared with well instrumented experiments for a complex mold geometry.

Production, properties, and applications of hydrocolloid cellular solids

Many common synthetic and edible materials are, in fact, cellular solids. When classifying the structure of cellular solids, a few variables, such as open vs. closed cells, flexible vs. brittle cell walls, cell-size distribution, cell-wall thickness, cell shape, the uniformity of the structure of the cellular solid and the different scales of length are taken into account. Compressive stress-strain relationships of most cellular solids can be easily identified according to their characteristic sigmoid shape, reflecting three deformation mechanisms: (i) elastic distortion under small strains, (ii) collapse and/or fracture of the cell walls, and (iii) densification. Various techniques are used to produce hydrocolloid (gum) cellular solids. The products of these include (i) sponges, obtained when the drying gel contains the occasionally produced gas bubbles; (ii) sponges produced by the immobilization of microorganisms; (iii) solid foams produced by drying foamed solutions or gels containing oils, and (iv) hydrocolloid sponges produced by enzymatic reactions. The porosity of the manufactured cellular solid is subject to change and depends on its composition and the processing technique. The porosity is controlled by a range of methods and the resulting surface structures can be investigated by microscopy and analyzed using fractal methods. Models used to describe stress-strain behaviors of hydrocolloid cellular solids as well as multilayered products and composites are discussed in detail in this manuscript. Hydrocolloid cellular solids have numerous purposes, simple and complex, ranging from dried texturized fruits to carriers of vitamins and other essential micronutrients. They can also be used to control the acoustic response of specific dry food products, and have a great potential for future use in countless different fields, from novel foods and packaging to medicine and medical care, daily commodities, farming and agriculture, and the environmental, chemical, and even electronic industries.