Abstract:

Objective Bicomponent spunbond nonwovens have many unique advantages by virtue of the combination of two components, and are widely used in medical and health materials, battery separators, filter materials, oil-absorbing materials and other fields. The reinforcement method has a great influence on the properties of bicomponent spunbonded nonwovens. However, most of the previous studies focused on the influence of the process parameters of the preparation process on properties of the material, while the research on the reinforcement technology is still less. Therefore, it is imperative to study the effect of thermal bonding reinforcement on the properties of bicomponent spunbond nonwovens.

Method Polyethylene/polypropylene (PE/PP) sheath/core bicomponent spunbond nonwovens were successfully prepared by bicomponent spunbond technology with PE as the sheath component and PP as the core component. By means of scanning electron microscope, the longitudinal and sectional morphology of sheath core fiber was observed. With the help of filter material automatic tester, pore size tester, multi-function electronic fabric strength tester, thickness gauge, water permeability tester, air permeability tester, etc., the structure and performance of the spunbond nonwoven materials with different reinforcement methods were tested and characterized.

Results The surface morphology of the bicomponent fiber is smooth and the core are completely covered. The cross section of the bicomponent fiber presents sheath/core type, and the interface between the sheath component and the core component is obvious. After calender bonding, the rolling point area of the surface bonding of the bicomponent spunbond nonwoven material forms a "filmed" state, while the fibers that are not bonded by the rolling point still maintain the original shape. The bicomponent fibers reinforced by through-air bonding are melted and consolidated at the junction point, and the sheath component PE is melted and bonded with each other under high temperature airflow, while the core component PP still maintains its supporting role. The direction (MD) strength of calender bonding bicomponent samples is greater than the cross direction (CD) strength, while the elongation of CD is greater than the MD elongation. With the increase of surface density, the average pore diameter of the five kinds of spunbond nonwovens with surface density of 20, 35, 50, 65 and 80 g/m² decreased successively, which were 49.24, 40.37, 34.89, 27.92 and 25.74 μm, respectively. It shows that the stacking of multilayer fiber web increases the number of fibers in unit volume, resulting in smaller pores between fibers. Considering that the porosity will affect the air permeability and water permeability of the material, the air permeability and hydrostatic pressure resistance of the sample are also tested and analyzed here. The results show that with the increase of the surface density of the sample, the air permeability is 3 501.65, 3 389.77, 3 226.64, 2 743.38, and 2 513.20 mm/s, respectively, showing a gradually decreasing trend. The hydrostatic pressure resistance of the five materials is 0.39, 0.92, 1.37, 1.90 and 3.14 kPa respectively, which increases with the increase of area density, which obviously conforms to the influence law of pore diameter change. The through-air bonding bicomponent spunbond nonwovens perform better than the calender bonding samples in terms of low resistance, high dust volume and quality factor. When the test flow is 32 L/min and the median mass diameter of NaCl aerosol is 0.26 μm, the filtration efficiency of through-air bonding bicomponent spunbond nonwovens with a surface density of 80 g/m² after corona charging treatment is 76.62%, while the filtration resistance is only 15.85 Pa, and the dust holding capacity is 4.82 g/m². The phenomenon of "growing dendrites" formed by particles trapped and accumulated during the filtration of through-air bonding bicomponent spunbond materials.

Conclusion This paper mainly analyzes the influence of two kinds of thermal bonding reinforcement methods on the properties of the sheath/core bicomponent spunbonded nonwovens, and studies the fiber morphology, mechanical properties, pore size, hydrostatic pressure resistance, permeability, filtration performance and other indicators. Moreover, the filtration mechanism of the bicomponent spunbond nonwovens was analyzed. The filtration performance of the fiber filter material is closely related to the porosity. The larger the porosity, the smaller the filtration resistance and the higher the dust content. It is hoped that this study can provide a reference for the production and performance analysis of bicomponent spunbond nonwovens, and provide a new idea for the design of fiber filter materials.

Key words: polyethylene, polypropylene, bicomponent fiber, spunbond nonwoven material, thermal bonding, air filtration material, filtration mechanism, corona charging