of measured area, allowing for analysis via scanning electron microscopy. Then an analysis software is used to measure the diameter and area of each lignin particle. Typically, the meas- ured area includes 10000–15000 particles, ensuring reliable quantitative analysis of dispersion. Optimizing the mixing parameters to Improve the lignin dispersion High shear forces are typically used to break down carbon black and silica agglomerates to achieve an adequate particle size during compounding. Optimal particle size is gained when mixing temperature, rotor speed and fill factor of the mixing machine are set to their optimal values. For instance, if the mixing temperature is too high, the viscosity decreases, leading to poor dispersion. In our study, we investigated the optimal mixing conditions for lignin. The results indicated that shear forces are not as critical for lignin as they are for other materials. Instead, higher mixing temperatures significantly improve lignin dispersion. When test compounds were mixed at temperatures between 120 °C and 200 °C, dispersion improved significantly, especially at temperatures above 160 °C, as shown in Fig. 1. However, while mixing temperature above 160 °C enhance lignin dispersion in rubber, it can also lead to the degradation of the polymer matrix. This degradation can negatively impact the mechanical properties of the final rubber product. Dispersion analysis revealed that higher mixing temperatures reduce the number of particles larger than 5 µm. There is a strong correlation between mechanical properties (such as tensile strength and abrasion resistance) and the number of large particles; as the number of large particles decreases, these properties improve. Other mixing parameters, such as mixing time, rotor speed, and fill factor, showed no noticeable effect on dispersion. Optimizing the mixing parameters can further enhance the thermal and mechanical properties of lignin-filled rubbers. Lignin as a filler in rubber composites can reduce heat buildup during loading, largely due to its thermal stability and antiox- idant properties. Moreover, well-dispersed lignin can form a network within the rubber matrix, potentially reducing friction between polymer chains and thus decreasing energy dissipa- tion and heat generation during cyclic loading. However, high concentrations of lignin could potentially lead to increased in- ternal friction, resulting in more heat generation under certain conditions. In summary, the increasing global demand for rubber materi- als necessitates the development of sustainable reinforcing fill- ers. Lignin indicates great promise as an alternative to tradition- al fillers like carbon black and silica. However, the effective use of lignin has been limited by challenges in achieving uniform lignin particles dispersion. While chemical modifications and high mixing temperatures can improve dispersion, precise con- trol is needed to avoid degrading the polymer matrix. Overall, optimizing mixing conditions is essential for enhancing the per- formance of lignin as a sustainable filler in rubber products.
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