Semicrystalline Stmcture

Since its introduction, the LH theory has revealed several serious problems in describing the main parameters of the semicrystalline stmcture. Some of these problems such as the... 

Figure 27 shows a TEM micrograph of a lamellar stack in a binary blend of PET and amorphous PEI. A rather diluted PET/PEI blend was used for this experiment, which helps to open up the semicrystalline stmcture and to spatially isolate the lamellar stacks, which was the main objective here. In this case, a competition between crystallization and vitrification produces an incompletely space-filling stmcture containing small-size immature sheafs. These crystallization conditions allow to examine individual lamellar stacks in great detail. It has been verified that the stain selectively marks amorphous regions of PET and leaves PEI practically unmodified. Thus, in... 

Polyethylene (PE) is a genetic name for a large family of semicrystalline polymers used mostiy as commodity plastics. PE resins are linear polymers with ethylene molecules as the main building block they are produced either in radical polymerization reactions at high pressures or in catalytic polymerization reactions. Most PE molecules contain branches in thek chains. In very general terms, PE stmcture can be represented by the following formula ... 

Mechanical Properties. Although wool has a compHcated hierarchical stmcture (see Fig. 1), the mechanical properties of the fiber are largely understood in terms of a two-phase composite model (27—29). In these models, water-impenetrable crystalline regions (generally associated with the intermediate filaments) oriented parallel to the fiber axis are embedded in a water-sensitive matrix to form a semicrystalline biopolymer. The parallel arrangement of these filaments produces a fiber that is highly anisotropic. Whereas the longitudinal modulus of the fiber decreases by a factor of 3 from dry to wet, the torsional modulus, a measure of the matrix stiffness, decreases by a factor of 10 (30). 

Abrasion resistance is usually measured by the Taber Test procedure described by ASTM D1044. Abrasion resistance of unfilled semicrystalline polymers is linked to the degree of crystallinity that is itself related to the molecular stmcture and weight of the resin and its processing. Table 3.54 includes the results of testing two types of perfluoroalkoxy polymers, PFA and MFA, and ECTFE. Notice the large difference between wear index (weight loss by abrasion in 1000 cycles) of ECTFE which is a partially... 

Figure 20-3 Proposed stmcture of a molecule of amylopectin in a starch granule. The highly branched molecule lies within 9 nm thick layers, about 2 / 3 of which contains parallel double helices of the kind shown in Fig. 4-8 in a semicrystalline array. The branches are concentrated in the amorphous region.starch granules contain no amylose, but it may constitute up to 30% by weight of the starch. It may be found in part in the amorphous bands and in part intertwined with the amylopectin.

Figure 16.17 (a) Amorphous polymer stmcture (b) semicrystalline polymer stmcture with... 

Fig. 1 (a) Schematic representation of the mechanically induced transformation of a disordered semicrystalline polymer comprising small aggregates of self-assembled ehromophores (small-molecule or polymeric) into an oriented structure in which the guest moleeules are well dispersed, (b) Stmcture of EHO-OPPE, a poly(p-phenylene ethynylene) derivative... 

Fig. 5.5 Schematic hierarchy of microscopic stnictuie of PE blend sphtaulites consisting of semicrystalline lamellar ribbons. Green in the composite image indicates D-HDPE, and red indicates H-LLDPE. The dotted rectangular box in the molecular stmcture indicates the unit cell of crystalline PE, with the unit cell parameters (a, b, c) as indicated [28]...

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