Preparation of ultra-thin fibres from polymer mixtures

Abstract

low linear density (0.12 rex), based on nonwoven, needle-punched materials, satisfies the requirements imposed on materials for shoe uppers in its basic properties, but has a number of important defects: an increased stiffness, and insufficient mobility of its "structural" elements, which shows up adversely in its comfort. The reason for these indicated defects is insufficient fineness of the elementary filaments whichform the structure of the nonwoven base of the leather. Natural leather is a unique natural composite material, the base of which is very thin collagen fibres, consisting of protein molecules. The transverse dimensions of the collagen fibres are 1-4 ~. Consequently, the decisive factor in the preparation of artificial leather which approaches natural leather in its properties is the preparation of ultra-thin fibres with cross-sectional dimensions of less than 10 ~ from fibre-formlng polymers. The technological and apparatus design of processes for the manufacture of man-made fibres which exists at present does not permit one to spin elementary filaments of such fineness from polymers, since the "noise-sensitivity" of the spinning process rises abruptly on reducing the diameter of the elementary filament below i0 ~ [2]. Th~s is especially true of the melt-spinning method, by which the polyester, polyamide, and po%yolefin fibres are produced which are most widely used in making artificial leather. This leads to an increase in breakage and nonuniformity in the linear density of the fibres obtained. At present, a number of specific methods of spinning ultra~hin fibres have been developed, which, in principle, can be used in the manufacture of a h~gh-quality artificial leather. These are: deformation of fibres with a high degree of s~retch (unoriented stretch) [3], spinning from an emulsion [4], electrostatic spinning [5], and others. However, its own set of difficulties arises in each of these methods, Contemporary textile technology equipment (needle punching, combing, or roving machines) which is used in the manufacture of nonwoven materials is practically unfit for processing such thin fibres. Therefore a compromise should be accepted between fibre (i.e., raw mater%al) fineness and the conditions of textile processing. In this connection, exceptional interest is being displayed at present in developments in the region of preparing ultrathin fibres via the stage of spinning them from polymer mixtures with a two-phase structure of the "fibrils in a matrix" structure (Fig. ib) or "island in the sea" type (Fig. la). The "fibr%is in a matrix" structure is characterized by a multiplicity of very thin fibrils of one polymer, disposed in an unordered fashion in a matrix of the other polymer. By an "island in ~he sea" type of struc