Search

The search for alternative ways to give a second life to materials paved the way for detailed investigation into three silica-polyethylenimine (Si-PEI) materials for the purpose of CO 2 adsorption in carbon capture and storage. A solvent extraction procedure was investigated to recover degraded PEIs and silica, and concomitantly, pyrolysis was evaluated to obtain valuable chemicals such as alkylated pyrazines. An array of thermal (TGA, Py-GC-MS), mechanical (rheology), and spectroscopical (ATR-FTIR, 1 H- 13 C-NMR) methods were applied to PEIs extracted with methanol to determine the relevant physico-chemical features of these polymers when subjected to degradation after use in CO 2 capture. Proxies of degradation associated with the plausible formation of urea/carbamate moieties were revealed by Py-GC-MS, NMR, and ATR-FTIR. The yield of alkylpyrazines estimated by Py-GC-MS highlighted the potential of exhausted PEIs as possibly valuable materials in other applications.

Graphene (G) can effectively enhance polymers' and polymer composites' electric, thermal, and mechanical properties. Nanofibrous mats have been demonstrated to significantly increase the interlaminar fracture toughness of composite laminates, hindering delamination and, consequently, making such materials safer and more sustainable thanks to increased service life. In the present paper, poly(ethylene oxide) (PEO), polycaprolactone (PCL), and Nylon 66 nanofibers, plain or reinforced with G, were integrated into epoxy-matrix Carbon Fiber Reinforced Polymers (CFRPs) to evaluate the effect of polymers and polymers + G on the laminate mechanical properties. The main aim of this work is to compare the reinforcing action of the different nanofibers (polyether, polyester, and polyamide) and to disclose the effect of G addition. The polymers were chosen considering their thermal properties and, consequently, their mechanism of action against delamination. PEO and PCL, displaying a low melting temperature, melt, and mix during the curing cycle, act via matrix toughening; in this context, they are also used as tools to deploy G specifically in the interlaminar region when melting and mixing with epoxy resin. The high extent of modification stems from an attempt to deploy it in the interlaminar layer, thus diluting further in the resin. In contrast, Nylon 66 does not melt and maintain the nanostructure, allowing laminate toughening via nanofiber bridging. The flexural properties of the nanomodifed CFRPs were determined via a three-point bending (3PB) test, while delamination behavior in Mode I and Mode II was carried out using Double Cantilever Beam (DCB) and End-Notched Flexture (ENF) tests, respectively. The lack of a positive contribution of G in this context is an interesting point to raise in the field of nanoreinforced CFRP.

Delamination is the most severe weakness affecting all composite materials with a laminar structure. Nanofibrous mat interleaving is a smart way to increase the interlaminar fracture toughness: the use of thermoplastic polymers, such as poly(ε-caprolactone) and polyamides (Nylons), as nonwovens is common and well established. Here, electrospun polyethylene oxide (PEO) nanofibers are proposed as reinforcing layers for hindering delamination in epoxy-based carbon fiber-reinforced polymer (CFRP) laminates. While PEO nanofibers are well known and successfully applied in medicine and healthcare, to date, their use as composite tougheners is undiscovered, resulting in the first investigation in this application field. The PEO-modified CFRP laminate shows a significant improvement in the interlaminar fracture toughness under Mode I loading: +60% and +221% in G I,C and G I,R , respectively. The high matrix toughening is confirmed by the crack path analysis, showing multiple crack planes, and by the delamination surfaces, revealing that extensive phase separation phenomena occur. Under Mode II loading, the G II enhancement is almost 20%. Despite a widespread phase separation occurring upon composite curing, washings in water do not affect the surface delamination morphology, suggesting a sufficient humidity resistance of the PEO-modified laminate. Moreover, it almost maintains both the original stiffness and glass transition temperature ( T g ), as assessed via three-point bending and dynamic mechanical analysis tests. The achieved results pave the way for using PEO nanofibrous membranes as a new effective solution for hindering delamination in epoxy-based composite laminates., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Highly functionalized pyrroles with appropriate regiochemical functionality represent an important class of marine natural products and potential drug candidates. We describe herein a detailed study of the reaction of α-aminoacid esters with vinylogous amides and also β-halovinylaldehydes for the regiospecific synthesis of 2,3,4-trisubstituted and 1,2,3,4-tetrasubstituted pyrroles. Since the vinylogous amides and β-halovinylaldehydes are readily available precursors, rapid access to a wide variety of unsymmetrically substituted pyrroles is accomplished via this methodology.

New microtubule depolymerizing agents with potent cytotoxic activities have been prepared with a 5-cyano or 5-oximino group attached to a pyrrole core. The utilization of ortho activation of a bromopyrrole ester to facilitate successful Suzuki-Miyaura cross-coupling reactions was a key aspect of the synthetic methodology. This strategy allows for control of regiochemistry with the attachment of four completely different groups at the 2, 3, 4 and 5 positions of the pyrrole scaffold. Biological evaluations and molecular modeling studies are reported for these examples., (Copyright © 2017 Elsevier Ltd. All rights reserved.)