Cellulose fiber anisotropy

As discussed above, processing the fibers introduces an anisotropy in the sheet even if one uses only pure cellulosic... 

Kulshreshtha et al. [83], as well as Mitra and Mukherjee [118], postulate the existence of paracrystallinity in ramie, jute, and hemp. The latter claim to have developed refinements to the techniques of measurement of parameters of the three-phase model for cellulose I [117]. Subsequently, by measuring the structural parameters relative to [002], [101], and [101] reflections, they show that the degrees of crystallinity and paracrystallinity determined for each of the three reflections are different (anisotropy) for each of the three fibers (ramie, jute, and hemp) [122]. The results also confirm that the greater the paracrystalline distortion, the smaller the paracrystallite size. 

Table 15.4 clearly shows that anisotropic composite films present better mechanical properties. It is worth noting that anisotropic composites also have higher Young s modulus, yield stress and ultimate tensile strength than cross-linked isotropic homo-logues [13]. This, along with results presented in Table 15.4, seems to indicate that the mechanical properties of these all-cellulosic based composites depend on matrix anisotropy and fiber orientation rather than on cross-linking. 

This order parameter is a macroscopic measure of the anisotropy of the composites but it, nevertheless, reflects the microstrutural organization of the all-cellulosic based composites. The variation of Se with HPC content is similar to that observed for5(Fig. 15.3) and A (Fig. 15.4). Table 15.3 (and also Fig. 15.2c)shows that HPC matrix (0% w/w HPC of fibers) is clearly anisotropic and therefore the anisotropy in these composites arises from the synergy between the Uquid crystalline character of the matrix and the fiber orientation. 

In this section the mechanical properties (Young s modulus) and the strength of the fiber-matrix interface (quality of the interface) of isotropic all-cellulosic based composites will be analyzed using theoretical models existing in literature. For the anisotropic composites such an approach was not performed. The anisotropy in these composites arises mainly from the liquid crystalline character of the matrix. 

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