The longest natural fibers normally encountered in papers are about one fourth of an inch in length and the shortest about one-sixteenth of an inch. Fibers are generally about 100 times longer than they are wide, although some fibers, such as cotton, have a length to diameter ratio of more than 1,000 to 1. The walls of all fibers are composed of small strands called FIBRILS .
Chemically the fibrils are composed of a number of cellulose chains. Other chemical components in fibers other than cellulose include hemicelluloses and lignin.
The physical properties of length, diameter, wall thickness, and FINES content are the most significant in determining the characteristics of paper made from natural fibers. The approximate relationships between fiber characteristics and paper properties are:
Property of the Paper: Increased by: Decreased by: tensile strength long fiber large diameter stretch long fiber thick cell wall tearing resistance long fiber, thick cell wall folding endurance long fiber thick cell wall opacity thick cell wall, long fiber high fines content bulk long fiber, thick cell wall porosity long fiber, large diameter thick cell wall formation thick cell wall, long fiber high fines, large diameter
The chemical characteristics also have a significant effect on the properties of the paper. The length of the CELLULOSE CHAIN , for example, which is the basic unit in a fiber, contributes greatly to the strength of the fiber. If these chains are naturally short, or have been shortened either by chemical or mechanical treatment or influences, the strength of the fibers will be naturally lower or else reduced; therefore the paper will be weaker. In addition, the paper loses strength if the cellulose chains are shortened due to chemical action subsequent to manufacture of the paper.
Paper pulps that contain a high degree of hemicelluloses are easy to refine, have good bonding strength and low tearing resistance, and goodRATTLE .
Excessive bleaching of the fibrous stock, especially when done with strong caustic extractions, results in removal of hemicelluloses. The fibers then have greater flexibility but do not bond together effectively, resulting in a paper that is soft and absorbent.
Unbleached paper pulps tend to contain more lignin than is found in bleached pulps. The presence of lignin results in stiffer, tougher fibers which do not collapse against each other very well, resulting in fewer interfiber bonds being formed during manufacture. Bleached fibers, on the other hand, conform better and afford greater contact between fibers, resulting in a stronger paper. While bleached fibers conform better than unbleached, improper bleaching may result in the loss of hemicelluloses and damage to the cellulose chains. 2. The complex proteinaceous structure, composed of ropelike bundles of fibrils organized in long, wavy bundles that vary in diameter from approximately 1 to 20 microns. These proteinaceous fibers make up the principal constituent of COLLAGEN . (18 , 72 , 323 , 363 )