Crystal perfection in axially oriented poly(ethy1ene terephthalate) fibers and films and its dependence on process variables

Gupta, V. B.; Jain, Anurag; Radhakrishnan, J.; Chidambareswaran, P. K.

doi:10.1080/00222349408248087

Cited by 14 publications

(11 citation statements)

References 20 publications

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“…The slow crystallization behavior of PET, on the other hand, offers a broader experimental access to the study of its crystallization kinetics. In fact, owing to these attractive and suitable properties, almost every aspect of its crystallization behavior has been dealt with by many scholars over the years [4][5][6][7][8][9] . Jun et al [10] prepared poly(ethylene terephthalate) nanocomposites reinforced with multiwall carbon nanotubes (MWCNTs) through melt compounding in a twin-screw extruder.…”

Section: Introductionmentioning

confidence: 99%

Non-isothermal crystallization kinetics of kaolin modified polyester

Zhang

Chen

2011

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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Fiber-class modified kaolin and PET have been blended in the twin-screw and granulated to chips containing 4 wt% of kaolin. Non-isothermal crystallization process of kaolin modifi ed polyester was investigated using a differential scanning calorimetry (DSC), and the addition of kaolin enhances either the melting temperature (T m ) or the crystallization temperature (T c ). The morphology of kaolin modifi ed polyester, the melt of which is cooled at different cooling rate, was observed by scanning electron microscope (SEM). The relationship between T c and cooling rate F was studied. Semi-crystalline phase t 1/2 makes an exponential decline with increasing F, and the higher the cooling rate, the shorter the time of crystallization completion. Non-isothermal crystallization kinetics parameters and the activation energy were calculated, indicating that the higher rate of cooling needs the higher relative crystallinity in the unit crystallization time, the crystallization rate increased while speeding up the temperature reduction, and the activation energy E was calculated to be -204.1566 kJ/mol for the non-isothermal crystallization processes by the Kissinger's methods.

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Section: Introductionmentioning

confidence: 99%

Non-isothermal crystallization kinetics of kaolin modified polyester

Zhang

Chen

2011

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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“…Ellis et al 67 report that the crystallinity of a sample drawn at a draw ratio of 4 is measured by DSC experiments to be about 31%, whereas the WAXD curves reveal much lower values. In other studies 79 of drawn PET samples at 70 ЊC where density measurements took place, the crystallinity appeared to be about 31%, while the X-ray measurements for the same samples gave a value of 7-8%. The fact that the ''intermediate'' phase in reality has no detectable crystallinity was proven by a very recent study 80 in which the structural development in amorphous PET under uniaxial deformation above T g was investigated in situ using synchrotron WAXD.…”

Section: Resultsmentioning

confidence: 81%

Vibrational Spectroscopic Study on the Origin of Stress Oscillation during Step-Wise Stretching in Poly(Ethylene Terephthalate)

2004

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The origin of the phenomenon of stress oscillation during step-wise stretching at room temperature for amorphous poly(ethylene terephthalate) (PET) was investigated using vibrational spectroscopy. For the first time, transmission Fourier transform infrared (FT-IR), attenuated total reflection (ATR) FT-IR, and micro-Raman spectroscopies were used in order to investigate the correlation of the orientation of the molecular chains, their conformational transformations, and the appearance of stress-induced crystallization to the phenomenon of stress oscillation during the step-wise stretching procedure. The phenomenon of stress oscillation occurs when amorphous PET is exposed to mechanical stress during which the extension rate is increased in a step-wise manner. This phenomenon leads to the formation of a pattern of opaque and transparent stripes (''striated'' or oscillating region), clearly distinguished from the unstretched (''bulk'') and the ''necking'' regions. Both infrared and Raman spectroscopic investigations revealed that the main conformational transformations and a significant increase of the crystallinity occur simultaneously in the ''striated'' region. Polarized infrared experiments showed the presence of increased molecular orientation, which is more profound for the ''intense striated'' region. Finally, micro-Raman spectroscopy allowed the study of opaque and transparent stripes individually and showed that the opaque stripes are more crystalline. Thus, our findings provide conclusive experimental support for the theory, which directly correlates the appearance of the stress-oscillation phenomenon with the induction of crystallinity and heat release and is based on Barenblatt's model. Our study also provides new conformational assignments for the infrared bands in PET for the high-frequency region from 3200 to 3800 cm(-1). Specifically, the bands at 3336 cm(-1) and at 3298 cm(-1) have been attributed to the trans and gauche conformations, respectively.

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“…8 orientation function data are plotted against the draw ratio of PET fibers. The data are those of Dumbleton [155], Padibjo and Ward [78] and Gupta and associates [156]. The data clearly indicate that at any given draw ratio the crystal orientation is higher than the amorphous orientation.…”

Section: Orientation Effectsmentioning

confidence: 80%

“…The parallel arrays or bundles will have a higher polymer density than the unaligned polymer and, as long as the repeat units in the aligned chain segments are not in register, these segments will remain amorphous yet aligned and of higher density than the unaligned amorphous phase of the same polymer. [155]; & data from [156];~, ! data from [78].…”

Section: Orientation Effectsmentioning

confidence: 99%

Increased glass transition temperature in motionally constrained semicrystalline polymers

Aharoni¹

1998

Polym. Adv. Technol.

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A large number of experimental results in the literature support and illuminate a model of behavior of chains and chain segments in the amorphous phase of semicrystalline polymers connecting the elevation of the glass transition temperature (Tg) above its normal value to several kinds of motional restrictions imposed on the chains and parts thereof. Accordingly, polymer chain, chain‐segment and chain‐fragment motions of all kinds comprise one or more torsions around main‐chain bonds from one stable conformation to another, known as rotational isomerizations. When impediments are placed in front of thermal fluctuations and larger transversal and longitudinal motions of polymer chains, segments and shorter fragments in the amorphous phase, and the motions are thus restricted, the glass transition temperature is elevated relative to that of the same amorphous phase in the bulk under normal conditions. The obstructions may prevent either the onset of rotational isomerizations or of their completion once started. The completion of the torsional isomerizations and larger motions may be prevented by eliminating the free spaces necessary to accommodate the volumes of the interconverting chain fragments and segments even when they move in concert, or by preventing the creation of such free spaces. Another way to hinder the completion of such motions is by the introduction into the system of many rigid walls and other interfaces with strong attractive interactions with the polymer, that by geometrical constraints and attractive interactions suppress the rotational and larger motions and prevent their completion. Elimination of the necessary free volume is achievable by the application of compressive pressure, while the introduction of rigid attractive walls may be accomplished by the incorporation of crystallites, as in semicrystalline polymers, or by the addition of rigid finely comminuted foreign additives with very large surface areas or confining voids with high tortuosity. It is believed that motional restrictions imposed on the amorphous phase by the growth faces of polymer crystallites, especially in oriented semicrystalline polymers, are more effective than the restrictions imposed by the fold surfaces of these crystallites. The prevention of the onset of rotational isomerizations and larger motions may be achieved by stretching the polymer chains and chain segments in the amorphous phase and, by one means or another, pinning down the taut chains such that essentially all their rotational isomers are in the trans conformation: they cannot interconvert to the gauche conformation since it requires the chain’s end‐to‐end distance to decrease. Parallel alignment of relatively taut chain‐segments may impose additional geometrical restrictions on both the onset and completion of rotational isomeric torsions and, of course, on longer‐range motions. In all cases, the Tg of the motionally constrained parts of the amorphous phase, especially in semicrystalline polymers, is expected to rise. It is likely that the cha...

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Crystal perfection in axially oriented poly(ethy1ene terephthalate) fibers and films and its dependence on process variables

Cited by 14 publications

References 20 publications

Non-isothermal crystallization kinetics of kaolin modified polyester

Non-isothermal crystallization kinetics of kaolin modified polyester

Vibrational Spectroscopic Study on the Origin of Stress Oscillation during Step-Wise Stretching in Poly(Ethylene Terephthalate)

Increased glass transition temperature in motionally constrained semicrystalline polymers

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