Environmentally benign fast-degrading conductive composites

Abstract

An environmentally benign conductive composite that rapidly degrades in the presence of warm water via enzyme-mediated hydrolysis is described. This represents the first time that hydrolytic enzymes have been immobilized onto eco-friendly conductive carbon sources with the express purpose of degrading the encapsulating biodegradable plastic. Amano Lipase (AL)-functionalized carbon nanofibers (CNF) were compounded with polycaprolactone (PCL) to produce the composite film CNFAL-PCL (thickness ∼ 600 μm; CNFAL = 20.0 wt %). To serve as controls, films of the same thickness were also produced, including CNF-AL5-PCL (CNF mixed with AL and PCL; CNF = 19.2 wt % and AL = 5.00 wt %), CNF-PCL (CNF = 19.2 wt %), ALx-PCL (AL = x = 1.00 or 5.00 wt %), and PCL. The electrical performance of the CNF-containing composites was measured, and conductivities of 14.0 ± 2, 22.0 ± 5, and 31.0 ± 6 S/m were observed for CNFAL-PCL, CNF-AL5-PCL, and CNF-PCL, respectively. CNFAL-PCL and control films were degraded in phosphate buffer (2.00 mg/mL film/buffer) at 50 °C, and their average percent weight loss (Wtavg%) was recorded over time. After 3 h CNFAL-PCL degraded to a Wtavg% of 90.0% and had completely degraded after 8 h. This was considerably faster than CNF-AL5-PCL, which achieved a total Wtavg% of 34.0% after 16 days, and CNF-PCL, which was with a Wtavg% of 7.00% after 16 days. Scanning electron microscopy experiments (SEM) found that CNFAL-PCL has more open pores on its surface and that it fractures faster during degradation experiments which exposes the interior enzyme to water. An electrode made from CNFAL-PCL was fabricated and attached to an AL5-PCL support to form a fast-degrading thermal sensor. The resistance was measured over five cycles where the temperature was varied between 15.0–50.0 °C. The sensor was then degraded fully in buffer at 50 °C over a 48 h period.