Marijn M.C.G. Warmoeskerken

Modeling of the acoustic pressure fields and the distribution of the cavitation phenomena in a dual frequency sonic processor

An attempt has been made to model the acoustic pressure field and the spatial distribution of the cavitation phenomena in a dual frequency sonic processor. A methodology has been presented with numerical simulations to optimize the conditions of the dual frequency acoustic field. The simulations presented in this work reveal that with manipulation of the parameters (viz., frequency ratio and the pressure amplitude ratio of the two acoustic waves and the phase difference between the two waves) of the dual frequency acoustic field it is possible to control the mode (stable or transient) and spatial distribution of the cavitation events in the sonic processor. It has been shown that two major shortcomings of the sonic reactor, viz., directional sensitivity of the cavitation events and erosion of the sonicator surface can be overcome by application of a dual frequency acoustic field.

Acoustical characteristics of textile materials

An attempt is made to identify the acoustical characteristics of textile materials using precision woven monofilament fabrics as model textiles. The experiments try to eliminate the effect of entrapped air pockets in the fabric on an ultrasound wave field. The results of the experiment reveal that the power consumption of the ultrasound horn remains practically constant after introducing the textile at different positions in the standing wave field. Measurements of transmitted acoustic pressure amplitude through the textile reveal that fabrics form an almost transparent boundary for acoustic waves. A simple model involving the structural and hydrodynamic characteristics of the textiles is proposed to determine their acoustic impedance, and the results of the experiments are explained on the basis of this model. The overall conclusion of the study is that in the absence of entrapped air, textiles do not have any individual impact on the ultrasound wave field.

Characterization of an ultrasonic system using wavelet transforms

A new method has been developed for the determination of the spatial distribution of the cavitation intensity in an ultrasound processor. The method uses wavelet transform analysis of the acoustic emission profiles. The periodic modulation of the acoustic pressure field in an ultrasound processor causes unsteady radial motion of the bubbles, resulting in non-stationary acoustic emission profiles that cannot be analyzed by Fourier transform. The cavitation intensity has been judged experimentally and numerically. The experimental method used the “cavitation noise coefficient” defined as the sum of the energy at different scales (or levels) in the wavelet transform of the measured signal containing the subharmonic and harmonics of the fundamental frequency. The numerical method involved the simulation of the radial motion of a bubble and the pressure waves radiated by it, applying experimentally measured acoustic pressure signals as the forcing function. The numerically predicted spatial variation of the cavitation intensity was in agreement with the experimental measurements. It is proposed that the conical divergence of the acoustic waves from the transducers and the differences in the electrical and acoustical characteristics of the adjacent transducers in the bath give rise to a non-uniform cavitation intensity distribution.

Functional finishing of aminated polyester using biopolymer-based polyelectrolyte microgels

This study focuses on a microgel-based functionalization method applicable to polyester textiles for improving their hydrophilicity and/or moisture-management properties, eventually enhancing wear comfort. The method proposed aims at achieving pH-/temperature-controlled wettability of polyester within a physiological pH/temperature range. First, primary amine groups are created on polyester surfaces using ethylenediamine; second, biopolymer-based polyelectrolyte microgels are incorporated using the natural cross-linker genipin. The microgels consist of the pH-responsive natural polysaccharide chitosan and pH/thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid) microparticles. Scanning electron microscopy confirmed the microgel presence on polyester surfaces. X-ray photoelectron spectroscopy revealed nitrogen concentration, supporting increased microscopy results. Electrokinetic analysis showed that functionalized polyester surfaces have a zero-charge point at pH 6.5, close to the microgel isoelectric point. Dynamic wetting measurements revealed that functionalized polyester has shorter total water absorption time than the reference. This absorption time is also pH dependent, based on dynamic contact angle and micro-roughness measurements, which indicated microgel swelling at different pH values. Furthermore, at 40 °C functionalized polyester has higher vapor transmission rates than the reference, even at high relative humidity. This was attributed to the microgel thermoresponsiveness, which was confirmed through the almost 50% decrease in microparticle size between 20 and 40 °C, as determined by dynamic light scattering measurements.

Time survivor study of Escherichia coli with polyhexamethylene biguanide on cotton

Time survivor or time kill studies are commonly used to investigate the efficacy of antimicrobial agents in homogeneous solutions. Such a study was attempted via a textile treated with an antimicrobial agent. For this study, a finished undyed cotton fabric and a commercially available antimicrobial agent, polyhexamethylene biguanide, were used. The release of the antimicrobial agent from the cotton fabric when submerged in water with a liquor-to-cloth ratio of 20:1 was evaluated. The antibacterial agent-treated cotton fabric was also tested according to the JIS L 1902 absorption antibacterial testing method at various agent concentrations applied to the fabric and incubation times. The treated textile showed a quick release of agent when submerged in water and the results of the antibacterial tests showed increasing antibacterial activity with increases in concentration, as has been found in homogeneous solutions. Fabrics treated with lower concentrations of the agent show bacteriostatic action. A regrowth of microorganisms was additionally noted at certain incubation times.

Ultrasound-boosted enzymatic cotton scouring process with cutinase and pectate lyase

Abstract The synergistic effect between power ultrasound and enzymes in an enzymatic scouring process has been studied. The scouring enzymes were Fusarium solani pisi cutinase (EC 3.1.1.74) and pectate lyase (EC 4.2.2.2). In different stages of the scouring process, power ultrasound with a pre-optimized power of 0.57 W cm−2 and a frequency of 30 kHz was applied. It was found that ultrasound shortens the enzymatic scouring process time dramatically; less than 5 min was required to achieve the desired scouring expressed in terms of hydrophilicity of the cotton fiber. The results obtained have been explained in terms of mass transfer intensification by ultrasound (so-called ‘sono-mechanics’) and its effect on the enzyme kinetics (so-called ‘sono-chemistry’). This latter effect has been found by applying ultrasound in a homogeneous enzymatic reaction in which mass transfer did not play any role. The kinetics of product formation in a homogeneous system was carried out using poly-d-galacturonic acid as a model substrate.

Biocatalytic pre‐treatment processes of cotton: Industrial application of academic research

Much research effort is invested in developing enzymatic treatments of textiles by focusing on the performance of enzymes at the laboratory scale. Despite all of this work, upgrading these developments from the laboratory scale to an industrial scale has not been very successful.Nowadays,companies are confronted with rapid developments of markets, logistics, and social and environmental responsibilities. Moreover, these organizations have to supply an ever-increasing amount of information to the authorities, shareholders, lobbyists, and pressure groups. Companies have tried to fulfill all of these demands, but this has often led to the loss of focus on new products and process development. However, both theory and practices of breakthrough innovations have shown that those rightfully proud of previous successes are usually not the ones that led the introduction of new technology, as shown and excellently documented by Christensen [1]. The textile industry is no exception to this observation.With the lack of management impetus for new product and process developments, companies began to reduce investments in these activities.However, this results in a reduction of the size of the company or even closure. Besides the hesitation from the top management of textile companies to focus on new developments,middle management level is also reluctant to evaluate and implement developments in new products and processes. One of the reasons for this reluctance is that many processes in the textile industry are notfully explored or known. From this lack of knowledge, it is easy to explain that there is hesitation for change, since not all consequences of a change in processing or production can be predicted. Often new developments cannot be fully tested and evaluated on the laboratory- or pilot-scale level.This is caused by the impossibility of mimicking industrial-scale production in a laboratory.Additionally, pilot-scale equipment is very expensive and for many companies it is not realistic to invest in this type of equipment. Fortunately an increasing number of textile companies have realized that they have to invest in new products and processes for their future survival and prosperity. New developments are decisive for future successes. If such companies decide to invest in new developments, it is clear that with the scarcity of capital for product and process developments, the chance of failure should be minimized. For successful process and product development, it is necessary to organize the development process with external partners because it is clear that it is almost impossible for individual textile companies to control the process from idea generation to academic research, implementation research, and development and industrial testing. These issues are especially characteristic for small- and medium-sized enterprises (SMEs). Herein, the collaboration has been organized on two research levels. The first research level is knowledge and know-how based. The universities and chemical suppliers worked closely together to investigate the new process.The aim was to explore the influence of process conditions and interactions of chemicals in sub-process steps as a result of the treatment.The second level is that of the industrial implementation of the new process. The universities and chemical suppliers worked closely together with different industries to implement the newly developed process. The focus in this part of the research was the interaction between the chemistry of the new process, equipment, and fabrics. A co-operation between the beneficiaries of the new process was established.The selection criterion for the co-peration was “who will earn something with the new process”. To answer this question, the value chain has been drawn as the simplified scheme shown in Fig. 1 [2].