Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites

Researchers and legislators have both claimed the necessity to standardize the exposure assessment of polymer nanocomposites throughout their life cycle. In the present study we have developed and compared three different and independent operational protocols to investigate changes in particle emission behavior of mechanically degraded polypropylene (PP) samples containing different fillers, including talc and two types of nanoclays (wollastonite-WO- and montmorillonite-MMT-) relative to not reinforced PP. Our results have shown that the mechanical degradation of PP, PP-Talc, PP-WO and PP-MMT samples causes the release of nano-sized particles. However, the three protocols investigated, simulating industrial milling and drilling and household drilling, have produced different figures for particles generated. Results suggest that it is not possible to describe the effects of adding nano-sized modifiers to PP by a single trend that applies consistently across all different protocols. Differences observed might be attributed to a variety of causes, including the specific operational parameters selected for sample degradation and the instrumentation used for airborne particle release characterization. In particular, a streamlined approach for future assessments providing a measure for released particles as a function of the quantity of removed material would seem useful, which can provide a reference benchmark for the variations in the number of particles emitted across a wider range of different mechanical processes

Characterization and evaluation of carbon nanotube Bucky-Paper membranes for direct contact membrane distillation

Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties which can be utilised in many applications. In this work we characterised pure self-supporting CNT membranes, where CNTs were held together only by Van der Waals forces, and evaluated their potential and performance in direct contact membrane distillation. The membranes were found to be highly hydrophobic (contact angle of 113°), highly porous (90%), and to exhibit a thermal conductivity of 2.7 kW/m2 h. We demonstrate, as a proof of concept, that self-supporting CNT Bucky-Paper membranes can be used for desalination in a direct contact membrane distillation setup with 99% salt rejection and a flux rate of 12 kg/m2 h at a water vapour partial pressure difference of 22.7 kPa. Ageing of the membranes by delamination is a main factor limiting their performance and work is currently under way to address this issue by investigating composite material structures

The Impact of Hydrophobic Coating on the Performance of Carbon Nanotube Bucky-Paper Membranes in Membrane Distillation

PTFE coated carbon nanotube BPs were processed and tested as potential membranes in DCMD. They exhibited improved properties compared to both their untreated counter parts and to commercial membranes. The difference was attributed to the higher hydrophobicity of the smooth surface and to an increased porosity compared to the PTTE membranes making of those membranes very promising structures for use as separation means in membrane distillation

Improving Transverse Compressive Modulus of Carbon Fibers during Wet Spinning of Polyacrylonitrile

The performance of carbon fibers depends on the properties of the precursor polyacrylonitrile (PAN) fibers. Stretching of PAN fibers results in improved tensile properties, while potentially reducing its compressive properties. To determine optimization trade-offs, the effect of coagulation conditions and the stretching process on the compressive modulus in the transverse direction (ET) was investigated. A method for accurately determining ET from polymer fibers with non-circular cross-sectional shapes is presented. X-ray diffraction was used to measure the crystallite size, crystallinity, and crystallite orientation of the fibers. ET was found to increase with decreasing crystallite orientation along the drawing direction, which decreases the tensile modulus in the longitudinal direction (EL) proportionally to crystallite orientation. Stretching resulted in greater crystallite orientation along the drawing direction for fibers formed under the same coagulation conditions. Increasing the solvent concentration in the coagulation bath resulted in a higher average orientation, but reduced the impact of stretching on the orientation. The relationship between ET and EL observed in the precursor PAN fiber is retained after carbonization, with a 20% increase in ET achieved for a 2% decrease in EL. This indicates that controlled stretching of PAN fiber allows for highly efficient trading off of EL for ET in carbon fiber

Enhanced Durability and Hydrophobicity of Carbon Nanotube Bucky Paper Membranes in Membrane Distillation

Carbon nanotubes (CNTs) are very stable structures. Their chemistry is still little known. For health and water purification, new treatment techniques that can respond to the growing demand for fresh water are required. These include Bucky-paper fabrication and characterisation and direct contact membrane distillation. These techniques require further testing and for longer periods