Orientation drawn fibers

In the fiber structure, molecular chains in the crystalline region are highly oriented parallel to the fiber axis and a majority of molecular chains in the noncrystalline region are also highly oriented, so that both the conformational versatility and the mobility of molecular chains are much limited. But even in highly drawn fibers a significant, albeit minor, amount of amorphous material with a liquidlike mobility still exists. 

White (1955) believes that differential thermal analysis curves obtained by him on heating drawn fibers of 6, 6-6 and 6-10 nylons as well as polyethylene terephthalate, indicate that at first crystallites disorient and then melt. He found two peaks in what would correspond to a specific heat-temperature curve. However, it is difficult to understand why the disorientation of oriented crystals would involve the absorption of energy. 

PTFE fibers are made by spinning from aqueous dispersions, which are mixed with matrix-forming medium and forced through a spinneret into a coagulating bath. Then the matrix material is removed by heating and the fibers are sintered and oriented (drawn) in the molten state to develop their full strength.15... 

Studies of craze microstructure and the surrounding displacements of crazes have established that the only parts around a craze that undergo plastic deformation are concentrated into a process zone at the tip of the craze, and into a fringing layer all around the entire craze body. In the process zone craze matter is generated by one of the two processes discussed above, and fibrils are necked down to the final extension ratio. In the fringing layer, additions are made to craze fibrils by drawing polymer out of half space. Outside the idetifiable parts of a craze, the solid polymer remains entirely elastic while inside the craze body the fully drawn fibers carry the required craze tractions purely elastically in their orientation hardened state at the... 

Highly oriented PP monofilaments (drawn to break at 25 ) are more resistant to photo-oxidation than medium drawn fiber ( x5 orientation at 230 C) as measured both by oxidation product build up and mechanical deterioration (2 ). Both types of PP monofilaments also show crack formation during photooxidation CFlgure 7). The lower orientation material shows quite wide, deep cracks whereas the fully oriented fiber shows many short, narrow cracks for... 

The PLA fibers show neither embrittlement nor deterioration of properties due to the secondary crystallization, which means that the structures of PLA fibers are stable at these conditions and during this time. The reason for this could be the high crystallinity and the high orientation of the polymer chain of the highly drawn fibers to avoid the secondary crystallization. 

The uniform oxidation of the cold-drawn filament results in a high overall degree of oxidation and associated backbone scission before surface deterioration reaches the level at which spontaneous restructuring and crack formation can occur. Lateral cohesion of these fibers was much greater than for the highly oriented filaments. For example, the latter could be easily peeled, whereas the cold-drawn fiber stretched rather than fibrillated after notching. 

The orientation of fibers discussed above has led to the use of uniaxially drawn polymeric material such as polyethylene or poly(vinyl) alcohol containing a guest molecule of interest to be used for fundamental studies on the optical transition moments of the guest. Molecules studied in this may Include pyrex, acenaphthylene, benzo(g.h.1.)perylene, benzo(g.h.l.)fluoranthene, naphtha-cene, perylene, and coronene, and the fluoranthenes (99-102). 

Self-reinforced PP is an intriguing avenue for creating a more recyclable, single-polymer, reinforced material. Such a composite system is reinforced by oriented, drawn PP fibers within a PP matrix, or as part of a laminated system. However, current cost disadvantages have limited their use [7-42]. 

The increase in oxygen concentration accompanies the deterioration of fiber physical properties, but the deterioration does not necessarily relate to the increase directly. Factors such as fiber orientation and the conditions, primarily temperature at which the fiber is drawn, can affect the rate of deterioration [113], The reduction of elongation that accompanies exposure to UV light is less for a highly oriented fiber because the photooxidation reaction is initially limited to the fiber surface. The photooxidation reaction is accompanied by the formation of cracks on the thin surface [114]. Cold-drawn fiber reacts throughout, degrades faster, but does not form surface cracks. Fiber wettability increases with increased UV exposure [112], which is additional evidence of the formation of surface oxygen bonds. 

In spite of the complex nature of the aggregations of the crystalline and amorphous regions in polypropylene fibers, it has been found that the mechanical properties of both spun and drawn fibers depend largely on the relative amounts of the amorphous and crystalline regions present and the molecular orientation of each of the phases [79,183,184]. 

FIGURE 3.56 High-temperature endotherm peak, T2M versus c-axis orientation function (O) drawn fiber (x) heat-set fiber. (From Samuels, R.J. J. Polym. Sci., Polym. Phys., 1975, 13, 1417. With permission.)... 

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