Mechanical, Crystallization, Rheological, and Supercritical CO2 Foaming Properties of Polybutylene Succinate Nanocomposites: Impact of Carbon Nanofiber Content

As a substitute for conventional polymers for the preparation of biodegradable microcellular polymeric foams, polybutylene succinate (PBS) presents one of the most promising alternatives. However, the low melt strength of PBS makes it difficult to produce high-performance microcellular foams. This study aimed to improve the melt strength of PBS and explore the mechanical, thermal, crystalline, rheological, and supercritical CO2 foaming properties of PBS nanocomposites by using carbon nanofibers (CNFs). This study found that nanocomposites containing 7 wt% CNF exhibited the highest tensile strength, Young's modulus, and bending strength. Moreover, the CNF nanofillers were well dispersed in the PBS matrix without significant agglomeration, even at high filler concentrations. Furthermore, the nanocomposites demonstrated improved melting temperature and crystallinity compared with pure PBS. The rheological analysis showed that the addition of CNFs significantly increased PBS viscosity at low frequencies due to the interaction between the PBS molecular chains and CNFs and the entanglement of CNFs, resulting in a more complete physical network formation when the CNF content reached above 3 wt%. During the supercritical CO2 foaming process, the addition of CNFs resulted in increased cell density, smaller cells, and thicker cell walls, with good laps formed between the fibers on the cell walls of nanocomposite foams. Moreover, the electrical conductivity and electromagnetic interference (EMI) shielding properties of the foamed material were studied, and a nanocomposite foam containing 7 wt% CNF showed good electrical conductivity (4.5 × 10-3 S/m) and specific EMI shielding effectiveness (EMI SE) (34.7 dB/g·cm-1). Additionally, the nanocomposite foam with 7 wt% CNF also exhibited good compression properties (21.7 MPa). Overall, this work has successfully developed a high-performance, multifunctional PBS-based nanocomposite foam, making it suitable for applications in various fields.

The Influence of Fly Ash on the Foaming Behavior and Flame Retardancy of Polyurethane Grouting Materials

Polyurethane (PU) grouting material has been widely utilized to control water inrush in mining fields. However, the application has been limited by its high cost and poor flame retardancy. Here, we use the fly ash (FA), a waste from coal of the iron-making industry and power plants, as a partial replacement of conventional filler in PU grouting materials to reduce the production cost and the environmental pollution of FA. The surface-modified FA-filled PU (PU/FA) composites were prepared by room-temperature curing. The effects of FA contents (φ) on the structure, foaming behavior, thermal stability, mechanical properties, hydrophobic properties, and flammability of PU grouting materials were examined. Results showed that the higher the φ, the more porous the PU/FA composites are, resulting in a lower density and lower mechanical properties. The relationship between the compression modulus E and the density ρ of the PU/FA composites was E ∝ ρ^1.3. In addition, the surface-modified FA improved the compatibility between the hard and soft segment of PU in the PU/FA composite, giving the composites enhanced thermal stability, high hydrophobicity, and flammability resistance.