Improving flame retardancy of in-situ silica-epoxy nanocomposites cured with aliphatic hardener: Combined effect of DOPO-based flame-retardant and melamine

Silica-epoxy nanocomposites were prepared via an “in-situ ”sol-gel synthesis process and a phosphorus (P) flame-retardant i.e. 6H-dibenz[c,e][1,2]oxaphosphorin,6-[(1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]oct- 4-yl)methoxy]-, 6-oxide (DP) and melamine (Mel) were further added to the matrix to improve its fire perfor- mance. The main components of epoxy resin were bisphenol A diglycidyl ether (DGEBA) and isophorone diamine (IPDA) hardener. The addition of DP as well as silica alone into the epoxy system stopped the melt dripping phe- nomena in the vertical fire test (UL 94), however, the addition of melamine was crucial for achieving the highest fire classification (UL 94-V0 rating). The presence of DP and Mel in the silica-epoxy nanocomposite promoted a large reduction (ranging from 53% up to 80%) in the heat release rate (HRR) and a delay (up to 31%) in the igni- tion time in the cone calorimetry experiments. Improved fire performance of the epoxy system was attributed to i) a condensed phase activity of silica, DP and melamine to form a protective thermal barrier during combustion and ii) a minor gas phase flame inhibition activity of DOPO component of DP. The mechanical characterization of the epoxy nanocomposites through tensile tests showed that the addition of DP increases the stiffness of the epoxy resin, resulting in a strong increase of Young modulus (up to 32%) and in a slight decrease of fracture strength, elongation at break and toughness. An increased glass transition temperature (up to 8%) of the epoxy system possibly due to hydrogen bonds and polar interactions of DP with the matrix was also observed

Fire and mechanical properties of DGEBA-based epoxy resin cured with a cycloaliphatic hardener: combined action of silica, melamine and DOPO-derivative

The effect of the addition of additives such as melamine (Mel), silica nanoparticles and a phosphorus-based compound, i.e. 3-(6-oxidodibenzo[c,e][1,2]oxaphosphinin-6-yl)propenamide (DA), on the fire and mechanical performance of a bisphenol A diglycidyl ether (DGEBA)-based epoxy resin cured with isophoronediamine has been investigated. A UL 94-V0 classification was achieved for epoxy resin containing DA at 2 wt% of phosphorus loading. However, addition of silica nano particleswas necessary to avoid melt dripping. The incorporation of DA and Mel to the epoxy resin promoted a remarkable reduction (48% to 70%) in the heat release rate (HRR) values, a significant delay (up to 47%) in the ignition time in cone calorimetry experiments, and thus an increase (~75%) in the time to flashover. Evolved gas, thermal and fire analysiswas used to propose the combined mode of action of DA, Mel and silica in the fire performance improvement of the epoxy system. Tensile and three-point bending flexural tests showed that the addition of DA increases the rigidity of the resin, resulting in a strong increase in the Young's modulus (up to 34%) and in a slight reduction in fracture strength, elongation break and toughness which is typical for non-reactive additives

A Method for Quantifying Interaction Forces in Wearable Robots

Immobility due to movement impairments causes many secondary conditions that are a threat to a person's health and quality of life. Wearable robotic mobility aids such as exoskeletons and exosuits are a promising technique to tackle immobility. These devices are attached to the human with cuffs. However, the physical interaction at the human-robot interface is not yet well understood. Misplacement and compression of soft tissue diminish the efficiency of the robot and the comfort for the human. We developed a measurement method that allows us to simultaneously measure cuff interaction forces in normal and tangential direction. The measurement setup was validated in a friction test bench. The test-retest reliability was evaluated in an isolated attachment cuff mounted on a human forearm. Force measurements were repeatable, with error ranges up to 28.7% or 7.8 N in normal, 28.7% or 2.3 N in tangential direction. Our method is the first approach that simultaneously measures normal and tangential forces at the physical interface of wearable robots. The test-retest reliability is within the range of methods that assess only normal forces

Mechanical Predictors of Discomfort during Load Carriage

Discomfort during load carriage is a major issue for activities using backpacks (e.g. infantry maneuvers, children carrying school supplies, or outdoor sports). It is currently unclear which mechanical parameters are responsible for subjectively perceived discomfort. The aim of this study was to identify objectively measured mechanical predictors of discomfort during load carriage. We compared twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt. The pressure distribution under the hip belt and the shoulder strap, as well as the tensile force in the strap and the relative motion of the backpack were measured. Multiple linear regression analyses were conducted to investigate possible predictors of discomfort. The results demonstrate that static peak pressure, or alternatively, static strap force is a significant (p<0.001) predictor of discomfort during load carriage in the shoulder and hip region, accounting for 85% or more of the variation in discomfort. As an additional finding, we discovered that the regression coefficients of these predictors are significantly smaller for the hip than for the shoulder region. As static peak pressure is measured directly on the body, it is less dependent on the type of load carriage system than static strap force. Therefore, static peak pressure is well suited as a generally applicable, objective mechanical parameter for the optimization of load carriage system design. Alternatively, when limited to load carriage systems of the type backpack with hip belt, static strap force is the most valuable predictor of discomfort. The regionally differing regression coefficients of both predictors imply that the hip region is significantly more tolerant than the shoulder region. In order to minimize discomfort, users should be encouraged to shift load from the shoulders to the hip region wherever possible, at the same time likely decreasing the risk of low back pain or injury.ISSN:1932-620

Prognostic power of NT-proBNP in left ventricular non-compaction cardiomyopathy

Background: The risk of adverse events in patients with left ventricular non-compaction cardiomyopathy (LVNC) is substantial. This study was designed to determine the prognostic value of NT-proBNP, left ventricular ejection fraction (LVEF), NYHA class, and exercise capacity in LVNC patients. Methods: Cox regression analyses were performed for evaluating the prognostic value of NT-proBNP, LVEF, NYHA class, and exercise capacity on the occurrence of death or heart transplantation. 153 patients were included. Results: During 1013 person-years (longest follow-up 18.5 years) 23 patients (15%) died or underwent heart transplantation. We observed a significant relationship of NT-proBNP (adjusted HR 2.44, 95% CI 1.45–4.09, for every NT-proBNP doubling, p = 0.0007) and LVEF (adjusted HR for age 60 years: 2.68, 95% CI 1.62–4.41, p = 0.0001) with the risk of death or heart transplantation. Combined covariate analysis indicated a strong influence of NT-proBNP (adjusted 2.89, 95% CI 1.33–6.26, p = 0.007), whereas LVEF was no longer significant (adjusted HR 0.82, 95% CI 0.42–1.67, p = 0.66) demonstrating a favorable prognostic power of NT-proBNP over LVEF. An increase in NYHA class was associated with a worse outcome, and exercise capacity revealed a trend in the same direction. For all the abovementioned analyses, similar results were obtained when assessing the values at first presentation. Conclusion: This study provides evidence that an increase in NT-proBNP is a strong predictor of outcome in patients with LVNC. The prognostic power of NT-proBNP is at least as good as that of LVEF, indicating that routine NT-proBNP measurement may improve risk assessment in LVNC

Enhanced Piezoelectric Performance of Electrospun PVDF-TrFE by Polydopamine-Assisted Attachment of ZnO Nanowires for Impact Force Sensing

In this work, piezoelectric PVDF-TrFE electrospun fibers (EFs) were fabricated using a high-throughput nozzle-free electrospinning process. Zinc oxide (ZnO) nanoparticles were robustly anchored to the PVDF-TrFE EFs, assisted by a self-polymerized polydopamine (PDA) layer, and subsequently grown into ZnO nanowires (NWs) using a low-temperature hydrothermal growth method. The EF mats were investigated for active impact force transduction and the piezoelectric voltage outputs of different combinations of PVDF-TrFE and ZnO nanomaterials were compared using two different impact force testing setups. The horizontal impact force test saw an increase in force sensitivity by a factor of 2.5 for the nanowires compared to the unmodified PVDF-TrFE EFs. Similarly, vertical drop impact testing demonstrated a 5.8-fold increase in sensitivity with a linear response (R-2 = 0.986) for a large range of impact forces up to 970 N. The EFs were also tested as a wearable impact force sensor to quantify soccer ball heading force, which was measured as 291.3 +/- 51.0 N for a vertical ball speed of 7.8 +/- 1.5 ms(-11) with an 8.2% average error compared to theoretical force values. It is believed the enhanced piezoelectric performance of these materials could provide a useful platform for wearable sensing and energy harvesting.ISSN:1438-7492ISSN:1439-205

Assessment of the thermal outcome during steam-pulse ablation for sheep tissue

Thermal ablation has attracted attention as a minimally invasive tissue ablation treatment. Steam flow was recently introduced as a novel ablation procedure. This work aimed to assess the applicability of pulsated steam flow for tumor ablation. Ex vivo ablation was performed using liver, muscle, and fat tissues of sheep. Three experimental protocols of pulse number were administered to these tissues, while computational simulation was conducted according to the ex vivo tests for each tissue. Real-time measurements of temperature revealed heat propagation during and subsequent to ablation. The peak temperature was achieved after ablation. The time to reach the peak (highest temperature) increased with the distance from the thermal sensor to the steam needle according to thermal conductivity, except for steam leakage along to gap between the tissue and blood vessel. A cross-section of the ablated specimen clearly revealed the boundaries of cell defects. The ablated area was droplet shaped up to the steam needle. Computational simulations revealed that the ablated area was consistent with the area with the highest temperature. Though several limitations still remain such as no blood circulation, pulsated steam flow can ablate diverse animal tissues

List of independent variables included in multiple linear regressions.

<p>The dependent variable was regional discomfort.</p><p>List of independent variables included in multiple linear regressions.</p