Test Jun. 2014 | Page 11

J Polym Environ Fig. 11 a Photo micrograph of CA film with TiO2 pigments irradiated in a weatherometer with near UV light. b Scanning Electron Microscopy (SEM) of acetate fibers from cigarette filters after few months outdoor exposure ultrafine titanium dioxide in fibers and demonstrated the enhanced degradation in the accelerated test and under outdoor exposure conditions. In the humid and sunny climate of South Florida a weight loss of 65% for acetate cigarette filters (without wrapping paper) could be achieved within 6 months exposure using 0.7% ultrafine titanium dioxide in the fibers, compared to 17% for the standard material [70, 71]. Itoh et al. have also evaluated the use of TiO2 to enhance CA degradation with a DS\2.15 adding TiO2 with particle sizes 0.01 to 1 lm which will provide more degradable material [72]. In US Patent 5,804,296, Itoh et al. disclose the benefits of CA fibers with high surface area TiO2 additives, (C50 m2/g) that provide enhanced photo degradation rates [73]. Mechanism Synergy and Disintegration In the outdoors environment, the degradation of CA materials can include multiple mechanisms. Deacetylation seems to be the first step in both, photochemical and biological degradation [69]. In cases where the DS is too high for esterases, the first step of biodegradation can be initiated by UV light irradiation or by chemical hydrolysis, with the latter being subject to pH change. Also in already partly hydrolyzed CA, like commercial acetate with a DS of 2.5, the critical deacetylation step can be accelerated by non-biological mechanisms under the influence of sunlight, temperature and water. With decreasing DS there is a better chance for biological systems to attack CA, especially if the DS reaches a region of about 1.5 to 1.8. Acetyl esterases, designed by nature for acetylxylan and chitin biodegradation, are the first enzymes which remove the acetyl substituents until a DS *1 is reached. When the DS approaches a region B0.9, CA becomes water-soluble and the polymer readily disperses [2]. In addition, at this point CA becomes available to endoglucanases, shortening the CA chain in a random fashion preferably at those regions where acetyl substituents do not hinder the contact to the substrate. A synergistic process between acetylesterases and endoglucanases starts with the result of a quick liberation of free sugars and acetic acid. Since deacetylation is the rate determining step in biodegradation of CA, followed by the comparatively faster enzymatic hydrolysis of the cellulose backbone, the overall DS of the remaining material will stay nearly unchanged during degradation. But the specific surface area of the material increases with ongoing degradation, due to pitting caused by different rates of degradation at different spots depending on local conditions at micro scale. This increase