# Impact of Retention Agents on Functional Properties of Recycled Paper in Sustainable Manufacturing
## 3 Results and Discussion
This approach underscores the importance of a holistic understanding of material interactions in recycled paper production. Another tested parameter, i.e., roughness, is closely related to porosity. The tests performed indicate that the roughness of reference papers (406 \(\upmu\)m for 1.3 wastepaper and 553 \(\upmu\)m for 3.2 wastepaper) is significantly lower compared to the samples with the highest addition of retention agent, where the maximum roughness reached 1281 \(\upmu\)m and 1084 \(\upmu\)m for pulps 1.3 and 3.2, respectively. This significant increase highlights the impact of retention agent dosage on paper structure. The data (Figure 1) show a general trend: increasing the addition of the retention agent typically leads to higher roughness, although certain deviations are observed. For 1.3 wastepaper, roughness increases steadily from 525 \(\upmu\)m at a 0.1% addition to a peak of 1281 \(\upmu\)m at 0.5% before declining slightly at higher dosages. Conversely, for 3.2 wastepaper, roughness increases more linearly, reaching its maximum at 1.0% retention agent addition (1084 \(\upmu\)m). This behavior may be attributed to the interaction between the retention agent and fiber structure. According to research, rougher paper surfaces can result from uneven distribution of fines and fillers caused by excessive retention agent usage. Initially, the retention agent facilitates the formation of a more porous network by promoting better flocculation, which increases roughness. However, beyond a certain dosage, excessive  
Figure 1: Roughness of tested wastepaper as a function of retention agent addition. flocculation could lead to denser fiber packing, explaining the slight reduction in roughness observed for pulp 1.3 at higher dosages. These variations in roughness can influence the final application of the paper. For example, rougher papers, with higher porosity, are advantageous for tissue applications, where air and moisture permeability are desirable. In printing applications, however, such an increase in roughness may pose challenges due to greater ink absorption, potentially compromising print quality. Thus, paper manufacturers must carefully balance retention agent addition to achieve optimal roughness for specific end uses. The differences in roughness trends between wastewater 1.3 and 3.2 also suggest a potential influence of pulp composition and processing history. Pulp 3.2 consistently exhibits higher roughness values across all retention agent levels, possibly due to differences in fiber morphology or the presence of specific contaminants. These findings underscore the importance of tailoring retention aid dosages to the unique characteristics of the recycled paper furnish. In summary, roughness increases with the addition of retention agents, with distinct differences observed between the two pulp types studied. The results provide valuable insights for optimizing retention agent use in recycled paper production to achieve desired properties while addressing the specific requirements of various paper grades. The tensile properties of wastewater sheets are critical for determining their suitability in manufacturing and processing [40; 41]. Retention aids can enhance fiber retention and inter-fiber bonding, leading to improved tensile strength. However, the effects of these additives are not uniform and depend significantly on their type and concentration, the characteristics of fibers, and other papermaking components. Papermakers carefully select and optimize retention aids to achieve the desired strength properties for different paper types and applications. The tensile properties of the recycled paper sheets are primarily affected by the retention agent's ability to promote fiber bonding through charge neutralization and flocculation. By reducing the negative charge of the fibers, the retention agent enhances inter-fiber attraction, leading to stronger bonds between fibers.