Analysis of thermal transitions in polycaproamide fibres

It was shown that the parallel use of mechanical and structural methods of investigation forms the basis for a more reliable interpretation of the thermal transitions in polymer fibres, polycaproamide fibres in particular. In studying the thermal transitions in PCA fibres at T > 293 K, three transitions related to crystallites and two related to unordered regions were observed. It was found that from a practical point of view, not only the relaxation transition caused by conformational changes in the main chain in amorphous regions of the polymer, i.e., the glass transition, but also the transition in crystallites at 440–450 K, where the level of the intermolecular interaction in the crystallites, which stop being strong physical nodes, decreases sharply, are important. This situation facilitates plastic deformation of the fibres at T > 450 K, which is important in selecting the temperature of orientational drawing and the optimum temperature of heat treatment of the fibres to remove internal stresses or rearrange the structure in a given direction. Translated from Khimicheskie Volokna, No. 5, pp. 48–52, September–October, 1998.     

Preparation of fire-resistant polycaproamide fibres

Conclusions A method had been developed for the preparation of fire-resistant polycaproamide fibres; it uses a three-component synergistic system of combustion retarders: boric acid + brominated pentaerythritol + antimony oxide.The effect of the synergistic system of combustion retarders is supported by the value of the oxygen index for the fire-protected polycaproamide fibres and by data from differential thermogravimetric analysis.Translated from Khimicheskie Volokna, No. 1, pp. 51–52, January–February, 1988.     

Prediction of creep of oriented polycaproamide fibres

A method of predicting permanent creep with dynamometric curves was proposed for oriented PA-6 monofilament. The curves of the changes in the modulus of elasticity in different stretching modes were used to estimate the effect of the change in the modulus of elasticity on the deformability of the monofilament in the creep mode.Blagoveshchensk Institute of Technology. Institute of Textile and Light Industry, St. Petersburg. Translated from Khimicheskie Volokna, No. 6, pp. 38–41, November–December, 1992.     

Degradation processes in texturing of vidlon polycaproamide fibres

It was found that during texturing, complex changes caused by degradation, primarily mechanical degradation, processes take place in the structure of PCA fibres. The most pronounced changes in the fibres are observed in texturing on FZ-27S machines, characterized by the highest degree of thermooxidative and mechanical degradation. The degradation processes that take place during texturing significantly affect the coloring of PCA fibres: fibres textured on FT-417 machines are colored at the highest rate. Ekomedbio EAD Business-Innovation Center, Sofia, Bulgaria. Translated fromKhimicheskie Volokna, No. 3, pp. 49–51, May–June, 1999.     

Sorptive properties of polycaproamide fibres containing antistats

Conclusions Modification of polycaproamide fibres with ethoxylated amines increases free volume and the combinatorial entropy of the polymer.The indicated changes in fibre structure cause an increase in their hygroscopicity.Bulgaria. Translated from Khimicheskie Volokna, No. 4, pp. 55–56, July–August, 1984.     

Increasing the fire resistance of polycaproamide fibres

It was found that the proposed impregnating compositions can be widely used in manufacturing difficultly combustible fibres with improved properties.     

Modification of polycaproamide fibres with ethoxylated compounds. Preparation of polycaproamide with antistatic properties

Conclusions The possibility of using diethylenetriamine which has been ethoxylated to various degrees to give antistatic properties to PCA has been discussed; the antistatic effect is expressed most strongly in the case of DETA 60.It has been found that the antistatics studied exert a regulating action on the degree of polymerization of the -caprolactam, displayed in a decrease in the molecular weight of the PCA and an increase in the LMC content of the polymer. This brought about by the fact that the products examined contain, even though in slight amounts, free amino groups. DETA 100 exerts the weakest action.Under otherwise equal conditions in PCA synthesis, the introduction of DETA increase the rate of polymerization in the initial stage of the process.In view of the effects described, it is advisable, in preparing PCA fibres, to use products which contain 60 to 80 moles of ethylene oxide.Bulgaria. Translated from Khimicheskie Volokna, No. 1, pp. 42–44, January–February, 1984.     

The problem of orientation strenghthening of polycaproamide fibres

It is shown that the absolute strength of PCA fibre at 291 K is almost independent of the preliminary draw ratio and the relative strength increases proportionally to the total draw ratio attained in orientation drawing and subsequent stretching at a constant rate. The values of the breaking load and total draw ratio of the oriented fibre can be lower than for the unoriented fibre. The data obtained suggest the existence of temperature-force conditions that allow significantly increasing the orientation draw ratio of PCA fibres.Translated from Khimicheskie Volokna, No. 5, pp. 20–21, September–October, 2004.     

Intensifying graft-polymerization in the process of modifying polycaproamide fibres

Conclusions -- The kinetics of the graft polymerization of dimethylaminoethyl methacrylate to polycaproamide fibre initiated by the redox systems Fe²⁺ - H₂O₂, Cu²⁺ - H₂O₂, and by an ROC containing a complex copper compound (Cu _c ²⁺ - H₂O₂) has been studied.-- An increase in the rate of graft polymerization, in the amount of grafted component, and the degree of useful conversion of the monomer has been found when the reaction is initiated by the ROS Cu _c ²⁺ - H₂O₂.Moscow Textile Academy. Translated from Khimicheskie Volokna, No. 3, pp. 11–12, May–June, 1992.     

Preparation of high-molecular polycaproamide on industrial units

Conclusions The possibility of preparing a high-molecular polycaproamide having a relative viscosity of 3.05–3.25, of improved quality, has been demonstrated on existing industrial apparatus, carrying out the final polycondensation process in a single step.An empirical relationship between the final value of the relative viscosity of polycaproamide and the reduced nitrogen flow rate has been formed.Translated from Khimicheskie Volokna, No. 4, pp. 40–41, July–August, 1985.     

Length changes in PAN fibres during their pyrolysis to carbon fibres

A systematic study of the shrinkage taking place during the carbonization of polyacrylonitrile (PAN) fibres is reported. Shrinkage occurs from 200°C to 1000°C, the extent of which has been found to depend on (a) the time of preoxidation, (b) the type of oxidizing gas and (c) the carbonization conditions. The carbonization shrinkage is found to be independent of length changes during the preoxidation but can decrease from the usual 23% to about 2% by applying tension during the carbonization. A reaction is proposed to explain the shrinkage between 600°C and 800°C. The strength as well as Young's modulus of carbon fibres of under-oxidized fibres can be improved by applying tension during the carbonization. It is further predicted that the mechanical properties of carbon fibres preoxidized to the optimal level would decrease if carbonized under excessive tension.     

Decontamination of the gaseous wastes in the manufacture of polycaproamide fibres

Conclusions Absorbers with a three-phase fluidized bed (centralized clean-up) and straight-through injectors (local clean-up) are very effective for decontaminating ventilation discharges containing caprolactam.The absorption process has been calculated in the recirculation of the absorbing agent in a closed loop.Translated from Khimicheskie Volokna, No. 2, pp. 57–59, March–April, 1983.     

Structural changes during the thermal stabilization of modified and original polyacrylonitrile precursors

A polyacrylonitrile (PAN) precursor fiber of a special grade for preparing carbon fibers was modified by the impregnation of an aqueous KMnO₄ solution. The effects of the modification on the lateral and morphology structure, related to the crystalline properties of both the precursors and preoxidized fibers, such as the orientation index, crystal size, and crystallinity index, were measured by wide‐angle X‐ray diffraction. For both modified and original PAN fibers, a comparative study of the changes of the elemental content during the process of preoxidation, the relations between the thermal stress and heat‐treatment temperature, and the effect of the modification on the skin/core structure of a preoxidized fiber were also introduced by the use of elemental analysis, optical microscopy, and so on. The modification of KMnO₄ was demonstrated to increase the density, increase the crystallinity index, increase the preferred orientation index, and decrease the crystal size for a modified precursor fiber and for a preoxidized fiber developed from a modified precursor fiber after a different heat‐treatment temperature. KMnO₄ also showed a catalytic action, accelerating the rate of preoxidation and reducing the time of thermal stabilization; this improved the homogenization of the cross‐section structure and led to an improvement in the tensile strength of 15–20% and an improvement in the elongation of 20–30% in the resulting carbon fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2047–2053, 2005