Carbon nanotubes (CNTs) are currently blended into polymer matrices to improve thermal, mechanical, and electrical properties for use in commercial products. These polymer nanocomposites can then enter the environment post-consumer use and potentially degrade and release CNTs following exposure to microorganisms. Thus, the effect of embedded CNTs on polymer biodegradation rates was investigated. To facilitate the acquisition of experimental data on a reasonable timescale the biodegradable polymer, poly-?-caprolactone (PCL) and the model microorganism, Pseudomonas aeruginosa were used since this particular combination led to extensive biodegradation of PCL ( > 60%) over a time period of 15-30 weeks. Nanocomposites containing commercially relevant carbon nanotube loadings of < 0.1 - 5% w/w in PCL were prepared using both solution blending and melt-mixing methods. To initiate biodegradation, PCL and CNT-PCL nanocomposites were inoculated with Pseudomonas aeruginosa in defined media shaken at 125 rpm and 30�C. Mass loss due to biodegradation was assessed every two weeks by removal of the nanocomposites from inoculum, gentle removal of bulk biofilms, desiccation, and weighing followed by sterilization and re-inoculation. For nanocomposites containing CNT loadings below 1% w/w, biodegradation occurred, but at slower rates than for pure PCL. However, at 2% w/w, biodegradation of the nanocomposites was essentially shut down  , even though 98% w/w of the nanocomposite contained biodegradable PCL. This result has important implications for the long term persistence and fate of CNT-containing polymer nanocomposites. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to compare nanocomposite properties before and after exposure to P. aeruginosa while LIVE/DEAD staining coupled to confocal laser scanning microscopy (CLSM) was used to assess biofilm formation on nanocomposite surfaces. The ability of these analytical techniques to identify the underlying mechanism responsible for the effect of CNT loading on biodegradation rates will also be discussed.

Influence of carbon nanotube loading on the biodegradation of polymer nanocomposites

248th National Meeting (2014)

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