Biobased additives as biodegradability enhancers with application in TPU-based footwear components

Among the wide variety of materials employed in the manufacture of shoes, thermoplastic polyurethanes (TPUs) are one of the most widely used. Given its widespread use, and associated waste management problems, the development of more biodegradable and evironmentally compatible solutions is needed. In this work, a polyester-based TPU used in the footwear industry for outsoles production was modified by compounding with lignin, starch and cellulose at content of 4% (w/w). The biodegradability was evaluated by using agar plate tests with the fungi Aspergillus niger ATCC16404, the Gram-negative bacteria Pseudomonas aeruginosa ATCC9027 and an association of both (consortium), and soil tests at 37 °C and 58 °C. The obtained results evidenced a positive effect of the tested biobased additives, the most favourable results being registered with lignin. These results were corroborated by the structural modifications observed by FTIR analysis. Additionally, mechanical tests prove the suitability of using the lignin modified TPUs for footwear outsoles production.

Role of nitrogen doping on the performance of carbon nanotube catalysts: a catalytic wet peroxide oxidation application

Four magnetic carbon nanotube samples (CNTs: undoped, completely N-doped and two selectively N-doped) have been synthesized by chemical vapor deposition. The materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4 nitrophenol solutions (4-NP, 5 g L-1). Relatively mild operating conditions were considered (atmospheric pressure, T = 50 ºC, pH = 3), using a catalyst load of 2.5 g L-1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. N doping was identified to influence considerably the CWPO performance of the materials. In particular, undoped CNTs, with a moderate hydrophobicity, favor the controllable and efficient decomposition of H2O2 into highly reactive hydroxyl radicals (HO•), thus showing high catalytic activity for 4-NP degradation. On the other hand, the completely N-doped catalyst, fully hydrophilic, favors a quick decomposition of H2O2 into non-reactive O2 and H2O species. The selectively N-doped amphiphilic catalysts, i.e. hybrid structures containing undoped sections followed by N-doped ones, provided intermediate results, namely: a higher N content favored H2O2 decomposition towards non-reactive H2O and O2 species, whilst a lower N content resulted in the formation of HO•, increasing 4-NP mineralization. Catalyst stability and reusability were also investigated by consecutive CWPO runs.