The ease or otherwise of the passage of air is of importance for a number of fabrics end uses such as industrial filters, tents, sailcloth’s, parachutes, bulletproof, windproof, raincoat materials, shirting’s, down proof fabrics and airbags.In this article, Knitting Expo will introduce you the importance of Air Permeability.
Fabric air permeability is a measure to what extent it gives air passing through the fabric. Air permeability, a given area in the vertical direction of the air flow rate, a given time period, as measured by the fabric test area inside the pressure difference of the fabric. Basically, it depends on weight, thickness and porosity of fabric. The porosity of fabric is the demonstration of the air gap as a percentage within the fabric. It has been important for especially the tent fabric and parachute.
The reciprocal of air permeability, air resistance, can be defined as the time in seconds for ImI of air to pass through 100s mm2 of fabric under a pressure head of 10mm of water. The advantage of using air resistance instead of air permeability to characterize a fabric is that in an assembly of a number of fabrics, the total air resistance is then the sum of the individual air resistance.
Fabrics, are porous materials which allow the transmission of energy and substances and are therefore interesting materials for different applications. In general, they are used for clothing, interior and wide range of technical applications
Garments must be characterized by good air circulation between the skin surface and the environment, good ventilation at skin level and the possibility of eliminating the excess humidity generated through perspiration.
Air permeability, simply a physical ability of a fabric to let certain air flow through under differential pressure between either surface, refers to the speed at which water vapour molecules transmit into the top layer. Fabrics with different surface textures on either side can have a different air permeability depending upon the direction of air flow. Air permeability and fabric porous structure are correlated and indicate the breathability which makes great differences in the performance of materials. That is to say, air permeability and porous fabric structure affect how breathable a garment is; besides, air permeability can be measured, whereas breathability is more subjective.
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In the British Standard test, the airflow through a given area of fabric is measured at a constant pressure drop across the fabric of 10mm head of water. The specimen is clamped over the air inlet of the apparatus with the use of rubber gaskets and the air is sucked through it by means of a pump as shown in Fig.A. The air valve is adjusted to give a pressure drop across the fabric of 10mm head of water and the air flow is then measured using a flow meter.
Five specimens are used each with a test area of 508mm2 (25.4mm diameter) and the mean air flow in ml per second is calculated from the five results. From this, the air permeability can be calculated in ml per 100mm2 per second.
Classification of fabrics: based on fabric type there are four types of fabrics
Woven fabric: this has been defined as the interlacing/ interlacement of warp and weft yarns where minimum two sets of yarns are needed and warp yarn stay in vertical and parallel to the selvedges.
Knitted fabrics: This has been defined as the interloping/interlocking/ intermeshing of warp yarn where minimum one set of yarn is needed.
Non-Woven fabrics: this has been defined as the mechanical/chemical/thermal bonding to make non-woven fabrics.
Braided fabrics: this is defined as the intertwining/diagonal/interlacement to make braided fabric where minimum three sets of yarns are needed.
Correlation between porosity and air permeability of fabric is very complicated because changes of the textile structure (by the influence of the venting system), can be possibly classified as a horizontal increase in porosity. A correlation relationship has been elaborated between the percentage of open porosity for double layer fabrics and air permeability, considering the use of the different system of reed denting.
Fabric porosity is an important parameter in the assessment of clothing comfort and physical properties of technical textiles and the porosity are defined by the ratio of free space to fibre in a given volume of fabric. The porous are by voids between weft and warp yarns in the fabrics. The air passes through the pores from the surface of the fabric. Tightness factor can be used for fabric air permeability forecasting. The high correlation between the permeability to air and the tightness factor confirms that. Porosity is affected by yarn number or yarn count number. … Increasing loop length, looser the structure and so the values of air permeability increases.
Source: textile school
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As far as Knitting Fair knows, the textile industry (cotton printing and dyeing) clean production standards being as reference and green production full control in the whole process as the guiding ideology, the green evaluation indexes are formed and have better feasible manipulation.
Consumption of water and energy (CWE)
The textile industry is one of the industry sectors consuming water largely. The main water consumption is generated from production technical processes including bleaching and boiling, dyeing, printing, finishing, washing of wool, reeling in a cocoon, etc. In addition, there is a large amount of water consumption coming from textile plant conditioners and staff living. Water consumption can be measured by ton per ten thousand.
Chemical fiber, cotton textile and printing and dyeing plants are also main energy consumption industries. At present, domestic main textile product per unit energy consumption is 40% higher than that of an international advanced level. Plants rough management results in not only numerous waste of resources, serious environment pollution but also high cost. Assessing water and energy consumption can help to lower production cost, save resource and reduce environment press. Energy consumption can be measured by tons of standard coal per ten thousand.
Treatment of wastewater, gas, and materials (TWWGM)
Wastewater mainly comes from textile and dyeing process. Textile wastewater contains natural impurities, organic matter of fat and asylum. Printing and dyeing wastewater contains organic matter of dyes, amylum, cellulose, lignin, detergent, and inorganic matter of alkali, sulfide and various salts. Waste gas mainly includes sulfur dioxide, fume, and dust, which generate during coal burning and pollute environment seriously. Waste materials mainly include offal short fiber coming from a chemical and mechanical action, waste yarn and waste materials during spinning and weaving production, corner or excess cloth during clothing cutting process. These waste materials are treated by burning or burying which pollute environment seriously.
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Control of harmful materials to human health (CHM)
During planting of natural fiber, chemical fertilizers and pesticides are used inevitably. Some poisonous substances and chemical residue will remain in the final products which cause crimes to people. Some dyes and auxiliaries such as antiseptics, preservatives, azo dyes, and formaldehyde, which are used during dyeing and printing production, have powerful toxicity too. These chemical substances may cause various hazards such as skin allergies, dermatitis, and respiratory discomfort.
This index evaluates poisonous substance contents of raw materials, semi-finished products, and final products. Oeko-Tex Standard 100 is the most authoritative standard system in the world. It tests properties of PH value, formaldehyde, insecticide, colorfastness, banned azo dyes aryl amine, etc.Raw material and accessories and end product are needed to reach Oeko-Tex Standard 100.
Advanced technology, product, and design idea (ATP)
This index includes three-second level indexes to evaluate the green level of production technology, new products, and design idea. In recent years, many new green production technologies, green fibers and environmentally friendly dyes and auxiliaries are used which can improve the green level of textile and clothing production chains and increase the added value. Green design of textile and clothing is a new esthetics field. Its design ideas play an important role in publicity and consumption. Currently, many international famous designers and brands of textile and clothing have used kinds of ways to express green design idea. For example, recycle old materials to create new products, use pure nature and no polluted raw materials to produce clothing, design simple and fresh styles, etc
Package consumption (PC)
Textile and clothing package is not only a larger consumption and environmental pollution. According to statistics, to an annual output of 900 million shirts, the paper consumption of shirt box will reach 180,000 tons which are equal to 1,260,000 trees. So it has significance to control packing costs and use degradable packing materials. This index has two second-indexes to evaluate package pollution degree (whether use materials of environmental protection) and resource consumption (g/10,000 Yuan of industrial added value).
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The working environment of workshops (WEW)
Noise pollution is a serious problem in textile and clothing industry; especially in cotton textile industry. Due to a widespread use of shuttle looms, a noise in the weaving workshop can reach 90~106dB while the maximum allowable value to the ear is 85dB. As the report indicates, the effects of noise include tinnitus, headache, insomnia etc. This index includes two-second indexes to test and evaluate noise and an average density of dust (mg/m3) in textile and clothing workshop.
Source: textiles school
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