A structural study of the tensile drawing behaviour of poly(ethylene terephthalate)

A study of single-stage and two-stage drawing of poly(ethylene terephthalate) has been undertaken. Measurements of the modulus of the drawn films were combined with a range of structural measurements, including refractive index, X-ray diffraction and infra-red spectroscopy. The development of molecular orientation during drawing is discussed in terms of the deformation of a molecular network, and reasons for the differences between single stage and two-stage drawing are proposed. The relationships between different measures of molecular orientation are considered with the aim of obtaining an understanding of the factors which influence the modulus values. It appears that the modulus relates primarily to the molecular chains which are in the extended trans conformation, irrespective of crystallinity.     

Tensile drawing behaviour of poly(ethylene terephthalate)

A detailed study has been undertaken of the drawing behaviour of poly(ethylene terephthalate) over the temperature range 20° to 80°C. Cold drawing behaviour was observed at the lower temperatures and homogeneous deformation at 80°C. Samples were also subjected to two-stage drawing: homogeneous draw at 80°C followed by cold drawing at 20°C. In all cases the geometry of the deformation was monitored by measuring the changes in macroscopic dimensions. In addition, measurements were made of the final birefringence, and the shrinkage force developed when the drawn samples were heated to a temperature above T_g. The results are discussed in terms of continuum models for the deformation of polymers. In particular, the relevance of a simple molecular network model is considered. It is shown that many of the observations are consistent with the deformation of a molecular network, although our understanding of the molecular processes involved in cold drawing is still incomplete.     

Crystallization behavior of poly(ethylene terephthalate)

The crystallization behavior of poly(ethylene terephthalate) (PET) was studied by the methods of small angle light scattering, depolarized light intensity and density measurements. Spherulite growth rates and the overall rates of crystallization were determined at various temperatures. A detailed analysis of the crystallization course has been made with special emphasis on the early stages of crystallization. The results indicate that a significant amount of crystallization takes place in the extraspherulitie material during isothermal crystallization.     

Heat generation associated with drawing of poly(ethylene terephthalate)

The heat associated with drawing of poly(ethylene terephthalate) fiber is estimated on the basis of equations developed in the literature on films undergoing deformation by neck propagation. The deformation process is divided into two steps: neck propagation or drawing to the natural draw ratio and uniform deformation accompanied by crystallization. The results show that heat loss is negligible during deformation by necking and the temperature rise is estimated to be about 60K in yarns with a spun birefringence of 0.011. The heat released in step 2 is sufficient to raise the fiber temperature about 55K under adiabatic conditions, of free air convection, the temperature rise is estimated to be only about 5–1 0K.     

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25-110 °C) and strain rates (.005-1.0 s⁻¹). The stress-strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature (θ_g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress-strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub-θ_g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress-strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.     

Mechanism of cold drawing in melt-spun poly(ethylene terephthalate) fibers

An investigation has been made into the mechanism of cold drawing in melt-spun poly(ethylene terephthalate) (PET) fibers. An analysis of the cold-drawing behavior using wide-angle x-ray diffraction, orientation measurements, calorimetric and mechanical techniques was performed. The evidence suggests that the cold-drawing process involes stress-enhanced crystallization which occurs in conjuction with incresing orientation of the crystalline and amorphous regions. A degradation in the fiber properties after cold drawing was observed for fibers spun below 1,000 m/min while fibers spun above 1,000 m/min exhibited an improvement in fiber properties with cold drawing. This behavior was explained by the existence of two distinct irreversible deformation micromechanisms for fibers spun below and above 1,000 m/min.     

Miscibility and melting behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting behavior of binary crystalline blends of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) have been investigated with differential scanning calorimetry and scanning electron microscope. The blends exhibit a single composition‐dependent glass transition temperature (T_g) and the measured T_g fit well with the predicted T_g value by the Fox equation and Gordon‐Taylor equation. In addition to that, a single composition‐dependent cold crystallization temperature (T_cc) value can be observed and it decreases nearly linearly with the low T_g component, PTT, which can also be taken as a valid supportive evidence for miscibility. The SEM graphs showed complete homogeneity in the fractured surfaces of the quenched PET/PTT blends, which provided morphology evidence of a total miscibility of PET/PTT blend in amorphous state at all compositions. The polymer–polymer interaction parameter, χ₁₂, calculated from equilibrium melting temperature depression of the PET component was ?0.1634, revealing miscibility of PET/PTT blends in the melting state. The melting crystallization temperature (T_mc) of the blends decreased with an increase of the minor component and the 50/50 sample showed the lowest T_mc value, which is also related to its miscible nature in the melting state. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A comparative study of fracture behavior between carbon black/poly(ethylene terephthalate) and multiwalled carbon nanotube/poly(ethylene terephthalate) composite films

Fracture behavior of amorphous poly(ethylene terephthalate) (PET) films added multiwalled carbon nanotube (MWCNT) has been compared with that of the PET films added with carbon black (CB) to elucidate the effects of the large aspect ratio of MWCNT. Fracture toughness has been evaluated using the essential work of fracture tests. Evolution of the crazes has been analyzed by conducting time‐resolved small‐angle X‐ray scattering measurements during tensile deformation of the films at room temperature using synchrotron radiation. CB and MWCNT increased the fracture toughness of the PET film by increasing the plastic work of fracture. This resulted from the effects of the fillers to prevent the localization of deformation upon the crazes formed at earlier stages of tensile deformation and to retard the growth of the fibrils in the crazes to a critical length. The CB particles provided a number of sites where the crazes were preferably formed due to stress concentration. In the case of MWCNT, on the other hand, the widening of the crazes formed at earlier stages was suppressed due to the bridging effect arising from the large aspect ratio of MWCNT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

聚(对苯二甲酸乙二醇酯-co-对苯二甲酸异山梨醇酯)等温结晶行为研究

以对苯二甲酸(PTA)、乙二醇(EG)、异山梨醇(ISB)为原料,通过直接熔融缩聚法合成聚(对苯二甲酸乙二醇酯-co-对苯二甲酸异山梨醇酯)(PEIT)共聚酯。利用差示扫描量热法(DSC)研究了共聚酯的结晶行为,采用Avrami方程分析了共聚酯的等温结晶动力学。结果表明,PEIT共聚酯结晶行为受共聚组成和结晶温度影响。随着ISB用量的增加或结晶温度的降低,共聚酯半结晶周期t1/2增加、结晶速率变慢;ISB摩尔分数超过20%,共聚酯无法结晶。     

Micromechanical behavior of impact modified poly(ethylene terephthalate)

The micromechanical behavior of poly(ethylene terephthalate), PET, modified with a metallocene polyolefin copolymer (mPE) was investigated. Uniaxial deformation tests were performed using a tensile stage in a scanning electron microscope. This technique allowed the identification of the main deformation mechanisms that are associated with energy dissipation and toughness improvement. The poly(ethylene terephthalate) was blended with 5 wt% mPE by single‐screw extrusion. Films with thicknesses ranging from 200 to 500 μm were produced. Observation of the surfaces of the films during uniaxial deformation revealed the sequence of events leading to the full yielding of the matrix. In the early stages of deformation, the particles deform together with the matrix. As the deformation is increased, cavitation inside the particles occurs and fibrillation at the particle/matrix interface is observed, as well as the onset of shear banding. In order to study the effect of interfacial adhesion of the deformation mechanisms, the PET/mPE blends were compatibilized by grafting with glycidyl methacrylate (GMA). The reduction of the particle size was significant, which is indicative of the efficiency of GMA grafting in this type of blend. In this case, the particles were difficult to detect on the surface. Cavitation and shear banding occurred simultaneously. A similar behavior was observed in the case of oriented blends.     

Cold-drawing behavior of naturally aged poly(ethylene terephthalate)

The cold-drawing behavior of naturally aged poly(ethylene terephthalate) (PET) is investigated and an attempt is made to compare the mechanical behavior of unaged commercial PET and material which has been naturally aged for 11 years. Mechanical, viscometric, DSC and IR measurements are applied. The previously observed unusual ability of fresh PET bristles to be cold drawn up to 15:1 is not achieved for the naturally aged material. This fact is related to chemical cross-linking occurring on the surface of bristles after drawing and thermal treatment. The cross-linked skin is unsoluble, infusible, and uncrystallizable. The natural aging defeats the ability of PET to respond to external treatments which would otherwise change the internal structure. Such a “stabilization” of material properties is a result of the transformation, during natural aging, of the original physical network into a chemical network consisting of covalent bonds.     

Preparation of high-modulus poly(ethylene terephthalate) fibers by vibrating hot drawing

A novel drawing method, vibrating hot drawing, was successfully applied to poly(ethylene terephthalate) fiber, which has a normal molecular weight (IV = 0.7 dL/g) and was prepared by melt spinning. The process was divided into three steps, with differing conditions in drawing temperature, applied tension, vibrating frequency, and amplitude. The drawing temperature and vibration frequency were decided by considering the α_a dispersion of the polymer. In spite of a low draw ratio (7.7) and a low crystallinity (0.55), the birefringence and dynamic storage modulus at room temperature of the 3rd-step fiber reached 0.260 and 36 GPa, respectively. The modulus remains at a high level at elevated temperatures, for example, 29 GPa at 100°C and 17 GPa at 200°C. Further, it was found from temperature and intensity of the α_a dispersion peak that the movements of amorphous chains are strongly inhibited. © 1996 John Wiley & Sons, Inc.     

The thermal shrinkage of the drawing poly(ethylene isophthalate terephthalate) copolyester films

The objective of this study is to use the copolymerization method to improve the thermal shrinkage property of poly(ethylene terephthalate) (PET), so that the resultant copolyester can be used for the application of thermal shrinkage packing materials. The poly(ethylene isophthalate terephthalate) (PEIT) copolyester films were prepared and studied. The thermal shrinkage rate of PET films and the thermal shrinkage rate of the copolyester films were measured by using a thermomechanical analyzer (TMA). The thermal shrinkage of copolyester was found to be dependent on such factors as composition, molecular weight, and draw temperature. The highest thermal shrinkage was obtained when the copolymer contained 40 mol % of ethylene isophthalate. Its shrinkage ratio and shrinkage rate were consistently 1.3 and 2.4 times those of PET. The increase of molecular weight and decrease of drawing temperature resulted in the increase of the thermal shrinkage. The best drawing temperature range was between glass transition temperature and soft temperature of the copolymer. The relationship of shrinkage rate and temperature indicate that the shrinkage mechanism of the copolyester belongs to two-step thermal shrinkage.     

Orientation and crystallisation mechanisms during fast drawing of poly(ethylene terephthalate)

Summary Synchrotron radiation has been used to record the diffraction patterns from Poly(ethylene terephthalate) for a range of draw rates (0.1 to 10sec⁻¹) and temperatures (90 to 120°C). The patterns were analysed to derive the development of the <P ₂(cosθ)> order parameter and the rates of crystallisation. The effects of temperature and draw rate can be unified with a WLF time-temperature shift factor. Comparison with estimates of chain relaxation processes show that, when the draw rate is faster than the chain retraction process, the onset of crystallisation is delayed until the end of drawing. Crystallisation is very sensitive to both temperature and orientation and has an approximate 4th power dependence on <P₂(cosθ)>. Received: 26 October 1998/Accepted: 12 February 1999     

A comparison of the flow behavior of linear polyethylene,poly(butylene terephthalate), and poly(ethylene terephthalate)

The viscous and elastic properties of linear high density polyethylene (HDPE), poly(butylene terephthalate) (PBT), and poly(ethylene terephthalate) (PET) are investigated using an Instron capillary rheometer and the Philippoff–Gaskins–Bagley analysis. The viscous properties studied are the shear viscosity and the constant shear rate activation energy and the elastic properties studied are the entrance pressure drop and the end correction. The variables are shear rate and temperature. The order of decreasing viscosity is HDPE>PET>PBT; the order of decreasing activation energy is PB>PET>HDPE; the order of decreasing entrance pressure drop is HDPE>PET>PBT; and the order of decreasing end correction is PBT>PET>HDPE. As temperature increases, both viscosity and entrance pressure drop decrease. The observed behavior is discussed in terms of the difference in number of terephthalic acid moities in the polymer chains and in terms of oligomer plasticization.     

Fibers from poly(ethylene terephthalate) and poly(butylene terephthalate) blends I. Mechanical behavior

Fibers prepared from poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) blends show a sharp decrease in tensile strength and modulus when blends are on the verge of phase segregation. The modulus values differ for homopolymers for their differences in chain configuration and methylene groups and that of the blends are in proportion. The experimental strength values are higher than the predicted values according to Paul's model for incompatible polymers. At 90/10 PET/PBT blend, the modulus is high, which may be a relative factor to the smaller crystal size of the components.     

Molar mass of poly (ethylene terephthalate) (PET) during ultimate uniaxial drawing

The changes of the average molar mass M_w, M_n, M_z, and molar mass distributions during multistep uniaxial drawing of poly(ethylene terephthalate) (PET) to achieve ultimate mechanical properties have been studied in detail by means of size exclusion chromatography (SEC) with triple detection: concentration, viscosimetry, and light scattering, using HFIP as solvent. An increase in molar mass of PET due to post‐polycondensation and/or transesterfication during drawing at a high temperature of 160 to 230°C was found. Moreover, drawing leads to crystallization and large orientation in the amorphous phase, which results in lower molecular mobility and prevents a further growth in chain length. Crazing under extreme drawing conditions occurs and affects a decrease in molar mass.     

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     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005     

Ultrasonic characterization of the crystallization behavior of poly(ethylene terephthalate)

On the basis of the previous observations that the ultrasonic signals are sensitive to the crystallization of polymers (Tatibouet and Piché, Polymer 1991, 32, 3147), we have expanded our efforts to study the detail relationship between the ultrasonic signals and crystallization process in this work. The nonisothermal and isothermal crystallization of virgin poly(ethylene terephthalate) (PET) and PET samples after degradation were studied by using a specially designed pressure‐volume‐temperature (PVT) device, with which an ultrasonic detector was combined. The results showed that the evolution of the ultrasonic signals not only can be used to probe the crystallization process but also can qualitatively characterize the crystallization rate, crystallinity, crystallite size, and amorphous. DSC measurement was used to verify such results. Ultrasonic signals could be as a complementary tool to polymer chain movement and well be applied to characterize the crystallization behavior. Furthermore, the ultrasonic measurement has the potential use to characterize crystallization of products in‐line during processing (i.e., injection molding, micromoulding). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009