Preparation of uniform lignosulfonate-based colloidal spheres for UV-absorbing thermoplastics

Lignosulfonate-based colloidal spheres were prepared from sodium lignosulfonate and cetyltrimethylammonium bromide (NaLS/CTAB) complex through electrostatic and hydrophobic self-assembly. Due to the stronger hydrophobicity and UV-blocking performance, NaLS/CTAB colloids were easier to be blended with HDPE than lignosulfonate, and therefore applied to UV-absorbing thermoplastics. Results showed NaLS/CTAB colloidal spheres had a particle size of 160 nm with a polydispersity index of 0.081. NaLS/CTAB molecules started to form spheres at critical water content of 64 vol% when the initial concentration of NaLS/CTAB in EtOH was 0.5 mg/cm³ and the obtaining of colloids was completed at a water content of 90 vol%. The size and polydispersity of spheres were well controlled by adjusting initial concentrations of NaLS/CTAB in EtOH. Since NaLS/CTAB colloidal spheres retained phenylpropane units and phenolic hydroxyl groups of NaLS, NaLS/CTAB/HDPE composites displayed excellent UV-absorbing properties. Meanwhile, the mechanical property of NaLS/CTAB/HDPE composites was also superior to that of frequently-used CaCO₃/HDPE materials in industry, reaching the requirement of industrial uses. However, too high additions would result in the increased agglomeration of NaLS/CTAB spheres in HDPE, and thus the deteriorated mechanical property. Additionally, the added spheres played a role of "ball", which caused the decreased viscosity, improved flowability and processability of composites.