Opto‐thermal properties of fibers: XVII. Structure characterization of cold drawn boiled viscose fibers

A two‐beam interferometric method is used to study the change of optical parameters of cold drawn boiled viscose fibers at different times. A stress–strain device conjugated to the Pluta polarizing interference microscope is used to investigate the dynamical behavior of opto‐mechanical properties at room temperature. Some structural parameters such as the number of molecules per unit volume, the virtual and isotropic refractive indices, the optical orientation factor and angle, the strain and the stress optical coefficients are evaluated. Some mechanical parameters such as, Young's modules, elastic shear modules and the compressibility are calculated over different strain values. Also the number of network chain per unit volume N_c, work per unit volume W, average work per chains W′, reduction in entropy ΔS, and the optical configuration parameter Δα are determined. Also calculation of the constants of Moony–Rivilin equation are given. A systematic study over different wavelengths range extending from 405 to 590 nm was carried out to obtain the dielectric constant at infinity. The obtained results clarify that new reorientations occurred due to cold drawing at different conditions. Empirical formula is suggested to correlate the change in Δn, f(θ), W, W′, A, θ, and N_c with different draw ratio, and its constants were determined. Microinterferograms and curves are given for illustrations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1185–1201, 1999     

Enzymatic degradation of poly(L‐lactic acid) fibers: Effects of small drawing

The enzymatic degradation of poly(L ‐lactic acid) (PLLA) fibers with different low draw ratios (1.0, 1.2, and 1.4 times) was investigated in tris‐HCl buffer solution (pH = 8.6) with proteinase K by the use of gravimetry, scanning electron microscopy (SEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and tensile testing. Surprisingly, even the small drawings (1.2 and 1.4 times) disturbed the proteinase K catalyzed enzymatic degradation of the PLLA fibers. This should have been because the enzyme could not attach to the extended (strained) chains in the amorphous regions of the uniaxially oriented PLLA fibers or could not catalyze the cleavage of the strained chains. The accumulation of crystalline residues formed as a result of selective cleavage, and removal of the amorphous chains was not observed, even for as‐spun PLLA fibers. This indicated the facile release of formed crystalline residues from the surface of the as‐spun PLLA fibers during enzymatic degradation. Such release may have been because the crystalline regions of the as‐spun PLLA fibers were oriented with their c axis parallel to the machine direction, as reported for biaxially oriented PLLA films. Gravimetry, SEM, and tensile testing could trace the enzymatic degradation of the PLLA fibers, although the enzymatic degradation of the PLLA fibers was untraceable by GPC and DSC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2064–2071, 2007     

Structure–properties relations of the drawn poly(ethylene terephthalate) filament sewing thread

This article presents research into draw ratio influence on the structure–properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Real‐time FTIR and WAXS studies of drawing behavior of poly(ethylene terephthalate) films

The development of molecular orientation and crystallization was studied during uniaxial drawing of poly(ethylene terephthalate) (PET) films, which was immediately followed by subsequent taut annealing at the drawing temperature. The behavior was monitored in real time throughout the drawing and annealing using dynamic FTIR spectroscopy and in situ WAXS measurements using the Daresbury Synchrotron Radiation Source. Films were drawn at 80 and 85°C at varying strain rates (0.001–0.7 s⁻¹). The true stress–strain behavior was determined at each of the drawing conditions and the density and optical anisotropy of unloaded samples was measured. The IR spectra were analyzed using curve reconstruction procedures developed previously, and they showed that orientation of the phenylene groups and the trans glycol conformers occurred before significant gauche–trans conformational changes could be seen. The onset of crystallization, defined as the point that the crystalline 1 05 reflection could be first observed using WAXS, was not found to correlate with any specific change in the proportions of trans and gauche isomers nor with any feature on the stress–strain curve. However, it was clear that, for these comparatively low strain rates, crystallization occurred during the drawing process while the crosshead was moving and the draw ratio was increasing. The orientation of the crystallites was calculated from the 1 05 reflection observed in a tilted film, transmission geometry. The crystallites were found to form at a draw ratio of about 2.5 with high orientation values (P₂ > 0.8) that increased during drawing and annealing to P₂ values of 0.95, irrespective of the drawing conditions. Semiquantitative measurements of crystallinity showed that the fraction of crystalline material that developed during drawing decreased with increasing strain rate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1825–1837, 2001     

超高分子质量聚酯(UHMW-PET)纤维牵伸工艺及结构性能研究(Ⅰ)

研究了超高分子质量聚酯 (UHMW PET)纤维的一级牵伸工艺条件对纤维结构性能的影响。结果表明 :在两级牵伸工艺条件下 ,采用较低的一级牵伸温度和牵伸速率 ,有利于得到结晶度较低 ,双折射、强度及牵伸倍率较高的纤维 ,从而保证能够制取高强度纤维     

Effect of winding speed on the structure and properties of as‐spun poly(trimethylene 2,6‐naphthalenedicarboxylate) fibers as compared to poly(ethylene terephthalate) fibers

We present a comparative study of melt spinning of poly(trimethylene 2,6‐naphthalenedicarboxylate) (PTN) and poly(ethylene terephthalate) (PET) fibers with respect to the effect of winding speed (2000–6000 m/min): Structural changes were followed by X‐ray analysis, calorimetry, and measurements of density, boiling water shrinkage, and birefringence. As‐spun PTN fibers exhibited a low degree of crystallinity at relatively low speeds (< 2000 m/min). An increase in winding speed up to 6000 m/min only resulted in a minor enhancement of crystallinity and orientation. The small change of structural parameters accounted for the fact that tenacity and modulus did not rise significantly with increasing winding speed, contrary to the PET fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2489–2497, 2002     

Optothermal properties of fibers: 12‐Interferometric investigation for thermally treated viscose fibers

The present article studies the structure of annealed viscose fibers interferometrically at a constant temperature of 100 ± 1°C at different times. The Pluta polarizing interference microscope has been used for determining the mean refractive indices and mean birefringence. The results were used to calculate the optical orientation function and the angle of orientation. The value (Δα/3α₀), which depends on the molecular structure of the polymer, remains constant. Relationships between the mean refractive indices, birefringence, isotopic refgractive index, and polarizabilities per unit volume with different times were given for these fibers. The samples were subjected to X‐ray diffraction to clarify the variation of crystallinity with the annealing conditions. Differential thermal analysis measurements were used to determine the glass transition temperature of viscose fiber. Measurements of the volume swelling parameter of the viscose fibers with different liquids were given. Also, determinations of Cauchy's constants, dispersive power, and dielectric constant at infinity were carried out. Illustrations are given using graphs and microinterferograms. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 361–369, 1999     

Optothermal properties of fibers. XIII. Evaluation of the form birefringence and some other structural parameters due to thermal annealing for polyester (PET) fibers

In this work, changes in the structure of polyester [poly(ethylene-terephtalate) (PET)] fibers after annealing at constant temperature (120 and 140°C) and different times were studied interferometrically. The density of annealed PET fibers were measured by a system based on vibrating string. The Pluta polarizing interference microscope was used to determine the optical parameters of these fibers. The density and optical results were used to calculate the degree of crystallinity, the form birefringence, the number of monomeric units per unit volume, harmonic mean polarizability of the dielectric, harmonic mean specific refractivity, and the virtual refractive index. The behavior of fiber crystallinity at different annealing conditions were discussed with different optical parameters. Hermans optical orientation function have been compared with the generalized Lorentz–Loranz equation given by de Vries. Microinterferograms and curves are given for illustration. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:1955–1963, 1998     

Superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under critical necking tension

The superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under a critical necking tension (σ_c) were studied. σ_c was defined as the minimum tension needed to generate a neck at a given drawing temperature (T_d) and was measured over a temperature range of 70–120°C. The σ_c value increased rapidly with decreasing T_d in the temperature range below 85°C, but the temperature dependence of σ_c was small above 85°C. The neck profile relied on T_d, becoming more shapely with decreasing T_d. A neck with a gradual decrease in diameter was observed in the fibers drawn at 100°C and above. The draw ratio increased significantly with increasing T_d above 90°C, but birefringence decreased. Density decreased gradually with increasing T_d, and fiber drawn at 120°C had a density of 1.347 g/cc. Wide‐angle X‐ray diffraction photographs of the fibers drawn at 100°C and below showed reflections due to crystallites, but a photograph of the fiber obtained at 120°C showed a ring‐like amorphous halo. The storage modulus (E′) at 25°C increased progressively with decreasing T_d, and the fiber drawn at 70°C had the maximum E′ value among the fibers drawn at a series of T_d's. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 179–185, 2002     

Effects of spinning and drawing conditions on the crimp contraction of side‐by‐side poly(trimethylene terephthalate) bicomponent fibers

The crimp properties in the melt‐spinning and drawing processes of side‐by‐side bicomponent fibers with poly(trimethylene terephthalate)s (PTTs) of different viscosities were studied. Two PTTs of different intrinsic viscosities (1.02 and 0.92) were selected to make latent crimp yarn. The spinning and drawing conditions were changed to investigate the relation between the process conditions and crimp contraction. An orthogonal array was used to rule out the weak variables. The draw ratio, heat‐set temperature, and portion of high‐viscosity PTT were selected as variables having an effect on the crimp contraction. An analysis of the effects of the spinning and drawing conditions on the crimp contraction showed that the draw ratio was the most critical variable. Increasing the draw ratio caused a difference in the shrinkage between the two parts of PTT and caused the self‐crimping of the bicomponent fibers. Although changing the heat‐set temperature and the portion of high‐viscosity PTT did not produce a dimensional change, the crimp contraction varied with those variables. As the heat‐set temperature and the high‐viscosity portion increased, the crimp contraction increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1322–1327, 2006     

Physical properties of poly(vinyl alcohol) fibers prepared from wet spinning/multi-step drawing

The preparation of poly(vinyl alcohol) (PVA) fibers by multi-step drawing was examined. The high draw ratio was attained when the drawing just before melting point was repeated. The influences of the draw ratio on mechanical and thermal properties of the fibers were studied. We utilized the wide angle x-ray diffraction (WAXD) as a medium to observe the erystallinity and the orientation of PVA fibers to study their effects on the physical properties of the fibers. With various coagulation bath concentration, both the tenacity and Young's modulus of fibers would increase as the draw ratios increased, the elongation would decrease at the same time. The tenacity was able to reach 41.0 cN/tex with the Young's modulus being 856.2 cN/tex; also, as the draw ratios increased, both crystallinity and orientation would increase. The crystallinity was about 67.2 % and the orientation was about 86.4%.     

Study on poly(ethylene terephthalate)/polypropylene microfibrillar composites. II. Solid‐state drawing behavior

A (20/80) blend of poly(ethylene terephthalate)/polypropylene (PET/PP) was solid‐state drawn to enhance the molecular orientation of the PET microfibers. Effects of drawing temperature (23–140°C) and drawing speed (max. 1000 mm/min) on the morphology and draw ratio of the blend were studied and discussed based on the drawing behaviors of the pure polymers. In cold drawing, there seemed to be a critical drawing speed below which the natural draw ratios of the polymers remained constant, but above which the draw ratios first decreased slightly because of suppression of molecular relaxation and then increased because of breakage of highly strained molecules and disintegration of lamellar crystals into finer mosaic blocks. Macroscopically, the pure PP and the PET/PP composite extrudates gave similar draw ratios at the same speeds. SEM showed that the PET microfibers suffered a smaller elongation than the PP matrix and severe voiding occurred at the PET/PP interface. Furthermore, substantial fiber breakage occurred during cold drawing at speeds above 200 mm/min. In comparison, drawing at 100°C caused no obvious interfacial voiding and fiber breakage. Furthermore, the natural draw ratio of the blend was lower than that of the pure PP extrudate, indicating that the PET microfibers had constrained the deformation of the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1989–2000, 2004     

Study of the thermal behavior of alkali‐treated jute fibers

Jute fibers were treated with 5% NaOH solution for 2, 4, 6, and 8 h to study the performance of the fibers as a reinforcing material in the composites. Thermal analysis of the fibers was done by the DTG and DSC technique. The moisture desorption was observed at a lower temperature in the case of all the treated fibers, which might be a result of the increased fineness of the fibers, which provides more surface area for moisture evaporation. The decrease in percentage moisture loss for the fibers treated with alkali for 6 and 8 h could be the result of the increased crystallinity of the fibers. The percentage degradation of the hemicellulose decreased considerably in all the treated fibers, conforming to the fact that the hemicellulose content was lowered on alkali treatment. The decomposition temperature for α‐cellulose was lowered to 348°C from 362.2°C for all the treated fibers, and the residual char formation increased to a significant extent. The enthalpy for the thermal degradation of α‐cellulose showed a decreasing trend for the fibers treated for 2 and 4 h, which could be caused by the initial loosening of the structure, followed by an increase in the enthalpy value in the case of the 6‐ and 8‐h‐alkali‐treated fibers resulting from increased crystallinity, as evident from the X‐ray diffraction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2594–2599, 2002     

Solid‐state polymerization of melt‐spun poly(ethylene terephthalate) fibers and their tensile properties

The production of high modulus and high strength poly(ethylene terephthalate) fibers was examined by using commercially available melt‐spun fibers with normal molecular weight (intrinsic viscosity = 0.6 dL/g). First, molecular weight of as‐spun fibers was increased up to 2.20 dL/g by a solid‐state polymerization, keeping the original shape of as‐spun fibers. Second, the polymerized as‐spun fibers were drawn by a conventional tensile drawing. The achieved tensile modulus and strength of as‐drawn fibers (without heat setting) were 20.0 and 1.1 GPa, respectively. A heat setting was carried out for the as‐drawn fibers. Tensile properties of the treated fibers were greatly affected by the condition of the heat setting. This was related to the increase of sample crystallinity and molecular degradation during the treatments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1791–1797, 2007     

Novel CO2 laser drawing of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

Thermotropic liquid crystal polymer (TLCP)/poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin‐draw process. In this study, we suggest novel drawing technology using the CO₂ laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 135°C for 10 min. It was confirmed that the CO₂ laser drawing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO₂ laser‐drawing method has a great potential for industrial applications as a novel fiber‐drawing process, and it can also be applied continuously to conventional spin‐draw system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 205–211, 2007     

Effect of zone drawing on the structure and properties of melt‐spun poly(trimethylene terephthalate) fiber

Melt‐spun poly(trimethylene terephthalate) (PTT) fibers were zone‐drawn and the structures and properties of the fibers were investigated in consideration of the spinning and zone‐drawing conditions. The draw ratio increased up to 4 with increasing drawing temperature to 180°C, at a maximum drawing stress of 220 MPa. Higher take‐up velocity gave lower drawability of the fiber. The PTT fiber taken up at 4000 rpm was hardly drawn, in spite of using maximum drawing stress, because a high degree of orientation had been achieved in the spinning procedure. However, an additional enhancement of birefringence was observed, indicating a further orientation of PTT molecules by zone drawing. The exotherm peak at 60°C disappeared and was shifted to a lower temperature with an increase in the take‐up velocity, which means that the orientation and crystallinity of the fiber increased. The d‐spacing of (002) plane increased with increasing take‐up velocity and draw ratio, whereas those of (010) and (001) planes decreased. In all cases, the crystal size increased with take‐up velocity and draw ratio. The cold‐drawn PTT fiber revealed a kink band structure, which disappeared as the drawing temperature was raised. The physical properties of zone‐drawn PTT fibers were improved as the draw ratio and take‐up velocity increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3471–3480, 2001     

A study of the drawing behavior of poly(ethylene terephthalate)

Cold-drawn and hot-drawn samples of poly(ethylene terephthalate) were studied by means of measurements of shrinkage stress, birefringence and differential scanning calorimetry (DSC). The values of shrinkage stress were comparable for both types of sample, implying that the deformation of a molecular network is important for both cold drawing and hot drawing. The DSC results indicate that substantial crystallization occurs in hot drawing for other than the lowest draw ratios, and this crystallization gives rise to an additional peak in the shrinkage stress measurements. In addition to temperature, strain rate is also an important variable, and changes in strain rate caused significant changes in both hot-drawn and cold-drawn samples.     

Thermal behavior and tensile properties of poly(ethylene terephthalate‐co‐ethylene isophthalate)

Poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI) homopolymers were synthesized by the two‐step melt polycondensation process of ethylene glycol (EG) with dimethyl terephthalate (DMT) and/or dimethyl isophthalate (DMI), respectively. Nine copolymers of the above three monomers were also synthesized by varying the mole percent of DMI with respect to DMT in the initial monomer feed. The thermal behavior was investigated over the entire range of copolymer composition by differential scanning calorimetry (DSC). The glass transition (T_g), cold crystallization (T_cc), melting (T_m), and crystallization (T_c) temperatures have been determined. Also, the gradually increasing proportion of ethyleno‐isophthalate units in the virgin PET drastically differentiated the tensile mechanical properties, which were determined, and the results are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 200–207, 2000     

Extrusion drawn amorphous and semicrystalline poly(ethylene terephthalate): 3. Linear thermal expansion analysis

Thermal expansion analysis of uniaxially-oriented poly(ethylene terephthalate) (PET) films has been carried out from 123 K up to the PET glass transition temperature, T_g. The films are prepared by solidstate co-extrusion, from different premorphologies (amorphous, 33% and 50% crystalline), to draw ratios (EDR) up to 4.4, over a wide temperature range (T_ext). The coefficients of linear thermal expansion exhibit anisotropy: normal to the draw direction (α_⊥) it increases, whereas along the draw direction (α_∥) it always decreases with draw, independent of the initial morphology. Results are interpreted by treating PET as a simple two-phase composite structure. Tie-molecules occurring in the amorphous domains and bridging adjacent crystallites have a major influence. At EDR=4.4, a significant number of taut tiemolecules are developed, resulting in α_∥ becoming negative (α^max_∥=?1.0×10^?5°C^?1) at temperatures below ambient. This appears to be the first report of a negative α for a polymer of relatively low crystallinity. Temperature for extrusion draw significantly affects α. Normal to the draw direction, α_⊥ decreases with T_ext whereas α_∥ increases. The results show the thermal expansion of PET depends primarily on orientational effects. Only in the absence of anisotropy does per cent crystallinity have a dominant influence. In addition, the TMA thermograms display sharp transitions which are attributed to irreversible shrinkage of the oriented films. The shrinkage temperature (T_s) shows a strong dependence on both orientation and crystallinity, and it is discussed in association with T_g.     

Optothermal properties of fibers—20—relation between physical structure and mechanical properties of cold drawn polypropylene fibers

The structure of annealed polypropylene (PP) fibers is studied interferometrically using two-beam Pluta polarizing interference microscope connected to a device to study the draw ratio with birefringence changes dynamically. Relations of drawing changes with some optical and physical parameters are given. Evaluation of average work per chain, work per unit volume, reduction in entropy caused by elongation, and the work stored in the body as strain energy were determined. Also the resulting optical data were utilized to evaluate the orientation factor, the orientation angle, the virtual refractive index, and the number of molecules per unit volume. The value of (Δα/3α₀), which depends upon the molecular structure of the polymer, remains constant. Relations between the physical and optical parameters with different strains are given for these fibers. The generalized Lorentz–Lorenz equation given by de Vries is used to determine polypropylene fiber structural parameters. Comparison between Hermans optical orientation function formula and the corrected formula by de Vries are given. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 819–831, 1999