Dipayan Das

Study of oil sorption behavior of filled and structured fiber assemblies made from polypropylene, kapok and milkweed fibers

This article reports on oil sorption behavior of fiber assemblies made up of single natural and synthetic fibers as well as blend of natural and synthetic fibers when tested with high density oil and diesel oil. A series of filled fiber assemblies were prepared from 100% polypropylene, kapok, and milkweed fibers and another series of bonded structured fiber assemblies were prepared from a 70/30 blend of kapok and polypropylene fibers and a 70/30 blend of milkweed and polypropylene fibers. It was observed that the porosity of the fiber assemblies played a very important role in determining its oil sorption capacity. The polypropylene fiber assembly exhibited the highest sorption capacity (g/g) followed by the kapok and milkweed fiber assemblies at porosity <0.98. At higher porosities (above 0.98), polypropylene filled fiber assembly has poor sorption capacity due to large sized inter fiber pore. The kapok and milkweed fibers have intra fiber porosities of 0.81 and 0.83, respectively. All the fiber assemblies showed higher oil sorption capacity with the high density oil as compared to the diesel oil. As the kapok and milkweed fiber have low cellulose content, hence their slow degradation is an advantage in fresh and marine water applications. The good sorption capacity of kapok and milkweed fiber assemblies along with their bio-degradable nature offer great scope for structuring them into fiber assemblies with large porosity and uniform pores to have efficient oil sorbents.

Electret Air Filters

This review summarizes the research progress made so far on electret air filters used for separation of airborne particles from complex air stream. A set of different categories of these filters are delineated and the methods of manufacturing of these filters are described. The principles and mechanisms of filtration and modeling of pressure drop by these filters are analyzed. The filtration performance of these filters is discussed along with their specific advantages and limitations. The reliability of these filters is reported in terms of their charge storage capability. Many interesting inventions as reported on electret air filters in the recent patents are discussed. The latest regulations on air filters are described and how they are driving electret filter research is indicated. Specific research needs are highlighted with a view to further improve the filtration performance and long-term effectiveness of these filters.

An Investigation into Fiber Dispersion Behavior in Water with Reference to Wet-Lay Nonwoven Technology

This article reports on fiber dispersion behavior in water with reference to wet-lay nonwoven technology. The effects of fiber material characteristics and dispersion process conditions on the quality of the nonwoven webs were examined. The webs were characterized for their area-based uniformity by means of an imaging system in conjunction with quadrat analysis. It was found that the area occupied by the fibers in the webs followed the lognormal probability distribution and the angular orientation of the fibers in the webs followed the bimodal distribution. The web prepared by using scoured fibers was almost equally uniform as compared to the web prepared by using bleached fibers. The web made up of shorter and coarser fibers was more uniform than that made up of longer and finer fibers. The higher concentration of cationic surfactant resulted in more uniform webs. It was observed that the webs prepared at optimum stirring rate and dispersion time were found to possess the highest uniformity.

Optimal design of nonwoven air filter media: Effect of fibre shape

In this work, a series of needle-punched nonwoven filter media was prepared by using polyester fibres of three different cross-sections (circular, trilobal, and deep-groove) in accordance with a three-component augmented simplex lattice design. The experimental data of filtration efficiency and pressure drop were analyzed by means of response surface methodology. Statistical model equations were developed for filtration efficiency and pressure drop by using Design-Expert® software. The filtration efficiency and pressure drop were expressed as linear functions of proportion of fibres of different shapes. Statistical checks (ANOVA, R2 and p-value) indicated that these models were adequate for representing the experimental data. By means of contour plots, the effect of filter constituents on filtration performance was analysed. The filter media consisting of deep-grooved fibres exhibited highest filtration efficiency but at the cost of highest pressure drop. On the other hand, the filter media consisting of circular fibres displayed lowest pressure drop but at the cost of lowest filtration efficiency. As a compromise for simultaneously achieving maximum filtration efficiency of 61.52 % and minimum pressure drop of 13.6 Pa, the optimum mixture was predicted to consist of 53.7 % deep grooved fibres and 46.3 % circular fibres. The predicted response was found in close agreement with the experimental data. This demonstrates the effectiveness of the approach reported here for achieving good predictions, while minimizing number of experiments.

Studies on electro-conductive fabrics prepared by in situ chemical polymerization of mixtures of pyrrole and thiophene onto polyester

This article reports on development, characterization, and performance of electro-conductive textiles prepared by in-situ chemical polymerization of mixtures of pyrrole and thiophene onto a polyester fabric. It was observed that a mixture of pyrrole and thiophene at 4:1 molar ratio resulted in the lowest surface resistivity among all the mixtures and the individual monomers studied. This electro-conductive fabric exhibited exponential voltage-current relationship. Further, it showed substantial fall in surface resistivity under the exposure of ultra-violet radiation. Under the application of DC voltage across it, an exponential rise in surface temperature was observed and the coefficient of rise in temperature was found to be directly related to the duration of voltage applied. Further, when subjected to mechanical straining, it displayed a decrease in resistivity followed by an increase of resistivity.

Modelling of fibre orientation in fibrous materials

In this article, mathematical models of fibre orientation in fibrous materials are derived and demonstrated with the help of case studies of real fibrous materials. The theoretical results on fibre orientation in plane are found to be in good agreement with the experimental results obtained from real fibrous structures.

Alkali treatment on nettle fibers part II: design of experiment and desirability function approach to study enhancement of tensile properties

Abstract In this work, an attempt was made to enhance the tensile properties of nettle fibers by alkali treatment. The role of alkali treatment in determining tensile strength, elongation-at-break, and initial modulus of nettle fibers was examined using a fractional factorial design of experiments. Alkali concentration, alkalization time, alkalization temperature, drying time, and drying temperature were found to play significant roles in deciding the tensile properties of nettle fibers. Simultaneous optimization of tensile properties was performed using desirability function approach. The optimum alkali treatment yielded about 30% improvement in tensile strength, 71% improvement in elongation-at-break, and 9% reduction in initial modulus as compared to those of untreated nettle fibers.

Tensile behavior of staple fiber yarns part I: theoretical models

Abstract In this work, an attempt is made to create theoretical models on tensile behavior of staple fiber yarns and verify them with experimental results. While the first part of this work deals with model development, the second part reports on model validation. This part starts with a description of stress–strain diagrams of fiber and yarn. It then discusses the tensile behavior of twisted yarns according to helical model. Afterward, it proceeds to partial generalization of helical model by taking into account of the influence of fiber orientation distribution on fiber stress utilization in yarn. At the end, it provides a theoretical example for better illustration of the models. In the second part of this work, we report on comparison of the models with experimental results.

Studies on needle-punched natural and polypropylene fiber nonwovens as oil sorbents:

This article reports on oil sorption behavior of needle-punched nonwoven fabrics made from milkweed, kapok, cotton and polypropylene fibers using air-lay and carding technologies. The effects of fiber and fabric parameters on oil sorption and retention capacities, and oil sorption rate and fabric strength were investigated. Fabrics made using natural fibers such as milkweed and cotton were found to selectively absorb oil over water. Milkweed and kapok nonwovens displayed higher oil sorption and retention capacities as compared to cotton and polypropylene nonwovens. Further, milkweed and kapok nonwovens exhibited higher oil sorption rate as compared to cotton and polypropylene nonwovens. The porosity of nonwoven fabric was found to play a vital role in determining the oil sorption capacity. Although the web-forming technology did not affect the oil sorption and retention capacities and oil sorption rate, it affected the fabric strength significantly. Cotton nonwoven kept on artificial sea water for 10 days displayed very low water sorption capacity, although the nonwovens produced using natural fibers exhibited preferential sorption of oil over water and high oil sorption and retention capacities; which are advantageous in using them as oil sorbents to cleanup oil spills on oceans, but they offered low fabric strength. These findings indicate that further research works are required to improve the strength of natural fiber nonwovens for sustainable oil spill removal.

Optimization of charge storage in corona-charged fibrous electrets

This article deals with optimization of charge storage in corona-charged fibrous electrets by using desirability function approach in conjunction with design of experiments and response surface methodology of analysis. A set of fibrous electrets were prepared by varying the corona charging process factors namely applied voltage, charging time, and distance between electrodes in accordance with a full factorial design of experiment. The experimental data of initial surface potential and half-decay time were analyzed by using response surface methodology. The initial surface potential was found to be higher at higher applied voltage, longer duration of charging, and lower distance between electrodes. But, the half-decay time was found to be higher at lower applied voltage. Further, the half-decay time increased initially with the increase in charging time and distance between electrodes, but an increase in both the process factors beyond the optimum regions resulted in a decrease in half-decay time. As a compromise for the simultaneously achieving maximum amounts of 10.56 kV initial surface potential and 4.22 min half-decay time, the optimum charging conditions were found with 15 kV applied voltage, 29.4 min charging time, and 26.35 mm distance between electrodes. The predicted results showed close agreement with the experimental ones, which demonstrates the effectiveness of this approach for achieving higher charge storage in fibrous electrets.