Processing, structure and properties of poly(ether ketone) grafted few wall carbon nanotube composite fibers

Poly(ether ketone) (PEK) was grafted onto few wall carbon nanotube (FWNT) using in-situ polymerization of 4-phenoxybenzoic acid (4-PBA) in poly(phosphoric acid) (PPA), and fibers were processed using dry-jet wet-spinning. The PEK/FWNT weight ratio was in the range of 99/1 to 80/20. The fibers have been characterized for their morphology, structure, mechanical properties, as well as electrical conductivity. The toughness (work of rupture) of the PEK fibers, as measured from the area under the stress-strain curves, was as high as 130 J/g and often exceeded the toughness of the toughest synthetic fibers such as Kevlar™ (∼45 J/g) and Zylon™ (∼50 J/g) and approached values closer to that of spider silk (∼170 J/g). PEK and PEK-g-FWNT fibers exhibit good thermal stability with degradation onset of above 500 °C under nitrogen environment, and possess high char yield (∼50% for 5 wt% FWNT containing PEK fiber). PEK-g-FWNT fibers can be processed that exhibit good dimensional stability up to 300 °C (coefficient of thermal expansion ∼−1.2 × 10⁻⁵/°C) and the axial electrical conductivity was as high as 240 S/m at 20 wt% FWNT loading.     

Investigating particle emissions and aerosol dynamics from a consumer fused deposition modeling 3D printer with a lognormal moment aerosol model

ABSTRACT

Particle emissions from consumer-fused deposition modeling 3D printers have been reported previously; however, the complex processes leading to observed aerosols have not been investigated. We measured particle concentrations and size distributions between 7 nm and 25 μm emitted from a 3D printer under different conditions in an emission test chamber. The experimental data was combined with a moment lognormal aerosol dynamic model to better understand particle formation and subsequent evolution mechanisms. The model was based on particles being formed from nucleation of unknown semivolatile compounds emitted from the heated filament during printing, which evolve due to condensation of emitted vapors and coagulation, all within a small volume near the printer extruder nozzle. The model captured observed steady state particle number size distribution parameters (total number, geometric mean diameter and geometric standard deviation) with errors nominally within 20%. Model solutions provided a range of vapor generation rates, saturation vapor pressures and vapor condensation factors consistent with measured steady state particle concentrations and size distributions. Vapor generation rate was a crucial factor that was linked to printer extruder temperature and largely accounted for differences between filament material and brands. For the unknown condensing vapor species, saturation vapor pressures were in the range of 10^?3 to 10^?1 Pa. The model suggests particles could be removed by design of collection surfaces near the extruder tip.

Copyright © 2018 American Association for Aerosol Research     

Fire Risk Index for Historic Buildings

Fire protection engineers and preservation architects have long recognized the difficulty in applying building and fire codes to historic buildings. Small, older buildings of significant historic value need an efficient approach to performance-based evaluation. One technique that has gained acceptance is fire risk indexing. The Historic Fire Risk Index described in this paper uses a linear additive model of multiple attribute evaluation to produce a measure of relative fire risk. Weights are established to indicate the importance or significance of fire risk parameters. Then, for each specific historic structure, parameter grades, i.e., the amount or degree that a parameter is present, are determined from information collected in a detailed site survey. Fire risk is evaluated by the scalar product of the parameter weights and grades, producing a single numerical value representing the level of fire safety provided in the building. This is a more rational and more transparent method than the risk indexing systems currently published in model codes and standards.