Optimization of poly(ethylene terephthalate) bottles via numerical modeling: A statistical design of experiment approach

Poly(ethylene terephthalate) bottles, commonly used for carbonated soft drink packaging, occasionally fail because of environmental stress cracking at the petaloid base. At raised temperatures, particularly during hot summer months, increased carbonation pressure of the contents aggravates susceptibility to stress cracking. In this study, numerical modeling with finite element analysis techniques was used to redesign the petaloid base of bottles to improve stress‐crack resistance. An experimental design based on an algorithmic partial cubic method was employed. Mathematical modeling of the principal internal stress as a function of key design parameters identified optimal dimensions for the petaloid base. The improvement in stress‐crack resistance was verified by experimental studies. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

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.     

Modeling of ethylene polymerization with difunctional initiators in tubular reactors

The severe thermodynamic conditions of the high‐pressure ethylene polymerization process hinder ethylene from going to full conversion. One remedy to improve the monomer conversion is to make effective use of difunctional peroxides. Multifunctional peroxides can accelerate the polymerization rate, produce branching, and modify the rheological properties of molten polymers. This article proposes a kinetic model based on a postulated reaction mechanism for ethylene polymerization initiated by difunctional initiators in a high‐pressure tubular reactor. Three peroxides suitable for ethylene polymerization were compared for their effectiveness. Compared to dioctanoyl peroxide, the two difunctional peroxides considered performed much better for the higher temperature regions of the reactor and gave ethylene conversions nearly twice as high for only half of the initial amount of dioctanoyl. They also generated low‐density polyethylene polymer with a broader molecular weight distribution and longer chain branching. These two important polymer characteristics can influence the end‐product rheological properties. Injecting fresh ethylene at different points along the reactor improved the conversion and produced more branched polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

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     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Processing effects on poly(ethylene terephthalate) from bottle scraps

Processing of virgin and recycled poly(ethylene terephthalate) (PET) in a twin screw extruder evidences the degradative effect caused by thermal decomposition of poly(vinyl chloride) (PVC) and other impurities, e.g. adhesives, at the processing temperature. Lower melt viscosity and molecular weight, along with higher carboxylic end group concentration, were observed for recycled PET, the extent depending on PET purity. In an attempt to investigate the correlation between the kinetics of degradation phenomena and the level of thermomechanical stress, a novel dynamic method of evaluating thermal stability in processing conditions was developed. Such a method allows the achievement of long equivalent residence times while using lab-scale extruders. As a result of these experiments, PVC-rich recycled PET was shown to reach very low melt viscosity after less than 10 min in processing conditions, while virgin PET retained high viscosity even after 30 min.     

Modeling of solid-state polymerization of poly(ethylene terephthalate)

A mathematical model for solid-state polymerization of poly(ethylene terephthalate) was developed. The effects of temperature and chain entanglement on chain mobility were considered to estimate the rate constants of chemical reactions. The diffusivities of volatile byproducts could be determined using the free volume theory.^13,14 The model predictions were validated with experimental data reported in the literature. In addition, assuming that the concentration profiles of volatile byproducts in spherical particles are described by a sinusoidal function, the mass transfer rate of the byproducts at a given time could be derived as an ordinary differential equation that can be easily treated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:837–846, 1998     

Hot compaction of woven poly(ethylene terephthalate) multifilaments

Here we describe the development of a process, and the resulting mechanical properties, for hot‐compacted sheets of woven poly(ethylene terephthalate) (PET) multifilaments. Investigation of the various processing parameters showed that a key aspect was the time spent at the compaction temperature, termed the dwell time. Molecular weight measurements, using intrinsic viscosity, showed that hydrolytic degradation occurred rapidly at the temperatures required for successful compaction, leading to embrittlement of the resulting materials with increasing dwell time. A dwell time of 2 min was found to be optimum because this gave the required percentage of melted material to bind the structure together, while giving only a small decrease in molecular weight. A combination of techniques, including mechanical tests, differential scanning calorimetry, and scanning electron microscopy, was used to examine the mechanical properties and morphology of the optimum compacted sheets. These tests reinforced the view from previous studies on hot‐compacted polypropylene, of hot‐compacted sheets as self‐reinforced composites, whose behavior is a combination of the properties of the two components, that is, the original oriented multifilaments and the melted and recrystallized matrix. Other key findings from the research included a confirmation of the importance of obtaining high ductility in the melted and recrystallized phases, promoted by using a high molecular weight or by suppressing crystallinity during processing, and the proportionately high‐impact performance of hot‐compacted sheets, compared with that of other materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2223–2233, 2004     

Aminolytic depolymerization of poly(ethylene terephthalate) waste in a microwave reactor

The aminolytic depolymerization of poly(ethylene terephthalate) (PET) taken from waste soft‐drink bottles, under microwave irradiation, is proposed as a recycling method with possible substantial energy savings. The reaction was carried out with ethanolamine and without the use of any other catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments under constant temperature or microwave power were carried out for several time periods. The main product, bis(2‐hydroxyethyl) terephthalamide, was identified from Fourier transform infrared (FTIR) spectra and DSC measurements. It was found that PET depolymerization is favoured by increasing temperature, time and microwave power. The average molecular weight of the PET residues, determined using viscosity measurements, was found to decrease with the percentage of PET degradation, indicating a random chain scission mechanism to some extent. From a simple kinetic model, the activation energy of the reaction was evaluated. Complete depolymerization was found to occur in less than 5 min when the irradiation power applied was 100 W or the temperature was 260 °C. These results support the use of microwave‐assisted aminolytic degradation as a very beneficial method for the recycling of PET wastes. Copyright © 2010 Society of Chemical Industry     

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     

Glycolysis of poly(ethylene terephthalate) wastes in xylene

To reclaim the monomers or prepare intermediates suitable for other polymers zinc acetate catalayzed glycolysis of waste poly(ethylene terephthalate) (PET) was carried out with ethylene or propylene glycol, with PET/glycol molar ratios of1 : 0.5–1 : 3, in xylene at 170–245°C. During the multiphase reaction, depolymerization products transferred to the xylene medium from the dispersed PET/glycol droplets, shifting the equilibrium to glycolysis. Best results were obtained from the ethylene glycol (EG) reaction at 220°C, which yielded 80 mol % bis-2-hydroxyethyl terephthalate monomer and 20 mol % dimer fractions in quite pure crystalline form. Other advantages of employment of xylene in glycolysis of PET were improvement of mixing at high PET/EG ratios and recycling possibility of excess glycol, which separates from the xylene phase at low temperatures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2311–2319, 1998     

Thermostimulative shape‐memory effect of reactive compatibilized high‐density polyethylene/poly(ethylene terephthalate) blends by an ethylene–butyl acrylate–glycidyl methacrylate terpolymer

High‐density polyethylene (HDPE)/poly(ethylene terephthalate) (PET) blends were prepared by means of melt extrusion with ethylene–butyl acrylate–glycidyl methacrylate terpolymer (EBAGMA) as a reactive compatibilizer. The effects of the EBAGMA and PET contents, recovery temperature, and stretch ratio on the thermostimulative shape‐memory behavior of the blends were studied. The results show that the addition of EBAGMA to the HDPE/PET blends obviously improved the compatibility and the shape‐memory effects of the blends. The response temperature was determined by the melting point of HDPE, and the shape‐recovery ratio of the 90/10/5 HDPE/PET/EBAGMA blend reached nearly 100%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of irradiation on the melting and crystallization behavior of ethylene polymers with different thermal history

Ethylene polymers, including HDPE, Ziegler–Natta‐catalyzed LLDPE (Z–N LLDPE), metallocene‐catalyzed LLDPE (m‐LLDPE), and LDPE were thermally treated by different procedures, that is, quenching, slow cooling, and thermal segregation. These PE samples, having different thermal histories, were then irradiated with various doses, that is, 0, 13, 35, and 70 Mrad, by gamma ray using a ⁶⁰Co radiation source. The melting and crystallization behaviors of these irradiated samples were studied by a differential scanning calorimeter (DSC). The effects of the thermal histories and irradiation on the polymers were evaluated by their melting temperatures (T_m), crystallization temperatures (T_c), and heat enthalpies (ΔH) in the heating and cooling scans. The results indicated that irradiation affects the samples having different thermal histories in different ways. The effects of the dosage on each kind of sample are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 536–544, 2003     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Biodegradability of poly(ethylene terephthalate) copolymers with poly(ethylene glycol)s and poly(tetramethylene glycol)

Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (T_m), cold crystallization and glass transition (T_g) decreased with the copolymerization. T_m depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. T_g was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.     

Microwave irradiation as an energy source in poly(ethylene terephthalate) solvolysis

Solvolysis by glycols and alcohols is an established method for the chemical recycling of poly(ethylene terephthalate) (PET). In our work, we investigated the use of microwave radiation as the energy source in PET solvolysis reactions, and the conditions that govern its effectiveness. The main advantage of microwave use are short reaction times, between 4 and 10 min, in which complete PET degradation is achieved. Solvolysis reagents used were methanol, propylene glycol, and polyethylene glycol 400. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1115–1118, 1998     

Poly(ethylene‐co‐methacrylic acid)–lithium ionomer as a compatibilizer for poly(ethylene terephthalate)/linear low‐density polyethylene blends

Poly(ethylene terephthalate) (PET)/linear low‐density polyethylene (LLDPE) blends (75/25), with contents of poly(ethylene‐co‐methacrylic acid) partially neutralized with lithium (PEMA–Li) that were systematically changed from 0 to 45% relative to the LLDPE, were obtained by direct injection molding in an attempt to (1) ameliorate the performance of the binary blend and (2) find the best compatibilizer content. PEMA–Li did not modify the PET or LLDPE amorphous‐phase compositions or the crystalline content of PET. However, PEMA–Li did lead to a nucleation effect and to the presence of a second smaller and less perfect crystalline structure. PET induced a fractional crystallization in LLDPE that remained in the presence of PEMA–Li and reduced the crystallinity of LLDPE. The ternary blends showed two similar dispersed LLDPE and PEMA–Li phases with small subparticles, probably PET, inside. The compatibilizing effect of PEMA–Li was clearly shown by the impressive increase in the break strain, along with only small decreases in the modulus of elasticity and in the tensile strength. With respect to the recycling possibilities of LLDPE, a ternary blend with the addition of 22.5% PEMA–Li, which led to very slight modulus and yield stress decreases with respect to the binary blend and a break strain increase of 480%, appeared to be the most attractive. However, the highest property improvement appeared with the addition of 37.5% PEMA–Li, which led to elasticity modulus and tensile strength decreases of only 9%, along with a very high break strain increase (760%). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1322–1328, 2003