Effect of culm age on the structure and service performance of bamboo toothbrushes as sustainable substitutes for plastic

The development of renewable alternatives for petroleum-based plastics has become increasingly critical, particularly for short-lifespan consumer products such as toothbrushes. Bamboo has emerged as a promising candidate for sustainable toothbrush due to its biodegradability, wide availability, and low processing demand, however, the influence of culm age on its functional performance in toothbrush applications remains unclear. Here, toothbrush handles were fabricated from bamboo culms harvested at 2- and 4 years of age to investigate age-dependent differences in mechanical performance, water resistance, and their underlying structural origins. The results showed that 4-year-old bamboo possessed a higher fiber volume fraction, thicker fibers diameter, and a higher degree of lignification than 2-year-old bamboo. These structural advantages, together with age-related changes in chemical composition, resulted in significantly improved bristle pull-out force and water resistance. It is worth noting that the bristle pull-out force of toothbrushes made from 4-year-old bamboo reached 19.36 N, which is comparable to that of commercially available plastic toothbrushes (18.8 N). After six dry–wet cycles, the pull-out force remained at 18 N. In addition, after 24 h of water immersion, the wet pull-out force was still higher than 16 N, indicating good water resistance and potential reusability. Finite element simulation and fracture morphology analysis consistently revealed that the improved durability of older bamboo was primarily associated with its greater fiber volume fraction and enhanced load-transfer capability in the bristle region. These findings provide useful guidance for the selection of bamboo materials for toothbrush applications and support the development of bamboo-based alternatives to disposable plastic products.