The Study Of Hydrophobicity And Oleophilicity Of 3D Weft-knitted Spacer Fabrics Coated With Silica Aerogels

Nowadays,industrial discharges,oil spills,and oily water wastages have constituted a dreadful hazard to the world’s ecological environment.These oily wastewaters and advanced manufacturing organic pollutants are not only posing a serious global threat to the environment but also creating a serious problem to the living beings.There are many methods for separating the oil from the contaminated zones,i.e.,flocculation,skimming,centrifugation,flotation,in-situ burning,chemical dispersion,and gravity separation.However,they have inefficient separation,higher operating costs,complicated machinery,and high power consumption.In order to separate oil from the polluted regions,mechanical oil recovery using sorbent material is the most widely used method due to its high removal efficiency,low cost,reusability,and so on.The interest in multifunctional textile materials has been increased due to the health and safety measures of living beings,especially in severe conditions.Therefore,different types of3D weft-knitted spacer fabrics（WKSFs）with various concentrations of silica aerogels（SAs）prepared by a sol-gel process are the deep attention of the present research work.The combination of 3D WKSFs and SAs has played an important role together with coatings for presenting a new sort of hydrophobic and oleophilic sorbent material.As an ideal oil sorbent material,3D WKSFs with SAs coatings have all properties,i.e.,light weight,hydrophobicity,oleophilicity,high oil absorption ability,retention ability,oil-water separation,buoyancy,wetting,wicking,spreading,intercepting,thermal properties,mechanical properties,bending properties,elastic properties,compression properties,and absorption selectivity.Moreover,they are extremely durable,efficient,reusable,cost-effective,and easy to produce.The classic and main research work of this thesis has been divided into five sections.In the first section:the study developed and investigated a new and innovative sorbent material for hydrophobic（water-repellent）and oleophilic（oil absorption capacity and retention capacity）applications with untreated or uncoated and treated or coated 3D weft-knitted spacer fabric samples（92%polyester/8%spandex）,i.e.,sample 1,sample 2,and sample 3,having thicknesses of 2 mm(300 g·m^-2),3 mm(350 g·m^-2),and 4 mm(540 g·m^-2),respectively,using silica aerogels（SAs）through the sol-gel method.SEM,ATR-FTIR,contact angle,surface roughness,and surface energy test of fabric samples were analyzed to comprehend the influence of SAs.The experimental results revealed the excellent hydrophobicity and oleophilicity of all the treated 3D weft-knitted spacer fabric samples,providing a higher water contact angle（WCA）of 142±0.84°and an oil absorption and retention capacity of（7.51±0.08 g/g and 87.06±0.34%）and（6.88±0.06 g/g and 90.22±0.31%）for vegetable oil and engine oil,respectively,especially of sample 2 owing to the most silica particles.The correlations among WCA,oil absorption,and oil retention capacity proved the better hydrophobic and oleophilic properties of the 3D samples.The hydrophobicity and oleophilicity outcomes were linear,where the r-square correlation fitting was around 0.985 and 0.983.Moreover,the results specified that the treated3D weft-knitted spacer fabrics showed excellent oil separation efficiency of more than 97.5±0.54%for oil/water mixtures.The fabric structures and silica aerogel add-on%played a vital role in the excellent hydrophobic and oleophilic properties.The statistical analysis also demonstrated a significant performance（P<0.05）of treated spacer fabric samples at the 0.05level.The overall outcomes of the samples were stable,which was confirmed by repeatable and reusable tests.Thus,these fabrics are suitable for an industrial application of hydrophobic and oleophilic properties.In the second section:the main objective of this study was to define the influence of silica aerogels（SAs）through the sol-gel method and oil properties on 3D weft-knitted spacer fabric sorbents for oil wicking,spreading,swelling,and interception properties（used as an interceptor barrier for vegetable and engine oil in static and dynamic water tests）.The characteristics like oil contact angle,oil absorption,oil retention,wetting,swelling,and bending were also explored.Surface and physical properties were analyzed through SEM.The experimental results revealed that all the treated samples have greater oil absorption capacity,retention capacity,and intercepting capacity.Most specifically sample 2（S2）showed highest outcomes followed by sample 3（S3）and sample 1（S1）,respectively.The dynamic oil spreading rate exposed that the higher porosity（87.54%）and the higher silica add-on（38.75%）unveiled the higher wicking height（78.4 mm and 72.6 mm）for vegetable and engine oils.The demonstrative oil leakage rate was alienated into 3 stages where oils drained sharply increasing,gradually lowering,and lastly steadily.The static water test exhibited the highest oil interception efficiency（98.80%and99.79%）with an initial leakage time of 28 min and 30 min while the dynamic water test exhibited the higher interception efficiency（98.75%and 99.67%）under the water flow rates of150 m L/s,and with the initial leakage time of 14 min and 17 min for both oils.Both dynamic and static conditions revealed excellent consequences in term of oil leaking and intercepting properties.However,the oil leakage occurred rapidly in dynamic condition as compared to the static condition.The untreated 3D sample 1 had a higher oil swelling thickness value of 7.8%,whereas the treated 3D sample 2 had a lower oil swelling thickness value of 1.4%after 7 days of immersion in oil.Moreover,the statistical studies on oil contact angle（vegetable oil and engine oil）and bending rigidity（transverse direction and longitudinal direction）proved a significant verification（P<0.05）of treated WKSFs at the 0.05 level.Hence,WKSFs are an inordinate encouraging eco-friendly sorbent substantial for various oil clean-up uses in water treatment.In the third section:silica aerogels prepared from tetraethyl orthosilicate（C8H20O4Si）by sol-gel method were coated on various 3D weft-knitted spacer fabrics（WKSFs）to study and compare the oil spill cleanup behavior in different temperatures（20°C,30°C,40°C,50°C,and60°C）,oil,and water medium.SEM and BET were used to observe the surface morphology and specific surface area of WKSFs.ATR-FTIR and XRD for the microstructure of fabrics were used to characterize the surface changes induced by the silica aerogel coating.TGA was performed to clarify the thermal degradation of WKSFs.The findings demonstrated that entirely the sorbents,particularly sorbent 2,ensured significant oil weight gain（%）and retention rate（%）in all cases.Sorbent 2(with a weight of 350 g·m^-2,a thickness of 3 mm,a stitch density of1.58/inch,a fabric density of 117 kg·m^-3,and a spacer yarn arrangement angle of 79.96°)showed a higher oil weight gain（%）and retention rate（%）of（（763±2.31%,758±2.08%,and740±2.52%）and（88.92±0.87%,88.74±0.68%,and 85.88±1.02%））for vegetable oil in temperature,oil,and water medium,respectively.Likewise,it revealed a higher oil weight gain（%）and retention rate（%）of（（698±2.65%,693±2.52%,and 673±2.65%）and（91.18±0.83%,90.82±0.75%,and 88.16±0.90%））for engine oil in temperature,oil,and water medium,respectively.The outcomes of vegetable oil weight gain（%）were higher than engine oil in all conditions（temperatures,oils,and water mediums）.Similarly,the outcomes of engine oil retention rate（%）were higher than vegetable oil in all circumstances.At 40°C,the coated samples exhibited the highest oil weight gain（%）and oil retention rate（%）.The correlations among WCA,oil weight gain（%）,and retention（%）indicated the excellent development of a new sorbent material,where the value of linear fitting curve was about 0.995.Moreover,Si O2aerogels treated 3D spacer fabrics exhibited a high self-cleaning ability,where the coffee powder was fully removed and cleaned by water.The statistical study revealed that coated WKSFs performed significantly at the 0.05 level（P=0.000）.The outcomes also revealed that the varieties of 3D fabric physical structures,specific surface areas,pore sizes,pore volumes,porosity ratios,water contact angles,silica aerogel add-on%,surface roughness,thermal behaviors,temperatures,and oil characteristics all played a significant effect on oil weight gain and retention capacity,especially in the oil spill cleanup performance.In the fourth section:five various concentrations of silica aerogels were made from tetraethyl orthosilicate by the sol-gel method and coated on the 3D weft-knitted spacer fabrics（WKSFs）to explain the interaction of the silica aerogel coatings.SEM,ATR-FTIR,surface roughness,surface energy,XRD,and BET analysis were used to observe and characterize the surface morphology,molecular interaction,surface changes,surface tension,and specific surface area of fabric samples or sorbents.Consequently,this study investigated the wettability,oil absorption capacity,oil retention capacity,and reusability of untreated and treated 3D WKSF sorbents.The outcomes exposed the excellent hydrophobic and oleophilic properties of all treated 3D WKSF sorbents,showing a greater water contact angle of 145.1±0.42°,and an oil absorption and retention capacity of（7.87±0.09 g/g and 7.53±0.06 g/g）and（89.98±0.79%and 92.48±0.56%）for vegetable oil and engine oil,respectively,with notable reusability,most particularly for sorbent 5,due to the higher silica aerogel add-on%,pore diameter,and pore volume.Moreover,the oil spreading rate exposed that the higher pore diameter,specific surface area,surface roughness,silica add-on%,water contact angle,and lower surface energy of sorbents exhibited the higher wicking height of 91.5 mm and 85.6 mm for vegetable oil and engine oil,respectively（TS 5）.Similarly,the static intercepting experiment showed the higher oil interception efficiency of 99.01%and 99.89%with the initial leaking time of 24 min and 26min for vegetable oil and engine oil,respectively.Likewise,the dynamic intercepting test（with water flow rates of 150 m L/s）revealed the higher oil interception efficiency of 98.89%and99.77%with the initial leaking time of 10 min and 12 min,individually.Moreover,after 7 days of immersion in oil,the treated sample showed the lowest oil swelling thickness（0.2±0.1%）whereas the untreated sample showed the highest oil swelling thickness（7.3±0.5%）.The findings verified that the chemical composition and fabric structure played an important role in the tremendous hydrophobic and oleophilic behavior.Besides,the experimental results discovered that silica aerogels,fabric properties,and oil features had a substantial impact on oil wicking,spreading,swelling,static,and dynamic tests.The statistical study on the specific surface area,pore diameter,pore volume,surface roughness,water contact angle,oil contact angle,oil absorption capacity,and oil retention capacity also revealed that treated fabrics performed significantly（P<0.05）in hydrophobic and oleophilic features at the 0.05 level.The progressive relationships were found among water contact angle,oil contact angle,oil absorption capacity,and oil retention capacity,where the r-square correlation of linear fitting was about 0.992.Hence,these fabrics could be used in industrial usages that need hydrophobic and oleophilic qualities.In the fifth section:the work investigated the thermal,mechanical,and oil absorption-retention properties in various temperatures（20°C,30°C,40°C,50°C,and 60°C）of 3D weft-knitted spacer fabrics（WKSFs）with optimal performance of silica aerogel coating that demands exceptional attention.Silica aerogels and（silica aerogels+poly（vinyl-alcohol））sols were prepared and coated on 3D WKSFs to study and compare the basic properties,i.e.,thermal resistance,thermal conductivity,tensile strength,initial modulus,compression,bending rigidity,wettability,oil absorption,and retention capacity.The SEM and FTIR studies were completed to understand the influence of both coatings on 3D WKSFs such as surface morphology and molecular interaction.The tensile,bending,and compression tests of 3D WKSFs were accomplished to check their durability,bendability,and compressibility.All the coated samples（both silica aerogels and（silica aerogels+poly（vinyl-alcohol）））showed greater thermal resistance of(0.0971±0.0003 m²KW^-1 and 0.0912±0.0005 m²KW^-1)and lower thermal conductivity of(0.0309±0.0001 Wm^-1K^-1 and 0.0329±0.0002 Wm^-1K^-1)with better thermal stability than the uncoated samples,most specifically coated sample 5（CS 5）.Besides,CS 5exposed higher oil absorption capacity of（（7.91±0.06 g/g and 7.88±0.06）and（7.56±0.04 g/g and 7.53±0.04 g/g））and retention capacity of（（90.10±0.53%and 89.07±0.55%）and（92.47±0.49%and 91.43±0.47%））for vegetable oil and engine oil in all conditions,especially at40°C.The water contact angles were found more than 145°and 143°for silica aerogel coated3D WKSFs and（silica aerogel+PVA）coated 3D WKSFs.The correlation between water contact angle and oil contact angle verified the successfully creation of hydrophobic oil sorbent material,where the r² correlation of linear fit curve was around 0.997.The outcomes demonstrated that both coatings played a vital role in the thermal,mechanical,and wettability properties of 3D WKSFs with statistically significant performance（P<0.05）at the 0.05 level.Moreover,these new types of sorbents（3D WKSFs）have better consequences in most cases than conventional plain knitted,woven,nonwoven,and/or hybrid sorbents.Hence,these 3D WKSFs could be used for industrial applications as eco-friendly and multifunctional oil sorbent materials.