Water vapour transport

It will be clear that the diffusive transport (permeability) of water in and through polymers is of extreme importance, since all our clothes are made of polymeric materials and water vapour transport is one of the principal factors of physiological comfort. 

Coefficient of water vapour transport in a frozen foam of various compositions... 

Composition of foam sample Average flow of water vapour q 0 9 g cm 1 s 1 Coefficient of water vapour transport cm s... 

Fabrics to protect human body are, in most cases used under nonequilibrium conditions therefore, characteristics of fabrics under nonisothermal and nonequilibrium conditions are important in evaluating overall performance. Furthermore, in colder environments, layered fabrics rather than a single fabric are used in most cases. Under such conditions, the two most important characteristics of fabrics are water vapour and heat transport. However, the water vapour transport may not influenced significantly by surface characteristics-the hydrophilic or hydrophobic nature of fabrics. On the other hand, when liquid water contacted a fabric, such as in the case of sweating, the surface wetability of fabric play a dominant role in determining the water vapour transport through layered fabrics [48-50],... 

In such a case, the wicking characteristics, which determines how quickly and how widely liquid water spreads out laterally on the surface of or within the matrix of the fabric, determines the overall water vapour transport rate through the layered fabrics. 

Farnworth [66] reported a numerical model describing combined heat and water vapour transport through clothing. 

Consequently, it appears that the L/D ratio of PLA influences the gas permeability but no conclusion can be reached regarding the water vapour transport in this pol)uner. Moreover, generally speaking, the crystallization of the PLA matrix makes it possible to decrease the gas permeability and the organic compound sorption in PLA. However, no agreement has been formed regarding the influence of crystallinity degree on water vapour transport in PLA due to the variety of PLA composition (L-lactic acid content) and measurement systems. 

Microporous membranes are thought to function less effectively when the surface is covered with a layer of condensation. Solid film hydrophilic films, on the other hand, transport the water effectively without the need for re-evaporation. The high water content of the polymer caused by condensation plasticises and swells the polymer, improving the water vapour transport at relatively high temperatures. However, low temperatures offset the benefit of plasticisation and so the lining material should be chosen to optimise the overall performance of the garment. 

Table 2.3 Water vapour transport (WVT) through rainwear fabrics under different conditions ...

All three models propose a linear relationship between the vapour flux and the vapour pressure difference, so Kunz et al. (1996) proposed a general expression for describing the mass flux. This is related through the overall mass transfer coefficient, which accounts for all three resistances (feed, membrane and stripping) of water vapour transport to the driving force. 

C = The speed of the water vapour transportation (m s ) lies in the range from approximately 80-90 m s with an efficiently designed system concept... 

Fluid handling properties permeability, liquid absorption (liquid absorbency, penetration time, wicking rate and wicking height, rewet, bacteiia/particle collection, repellency and barrier properties, run-off, strike time), water vapour transport, and breathability. 

The overall water vapour and heat transport characteristics of a fabric should depend on other factors such as the water vapour absorbability of the fibres, the porosity, density and thickness of the fabric, etc. In this study, the major emphasis was on the influence of the chemical nature of the fibres that constitute a woven fabric. Dynamic water vapour and heat transport in the transient state were investigated for fabrics made of polyester, acrylic, cotton and wool fibres (Table 4.8). The overall dissipation rate of water vapour depends on both the vapour transport rate and the vapour absorption by fibres, which are mutually interrelated. Water vapour transport is governed by the vapour pressure gradient that develops across a fabric layer (Fig. 4.2). When a fabric is subjected to given environmental conditions, the actual water vapour transport rate differs greatly depending on the nature of the fibres, even... 

Rim is a common and easily achieved shape for most polymers. Shape memory film or foam has a number of applications in laminated smart fabrics. Various properties of SMP films have been investigated such as thermomechanical properties, different structural factors on the physical and water vapour transport properties, " effects of crystal melting, " molecular weight and influence of different processing temperatures. ... 

Elberaichi, A., Daro, A., and David, C. (1999) Water vapour transport in polyethylene oxide/ polymethylmethacrylate blends. Eur. 

Piroux, F., Fspuche, F., Mercier, R., Pineri, M. (2003) Water vapour transport mechanism in naphthalenic sulfonated polyimides. Journal of Membrane Science, 223, 127-139. 

In the case of water vapour transport, the micro-composites as well as the intercalated nanocomposites show diffusion parameters very near to PCL, while the exfoliated nanocomposites strongly deviate showing much lower values, even at low montmorillonite content (Fig. 11.4). This is an indication that in the former cases the water molecules on specific sites are not immobilized but can jump fi om one site to another. Only in the case of the exfoliated samples, the inorganic platelets, dispersed in a disordered distribution, can constitute a barrier to the path of the hydrophilic molecules. 

The present chapter is a brief summary of the work, on the application of Poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) and modified PPO carried out at the Industrial Membrane Research Institute, University of Otawa, Canada [1]. The approach has been to seek a better understanding of the processes that govern gas and water vapour transport across the membrane. 

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