Nanoscale disintegration kinetics of mesoglobules in aqueous poly(N-isopropylacrylamide) solutions revealed by small-angle neutron scattering and pressure jumps

Identification and control of the disintegration mechanism of polymer nanoparticles are essential for applications in transport and release including polymer delivery systems. Structural changes during the disintegration of poly(N-isopropylacrylamide) (PNIPAM) mesoglobules in aqueous solution are studied in situ and in real time using kinetic small-angle neutron scattering with a time resolution of 50 ms. Simultaneously length scales between 1 and 100 nm are resolved. By initiating phase separation through fast pressure jumps across the coexistence line, 3 wt% PNIPAM solutions are rapidly brought into the one-phase state. Starting at the same temperature (35.1 °C) and pressure (17 MPa) the target pressure is varied over the range 25-48 MPa, allowing to systematically alter the osmotic pressure of the solvent within the mesoglobules. Initially, the mesoglobules have a radius of gyration of about 80 nm and contain a small amount of water. Two disintegration mechanisms are identified: (i) for target pressures close to the coexistence line, single polymers are released from the surface of the mesoglobules, and the mesoglobules decrease in size, which takes ∼30 s. (ii) For target pressures more distant from the coexistence line, the mesoglobules are swollen by water, and subsequently the chains become more and more loosely associated. In this case, disintegration proceeds within less than 10 s, controlled by the osmotic pressure of the solvent.

Solvent-based separation and recycling of waste plastics: A review

Since the creation of first man-made plastic, the global production and consumption of plastics have been continuously increasing. However, because plastic materials are durable and very slow to degrade, they become waste with high staying power. The over-consumption, disposal, and littering of plastics result in pollution, thus causing serious environmental consequences. To date, only a fraction of waste plastics is reused and recycled. In fact, recycling plastics remains a great challenge because of technical challenges and relatively insufficient profits, especially in mixed plastics. This review focuses on an environmentally friendly and potentially profitable method for plastics separation and recovery and solvents extraction. It includes the dissolution/reprecipitation method and supercritical fluid extraction, which produce high-quality recovered plastics comparable to virgin materials. These methods are summarized and discussed taking mass-produced plastics (PS, PC, Polyolefins, PET, ABS, and PVC) as examples. To exploit the method, the quality and efficiency of solvent extraction are elaborated. By eliminating these technical challenges, the solvent extraction method is becoming more promising and sustainable for plastic issues and polymer markets.