# Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications
## 3 Results
### Glass Degradation and Storage
#### 3.3.3 Examination of the Fibres with SEM  
In order to be able to determine the reactions at the fibre surface during dissolution more precisely, SEM examinations were carried out. Due to the large sample size and time required, the fibres of all glasses stored in water and SBF were only prepared and observed at the first three sampling times. The surface and the cross-section of the fibres were examined. Figure 9 shows the unreacted fibres. All fibres feature light and dark areas and bumps on the fibre surface, which indicates segregation and the formation of crystals during the drawing process. The dissolution of the fibres of glass 18-06 in deionised water and SBF is shown comparatively in Table 8.  
In the case of the fibres stored in water, it can be seen that after 7 days the surface of the fibre was slightly roughened. After longer storage, no unevenness could be detected on the surface. This is due to the formation of an outer corrosion layer, which has been dissolved as the storage time progressed. The fibres stored in SBF showed a rough surface with irregular dissolution after a storage period of 7 days. Even after 14 days, an uneven dissolution of the fibre could be observed. This is due to segregation across the fibre cross-section, which occurred during the drawing process. Furthermore, the roughness  
Figure 8: Ion concentration in deionised H2O in relation to time for glass 13-93. Figure 9: SEM images of the unreacted fibres (scale bars 2 μm). of the fibre surface increased with increasing storage time and the diameter of the fibres decreased. Which surface reactions have taken place and which layer might have been deposited on the surface must be clarified in further investigations. After storing the fibres in deionised water for one hour, an incomplete layer could be seen on the surface of the fibres. After two hours of storage, a roughened fibre surface was formed. This indicates the dissolution of the layer, which can already be observed after one hour. During further storage, the rough surface layer reacted with the surrounding medium and a smooth fibre surface was formed. The fibres stored in SBF already exhibited a very roughened surface after only one hour, which further reacted with increasing storage time to form a skeletal surface. The more strongly roughened areas of the fibres correspond to the dark areas that can be seen in the original fibres (cf. Figure 9a). These areas have a different composition due to the segregation and dissolve more easily (see SEM image after 2 h in SBF in Table 9). The diameter of the fibre decreased during storage in both media. The images of the glass fibres with composition 13-93 with increasing storage time and dissolution are shown in Table 10.  
In the case of fibres stored in deionised water, a slightly roughened surface layer formed after 1 h of storage, which dissolved again with increasing storage time. The fibre \begin{table}
\begin{tabular}{c c c} \hline
**Time** & **7 Days** & **14 Days** & **28 Days** \\ \hline \end{tabular}
\end{table} 
Table 8: SEM images of the dissolution of the fibres of the glass 18-06 (scale bars 2 \(\upmu\)m). \begin{table}
\begin{tabular}{c c c} \hline
**Time** & **1 h** & **2 h** & **4 h** \\ \hline \end{tabular}
\end{table} 
Table 9: SEM images of the dissolution of the fibres of the glass 1-06 (scale: 2 \(\upmu\)m). diameter considerably dropped after four hours. The fibres stored in SBF showed an incompletely reacted rough surface after one hour, which continued to react as storage progressed. After two hours, larger bumps were visible on the fibre. These are probably crystals. The diameters of the fibres decreased sharply, especially after 4 h of storage. At this time, a very strong reaction of the fibres with the surrounding medium could be observed, forming a very rough and uneven layer. The cause of this irregular reaction is the segregation of the fibres during production. Furthermore, the cross-sectional areas of the fibres were also examined.