Analysis and Optimization of the Concluding Stage of Orientation of Polypropylene Fibre

An algorithm and system for mathematical modeling and optimization of the concluding stage of orientation of PP fibre are proposed. The adequacy of the mathematical model was confirmed in different drawing regimes. Mathematical modeling of the process was conducted, which revealed the basic (formal) characteristics of the process and demonstrated the possibility of an analytical solution of the problem of optimizing the orientation process. The optimum regimes are obtained in linear and discrete orientational drawing that ensure attaining the maximum level of orientation with respect to the selected index. The algorithm and modeling system can be used in developing optimum process schemes and regimes, creating control systems, and in training process personnel.     

Deformation resonance in orientational drawing of high-modulus viscose fibre twist

Increasing the orientational draw ratio of a freshly spun high-modulus fibre above some limit causes the appearance of periodic thinning in the drawn twist. It was hypothesized that thinning is formed according to the mechanism of deformation resonance described previously for spinneret drawing of spinning solutions and melts. An explanation of the mechanism of deformation resonance was proposed, where this phenomenon takes place during drawing of an inhomogeneous material due to partial fracture of the weaker part of it. The proposed hypothesis is in satisfactory agreement with the experimental data. In production of high-modulus viscose fibres, the orientational draw ratio should not exceed 2.1–2.2 (110–120%), and the first drawing should be within the limits of 1.6–1.7 (60–70%).All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated from Khimicheskie Volokna, No. 6, pp. 34–38, November–December, 1995.     

Synthesis of a system for automatic control of the diameter of an optical fibre in conditions of high drawing speeds

Use of the root locus method allows selecting the optimum adjustment for the regulator in the system for controlling the diameter of an optical fibre in conditions of high drawing speeds. Use of a PIC regulator is sufficient for suppressing harmonic perturbations that arise in the optical fibre diameter control circuit at high drawing speeds.     

粗旦丙纶长丝不匀率的影响因素分析

分析了T30S,Z30S两种切片及其纺丝拉伸等工艺对粗旦丙纶长丝不匀率的影响。结果表明,聚丙烯的相对分子质量及其分布、等规度和纺丝温度、冷却吹风速度、拉伸比率、上热盘温度以及上油量等对纤维不匀率产生明显的影响。选择相对分子质量(18~36)×104,相对分子质量分布小于5,等规度大于95％,水质量分数小于0.1％,灰分质量分数小于100μg/g的原料,同时,控制Z30S切片纺丝温度250℃,T30S切片降温母粒加入量低于3％,侧吹风速度0.3~0.7 m／s,拉伸倍数4倍,油水比为7,可使粗旦丙纶长丝的不匀率降低。     

Probing the morphology of polypropylene fibres by scanning probe microscopy

This paper highlights the application of scanning probe microscopy, notably atomic force microscopy in contact mode supported by lateral force microscopy, to the investigation of changes in the morphology of polypropylene (PP) monofilaments during melt-extrusion and subsequent drawing. A gradual deformation at the fibre surface from a spherulitic structure to a shish-kebab type structure is observed for the gravity spun and as-spun variants. In the drawn PP filaments, the surface structure is predominantly fibrillar in character, though the nature of the fibrillar structure is influenced by the drawing conditions. Wide angle X-ray scattering analysis, in conjunction with SPM, indicates contrasting features of surface and bulk crystal structure both at the as-spun and drawn stages of production. In addition, an unusual WAXS diffraction pattern is observed for the cold drawn PP filament. Studies of the bulk structures of the fibres by investigating fibre cross-sections using SPM will be the subject of a companion paper.     

A morphological study of melt‐spun polypropylene filaments by atomic force microscopy

Surface morphology of melt‐spun polypropylene (PP) filaments, spun from an additive‐free PP powder and from a commercial‐grade PP with different draw ratios, were examined with atomic force microscopy (AFM). The surface morphology of as‐spun filaments was spherulitic. The gradual transformation of the surface structure from a spherulitic morphology to a fibrillar morphology during stretching was studied. In the filaments spun from the commercial‐grade PP, the transformation was initiated by deformation of spherulites with a draw ratio of 1.2 and continued with association of lamellar stacks into fibrillar chains with a draw ratio between 1.2 and 2.0. A hierarchical morphological microstructure of fibrils, microfibrils, and nanofibrils was developed with a draw ratio of 4.0. In the filaments spun from the additive‐free PP, the association of lamellar stacks into fibrillar morphology occurred considerably later, between draw ratios of 2.0 and 4.0. An oriented lamellar structure was found in these filaments, still with a draw ratio of 4.0. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1242–1249, 1999     

Isotactic polypropylene microfiber prepared by carbon dioxide laser‐heating

An isotactic polypropylene (i‐PP) microfiber was obtained by irradiating a carbon dioxide laser to previously drawn fibers. To prepare the thinner i‐PP microfiber, it is necessary to previously draw original i‐PP fibers under an applied tension of 7.8 MPa at a drawing temperature of 140°C. The drawn fiber was heated under an applied tension of 0.3 MPa using the laser operated at a power density of 39.6 W cm^?2. The thinnest i‐PP microfiber obtained under optimum conditions had a diameter of 1.8 μm and a birefringence of 30 × 10^?3. Its draw ratio estimated from the diameter reached 51,630. It is so far impossible to achieve such a high draw ratio by any drawing. The wide‐angle X‐ray diffraction photograph of the microfiber shows the existence of the oriented crystallites. Laser‐heating allows easier fabrication of microfibers compared with the conventional technology such as the conjugate spinning. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1534–1539, 2004     

Mathematical Model of the Final Stage of Orientation of Polypropylene Fibre

A mathematical model of the final stage of orientation of polypropylene fibre is constructed. The stress of the polymer in the hyperelastic state is used as an indirect estimation of the orientation index. A relaxation model with variable parameters is used for indirect evaluation of the change in the structure of the polymer during deformation. The curve of the parameters of the relaxation model as a function of the deformation and temperature is described by nonlinear regressive equations. The mathematical model is intended for evaluating the state of a polymer, imitation modeling, and selection of optimum orientation regimes.     

The structure of high-strength ultrahigh-molecular-weight polyethylene fibres fabricated by the gel-spinning method

In orientation drawing of UHMPE (ultrahigh-molecular-weight polyethylene) fibres, conformational rearrangements take place that enrich the conformation set of the polymer with T-isomers and impoverish it in G-isomers. The basic increase in the orientation of T-isomers is observed in the initial stages of drawing. In orientation drawing of UHMPE gel fibre, no significant increase was found in the concentration of molecular breaks, a necessary condition for effective strengthening of the fibre. Two types of crystallites (crystallites infolded and straightened chains) and a mesophase were found in samples of multifilament UHMPE fibres. There is a smooth transition from the structure of the folded-chain crystallite (FCC) type to a structure of the straightened-chain crystallite (SCC) type with an increase in the draw ratio due to formation of a rigid amorphous phase of straightened segments of the polymer chains. __________ Translated from Khimicheskie Volokna, No. 3, pp. 18–23, May–June, 2006.     

Technological Aspects of Orientational Strengthening of Poly(Ethylene Terephthalate). Modern Schemes for Production of High-Strength Polyester Fibres

Theoretical and technological aspects of orientational strengthening of polyester fibres are examined. High strength of polyester fibres is attained by the combination of the high molecular weight of poly(ethylene terephthalate) with stage-wise (in several stages) drawing. Current schemes for production of high-strength polyester fibres are reported.     

Melt spinning of β‐phase poly(vinylidene fluoride) yarns with and without a conductive core

When poly(vinylidene fluoride) (PVDF) is to be used as a piezoelectric material, the processing must include the formation of polar β‐phase crystallites, as well as the application of electrically conducting charge collectors, that is, electrodes. In this article, results from the melt spinning of PVDF yarns and a novel bicomponent PVDF‐yarn with a conductive carbon black/polypropylene (CB/PP) core are presented. Melt spinning has been done under conditions typical for industrial large‐scale fiber production. The effects on the resulting crystalline structure of varying the spinning velocity, draw rate, and draw temperature are discussed. The results show that, for maximum α‐to‐β phase transformation, cold drawing should take place at a temperature between 70 and 90°C, and both the draw ratio and the draw rate should be as high as possible. It was observed that the cold drawing necessary to form β‐phase crystallinity simultaneously leads to a decrease in the core conductivity of the bicomponent yarns. In this work, the melt spinning of bicomponent fibers with high‐β‐phase PVDF in the sheath and a CB/PP core was successfully accomplished. The core material remained electrically conductive, paving the way for the use of a CB‐polymer compound as inner electrode in the melt spinning of piezoelectric bicomponent fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

超拉伸过程中UHMWPE纤维结构与性能的研究

利用密度梯度仪、声速取向仪、Instron材料强力仪、WAXD、DSC等手段 ,对超高相对分子质量聚乙烯 (UHMWPE)纤维在超拉伸过程中的结构和性能进行了测试研究。结果表明 ,不同拉伸倍数的UHMWPE纤维的结晶度、取向度、力学性能和熔融温度随着拉伸倍数的增大而增加 ;DSC图谱上的 Tm4 峰和WAXD分析证实了在超拉伸过程中UHMWPE纤维发生了正交晶相向六方晶相的转变 ,超拉伸后期结晶结构的变化对纤维的力学性能影响很大。     

Formation of the Primary Supramolecular Structure of Some Fibre Types in Conditions of Wet Spinning

The supramolecular structure of Armos, polyacrylonitrile, and hollow polysulfone fibres was investigated by scanning electron microscopy using the solvent substitution method. The data obtained allow visualizing the characteristics of the structure in the initial stage of spinning each of the three types of fibres investigated. The supramolecular structure of the fibres found is transformed in the last stages, especially in orientational drawing, preserving some "memory" concerning the precipitation stage.     

Controlling of threadline dynamics via a novel method to develop ultra‐high performance polypropylene filaments

A detailed study was conducted to investigate the effects of horizontal isothermal bath (hIB) on the production of ultra‐high performance polypropylene filaments. Two different commercial PP polymers were used with the melt flow rate of 4.1 and 36 g/10 min. The optimum process conditions depended on polymer molecular weight. Fibers showed distinct precursor morphology for each at each optimum process condition. However, two sets of filaments demonstrated similar fiber tenacity and modulus of about 7 and 75 g d^?1, respectively, for as‐spun and more than 12 g d^?1 for tenacity and more than 190 g d^?1 for modulus values of drawn fibers after just 1.49 draw ratio. The mean value for the modulus after the drawing process for the high melt flow rate was 196 g d^?1. The theoretical modulus of PP is 35–42 GPa¹⁹, (275–330 g d^?1), shows the hIB fiber's modulus performance is approaching its theoretical maximum value. Fibers had greatly improved thermal properties, degree of crystallinity, crystalline and amorphous orientation factors. The hIB spinning system produced highly oriented and predominantly amorphous structure for as‐spun fibers and a well‐defined, highly oriented crystalline fibrillar and amorphous structure after drawing process with the draw ratios lower than 1.5. POLYM. ENG. SCI., 55:327–339, 2015. © 2014 Society of Plastics Engineers     

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     

Ultra-high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner-and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus ～ 30–35 GPa and tensile strength ～ 1,1 GPa), was determined.     

Fibre-forming properties of melts of polypropylene—Copolymer of ethylene with vinyl acetate blends

The rheological properties of melts of PP—CEVA blends include a decrease in the viscosity and an increase in the elasticity due to the specific features of fibre formation in flow of melts of the blends. The orientational draw ratio of composite PP—CEVA monofilaments increased in comparison to the λ of monofilaments of the starting polymers. Fibres with higher (by 1.6 times) strength and higher (by 2 times) initial modulus than for fibres of the starting PP can be obtained by spinning from a melt of PP—CEVA mixture. Ukraine State Academy of Light Industry, Kiev. Translated fromKhimicheskie Volokna, No. 1, pp. 18–20, January–February, 1999.     

Orientation distribution in the noncrystalline regions of biaxially drawn poly(ethylene terephthalate) film: A chain-intrinsic fluorescence study

We have studied development of the in-plane distribution of “amorphous orientation” during sequential and simultaneous biaxial drawing of poly(ethylene terephthalate) film, using polarized intrinsic fluorescence. The machine direction (MD) draw ratio was always fixed at 3.5, and the transverse direction (TD) draw ratio was varied. The rate of increase in the proportion of TD-oriented chains with increasing TD draw ratio is almost identical in the sequential and simultaneous processes up to a draw ratio of 2.7. At this point, sequential drawing starts to involve transverse realignment of MD-oriented chains, which accelerates redistribution of orientation from the MD to the TD. Consequently, in sequential drawing, a “balanced” biaxial orientation distribution is achieved at a TD draw ratio significantly below the MD draw ratio, whereas at the same TD draw ratio in the simultaneous process, MD orientation remains dominant. At equal MD and TD draw ratios, the non-crystalline chains in sequentially drawn film are predominantly oriented along the TD, but their orientation distribution is isotropic in simultaneously drawn film. High-temperature annealing at fixed dimensions diminishes the proportion of TD-oriented chains in films with transverse draw ratios < 2.5. We attribute this to a more highly developed crystallite network in the MD, which constrains orientational relaxation along the MD. A balanced distribution of amorphous orientation is directly responsible for achieving balanced tensile strength and balanced extensibility. © 1993 John Wiley & Sons, Inc.     

聚醚酯/聚丙烯纤维的制备及其卷曲、收缩性能研究

采用聚醚酯和聚丙烯共混熔融纺丝,经过一定拉伸松弛后得到自卷曲共混纤维。通过对卷曲性能和沸水收缩率等的测定,探讨了共混纤维的性能。结果表明:PP含量为16%,拉伸4倍的共混纤维具有较好的卷曲性能;当拉伸倍数增大时,沸水收缩率逐渐增加,但拉伸倍数为5倍时,沸水收缩率下降;随着PP含量的增加,纤维沸水收缩率逐渐降低,经紧张热定形的纤维沸水收缩率小于经松弛热定形处理的纤维。     

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.