Effects of porosity,fiber size,and layering sequence on sound absorption performance of needle‐punched nonwovens

The relationships between the material parameters, i.e., the fiber fineness, porosity, areal density, layering sequence, and airflow resistivity with the normal‐incidence sound absorption coefficient of nonwoven composites consisting of three layers have been studied. The monofiber or multifiber needle‐punched nonwovens included poly(lactic acid) (PLA), polypropylene (PP), glass fiber, and hemp fibers. Air flow resistivity was statistically modeled and was found to increase with decreasing fiber size and nonwoven porosity. The former models developed for glass fiber mats in the literature were found to be inconsistent with the air flow resistance of the nonwovens reported below. The effects of the layering sequence on air flow resistivity and sound absorption were obtained. It was found that when the layer including reinforcement fibers, i.e., hemp or glass fiber, faced the air flow/sound source, the air flow resistance and the absorption coefficient were higher than the case when the layer including reinforcement fibers was farthest from the air flow/sound source. The difference was more pronounced if there was a greater difference between the resistivity values of the constituent layers of the nonwoven composite. Sound absorption coefficient was statistically modeled in terms of air flow resistivity and frequency. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Simultaneous heterotrophic and sulfur-oxidizing autotrophic denitrification process for drinking water treatment: control of sulfate production

A long-term performance of a packed-bed bioreactor containing sulfur and limestone was evaluated for the denitrification of drinking water. Autotrophic denitrification rate was limited by the slow dissolution rate of sulfur and limestone. Dissolution of limestone for alkalinity supplementation increased hardness due to release of Ca²⁺. Sulfate production is the main disadvantage of the sulfur autotrophic denitrification process. The effluent sulfate concentration was reduced to values below drinking water guidelines by stimulating the simultaneous heterotrophic and autotrophic denitrification with methanol supplementation. Complete removal of 75 mg/L NO₃-N with effluent sulfate concentration of around 225 mg/L was achieved when methanol was supplemented at methanol/NO₃-N ratio of 1.67 (mg/mg), which was much lower than the theoretical value of 2.47 for heterotrophic denitrification. Batch studies showed that sulfur-based autotrophic NO₂-N reduction rate was around three times lower than the reduction rate of NO₃-N, which led to NO₂-N accumulation at high loadings.     

Fabrication of stretchable and high-filtration performance melt-blown nonwoven webs for PM0.3 aerosol filtration

Polypropylene (PP) is a semi-crystalline polymer that displays simple manufacturing, high stiffness, lightweight, chemical resistance, and inexpensive. However, PP has significant drawbacks, such as poor brittleness at low temperatures, high shrinkage ratio, and low impact resistance, which limit its development. Thermoplastic polyurethane (TPU) possesses recyclable and eco-friendly characteristics, along with the elasticity of rubber and exceptional mechanical properties. In this study, a flexible and high-filtration performance PP-TPU textile material was developed by melt-blowing for filtering PM_0.3 aerosols. For the first time, a melt-blown PP-TPU nonwoven was used as an air filter. The fiber morphological studies exhibited that addition of 10 and 20 wt.% TPU into PP resulted in a fiber diameter increment from 0.94 to 1.24 μm. Also, melt-blown PP-TPU forms helical fibers, which are different from fibers noticed in melt-blown PP. Corona-charged double-layer 80PP-20TPU nonwovens have a filtration efficiency of 99.25% and quality factor (QF) of 0.13 mm H₂O⁻¹ at an air flow rate of 95 L/min. Moreover, PP's tensile strength was increased by 72.22%, and elongation was raised by 38.1% with the addition of 20 wt.% TPU. Thus, PP-TPU melt-blown composites may bring novel perspectives into the design and development of high-performance filtering materials for a variety of applications.     

The effect of different types of water on the swelling behaviour of expansive clays

In the design of foundations of structures, especially light buildings, on clayey soils, the main soil behaviours to be considered are swelling properties and surface heave. Therefore, determination of swelling properties by means of swell percent and maximum swell pressure as well as estimation of the surface is very important in the investigation of such soils and light structures on them. In order to obtain the swelling parameters of clayey soils, experimental laboratory tests were carried out and standardised. Distilled water is generally used during these experimental tests; however, the soil in situ interacts with different types of water having different water chemistries. Therefore, the swelling behaviour of expansive soils tested with distilled water would naturally be different from the behaviour of expansive soils tested with different water types and chemistries. For this reason, it was anticipated that determination of the realistic swell behaviour in laboratory experiments requires the use of the same water as in the in situ condition. In this article, the effect of the water type and chemistry on the swelling behaviour of the clays was investigated by testing the clay samples with eight different types of water collected from the sea, river, lake and different rock formations. The main result of this research was that the anticipated clay swell percentages and pressures for different types of water were lower than for the distilled water routinely used in testing.     

Effects of material and treatment parameters on noise‐control performance of compressed three‐layered multifiber needle‐punched nonwovens

The effects of material and treatment parameters on airflow resistivity and normal‐incidence sound absorption coefficient (NAC) of compressed three‐layer nonwoven composites have been studied. Material parameters included fiber size and porosity, and treatment factors included applied pressure and duration of compression. Fibers used included poly(lactic acid) (PLA), polypropylene (PP), glassfiber, and hemp. Three‐layered nonwoven composites were classified based on material content and fiber blend. LHL and PGP were sandwiched structures consisting of PLA/Hemp/PLA and PP/glassfiber/PP layers, respectively. PGI consisted of three layers of an intimate blend of PP and glassfiber. Statistical models were developed to predict air flow resistivity from material parameters and the change in air flow resistivity from compression parameters. Independent variables in the first model were porosity and fiber size and, in the latter model, were compressibility, pressure, and initial material parameters. An increase in air flow resistivity was found with increased compression. No significant effect of compression duration was detected. Two additional statistical models were developed for the prediction of sound absorption coefficient based on material and treatment parameters. The independent variables of the first model were air flow resistivity, thickness, and frequency, and those of the second model were compressibility, initial thickness, and initial density of the composite, diameter and density of the fiber, compression pressure, and frequency. A decrease in sound absorption coefficient was detected with increasing compression, while no effect of duration was detected. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dispersion in the inclined plane model of trickling filters

In this paper an attempt has been made to set up a relationship between the removal efficiency and the hydraulic regimes of biological filters. For this purpose an equation has been first derived to determine the dispersion number. Using this equation, effluent concentration has been calculated by means of dispersed plug flow model in the range of channelized flow, and for large hydraulic loadings. Around the minimum wetting rate, the removal efficiencies are computed with equation of complete mixing. The application of this theory to the experimental results reported in literature has also been shown and the ranges of validity of dispersed plug flows and mixflows are determined. It has been demonstrated that the predicted concentrations are in good agreement with the measured values.     

Analysis of user's characteristics of three different playgrounds in districts with different socio-economical conditions

During childhood, playgrounds have a great impact on development of children. Not only do well designed playgrounds help children fast problem solving ability but also increase their social interactive relationships. User surveys are sources of data to aid for planning, designing and management processing of playgrounds. The aim of this study was to investigate the characteristics of the playground users in districts which have different socio-economical structures in Erzurum. The study focuses on users of three different playgrounds, who belong to poor-middle-high income family groups. To identify the characteristics of playground users of three districts, a questionnaire survey was performed. Results were evaluated using Chi Square (χ²) Correlation Test.     

Investigation of timber harvesting impacts on herbaceous cover,forest floor and surface soil properties on skid road in an oak (Quercus petrea L.) stand

In this study, we investigated the timber harvesting effects on some soil properties (sand, silt, clay, pH, electrical conductivity, fine soil <2 mm, coarse soil >2 mm, root mass, organic carbon, moisture equivalent, total porosity, bulk density, moisture and compaction) at soil depths (0–5 and 5–10 cm), herbaceous cover and forest floor (unit mass, organic matter and moisture) on skid road of an oak (Quercus petrea L.) stand in Istanbul Belgrad Forest of Turkey.