Microfibril length

Microfibrils are formed in PET fibers during the stretching of a solidified polymer stream. With an increase in the draw ratio, microfibrils become increasingly slender. The microfibril length is assumed to be proportional to the draw ratio (R), their lateral dimension proportional to Jr, while the length-to-lateral dimension ratio is proportional to... 

Some imperfections arise from dislocations at the interface of microcrystalline domains along the microfibril length. These imperfections were exploited to advantage by treatment of the sample with acid to produce nanocrystals called whiskers, having the same diameter as the starting mierofibrils but of much shorter lengfli. 

The observed contradiction regarding the microfibril lengths and the spheres diameters can be explained by assuming the following mechanism of microfibrils formation starting from the spherical particles. Considering the fact that the spheres are rather densely pop-... 

Figure 1 The structure of a microfibril. C - crystallite S -separating layer SL - surface layer IZ - intermediate zone mF - border of microfibril k - crystallite length U - separating layer length L - mean long period (spacing).

The mesomorphous phase, also called an intermediate phase or a mesophase, is formed by molecules occurring in surface layers of the crystallites. It can be assumed that the mesophase is made up largely by regularly adjacent reentry folds. However, it cannot be excluded that the mesophase is also composed of some irregular chain folds, which are characterized by a long length and run near the crystal face in the direction perpendicular to the microfibril axis. 

Except for biopolymers, most polymer materials are polydisperse and heterogeneous. This is already the case for the length distribution of the chain molecules (molecular mass distribution). It is continued in the polydispersity of crystalline domains (crystal size distribution), and in the heterogeneity of structural entities made from such domains (lamellar stacks, microfibrils). Although this fact is known for long time, its implications on the interpretation and analysis of scattering data are, in general, not adequately considered. 

The microfibrillar cellulose. This forms the skeletal scaffolding of the cell wall. Microfibrils are about 4 nm in diameter (6) and are of indeterminate length. 

Since the total contour length of a xyloglucan molecule is 40 to 400 times greater than the diameter of a microfibril (8), it would seem inevitable that most of the newly deposited xyloglucan chains will have the opportunity to bind to the several microfibrils across which they are randomly laid down (Fig. 2b) (25). 

The finished cellulose is in the form of crystalline microfibrils (Fig. 20-29), each consisting of 36 separate cellulose chains lying side by side, all with the same (parallel) orientation of nonreducing and reducing ends. It seems likely that each particle in the rosette synthesizes six separate cellulose chains simultaneously and in parallel with the chains made by the other five particles, so that 36 polymers arrive together on the outer surface of the cell, already aligned and ready to crystallize as a microfibril of the cell wall. When the 36 polymers reach some critical length, their synthesis is terminated by an unknown mechanism crystallization into a microfibril follows. 

Figure 7-31 A model for the structure of keratin microfibrils of intermediate filaments. (A) A coiled-coil dimer, 45-nm in length. The helical segments of the rod domains are interrupted by three linker regions. The conformations of the head and tail domains are unknown but are thought to be flexible. (B) Probable organization of a protofilament, involving staggered antiparallel rows of dimers. From Jeffrey A. Cohlberg297...

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