Undrawn Fibers Research Articles

Effect of drawing on creep fracture of polypropylene fibers

AbstractThe ultimate properties of polypropylene fibers, prepared by drawing the same undrawn fibers to different draw ratios, were determined by the creep fracture method at temperatures from 40 to 120°C. The composite curves of the engineering stress at break, the true stress at break, the ultimate extension ratio were constructed as a function of reduced time to break by assuming time–temperature superposition. The temperature dependence of the shift factor aT used in the superposition could be represented by a single equation of the Williams, Landel, and Ferry form. The composite curves of the true stress at break for the samples with different draw ratios were almost the same independently of draw ratio. The composite curves of the ultimate extension ratio for these samples could be reduced to a single curve by assuming that the ultimate extension ratio evaluated with respect to the unit length of the undrawn fibers were constant independently of draw ratio if the time to break and temperature conditions of the measurement were fixed constant. A possible fracture mechanism is discussed on the basis of the fracture mechanisms proposed by Samuels and Peterlin.

Physical aging of drawn polypropylene fibers

Drawn fibers of polypropylene have been shown to undergo spontaneous stiffening during storage for several weeks at room temperature after being quenched from higher temperatures below the melting region. The effect occurs in both drawn and undrawn fibers and does not depend on the details of heat treatment prior to the quench. Stress relaxation and density data are in quantitative agreement with an explanation in terms of a gradual collapse of free volume during storage. The effect appears to be identical to “physical aging” previously observed in isotropic molded samples of polypropylene.

Copolyester studies. VI. Melt spinning and mechanical properties of tetramethylene terephthalate–poly(tetramethylene oxide) random block copolymers

AbstractFibers were prepared from tetramethylene terephthalate–polytetrahydrofuran (PTHF) random block copolymers, containing the latter in the range of molecular weights 1000–5000 with up to 30% by weight incorporation, using a conventional melt spinning technique. The spinnability of the copolymer and the mechanical properties of these undrawn fibers were evaluated. The changes in mechanical properties brought about by the incorporation of PTHF groups in 4GT units were related to the PTHF block size and content in the copolymer. X‐ray diffraction data are also discussed briefly in terms of the structural differences.

Copolyester studies. IV. Dyeing behavior of drawn and undrawn fibers derived from tetramethylene terephthalate–tetramethylene sebacate copolymers

Drawn and undrawn fibers of tetramethylene terephthalate–tetramethylene sebacate copolymers, containing up to 20 mol % of the latter, have been dyed in an infinite dyebath with a disperse dye. The dyeing process has been interpreted in terms of the equilibrium dye absorption, the half-time of dyeing, and the diffusion coefficient. Increasing sebacate content has been found to have a marked effect on the rate and level of dye uptake. Deviations from Fickian behavior have been observed for the drawn fiber and related to presence of voids.

Copolyester studies. III. Melt-spinning, drawing, and mechanical properties of tetramethylene terephthalate–tetramethylene sebacate copolymer fibers

Fibers have been prepared from tetramethylene terephthalate–tetramethylene sebacate copolymers, containing up to 20 mol % of the latter, using a conventional melt-spinning technique. The mechanical properties of these undrawn fibers and of highly oriented fibers prepared from them have been evaluated. The changes in mechanical properties brought about by the introduction of sebacate groups in poly(tetramethylene terephthalate) have been related to the glass-transition temperatures of the copolymers and to the flexible nature of the sebacate unit. The formation of voids during a continuous drawing process and during mechanical testing is discussed.

The Radiation-Induced Grafting of Vinyl Monomers to Polyethylene Terephthalate Fibers. Part I. Styrene

Abstract Some kinetic features of the mutual radiation grafting of styrene to polyethylene terephthalare fibers have been investigated. The effects of type of swelling agent, monomer concentration, and temperature have been determined. In general a maximum in the grafting rate was found to occur both with the concentration of swelling agent and with temperature. Undrawn fibers were found to graft at higher rates and maximum yield than drawn fibers. These and other features are discussed in terms of a simple grafting scheme coupled with diffusion controlled kinetics.

TREATMENTS OF POLY-γ-METHYL-L-GLUTAMATE FIBERS WITH SULFURIC ACID

Undrawn and drawn poly-γ-methyl-L-glutamate (PMLG) fibers having different secondary structures were treated with 18N sulfuric acid, and the apparent weight loss was measured. From quantitative analysis by infrared spectra of the hydrolysis degree of side chain ester groups in insoluble residue, the apparent weight loss was devided into the weight loss due to hydrolysis of main chain and that of side chain. Besides, the density and intrinsic viscosity of insoluble residue were measured, and the accessibility of PMLG fibers to sulfuric acid is discussed in connection with secondary structures. The results were as follows;(1) In both PMLG fibers, the weight loss due to hydrolysis of main chain proceeds at two stages, the early stage of higher rate and the later one of lower and constant rate. The former is considered to be due to the dissolution of more accessible amorphous region from the decreasing behavior of intrinsic viscosity of insoluble residue. The weight loss due to hydrolysis of main chain in the first stage is larger in undrawn fiber and therefore it is considered that undrawn fiber has larger accessibility than drawn fiber.(2) Density of insoluble residue supports quantitative analysis of the hydrolysis degree of side chain by infrared spectra.(3) The difference of accessibility to sulfuric acid between undrawn and drawn fibers was concluded to be caused by the following facts. Since random-coil structure is difficult to be recognized in both fibers, the region where α-helix dose not stand side by side but stand random situation in undrawn fiber decrease during the α→β transformation by drawing.

WET SPINNING OF POLYGLUTAMIC ACID FIBER

The polyglutamic acid (PGA) fibers were spun from concentrated poly-sodium-L-glutamate (PSLG) aqueous solution, using inorganic acids such as HCl, H2SO4 and H3PO4, as coagulant. The relations between the spinning conditions, such as drafting and drawing and the properties of the spun fibers, such as the molecular conformation the crystallinity and the mechanical properties were investigated. The molecular chains of undrafted and undrawn fibers have the α-helix conformation regardless of acids used as coagulant, and the crystals were unoriented. On the other hand, the conformation of molecular chains of drafted and drawn fibers depended on acids as coagulant. The crystals comprised of molecular chains with β-structure were formed and the well-oriented fiber was obtained when H3PO4 was used as coagulant. The crystals of H2SO4-coagulated fiber were a mixture of α-helix and β-structure. However, with HCl-coagulant the α-helix conformation did not change and the crystals were oriented. The mechanical properties and the stability of the fibers against hot water varied widely depending on the acids used as coagulant and the spinning conditions. The fiber spun with H3PO4 coagulant was more stable against water than those spun with other coagulants.

SOME MECHANICAL PROPERTIES OF POLYETHYLENE-POLYPROPYLENE BLEND FIBERS

Polyethylene-polypropylene blend fibers were prepared from the melt-blended mixtures of lowpressure polyethylene and isotactic polypropylene at the weight ratios of (100/0), (95/5), (90/10), (80/20), (60/40), (40/60), (20/80), and (0/100). The spinnability and drawability of the blend polymers are nearly the same as those of polyethylene or polypropylene alone. Orientation of polyethylene or polypropylene molecules during drawing seems to be scarecely inhibited by blending. Some mechanical properties of undrawn and drawn fibers were investigated in terms of the composition. Undrawn fibers: The blend fibers show slightly lower yield stress, lower elongation, and higher tensile strength in comparison with polyethylene or polypropylene fibers. These effects can be elucidated by the decrease in crystallinity, and by the difficulty in slippage of molecules in the boundary layer of polyethylene and polypropylene phases in the blend fibers.Drawn fibers: The tensile strength, elongation, and Young's modulus of the blend fibers are, in most cases, between those of polyethylene and polypropylene fibers in the same drawing condition, and increase or decrease monotonically with the composition. Knot strength-composition curve has a maximum at the polypropylene content of 50_??_80%. At the maximum, the ratio of knot strength to tensile strength exceeds 90%. Elastic recovery of the blended fibers containing more than 40% of polypropylene is nearly the same as that of polypropylene which is much better than polyethylene in elastic properties. These anomalous, but favorable properties in the blend fibers are supposed to be derived from the fact that the blend polymer does not form so-called the “sea-island” structure, but forms the “network” structure which consists of isolated continuous phases of polyethylene and polypropylene.

Some observations concerning the behavior of polypropylene polymers and fibers

Data are presented which characterize the behavior of fibers produced from polypropylene polymers under experimental conditions designed to investigate the effect of extrusion temperature on various properties. At high extrusion temperatures molecular weight degradation takes place which results in a lowering of the average molecular weight and a narrowing of the molecular weight distribution. The orientation and crystallinity characteristics of the undrawn fibers also vary with extrusion temperature. The crystal structure of the fibers shows a gradual transformation from a highly ordered monoclinic crystal structure to paracrystalline structure of lower orientation as the extrusion temperature is increased. Drawing of the undrawn fibers of various molecular weights has been characterized by dynamic stress-strain curves and followed by sonic velocity measurements, the results of which suggest in agreement with other methods that the reduction in crystallinity during drawing is a function of the undrawn crystal structure, the drawing rate, and the drawing temperature. Drawn fibers produced from 21 isotactic polymers have been compared for tensile strength behavior by selecting fibers at the same average molecular weight but with different molecular weight distributions and also with similar molecular weight distributions but at different average molecular weights. These comparisons have shown that at a common draw ratio the tensile strengths of the fibers are lower for those fibers with broad molecular weight distributions when compared to fibers with narrow molecular weight distributions at same average molecular weight. The data also show that the tensile strengths of the fibers of the same molecular weight distribution and crystal structure increase with increased average molecular weight.

Differential thermal analysis of synthetic fibers

AbstractThe application of differential thermal analysis (DTA) for the characterization and the investigation of the thermal degradation of synthetic textile fibers, to include polyester, nylon 6, propropylene, and polytetrafluoroethylene fibers, has been studied. The temperature range was from 50 to 650°C. using laboratory‐built DTA apparatus. Experimental considerations and techniques are discussed and such variables as sample preparation, size, cell packing, atmosphere control, and heating rate have been investigated. The conventional technique of grinding or milling DTA samples is shown to cause significant changes in certain samples, particularly in undrawn fibers. The control of sample atmosphere by dynamic gas flow through the sample cell gave peaks that were generally sharper and larger than those found when control was by gas diffusion. Data are given on the various low temperature transitions found in such fibers. Significant differences in low temperature transitions were observed between polypropylene fiber and the bulk polymer as well as between drawn and undrawn nylon 6 fibers. The interpretation of the DTA curves for the decomposition and other reactions at elevated temperatures is discussed. Nylon 6 and polypropylene showed only endothermic reactions indicative of depolymerization processes whereas other fibers showed both endothermic and exothermic reactions in the decomposition range.

The Extension of Unoriented Nylon 66 Filaments: Part II: Phenomenological Relationships

Previous experimental investigations of cold drawing have employed two different techniques, (i) a study of load-elongation curves obtained on a constant-rate-of-elongation apparatus, and (ii) the operation of a two-roller drawing machine. In the first case, the length of yarn is fixed and the travel of the neck is followed along this length. In the second case, the neck is fixed in space by adjusting the speed and draw ratio applied to the traversing fiber. A third experimental method is to apply a constant load to an undrawn fiber and measure the increase in length with time (creep). In this experiment, cold drawing is observed by a marked yield region on the logarithmic time scale. Prior to the yield point, there is a region of uniform extension or pre-yield creep. Following the yield point, there is also a region of uniform extension or post-yield creep. These creep curves can be used to predict cold drawing behavior on both a two-roller drawing machine and a constant-rate-of-elongation apparatus. In particular, the location of the neck between feed and draw rolls, the drawing tension, and the speed dependence can be understood. These concepts are illustrated using results on nylon 66 monofilaments.

The Orientation of the Structure of 6.6 Nylon Fibres

The optical and x-ray diffraction properties of a model fibre have been considered. The fibre is assumed to consist of an assemblage of structural units to which simple optical and crystalline properties have been assigned. It is further assumed that the random orientation of units in the undrawn fibre is modified by drawing according to a simple geometrical pattern. Good agreement has been found between the observed variation of the birefringence with drawing, and the variation calculated from the model, and between some of the observed changes with drawing of the x-ray diffraction pattern, and the corresponding changes shown by the model.

Force-Temperature Behavior of Nylon Filaments at Fixed Extensions

By use of the thermodynamic equations for elasticity, force-temperature measurements on nylon filaments at fixed extensions in water have been related to the molecular mechanism of elasticity. Drawn fibers at low extensions were found to have an entropy force component larger than the total force. This effect was less pronounced in undrawn fibers, but persisted over a wider range of extensions. For undrawn nylon, a transition in the force-temperature behavior has been found which differs markedly from the second-order transition in rubber; rubberlike elasticity was found below rather than above the transition temperature. The transition temperature was ca. 47°C for 5% extension, and increased rapidly with increasing extension. Both nylon 6-6 and nylon 6 were found to have the same force-temperature be havior, except that the former showed evidence of impending glasslike elasticity near 0°C.