A Research on the Air Permeability of High Polymer Materials Used to Produce Sports Clothing Fabrics

Composite fabrics based on Polytetrafluoroethylene(PTFE)polymer displays several notable properties.They are waterproof,windproof,permeable to moisture and thermally insulating at the same time.In the present study,PTFE fibers are used as raw material to make fiber membranes.The film is formed by crisscrossing interconnected fiber filaments and the related air permeability:tensile creep characteristics and other properties are tested.The results show that the pore size,thickness,and porosity of the film itself can affect the moisture permeability of the film.The water pressure resistance of the selected fabric is 8.5 kPa,and the moisture permeability is 7038 g/(m^(2)·24 h).

Anisotropic Structure of Glass Wool Determined by Air Permeability and Thermal Conductivity Measurements

We want to conclude on the interest of the “crimping” process used to produce the glass wool and to make a comparison for anisotropic factor obtained from structural property (air permeability) as well as thermal property (thermal conductivity and diffusivity). The main structural (densities, porosity, specific surface, air permeability) and the thermal (conductivity, diffusivity, heat capacity) characteristics of this glass wool are presented. Thermal results are determined by using several methods (Hot disc (HD), Heat Flow Meter (HFM) and Guarded Hot Plate).

Water-repellent efficiency of thermally modified wood as affected by its permeability

This study shows how the air permeability of thermally modified wood contributes to its water-repellent efficiency. For this purpose, freshly cut boards of hornbeam(Carpinus betulus), poplar(Populus nigra), and heartwood of oak(Quercus castanifolia) were modified at a steam temperature of 180 °C for 3 h inside a Thermo Wood kiln.The porous structure, permeability, and water uptake of wood were affected differently by thermal modification,depending on the wood species. The creation of microcracks in the cell walls, due to collapsing of fiber cells,resulted in a noticeable increase in the permeability of hornbeam. Despite checking in the poplar wood structure,its permeability was negatively affected by thermal modification. In contrast to oak and poplar, a negative waterrepellent efficiency was observed for the modified hornbeam, caused by an increase in the permeability.

Effect of H_(2)O_(2) Addition on Anti-explosion Performance of p-Al_(2)O_(3) Bonded Corundum Castables

In order to improve the anti-explosion performance ofρ-Al_(2)O_(3) bonded corundum castables,H_(2)O_(2) was added(0,0.025%,0.050%,0.075%,0.100%and 0.125%,by mass)as the anti-explosion agent.After mixing and casting,specimens were prepared.Some specimens were cured at room temperature for 12 h and demoulded for the anti-explosion performance test at different temperatures(450,500,550,600,650,700,750 and 800℃);the other specimens were cured,dried and fired,and tested in terms of the apparent porosity,the density,the cold mechanical properties,the air permeability and the pore size distribution.The results show that:(1)with the increase of the H_(2)O_(2) addition,the anti-explosion performance of castables increases gradually,the average pore size increases gradually,and the density and the strength decrease gradually;(2)by comprehensive consideration,the appropriate addition of H_(2)O_(2) shall be within 0.075%.

Prediction for permeability index of blast furnace based on VMD-PSO-BP model

The permeability index is one of the important production indicators to monitor the operation of blast furnace.It is crucial to grasp the trends of changes in the new permeability index in time.For the complex vibration spectrum of the permeability index,a prediction model of the permeability index based on the VMD-PSO-BP(variational mode decomposition-particle swarm optimization-back propagation)method was proposed.Firstly,the key factors that affect the permeability index of blast furnace were studied from multiple perspectives.Then,the permeability index was divided into multiple sub-modes based on the difference of frequency bands by the VMD algorithm,and a PSO-BP prediction model was established for each sub-mode.Finally,the prediction results of each sub-mode were summed to obtain the final one.The results show that the composite prediction accuracy by using the VMD algorithm is 3%higher than that of the traditional prediction method,which has better applicability.

Long-term Durability of Cement-based Materials with Very Low w/b

To investigate the durability, especially the long-term stability of cement-based materials with very low w/b, the air permeability test, carbonation test, capillary absorption rate test and dilation potential test were adopted under long-term heat treatment condition. Microstructure of these materials is also analyzed by scanning electronic microscopy （SEM） and mercury intrusion porosimeter （MIP） in order to further unveil its mechanism and interrelation between microstructure and its properties. The results indicate that in the area investigated, cement-based material with w/b 0.17, like RPC, possesses low porosity and excellent durability. Moreover, its porosity will further decrease under long-term heat treatment compared with normal heat treatment. Its long-term durability is much superior to that of other cement-based materials with w/b 0.25 or 0.35 as high strength concrete（HSC）.

Microstructure and Properties of PET Fabric Grafted by Polyacrylic Acid with Inverse Microemulsion Polymerization

Annual production output of poly(ethylene terephthalate)(PET) fiber has been over 15 million tons in China due to its good mechanical properties and processability,but the shortage of hydrophilic group of PET has imposed many limitations to further extend its application.The PET fabrics were grafted with polyacrylic acid in inverse microemulsion after low pressure plasma treatment,and the microstructure and properties of the grafted fabrics were investigated with infrared spectroscopy,scanning electron microscope(SEM),hydrophilic and mechanical tests.The grafting yield was increased with the grafting time.The grafting polymer was in the granular form with its particle size ranging from a few micrometers to a dozen of micrometers,normally smaller than the fiber diameter.The moisture regain and water uptake increased while the air permeability of the grafted fabrics decreased with the increase of grafting yield.The bending rigidity and tensile properties show slightly complicated behaviors with grafting yield.The inverse emulsion grafting technique can be used to control the grafting polymer architecture.

Comparative Study of Polypropylene Non-Woven Surgical Mask and Locally Manufactured Woven and Knitted Fabrics Facial Masks

The outbreak of coronavirus has led to an increase in the demand for facemasks globally. Unavailability of appropriate polypropylene non-woven fabrics face masks as a result of inadequate supply to satisfy the growing population has brought about the manufacturing of locally fabrics masks to augment or substitute standard medical class facemasks. The study aims at analyzing airflow of these locally manufactured fabrics to determine possible means of transmitting the virus as well as establish comfort of the user of these masks. Standard polypropylene non-woven, woven and knitted fabrics were considered for the study. Air permeability test was conducted on these fabrics using Frazier Air permeability tester. Depending on the property significant variation in the textile fabrics, polypropylene non-woven is widely accepted for facial masks. Nevertheless, this study illustrates that woven and knitted fabrics have more open structures, which allow a high rate of air penetration and so may require two or three layers to prevent antimicrobial or antiviral potential.

Highly stretchable,durable,and breathable thermoelectric fabrics for human body energy harvesting and sensing

Stretchable thermoelectrics have recently attracted widespread attention in the field of self-powered wearable electronics due to their unique capability of harvesting body heat.However,it remains challenging to develop thermoelectric materials with excellent stretchability,durable thermoelectric properties,wearable comfort,and multifunctional sensing properties simultaneously.Herein,an advanced preparation strategy combining electrospinning and spraying technology is proposed to prepare carbon nanotube(CNT)/polyvinyl pyrrolidone(PVP)/polyurethane(PU)composite thermoelectric fabrics that have high air permeability and stretchability(~250%)close to those of pure PU nanofiber fabrics.Furthermore,PVP can not only improve the dispersion of CNTs but also act as interfacial binders between the CNT and the elastic PU skeleton.Consequently,both the electrical conductivity and the Seebeck coefficient remain unchanged even after bending 1000 times.In addition,self-powered sensors for the mutual conversion of finger temperature and language and detection of the movement of joints to optimize an athlete's movement state were successfully fabricated.This study paves the way for stretchable thermoelectric fabrics with fascinating applications in smart wearable fields such as power generation,health monitoring,and human–computer interaction.

Use of the Appropriate Fabric for Cloth Face Mask: A Necessity in the Fight against COVID-19

The outbreak of coronavirus disease (COVID-19) has created a global health crisis that has had a deep impact on the way we perceive our world and our everyday lives. The call for the wearing of face masks as one of the ways of curbing the disease has resulted in the proliferation of cloth face masks on our markets. In the desperation to cash in on the season and make money at all costs, some manufacturers use inferior fabrics to produce face masks. Some of these fabrics do not meet the basic performance requirements of cloth face masks. This study was therefore carried out to research into the appropriate fabrics that will be suitable for the production of cloth face masks in terms of comfort, breathability and protection. To do this, 1225 participants were conveniently drawn for the study. The main research instrument employed for the study was the survey approach in which well-structured questionnaires were administered to solicit information from the participants. To determine the reliability and validity of data, the Cronbach’s Alpha test was conducted. Data were analyzed using the Stata statistical software to perform a multinomial logistic regression to estimate Odds Ratios (ORs) with 95% CIs. A multinomial logit model was constructed to determine the nominal variables. A major finding of the study was that people’s choice of fabric for cloth face masks is determined to a larger extent by their professions. The study also revealed that cotton, silk and linen possess good properties for the production of cloth face masks. Based on the findings, the study concludes that cloth face masks made from two-layered fabrics or three-layered fabrics are the best in terms of comfort and full protection of the wearer. It is recommended that the outer layer should be made from cotton and the inner layer made from linen, cotton-polyester blend or silk.

Impact of weather conditions and building design on contaminant infiltration from crawl spaces in Swedish schools-Numerical modeling using Monte Carlo method

Some Swedish school buildings built in the 1960s and 1970s experience indoor air quality problems,where the contaminants are suspected to come from the crawl space underneath the building.The poor indoor air quality causes discomfort among pupils and teachers.Installing an exhaust fan to maintain a negative pressure difference in the crawl space relative to indoors or increasing the ventilation in the classroom are two examples of common measures taken to improve the indoor air quality.However,these measures are not always effective,and sometimes the school building has to be demolished.The relation between pressure distribution,contaminant concentration in the classroom,outdoor temperature,wind,mechanical ventilation,and air leakage distribution is complex.A better understanding of these relations is crucial for making decisions on the most efficient measure to improve the indoor air quality.In this paper,a model for contaminant infiltration from the crawl space is used together with the Monte Carlo method to study these relations.Simulations are performed for several cases where different building shapes,building orientations,shielding conditions,and geographical locations are simulated.Results show,for example,that for a building with an imbalanced ventilation system,air is leaking from the crawl space to the classroom for the majority of cases and that concentration levels in the classroom are usually the highest during mild and calm days.

CFD analysis and experimental comparison of novel roof tile shapes

In tiled pitched roofs,a ventilated layer reduces the heat transfer between tiles and roof structure by means of natural and forced convection,thereby also reducing the cooling energy requirement.This effect could be enhanced by increasing the air permeability between the tiles by means of novel tile shapes,as proposed by the HEROTILE European project(UFE14 CCA/TT/000939),of which this work presents the preliminary analysis supporting the new tile designs.Using an experimental rig,the air pressure difference and the volumetric flow rate between tiles have been measured for an existing Portoghese tile design over a range of pressures.Then,in older to understand the air flows under different conditions,a three-dimensional computational fluid dynamics(CFD)model has been implemented to recreate the full geometry of the rig.The model was calibrated against the aforementioned experimental results,and ran with boundary conditions simulating different wind directions.Even in the low velocities typical of average local wind patterns,the fluid dynamic problem remains complex because of the geometry of the gaps between the tiles.analytical relationship between pressure drop and flow rate,taking into account the open area.The results have shown how the wind direction affects the air permeability and,therefore,important insights have been gathered for the design of novel tiles.