Targeted Control of the Structure Formation Process in Production of New Synthetic Leathers

Abstract

677.494.027.622 A. V. Lavrent'ev, and M. V. KalininWe have conducted systematic studies and provided a scientific basis for approaches to development of polyester urethane synthetic leathers based on a nonwoven base fabric, obtained by electrocapillary spinning. We propose a modified technology allowing us, with no additional costs or any increased environmental risks, to expand the range of competitive synthetic leathers with a heteroporous type of porous structure, leather-like organoleptic properties, and good performance parameters.Some of the major load-bearing elements in modern synthetic leathers are nonwoven fibrous base fabrics which traditionally are obtained by aerodynamic forming of the web from a blend of polyester (PET) and polypropylene (PP) (70:30) fibers, followed by needlepunching and heat shrinking. Such materials are rather thick, which results in the need for splitting them into 2-3 layers and buffing to simulate the organoleptics of the backside of natural leather. The linear density of individual fibers in such fabrics ranges from 0.33 to 0.44 tex, surface density ranges from 350-700 g/m 2 , bulk density 150-220 kg/m 3 , total porosity 76%-80%.Recently in production of synthetic leathers, multifibrillar fibers have been increasingly used with linear density 0.1-0.01 tex and diameter of a few micrometers, which are obtained from bicomponent "matrix (generally high pressure polyethylene) -fibril (polyester)" fibers as a result of extraction of the matrix by a boiling organic solvent (xylene, toluene, etc.) from an already formed nonwoven base fabric that has been treated with a polymer binder.This production process (which is rather complicated from the standpoint of ensuring environmental friendliness) is aimed at reducing the dimensional characteristics of the fibers in the nonwoven fabric, changing the structure of the fibrous web, increasing their total porosity (up to 90%-95%), their heteroporosity, specific surface area, and vapor permeability without changing the hydrophilicity and sorption activity relative to water vapor.In this work, in order to solve similar problems we have used electrospinning of nonwoven materials as a possible method for obtaining highly porous structures made from a wide variety of polymers, including hydrophilic polymers.In selecting a spin dope for electrospinning, we started from the necessary condition that the nonwoven fabric be insoluble in dimethylformamide (DMF), taking into account its subsequent soaking in a polyester urethane (PEU) solution, and also the increase in hydrophilicity of the finished material for comfortable human use.From a wide range of analyzed polymer solutions used to obtain the materials by electrospinning that satisfy these requirements, we selected a solution of PA 6/66 polyamide in a mixture of ethanol and water in 70:30 wt.% ratio. As a fiber-forming hydrophilic polymer, PA is insoluble in DMF and is quite compatible with PEU.The fibers were obtained on a electrocapillary pilot plant (Laboratory of Electrospinning of Fibrous M...

Microstructure analysis of polyurethane based polishing materials

“…Все вышеперечисленные структурные признаки свидетельствуют о формировании пористости материала методом фазового разделения раствора полиуретана в среде нерастворителя, при этом состояние поверхностного слоя, состоящего из достаточно больших по диаметру пор неправильной формы, чередующихся с участками мелкопористой структуры, позволяет сделать предположение о применении специальных условий структурообразования как на стадии приготовления растворов, так и на стадии их фазового разделения в осадительной ванне, которые обеспечивают определенные кинетические условия процессов, приводящих к отсутствию на поверхности материала «барьерного» слоя из мелких пор [10,11].…”