Fiber transformation

Specialty fibers are also produced by fiber transformation whereby preformed fibers are converted to the desired fibers by pyrolysis or reaction with other substances. Carbon, graphite, boronitride, and borocarbide filaments are obtained by this method. 

Note GAS PHASE GROWN CARBON FIBERS transform during GRAPHITIZATION HEAT TREATMENT into GRAPHITE FIBERS. The term vapor grown carbon fibers is also acceptable but, CVD fibers is not acceptable, as it also describes fibers grown by a chemical vapor deposition (CVD) process on substrate fibers. 

Cotton gin (Eli Whitney) Whitney s engine to separate cotton seed from the fiber transformed the American South, both bolstering the institution of slavery and growing the cotton is king economy of the Southern states. Five years later, Whitney develops an assembly line for muskets using interchangeable parts. 

Kazayawoko M, Balatineoz J J and Woodhams R T 1997 Diffuse refleotanoe Fourier transform infrared speotra of wood fibers treated with maleated polypropylenes J. Appl. Polymer Sci. 66 1163-73... 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

Most ceramics are thermally consoHdated by a process described as sintering (29,44,68,73—84), ia which thermally activated material transport transforms loosely bound particles and whiskers or fibers iato a dense, cohesive body. 

Fibers produced from pitch precursors can be manufactured by heat treating isotropic pitch at 400 to 450°C in an inert environment to transform it into a hquid crystalline state. The pitch is then spun into fibers and allowed to thermoset at 300°C for short periods of time. The fibers are subsequendy carbonized and graphitized at temperatures similar to those used in the manufacture of PAN-based fibers. The isotropic pitch precursor has not proved attractive to industry. However, a process based on anisotropic mesophase pitch (30), in which commercial pitch is spun and polymerized to form the mesophase, which is then melt spun, stabilized in air at about 300°C, carbonized at 1300°C, and graphitized at 3000°C, produces ultrahigh modulus (UHM) carbon fibers. In this process tension is not requited in the stabilization and graphitization stages. 

To date, there has been relatively little work reported on the mesophase pitch rheology which takes into account its liquid crystalline nature. However, several researchers have performed classical viscometric studies on pitch samples during and after their transformation to mesophase. While these results provide no information pertaining to the development of texture in mesophase pitch-based carbon fibers, this information is of empirical value in comparing pitches and predicting their spinnability, as well as predicting the approximate temperature at which an untested pitch may be melt-spun. 

Not all of the strength and stiffness advantages of fiber-reinforced composite materials can be transformed directly into structural advantages. Prominent among the reasons for this statement is the fact that the joints for members made of composite materials are typically more bulky than those for metal parts. These relative inefficiencies are being studied because they obviously affect the cost trade-offs for application of composite materials. Other limitations will be discussed subsequently. 

For each of the failure criteria, we will generate biaxial stresses by off-axis loading of a unidirectionally reinforced lamina. That is, the uniaxial off-axis stress at 0 to the fibers is transformed into biaxial stresses in the principal material coordinates as shown in Figure 2-35. From the stress-transformation equations in Figure 2-35, a uniaxial loading obviously cannot produce a state of mixed tension and compression in principal material coordinates. Thus, some other loading state must be applied to test any failure criterion against a condition of mixed tension and compression. 

In applications of the maximum stress criterion, the stresses in the body under consideration must be transformed to stresses in the principal material coordinates. For example, Tsai [2-21] considered a unidirec-tionally reinforced composite lamina subjected to uniaxial load at angle 6 to the fibers as shown in Figure 2-35. The biaxial stresses in the principal material coordinates are obtained by transformation of the uniaxial stress, a, as... 

The space lattice does not undergo polymorphous transformation. As with other kinds of fibers, no transformation of the space lattice under the effect of any physical or chemical treatment of PET fibers has yet been found. 

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