Dynamics of melt spinning processes accounting for the effects of flow-induced crystallizations has been studied by mathematical modeling and computers simulations of high-speed melt spinning [1-3] and pneumatic processes [4-8]. Axial profiles of melt spinning processes (polymer velocity, temperature, tensile stress and crystallinity as dependent on the process and material parameters are determined. Effects of crystallization on the dynamics of melt spinning and rheological behavior is discussed [1]. Effects of on-line zone heating during melt spinning of PET fibres was studied [2]. Crystallinity-dependent polymer viscosity results in limited take-up velocity and filament thickness and bifurcation leading to three regions of the processing conditions leading to amorphous, partly crystalline and inaccessible ranges [3].

     A model for stationary melt blowing of nonwovens [4-6] and pneumatic melt spinning by ultrasonic air jet in the Laval nozzle [7,8] is proposed and applied for iPP and PLA with the effects of on-line stress-induced crystallization on the polymer viscosity and rheological relaxation time. The role of the viscous friction heat in the polymer bulk has been discussed for fast air-drawing of the polymer melt. Axial profiles of the polymer velocity, temperature elongation rate, filament diameter, tensile stress, and extra-pressure were computed for the pneumatic processes of non-woven formation. The effects of the air-jet velocity, die-to-collector distance and polymer molecular weight are discussed. The model allows to discuss non-linear stress-optical relationship reflecting online molecular orientation, as well as online crystallization of the polymer filament if it occurs. Significant online extra-pressure in the filament was predicted in the case of supersonic air jets as resulting from polymer viscoelasticity, which could lead to longitudinal splitting into sub-filaments [5-7].

     The filament velocity at the collector increases significantly with increasing air compression, from the values typical for high-speed melt spinning up to values by two folds higher. The increase in filament velocity is limited by the effects of online oriented crystallization at higher air compressions. Influence of the inlet air compression, melt extrusion temperature and weight-average molecular weight on the axial profiles of the melt spinning functions is discussed, as well as on the development of amorphous orientation and online oriented crystallization.

 

Cross-sections of the longitudinal die assembly with the Laval nozzle and the example profiles of the axial air velocity and polymer velocity along the process axis computed for stationary PLA pneumatic melt spinning in the Laval nozzle [8].

 

[1]. Ziabicki A., Jarecki L., Sorrentino A., The role of flow-induced crystallization in melt spinning, E-POLYMERS, no. 072, 2004.

[2]. Blim A., Jarecki L., Effects of zone heating on PET fibers structures and dynamics of melt spinning process. Part II. Mathematical model), POLIMERY, 52, 686-700, 2007.

[3]. Ziabicki A., Jarecki L., Crystallization-controlled limitations of melt spinning, JOURNAL OF APPLIED POLYMER SCIENCE, 105, 215-223, 2007.

[4]. Jarecki L., Ziabicki A., Mathematical modeling of the pneumatic melt spinning of isotactic polypropylene Part II. Dynamic model of melt blowing, FIBRES AND TEXTILES IN EASTERN EUROPE, 16, 17-24, 2008.

[5]. Jarecki L., Ziabicki A., Lewandowski Z., Dynamics of air drawing in the melt blowing of nonwovens from isotactic polypropylene by computer modeling, JOURNAL OF APPLIED POLYMER SCIENCE, 119, 53-65, 2011.

[6]. Jarecki L., Błoński S., Zachara A., Blim A., Computer modeling of pneumatic formation of superthin fibres, COMPUTER METHODS IN MATERIALS SCIENCE / INFORMATYKA W TECHNOLOGII MATERIAŁÓW, 11, 74-80, 2011. 

[7]. Jarecki L., Błoński S., Blim A., Zachara A., Modeling of pneumatic melt spinning processes, JOURNAL OF APPLIED POLYMER SCIENCE, 125, 4402-4415, 2012.  

[8]. Jarecki L., Błoński S., Zachara A., Modeling of Pneumatic Melt Drawing of Poly-L-lactide Fibers in the Laval Nozzle, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 54, 10796-10810, 2015.