By: Dr. Prabhakar Bhat and H. U. Bhonde

ABSTRACT

Protective clothing for defense personnel has to exhibit many unique performance characteristics due to the diverse hostile conditions and wide range of threats under which it has to function. Although the functional requirements for this clothing are of major interest, comfort aspects of the same have to be considered seriously during designing of garment and selection of basic textile material, especially for hot climatic conditions. Because the ultimate success of combat troop would much depend on the comfort, mobility and protection provided by the particular garment

The clothing comfort is an extremely complex phenomenon, which may lead, inevitably, to incompatibility with the protection requirements, posing a serious challenge for the textile technologist and the garment designer. In this paper, we have discussed the important comfort properties in particular reference to the hot climate weather conditions in relation with defense protective clothing. There are various innovative techniques by which comfort properties of garment can be enhanced. These include the use of various types of new generation fibres, engineered yarn and fabric constructions as well as advance finishing techniques. The authors have discussed, in detail, the above aspects of improving the comfortness and suggested workable method for engineering the clothing for the defense personnel operating under hot climatic conditions.

1.0 Introduction

Defense clothing requirements are becoming more complex as the defense personnel have to perform at unprecedented levels, while threatened by array of ballistic, chemical, biological, thermal and environmental threats and hazards. Basic requirement of defense textiles can be listed as follows:
Physical lightweight, durable, comfortable, low noise emission and antistatic.

Windproof, water repellent, water vapour permeable, UV light resistant, air permeable and biodegradable.

Camouflage from visual spectrum, detection and surveillance system like radar, UV, heat and for infrared.

Flame retardancy, heat-resistance, ballistic protection, and nuclear, chemical, biological protection.
Minimal cost, easy maintenance, long storage life and readily available.

Apart from these basic requirements, India has hot tropical weather with variation from region to region, from the sub-freezing Himalayan winter to the tropical climate of coastal region and from the dump, rainy climate in the eastern states to the arid Great Indian Desert. The temperature ranges are wide from 15C to 38C in most of the climatic areas and in some region temperature can reach as high as 48C during the day in summer. Hence, the requirement of defense clothing, particularly for the hot Indian climatic condition, is very complex and also the human comfort factor should not be neglected. Because, on the battlefield under hostile conditions, it is the defense personnel who will take the ultimate decision and action that will be an important factor in deciding the final outcome of war. Because human performance is affected by clothing comfort, it will have serious implications on the ultimate result of war.

2.0 Clothing Comfort

Comfort is related to complex interactions between the fabric, climatic, physiological and psychological variables. A person feels comfortable in a particular climatic condition if his energy production and energy exchange with environment are evenly balanced so that heating or cooling of the body is within tolerable limits. A core body temperature of approximately 37C is required by an individual for his well-being. Hence, the body temperature is the most critical factor in deciding comfort.


Heat is gained by the body from the sun or intermediate source of energy, by internal metabolism, by physical exercise or activity, or by involuntary contractions of skeletal muscles in shivering. Heat loss by conduction, convection, or radiation, depends partly on the temperature gradient between the skin and the environment and this gradient is modified by varying the skin temperature. Excessive heat may be dissipated rapidly by vaporization of body water and the clothing system that hinders the free evaporation to any appreciable extent will thus be uncomfortable. On the other hand, undesirable heat loss can be prevented by increasing the thermal resistance of the barrier between the body and its environment and a fabric with low resistance will again result in discomfort to the wearer.

Thus it has to be conceptualized that the clothing comfort has three independent sensory factors.

i) Thermal wear comfort is mainly related to the sensations involving temperature and moisture. This factor responds mainly with the thermal receptors in the skin and relates to the transferring properties of clothing such as heat transfer, moisture transfer and air permeability.

ii) Tactile comfort is associated with the sensations involving direct skin-fabric mechanical interactions. This factor responds largely with the pain receptors in the skin and relates mainly to the surface characteristics of the fabric, its density, smoothness of the surface and the diameter of the fibre ends.

iii) Pressure comfort is more complex and involves a number of synthetic sensations. This factor may mainly correspond to the pressure receptors in the skin and may come from some combination of a number of simple sensory responses. Fabric bulk, mechanical behaviour and overall fit of the garment to the body may be responsible to this dimension of comfort.

2.1 Thermal properties and comfort

ISO 7330 defines thermal comfort as that condition of mind, which expresses satisfaction with the thermal environment. The thermal comfort depends on the desired physiological state and users can be comfortably hot or cold. Thermal comfort is affected by air temperature, radiant temperature, relative humidity, air velocity, activity and clothing. Generally, clothing thermal comfort is measured as clothing insulation and expressed in units of clo (1 clo = 0.155 m2c/w). The lowest clo value is 0 (naked body), while the highest practical clo value is 4 (Eskimo clothing, fur pants, coats, head and gloves, etc.). The summer clothing has to be around 0.6 clo.

2.2 Moisture-vapour transmission

It is incontestable that moisture-vapour transmission is crucial to comfort in both hot and cold weather. Free movement of water to the fabric surface is essential if perspiration discomfort causing fabric wetness, which results in clamminess in summer or freezing in winter, is to be prevented. The movement of water vapour through a fabric depends considerably on the micro porous nature of the material and, therefore, this movement can be modified by any operation that brings about a change in this structure. Moisture vapour transport is affected by yarn twist, texturing, fabric structure, mechanical treatments and chemical finishing. Now-a-days, coating or lamination techniques are used to improve moisture vapour transmission.

2.3 Liquid moisture transmission

Water from an external source, such as rain, should be prevented from reaching the body, which can be achieved by using water resistant barrier. On the other hand, water generated at the body surface as perspiration should be removed as quickly and efficiently as possible for the desired comfort, a process that is encouraged by the absorption within a body covering. In an ideal case, the pores of a fabric should be of sufficient size to permit free access of water vapour but the combination of pore size and material surface should be such that liquid water is prevented from entering the structure by surface tension. A fabric construction that includes a double structure, a close woven outer layer encasing a more open layer with moisture holding ability also appear to be a feasible way.


2.4 Air permeability

Comfort behaviour of the fabric is influenced in several ways by the air permeability of the fabric. A material that is permeable to air is also, in general, likely to be permeable to water, in either the vapour or the liquid phase. Thus, the moisture vapour permeability and liquid moisture transmission are normally closely related to air permeability. The thermal resistance of the fabric is strongly dependent on the enclosed still air and this factor is, in turn, influenced by the fabric structure, as also is the air permeability.

2.5 Comfort fit

No matter how well a fabric is engineered to have optimum values of heat, water and air transmission, any garment made from it cannot be regarded as comfortable if it does not fit properly. Comfort of fit during stress is important. Gilling describes the procedure for comfort testing of military clothing. Denton recognises four principal mechanical features that affect the garment comfort, these being weight, ease of movement, pressure on the body surface and ventilation.

3.0 Methods for Improving Comfort

Construction of a garment from raw material involves many steps, and each of the various elements (i.e. the fibre, yarn, fabric, material structure and finishing) makes relative contribution to the wearers performance. Very few studies have made attempts for assessing the effect of any of these elements on human performance. However, much work is being done around transport of liquid water and water vapour and thermal properties. This involves refinements of existing fibre types, creation of different fabric structures, and application of new finishes, engineered to enhance human performance.

3.1 Improved fibres

For clothing comfort, body vapour must have the opportunity to pass immediately from the skin to the outer surface of the clothing. Many fibres are capable of doing this in dry state, but the problem starts with perspiration. In contrast to the man-made fibres, natural fibres become saturated and the body vapour and perspiration fail to pass through the fibres which are virtually stacked together. Micro-climate is a general term that describes the temperature, humidity and microscope air stream between the skin and the clothing. It is an important factor in wear comfort and depends on the properties such as moisture and heat transport through the material, physiological and environmental conditions. Micro-climate factors and interaction with the skin are shown in Fig.1, while Fig.2 illustrates the micro-climate regimes and the associated comfort levels.


The process of moisture diffusion into a fabric depends on the number of fibre properties like moisture sorption capacity, diameter and surface area, water vapour diffusion coefficient, density and heat of sorption. The man-made fibre cross sections are suitably modified to increase surface area and also increase the wicking properties. Today, internationally, there are a number of fibre manufacturers making this kind of fibres, some of these types of fibres are illustrated as follows:

Coolmax has tiny irregular stumped polyester fibres that generate a high surface area to rapidly wick perspiration away from the skin. It also dries very quickly about two times faster than cationic. Undergarments made from Coolmax fabrics are being used by Canadian military personnel.



Triactor is a newly developed Y shaped cross-sectional polyester filament yarn which has a textile surface that absorbs moisture quickly. It absorbs sweat and dries much faster than conventional polyester, thus keeping the inside of the garment dry. Its construction reduces the amount of material touching the skin, generating cool and refreshing feel.


Superfine or microfibre yarn enables very dense fabrics to be produced with extended specific fabric or fibre surface area, developing more pores to transport vapour out by their superior capillary action. The higher pore density also provides better thermoregulation. The finer the fibrils,

- the greater the specific surface areas
- the greater the vapour transmission
- the softer the handle
- the greater the fabric density and cover
- the lower the flexing resistance.

3.2 Improved yarns structure

Today, various types of yarns, each having unique structure, like composite yarns, air-textured yarns, core-stretch friction spun yarns, air-jet spun yarns, etc., are available in the market. Some of these yarns can be suitably used in defense clothing. The physiologically desirable maximum load for human being is around 18.5 kg, however, during combat; the soldier has to carry a load in the range of 39-55 kg. Excessive weight impedes the mobility of a soldier and reduces his effectiveness. Every thing possible has to be done to reduce the load carried by the soldier. In this case, clothing is best suited for weight reduction purpose. In most countries, cotton fabric with 305 gsm is used in clothing. As an alternative, core-spun 50/50 cotton/nylon blend, twill 237 gsm fabric can be effective solution. The core-spun yarn gives required strength to the fabric and also reduces the weight of the fabric.

For optimum microclimate within the clothing, multi-layer yarn constructed using both hydrophilic and hydrophobic fibres can be considered. Toyobo company is offering such type of yarn PRH 50, which consists of three layer structure as shown in Fig.6.

Fig.6 PRH 50 Yarn structure

3.3 Engineered fabric construction


The fabric properties can be altered by suitable engineering of the textile structure and is mainly based on the selection of appropriate fibres, yarns and fabric structural parameters to meet the end-use requirements. The textile structures have been developed to enhance the human performance by focusing principally on the thermal and mechanical properties. Functioning of some of these branded materials is as follows:



The fabric Field Sensor reportedly is able to absorb sweat continuously, this being attributable to a three-layer structure knitted from synthetic yarns. Fibres in the yarns differ in diameter and this, according to the explanation, improves capillarity. Because the inner surface of the fabric was uneven, non-continuous contact with the skin is obtained.

Technofine is high-tech polyester yarn that has a specially designed W shape cross-section. The overlap of the W shape speeds up a fabrics ability to transport water away from the skin. Its increased surface area increases the evaporation rate. So, Technofine garments are quick drying. Uncomfortable perspiration is rapidly absorbed and the skin remains drier and more comfortable than with other polyester.

Aquamiracle is a quick light weight material consisting of a face side of Sunpaque fibre which contains a high density titanium core that blocks UV rays and a back side of Technofine yarn for moisture transfer. Aquamiracle is a high performance fabric that resists sweat stains, provides comfort, sun protection and a wonderful soft-hand feel.

3.4 Multiple layer structures and membranes

Materials may comprise of two or more layers at the initial or a subsequent fabrication stage as per the functional requirement of the end-use. Recently, membranes are included in multiple-layered clothing assemblies in an attempt to increase the resistance of assembly to penetration of liquids (usually water) from external sources. This generated the concept of breathable fabrics.

One of the first types of fabric material to confer improved insulation and breathability was Gore-tex fabrics. These fabrics are constructed by laminating a waterproof bi-component membrane to a range of substances such as expanded polytetrafluoroethylene (PTFE) impregnated with an oleophobic polymer. The membrane is highly porous consisting of about 9 billion microscopic pores per square inch which allows perspiration vapour to easily pass through while effectively blocking water droplets.

Altima is a new type of double layer knit fabric consisting of a dry layer and a moisture absorbing layer. It offers perspiration absorption and transpiration properties that are ideal for rigorous activities in which the wearer perspires heavily.

Another new development is Hydroweave, a performance enhancing fabric that cools through evaporation. Designed with three layers when soaked with or immersed in water, the central layer absorbs and retains moisture. As the waver evaporates from this layer, the fabric cools the wearer while its shell and lining keep the wearer dry. Hydroweaves principle starts with a super water absorbing polymer fibre that is blended into fibrous matting. This matting is positioned between a breathable exterior shell and a conductive waterproof lining. It is this combination of an outer shell, water absorbing matting and conductive lining that make up this patented product. Research work has shown that wearing Hydroweave vest, core body temperature can be kept under control and about 15% increase in work time can be obtained over non-vest condition.


3.5 Improved finishes and coating

The modern finishing techniques and coating materials tends to increase the breathability and condensation resistance, providing an ideal micro-climate within the clothing. These coatings are infused with an extremely moisture absorbing material or other additives like proteins, ceramics, etc. Nowadays, micro-encapsulated Phase-Change-Materials (PCM) are incorporated on the fabrics. These materials change phases on the change in ambient temperature, e.g. from solid to liquid at the materials melting point by absorbing large quantity of heat. But, still some of problems which persist today are with durability to abrasion, washing and fabric handle.

4.0 Conclusions: Future Some Concepts

Defense requirements are becoming increasingly complex as treating techniques are advancing. Low weight, flexible, protective, comfortable and low cost materials are the basics needed for defense personnel clothing. With the advances in intelligence system and information technology, electronics gadgets and devices will have to be successfully incorporated in the combat uniforms. Some of the enlisted key technologies which may have to be embedded in defense clothing for getting enhanced performance are:

a) Lightweight protective material.
b) Human factors, engineered fabric.
c) Microclimate conditioning.
d) Selectively permeable membranes and precutaneous filters.
e) Status monitoring sensors, connectors and electro textiles.

Extensive research work has to be carried out for effective process integrations of available advance techniques for ensemble of lightweight, durable, protective, comfortable, stress-free and economical defense clothing system.

The authors are working on development of such comfort clothing and also towards development of new solutions for the elimination of incompatibility of requirements and will have a lot to offer in future for the defense of our nation.

About the Author:

Dr.Prabhakar Bhat, Ph.D.(IIT Delhi),
Professor and Head,
Dept. of Textile Technology,
Shri Vaishnav Institute of Technology and Science,
Baroli, Sawer road, Indore

Mr.H.U.Bonde,
Lohia Group
Kanpur


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