Study On Negative-Ion Properties Of Textiles And Measuring Systems

Nowadays negative-ion textiles have been developed as new functional textiles, which can generate negative ions through applied mechanical forces. Because of the benefits from negative ions, such as invigorating the transportation of oxygen, speeding up metabolism, promoting revitalization and maintaining good health, negative-ion textiles have attracted more and more attention since 1990s. With the increase knowledge about fiber materials and improved measurement technology, it was found that many natural fiber fabrics and man-made fiber, especially soybean protein fiber (SPF) fabric, also can generate negative ions. Therefore, negative-ion textiles can be divided into three types, textiles blended with negative-ion generator materials, natural fiber fabrics (like cotton, wool, silk and linen), and SPF fabric. The first type of negative-ion textiles are formed using nanotechnology, blending technology or finishing technology to combine negative-ion generator materials such as natural silicate minerals (ceramic/tourmaline) and natural sediments (coral fossil) with textile materials. The other two can both generate negative ions by themselves without any additive. For the first type of negative-ion textiles, the mechanism of negative-ion generation has been researched thoroughly, but the study on the quantitive rule has not been done yet. For the other two, the research on properties of negative-ion generation is just at the beginning. Hence, it is necessary to study the mechanism, rules and properties of negative-ion generation of textile materials systematically in order to accelerate the development and application of negative-ion textiles, especially for SPF fabrics.In the thesis, the properties of negative-ion generation from natural fiber fabrics and SPF fabric have been studied and compared with polyurethane (PU) leather, viscose fiber fabric and polyester fiber fabric, which are blended with negative-ion generator materials. The measuring methods and systems for negative-ion textiles were developed and the factors influencing negative-ion properties of textiles and the mechanism of negative-ion generation have been researched.Because there is no standard measuring method for negative-ion emission from textiles, the measurement results vary with the researcher and type of instruments. As a result, the first step as inventing the measurement method and developing the measuring system for negative-ion emission is important and critical for the study. Instead of the traditional hand rubbing method, the flat rubbing negative-ion generating device and the overhanging vibrating negative-ion generating device were developed respectively based on the influence of mechanical force on negative-ion generation. These two devices produce rubbing and vibrating movements to simulate the movement of textiles during real wearing process. They can provide negative-ion measurement for different kinds of textiles at various movements. The DLY-2 Air Ion Counter was connected with computer to provide data process functions, such as drawing, statistic analysis and digital signal processing, thus the automatization of the measuring systems was enhanced. Through the experimental analysis, the flat rubbing negative-ion measuring method and overhanging vibrating negative-ion measuring method were established respectively, including measurement procedures and measurement conditions. Compared with hand rubbing negative-ion measurement, the new developed negative-ion measuring systems are normative, highly automatic and sophisticated, which provide effective and precise measurements for negative-ion properties of textiles.Using the developed negative-ion measuring methods and systems, this thesis researched the negative-ion properties of natural fiber fabrics and SPF fabric. The experiments were carried out to study the effect of rubbing time and pressure on quantity of negative-ion generation and surface static electricity under the action of flat rubbing; the effect of vibrating time, vibrating rate, temperature and relative humidity on quantity of negative-ion generation, the optimization of experimental condition and the negative-ion dynamic change under the action of overhanging vibrating.The conclusions based on the experiment results are as follows: 1) Natural fiber fabrics and SPF fabric can both generate negative ions by the action of flat rubbing or overhanging vibrating. Under the action of flat rubbing, with small size samples at 20±2°C and 60±3%r.h., negative-ion generation from natural fiber fabrics and SPF fabric is less than 500ions/cc, lying between negative-ion polyester fabric and negative-ion viscous fabric.2) Under the action of overhanging vibrating, with big size samples at 25±3°C and 65±3%r.h., negative-ion generation from natural fiber fabrics and SPF fabric is between 1400～2300 ions/cc (negative-ion PU leather is 1580 ions/cc). By contrast, cotton fabric has lower negative-ion generation. Linen has nearly same negative-ion generation with silk and wool, and SPF fabric has higher negative-ion generation.3) Negative-ion generation has saturation that an increase in applied acting duration or acting strength does not produce extra negative-ion generation after a certain level.4) Negative-ion generation alters with the change of measuring conditions. Usually negative-ion generation is little at low temperature. Once above certain temperature, it rises quickly as the temperature increases. Humidity has both positive and negative influence on negative-ion generation, so when the humidity increases negative-ion generation first increases, then decreases slightly and finally increases dramatically.5) Negative-ion properties are correlative with the microstructure of materials. The protein fiber fabrics have similar negative-ion generation properties while the cellulose fiber fabrics have like negative-ion properties.6) Under different actions of mechanical forces, the negative-ion effects of fabrics are not same. For instance, silk or SPF fabric has better negative-ion effect under the action of overhanging vibrating than that under the action of flat rubbing.7) Static electricity of materials has important influence on negative-ion properties. The negative-ion concentration depends on the surface potential of fabrics, so the factors influencing electrostatic properties also affect negative-ion properties.The thesis explored the mechanism of negative-ion generation from natural fiber fabrics and SPF fabric. The results of static experiment show that when the mechanical manipulation acts on these fabrics, such as rubbing or vibrating, there are some amounts of charges produced on their surfaces. These charges could be regard as the energy source of negative-ion generation. By tip discharge of hairiness, the air is ionized or the water molecules are dissociated, resulting in negative-ion generation. The results of hairiness experiment indicate that when hairiness of fabric increases, negative-ion concentration increases, and the surface potential decreases. Same experiment was conducted with polytetrafluoroethylene (PTFE) plate and pure polyester fabric, but there was no negative-ion generation. Although the static potential of PTFE plate is up to 20kV and that of polyester fabric is also high, neither of them can produce negative ions because of less hairiness. Thus, negative-ion generation is primarily introduced by both electrostatic effect and tip discharge of hairiness.As polymer materials, wool, silk, cotton, linen and SPF fiber all have the polar crystalline region in fiber structure, however, the piezoelectricity of these fabrics is low unless using the treatment of polarization. Through the analysis on the source of piezoelectric effect in polarized fabrics, it is found that piezoelectric effect is mainly caused by the trapped charge injected during the polarizing process. Therefore, the piezoelectricity of natural fabrics is very slight and plays a minor role in negative-ion generation.