Fiber chain stiffness

Chain stationary insertion, 16 110 Chain stiffness, of fiber polymers, 11 175 Chain-stopped alkyds, 2 152 Chain structure of PVDC, 25 699... 

It is important to be able to regulate the degree of chain stiffness, as rigid chains are preferred for fiber formation whereas flexible chains make better elastom. The flexibility of a polymer depends on the ease with which the backbone chain bonds can rotate. Highly flexible chains will be able to rotate easily into the various available conformations, whereas the internal rotations of bonds in a stiff chain arc hindered and impeded. 

Fiber modulus can be regulated by orientation and crystalhnity, but a third parameter, chain stiffness, is available for modification if additional control is required. 

X-ray analysis reveals that poly(ethylene terephthalate) (Dacron ) belongs to the triclinic system (25). The cell dimensions are a = 4.56, b = 5.94, c = 10.75 A, with the angles being a= 98.5°, J5 = 118°, y= 112°. Both the polyamides and the aromatic polyesters are high melting polymers because of hydrogen bonding in the former case and chain stiffness in the latter case (see Table 6.1). As is well known, both of these polymers make excellent fibers and plastics. 

A liquid crystalline polymer contains rigid rod like structure as discussed earlier which forms the hquid crystal phases. This rod like molecular conformations and chain stiffness give LCPs their most important self-reinforcing properties that are close to that of glass fiber reinforced composites. 

Due to their chain stiffness and their particularly high melting points, aramides cannot be processed by usual techniques applicable to thermoplastics. As in the case of polyacrylonitrile (PAN), they can only be utilized as fibers, which are obtained from the corresponding collodions either by dry spinning or wet spinning processes. 

The approximate formula weight of this monomer is x 162 Da which attributes 8,000 and 4,400 to the two higher molecular weight samples (M3 and M2) of HEC molecules, respectively, as degree of polymerization which yields the value for Ec. Thus, the persistence length was estimated from Eq. (4) in chapter Polyelectrolyte Science and Application as. Ip 10 nm (assuming Rg = 120 nm) which attributed considerable chain stiffness to HEC fibers. 

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

The rigid chemical structure of a conjugated polymer helps in the movement of electrons. That stiff structure, however, has limited its use. They are like uncooked spaghetti and do not easily entangle themselves. Polymer chain entanglements are necessary to achieve high viscosities, which are required to create fibers out of these polymers. 

Finally, we were led to the last stage of research where we treated the crystallization from the melt in multiple chain systems [22-24]. In most cases, we considered relatively short chains made of 100 beads they were designed to be mobile and slightly stiff to accelerate crystallization. We could then observe the steady-state growth of chain-folded lamellae, and we discussed the growth rate vs. crystallization temperature. We also examined the molecular trajectories at the growth front. In addition, we also studied the spontaneous formation of fiber structures from an oriented amorphous state [25]. In this chapter of the book, we review our researches, which have been performed over the last seven years. We want to emphasize the potential power of the molecular simulation in the studies of polymer crystallization. 

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