Hot compaction of woven nylon 6,6 multifilaments

We describe a study of the hot compaction of woven nylon 6,6 multifilaments produced by a patented procedure, developed at the University of Leeds, for creating novel single‐polymer composites. In this process, an assembly of oriented elements, often in the form of a woven cloth, is held under pressure and taken to a critical temperature so that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the single‐polymer composite. This process is therefore a way of producing novel high‐volume‐fraction polymer/polymer composites in which the two phases are chemically the same material. Nylon is an obvious candidate material for this process because oriented nylon multifilaments are available on a commercial scale. The aim of this study was first to establish the conditions of temperature and pressure for the successful hot compaction of oriented nylon 6,6 fibers and second to assess the mechanical properties of the manufactured hot‐compacted nylon sheets. A crucial aspect of this work, not previously examined in hot‐compaction studies of other oriented polymers, was the sensitivity of the properties to absorbed water, with a significant change in the properties measured immediately after hot‐compaction processing and 2 weeks later when 2% water had been absorbed by the compacted nylon sheets. As expected, the water uptake had a greater effect on those properties that depended on local chain interactions (e.g., the modulus and yield strength) and less effect on those properties that depended on the large‐scale properties of the molecular network (e.g., strength). The only negative aspect of the properties of the hot‐compacted nylon sheets was the elevated‐temperature performance of the wet sample, with the modulus falling to a very low value at a temperature of 80°C. However, apart from the elevated‐temperature performance, the majority of the measured properties of the hot‐compacted nylon sheets were comparable to those of hot‐compacted polypropylene and poly(ethylene terephthalate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 991–997, 2006     

Effects of preform deformation behavior on the properties of the poly(ethylene terephthalate) bottles

Plastics bottles made out of poly(ethylene terephthalate) (PET) are usually produced by injection stretch blow molding. Optimization of the process parameters is necessary to achieve bottles with adequate top load and burst strength. However, doing so experimentally is time‐consuming and costly. To overcome this difficulty, simulation packages based on finite element analysis methods have been developed. In this study, process optimization of a 350‐mL PET fruit juice bottle was carried out by means of BlowView and ANSYS simulation packages. BlowView was used for the ISBM process simulation and ANSYS for structural analysis of the bottles. The bottles were produced under different process conditions where the timing of the stretch rod movement was varied in relation to the activation of the blow pressure. The simulation results obtained through the both simulation packages were compared with experimental results. It was found that bottles of highest quality were produced if the sequencing of axial stretching and radial inflation results in simultaneous biaxial deformation of the preform. Truly biaxial orientation of PET molecules improved both top‐load and burst resistances of the bottles. The structural simulation studies performed by the ANYSYS simulation package validated most of our experimental findings. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hot compaction of polyethylene naphthalate

In this article, we describe the production of single polymer composites from polyethylene naphthalate (PEN) multifilaments by using the hot compaction process. In this process, developed at Leeds University, highly oriented tapes or fibers are processed at a critical temperature such that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the composite. This process is, therefore, a way to produce novel high‐volume fraction polymer/polymer composites where the two phases are chemically the same material. A variety of experimental techniques, including mechanical tests and differential scanning calorimetry, were used to examine the mechanical properties and morphology of the compacted PEN sheets. Bidirectional (0/90) samples were made at a range of compaction temperatures chosen to span the melting range of the PEN multifilaments (268–276°C). Measurement of the mechanical properties of these samples, specifically the in‐plane modulus and strength, allowed the optimum compaction temperature to be ascertained (～ 271°C), and hence, the optimum mechanical properties. The optimum compacted PEN sheets were found to have an initial modulus close to 10 GPa and a strength of just over 200 MPa. The glass transition temperature of the optimum compacted sheets was measured to be 150°C, nearly 40°C higher than compacted poly(ethylene terephthalate) (PET) sheets. In previous work on polypropylene and PET hot compacted materials, it proved instructive to envisage these materials as a composite where the original oriented multifilaments are regarded as the reinforcing phase, and the melted and recrystallized material are regarded as the matrix phase. Dynamic mechanical bending tests (DMTA) were used here to confirm this for PEN. DMTA tests were carried out on the original fibers and on a sample of completely melted material to determine the fiber and matrix properties, respectively. The composite properties were then predicted by using a simple rule of mixtures and this was found to be in excellent agreement with the magnitude and measured temperature dependence of the hot compacted PEN material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 796–802, 2004     

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     

Surface analyses of corona-treated poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) Mylar® samples were treated by corona discharge in order to improve their adhesive properties. The corona treatments were performed in different atmospheres including nitrogen, ammonia and air. X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical modifications induced at the PET surface by these corona treatments. XPS results show that nitrogen incorporation takes place in the form of non-oxygenated nitrogen functionalities, like amine or cyano groups. These are present at the surface of all the corona-treated samples but in different concentrations depending on the gases used in the corona discharge. Furthermore, XPS analyses performed after heating of the treated samples show a higher thermal stability of the corona-induced surface modifications in the case of nitrogen and ammonia. Ion scattering spectroscopy (ISS) and static secondary ion mass spectroscopy (SIMS) analyses were also performed because of their higher surface sensitivity compared with XPS: ISS reveals that nitrogen is not present at the topmost surface layer of the treated samples but is incorporated just beneath. The outermost surface layer presents a composition rich in oxygen. Finally, static SIMS spectra show that corona treatment induces more surface degradation when performed in air compared with nitrogen or ammonia. These results are discussed in relation to adhesive properties of PET.     

Effects of the recycled poly(ethylene terephthalate) fibers on the rigid polyurethane foam

Recycled poly(ethylene terephthalate) (PET), subjected to the treatment with the flame retardant first, was used to reinforce the rigid polyurethane foams (RPUFs). Different loadings of PET fibers (3–12 wt %) of different lengths (5, 10, 15, and 20 mm) were added into RPUF. The mechanical properties of composites were studied by compressive strength test and shear stress test. The flame-retardant properties were evaluated by cone calorimeter and limited oxygen index test. The results showed that the proper addition of PET fibers could improve the mechanical and flame-retardant properties of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47758.     

Fine structure and physical properties of polyethylene/poly(ethylene terephthalate) bicomponent fibers in high‐speed spinning. I. Polyethylene sheath/poly(ethylene terephthalate) core fibers

The high‐speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take‐up velocity was investigated. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50, [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [HDPE(11)/PET and LLDPE(50)/PET bicomponent fibers] were studied. The fiber structure formation and physical property effects on the take‐up velocities were investigated with birefringence, wide‐angle X‐ray diffraction, thermal analysis, tensile tests, and so forth. In the fiber structure formation of PE/PET, the PET component was developed but the PE components were suppressed in high‐speed spinning. The different kinds of PE had little affect on the fine structure formation of bicomponent fibers. The difference in the mechanical properties of the bicomponent fiber with the MFR was very small. The instability of the interface was shown above a take‐up velocity of 4 km/min, where the orientation‐induced crystallization of PET started. LLDPE(50)/PET has a larger difference in intrinsic viscosity and a higher stability of the interface compared to the HDPE(11)/PET bicomponent fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2254–2266, 2000     

Sorption of lower alcohols in poly(ethylene terephthalate)

This paper presents equilibrium sorption and kinetics of lower alcohols in a 1.5 μ thick, biaxially oriented PET film. Methanol, ethanol, n-propanol and iso-propanol have been studied for the solubility and sorption kinetics in this film to understand how these properties change with penetrant size and branching. It is observed that n-propanol shows dual mode characteristics at all activities whereas the other three penetrants show Flory-Huggins uptake at high activities. Infinite dilution solubility is estimated and compared with that of esters, ketones and other hydrocarbons previously reported. The dispersive solubility parameter, δ_d is found to correlate well with the solubility of penetrants with the same functional group. The hydrogen bonding parameter, δ_h is observed to influence the solubility of penetrants with the same carbon number but different functional groups. This correlation with the solubility parameters may be extended to other functional groups and used to predict the infinite dilution solubility of larger penetrants in PET. Diffusion coefficients in the Fickian kinetics regime and Berens-Hopfenberg parameters in the non-Fickian kinetics regime have been evaluated. Diffusivity increases with concentration and decreases with size. Diffusion coefficient of iso-propanol is an order of magnitude lower than that of n-propanol due to branching effects.     

Efficient method for recycling poly(ethylene terephthalate) to poly(butylene terephthalate) using transesterification reaction

A method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)₄ and Sb₂O₃ as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004     

Mechanical and thermal properties of poly(ethylene terephthalate) fibers crosslinked with disulfonyl azides

A novel method for the crosslinking of poly(ethylene terephthalate) fibers is described using 1,6‐hexanedisulfonyl azide, 1,3‐benzenedisulfonyl azide, and 2,6‐naphthalenedisulfonyl azide. The azides are diffused into poly(ethylene terephthalate) fibers (Dacron) from perchloroethylene solution, and the fibers are heat treated to bring about decomposition of the sulfonyl azide and give rise to crosslinking. A study is made of the mechanical and thermal properties of the resultant fibers, which are changed considerably in comparison to the untreated fiber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1517–1527, 2002     

Optically transparent self-reinforced poly(ethylene terephthalate) composites: molecular orientation and mechanical properties

Self-reinforced composites have been fabricated by compaction of oriented polyethylene terephthalate (PET) fibers under pressure at temperatures near, but below, their melting point. The originally white fiber bundles, which were about 40% crystalline, show increased crystallinity (55%) but optical translucency after processing. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were used to study the crystallization and orientation of the fibers, revealing that the degree of crystallinity was somewhat insensitive to compaction conditions while the melting point increased substantially with increasing compaction temperature. Crystalline orientation, gauged using the Hermans orientation parameter from WAXD data, indicated that no significant loss in orientation of the crystalline fraction occurs due to compaction. Mechanical characterization revealed a stepwise decrease in flexural modulus (9.4-8.1 GPa) and concomitant increase in transverse modulus and strength on increasing the compaction temperature from 255 to 259 °C. This transition in behavior was accompanied by a loss of optical transparency and a change in the distribution of amorphous fraction from fine intrafibrillar domains to coarse interfibrillar domains as seen with electron microscopy. We argue then that the mechanical properties of PET compactions are influenced more by orientation of the amorphous phase than that of the crystalline phase. The impact properties of compacted materials, characterized using an unnotched Charpy test method, showed remarkable impact resistance after compaction, with impact toughness decreasing as compaction temperature was increased.     

Surface nature of UV deterioration in properties of solid poly(ethylene terephthalate)

We investigated the changes in the molecular weight and also in the mechanical properties with the distance to the exposed surface of the irradiated stacked poly(ethylene terephthalate) (PET) film samples. A relation between the molecular weight and the mechanical properties of the irradiated PET was established. The relation demonstrates that the decrease in molecular weight is one of the main origins causing the deterioration in the mechanical properties. The photodegradation process developing in PET was quantitatively studied by investigating the degradation kinetics of stacked PET film samples. Our results show that the strongest degradation takes place at the exposed surface, and the degradation rate decreases with increasing the distance. This further implies that the capability to bear a tensile stress in the area near the exposed surface is much lower than that in bulk. Therefore, irradiated PET may be fractured in a lower stress. These results indicate the surface nature of ultraviolet deterioration in the physical properties of PET. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 705–714, 1998     

Synthesis and characterisation of copolyesters from poly(ethylene terephthalate) and poly(hexamethylene terephthalate)

Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (T_g). melting points (T_m) and crystallisation temperatures (T_c) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in T_g, T_m and T_c. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation.     

Improving low‐density polyethylene/poly(ethylene terephthalate) blends with graft copolymers

Blends of low‐density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) were prepared with different weight compositions with a plasticorder at 240°C at a rotor speed of 64 rpm for 10 min. The physicomechanical properties of the prepared blends were investigated with special reference to the effects of the blend ratio. Graft copolymers, that is, LDPE‐grafted acrylic acid and LDPE‐grafted acrylonitrile, were prepared with γ‐irradiation. The copolymers were melt‐mixed in various contents (i.e., 3, 5, 7, and 9 phr) with a LDPE/PET blend with a weight ratio of 75/25 and used as compatibilizers. The effect of the compatibilizer contents on the physicomechanical properties and equilibrium swelling of the binary blend was investigated. With an increase in the compatibilizer content up to 7 phr, the blend showed an improvement in the physicomechanical properties and reduced equilibrium swelling in comparison with the uncompatibilized one. The addition of a compatibilizer beyond 7 phr did not improve the blend properties any further. The efficiency of the compatibilizers (7 phr) was also evaluated by studies of the phase morphology (scanning electron microscopy) and thermal properties (differential scanning calorimetry and thermogravimetric analysis). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Utilization of poly(ethylene terephthalate) waste for preparing disodium terephthalate and its application in a solid polymer electrolyte

A widespread application and nonbiodegradability of the poly(ethylene terephthalate) (PET) have created a huge amount of waste, which is imposing a serious life-threatening environmental problem. In this study, we have utilized the PET waste to synthesize disodium terephthalate (DST), an organic salt having two Na⁺ ions per molecule. The purity of the DST phase was confirmed by Fourier transform infrared spectroscopy, X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). A new poly(ethylene oxide)–DST polymer electrolyte was synthesized for utilizing Na⁺ ions of the DST. The electrical conductivity of the electrolyte was optimized by varying the [O]/[Na⁺] mole ratio with temperature and the results were explained using the XRD and differential scanning calorimetry studies. The TGA study showed that the electrolyte is thermally stable up to 200 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47612.     

Effects of hydrolysis on the physical properties of short glass-fibre reinforced poly(ethylene terephthalate)

The mechanical fracture strength and toughness of short-fibre composites, injection moulded from compounds of poly(ethylene terephthalate) (PET) containing 10 and 30% (by weight) (w/o) glass, have been investigated and the dependence upon matrix hydrolytic stability determined. Mouldings have been characterised by several physical techniques to evaluate molecular weight, degradation rates, crystallinity and morphology, whilst time-dependent gravimetric data were derived to quantify sorption kinetics and allow comparisons with theoretical reaction rates to be made. During melt processing, PET is hydrolysed extremely rapidly by traces of moisture (<0.02w/o). yet the inherent strength of moulded composites declines significantly only below an apparently critical molecular weight. However, on long-term humid ageing in hot water, impact behaviour especially is rendered more complex by simultaneous crystallisation, molecular reorder and losses of interfacial bond strength.     

Linear thermoelastic characterization of anisotropic poly(ethylene terephthalate) films

All nine independent elastic constants have been determined for a biaxially stretched poly(ethylene terephthalate) (PET) film using novel mechanical methods. The orthotropic directions and the in‐plane Poisson's ratios were first characterized using vibrational holographic interferometry of tensioned membrane samples. The out‐of‐plane Poisson's ratio was obtained by measuring the change in tension with the change in pressure for constant strain conditions. Pressure–volume–temperature (PVT) equipment was used to measure the bulk compressibility as well as the volumetric thermal expansion coefficient (TEC). The in‐plane Young's moduli were obtained by tensile tests, while the out‐of‐plane modulus was calculated from the compressibility and other elastic constants that describe the in‐plane behavior. The in‐plane TECs in the machine and transverse directions were determined using a thermal mechanical analyzer (TMA). The out‐of‐plane TEC was determined using these values and the volumetric TEC determined via PVT. The resulting compliance matrix satisfies all of the requirements of a positive‐definite energy criterion. The procedure of characterization utilized in this article can be applied to any orthotropic film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2937–2947, 2002     

Preparation of microcellular poly(ethylene terephthalate) and its properties

Engineering plastics poly(ethylene terephthalate) (PET) is relatively difficult to process microcellularly compared to general thermal plastics because of its low melting viscosity. A new method was developed to microcellularly process PET in this study with a general hydraulic press above PET's crystallization temperature and below its melting temperature within times of a few minutes. A processing window existed in which to prepare microcellular PET under certain foaming time, pressure, temperature, and foaming reagent content scope. The effects of foaming time, temperature, pressure, and foaming reagent content on the thermal, mechanical, and dynamic mechanical thermal properties of microcellular PET foam were investigated. Differential scanning calorimetry (DSC) analysis showed that the transition temperature and crystallinity of microcellular PET had small changes with increasing foaming time. Under some processing conditions used in this study, the tensile strength and breaking extension of microcellular PET foam were both increased at the same time, indicating strengthening and toughening effects. The variation of storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with DSC analysis and mechanical measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1956–1962, 2003     

The effect of physical ageing on the properties of poly(ethylene terephthalate)

Physical ageing rates of poly(ethylene terephthalate) have been measured, and ageing is interpreted to be associated with the conventional glass formation process, which occurs at a more rapid rate at higher temperatures. Ageing is accompanied by a marked change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding of the polymer and a marked decrease in impact strength. The fracture results have been attributed to the increased yield stress and a change in contribution of plane stress and plane strain conditions in the samples. Fracture surfaces show evidence of mixed modes of fracture.