PHB fiber

Table 2 Young s modulus, Et, tensile stress at break, h> and elongation at break, h, of PHB fiber samples [104]...

PLA fibers show a considerably higher level of strength at a lower elongation at break than PHB fibers. Differences in the crystallization and orientation behavior during the structure formation are seen as the cause. 

PHB Characteristic for PHB fibers within the context of knowledge about structure formation are considerable deviations of changes within the textile physical values of PHB filaments which had been spin drawn using different draw ratios. Figure 5 shows the stress-strain curves of the spin-drawn fibers at different draw ratios in the range of 4.0-7.0. 

Figure 7a and b show typical three-dimensional surface topographic images of the PHB fibers drawn at a draw ratio of 4.0 and 7. The surfaces of the fibers differ considerably. Depending on the draw ratio, spherulitic or fibril-like surface structures were formed. The textile physical properties of the fibers can be explained by these different structures. The fibers, spun at a draw ratio of 4.0, are brittle without a sufficient elongation at break visible in the stress-strain curve (Fig. 5). The fibers spun at a draw ratio of 7 show a completely different stress-strain behavior with a sufficient elongation at break and a sufficient tenacity, as can be seen from the stress-strain curve (Fig. 5).

Table 3 Textile physical properties of conditioned PLA und PHB fibers...

For PHB fibers certain variations concerning the E-modulus can be seen, which may be connected with a slight recrystallization within the noncrystalline areas, whereas the tenacity and the elongation at break are not changed in the context of limit of error. 

PHB fibers with high tensile strength were prepared by stretching the fibers after isothermal crystallization near the glass-transition temperature (Tanaka et al. 2007). 

Ma et al. studied the effea of organic-soluble chitosan/PHB fibers for skin regeneration that was prepared by electrospinning.The cytotoxic study was evaluated with mouse fibroblast cells (L929) and the cell culture results revealed that it benefits promoting the cell attachment and proliferation and can be used as tissue engineering for skin regeneration. 

PHB fibers are characterized by strongly pronounced molecular anisotropy. 

SCI in adult rats (Novikov et al. 2002). PHB fibers demonstrated improved neuronal survival in comparison with the implantation of only alginate hydrogel or fibronectin. Novikova et al. demonstrated PHB scaffold seeded with Schwann cells significantly promote spinal cord repair (Novikova et al. 2008). Silk (Uebersax et al. 2007), chitosan (Nomura et al. 2008 Li et al. 2009), self-assembling peptide nanofibers (Guo et al. 2009), and hyaluronic acid (Wang and Spector 2009) are more examples of natural materials that have been examined in spinal cord research. 

The results of powder diffraction analysis of PHB powder (a) and PHB fibers obtained from 7% solution with modifying additives (b) and the nanosized Ti02 modifications (c, d) are presented in Fig. 4. 

The morphology of main PHB crystallites in powder and fibers is kept unchanged. However, the fibers show the low-melting shoulder (small and imperfect crystals). The Ti02 obstructs crystallization. PHB fibers are characterized by strongly pronounced molecular anisotropy. 

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