Effects of ultrasound on polymeric foam porosity

Abstract

A variety of materials require functionally graded cellular microstructures whose porosity is engineered to meet specific applications (e.g. mimic bone structure for orthopaedic applications; fulfil mechanical, thermal or acoustic constraints in structural foamed components, etc). Although a huge variety of foams can be manufactured with homogenous porosity, there are no generic processes for controlling the distribution of porosity within the resulting matrix.Motivated by the desire to create a flexible process for engineering heterogeneous foams, the authors have investigated how ultrasound, applied during the formation of a polyurethane foam, affects its cellular structure. The experimental results demonstrated how the parameters of ultrasound exposure (i.e. frequency and applied power) influenced the volume and distribution of pores within the final polyurethane matrix: the data demonstrates that porosity (i.e. volume fraction) varies in direct proportion to both the acoustic pressure and frequency of the ultrasound signal.The effects of ultrasound on porosity demonstrated by this work offer the prospect of a manufacturing process that can adjust the cellular geometry of foam and hence ensure that the resulting characteristics match the functional requirements.

Identification of formation stages in a polymeric foam customised by sonication via electrical resistivity measurements

“…When samples were sonicated, a range of frequencies and powers were systematically explored. Details of the arrangement of ultrasonic sources/receivers for the experimental sessions and sensors within the water bath can be found elsewhere [35].…”

“…The foams were irradiated for 20 minutes in a duty cycle of 2min on/1min off, starting after adding the distilled water. The level and frequency of this cyclic irradiation was established by initial experimentation [35] and was sufficient to induce changes in the foam structure without causing collapse.…”

Investigation of the effects of the microstructure on the sound absorption performance of polymer foams using a computational homogenization approach

“…Considering the cubic symmetry of the Kelvin cell, five loading conditions (listed in Table 1) are used to extract the effective material parameters. (9). In these simulations, the foam is surrounded by a rigid wall and backed by an impermeable wall.…”

“…Ghaffari Mosanenzadeh et al applied a combination of a particulate leaching technique and a compression molding method to closely control the cell structure of open-cell foams with a graded cell size changing from 200 µm to 600 µm [8]. It is also reported that ultrasound can be applied for a better control and monitoring of the production process [9,10,11,12]. Moreover, it was shown that the opening ratio of the membranes is influenced by the concentration of the reactants [6].…”

Morphological and biological characterization of density engineered foams fabricated by ultrasonic sonication

“…In this method, first reported in 2008 [23], a polymeric melt undergoing foaming is irradiated using low power ultrasound in the range of 20-30kHz. By controlling the acoustic field that the polymerizing mixture is subject to, maxima and minima of energy (i.e.…”