Effect of supermolecular structure on the relaxation properties of polyformaldehyde in tension and compression

An experimental investigation of the stress relaxation at various strain values in polyformaldehyde blocks has revealed two regions with different stress relaxation mechanisms. The effect of the supermolecular structure on each of these regions is discussed.Scientific Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 787–792, September–October, 1969.     

Effect of structural changes on the sorptivity and mechanical properties of polyformaldehyde fibers

The dependence of the mechanical and sorption properties and structure of polyformaldehyde fibers on the degree of extension has been investigated. By x-ray structural analysis and sorption techniques it is shown that an increase in stretch ratio is accompanied by an increase in structural orientation with a simultaneous increase in porosity. It is established that the change in the mechanical properties associated with drawing depends both on orientation and on the presence of macrodefects in the fiber.Kiev Technological Institute of Light Industry. Translated from Mekhanika Polimerov, No. 6, pp. 1103–1106, November–December, 1971.     

Effect of molding conditions on fracture mechanisms and stiffness of a composite of grid structure

Methods of determining a complex of stiffness and deformability characteristics of a composite with rhomb-type grid structure were elaborated. Rhomb-type specimens were used for testing the ribs of the structure in tension, compression, and bending and the nodal points in shear in the plane of the ribs. The effect of additional tensioning of the ribs preceding the curing of the binder was investigated (ten tensioning levels ranging from 8 to 70 N/bundle with a linear density of 390 tex were applied). In testing epoxy-carbon specimens (UKN-5000+EHD-MK) in compression and tension, the failure mode changed depending on the tensioning level, i.e., the presence or absence of delamination and the appearance of dry fibers were detected. Dependences of the mechanical properties on tensioning were of a markedly pronounced extreme nature. The methods elaborated allow us to investigate the effect of other molding parameters, as well as the conditions and nature of loading, on the mechanical characteristics of composites.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 71–78, January–February, 1999.     

Effect of processing conditions on the supramolecular structure and strength properties of polycaprolactam

The formation of supramolecular structures in block polycaprolactam is considered. It is shown that technological factors have a considerable effect on the nature of the supramolecular structure. Two of these factors are the temperature gradient of the polymer melt and the nature of its motion in the cylinder of the injection molding machine up to the moment of injection into the mold. It is shown that the nonuniformity of deformation and the considerable number of defects associated with large supraspherulitic formations lead to a deterioration in the strength and deformation properties of polymers.Mekhanika Polimerov, Vol. 2, No. 5, pp. 659–663, 1966     

Effect of a filler,aging, and remelting on the distribution of the spherulitic structure in polyformaldehyde

The distribution of the spherulitic structure of a crystalline polymer has been experimentally investigated with reference to the example of polyformaldehyde (PF). Experimental histograms and distribution curves have been constructed for the distances between the centers of the spherulites in unfilled PF and PF filled with mullite particles of varying shape and size before and after aging and multiple melting. Similar data have also been obtained for the angles between the lines of centers of the spherulites. The results are closely correlated with the changes in the structure and the physicochemical and mechanical properties of PF accompanying the above-mentioned processes.Shevchenko Kiev State University, Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 1, pp. 11–16, January–February, 1971.     

Dynamic properties of teflons obtained under various molding conditions

The natural frequencies and decrements, velocities of sound, dynamic moduli of elasticity, and Poisson's ratios of teflon specimens have been investigated in relation to the nature of the starting powder and molding conditions. The optimal dynamic characteristics are determined and it is shown that chey can be used to optimize the molding conditions and control the quality of teflon products.Mekhanika Polimerov, Vol. 2, No. 6, pp. 917–922, 1966     

Investigation of the supermolecular structure of polyformaldehyde in an injection-molded block

The process of variation of the spherulitic and "superspherulitic" structure in an injection-molded block of polyformaldehyde has been investigated as a function of the molding conditions with allowance for the structural inhomogeneity of the block. The molding conditions corresponding to the formation of "superspherulitic" structures have been determined. The thermal stability of these structures has been investigated.Mekhanika Polimerov, Vol. 4, No. 3, pp. 394–401, 1968     

Some physicomechanical properties of polyformaldehyde (acetal resins)

A method of testing polyformaldehyde (acetyl resin) film has been developed. Comparative tests have been carried out on the homopolymer and trioxane-dioxolan copolymer. Certain physicomechanical characteristics of these polymers have been obtained.Mekhanika Polimerov, Vol. 3, No. 5, pp. 812–820, 1967     

Effect of the nature of the filler surface on the properties of phenol-formaldehyde molding powders

The physicomechanical properties and microstructure of phenolic molding powders containing fillers with different surface energies have been investigated. It has been found that an increase in filler surface energy leads to an increase in the density of the resin around the filler particles and hence to an improvement in the physicomechanical properties of the molding powder. A parallel investigation of a molding powder containing a lubricant shows that adsorption of the lubricant on the filler surface reduces the density of the resin, which is accompanied by a deterioration in the properties of the material.Scientific-Research Institute of Precision Engineering Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 677–681, July–August, 1968.     

Investigation of the supermolecular structure of polyformaldehyde in an injection-molded block. I

The supermolecular structure of polyformaldehyde has been investigated in an injection-molded block. This structure is a complex one in relation to the distribution of spherulites of various sizes and the ordering of the spherulites within the block.Mekhanika Polimerov, Vol. 4, No. 2, pp. 205–209, 1968     

Effect of powdered mineral fillers on the crosslinking of phenol-formaldehyde oligomers and the mechanical properties of the molding materials

By investigating the effect of various powdered oxides on network formation in phenolformaldehyde oligomers, it has been established that nonionogenic oxides increase the number of network defects in proportion to the surface energy of the powder. Small amounts of ionogenic oxides with a divalent cation cause the formation of new ionic or ionic-coordination linkages in the polymer network. The effect of mineral powders on polymer network formation is correlated with the mechanical properties of molding materials based on phenol-formaldehyde polymers with different network densities.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1033–1042, November–December, 1968.     

Effect of processing technology on the structure and properties of polypropylene

The methods of macro- and microstructural analysis are used to investigate the relation between the injection molding parameters, on the one hand, and the structure and physico-mechanical properties of the molded polypropylene block, on the other. It is shown that the structure takes the form of layers of different thickness and shape. Certain properties of molded products are determined not only by the spherulitic structure but also by the nature of the macrostructure of the polymer in the block.Voronezh Technological Institute. Translated from Mekhanika Polimerov, No. 2, pp. 200–204, March–April, 1971.     

Effect of fillers on the structure and properties of cured resins

The elastic (modulus of elasticity and equilibrium high-elastic modulus) and thermal (volume coefficients of thermal expansion below and above the glass transition temperature) properties of compositions based on ÉD-5 epoxy resin cured with polyethylenepolyamine have been investigated. Quartz powder and aluminoborosilicate glass powder were employed as fillers at concentrations from 0 to 0.413. The thermal expansion coefficients of the compositions were studied in a dilatometer, in which the specimen is free of mechanical loads. The Young's modulus at 25°C and the equilibrium high-elastic modulus at 125°C of the compositions were determined in the compression regime in an instrument based on the IZV-2 optical length gage. The thermal expansion coefficients of the polymer matrix were calculated with allowance for the elastic properties of the resin and the filler. It is shown that, as the filler concentration increases, the thermal and elastic properties of the resin in the filled system change. This can be interpreted as a change in the properties of the resin as it approaches the surface of the filler particles. Increased interaction between the filler surface and the epoxy resin tends to stiffen the polymer network.Scientific Research Institute of Precision Technology, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1018–1022, November–December, 1969.     

Effect of fillers on the structure and properties of cured resins

It is shown for the first time that the increased strength of filled plastics is associated with an increase of the internal pressure in the resin determined by the nature of the filler surface and the curing conditions.For communication 1, see [1].Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 54–58, January–February, 1970.     

Effect of structure on the mechanical properties of block copolymers

Experimental data are given on the transitions in three block types in styrene-butadiene copolymers; these transitions were obtained by the dynamic-mechanical method on a torsional pendulum in the –180° to +170° temperature range. Based on these data, kinetic aspects have been advanced on the nature of the transitions based on the formation and decomposition of supramolecular structures of varying type and dimensions.Voronezh Technological Institute. Translated from Mekhanika Polimerov, No. 5, pp. 774–779, September–October, 1972.     

Mechanical properties of polymers at 4.2°K and their dependence on chemical structure and the conditions of physical structure formation

Values of the modulus of elasticity, proportionality limit, and fracture strains and stresses have been measured at 4.2°K for polymers with different chemical structure and for a series of physically modified polymers. Relations have been established between the cryogenic values of the mechanical properties, the chemical structure of the macromolecules, and the conditions of formation of the physical structure of the polymer.     

Effect of formation conditions on the supermolecular organization and mechanical properties of polyethylene film

Films formed by extruding medium-pressure polvethylene through a flat-slot have a spherulitic supermolecular organization whose principal parameters (size and shape of the spherulites) are determined by the extrusion conditions. Thus, as the draw-down ratio increases, the radius of the spherulites decreases, and their degree of flattening relative to the direction of extension increases. Stretching these films leads to a transition from a spherulitic to an orientational supermolecular order, whose period is genetically related to the diameter of the starting spherulites. Films containing flattened spherulites have a yield point anisotropy opposite in sign to the degree of flattening. The mechanical anisotropy, like the degree of flattening, increases with increase in the draw-down ratio. The probable cause of flattened spherulite formation is the draw-down process, whose mechanical field may retard the radial growth of the spherulites in the take-off direction.Institute of High-Molecular Compounds, Academy of Sciences of the USSR, Leningrad. Scientific-Research Institute of Polymerization Plastics, Leningrad. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 207–212, March–April, 1969.