ABSTRACT
In the present work, the effectiveness of four non-halogenated flame retardants (FR) (aluminium trihydroxide (ATH), magnesium hydroxide (MDH), Sepiolite (SEP) and a mix of metallic oxides and hydroxides (PAVAL)) in blends with recycled acrylonitrile-butadiene-styrene (rABS) was studied in order to develop a more environmentally friendly flame-retardant composite alternative. The mechanical and thermo-mechanical properties of the obtained composites as well as their flame-retardant mechanism were evaluated by UL-94 and cone calorimetric tests. As expected, these particles modified the mechanical performance of the rABS, increasing its stiffness at the expense of reducing its toughness and impact behavior. Regarding the fire behavior, the experimentation showed that there is an important synergy between the chemical mechanism provided by MDH (decomposition into oxides and water) and the physical mechanism provided by SEP (oxygen barrier), which means that mixed composites (rABS/MDH/SEP) can be obtained with a flame behavior superior to that of the composites studied with only one type of FR. In order to find a balance between mechanical properties, composites with different amounts of SEP and MDH were evaluated. The results showed that composites with the composition rABS/MDH/SEP: 70/15/15 wt.% increase the time to ignition (TTI) by 75% and the resulting mass after ignition by more than 600%. Furthermore, they decrease the heat release rate (HRR) by 62.9%, the total smoke production (TSP) by 19.04% and the total heat release rate (THHR) by 13.77% compared to unadditivated rABS; without compromising the mechanical behavior of the original material. These results are promising and potentially represent a greener alternative for the manufacture of flame-retardant composites.
ABSTRACT
PURPOSE: This investigation aims to provide outcomes from a clinical perspective on the validity and efficacy of a wireless automated audiometer system that could be used in multiple settings when a sound booth is not accessible. Testing was conducted in a clinical setting under modified protocols meeting safety precautions during the COVID-19 pandemic. METHOD: Four doctoral students in audiology served as examiners. Participants were 69 adults between the ages of 20 and 69 years, with normal hearing (≤ 25 dB HL; n = 110 ears) or hearing loss (> 25 dB HL; n = 25 ears). Two versions of a pure-tone air-conduction threshold test following a modified Hughson-Westlake approach were performed and compared at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz (a) in a sound-treated test booth using standard manual audiometry and (b) in a quiet, nonsound-treated clinical room (sound booth free) using automated KUDUwave audiometry. Participants were asked to complete a five-item feedback questionnaire, and examiners were interviewed to report on their experience. RESULTS: Clinical validity to within ±10 dB of standard audiometry was demonstrated for 94.5% of the total thresholds (n = 937) measured with the sound booth-free approach. Less accuracy (73.3%) was observed using a ±5 dB comparison. When comparing the mean thresholds, there were significant differences (p < .01) between the mean thresholds at most frequencies, with mean sound booth thresholds being higher than the sound booth-free mean thresholds. A strong threshold correlation (.91-.98) was found between the methods across frequencies. Participant and examiner feedback supported the efficacy of the sound booth-free technology. CONCLUSIONS: Findings support sound booth-free, automated software-controlled audiometry with active noise monitoring as a valid and efficient procedure for pure-tone hearing threshold assessment. This method offers an effective alternative when circumstances require more transportable hearing assessment technology or do not allow for standard manual audiometry in a sound booth.
