Semicrystalline definition

By definition, thermoplastics have limitations at elevated temperatures. It is in this particular property that fibrous glass can lead to remarkable improvements. However, a sharp division exists for reinforced thermoplastics. The various reinforced thermoplastics can be put in two groups relative to DTUL. These consist of amorphous and crystalline or semicrystalline polymers. The amorphous polymers such as styrene-acrylonitrile, polystyrene, polycarbonate, poly (vinyl chloride), and acrylo-nitrile-butadiene-styrene are generally limited to modest DTUL improvements, usually on the order of 20°F with 20% glass. However, crystalline polymers such as the nylons, linear polyethylene, polypropyl-... 

The present study has shown that low crystallinity ePP crystallizes from the melt into well-defined morphologies. This smdy presented definitive evidence that this class of materials, when crystallized isothermally from the melt, exhibits morphologies that are reminiscent of classical semicrystalline polymers. The presence of lamellae, crosshatching, and spherulites was revealed by high resolution tapping mode AFM and optical microscopy. The nonisothermally crystallized ePP specimens also display the hierarchical ordering as seen in the case of iPP. 

The addition of glass fibers increases the number of nucleation sites in semicrystalline jxrlymers. This produces an increase in the degree of crystallinity and, consequently, an enhanced heat distortion temperature. By definition, amorphous polymers are noncrystalline and, as such, this mechanism is inoperable. 

Definition A semicrystalline thermoplastic formed by polymerization of 1-butene Empincal (C4Hs)x Formula [CHzCHCCzHsjjn Properties Colorless vise, liq. misc. with min. oil insol. in water m.w. 500-75,000 dens. 0.910 pour pt. -60 to 50 C... 

Due to their higher dimensions, the macromolecules may successively penetrate several crystalline domains, thus interconnecting them. The spaces between these crystalline regions do not have a ordered structure, any longer, appearing as amorphous regions. In practice, there are no polymers with 100% crystallinity degree. The correct and common definition of these polymer types is semicrystalline polymers . 

The principal forms of spinning are listed in Table 11-1, together with the phase-transformation process as well as the principal commercial fibers formed by each technique. Generally, the selection of a particular type of spinning process is related to the material being spun. For example, nylons are semicrystalline in the solid state and have a definite melting point. Whereas the nature of solid nylon makes it difficult to put it into a solution, it does not prevent a melt from being formed. Hence, nylon is a melt-spun fiber. On the other hand, polyacrylonitrile is an amorphous solid and, as such, is dissolved more readily than a semicrystalline polymer. Here, the result is that polyacrylonitrile is either dry-... 

It may come as a surprise to many that a large number of the common plastic items in everyday use are semicrystalline. As the lUPAC definition states, A crystalliz-able polymer. .. is able to partially crystallize. ... 

The large strain response in the glassy or semicrystalline state is that of a nonlinear viscoelastic solid. However, both engineering and theoretical approaches to plasticity in polymers have largely developed as an independent discipline, in which (Ty plays a central role, in spite of its somewhat arbitrary definition (indeed it is not always possible to associate cty with a maximum in the force-deformation curve [5]). This is because in practice the yield point, rather than the ultimate strength, is usually considered to be the failure criterion for ductile materials. 

Hence, the stated above results demonstrate nonzero contribution of noncrystalline regions in yield stress even for such semicrystalline polymers, which have devitrificated amorphous phase in testing conditions. At definite conditions noncrystalline regions contribution can be prevailed. Polymers yield stress and elastic constants proportionality is not a general rule and is fulfilled only at definite conditions. 

As it has been noted in Ref. [60], the generalized Renyi dimension (or Z) characterizes the most concentrated system set. In Ref. [55] it has been shown, that for amorphous polymer matrix the cluster are such set and the linear correlationwas obtained. It is obvious that for the considered componors with polymer semicrystalline matrix the crystalline regions will be the most concentrated set that assumes a definite correlation between and K. Actually, such correlation exists, as it follows from the data of Fig. 14.15 and it is described by the simple analytical relationship [56] ... 

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