Effect of spinning speed on the structure and physical properties of filament yarns produced from used PET bottles

In the previous work (S. Kiantash, MS Thesis, Amirkabir University of Technology, Textile Engineering Department, Tehran, Iran, 2002), the possibility of producing filament yarns from used PET bottles was investigated and the production was successfully carried out. To improve physical properties and to have a detailed understanding of the molecular structure, spinning variables such as the take‐up speed (one of the most influencing factors) should be varied and studied. In the present work, continuous filament yarns from virgin PET chips and used PET bottles were produced at the two take‐up speeds of 2500 and 3000 m/min. Optical birefringence, crystallinity (obtained from three methods including density, calorimetry, and FTIR), tenacity, breaking elongation, initial modulus, and shrinkage of yarns were measured and compared. Optical birefringence and crystallinity (obtained from all three methods) of used samples show higher values compared with those of virgin samples produced at both take‐up speeds. Consequently, the tenacity of used samples is higher and breaking elongation is lower. Generally, samples having bigger crystallinity present higher initial modulus and smaller shrinkage. However, results of initial modulus and shrinkage do not correspond to this assumption. As it was predicted, increasing the take‐up speed resulted in an increase in the optical birefringence, crystallinity, tenacity, and initial modulus and a reduction in the breaking elongation of both virgin and used samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3972–3975, 2007     

Rapid structural changes that take place during constrained annealing of biaxially stretched pet films

The aim of this work is to study the structural changes that take place during the heat setting of simultaneously and sequentially biaxially stretched polyethylene terephthalate films. The rate of structural rearrangement, as detected by real‐time birefringence and off‐line Raman spectroscopy, DSC thermal analysis and X‐rays, was found to be dependent on the state of the orientation and crystallinity attained by the samples during the stretching step. This suggested that the annealing behavior can be categorized into three regimes according to the birefringence behavior of the samples. At low deformations, the films not crystallized by strain exhibit complete birefringence relaxation without showing any sign of crystallization. The intermediate ratio samples that were stretched to the onset of the strain‐induced crystallization exhibited the highest levels of birefringence increase after a short relaxation. The samples stretched well above the onset of the strain‐induced crystallization exhibited intermediate level of birefringence and crystallinity increase. Therefore, the classification of the three regimes was found to be related to the onset of the strain‐induced crystallization during the stretching step. POLYM. ENG. SCI., 57:550–562, 2017. © 2016 Society of Plastics Engineers     

Thermai treatment of cold-formed poly(vinyl chloride)

Cold-drawing poly(vinyl chloride) at 24°C increased the yield strength by 25 percent, modulus by 50 percent, and the ultimate strength by 100 percent. The onset of thermal shrinkage was reduced from 80°C (T_g) to 45°C. This thermal instability can be a significant disadvantage of cold-forming for many applications. It is shown in this study that subsequent thermal treatment at 70°C (T < T_g) re-establishes a shrinkage onset temperature of 80°C without reducing property levels. The structural changes associated with both orientation and thermal treatment were investigated using DSC, X-ray diffraction and birefringence. Cold-drawing produces molecular alignment as measured by birefringence and X-ray. Thermal treatment of unstretched samples, as well as stretched samples under constraint and stretched samples unconstrained, always leads to a small reduction in free volume as revealed by a measured increase in enthalpy at T_g. However, this free volume change, produces a thermally-stable oriented structure only when the samples are treated under constraint. Thermal treatment does not stabilize unconstrained samples. Rather it causes almost complete molecular relaxation and a reduction of physical property levels.     

An optical investigation of high‐tenacity polyester (H‐T PET) fibers annealed at different temperatures

A two‐beam “Interphako” interference microscope was used to study the effect of annealing on the physical properties of high‐tenacity poly(ethylene terephthalate) H‐T PET fibers. The PET fibers were annealed with free ends for 1 h at temperatures ranging from 100 to 200°C. The shrinkage, refractive indices, and orientation angle of the PET fibers were determined for different annealing temperatures. The measured birefringence and orientation function were found to have decreased with increasing temperature, whereas the degree of crystallinity and the onset temperature (DSC) increased. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Influence of heat‐setting temperature on the properties of a stretched polypropylene microporous membrane

The influence of heat‐setting temperature on the stress–strain curves, differential scanning calorimetry (DSC) curves and properties of a stretched polypropylene microporous membrane was studied. It was found that with an increase of heat‐setting temperature, a plastic plateau region in the stress–strain curves and a melting endotherm plateau in the DSC curves became apparent. The permeability and porosity firstly increased with the temperature to 145 °C and then decreased. The pore structure arrangement showed similar changing trend. On the one hand, higher heat‐setting temperature could decrease the shrinkage of the microporous membrane. On the other hand, the crystallization of some chains around separated lamellae during heat‐setting was unfavorable to the properties of the microporous membrane. The occurrence of crystallization during heat‐setting explained the origin of the plastic plateau. For the fabrication of microporous membranes based on the melt‐stretching mechanism with good dimensional stability, heat‐setting is necessary, but too high a heat‐setting temperature can destroy the permeability. © 2013 Society of Chemical Industry     

Thermal Characteristics of Para-Aramid Fibres

Comparative studies of the thermal characteristics of para-aramid fibres (Armos, Rusar, Terlon, Twaron, and Kevlar) were conducted using thermomechanical analysis (TMA), dynamic thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). According to the TMA data, the para-aramid fibres studied are characterized by dimensional stability up to temperatures of 400-450°C; shrinkage or spontaneous elongation does not exceed 0.5-1%. TGA and DSC revealed the temperature characteristics of the para-aramid fibres corresponding to the occurrence of thermooxidative degradation. These processes begin at 400-450°C and are accompanied by shrinkage; 4% weight loss takes place at temperatures above 490-500°C.     

Optimization of stabilization and carbonization treatment of PAN fibres and structural characterization of the resulting carbon fibres

The properties of carbon fibres made from PAN are controlled by the heat treatment cycles during stabilization and carbonization. Optimum conditions can be derived by simple but time-consuming trials. The paper presents an indirect laboratory method, which is based on TMA and DSC measurements during the stabilization period. Results from this method contribute additionally to the explanation of the various simultaneously occurring chemical reactions, mainly dehydrogenation, intra- and intermolecular cyclization.Shrinkage measurements during stabilization under time linear heating show the start and end of the chemical stabilization reactions. The optimum stabilization conditions are derived from the shrinkage behavior as a function of the heating rate. As the stabilization is strongly affected by the heat of reaction, DSC measurements contribute to the accuracy but also to the explanation of the results from the TMA method.These stabilization conditions were applied for the preparation of carbon fibres which are characterized by mechanical and physical methods.     

Dynamic mechanical analysis of fibers. II. Estimation of fiber orientation and characterization of heat set PET yarns

A drawn PET yarn was heat set (annealed) at temperatures between 110°C and 245°C in an unconstrained mode and the samples characterized by dynamic mechanical analysis (DMA). A method for estimating the fiber orientation factor (α) is proposed using DMA and shown to be more sensitive than the crystalline orientation (x-ray diffraction) or total orientation (birefringence) measurements of the heat set yarns. The extension/shrinkage behavior of the heat set yarns has been discussed in the light of morphological changes, e.g., degree of orientation and the micro-crystallite formation. Unlike in the unconstrained mode, heat setting under constraint does not lead to the formation of micro-crystallites as revealed by differential scanning calorimetry. As a consequence, although the modulus and degree of orientation increase upon constrained annealing, the thermal stability, i.e., loss of orientation (reflected by shrinkage) could not be improved.     

Effect of gamma radiation and annealing on ultra-oriented polyethylene

Filaments of ultra-oriented high density polyethylene were solid-state extruded at an extrusion (draw) ratio of 26 and subsequently irradiated under vacuum by a cobalt-60 source at doses of 10,15, 20, 40 and 60 megarads (MRad). Several identically prepared but unirradiated strands were also tested. One set of samples at each dose was immersed in a silicone oil bath for one half hour at 128°C and one set was given no post-irradiation thermal treatment. Characterization of the resultant morphologies included differential scanning calorimetry (DSC), birefringence, thermomechanical analysis (TMA), and tensile testing. Results from DSC measurements indicate that initial radiation crosslinking only slightly disrupts the crystal lattice, but on subsequent melting and re crystallization, the chains are unable to recrystallize effectively in their former habit. In all cases, melting point and crystallinity decrease with increasing radiation dose. Birefringence and TMA results indicate that orientation is not disrupted by irradiation. For unannealed samples, Young's modulus increases slightly then levels off while tensile strength and elongation at break increase initially, then drop, For annealed irradiated samples, Young's modulus rises at first, then levels off at higher doses. Tensile strength and elongation at break increase significantly with increasing radiation treatment, then essentially reach constant values at highest doses.     

Far infrared birefringence versus other orientational measurements of high-pressure injection-molded high-density polyethylene

Far infrared (FIR) birefringence is a new tool for measuring orientation in semicrystalline polymers. In this work FIR birefringence of high-pressure injection-molded high-density polyethylene (HDPE) was compared with wide-angle X-ray scattering (WAXS) and shrinkage for the first time. An indirect measure of orientation was obtained by differential thermal analysis (DTA). The content of high-temperature melting crystals was found to increase with increasing orientation. A high correlation was found between FIR birefringence and the other orientational measurements. Contrary to the other orientational methods used, FIR birefringence does not saturate with highly oriented samples. It is furthermore faster, nondestructive, and can be used for probing fairly thick samples.     

Melt spinning and drawing of 2‐methyl‐1,3‐propanediol‐substituted poly(ethylene terephthalate)

The structure and properties of fibers prepared from copolymers of poly(ethylene terephthalate) (PET) in which 2‐methyl‐1,3‐propanediol (MPDiol® Glycol is a registered trademark of Lyondell Chemical Company) at 4, 7, 10, and 25 mol% was substituted for ethylene glycol were studied and compared with those of PET homopolymer. Filaments were melt spun over a range of spinning conditions, and some filaments that were spun at relatively low spinning speeds were subjected to hot drawing. The filaments were characterized by measurements of birefringence, differential scanning calorimetry (DSC) crystallinity, melting point, glass transition temperature, wide‐angle X‐ray diffraction patterns, boiling water shrinkage, tenacity, and elongation to break. Filaments containing 25 mol% MPDiol did not crystallize in the spinline at any spinning speed investigated, whereas the other resins did crystallize in the spinline at high spinning speeds. However, compared with PET homopolymer, increasing substitution of MPDiol reduced the rate at which the crystallinity of the melt spun filaments increased with spinning speed and reduced the ultimate crystallinity that could be achieved by high‐speed spinning. The rate of development of molecular orientation, as measured by birefringence, also decreased somewhat with increasing MPDiol content. Shrinkage in boiling water decreased at high spinning speeds as the amount of crystallinity increased; however, the shrinkage decreased more slowly with increase in spinning speed as MPDiol content increased. Tenacity also decreased slightly at any given spinning speed as MPDiol content increased, but there was no significant effect on elongation to break. The addition of MPDiol in amounts up to 7 mol% increased the maximum take‐up velocity that could be achieved at a given mass throughput. This result indicates that the use of higher spinning speeds could potentially increase the productivity of melt spun yarns. Copolymer filaments spun at low speeds were readily drawn to produce highly oriented fibers with slightly less birefringence, crystallinity, and tenacity than similarly processed PET homopolymer. Preliminary dyeing experiments showed that the incorporation of MPDiol improved the dyeability of the filaments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2598–2606, 2003     

Kinetics of rapid structural changes during heat setting of preoriented PEEK/PEI blend films as followed by spectral birefringence technique

The influence of composition and preorientation on the development of structural hierarchy during heat setting of PEEK/PEI films was investigated using on-line birefringence, and off-line wide-angle and small-angle X-ray scattering, infrared dichroism and thermal analysis techniques. When the PEEK/PEI blends are drawn to deformation levels below the onset of strain hardening, the subsequent heat setting at high temperature starts with a large relaxation process followed by a fast crystallization and a long-term slow structural rearrangement stages. When the films are predrawn beyond a critical structural level (crystallinity and orientation), the initial relaxation stage disappears. This signifies that beyond a critical structural order a long-range physical network, where the nodes consist of crystallized domains and chain—self and cross-entanglements—are formed. This physical network allows the entropy driven shrinkage stresses to be maintained that results in the development of oriented crystalline phase. The addition of non-crystallizable PEI chains was found to retard the formation of this ‘network structure’ resulting in lower orientation levels.     

直接纺丝法制备超高强度涤纶短纤维的工艺研究

通过对熔体输送、纺丝成形和后处理工艺的计算机模拟等研究,成功地在大容量、直接纺生产线上生产纤度1.33 dtex、断裂强度大于6.88 cN/dtex、断裂伸长17.2%、180℃干热收缩率小于5.1%的缝纫线用超高强涤纶短纤维。实践表明,熔体输送采用相对较短的停留时间和熔体冷却器的应用是先决条件;用计算机模拟纺丝过程,多元回归的方法得到定性和定量的结果,是工艺制订和稳定运行的关键;后处理可无级变速的拉伸工艺和多段式可调节张力的热辊紧张热定形方式,使各工艺得到优化。     

聚丙烯高速纺丝工艺的研究——卷绕丝超分子结构与后加工性能的工艺控制

利用X射线衍射、DSC、双折射、密度梯度等方法探讨了在3km/min高纺速下,纺丝温度对丙纶POY的超分子结构与后加工性能的影响,对冷却条件的影响也进行了讨论。指出在280℃以下范围提高纺丝温度可以降低聚丙烯高速纺程上的流变张力,使卷绕丝的结晶度降低,结晶成分中次晶含量增加,非晶区取向度提高。采用缓慢冷却有和于提高POY的非晶区预取向。采用MI=35的聚丙烯树脂,在纺丝温度270℃和缓冷条件下可得具有优良后加工性能的丙纶POY,在414m/min速度下经加弹所得DTY的强度为41.1cN/t(?)x,伸长为34.1%,卷曲率为20%,卷曲稳定性为92%。     

Shrinkage in extruded moisture crosslinked silane‐grafted polyethylene wire insulation

Shrinkage studies were conducted on silane‐grafted moisture crosslinkable linear low‐density polyethylene (LLDPE) insulation stripped from extrusion‐coated copper conductors. The insulation, which possesses orientation imparted during melt processing, showed remarkable levels of shrinkage when heated above the melting point of the polymer, though the shrinkage can be greatly reduced by moisture crosslinking the insulation below the melting point of the LLDPE. Shrinkage along the direction of orientation was accompanied by swelling in the other dimensions. Differential scanning calorimetry (DSC) revealed several trends, including a decrease in both melting point and degree of crystallinity with increasing crosslinking. In the first heat after annealing, crosslinked samples exhibited a shoulder in the DSC endotherm several degrees below the normal melting point of the LLDPE. In agreement with prior studies in silane‐grafted HDPE, relaxation of orientation by annealing appeared to result in an increase in the enthalpy of melting. The degree of shrinkage was also found to be dependent on the insulation thickness, which is attributed to faster cooling in thinner insulation immediately following extrusion coating. The results highlight the extensive built in stresses that can be frozen into polymer layers in fabricated articles due to melt orientation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

New degradable thermosets obtained by cationic copolymerization of DGEBA with an s(γ-butyrolactone)

Diglycidylether of bisphenol A (DGEBA) was cured with different proportions of 1,6-dioxaspiro[4.4]nonane-2,7-dione (s(γ-BL)) with ytterbium triflate as initiator. The curing was studied with differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated total reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the conversion of the epoxide, lactone and intermediate spiroorthoester (SOE) groups. The shrinkage undergone during curing was monitored by means of thermomechanical analysis (TMA). By combining the results obtained by FTIR/ATR and TMA, the processes that were and were not responsible for shrinkage were identified. The thermal and dynamic mechanical properties of the cured materials were determined by DSC and by dynamic mechanical thermal analysis (DMTA), respectively. The kinetic triplet associated with calorimetric curing was determined by means of isoconversional analysis. An increase in the proportion of lactone results in an increased curing rate, a decrease in shrinkage after gelation and a decrease in the glass transition temperature (T_g). Finally, as a preliminary measure, we examined the potential of the systems studied as reworkable materials by means of hydrolytic and thermal degradation. An increase in the ester units in the network results in materials that are less thermally stable and whose controlled degradability is greater.     

Orientierung und Streckmechanismen in amorphen und teilkristallinen Polycarbonatfäden

Heat-stretched fibres of bisphenol-A-polycarbonate may be produced in the fully amorphous as well as in the semi-crystalline state, depending on the choice of the molecular weight of the polymer and the spinning and stretching conditions. Investigations are made as to the influence of the stretching conditions on the orientation of the amorphous regions of the semi-crystalline material and on the orientation of the fully amorphous fibres. The orientation of the fully amorphous fibres is determined by measuring the birefringence, whereas that of the amorphous regions in semi-crystalline material results from the difference in birefringence of the entire structure of the fibres and the birefringence of the crystalline regions. The latter is calculated from the factor of orientation \documentclass{article}\pagestyle{empty}\begin{document}$ \[ \text{f}_\text{k} \text{ = }\frac{1} {2}(3\overline {\cos ^2 } \text{ }\varphi −1) \] $\end{document}, which in turn is measured by wide-angle X-ray scattering. From the polarizabilities of the individual atomic bonds it was possible, on the basis of known interatomic distances and valence angles, to calculate the components of the polarizability tensor for polycarbonate. These values were used to determine the maximum birefringence of amorphous and crystalline polycarbonate. It was shown that the calculated values for birefringence, which were obtained using orientation functions determined by X-ray scattering, agreed very well indeed with those measured from the optical birefringence. Equally good agreement for the oriented filament yarns was obtained between the values for the mean angle existing between chain direction and fibre axis as determined by X-ray examination, and the results calculated from IR-dichroism. In the case of the highly stretched polycarbonate filament yarns, it was observed that, despite the rigid molecule structure, the orientation of the crystalline regions was as high as with, for example, polyethylene-terephthalate fibres. (Mean angle between chain direction and fibre axis approx. 16°). The formation of stretch-induced crystallites with fibres of higher molecular weight polycarbonate can be explained by assuming a heterogeneous stretching mechanism with necking. In the case of low molecular weight polycarbonate fibres consolidated domains of high density cannot be destroyed by heat stretching; instead, they merely slide past each other, with the result that the stretching process takes place homogeneously without initiating any crystallization.     

Shrinkage behavior after the heat setting of biaxially stretched poly(ethylene 2,6‐naphthalate) films and bottles

Amorphous preforms of poly(ethylene 2,6‐naphthalate) (PEN) were biaxially drawn into bottles up to the desired volume under industrial conditions. These bottles were used to characterize the shrinkage behavior of the drawn bottles with or without heat treatment and to study structural variations during heat setting. During drawing, a rigid phase structure was induced, and the amount of the induced rigid phase structure was linearly related to the square root of the extra first strain invariant under equilibrium conditions. During the production of these bottles, this equilibrium was not attained because of high stretching conditions and rapid cooling after stretching. The structure after orientation contained a rigid amorphous phase and an oriented amorphous phase. The shrinkage behavior was a function of the temperature and time of heat setting. Long heat‐setting times, around 30 min, were used to characterize the possible structural variations of the oriented PEN after heat setting at equilibrium. Under the equilibrium conditions of heat setting, the start temperature of the shrinkage was directly related to the heat‐setting temperature and moved from 60°C without heat treatment up to a temperature of 255°C by a heat‐setting temperature of 255°C; this contrasted with poly(ethylene terephthalate) (PET), for which the start temperature of shrinkage was always around 80°C. For heat‐setting temperatures higher than 220°C, the structural variations changed rapidly as a function of the heat‐setting time, and the corresponding shrinkage of the heat‐set samples sank below 1% in a timescale of 30–60 s for a film thickness of 500 μm. The heat treatment of the oriented films taken out of the bottle walls with fixed ends stabilized the induced structures, and the shrinkage of these heat‐set films was zero for temperatures up to the heat‐setting temperature, between 220 and 265°C, if the heat‐setting time was sufficient. According to the results obtained, a heat‐setting time of 30 s, for a film thickness of 500 μm, was sufficient at a heat‐setting temperature of 255°C to stabilize the produced biaxially oriented PEN bottles and to take them out the mold without further shrinkage. During the drawing of PEN, two different types of rigid amorphous phases seemed to be induced, one with a mean shrinkage temperature of 151°C and another rigid amorphous phase, more temperature‐stable than the first one, that shrank in the temperature range of 200–310°C. During heat setting at high temperatures, a continuous transformation of the less stable phase into the very stable phase took place. The heat‐set method after blow molding is industrially possible with PEN, without the complicated process of subsequent cooling before the molds are opened, in contrast to PET. This constitutes a big advantage for the blow molding of PEN bottles and the production of oriented PEN films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1462–1473, 2003     

热定型对嵌段聚醚酯弹性纤维结构与性能的影响

研究了热定型时间、温度和方式对嵌段聚醚酯弹性纤维的结构和性能的影响 ,采用 DSC、X-射线衍射测定了纤维热定型前后结晶结构及结晶度的变化 ,同时测定了纤维的断裂强度、断裂伸长、回弹率和热水收缩率的变化 ,结果表明 ,热定型处理使嵌段聚醚酯纤维的结晶结构发生了变化并使结晶度提高 ,从而提高了纤维的回弹性能和力学性能 ,纤维的热水收缩率与氨纶相当     

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