# Anti-Frothing Effect of Poultry Features in Bio-Based, Polycondensation-Type Thermoset Composites
## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multirow{2}{*}{**System a**} & \multicolumn{2}{c}{**Mass Loss at**} & \multirow{2}{*}{\(n\) b**} & \multirow{2}{*}{\(n_{\text{thoe}}\) c**} & \multirow{2}{*}{\(k/\text{s}^{-1}\)} \\  & & **Equilibrium**/\% & & & & \\ \hline
1 & Cp1-1 & 12 & 1.8 & 2 & \(1.2\times 10^{-4}\) \\
2 & Cp2-3 & 17 & 2.9 & 3 & \(2.4\times 10^{-4}\) \\
3 & Cg1-1 & 11 & 1.7 & 3 & \(1.2\times 10^{-4}\) \\
4 & Cg1-1F d & 17 e & 2.1 & 3 & \(1.6\times 10^{-4}\) \\
5 & Gp1-1 & \(-\) f & \(-\) f & 2 & \(-\) f \\
6 & Gg1-1 & 20 & 2.5 & 2 & \(7.5\times 10^{-5}\) \\
7 & Gg1-1F d & 25 e & 3.1 & 2 & \(-\) g \\
8 & Gg3-2 & 17 & 2.7 & 3 & \(7.2\times 10^{-5}\) \\ \hline \hline \end{tabular}  
* Abbreviations according to Figure 1; b number of water molecules calculated according to Equation (1); c theoretical amount of water molecules based on the stoichiometry; d mixture containing 20 wt% of feather shreds; e value calculated with regard to the feather content; f value not calculated due to the joint evaporation of water and diol; f value not calculated due to decomposition.  
\end{table} 
Table 1: Results of the kinetic evaluation using pseudo first order kinetics. transparent, the addition of feathers caused the mixtures to turn reddish-brown (Figure S5 in the Supplementary Material). This apparent decomposition was also manifested in the rather large mass loss at equilibrium of 25%, which can be calculated as a total of three water molecules being liberated per molecule glutaratic acid, while in theory it should only be two. Although citric acid is approximately one order of magnitude more acidic than glutaratic acid, a similar decomposition was not observed in the Cg1-1F system and this could be due to the esterification occurring faster. From the above mixtures, those based on citric acid appear more suitable for the preparation of engineering materials, particularly the Cg1-1 combination. However, the combination of citric acid and glycerol is known to froth massively, which prevents the formation of compact workpieces [12]. A plausible reason is that due to the rapid increase in viscosity already at low conversions, most of the water formed in the condensation reaction is trapped inside the viscous mixture in the form of bubbles. Based on the positive effects on the kinetics observed in the Cg1-1F system, the incorporation of shredded feathers was thought to enable the preparation of compact test specimens from citric acid and glycerol for the first time. Indeed, increasing the amount of feathers incorporated into Cg1-1 mixtures clearly reduced frothing and the number of visible bubbles, such that with 20 wt% of feathers, compact and macroscopically defect-free samples could be obtained (Figure 9). The incorporation of higher amounts of feathers appears possible and could potentially give rise to materials with improved properties, but requires more sophisticated mixing techniques. The Cg1-1F samples were obtained as solid and hard, but also rather brittle objects, which made testing in the set-up shown in Figure 3 somewhat difficult. It should be noted that all Cg1-1F samples failed close to the receiving rollers (cf. Figure S6 in the Supplementary Material), most likely because they did not fit precisely to the curvature of the specimen. This indicates that the properties shown in Table 2 and Figures S7-S10 do not represent the best performance of the tested materials. For comparison, the Gg1-1F and the Gg1-1 mixtures were also cured in dog-bone shaped moulds and tested. Due to the lower degree of cross-linking, both specimens were rubbery. Figure 9: The Cg1-1 series containing an increasing amount of shredded feathers cured in dog-bone shaped moulds. From left to right: 0 (Cg1-1), 5, 10, 15, and 20 wt-% (Cg1-1F). The thermal stability of the composites was investigated by TGA measurements under both nitrogen and oxygen atmosphere (Figure 10). The former represents rather a pyrolysis, the latter a combustion.