INTRODUCTION: Nonwoven webs prepared through the melt-blowing process of polypropylene (PP) are widely used for various applications such as the filtration layer in multi-layered masks. Preparation of webs consisting of fibers with thinner diameters is required for the improvement of filtration properties. Reduction of the through-put rate and increase of the speed of blowing air in the melt-blowing process generally leads to the production of thinner fibers, however, fiber diameter distribution tends to become wider under extreme conditions. In this research, PP for the melt-blowing grade was modified by blending a small amount of long-chain branched PP to improve the occurrence diameter fluctuation in the melt-blowing process and thereby reduce the average fiber diameter. EXPERIMENTAL: The polymers used in this research were linear polypropylene melt blowing grade (STD-PP, MFR = 1500 g/10 min) and long-chain branched polypropylene (LCB-PP, MFR=9 g/10 min). Melt-blowing of the blend of STDPP and LCB-PP was performed using an extrusion system equipped with a melt-blowing spinning head of 10 cm width, where 10 nozzles of 0.2 mm diameter were evenly arranged. Spinning behavior near the nozzle was observed using a high-speed camera. The diameter distribution of the fibers in the melt-blown web was analyzed using a scanning electron microscope. The specific surface area of the webs was analyzed using a constant volume adsorption apparatus. RESULTS AND DISCUSSION: Observation of the melt-blowing process near the spinneret using a high-speed camera revealed the occurrence of fiber diameter fluctuation of high frequency. The degree of diameter fluctuation intensified when production of the fibers of small diameter was attempted, and the melt-blown webs consisting of fibers with bi-modal diameter distribution were produced. It was found that the introduction of low MFR long chain branched PP suppressed the decrease in elongation viscosity in the high strain rate range, and eventually spinning was stabilized. The impact of each element, i.e. suppression of elongational viscosity reduction and enhancement of stabilization, changed with the concentration of LCB-PP. Stable spinning reduced the peak diameter of thick fibers in the web and thereby narrowed the fiber diameter distribution. Eventually, the optimum concentration of LCB-PP was found to exist, where the formation of webs with minimum average fiber diameter and maximum specific surface area was accomplished as shown in Figure 1 [1]. [ABSTRACT FROM AUTHOR]