Surface properties fibers

In preparation of permselective hoUow-fiber membranes, morphology must be controUed to obtain desired mechanical and transport properties. Fiber fabrication is performed without a casting surface. Therefore, in the moving, unsupported thread line, the nascent hoUow-fiber membrane must estabUsh mechanical integrity in a very short time. 

Because fiber frictional properties are so important in the conversion of staple yams to spun yams, ASTM D2612 has been designed to measure the cohesive force encountered in the drafting or fiber alignment of sHver and top under static conditions. This frictional force is affected by surface lubrication, linear density, surface configuration, fiber length, and fiber crimp. 

Reinforcing fibers can be modified by physical and chemical methods. Physical methods, such as stretching [22], calandering [23,24], thermotreatment [25], and the production of hybrid yarns [26,27] do not change the chemical composition of the fibers. Physical treatments change structural and surface properties of the fiber and thereby influence the mechanical bondings in the matrix. 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

When any polymer is to be used as film, plate, fiber, or molded material, the surface properties are as important as the bulk properties. In comparison with the large number of works devoted to the development of new polymers, relatively minor efforts have been directed to the modification of polymer surface. In particular, owing to the difficulties of studying chemical and physical properties of polymer surface, few articles have been published on the correlation between the condition of surface treatments and the imparted surface properties. 

While direct, this method is the most difficult experimentally due to the diminutive nature of fiber diameters and the uncertainty involved with contact angle measurements and hysteresis. The value i ) can also be measured on flat sheets of the fiber material but due to fabric finishes and different surface properties incurred during manufacture, the surface energetics of the sheet and fiber may be very dissimilar. Therefore, the value of co8i i was determined in the following manner from detergency data. The Kubelka-Munk Equation (12-13),... 

Composite system Fiber surface condition Fiber pull-out parameters Interfacial properties ... 

The surface properties of carbon fibers are intimately related to the internal structure of the fiber itself, which needs to be understood if the surface properties are to be modified for specific end applications. Carbon fibers have been made from a number of different precursors, including polyacrylonitrile (PAN), rayon (cellulose) and mesophase pitch. The majority of commercial carbon fibers currently produced are based on PAN, while those based on rayon and pitch are produced in very limited quantities for special applications. Therefore, the discussion of fiber surface treatments in this section is mostly related to PAN-based carbon fibers, unless otherwise specified. 

Bascom. W.D. and Drzal, L.T. (1987). The surface properties of carbon fibers and their adhesion to organic polymers. NASA contract Report 4084. 

Silverstein, M.S, and Breuer, O. (1993c). Relationship between surface properties and adhesion for etched UHMW-PE fibers. Composites Sci. Tecimol. 48, 151-157. 

In summary, the surface properties of fibers are influenced by the composition of the material, the environment during growth or generation, and the history of the particle. The term history refers to any changes in the surface after the fiber is formated. The charge or charge distribution affects the reactions of a fiber. 

The mass transfer coefficients k and ko in Eqs. (42) - (44) are important parameters and their values depend on the surface properties (hydrophobic or hydrophilic) of the hollow fiber membrane and whether the organic/aqueous phase flows in shell or tube side of the fiber, kj and k can be estimated from well established correlations [29] which have been successfully used for simulation purposes. 

---