Fibers moisture effects

Effect on Fiber The effect of extrusion on fiber is related primarily to its bulk density. As a result of the mechanical action, grinding, and attrition, the hollow structure of fibrous materials is crushed, thus changing the bulk density. High fiber ingredients are normally low in moisture and take on moisture slowly, which requires some type of preconditioning prior to extrusion. 

Farnworth [14] reported a numerical model describing the combined heat and water-vapor transport through clothing. The assumptions in the model did not allow for the complexity of the moisture-sorption isotherm and the sorption kinetics of fibers. Wehner et al [30] presented two mechanical models to simulate the interaction between moisture sorption by fibers and moisture flux through the void spaces of a fabric. In the first model, diffusion within the fiber was considered to be so rapid that the fiber moisture content was always in equilibrium with the adjacent air. In the second model, the sorption kinetics of the fiber were assumed to follow Fickian diffusion. In these models, the effect of heat of sorption and the complicated sorption behavior of the fibers were neglected. 

These references are concerned with the mechanisms through which moisture is absorbed by the fiber. The effect it has on fiber properties however varies from fiber type to fiber type, and although the effects are wider than merely the effect on tensile properties, it is on these properties that the standard methods of test are mainly concerned. Many of the standard tests previously cited, such as ISO 5079. ISO 2062. ASTM D 2256. and ASTM D 3217. all make provision for conducting the tests with the fiber or yarn in the wet rather than the conditioned state. 

Y. Ren, C. Wang, and Y. Qiu. Influence of aramid fiber moisture regain during atmospheric plasma treatment on aging of treatment effects on surface wettability and bonding strength to epoxy. Appl. Surf. Sci., 253(231 9283-9289, September 2007. 

Figure 5.70 Example of moisture effect on glass fiber/PET RPs...

Textile fibers that absorb moisture also change their axial and transverse dimensions. This phenomenon has important practical consequences for example, the swelling of fibers could effectively close the pores in a tightly woven fabric and alter its mechanical characteristics. 

Hertz, J., Moisture Effects on the High Temperature Strength of Fiber-Reinforced Resin Composites, 4th National SAHPE Conference, Palo Alto, Calif. Oct. 1972. 

Blankenhom, P.R. et al (1999) Temperature and moisture effects on selected properties of wood fiber-cement composites. Cement and Concrete Research 29,737-741. 

Figure 17.4 The effect of moisture on the measured density of oxidized fiber. moisture regain=0.04.

A fiber is selected for a specific product based on its ability to be processed and converted into the desired finished device and its potential for assisting the product in effectively performing the required function. There are six primary physical characteristics that are considered essential for this purpose. These are fiber size and shape fiber tensile properties fiber bending properties fiber thermal transitions and heat setting properties fiber surface energetics and fiber moisture absorption... 

Mandell, J.F., Chen, J.-H. and McGarry, F.J., A microdebonding test for in-situ fiber-matrix bond and moisture effects. Department of Materials Science and Engineering. Massachusetts Institute of Technology, Cambridge, MA, Feb. 1980, Research Report R80-1. 

Fiber-reinforced composites do however have some potential drawbacks. These include high cost, brittle behavior, susceptibility to deformation under long-term loads, ultra-violet degradation, temperature and moisture effects, and a lack of design codes. 

Control of relative humidity is needed to maintain the strength, pHabiUty, and moisture regain of hygroscopic materials such as textiles and paper. Humidity control may also be required in some appHcations to reduce the effect of static electricity. Temperature and/or relative humidity may also have to be controlled in order to regulate the rate of chemical or biochemical reactions, such as the drying of varnishes, the appHcation of sugar coatings, the preparation of synthetic fibers and other chemical compounds, or the fermentation of yeast. 

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