Rayon fiber Properties

In this chapter we will elaborate on recent advances in dissolution and derivatization of cellulose and follow up with a description of new processes that lead to regenerated cellulose fibers. Finally, we will describe viscose processes and rayon fiber properties. 

Table 2. Properties of Selected Commercial Rayon Fibers...

For rayon fiber based eomposites (Seetions 3 and 4) the fiber and powdered resins were mixed in a water slurry in approximately equal parts by mass. The isotropie piteh earbon fiber eomposites (Seetion 5) were manufaetured with less binder, typically a 4 1 mass ratio of fiber to binder being utilized. The slurry was transferred to a molding tank and the water drawn through a porous sereen under vacuum. In previous studies [2] it was established that a head of water must be maintained over the mold screen in order to prevent the formation of large voids, and thus to assure uniform properties. The fabrieation proeess allows the manufaeture of slab or tubular forms. In the latter case, the cylinders were molded over a perforated tubular mandrel covered with a fine mesh or screen. Moreover, it is possible to mold eontoured plates, and tubes, to near net shape via this synthesis route. 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

Fiber Properties of Cottons Washed on Rayon Wash Line,... 

Fiber Properties of Mississippi, California, and Texas Cottons — Rayon Wash Line, Second Experiment... 

This is the first reported study of the spinning of mesomorphic cellulose solutions, but no fiber properties were given. Quenin et al. (14) used a d -jet, wet spinning system to spin cellulose/MMNO-H20 solutions. Fiber properties equiv dent to the best viscose rayon fiber were obtained. 

Because the polymer-polymer grafting reactions in cold plasma conditions are superficial, the physico-mechanical properties of the grafted rayon fibers are similar to those of standard rayon. 

After precipitation and regeneration of cellulose have been completed and raw rayon fiber has been formed, the subsequent steps must be controlled so that differences in treatment are minimized otherwise such sensitive properties... 

Carbon and graphite fibers are made by the pyrolysis of certain naturally occurring and man-made fibers, such as regenerated cellulose (rayon) fibers. A wide range of physical, mechanical and chemical properties may be obtained dependent on amount of dehydration. This product is one of the most structurally efficient reinforcements. Unlike any other reinforcement, it retains its 2,800 MPa (400,000 psi) tensile strength when tested up to a temperature of 2700 C (4800F). 

II allomorph is known by the term regenerated cellulose. Regeneration involves either preparing a solution of cellulose in an appropriate solvent or of an intermediate derivative followed by coagulation and recrystallization. This process is used to produce rayon fibers. Mercerization involves intracrystalline swelling of cellulose in concentrated aqueous sodium hydroxide (NaOH), followed by washing and recrystallization. This process is used to improve the properties of natural yams and fabrics. The transition from cellulose I to cellulose II is not reversible, and fliis implies that cellulose II is a stable form as compared with the metastable cellulose I. 

The fiber properties of primary importance to adhesion are reactivity, surface characteristics, and finish. Rayon has many reactive hydroxyl groups. Nylon is less reactive but contains highly polar amide linkages. Polyester is relatively inert. Thus an adhesive system must be designed for each type of fiber. 

In the period 1965-1980 a wide variety of new, stronger, and more durable rayon fibers were developed. Rayon variants are now produced which utilize the comfort and aesthetic qualities of cellulose to compliment synthetic fibers in many textile applications. Considerable emphasis has been placed on the economics and ways to meet environmental and safety standards. Special effects, such as crimp or hollow filaments, may be obtained by appropriate viscose formulations, point-of-stretch applications, spin-bath compositions, and modifiers. Flame-retardant (FR), acid-dyeable, and superabsorbent rayons are typical of the properties that can be attained by incorporating various materials in the fiber structure. Rayon is unique in the respect that the fiber can be permanently modified for a wide variety of end uses simply by adding the appropriate material to viscose. 

After shredding, the alkali cellulose crumb is aged to obtain the DP for the type of rayon to be produced. Not only is the DP important to fiber properties, but it also affects the processing characteristics of the viscose. Solution viscosity is proportional to the DP and polymer concentration. Consequently, those fibers requiring a relatively high DP for reasons of strength must be made from viscose containing less cellulose [236]. 

The classification of viscose rayon fibers into different types is done mostly on the basis of physical and chemical properties. Fibers produced by nonviscose processes are usually identified separately. It has already been described how the fiber can be produced to have almost any desired structure, and it is considered to be the most versatile of all human-made fibers. It is available in various cross-sectional shapes, from multilobed, serrated, and round to flat longitudinally, it may be straight or curled (crimped). It comes in fine deniers... 

Two fibers with exceptionally high wet-modulus were developed years ago, but the importance of this property to dimensional stability in fabrics was not recognized at the time. Surprisingly, one of the stronger rayon fibers with conditioned tenacity of 6-7 g/den (5.4-... 

Table 38-2, Properties of Some Rayon Fibers with Titers of About 2 dtex After W. Albrecht)...

CFRPs are strong and light fiber-reinforced polymers. Carbon fibers are a new breed of high-strength materials. Carbon fiber contains at least 90% carbon prepared by controlled pyrolysis of rayon fibers [34]. The subsistence of carbon fiber came into use in 1879 when Edison took a patent for the fabrication of carbon filaments used in electric lamps [35]. The composites manufactured using carbon fiber reinforcements exhibit a range of mechanical properties suitable for many constructional, industrial, and automobile applications. 

One of the disadvantages of PLA for many applications is its brittleness (20 kJ/m and 2 kJ/m for unnotched and notched Charpy, respectively). Instead of using common impact modifiers which reduce strength and stiffness, rayon fibers generate improved impact properties both in the unnotched and notched testing modes, as demonstrated in Fig. 18.19. Again, with wood or natural fibers, such a behavior caiuiot be generated [30]. 

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