Recycled poly(ethylene terephthalate) chain extension by a reactive extrusion process

A commercial‐scale reactive extrusion processing system for recycled poly(ethylene terephthalate) (PET) flakes with an added chain extender, pyromellitic dianhydride (PMDA), was investigated. The PMDA concentration was varied with the intention of reaching a higher recycled PET intrinsic viscosity ([η]). The effect of changing the extruder residence time on the system's stability and the recycled PET [η] was also investigated. Reactive extruded PET with a PMDA concentration up to 0.3 wt% was found to have a higher [η] and lower carboxyl content than recycled PET processed in a normal extrusion system. A shift in [η] of about 0.18 dl/g was obtained with a 0.3 wt% PMDA concentration. A PMDA concentration above 0.3 wt% produced chemical, thermal and hydrodynamic instability in the system, causing crosslinking reactions and gel formation. The reactive extrusion system was stable at low residence time (45 s) and moderate (0.15 wt%) PMDA concentration; however, using 0.2 wt% PMDA produced higher reactive extruded recycled PET [η] with lower carboxyl content than other PMDA concentration levels examined. Residence times higher than 45 s produced higher reactive extruded recycled PET [η]. Reactive extruded recycled PET was also tested for mechanical properties. Polym. Eng. Sci. 44:1579–1587, 2004. © 2004 Society of Plastics Engineers.     

Properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

Blends composed of poly(ethylene terephthalate) (PET) as the majority component and poly(ethylene naphthalate)(PEN) as the minority component were melt-mixed in a single screw extruder at various PET/PEN compound ratios. Tensile and flexural test results reveal a good PET/PEN composition dependence, indicating that the compatibility of the blends is effective in a macrodomain. In thermal tests, single transitions for T_g, T_m and T_c (crystallization temperature), respectively, are observed from DSC as well as single T_g from DMA except for 50/50 blends. These results suggests that the compatibility is sufficient down to the submicron level. Moreover, isothermal DSC tests along with Avrami analysis indicate that PET's crystallization is significantly retarded when blended with PEN. Results in this study demonstrate that PEN is a highly promising additive to improve PET's spinnability at high speeds.     

Sequence analysis of poly(ethylene terephthalate)/poly(butylene terephthalate) copolymer prepared by ester-interchange reactions

The molecular structure of the copolyester formed through the interchange reaction in poly(ethylene terephthalate)/poly(butylene terephthalate) blends was investigated with ¹³C-NMR spectroscopy. The molar fractions of heterolinkage triads in the copolyesters were lower than the values calculated by Bernoullian statistics; this indicates that the sequence of heterolinkages was far from a random distribution at the initial stage of the interchange reaction. However, the randomness increased and the number-average sequence length decreased with reaction time. The solubility of the blend decreased with increasing sequence length, resulting from the formation of block copolymers with long sequence lengths at the initial stage of the interchange reaction. The solubility of the copolyester formed by a dibutyltin dilaurate (DBTDL)-catalyzed reaction was higher than that of the copolyester formed by a titanium tetrabutoxide-catalyzed reaction; this is related to the fact that alcoholysis prevailed in the DBTDL-catalyzed reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 159–168, 2001     

Molecular weight control of poly(ethylene terephthalate) in extrusion process

A control strategy is developed to control molecular weight of recycled poly(ethylene terephthalate), PET, to overcome its degradation through an extrusion process. To obtain dynamic model of a twin screw extruder, steady‐state, and unsteady‐state experiments were performed. Discrete convolution models between inputs and outputs were obtained. Process inputs were considered as screw speed (SS), feed rate, and barrel temperatures and the output was viscosity average molecular weight (M_v) of the extrudate. SS and molecular weight of the product were chosen as the manipulated, controlled variable pair by considering singular value decomposition (SVD) technique. Model based PID controller and model predictive controller were used in the designed control scheme. By the simulation studies, both controllers were found to be successful for set‐point tracking, disturbance rejection cases; and were proven to be robust under modeling errors. POLYM. ENG. SCI., 54:459–465, 2014. © 2013 Society of Plastics Engineers     

In-line monitoring of titanium dioxide content in poly(ethylene terephthalate) extrusion

Peak absorbance changes correlated to changes in species concentration have been the norm in applied spectroscopy, while baseline shifts have been more of an inconvenience. Taking the first or second derivative of the spectra eliminates these baseline shifts. However, with multivariate techniques becoming more readily available, repeatable baseline changes may now be monitored and correlated to specific physical changes. This concept has been studied by monitoring the concentration of titanium dioxide (TiO₂), a white inorganic filler, in molten poly(ethylene terepthalate) (PET). Various mixtures of filled and unfilled PET resins were run through a single-screw extruder, and near infrared spectra were collected in-line by using a flow cell, housing two fiber-optic probes, and mounted downstream of the extruder. The presence of titanium dioxide caused the scattering of light that resulted in a systematic baseline shift. The baseline shifts were correlated to the TiO₂ concentration data. Multivariate techniques involving the use of singular value decomposition (SVD) to perform partial least squares regression (PLS) were applied to quantitatively determine TiO₂ content in the PET melt stream. Standard error of prediction (SEP) values of about 1% were obtained for a model based on two factors.     

Rheological properties of high melt strength poly(ethylene terephthalate) formed by reactive extrusion

A reactive extrusion process was developed improving the rheological properties of PET via the coaddition of a dianhydride and polyol. Specifically, the coaddition of pyromellitic dianhydride (PMDA) with pentaerythritol resulted in a gel‐free polyester with superior melt strengths and viscosities compared to the addition of PMDA alone. The enhancement in rheological properties were dependent on the relative amounts of dianhydride and polyol with the resultant polyester structurally stable in the melt. These results are consistent with the formation of a hyperbranched polyester with long chain branches. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3646–3652, 2006     

Order-disorder transitions in the extrusion of fiber-filled poly (ethylene terephthalate) and blends

Order-disorder transitions occur in fiber orientation and distribution during extrusion of fiber-filled poly (ethylene terephthalate) and its blends with other polymers. Associated with these transitions are three characteristic regimes of extrudate surface morphology, cross-sectional structure and fiber distribution. Low wall shear rates result in a “smooth porcupine” surface, polygonal cross section, and uniform fiber distribution. Medium wall shear rates produce a “rough porcupine” surface, irregular cross section and tubular depletive fiber distribution with fibers depleting at a relative radial position r/R of 0.63 and accumulating at the surface and the axis. This is exactly opposite to the tubular pinch effect observed for neutrally buoyant rigid spheres which accumulate at r/R of 0.63 and deplete at the surface and the axis. High wall shear rates give a “shorn porcupine” surface, rounded or distorted polygonal cross section and radial migration of fibers toward the axis. The extant of disorder decreases with increasing pseudoplasticity, of the fluid, suggesting that the characteristic fiber orientation, distribution and transitions arise from normal stress effect and/or the eccentric rotation of fibers dictated by the complex velocity profile of the flowing fluid. These phenomena have not been previously reported.     

Functional poly(ethylene terephthalate) materials prepared by condensation copolymerization with ionic liquids

In this study, ionic liquid-modified polyethylene terephthalate was prepared for the first time via the condensation copolymerization of 1,3-bis(2-hydroxyethyl) imidazolium chloride (tetrafluoroborate, hexafluorophosphate) with dimethyl terephthalate and ethylene glycol using stannous chloride as the catalyst. The obtained functional materials were characterized using viscosity, infrared spectra, thermogravimetric analysis, scanning electron microscopy, and conductivity measurement. The wettabilities of the materials with different counterions were also tested by static water contact angle measurement. The results revealed that both the thermal stability and the hydrophilicity of functional material were enhanced greatly due to the introduction of ionic liquids. In addition, the antibacterial performances of the copolymers were also evaluated by in vitro assay, and the results proved that the ionic liquid-modified materials presented good antibacterial property. As a result, an effective and feasible method for the modification of polyethylene terephthalate was developed.     

Crystallization of poly(ethylene terephthalate) and poly (butylene terephthalate) modified by diamides

Poly(ethylene terephthalate) (PET) and poly (butylene terephthalate) have been modified by diamide units (0.1–1 mol%) in an extrusion process and the crystallization behavior studied. The diamides used were: for PET, T2T‐dimethyl (N, N′‐bis(p‐carbomethoxybenzoyl)ethanediamine) and for PBT, T4T‐dimethyl (N, N′‐bis(p‐carbomethoxybenzoyl)butanediamine). The above materials were compared to talc (0.5 wt%), this being a standard heterogeneous nucleator, and to diamide modified copolymers obtained by a reactor process. Two PET materials were used: a slowly crystallizing recycled grade obtained from soft drink bottles and a rapidly crystallizing injection molding grade. The crystallization was studied by differential scanning calometry (DSC) and under injection molding conditions using wedge shaped specimens; the thermal properties were studied by dynamic mechanical analysis. T2T‐dimethyl is effective in increasing the crystallization of PET in both of the extrusion compounds as well as in the reactor materials. It was also found that the crystallization temperature of poly(butylene terephthalate) could be slightly increased by the addition of nucleators.     

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     

Flame-retardant poly(ethylene terephthalate)

Poly(ethylene terephthalate) containing hexabromobenzene, tricresyl phosphate, or a combination of triphenyl phosphate and hexabromobenzene, pentabromotoluene, or octabromobiphenyl was extruded or spun at 280°C into monofilaments or low-denier yarn, respectively. Only combinations of the phosphorus- and halogen-containing compounds resulted in flame-retardant poly(ethylene terephthalate) systems, without depreciating their degree of luster and color quality. The melting temperature, the reduced viscosity, and the thermal stability above 400°C of these flame-retardant systems were in most cases comparable to those of poly(ethylene terephthalate) itself. Phosphorus-bromine synergism was proposed with flame inhibition occurring mostly in the gas phase.     

Powdered poly(ethylene terephthalate)

The influence of the conditions of preparation on the properties of powdered poly(ethylene terephthalate) was followed from the point of view of its specific surface. The powdered poly(ethylene terephthalate) prepared by reprecipitation from the melt of 6-caprolactam has a porous and structured surface, and consequently, also a large specific surface in comparison with the powedered poly(ethylene terephthalate) prepared by mechanical milling. The specific surface value is influenced by the cooling rate of the initial homogeneous melt of poly(ethylene terephthalate)-6-caprolactam, by the concentration of poly(ethylene terephthalate) in this melt and by its molecular weight, by the water temperature at the extraction of 6-caprolactam from the tough mixed melt, by the drying temperature of the powdered poly(ethylene terephthalate), and by the content of residual 6-caprolactam in the powdered product. In the examined area, the specific surface value of the powdered poly(ethylene terephthalate) prepared by reprecipitation from the melt of 6-caprolactam ranged from 10 to 110 m²·g^?1.     

Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion

The reactivity and efficiency of five low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers of a bottle grade poly(ethylene terephthalate) (PET) resin were evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Measures of melt viscosity, melt strength, intrinsic viscosity and carboxyl group content were used as criteria of the extent of the modification. Correlations of die pressure with extrudate swell during extrusion, and melt flow index (MFI) with melt strength by off‐line testing of the extrudates permitted the ranking of the modifiers according to their chain‐extending/branching efficiency. For some systems molecular weight increases (related to die pressure/MFI/intrinsic viscosity) accompanied by broadening of the molecular weight distribution (related to die swell/melt strength) were considered excessive. Extrusion foaming experiments with one particular dianhydride modifier that increased the intrinsic viscosity of the resin from 0.71 to 0.9 dl g^?1 indicate that production of low‐density foams by a process involving one‐step reactive modification/gas injection foaming is feasible, at conditions not significantly different from those employed in the simple reactive modification of the PET resin. The rheological and structural parameters determined in this work may be used as criteria to specify PET foamable compositions in terms of types and concentrations of modifiers. Copyright © 2004 Society of Chemical Industry     

Reactive extrusion of recycled poly(ethylene terephthalate) with polycarbonate by addition of chain extender

Poly(ethylene terephthalate) (PET) resin is one of the most widely used engineering plastic with high performance, but the poor impact strength limits its applications for the notch sensitivity. In this research, toughened PET alloy was prepared by blending recycled PET with polycarbonate (PC) and MDI (methylenediphenyl diisocyanate). Intrinsic viscosity and melt viscosity measurements proved increase of the molecular weights of PET via chain‐extending reaction. FTIR and DMA results proved that some PET–PC copolymers were produced and the compatibility of PET phase and PC phase was improved. In addition, the reaction induced by MDI also affected the crystallization behaviors of PET, as observed from DSC results, and the crytallinity of PET decreased with the increase of MDI content. For all of these effects of MDI of increasing of molecular weight, improving of compatibility, and limiting the crystallization behaviors of PET/PC alloy, the notched‐impact strength was greatly improved from 17.3 to 70.5 kJ/m². © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2602–2607, 2007     

Molecular characterization and rheological properties of modified poly(ethylene terephthalate) obtained by reactive extrusion

The use of a tetrafunctional epoxy‐based additive to modify the molecular structure of poly(ethylene terephthalate) (PET) was investigated with the aim of producing PET foams by an extrusion process. The molecular structure analysis and shear and elongation rheological characterization showed that branched PET is obtained for 0.2, 0.3 and 0.4 wt% of a tetrafunctional epoxy additive. Gel permeation chromatography (GPC) analysis led to the conclusion that a randomly branched structure is obtained, the structure being independent of the modifier concentration. The evolution of shear and extensional behavior as a function of molecular weight (M_w), degree of branching, and molecular weight distribution (MWD) were studied, and it is shown that an increase in the degree of branching and M_w and the broadening of the MWD induce an increase in Newtonian viscosity, relaxation time, flow activation energy and transient extensional viscosity, while the shear thinning onset and the Hencky strain at the fiber break decrease markedly.     

Crystallization in blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Blends composed of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) were melt-mixed in a Brabender cam mixer at different mixing speeds. The glass transition (T_g) and the crystallization behavior of the blends from glassy state were studied using DSC. It was found that although the blends had the same composition and exhibited the similar T_g, their properties of crystallization could be different; some exhibited a single crystallization peak and some exhibited multiple crystallization peaks depending upon experimental conditions. Results indicated that the behavior of crystallization from glassy state were influenced by entanglement and transesterification of chains. The crystallization time values were obtained over a wide range of crystallization temperature. From curve fitting, the crystallization time values and the temperature, at which the crystallization rate reaches the maximum, were found.     

High-impact poly(ethylene terephthalate) blends

Rubbers of different kind were tested as toughening agents of poly(ethylene terephthalate) (PET), noting significant morphological and mechanical differences. In particular, good results were obtained by using an ethylene–ethyl acrylate–glycidyl methacrylate copolymer. The resulting blend evidenced good particle distribution, and the latter was related to chemical interactions between the rubber epoxy groups and PET terminal groups, including the effect of low molecular weight and polymeric amine catalysts, and to extrusion conditions. © 1995 John Wiley & Sons, Inc.     

Properties of ultrasound-assisted blends of poly(ethylene terephthalate) with polycarbonate

This study investigated the effect of ultrasound irradiation on blends of polyethylene terephtalate (PET) and polycarbonate (PC). The blends of PET/PC were prepared by a twin-screw extruder with an attached ultrasonic device. Thermal, rheological, and mechanical properties and morphology of the blends with and without sonication have been analyzed. The two distinct T_gs of the blends measured by DSC showed immiscibility over all compositions. The theoretical PET content that is miscible in PC-rich phase calculated using the Fox equation showed that ultrasonic waves made the blends more miscible. From mechanical test results, when sonication was not applied, the 20/80 blend was the most miscible composition. At that composition, the impact strength of sonicated blend was surprisingly high. It was believed to be due to the enhancement of compatibility by a reaction such as transesterification. The results from the morphology of the 20/80 sonicated blend were in agreement with DSC and impact test results.     

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.     

Third phase in poly(ethylene terephthalate)

The concept of the oriented amorphous phase, which is also known as the intermediate or third phase, is discussed and a method is outlined for measuring it. It is suggested that the two phase models of polymer structure, which ascribe partial orientation to the amorphous regions, are in fact close to the three phase models, because the amorphous orientation factor and the third phase are representative of the same parameter, i.e. orientation in the amorphous phase.