Degradable cigarette filters: evaluating TiO2 additives.
Cigarette filters are a common litter item which can create a negative visual impact and increase clean-up costs. In the outdoors, the persistence of cellulose acetate-based filters can be reduced by photo degradation with the addition of select TiO2 additives. Most cigarette filters are composed of cellulose acetate fibers with titanium dioxide (TiO2), which is added as a delustrant. TiO2 is commercially available in two crystalline forms: anatase and rutile. Anatase TiO2 crystals have long been known to be more photo active than rutile, but recent work has shown that mixed phases – anatase and rutile - are even more photo active. Although most TiO2 is manufactured with an inorganic coating to facilitate particle dispersion, such coatings will hinder the TiO2 photo activity and impact the rate of degradation. Since photo degradation takes place at the particle’s surface, it is advantageous to utilize small and high surface area particles. Therefore to obtain a high rate of photo degradation, it is important to utilize small uncoated TiO2 particles consisting of mixed phase crystals. Based on these findings, it was shown that filters containing mixed phase TiO2 particles can be significantly degraded (~50% weight reduction) within a few months of outdoors exposure.