Dissolution of semicrystalline polymer fibers: Numerical modeling and parametric analysis

Increasing the Dissolution Rate of Polystyrene Waste in Solvent-Based Recycling

Solvent-based recycling of plastic waste is a promising approach for cleaning polymer chains without breaking them. However, the time required to actually dissolve the polymer in a lab environment can take hours. Different factors play a role in polymer dissolution, including temperature, turbulence, and solvent properties. This work provides insights into bottlenecks and opportunities to increase the dissolution rate of polystyrene in solvents. The paper starts with a broad solvent screening in which the dissolution times are compared. Based on the experimental results, a multiple regression model is constructed, which shows that within several solvent properties, the viscosity of the solvent is the major contributor to the dissolution time, followed by the hydrogen, polar, and dispersion bonding (solubility) parameters. These results also indicate that cyclohexene, 2-pentanone, ethylbenzene, and methyl ethyl ketone are solvents that allow fast dissolution. Next, the dissolution kinetics of polystyrene in cyclohexene in a lab-scale reactor and a baffled reactor are investigated. The effects of temperature, particle size, impeller speed, and impeller type were studied. The results show that increased turbulence in a baffled reactor can decrease the dissolution time from 40 to 7 min compared to a lab-scale reactor, indicating the importance of a proper reactor design. The application of a first-order kinetic model confirms that dissolution in a baffled reactor is at least 5-fold faster than that in a lab-scale reactor. Finally, the dissolution kinetics of a real waste sample reveal that, in optimized conditions, full dissolution occurs after 5 min.

Green Composites of Poly(3-hydroxybutyrate) Containing Graphene Nanoplatelets with Desirable Electrical Conductivity and Oxygen Barrier Properties

Poly(3-hydroxybutyrate), a green polymer originating from prokaryotic microbes, has been used to prepare composites with graphene nanoplatelets (GnP) at different concentrations. The films were fabricated by drop-casting and were hot-pressed at a temperature lower than their melting point to provide the molecular chains enough energy to reorientate while avoiding melting and degradation. It was found that hot-pressing increases crystallinity and improves mechanical properties. The Young's modulus increased from 1.2 to 1.6 GPa for the poly(3-hydroxybutyrate) (P(3HB)) films and from 0.5 to 2.2 GPa for the 15 wt % P(3HB)/GnP composites. Electrical resistivity decreases enormously with GnP concentration and hot-pressing, reaching 6 Ω sq^-1 for the hot-pressed 30 wt % P(3HB)/GnP composite. Finally, the hot-pressed P(3HB) samples exhibit remarkable oxygen barrier properties, with oxygen permeability reaching 2800 mL μm m^-2 day^-1, which becomes 895 mL μm m^-2 day^-1 when 15% GnP is added to the biopolymer matrix, one of the lowest values known for biopolymers and biocomposites. We propose that these biocomposites are used for elastic packaging and electronics.