Polycaprolactone Adsorption and Nucleation onto Graphite Nanoplates for Highly Flexible, Thermally Conductive, and Thermomechanically Stiff Nanopapers

Poly(ε-caprolactone-co-ε-decalactone)/carbon black or carbon nanofiber composites. Synthesis, morphological, and thermal/electrical properties

Much of the research on biodegradable polymers is currently aimed at developing alternative materials to fossil fuel plastics. Among the biodegradable polymers, the bio-based aliphatic polyesters (e.g. poly-ε-caprolactone, PCL) have had important success in replacing single-use plastics as well as durable consumer goods, mainly in the packaging and biomedical sectors. In other sectors, like electronics, the use of bio-based plastics has received little attention, despite e-waste (pollutant and difficult to handle) being the fastest growing solid waste stream in the world. In this work, P(CL-DL)/carbon black and P(CL-DL)/carbon nanofiber composites with enhanced thermal and electrical properties were prepared and studied. P(CL-DL) copolymers were synthesized via ring opening polymerization (ROP) at CL/DL molar compositions of 95/5, 90/10, 80/20, and 70/30. Their number-average molecular weight (M̄ n) and dispersity index (Đ) lie between 17.5 and 21.8 kDa, and 1.72 and 1.99, respectively. They are thermally stable to up to 300 °C, and show a melting temperature (T m) and a crystalline degree (X c) that decrease with increasing contents of DL in the polymer chains. The thermal (k) and electrical (σ) conductivities of copolymers were enhanced by adding, through melt blending, carbon black (CB) or carbon nanofibers (CNF) at 1.25, 2.5, and 5.0 wt%, reaching a maximum value of 0.55 W m-1 K-1 and 10-7 S cm-1, respectively. The frequency-dependence of the dielectric constant (ε') and dielectric losses (tan δ) was also measured. Two of the composites showed a marked increase of ε' near percolation whereas their tan δ remained low. The thermal and electrical conductivity performances, as well as the increment found in ε' near percolation, are discussed in terms morphology changes produced by variations in both the DL mol% and the nanoparticles wt%. Finally, biodegradable composites with heat and electron dissipative capacities are materials that can contribute to alleviating the problem of e-waste.

Detection of methyltransferase activity and inhibitor screening based on rGO-mediated silver enhancement signal amplification strategy

DNA methylation refers to the chemical modification process of obtaining a methyl group by the covalent bonding of a specific base in DNA sequence with S-adenosyl methionine (SAM) as a methyl donor under the catalysis of methyltransferase (MTase), which is related to the occurrence of multiple diseases. Therefore, the detection of MTase activity is of great significance for disease diagnosis and drug screening. Because reduced graphene oxide (rGO) has a unique planar structure and remarkable catalytic performance, it is not clear whether rGO can rapidly catalyze silver deposition as an effective way of signal amplification. However, in this study, we were pleasantly surprised to find that using H₂O₂ as a reducing agent, rGO can rapidly catalyze silver deposition, and its catalytic efficiency of silver deposition is significantly better than that of GO. Therefore, based on further verifying the mechanism of catalytic properties of rGO, we constructed a novel electrochemical biosensor (rGO/silver biosensor) for the detection of dam MTase activity, which has high selectivity and sensitivity to MTase in the range of 0.1 U/mL to 10.0 U/mL, and the detection limit is as low as 0.07 U/mL. Besides, this study also used Gentamicin and 5-Fluorouracil as inhibitor models, confirming that the biosensor has a good application prospect in the high-throughput screening of dam MTase inhibitors.

On the Development of Nanocomposite Covalent Associative Networks Based on Polycaprolactone and Reduced Graphite Oxide

In this work, the development of nanocomposite systems based on reduced graphite oxide (rGO) was combined with the development of crosslinked materials characterized by dynamic covalent bonds, i.e., a covalent associative network, starting from ad-hoc synthesized hydroxyl terminated polycaprolactone (PCL-OH). The crosslinking reaction was carried out using methylenediphenyl diisocyanate (MDI) to create systems capable of bond exchanges via transesterification and transcarbamoylation reactions, in the presence of stannous octoate as a catalyst. The above materials were prepared at two different temperatures (120 and 200 °C) and two PCL-OH:MDI ratios. FT-IR measurements proved the formation of urethane bonds in all the prepared samples. Crosslinking was demonstrated by contacting the samples with a solvent capable of dissolving the star-shaped PCL. These tests showed a significant increase in the crosslinked fraction with increasing the temperature and the PCL-OH:MDI ratio. In order to evidence the effect of crosslinking on rGO dispersion and the final properties of the material, a nanocomposite sample was also prepared using a linear commercial PCL, with the nanofiller mixed under the same conditions used to develop the crosslinked systems. The dispersion of rGO, which was investigated using FE-SEM measurements, was similar in the different systems prepared, indicating that the crosslinking process had a minor effect on the dispersibility of the nanofiller. As far as the thermal properties are concerned, the DSC measurements of the prepared samples showed that the crosslinking leads to a decrease in the crystallinity of the polymer, a phenomenon which was particularly evident in the sample prepared at 200 °C with a PCL-OH: MDI ratio of 1:1.33 and was related to the decrease in the polymer chain mobility. Moreover, rGO was found to act as a nucleating agent and increase the crystallization temperature of the nanocomposite sample based on linear commercial PCL, while the contribution of rGO in the crosslinked nanocomposite samples was minor. Rheological measurements confirmed the crosslinking of the PCL-OH system which generates a solid-like behavior depending on the PCL-OH:MDI ratio used. The presence of rGO during crosslinking generated a further huge increase in the viscosity of the melt with a remarkable solid-like behavior, confirming a strong interaction between rGO and crosslinked PCL. Finally, the prepared nanocomposites exhibited self-healing and recyclability properties, thus meeting the requirements for sustainable materials.