## 3 Results and Discussion
### Mechanical Properties of Composites  
After matrix characterization, this section is presenting the mechanical properties of the prepared composites with the aforementioned matrices (Table 3) and plain woven carbon fabric (Table 2). Five samples per composite configuration were prepared according to Figure 2.  
There is a rather large spread on the results of the stress-strain curves of samples with same composition (Figure 9). This is in part due to the manual production method that limits reproducibility. It is also worth pointing out that some ductile behavior was observed on the failure curves of the composites, as is the aim of making composites. In the first almost linear part, the textile and matrix work together. In the second part, the composite becomes damaged, and delamination or fiber failure can occur. This can be seen, for instance, from the sudden drop in stress. Hence, the prepared composites could be used for engineering applications where some ductility is required, including thin elements and lightweight panels. Figure 8: (**a**) Compressive strength, (**b**) flexural strength and (**c**) elastic modulus of matrices 100K, 80K20 MK, 80K20 MKm and 80K20 MKp after curing for 1 day at 80 \({}^{\circ}\)C and 3 days post-curing at room temperature to compare the effect of 2-methyl 2,4 pentanediol (“m”) and polyethylene glycol (“p”) on these mechanical properties. Both surfactants increased the compressive strength, but the effect is most pronounced on the flexural strength that increases with a factor of about 4. The volume fraction of fibers of the composites ranged between 25 to 40 vol% (Figure 10). This wide range is caused by the manual production and the differences in workability of the matrix. Due to the nature of the matrix, it was difficult to achieve composites with more than 40% fiber volume fraction. Considering the fact that flexural strength mainly depends on the fiber properties, because the matrix will crack long before the fibers, the higher the fiber volume fraction, the higher the flexural strength. It is somewhat unfortunate that the addition of MK renders the production of high volume fraction composites more difficult. As a result, these composites have the lowest fiber volume fractions of the series. The fiber volume fraction for the series 80K20 MK increased only a bit with surfactants, but remained between 25-30 vol%. Depending on the matrix composition, the flexural strength varied from about 19 to 83 MPa, while the Elastic modulus varied between 13 and 20 GPa (Figure 10). Both the addition of 2-methyl-2,4 pentanediol (Km) and polyethylene glycol (Kp) to Kor  
Figure 10: Fiber volume fraction, flexural strength (**a**) and elastic modulus (**b**) of the respective composites. Names indicate the matrices, as used in Table 3. For each composition, the average of five measurements is given. Figure 9: Sample of failure curves of composites made of four layers of carbon fiber 200 g/m\({}^{2}\) and five layers of matrix 80K20 MK. Measurement on four different samples with the same composition are shown. no or little effect on the flexural strength, and even showed a decrease in the elastic modulus with respect to K (Figure 10). This is in contrast to the increase in the flexural strength and elastic modulus with the surfactant observed in the pure matrices (Figure 8b). The fact that the surfactants do not increase the strength in composites as they do for the pure matrix shows that carbon fiber reinforcement is dominant on the flexural strength and that the difference in matrix properties resulting from surfactant addition did not prevail. The addition of 10 wt.% of metakaolinite (90K10 MK) shows an increase to 40 MPa in flexural strength, but no increase in elastic modulus (5 GPa) with respect to K. Higher performance was observed for samples with 20 wt.% metakaolinite (80K20 MK) in the matrix, up to 88 MPa in flexural strength and 20 GPa in elastic modulus.