L. S. Pinchuk

Melt Blowing Techniques

The melt blowing technique presents the unique possibility of varying the structure and properties of fibrous materials across a wide range, which attracts plastics manufacturers and designers. This variation might be realized at any stage of material molding, beginning with extrusion till cohesive bonding of cooled fibers on a substrate.

On the Mechanism of Thermoplasts Modification by Ultradispersed Inorganic Fillers

Abstract The polarizing mechanism enhancing service characteristics of thermoplasts filled with ultradispersed inorganic compounds (SiMeON) obtained by plasma-chemical synthesis has been studied. The results of examining spectra of thermostimulated currents and polarizing charge surface density of filled polyethylene, polyvinyl butyral and polytetrafluoroethylene have proved the presence of a spontaneous electric charge in the filler. Experiments have been conducted to simulate the effect of the filler particle electric field on the strength and permolecular structure of contacting surface layer of the polymer. Recrystallization of the binder in electric field of the filler particles is shown to result in varying crystalline structure and phase transition temperature as well as increased strength of the polymer surface layers at the filler particle boundary. The formation of filled by ultradispersed particles polymer material is accompanied by generation of the polarizing charge in the binder. The mechanism of polarization complements traditional ideas on physico-chemical nature of polymer filling.

Specific Properties of Melt-Blown PFM

The specific structure of melt-blown materials conditions their unusual service characteristics. which are determined by porosity. the large specific area of PFM, and the high physicochemical activity of the fiber surface layer. Such activity is caused by the specifics of the melt blowing process when fibers are formed from the polynmer melt at the boundary of thermal-oxidation destruction. Melt blowing leads to the generation of a spontaneons polarizing charge. which imparts unexpected properties to PFM. Some of them are considered in this chapter.

Magnetic Filtering PFM

The V.A. Belyi Metal-Polymer Research Institute of NASB (MPRI) has elaborated a new class of filtering materials — magnetic PFM [1-8]. The technological base for manufacturing such materials is the melt blowing technique involving the following procedures: extrusion of a polymer melt filled by ferrite (barium or strontium) powder, fiber extension by gas flow, and fiber treatment in a magnetic field. The polymer melt is extruded through spinneret holes whose diameter far exceeds that of the filler particle. The thermal regime of spraying provides for cohesive bonding of the fibers on the forming substrate. The material is also textured during spraying. The final stage of magnetic PFM or finished FE manufacture is filler particle magnetizing in a permanent or pulse magnetic field.

Structure of Melt-Blown Polymer Fibrous Materials (PFM)

The Method of melt blowing differs essentially from traditional methods of plastics processing. It proceeds at the boundary of oxidizing destruction of polymers when their technological properties are specified by low viscosity of the polymer mass in a viscous-flow state. This brings about active oxidation of the fiber surface layer, and intensified adhesive interaction between fibers and solid modifiers. The indicated phenomena. together with adsorptive interaction of fibers with modifiers in a liquid or gaseous state, condition the specific structure of melt-blown materials. They are characterized by the fiber diameter, the density of cohesive bonds hetween fibers. the porosity of the fibrous mass, the modifier concentration, etc. The structural parameters are determined by the technological regimes of material manufacture.

Fibrous Materials in Filtration Systems

One of the most positive trends in melt blowing technology is the production of fibrous materials for filtering systems. Filtration is the motion of liquids or gases through a porous medium. Liquid or gaseous media are separated from contaminants during filtration. In the process of filtration suspensions or aerosols are separated by porous screens letting liquid or gas pass but keeping solid particles back. Filtration is performed by filters whose major part is the filtering element (FE), which is a porous screen made of a filtering material (FM). A diversity of filtration conditions exist (various sihes and types of contaminants, volumes of media being filtered and velocity of filtration, degree of cleaning, and so on) which determine the use of a wide range of FM, including paper metal meshes, synthetic and natural fabric and fibers, porous plastics, and powder materials. Melt-blown polymer materials occupy their own merited place within the combinations of synthetic FM and are efficiently used in the techniques of purifying technological and working media, as well as industrial wastes.

Electret Filtering PFM

Cleaning of air and gas from suspended solid and liquid particles is of paramount importance in medicine, biochemistry, dectronics, the atomic power industry and many other fields. The most simple, reliable and economical way of cleaning gaseous media of highly dispersed aerosol is using filters with a fibrous FE. The search for highly efficient purification systems able to remove submicron particles from air has led to the development of electret filters consisting of a FE with charged polymer fibers [1-4].

Ecological and Social Problems

By now, the volume of consumption of melt-blown materials has reached a critical point in response to the perceptible influence of those products on society and the state of the environment.

Adsorptive and Microbicidal PFM

Adsorptive PFM are designed for combined deep filtration of industrial sewage where fine suspensions of solid particles, emulsified petroleum products, dissolved heavy metal salts, organic toxicants, and detergents are present simultaneously in significant variations in pH and waste composition.

PFM as Carriers of Microorganisms

A present trend in industrial technologies is the growing role of catalytic biotechnological systems, in particular, systems for biologically cleaning air and water by employing of biologically active polymer materials (BAPM). The functional mechanisms of these materials (where a high molecular weight matrix is the carrier of live cells of microorganisms, plants, animals, or men) are governed by the metabolism of immobilized cell cultures under given conditions. The rapid widening of the BAPM range in recent decades can be attributed to the strengthening of the biotechnology sectors in a number of the vital domains of economy, including fine organic synthesis, the pharmacentical and food industries, medicine, agriculture, and industrial ecology [1].