Characterization of aerosolized particles in effluents from carbon fibre composites incorporating nanomaterials during simultaneous fire and impact.

This work investigates the aerosols emitted from carbon fibre-reinforced epoxy composites (CFC) incorporating nanomaterials (nanoclays and nanotubes), subjected to simultaneous fire and impact, representing an aeroplane or automotive crash. Simultaneous fire and impact tests were performed using a previously described bespoke testing methodology with the capability to collect particles released from the front/back faces of the impacted composites plus the effluents. In this work the methodology has been further developed by connecting the Dekati Low Pressure Impactor (DLPI) and Mini Particle Sampler (MPS) sampling system in the extraction chimney. The aerosols emitted have been characterized using various devices devoted to the analysis of aerosols. The influence of the nanoadditives in the matrix on the number concentration and the size distribution of airborne particles produced, was studied with a cascade impactor in the 5 nm-10 µm range. The morphology of the separated soot fractions was examined by SEM. The measurement of aerodynamic size of particles that can deposit in human respiratory tract indicate that 75% of the soot and particles released from CFC could deposit in the lungs reaching the bronchi region at a minimum. There was however, a minimal difference between the number particle concentrations or particle-size mass distribution of particles from CFC and CFC containing nanoadditives. Moreover, no fibres were found in the effluents.

Occupational exposure to carbon fibers impregnated with epoxy resins and evaluation of their respirability.

Objectives: The study aims to investigate occupational exposure to carbon fibers impregnated with epoxy resins (carbon fiber reinforced [CFR]) in workers at an airplane fuselage section construction plant, by environmental and biological monitoring.Materials and methods: Determination of airborne CFR was done by environmental sampling with active samplers, 11 of which were stationary and 19 personal samplings. The subsequent analyses were performed in the scanning electron microscope fitted with an X-ray microanalysis system (SEM-EDXA). Biological monitoring was carried out by determining CFR in exhaled breath condensate (EBC) collected from 19 male workers who wore personal environmental samplers (exposed workers) and from 10 male workers at the same factory who had no occupational exposure to CFR (internal controls). CFR analysis was done by SEM, applying the method used for determining asbestos fibers in aqueous samples.Results: The airborne CFR concentrations were found to be significantly higher (p = 0.03) at personal samplings (median value 7.01 ff/L, range 1.24-11.16 ff/L) than stationary samplings (median value 1.93 ff/L, range 0.55-10.09 ff/L). The aerodynamic diameters calculated starting from the length and geometric diameter of the sampled CFRs were always higher than 20 µm. CFR was not found in any of the EBC samples collected from the exposed workers and controls.Conclusions: Despite the evidence of occupational exposure to low concentrations of CFR, the absence of such fibers in the EBC in the exposed workers confirms their non-respirability, as expected based on their aerodynamic diameter.

Kraft lignin-based piezoresistive sensors: Effect of chemical structure on the microstructure of ultrathin carbon fibers.

In an attempt to diversify lignin applications, in this study, electrospun mats composed of ultrathin carbon fibers from Eucalyptus globulus Lignin (EKL) and sugarcane bagasse Kraft lignin (BKL) capable of detecting certain human body motions were fabricated and their chemical structures fully investigated accordingly. Results suggested that the main chemical structure of EKL was slightly linear with sinapyl alcohol and coniferyl alcohol as the basic units and pinoresinol, arylglycerol-ß-aryl ether, phenylcoumaran, with diphenylethane as the main linkages. The slightly linear EKL and cross-linked BKL tended to form amorphous carbon and graphite crystallites under the same heat treatment process respectively, thereby resulting in a large difference in the resistance of fabricated sensors. The amplitude of signals due to changes in the relative resistance (△R/R0) for EKL ultrathin carbon fiber (CF)-based sensor was approximately 9 × 104 during the finger bending process, while large (△R/R0 ~380) and small (△R/R0 < 10) relative resistance variations due to BKL-CF-based sensors were detected during the arm bending and finger pressing motions respectively.

Sampling Techniques on Collecting Fine Carbon Nanotube Fibers for Exposure Assessment.

Carbon nanotube (CNT) sampling using an open-faced 25 mm cassette fiber sampling method and a newly developed direct sampling device was evaluated for the size fractioned analysis of collected airborne CNT fibers to improve the sampling and analytical methods. The open-faced 25 mm cassette fiber sampling method primarily collected large agglomerates, with the majority of collected particles being larger than two micrometer in size. Most of CNT structures collected by the new direct sampling device were individual fibers and clusters smaller than one micrometer with a high particle number concentration discrepancy compared to the open-faced 25 mm cassette method raising the concern of this sampling method to representatively characterize the respirable size fraction of CNT aerosols. This work demonstrates that a specialized technique is needed for collecting small fibers to provide a more representative estimate of exposure. It is recommended that an additional sampler be used to directly collect and analyze small fibers in addition to the widely accepted sampling method which utilizes an open-faced 25 mm cassette.

Pedicle screw anchorage of carbon fiber-reinforced PEEK screws under cyclic loading.

PURPOSE: Pedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws. METHODS: In the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm3 ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm3 ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from - 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion ("screw toggling") within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles. RESULTS: The nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard titanium screws (3701 ± 1228 vs. 3751 ± 1614 load cycles, p = 0.89). PMMA cement augmentation of CF/PEEK pedicle screws furthermore significantly increased the mean number of load cycles until loosening by 1.63-fold (5100 ± 1933 in augmented vs. 3130 ± 2132 in nonaugmented CF/PEEK screws, p = 0.015). In addition, angular screw motion assessed by stress fluoroscopy was significantly smaller in augmented than in nonaugmented CF/PEEK screws before as well as after failure. CONCLUSIONS: Using nonmetallic CF/PEEK instead of standard titanium as pedicle screw material did not affect screw loosening in the chosen test setup, whereas cement augmentation enhanced screw anchorage of CF/PEEK screws. While comparable to titanium screws in terms of screw loosening, radiolucent CF/PEEK pedicle screws offer the significant advantage of not interfering with postoperative imaging and radiotherapy. These slides can be retrieved under Electronic Supplementary Material.