Supermolecular structure of polymer fibres

Abstract

The problem of the structure of polymers in general and man-made polymer fibres in particular draws the continuous interest of researchers. The attention to this problem by production engineers who manufacture man-made fibres or process them into final products is based on the necessity of knowing the mechanism of formation of the structure of the polymer during spinning of fibres and predicting their behavior during use. We will limit the discussion here to the principal concepts concerning the organization of the structure of polymers in fibres alone and will cite illustrative and detailed published data to present these concepts. Following this restriction, if we successively examine the factors which determine the structural organization of the starting polymer and the structural features of the fibre manufactured from it, the following basic factors that affect the structure and properties of the fibre can be distinguished. The first factor which greatly determines the structural organiT~tion of the maeromolecules in the fibre, i.e., their reciprocal position and interaction, is the low kinetic mobility of the macromolecule as a whole, caused by the chain structure of the macromolecules, and the unusual mobility of the individual segments in this chain, which is a function of the structure and type of bonds between the elementary units (segments). Characterization of the macromolocules includes their power to form chemical or crystallization bonds between neighboring macromolecules. Continuous cross-linked structures in which the individual macromolecules have no kinetic independence can be created as a result. The next feature of polymers consists of their polydispersity with respect to the molecular weight, which in many cases makes the behavior of the polymers dependent on their fractional composition. Their phase inhomogeneity, related to both the regularity of the chemical structure of the macromolecules and noncompletion of phase transitions of the polymers both in the stage of synthesis and in the concrete conditions of technological operations in spinning of fibres (the.role of the "history" of the polymer materials), is an important property of polymers. Another important property of polymers is the heterogeneity of the maerostructure. It consists of the formation of both manifest, in the form of open or closed pores, and latent (hidden) boundaries between phase particles, which affects the kinetics of absorption of liquids and their vapors by the polymer. Finally, another main characteristic of polymers with respect to their structural organization is the presence of unrelaxed internal stresses in polymer materials. These stresses alter the structural organization of the polymer due to external mechanical effects, temperature conditions, and contacts with liquids or vapors which affect the glass transition temperature of the polymer and the appearance of segmental mobility in the macromolecules. As the list of the basic factors that determine the overall behavior of polymers (and thus the fibres made from them) and their structural organization indicates, there are two aspects of this problem. The first aspect concerns the molecular properties of the polymer which forms the fibre. The second aspect should be called the supermolecular structure. Although both aspects are closely correlated, it is nevertheless expedient to discuss them separately. The first aspect of the problem can be characterized as consideration of factors whose role is preferably determined by the chemical structure of the polymer, primarily the presence and structure of functional groups in the macromolecule, and *This article is a continuation of a series of reviews on physicochemical problems of the production and properties of manmade polymer fibres. Previous articles in this series were: "Problems of transport of solvents to polymers in production and use of chemical fibres" [No. 6, 9-13 (1993)] and "Swelling of man-made fibres as an important characteristic of their properties" [No. 3, 29-35 (1997)]. tDeceased.