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One of the most important characteristics that a filter must possess is high air permeability. A good filter fabric must be able to capture the dust particles while maintaining a good airflow through it in order to reduce high pressure drop. Therefore, producing a filter fabric with the desired air permeability can be challenging as several process parameters such as fiber types, area weight and water jet pressure will interact with each other during spunlacing process and influence the fabric air permeability. To study the effects of these independent variables on the air permeability of three different types of spunlaced fabrics, the Box–Behnken design was used to model their effects. The fibers used were polyacrylonitrile, polyphenylene sulfide and blend of polyphenylene sulfide/polyimide. In addition, filtration properties of some of the filter samples were also evaluated. Based on the effects of the fiber types, area weight and water jet pressure on the fabric air permeability, the optimum conditions for achieving higher air permeability were fiber types (+1 level), area weight (0 level) and pressure (−1 level), respectively. The air permeability of the fabrics decreased with increasing water jet pressure for all fiber types and increasing area weight decreased the air permeability. It was observed that the independent variables had a significant effect on the air permeability. Filtration efficiency of the selected filters samples were ≥95%. Among the selected samples, polyphenylene sulfide/polyimide (440 g/m2) fabric has the lowest pressure drop whereas polyacrylonitrile (560 g/m2) has the highest pressure drop.

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Determining the tensile strength of nonwoven fabrics is one of the important factors considered for operational performance of the fabrics, especially for fabrics that are exposed to acidic condition. Polyacrylonitrile (PAN), polyphenylene sulfide (PPS) and polyimide (PI) fibres are used to produce fabrics that can withstand harsh chemical condition and still possess the required tensile strength; however, over a period of time the tensile strength gradually decreases. The Box–Behnken design method results showed that it can model and describe the effects of process parameters on the tensile strength of spunlaced fabrics in both cross direction and machine direction. The contour plots’ results indicate that varying the fibres polyacrylonitrile (−1), polyphenylene sulfide (0) and polyphenylene sulphide/polyimide (1) from −1 to 1 increases the fabric tensile strength in both machine direction and cross direction. For water jet pressure 60 bar (−1), 80 bar (0) and 100 bar (1), increasing the pressure from −1 to 1 increases the fabric tensile strength in cross direction but in the machine direction the fabric strength decreases. Increasing the fabric area weight of 440 g/m2 (−1), 500 g/m2 (0) and 560 g/m2 (1) from −1 to 1 decreases the tensile strength. Exposing fabrics to sulphuric acid (H2SO4) decreases the fabric tensile strength in both machine direction and cross direction due to the degradation of the fibres and the loss decreases gradually with the duration of exposure. For PAN fabrics, the tensile strength decreases by 21% and that of PPS and PPS/PI fabrics decrease by 10% and 6%, respectively.