Cellulose fiber phenomena

Radioactive tracers adsorb not only on solid container surfaces and precipitates but on any kind of solid material suspended or in contact with the solution. Dust, cellulose fibers, glass fragments, organic materials, etc., are examples of substances that readily adsorb radioactive tracers from solution. If the solution contains large molecules as, for example, polymeric metal hydrolysis products, these also tend to adsorb trace elem ts. In addition to sorption, the presence of such material in the solution can lead to the phenomenon of radiocolloid formation, which is the attachment of radionuclides to semicolloidal aggregates in solution. If the solution is kept at sufficiently low pH and extremely free from foreign particles, sorption and radiocolloid formation are usually avoided as major problems. 

The physical macroscopic notion of porosity or pores in a solid and the phenomenon of absorption of a fluid in a porous object are both quite familiar to all of us. Further, wide varieties of natural or synthetic solids, compounds, species, and materials are known to be of porous nature, for example, minerals, wood, cellulose fibers, seashells. 

Opacity is an optical reflectance phenomenon. It is the resistance of an object to the transmission of light. For paper lower opacity means greater show-through . Sheet opacity is a fimction of the refractive index differences among air, cellulose fiber, and filler. As light enters the paper, it is either reflected, bent (refracted), absorbed, or passed through. Mineral... 

Another characteristic feature of cellulose-water interactions is the fact, that, depending on the moisture level, the properties of water associated with the cellulose can differ from those known under normal conditions. This phenomenon has a great technological meaning (e.g., pressing and drying efficiency). For this purpose, water in cellulose fibers is classified according to its properties and usually three main types of water are discerned (Fig. 2.9) ... 

Solubility, as well as the possibly related phenomenon of swelling, depends on the H bonding character of the solvent (or swelling agent). Indeed, the effect is not limited to proteins but also occurs for gelatin, cellulose, wood (1495), nylons, and probably for clays and other colloidal systems as well. Lloyd and co-workers discuss solubility and swelling of protein fibers (1250) (see, in fact, that entire discussion on swelling, 1252). 

Time-dependent drifts in permeability, such as those shown in Fig, 20.5-1 for cellulose acetate, are important practical features of asymmalric fibers that generally result in a loss in productivity over a period of time. When fouling is known not to be a factor, the so-called permeability creep phenomenon is believed to arise from one or a combination of the following factors ... 

The swelling of bast and leaf fibers in alkaline solutions is a complex phenomenon. Their structure is more complicated than in the case of pure cellulose. Different components of the middle lamella react in different ways, and rates, in relation to each other and to the cellulose. In addition, the composition of the fiber changes with the time of treatment. A part of the... 

The structure of bast fibers is very similar to all types of fiber. Elementary fiber consists of cellulose fibrils held together by a lignin and hemicellulose. Typical phenomenon observed in bast fibers structure is occurrence of lumen with different... 

---