The Impact of Fiber Dispersion on Filtration and Tensile Properties of Glass Fiber Filter Paper

Air quality control has become increasingly important in many industrial areas. Glass fiber filter paper is widely used for the collection of airborne particulate matter. Since glass fiber is fragile, fiber dispersion is believed to be important for controlling filter paper properties. In this paper, the impact of fiber dispersion on filtration performance and tensile properties was studied. Two types of glass fiber filter paper prepared from six different dispersing methods were used to analyze the impact of dispersion on filtration and tensile properties. Rotational viscosity was used to characterize the fiber dispersion process. Dispersing strength and time had no significant effect on filtration properties, namely the pressure drop, penetration and figure of merit. The fiber composition should be the determining factor of filtration properties. Dispersing strength and time had little effect on the virgin tensile strength of glass fiber paper, while the tensile strength retention after folding was highly affected by dispersion. It is suggested that fiber cutting should be reduced in the fiber dispersion process for higher tensile strength retention. INTRODUCTION Particulate matter control in the air is becoming crucial where requirements of air cleanliness are increasingly stringent. The food, biotechnology, pharmaceutical, semiconductor, micro-electronics industries and fields involving sensitive micromechanical work are among those industrial areas that demand air cleanliness as a prerequisite in everyday production [1]. Filters and other particle air cleaners are used extensively in buildings to remove particles from incoming outdoor air and from recirculated air to protect products, process equipment and personnel from being adversely affected by airborne contaminants [2, 3, 4]. For air filters, a crucial property is penetration or filtration efficiency, which represents the ability to capture particles. During the life cycle of a filter, the operating cost is considerably affected by pressure drop. Lower pressure drop means less energy consumption by air filtration systems [5, 6], which in turn leads to lower operating cost and longer service life. An ideal filter should have a low pressure drop and high capture efficiency [7]. The performance quality of filter media is typically characterized by figure of merit [8], which can be calculated by Eq. (1) ln( ) P Figure of Merit p − = ∆ (1) where P is the penetration ratio of the particle number concentration downstream of the filter media to the particle number concentration upstream and Δp is the pressure drop or filtration resistance, Pa. Mechanical properties of filers are also important. Good mechanical properties lead to good filtration performance. Mechanical property development in filtration media results from random and non-linear interactions between large numbers of fibers [9]. Tensile strength of a filter is defined as the maximum load it can endure without breaking when subjected to uniaxial tensile loading [10]. The pleating process is crucial to the development of filtration properties during the manufacturing of air filters. Pleating of filter media produces an increase in the filtration surface, and thus the particle collection efficiency. It also reduces the pressure drop, which increases filter life [11]. However, the pleating process may damage the filter media and cause leakage in the pleated part. The Institute of Environmental Sciences and Technology, IEST, recommends measuring the virgin tensile and creased tensile properties of filters as a means of evaluating the effect of pleating on the tensile strength [12]. In this study, these concepts are used to analyze the tensile properties for filter paper.