Self-bonding anisometric polymer masses and equipment for manufacturing them

Abstract

An anisometric polymer mass (APM) is a set of particles of complex form and relatively small size. The form of the particles, depending on preparation conditions, may be fibrous, dendritic-fibrous, film type, split-film type, or transitional between these. The length of the main stem of the particles is 0.1-10 ram, but most often it does not exceed 2-3 ram; and the diameter (thickness) varies in the range 2-50/~m; the number and length of the branchings are variable. A basic property of APM is their ability to undergo self-bonding in bulk, caused by the specific morphology of the particles. Self-bonding is assured by interweaving of the anisometric particles due to the flexible main branch of the particles and of the side branches with formation of a strong steric network. Thanks to this there is a possibility of obtaining both macrotwo-dimensional (sheet or band) materials and also of macro-three-dimensional (bulk) particles from APM only or in a composition with maumade fibres or other highly dispersed fillers. In particular, based on APM the following have been prepared and are widely used: very high classes of electrical insulating materials with respect to heat resistance; heat-resistant honeycomb constructions for flying apparatus and other forms of transport; and filter materials, including those for microfiltration, and others. In view of the specific and diverse morphology of particles of these masses, and their ability to undergo self-bonding and the process, mainly by the so-called vapor-making method, in the literature they are sometimes called fibrids (a hybrid of fibre and film), or synthetic pulps, or fibrous film binders (FFB) [1]. A number of ways are known for preparing APM directly from monomers, solutions, or polymer melts, or from twophase disperse systems or macromonolithic fibres or films. Selection of a manufacturing method is determined primarily by requirements for consumer properties in the end articles, and depends on the features of the raw material being processed and technico--economic indices in manufacturing. At present two ways of preparing APM have been realized on an industrial or pilot-plant schedule, called in technological jargon either hydrodynamic or explosive. The hydrodynamic method of preparing APM, whose block scheme is shown in Fig. 1, makes it possible to prepare a product from all soluble polymers, including in heat-resistant and high-boiling solvents. If we seek an analog in manmade fibre technology, this method may be formally assigned to the wet metho~ts, since it proposes the use of precipitation to separate the polymer from the solution. A description of this process in the part of interaction within the polymer--solvent--precipitant system may be performed from the thermodynamic, kinetic, or phenomenological positions, just as in spinning fibres by the wet method. The fundamental difference between spinning an APM and spinning fibres consists in the hydrodynamics of the process. In a short exposition it comes down to this, that while in fibre technology hydrodynamic processes should not negatively "affect the stability of the liquid polymeric jet, in APM technology the converse is true: the hydrodynamic processes are aimed at breaking up the polymer jet and elements in its breakdown to form liquid particles which are desired in form and dimensions and fixing them as a result of polymer solidification processes. The characteristics of the APM may be assigned by the type (Puazelian or Cuette) or by the regime (laminar, laminar spiral, or turbulent) of precipitation bath flow. And in essence the main scientific problem consists in separating in time the hydrodynamic phenomena and the processes which ensure polymer solidification. The observable hydrodynamic phenomena may be described on the basis of concepts previously developed in classical hydrodynamics. But by virtue of the complexity of the phenomena which take place in the variable field of a number of solution parameters (viscosity, density, surface tension, etc.), the results obtainable give only a qualitative picture. Standard equipment is used to make up and prepare the polymer solution and precipitation bath for spinning. Special types of apparatus have been developed for carrying out the spinning process: cylindrical (tank) with stirrers of various