4188670
Novel approach to quantitatively analyze lignin dispersion in rubber compounds
Date
March 24, 2025
There is a strong need to replace carbon black and silica with more sustainable reinforcing fillers, especially in tire industry. Lignin emerges as a viable alternative due to its wide availability, complex chemistry and sustainable origin. Kraft lignin particle size in dry form is smaller than 100 nm, yet it can aggregate into clusters exceeding 100 μm within the rubber matrix. For a filler to be classified as reinforcing, its particle size must range between 10-100 nm. Lignin has typically poor dispersion in rubber, which causes poor properties in tire applications. Generally, lignin dispersion is analyzed visually from small number of particles without systematic quantitative analysis. Therefore comprehensive understanding of the dispersion mechanisms of lignin, as well as the relations between lignin dispersion and the performance of a rubber compound, remains unclear.
In this study, a novel method to measure lignin dispersion in rubbers was developed. First, samples were prepared with cross section polisher, which uses argon gas as a polishing medium. The sample images were taken from this polished area with scanning electron microscopy (SEM) and the dispersion of lignin was analysed with Dragonfly image analysis software. The area and Feret diameter of each lignin particle was calculated, so the number of particles above certain size thresholds and the degree of dispersion could be calculated. The analysed area was 0.15 mm2, with particle counts ranging from between 10 000 to 22 000 enabling reliable quantitively analysis.
For the preparation of dispersion samples, kraft lignin was mixed with polybutadiene rubber. It was observed that the dispersion varied with different mixing temperatures, higher temperature leading to improved dispersion. This behavior contrasts with traditional fillers, likely due to the polymeric nature of lignin. The differences in dispersion were analyzed with the number of micrometer sized particles and dispersion degree of <1 µm particles. A clear dependence between dispersion quality and mechanical properties, including abrasion resistance, was observed.
In this study, a novel method to measure lignin dispersion in rubbers was developed. First, samples were prepared with cross section polisher, which uses argon gas as a polishing medium. The sample images were taken from this polished area with scanning electron microscopy (SEM) and the dispersion of lignin was analysed with Dragonfly image analysis software. The area and Feret diameter of each lignin particle was calculated, so the number of particles above certain size thresholds and the degree of dispersion could be calculated. The analysed area was 0.15 mm2, with particle counts ranging from between 10 000 to 22 000 enabling reliable quantitively analysis.
For the preparation of dispersion samples, kraft lignin was mixed with polybutadiene rubber. It was observed that the dispersion varied with different mixing temperatures, higher temperature leading to improved dispersion. This behavior contrasts with traditional fillers, likely due to the polymeric nature of lignin. The differences in dispersion were analyzed with the number of micrometer sized particles and dispersion degree of <1 µm particles. A clear dependence between dispersion quality and mechanical properties, including abrasion resistance, was observed.
