From crystalline fibers, numerical

The transition from crystalline to melt state, which is normal for crystalline polymers, is not observed with cellulose under normal conditions. It appears that the secondary bonds giving rise to the crystalline state are too strong and too numerous to be broken by a rise in temperature. Thermal degradation (beginning at ca. 180 °C) precedes melting under atmospheric pressure conditions. Nevertheless, a plastic deformation interpreted as melting has recently been reported for cellulose fibers exposed to laser radiation in a highly confined (pressurized) space [43]. The fracture surface of a thermoplastically deformed cellulose disc is shown in e Fig. 10. 

There are now numerous compositions of liquid crystalline polymers under consideration as fiber spinning and injection molding materials. However, the problems involved in processing these systems are similar. In particular, how can one process these polymers to yield desirable isotropic properties or at least have biaxial orientation how can one achieve the optimum properties from a given composition and how does the chemical composition and structure affect the properties In flexible chain systems one must quench in orientation in a time scale which is faster than the relaxation process of the molecules. Typically there is a distribution of relaxation times in which the longest relaxation time is a matter of a few seconds. This longest relaxation time also governs a number of other flow characteristics. 

The requirement of crystallinity can be met by other forms, e.g., the extended /3-configuration. Further, it is not necessary that the fiber be completely crystalline in order that this model be applicable. All that is required is partial crystallinity and preferential orientation of crystallites along the fiber axis. This requirement is met by numerous fibrous proteins and also by synthetic fibers made from globular proteins. 

Cellulose is the most abundant biopolymer on earth. It can be used in different applications, namely in the form of fibers, and cellulose can be converted into numerous cellulose derivatives. Cellulose micro- and nanofibers have been the subject of intense research in the field of composites. Cellulose derivatives can show liquid crystalline chiral nematic phases, which can be used for the production of diverse composite systems. All-cellulosic composites based on liquid crystalline cellulosic matrices reinforced by cellulose micro- and nanofibers can show enhanced mechanical properties due to fiber orientation induced by the liquid crystalline matrix. Cellulose-based fibers electrospun from liquid crystalline phases can develop different structures, which are able to mimic the shape of plant tendrils on the nano- and microscale, opening new horizons for ceDulosic membrane applications. 

Microbial cellulose derived from Acetobacter xylinum by fermentation process has been established to be a remarkably versatile biomaterial and can be used in wide variety of applied scientific endeavours, especially for medical devices. Due to its ultra-fine network architecture, high degree of crystallinity, hydrophilicity and moldability, microbial cellulose is a natural candidate for numerous medical and tissue-engineered apphcations. The use of direct nanomechanical measurement determined that these fibers are very strong, and when used in combination with other biocompatible materials, produce nanocomposites particularly suitable for use in human and veterinary... 

Lung or pleural lesions may result from numerous types of inorganic particles, including asbestos, erionite and refractory ceramic fibers, non-fibrous silicates (crystalline silica, talc mica, kaolinite, feld-... 

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