For comfort body heat should be transmitted away from the body to the outer side of the clothing. This dry heat transmission occurs through conduction,convection and radiation. The mechanism of heat transmission through a fabric depends on its constituent fiber type, fiber arrangement, fabric bulk density,thickness, and the compressibility of the fabric structure . Here, an attempt has been made to compare the thermal behavior of various cellulosic fabrics including union as well as pure fabrics with 100% cotton. The results for comparative analysis of thermal insulation value are listed in Table 3. From the results it can be seen that fabric samples containing cotton indicate thermal insulation values on higher side as compared to pure fabrics of unconventional fibers presumably due to the structure of cotton fiber. Cotton fiber contains hollow lumen and twists causing more air entrapping in yarn.
Whereas, the fibers of hemp, linen and ramie are smooth, straight and contain almost no lumen . Moisture and water vapor transmission plays a very important role in governing the physiological comfort of apparel fabrics. This is related to the moisture vapor transmission through the fabric. This decides the extent of comfort the wearer feels in a sweating or similar condition. The results of moisture vapor transmission rate are listed in Table 3. The findings reveal that all the pure fabrics of unconventional fibers and their respective union fabrics have increased volumes of moisture vapor transmission as compared to the reference cotton sample.This behavior can be attributed to the hygroscopic nature of the fibers used. Also the fiber properties like diameter, rigidness and cross-section play an essential role in deciding the extent of openness of structure that will be responsible for better moisture vapor transmission. The higher values of MVTR indicates that these fabrics can transfer liquid moisture very easily and quickly from next-to-skin to the outer surface.
The findings compiled in Table 4 reveal that all the pure fabrics of unconventional fibers and their respective union fabrics have increased values of Accumulative one-way transport index as compared to the reference cotton sample. Generally fabrics which possess high OWTC values indicate that the liquid can be quickly transferred from the inner surface next to the skin to the outside surface. Also it will be spread quickly over the fabric bottom surface with a large wetted area. This large area spread of liquid help its quick evaporation into the environment. This behavior can be attributed to the hygroscopic nature of the fibers used. Also the fiber properties like diameter, rigidness and cross-section play a major role in deciding. Hemp fabrics show a relatively higher OMTC values and bottom spreading speed. This indicates that hemp fabrics can manage liquid moisture very efficiently. The sweat will quickly transmit to the outer side of such clothing and so will be evaporated by larger spreading in no time. The bottom water radius is also higher than top in fabrics containing hemp.
The fabrics containing linen falls in the next position after hemp in such type of overall moisture management. It may be observed that the bending and shear hysteresis of cotton and cotton rich union fabrics are significantly higher than other fabrics. The tensile resiliency values of hemp and ramie fabrics are also significantly higher than other fabrics. Tensile linearity of all cellulosic fibers is almost similar; the same is also observed in case of low stress compressibility. This actually falls in the logic that at low stress levels both tensile and compression results behave alike. From surface properties point of view, banana and linen fabrics exhibit significantly higher geometrical roughness due to higher hairiness and surface roughness of these two yarns. The THV of the fabric samples is estimated with the help of various primary hand values using the Kawabata-Niwa equations by KES system and the results are displayed in Figure 1.
It may be observed that the linen fabric gives the highest THV for summer and lowest THV for winter applications. This behavior is reflected in its constituent low stress mechanical properties where it found that both bending and shear hysteresis are significantly lower than other fabrics.The results also depict that almost all the fabric samples exhibit higher THV for summer applications as compared to winter due to obvious reason of their suitability as a cellulosic fiber predominantly meant for tropical and sub-tropical climate. The values of summer THV of all pure unconventional fiber based fabrics and their respective union fabrics are either comparable or better than100% cotton. This trend strongly advocates the possibility of unconventional fiber fabrics to be used as an apparel fabric for summers.Hemp fibre has widely been used in many civilizations. It has been reported that the earliest use of hemp was over 6000 years ago.