Microwave assisted ecofriendly recycling of poly (ethylene terephthalate) bottle waste

Glycolysis of poly (ethylene terephthalate) bottle waste was carried out using microwave energy. A domestic microwave oven of 800 W was used with suitable modification for carrying out the reaction under reflux. The catalysts used for the depolymerization in ethylene glycol (EG) were zinc acetate and some simple laboratory chemicals such as sodium carbonate, sodium bicarbonate and barium hydroxide. Comparison of results was made from the point of view of the yield of bis (2-hydroxyethylene) terephthalate (BHET) and the time taken for depolymerization. It was observed that under identical conditions of catalyst concentration and PET:EG ratio, the yield of BHET was nearly same as that obtained earlier by conventional electric heating. However, the time taken for completion of reaction was reduced drastically from 8 h to 35 min. This has led to substantial saving in energy.     

Depolymerisation of poly(ethylene terephthalate) fibre wastes using ethylene glycol

Poly(ethylene terephthalate) [PET] fibre wastes from an industrial manufacturer was depolymerised using excess ethylene glycol [EG] in the presence of metal acetate as a transesterification catalyst. The glycolysis reactions were carried out at the boiling point of ethylene glycol under nitrogen atmosphere up to 10 h. Influences of the reaction time, volume of EG, catalysts and their concentrations on the yield of the glycolysis products were investigated. The glycolysis products were analysed for hydroxyl and acid values and identified by different techniques, such as HPLC, ¹H NMR and ¹³C NMR, mass spectra, and DSC. It was found that the glycolysis products consist mainly of bis(hydroxyethyl)terephthalate [BHET] monomer (>75%) which was effectively separated from dimer in quite pure crystalline form.     

Transport properties of poly(ethylene terephthalate) crystallized from the glassy state

Poly(ethylene terephthalate) was crystallized from the glassy state at 120 and 200°C. The structural organization of samples, after the primary and secondary crystallizations, was analyzed by density, X-rays, infrared and transport properties of dichloromethane vapor. The values of crystallinity derived with different methods do not agree, indicating that the crystallized samples cannot be considered simply biphasic. Since the fraction of the impermeable phase is much higher than the fraction of the crystalline phase, it suggested that the presence of mesomorphic form, impermeable to the vapors at low activity. With this hypothesis, the complete composition of the crystalline samples, in terms of fraction of crystalline, amorphous and mesomorphic form was derived. A value of density of the mesomorphic form of 1.39 g/cm³ was also derived.     

Electrospun fibers of poly(ethylene terephthalate) blended with poly(lactic acid)

Fibrous blends of polyethylene terephthalate (PET) and polylactic acid (PLA) were fabricated by electrospinning (ES) from a common solvent, at concentrations of PET/PLA = 100/0, 70/30, 50/50, 30/70, and 0/100. Oriented fiber mats were studied either as-spun, or after a cold-crystallization treatment. Scanning electron microscopy of as-spun amorphous fibers showed that addition of PLA into the ES solution prevents occurrence of beads. In some compositions, two glass transitions were observed by temperature-modulated differential scanning calorimetry indicating that the two components in the ES fibers were phase separated. Thermogravimetric analysis was used to study thermal degradation at high temperatures. PLA degrades at a temperature about 100 °C lower than that of PET, and holding or cycling the blends to high temperature can result in the degradation of PLA. Degree of crystallinity was determined using DSC for as-spun and cold-crystallized ES blend fibers. The degree of crystallinity of each blend component is reduced by the presence of the other blend component, and the overall crystallinity of the blend fibers is less than that of the homopolymer fibers. Wide-angle X-ray scattering results show that oriented crystals were formed in the blended electrospun fibers collected on a rotating collector. The cold-crystallization process leads to both PET and PLA crystallizations. Oriented crystallites form even when the fiber is crystallized with its ends free to shrink.     

The three-phase structure and mechanical properties of poly(ethylene terephthalate)

The relation between the mechanical properties and the microstructure of PET has been investigated, combining results from WAXS, SAXS, FTIR, DSC, and uniaxial compression tests. The rigid amorphous fraction in the PET was explicitly taken into consideration in interpreting structure–property relations. WAXS results prove that glass crystallized PET with a high volume fraction of rigid amorphous material and small crystal size, on uniaxial compression shows a considerable loss in crystalline fraction. FTIR results in combination with these WAXS results suggest that during this loss in crystallinity, short-range conformational order is retained, while long-range structural order is lost. At the same time, material with small crystals and a high amount of rigid amorphous material was found to show unexpectedly low yield stress. It is concluded that in the interpretation of these phenomena it is necessary to take the three-phase structure of PET, including the rigid amorphous fraction into account. This is expected to hold for other semicrystalline polymers, where a rigid amorphous fraction is prominent, such as PHB, PBT, PEN, PEEK, etc. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2092–2106, 2004     

Effect of catalysts on thermally stimulated current in poly(ethylene terephthalate)

The effect of catalysts on relaxation phenomena in poly(ethylene terephthalate) (PET) was studied by thermally stimulated current (TSC). Resins Sb-PET and Ge-PET were produced by the antimony and germanium main catalyst systems, respectively. Spontaneous, global and thermal sampling of TSC were compared in both PETs. The lower TSC peaks are observed in Ge-PET than those in Sb-PET for equivalent treatment. The compensation parameters were determined from the variation polarization temperatures (Tp) data. These parameters were used to calculate degree of disorder (DOD). The DOD of Sb-PET and Ge-PET were 36.14 and 66.23, respectively. The relaxation time at the maximum current and the dipolar relaxation strength in the Sb-PET has the higher values and wider distribution than that in Ge-PET. Furthermore, Sb-PET exhibited electrically softer. These results are attributed to the stiffening amorphous parts by the entanglement network in Ge-PET. This revised version was published online in July 2006 with corrections to the Cover Date.     

Morphology development and crystallization behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The spherulite morphology and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). The thermal analysis showed that PET and PTT were miscible in the melt over the entire composition range. The rejected distance of non-crystallizable species, which was represented in terms of the parameter δ, played an important role in determining the morphological patterns of the blends at a specific crystallization temperature regime. The parameter δ could be controlled by variation of the composition, the crystallization temperature, and the level of transesterification. In the case of two-step crystallization, the crystallization of PTT commenced in the interspherulitic region between the grown PET crystals and proceeded until the interspherulitic space was filled with PTT crystals. The spherulitic surface of the PET crystals acted as nucleation sites where PTT preferentially crystallized, leading to the formation of non-spherulitic crystalline texture. The SALS results suggested that the growth pattern of the PET crystals was significantly changed by the presence of the PTT molecules. The lamellar morphology parameters were evaluated by a one-dimensional correlation function analysis. The blends that crystallized above the melting point of PTT showed a larger amorphous layer thickness than the pure PET, indicating that the non-crystallizable PTT component might be incorporated into the interlamellar region of the PET crystals. With an increased level of transesterification, the exclusion of non-crystallizable species from the lamellar stacks was favorable due to the lower crystal growth rates. As a result, the amorphous layer thickness of the PET crystals decreased as the annealing time in the melt state was increased.     

Chemical recycling of poly(ethylene terephthalate) waste using ethanolamine. Sorting of the end products

There is a growing keen interest aimed at recycling post-consumer poly(ethylene terephthalate), PET, wastes for both environmental and economic reasons. In this study ethanolamine (EA) has been investigated for aminolytic degradation of PET waste in the presence of dibutyl tin oxide (DBTO) as a catalyst. The process proceeds at 190 °C and under atmospheric pressure. The yield of white precipitate was subject to spectroscopic measurements (FT-IR, NMR, XRD and MS), to thermal analyses (DSC, DTA and TG) and to chemical testing (elemental analysis and solubility characterization).Based on the data reached from various examinations, the product formed is identified as bis(2-hydroxyethylene) terephthalamide (BHETA) which could be consider a source for differing polyurethanes. These kinds of materials have potential for many applications such as adhesives and coatings.     

Effect of thermo-mechanical cycles on the physico-chemical properties of poly(lactic acid)

Polylactic acid (PLA) has now become an economically viable commodity plastic in many industries. This raises the question of recyclability of industrial production waste and some packaging wastes as well. The evolution of rheological and mechanical properties of polymer with the number of recycling cycles up to seven was investigated. For PLA, only the tensile modulus remains constant with the thermo-mechanical cycles. In contrast, stress and strain at break, rheological factors and the modulus and hardness probed by nanoindentation decrease for PLA. This dramatic effect is ascribed to a large decrease in the molecular weight due to several different complex degradation processes which are discussed. The effect of two stabilizers is also assessed.     

The role of crystalline, mobile amorphous and rigid amorphous fractions in the performance of recycled poly (ethylene terephthalate) (PET)

The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation of -OH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percentage of crystalline fraction remained nearly constant. A deeper analysis of the melting behaviour, the segmental dynamics around the glass-rubber relaxation, and the macroscopic mechanical performance, showed the role of each fraction leading to a loss of thermal, viscoelastic and mechanical features, particularly remarkable after the first processing cycle.     

Depolymerization of poly(ethylene terephthalate) recycled from post-consumer soft-drink bottles

Poly(ethylene terephthalate), recycled from post-consumer soft-drink bottles, is depolymerized by glycolysis in excess ethylene glycol at 190°C in the presence of a metal acetate catalyst. The glycolyzed products consist mostly of the PET monomer, bis(hydroxyethyl) terephthalate, and the dimer, and after long reaction time (up to and longer than 8 h), an equilibrium is attained between these two species. No other higher PET oligomers were detected in the study. Of the four metal acetates (lead, zinc, cobalt, and manganese) tested, zinc acetate is the best in terms of the extent of depolymerization, that is, the relative amount of monomer formed. The presence of green pigment in one type of recycled PET apparently has no effects on the glycolysis reaction.     

Application of continuous zone-drawing/zone-annealing method to poly(ethylene terephthalate) fibers

A continuous zone-drawing/zone-annealing method was applied to poly(ethylene terephthalate) fibers in order to improve their mechanical properties. Apparatus used for this treatment was assembled in our laboratory. The continuous zone-drawing treatment was carried out at a drawing temperature of 103°C under an applied tension of 6.6 MPa to fully orient amorphous chains in the drawing direction without inducing thermal crystallization. The continuous zone-annealing treatment was carried out twice at an annealing temperature of 160°C under 102.2 MPa and at 183°C under 161.1 MPa to crystallize the highly oriented amorphous chains. The fiber was continuously drawn and annealed at a rate of 420 mm/min. The fiber obtained had a birefringence of 0.260, a degree of crystallinity of 55%, a tensile modulus of 18 GPa, and a storage modulus of 21 GPa at 25°C. Despite the large difference in the treating speed between the continuous zone-annealing and zone-annealing, their values are approximately equal to those of the zone-annealed PET fiber that was reported previously. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 473–481, 1998     

Conformation of the ground-state dimer in poly(ethylene terephthalate)

Absorbance, excitation, and emission measurements have been performed with methyl benzoate and five model compounds, C₆H₅COO (CH₂)_xOOCC₆H₅, x = 2–6. Under appropriate conditions, three of the model compounds (those with x = 3, 4, 5) show evidence for the formation of intramolecular ground-state dimers. The model compound with x = 5 can form two types of dimers which emit with different energies. The model compound with x = 3 forms one of these dimers, and the model compound with x = 4 prefers the other ground-state dimer. Molecular modeling of the dimers suggests that the two conformations of the ground-state dimers differ in the orientation of the two C?O bonds. In the one dimer these two bonds are nearly parallel, but in the other they make an angle of about 120°. © 1993 John Wiley & Sons, Inc.     

Thermal behaviour of drawn semicrystalline poly(ethylene terephthalate) films

Behaviours of drawn semi-crystalline poly(ethylene terephthalate) films are investigated by DSC, X-ray diffraction and birefringence measurements. The comparison of the different results confirms the coexistence of two structures into the amorphous part of the material: a completely disordered amorphous phase and a mesomorphic amorphous one. Moreover, for the strongest draw ratio, the calorimetric results show that the drawing effect on the strain induced crystalline structure proceeds by a better orientation of this structure rather than by nucleation and growth of new oriented crystallites.     

New trends in chemical recycling of poly(ethylene terephthalate)

Chemical recycling of poly(ethylene terephthalate) (PET) by nonconventional transesterification and ammonolysis/aminolysis methods are discussed on the basis of literature and own experimental data. The obtained products of deep PET degradation using allylamine (N,N′-diallylterephthaldiamide), triethanolamine and other alkanolamines were prepared and characterized by DSC and elemental analysis.     

Carbon dioxide, ethylene and water vapor sorption in poly(lactic acid)

The objective of this work is to study the gas/vapor sorption in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio using a quartz crystal microbalance (QCM). For that purpose, the sorption of carbon dioxide, ethylene and water vapor in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio, in temperature range from 283 to 313 K and up to atmospheric pressure was measured. The measured isotherms indicate that the sorption mechanism is sorbate dependent, since carbon dioxide and ethylene seem to have predominantly a Langmuir type of mechanism while water is predominantly Henry controlled. Two temperature protocols were used and only ethylene sorption is affected by them. Comparisons with previously measured gas sorption data in PLA 80:20 using the same temperature protocol indicate that the l:d ratio plays a dominant role in gas/vapor sorption in PLA.     

Seawater ageing of flax/poly(lactic acid) biocomposites

Natural fibre reinforced biopolymer composites, or biocomposites, are an alternative to the glass fibre reinforced thermoset composites widely used today in marine applications. Biocomposites offer good mechanical properties and total biodegradability, but if they are to be adopted for marine structures their durability in a seawater environment must be demonstrated. In the present study unreinforced PLLA (Poly(l-Lactic acid)), injected and film stacked flax composites with the same PLLA matrix have been examined. All the samples were aged in natural seawater at different temperatures in order to accelerate hygrothermal ageing. Changes to physico-chemical and mechanical behaviour have been followed by weight measurements, thermal and gel permeation chromatography (GPC) analyses, and tensile testing, completed by acoustic emission recording and scanning electron microscopy (SEM) examination. The matrix tensile stiffness is hardly affected by seawater at temperatures to 40 °C but the composite loses stiffness and strength. Fibre/matrix interface weakening is the main damage mechanism induced by wet ageing, but both matrix and fibre cracks also appear at longer periods.     

Effect of dyeing on melting behavior of poly(lactic acid) fabric

The effect of the dyeing on the melting behavior of poly(lactic acid) fabrics was investigated by differential scanning calorimeter. The DSC melting peaks at 10°C min^-1 of the untreated poly(lactic acid) fabric were observed at a temperature higher than those of the dyed fabrics. The restricting force from the extended tie molecules along the fiber axis seems to decrease in the dyeing process. When the sample was rapidly heated, the crystallites melted at lower temperatures since recrystallization was restricted. It was estimated, based on the heating-rate dependency of melting behavior, that the original crystallites of the untreated sample melted at 146.1°C and those of the dyed samples melted at higher temperatures, suggesting that their crystallites are grown to be more perfect in the dyeing process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Alkyd resins derived from glycolized waste poly(ethylene terephthalate)

In this investigation the production of secondary value-added products, such as alkyd resins, derived from the glycolysis of poly(ethylene terephthalate) (PET) is examined as an effective way for its recycling. PET was taken from common soft-drink bottles and diethylene glycol (DEG) was used for the depolymerization at several initial molar ratios. The oligomers obtained were analyzed according to their average molecular weights. Furthermore, the glycolyzed PET products (oligomers) were reacted with maleic anhydride, phthalic anhydride and propylene glycol to form unsaturated polyester resins. These were subsequently mixed with styrene and cured using the benzoyl peroxide/amine initiator system to carry out the reaction in ambient temperature. The curing characteristics of the resins produced were investigated with respect to the initial molar ratio of DEG/PET as well as the initial initiator concentration. Finally, the mechanical properties (tensile strength and elongation at the break point) of the resins were compared with the conventional general purpose resin and were found to be comparable.     

Synthesis and characterization of poly(ethylene glycol) methyl ether endcapped poly(ethylene terephthalate)

Linear and branched poly(ethylene terephthalate) (PET) copolymers with polyethylene glycol) (PEG) methyl ether (700 or 2000 g/mol) end groups were synthesized using conventional melt polymerization. DSC analysis demonstrated that low levels of PEG end groups accelerated PET crystallization. The incorporated PEG end groups also decreased the crystallization temperature of PET dramatically, and copolymers with a high content of PEG (>17.6 wt%) were able to crystallize at room temperature. Rheological analysis demonstrated that the presence of PEG end groups effectively decreased the melt viscosities and facilitated melt processing. XPS and ATR-FTIR revealed that the PEG end groups tended to aggregate on the surface, and the surface of compression molded films containing 34.0 wt% PEG were PEG rich (85 wt% PEG). PEG end-capped PET (34.0 wt% PEG) and PET films were immersed into a fibrinogen solution (0.7 mg/mL BSA) for 72 h to investigate the propensity for protein adhesion. XPS demonstrated that the concentration of nitrogen (1.05%) on the surface of PEG endcapped PET film was statistically lower than PET (7.67%). SEM analysis was consistent with XPS results, and revealed the presence of adsorbed protein on the surface of PET films.