Low temperature solid‐state extrusion of recycled poly(ethylene terephthalate) bottle scraps

The processing of poly(ethylene terephthalate) (PET) involves thermal and hydrolytic degradation of the polymer chain, which reduces not only the intrinsic viscosity and molecular weight, but also the mechanical properties of recycled materials. A novel PET/bisphenol A polycarbonate/styrene–ethylene–butylene–styrene alloy based on recycled PET scraps is prepared by low temperature solid‐state extrusion. Hydrolysis and thermal degradation of PET can be greatly reduced by low temperature solid‐state extrusion because the extrusion temperature is between the glass‐transition temperature and cold‐crystallization temperature of PET. Modification of recycled PET by low temperature solid‐state extrusion is an interesting method; it not only provides an easy method to recycle PET scraps by blend processing, but it can also form novel structures such as orientation, crystallization, and networks in the alloy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2692–2699, 2006     

Decolorization of colored poly(ethylene terephthalate) bottle flakes using hydrogen peroxide

A novel process for the oxidative decolorization of green and blue colored poly(ethylene terephthalate) (PET) bottle flakes, using an aqueous solution of hydrogen peroxide (H₂O₂) has been developed. A strong dependence of H₂O₂ concentration and temperature on decolorization rate has been found. The decolorized flakes were characterized for color and intrinsic viscosity (IV) values; decolorized flakes exhibit color values similar to those of colorless recycled PET. The IV of peroxide bleached PET flakes indicated a decrease in PET molecular weight, which correlated with the severity of decolorization conditions. Despite decreases in PET IV values, the bleached flake still exhibited useful PET molecular weights. The consumption of H₂O₂ during the bleaching process was quantified titrating residual peroxide with a standardized potassium permanganate solution. H₂O₂ consumption rates of 0.3–0.9 g per gram of green PET flake were measured, depending on the specific bleaching conditions used. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008     

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.     

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.     

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     

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.     

Microwave heating of poly(ethylene terephthalate) bottle preforms used in the thermoforming process

Thermoforming (free blowing) of poly(ethylene terephthalate) preforms was successfully and quickly performed in a rotating system designed for dielectric hysteresis heating. Temperature profile modeling was carried out with the amorphous poly(ethylene terephthalate) permittivity at different temperatures. The Maxwell and heat equations were used to determine the best profile and power tuning. The determination of the theoretical boundary conditions was accomplished by the adjustment of the numerical transient external surface wall temperature with experimental infrared pyrometry results. In comparison with infrared, microwaves allowed high power density absorption inside the perform wall without a dramatic temperature gradient. Consequently, the heat blowing stage could be accelerated, and the process took at least 5 times less energy than infrared heating. Industrial applications involve the integration of the molding step and the design of the overall process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

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.     

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.     

Aminolytic depolymerization of poly (ethylene terephthalate) bottle waste by conventional and microwave irradiation heating

Poly (ethylene terephthalate) (PET) is the most popular thermoplastic polymer. The ever-growing production and utilization of PET has led to postconsumer waste disposal problems because of its nonbiodegradability. The chemical depolymerization of PET waste is a possible remedy, as it results in some recyclable products. The aminolytic depolymerization of PET bottle waste with hydrazine monohydrate by conventional and nonconventional (with microwave irradiation) heating was carried out with simple chemicals as catalysts, such as sodium acetate and sodium sulfate. The yield of the product was optimized through variations in the time of aminolysis, the catalyst concentration, and the PET:hydrazine monohydrate ratio. The pure product obtained in good yield (86%) was analyzed by Fourier transform infrared spectroscopy, NMR, and differential scanning calorimetry and was identified as terephthalic dihydrazide. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

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.     

Bottom design of carbonated soft drink poly(ethylene terephthalate) bottle to prevent solvent cracking

The use of a petaloid shape for the bottom design for carbonated PET bottles is widespread. Through this study, the causes of bottom cracking were investigated and a novel petaloid bottom was designed. The variations of the physical properties of PET according to the stretch ratio were examined and the stretch ratios in the blown bottle were analyzed. Cracking phenomena of the bottom were observed by a solvent‐cracking test. The effective stress and the maximum principal stress in a carbonated bottle were analyzed by computer simulation. It was concluded that the bottom crack occurs because of not only the insufficient strength of material due to the insufficient stretch of PET but also to the coarse design of the petaloid shape. The highest maximum principal stress occurred at the valley in the petaloid bottom of the bottle and this strongly affected the cracking in the bottom. The petaloid shape was redesigned to minimize the maximum principal stress, and this resulted in increasing the crack resistance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1145–1152, 2003     

Grafting of polyacrylamide from poly(ethylene terephthalate) films

Poly(ethylene terephthalate) (PET) films were modified via the grafting of polyacrylamide (PAAM) onto the surface by surface‐initiated atom transfer radical polymerization and UV‐initiated grafting. The surface composition and morphology of the modified PET films were characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy (SEM). The results show that the surface of the PET film was grafted by PAAM, with its own surface morphology different from that of PET. The properties of the modified PET films were studied by contact‐angle, peeling force, penetrability, haze, and friction factor measurements. The results indicate that the peeling force and friction factor of the modified PET films were higher than those of the unmodified PET film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Processing characteristics of poly(ethylene terephthalate): hydrolytic and thermal degradation

The effects of poly(ethylene terephthalate) (PET) resin moisture content and temperature exposure have been investigated in terms of material changes resulting from the injection moulding process. Two resins with initial carboxyl contents of 10 µeq/g PET and 20 µeq/g PET have been analysed. Preforms processed at different resin moisture contents and processing temperatures of 280, 290 and 300 °C were evaluated in terms of carboxyl end‐group concentration using a titration method. Intrinsic viscosities of the performs were also measured by solution viscosity. Mathematical models describing the relationships of carboxyl end‐group concentration and intrinsic viscosity to the processing conditions were generated from the experimental data. Carboxyl end‐groups formed were compared for both resins and shown to be dependent on initial carboxyl content in the resin. Reducing the initial carboxyl content in the resin has been shown to increase its hydrolytic stability. The hydrolytic effect on the overall molecular weight drop was separated from the thermal/thermal‐oxidative degradation and shown to be dependent on both the processing temperature and the resin moisture content. © 2002 Society of Chemical Industry     

Processing and characterization of multilayer films of poly(ethylene terephthalate) and surface-modified poly(tetrafluoroethylene)

Multilayer films were prepared from poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (PET) films together with using an adhesion promoting layer (tie-layer) consisting of ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer and low density polyethylene (LDPE) blend. Na/naphthalene treatment and subsequent acrylic acid grafting were applied on the surfaces of PTFE for chemical modification. FT-IR spectroscopy, XPS analysis and surface energy measurements were performed to characterize the modified PTFE films. The analyses showed defluorination and oxidation of PTFE surface, and supported the acrylic acid grafting. The surface energy of modified surfaces enhanced with respect to unmodified one, which promoted adhesion. The multilayers were subjected to T-peel tests to measure the adhesion strength between PET and modified PTFE. Peel strength between the films increased with increasing E-MA-GMA amount in the tie-layer. A proportional dependence of peel strength on Na/naphthalene treatment time was observed for multilayers containing acrylic acid grafted or ungrafted PTFE. From SEM analysis, it was observed that the texture of the PTFE surface after modifications became rougher when compared to untreated PTFE. The peeled surfaces were also analyzed by SEM. The micrographs evidence that the energy absorbing mechanism is the plastic deformation of the tie-layer, which is responsible for obtaining high peel strengths.     

Flame retardancy effects of halogenated phosphates on poly(ethylene terephthalate) fabric

A Chemical research on the flame retardancy effect of halogenated phosphates on poly(ethylene terephathalate) fabric was carried out by thermogravimetry, infrared spectral analysis, and mass spectrometry. The following conclusions were drawn: (1) The flame retardancy effect of halogenated phosphates such as tris(2,3-dibromopropyl) phosphate is due to altering the pyrolysis reaction of polyester by aldol condensation. (2) The probability that liberated halogen compounds from the phosphates act as radical acceptors in a flame zone may be low. (3) Incorporation of halogen elements into phosphates appear to depress evaporation of phosphates, which act as acidic catalysts in aldol condensation from the condensed phase.     

Solid-state polymerization of poly(ethylene terephthalate)

Solid -state polymerization of poly(ethylene terephthalate) (PET) is carried out by heating the low molecular weight prepolymer at temperatures below its melting point but above its glass transition temperature. Postcondensation occurs and the condensation byproducts can be removed by applying vacuum or inert gas. Polymers obtained usually have high molecular weight, low carboxyl and acetaldehyde content, and can be used for beverage bottle or industrial yarns. Polyesters for textile purposes are manufactured by a melt process. Chemical reactions involved in the solid state polymerization are transesterification, esterification, as well as the diffusion of byproducts. Overall reaction rate was governed by the molecular weight, carboxyl content of prepolymer, crystallinity, particle size, reaction temperature, and time. Prepolymer for solid state polymerization should have intrinsic viscosity 0.4 dL/g or more, density 1.38 g/mL, and minimum dimension 3 mm or less. The reaction temperature could be 200–250°C. When textile grade PET is used as prepolymer, crystallization at 180–190°C for 1–2 h increases the density to 1.38 g/mL. Polymerization at 240–245°C for 3–5 h can raise the intrinsic viscosity to 0.72 dL/g and carboxyl content less than 20 meq/kg. Appropriate reaction conditions are subject to the properties of prepolymers and the design of reactors. Reactor used for solid state polymerization could be vacuum dryer type or stationary bed. The former is suitable for a small capacity and is run batchwise. The latter is a continuous process and is economically feasible for large -scale production.     

Strain-induced crystallization of poly(ethylene terephthalate)

The fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress- or strain-induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide-angle X-ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide-angle X-ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.