# Impact of Retention Agents on Functional Properties of Recycled Paper in Sustainable Manufacturing
## 3 Results and Discussion
At 0.2%, the strain at break dropped sharply to 1.42% but improved to 2.13% at 1.0%. Similarly, the energy absorption index decreased to 0.262 J/g at 0.2% but recovered to 0.466 J/g at 1.0%. The results indicate a non-linear relationship between retention agent dosage and tensile properties, with an optimal range where the balance between fiber retention and bonding strength is achieved. Both wastepaper types exhibited a notable decline in tensile properties at lower concentrations of the retention agent (0.2-0.6%), with an average reduction in breaking length of 36% for 1.3 and 31% for 3.2. This reduction can be attributed to the over-dosage of the cationic polyelectrolyte, which may lead to flocculation and uneven fiber distribution, weakening the paper's structure, which aligns with the findings from other studies, underscoring the importance of optimizing retention agent levels to achieve desired mechanical performance without compromising structural uniformity. Interestingly, at higher concentrations (0.8-1.0%), the tensile properties showed recovery. This suggests that the retention aid's ability to enhance fiber bonding overcomes its adverse effects at higher dosages, although the recovered values did not surpass the reference. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Retention Agent Addition** & **I\({}_{\text{B}}\)** & **F\({}_{\text{B}}\)** & \(\sigma_{\text{T}}\)\({}^{\text{b}}\) & \(\sigma_{\text{T}}\)\({}^{\text{W}}\) & \(\epsilon_{\text{T}}\) & \(W_{\text{T}}\)\({}^{\text{b}}\) & \(W_{\text{T}}\)\({}^{\text{W}}\) & \(\text{E}\)\({}^{\text{b}}\) & \(E\)\({}^{\text{w}}\) & \(E\)\({}^{\text{a}}\) \\ \hline
**[\%]** & **[m]** & **[N]** & **[N/m]** & **[Nm/g]** & **[\%]** & **[J/m\({}^{\text{m}}\)]** & **[J/g]** & **[N/m]** & **[Nm/g]** & **[MPa]** \\ \hline Ref. & 3750 & 42.6 & 2932 & 36.2 & 2.53 & 54.2 & 0.669 & 408,133 & 5040 & 3662 \\
0.1 & 3200 & 36.6 & 2524 & 31.2 & 2.37 & 46.0 & 0.568 & 383,817 & 4740 & 3444 \\
0.2 & 2600 & 29.3 & 2018 & 24.9 & 1.42 & 21.2 & 0.262 & 376,967 & 4655 & 3382 \\
0.3 & 2450 & 27.6 & 1899 & 23.4 & 1.35 & 17.9 & 0.221 & 373,000 & 4606 & 3346 \\
0.4 & 2450 & 27.7 & 1907 & 23.5 & 1.23 & 18.3 & 0.226 & 372,867 & 4604 & 3345 \\
0.5 & 2450 & 27.8 & 1912 & 23.6 & 1.33 & 16.4 & 0.203 & 365,733 & 4516 & 3281 \\
0.6 & 2600 & 29.4 & 2022 & 25.0 & 1.67 & 27.2 & 0.336 & 356,433 & 4401 & 3198 \\
0.8 & 2600 & 29.7 & 2048 & 25.3 & 1.97 & 30.0 & 0.371 & 354,900 & 4383 & 3184 \\
1.0 & 3050 & 34.8 & 2395 & 29.6 & 2.13 & 37.7 & 0.466 & 347,217 & 4288 & 3115 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Tensile properties of paper from 3.2 white wastepaper. The higher strength values observed for the 3.2 wastepaper suggest greater fiber quality or heterogeneity compared to 1.3. This indicates that the effects of retention aids are influenced not only by their concentration but also by the intrinsic properties of the wastepaper. The study highlights the importance of optimizing retention aid dosage to balance its benefits and drawbacks. An excessive or insufficient addition can negatively impact tensile properties. While the 0.8-1.0% range provides a reasonable compromise for strength recovery, further refinements in dosage may be needed to maximize the performance for specific paper grades. The results underline the necessity of tailoring retention agent strategies to the type of wastepaper and desired paper properties, ensuring efficient and sustainable papermaking processes. It should also be noted that higher strength values were observed for the 3.2 wastepaper, indicating the heterogeneity of the raw material (Tables 2 and 3). The conclusions of the conducted study highlight the need for further innovation in the field of retention aids to improve paper properties without negatively impacting production processes. Future development directions include the creation of retention aids tailored to specific fiber types and wastepaper streams, which will help minimize adverse effects on the mechanical and surface properties of paper.