The use of melt rheology and solution viscometry for degradation study of post-consumer poly(ethylene terephthalate): The effects of the contaminants,reprocessing and solid state polymerization

Rheological measurements and intrinsic viscosity were performed to determine how the presence of contaminants, reprocessing and solid state polymerization (SSP) affects the degradation of post-consumer poly(ethylene terephthalate) (PET). First, post-industrial PET resin was contaminated with a series of surrogates according to a US-FDA protocol to simulate the worst-case scenario of misuse of PET packaging. The samples were submitted to recycling and SSP process in the presence of surrogates. The rheological data demonstrated that contaminated samples present degradation, even without any additional process. However, when the contaminated samples are submitted to melt extrusion the level of degradation increases. For the SSP process it was found that the surrogates do not interfere in the degradation process. In addition, an empirical analysis was derived based on the existing relationship. This analysis allowed the use of complex viscosity in higher frequencies, that is, out of the Newtonian plateau, and it shows to be as efficient as the zero-shear rate viscosity, allowing to associate the molar mass index of different samples. The data were corroborated from those obtained by the viscometric molar mass index, highlighting the importance of this new method to quantify the degradation in the polymer system.     

Supercritical Fluid Extraction (SFE) Optimization by Full-Factorial Design for the Determination of Irganox 1076, Irgafos 168, and Chimassorb 81 in Virgin and Recycled Polyolefins

The performance and feasibility of supercritical fluid extraction (SFE) applied to the extraction of some antioxidants (Irganox 1076, Irgafos 168) and one UV-stabilizer (Chimassorb 81) from both virgin and recycled low density polyethylene (LDPE), and virgin high density polyethylene (HDPE) are studied. Due to the high number of variables a full-factorial design has been applied to minimize the number of experiments required to reach the optimum extraction conditions. Further analysis has been carried out off-line by reversed-phase HPLC. Modification of the physical properties of the polymeric matrix and increased number of recycling cycles as well as the influence of physical properties on the efficiency of SFE are also discussed.     

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.     

A short review on latest developments in catalytic depolymerization of Poly (ethylene terephathalate) wastes

Chemical recycling of plastic wastes is top among the effective management of the solid wastes. Particularly the post-consumer polyethylene terephthalate (PET) plastic wastes mainly generated from the disposal of beverage bottles and placed third most produced polymeric waste. However, PET wastes could be chemically recycled using several types of homo-/heterogeneous acid or base catalysts, and an effective recycling process has yet to be achieved. Therefore, the present short review is intended to display recent reports on the depolymerization of PET polymer wastes. The review aimed to cover glycolysis and aminolytic depolymerization using various catalytic systems. There is a wide spectrum of catalytic systems such as metal oxides, ionic liquids, organic bases, nanoparticles, porous materials and microwave-assisted rapid depolymerization methods have been developed toward the yield enhancement of the depolymerized products. Ideologically, the present review would benefit the researchers in familiarizing themselves with the latest developments in this field.     

Extraction of polypropylene additives and their analysis by HPLC

Summary The polypropylene additives were extracted by dissolution-precipitation and Soxhlet. The Soxhlet method was adapted for the extraction of phosphorous antioxidants. The RP HPLC method with quaternary gradient elution separated five chemical groups of additives: lower molecular mass di-tert-butyl phenol (D.T.B.P.), hindered amine light stabilizers (Tinuvin 326), hindered phenolic antioxidants (Irganox 1010) and phosphorous antioxidants (Irgafos 168 and Ultranox 626) with their degradation products.     

Modelling of PET Quality Parameters for a Closed-Loop Recycling System for Food Contact

Summary: A rigorous process model has been developed which describes a closed-loop recycling system for PET beverage bottles. The reaction / mass transport model is aimed at the dominant quality parameters such as intrinsic viscosity, concentration of acetaldehyde, concentration of carboxylic end-groups, and concentration of vinyl end-groups, respectively. The model covers the main process steps being preform production (injection moulding), drying, solid-state polycondensation, and melt filtration. The simulation reveals that after a single recycling loop all the relevant quality parameters achieve the specification, if certain temperatures, residence times, and surface areas for degassing are provided during the recycling process. Another simulation showed the evolution of quality parameters in PET being subjected to an “infinite” number of recycling loops in a closed system. In this case, the concentration of acetaldehyde and vinyl end-groups decreases with the number of recycling loops, which is a desired effect. On the other hand, the concentration of carboxylic end-groups increases with every completed recycling loop. Higher concentrations of carboxylic end-groups make the polymer more susceptible to hydrolysis and increase the SSP process time needed to achieve the specified intrinsic viscosity for carbonated soft drink bottles. To overcome this problem, the recycled PET has to be blended with a certain amount of virgin PET in industrial processes.     

Recycling technology of poly(ethylene terephthalate) materials

Poly(ethylene terephthalate) (PET) has become one of major post consumer plastics wastes, in addition to polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). The challenge to large-volume plastics companies is to learn how to collect, separate, reprocess and market their low-cost products and make a profit, too. The effort of PET recycling, however, is the most successful story in the plastic recycling technology, including both reclaim and upgrade of PET waste. Beverage bottles made of PET are recycled more than 20% of the total production. The technology of today can reclaim the post-consumer PET bottles to produce high-quality granulated PET with better than 99% purity. A practical reclaim process for recycling PET bottles (including bottle, HDPE base cup, aluminum cap, liner, label and adhesive) is available by the Center for Plastics Recycling Research in USA. PET recycling process, like for other plastics, can be divided into three categories: incineration, physical recycling, and chemical recycling. To make the plastic recycling business pay requires more than simple recovery and marketing. Greatest profit potential is in upgraded and value-added reclaim products. Upgrading involves compounding with additives to make material more processable, adding reinforcement, or producing extrusions or finished parts from reclaim resins. For instance, a modified injection-moldable resin made from PET bottle scrap is claimed to provide high impact and processability at less cost than competitive materials. It is foreseen that chemical recycling of waste PET bottle becomes feasible if the price of raw material goes up. Three economical processes are involved in this technology: pyrolysis, hydrocracking, and hydrolysis. The hydrolysis process is presently employed to recover the raw material for unsaturated polyester resin manufacture or polyols for the production of polyurethane resin. It is reported in this presentation that polymer concrete could be a huge potential market for chemical reclaim of PET materials, especially for green or mixed-color PET, which are priced lower than colorless PET reclaim materials.     

Mechanical properties and molecular structures of virgin and recycled HDPE polymers used in gravity sewer systems

The widespread use of plastics in the conditioning, packaging and building material sectors generates an enormous amount of industrial waste which could be recycled for wastewater pipes and fittings. Nevertheless, current manufacturing standards in the piping industry recommend against the use of post-consumer recycled materials—a policy based on inadequate understanding of the properties and long-term mechanical performance of recycled materials. The present study compared the material characteristics of virgin and recycled high-density polyethylene (HDPE) plastics commonly found in the piping industry. Mechanical testing, oxidative induction time (OIT), melt flow index (MFI) and thermal analysis were used in conjunction with X-ray fluorescence (μ-XRF), size exclusion chromatography and ¹³C solid-state NMR to evaluate mechanical behavior and molecular structure as well as contaminant or filler contents. This study provides evidence for the degradation processes impact that can occur when post-industrial and post-consumer polymers are recycled. However, the study identified two measures to improve the material qualities of post-consumer recycled HDPE: 1) reducing the amount of contaminants or, alternatively, improving their compatibility with HDPE resins, and 2) improving current sorting and recycling processes to increase the amount of tie molecules in HDPE materials.     

Evaluation of long‐term performance of antioxidants using prooxidants instead of thermal acceleration

Evaluation of stabilization efficiencies of different antioxidants in polymers at low temperature and relatively short time was performed using incorporation of a prooxidant for catalytic oxidation. Comparisons were made between polypropylene films stabilized with primary antioxidants (Irganox 1076, Irganox 1010, and α‐tocopherol), with or without the prooxidant manganese stearate at different temperatures. A faster degradation was obtained in the presence of a prooxidant than without it. The relative efficiency of the antioxidants at prooxidant acceleration correlated better to low temperature long‐term test than at the thermal acceleration. The results were affected by initial differences in the amounts of the antioxidants present after the processing of the films. These differences were corrected for by a recalculation using microwave‐assisted extraction (MAE) and high performance liquid chromatography analysis from the exponential decrease in the amount of antioxidant in the films. The fastest comparison of the antioxidants efficiency was obtained from oxidation induction times, using total luminescence intensity measurements, but reliable results could also be obtained from the time to apparent failure. © 2005 Wiley Periodicals,Inc. J Polym Sci Part A: Polym Chem 43: 4537–4546, 2005     

Effect of residual contaminants and of different types of extrusion processes on the rheological properties of the post-consumer polypropylene

Rheological measurements were conducted to verify the influence of different mechanical recycling processes and the presence of contaminants on the degradation of post-consumer polypropylene. Firstly, polypropylene (PP) was contaminated to simulate a post-consumer material, following the protocol recommended by the FDA. PP was subsequently recovered (washed and dried) and the samples were submitted to different extrusion processes. The rheological data demonstrated that the different types of processing applied and the presence of contaminants altered the molecular structure of the samples. The contaminants acted as agents that accelerated the polymer degradation. The contaminated samples submitted to higher shear rates exhibited greater decrease in their molar mass and a slight narrowing in the molar mass distribution. Also, it was observed that the most degraded samples showed decrease in their molar mass, in the viscosity and in the level of their molecular entanglements. These samples also exhibited a more Newtonian behavior and their molar mass distribution showed a slight narrowing. By calculating the ratio of the molar mass it was possible to quantify the degree of degradation of PP samples, confirming the results obtained.     

Injection stretch blow moulding process of reactive extruded recycled PET and virgin PET blends

Reactive extruded recycled PET (RER-PET) was blended with virgin PET in order to find optimum composition for producing bottles using injection stretch blow moulding (ISBM) process. Two variables were investigated namely, RER-PET concentration in the blend with virgin PET and RER-PET intrinsic viscosity, [η]. The variability of [η] was facilitated by changing PMDA chain extender concentration in the production of RER-PET. Different molecular, mechanical, barrier and optical tests such as infrared, burst pressure, top load strength, drop impact, environmental stress cracking, liquid permeation, gas permeation, and clarity were conducted. The aim was to evaluate the properties of the bottles in response to different blends compositions. Bottles made from RER-PET and virgin PET blends showed similar and better mechanical and barrier properties at certain compositions to those made from Virgin PET. The effects of RER-PET molecular properties such as intrinsic viscosity, chain orientation and conformation on bottles mechanical, barrier and optical properties are detailed.     

Determination of antioxidants in polyolefins using total dissolution methodology followed by RPLC

Antioxidants are added to polyolefins to improve the stability of the resin from oxidation and degradation during processing of the finished article and to increase product lifetime. Without antioxidants, polyolefins would quickly degrade during and after the extrusion or thermoforming process, which would cause inferior appearance and physical properties. The proper level must be added to protect the polymer and to minimize cost. Antioxidants are usually extracted from the resin and the extract is analyzed by RPLC, GC, or Fourier transform infrared spectroscopy. Unfortunately, many of these procedures require significant manual labor, time, and solvent, rendering them impractical for high-throughput work processes. In addition, they may not provide complete extraction of the additives depending upon the type of resin. A validated analytical method was needed for the determination of three common antioxidants, Irganox(?) 1010, Irganox(?) 1076, and Irgafos(?) 168 in polyolefin resins. This paper shows the determination of these antioxidants using dissolution followed by precipitation with o-xylene and methanol. Direct analysis of the solution is achieved in 8?min using RPLC.     

Thermomechanical degradation of filled polypropylene

The main problem in post-consumer plastics recycling is due to the thermomechanical stress acting on the melt during the reprocessing operations. The macromolecules break because of the temperature and of the mechanical stress. The extent of degradation is then correlated to the level of mechanical stress which, in turn, is proportional to the viscosity of the melt. The presence of fillers increases the viscosity of the polymers and then it is expected that the level of thermomechanical degradation of these systems is larger than that of the unfilled material. In this work the thermomechanical degradation kinetic of a polypropylene sample is investigated as a function of the calcium carbonate content. It is shown that the decrease of viscosity, that is the decrease of molecular weight, is directly related to the increase of viscosity due to the filler content. The worsening of the mechanical properties are consistent with the change of viscosity.     

Analytical protocol to study the food safety of (multiple-)recycled high-density polyethylene (HDPE) and polypropylene (PP) crates: Influence of recycling on the migration and formation of degradation products

An analytical protocol was set up and successfully applied to study the food safety of recycled HDPE and PP crates. A worst-case scenario was applied that focused not only on overall migration and specific migration of accepted starting materials but also on migratable degradation products of polymers and additives that may be formed during mechanical recycling.The analytical protocol was set up to cover a wide variety of possible migrants. Identification and semi-quantification were possible for almost all migrants that increased significantly with increasing mechanical recycling steps for both the HDPE and PP crates.It was concluded that the analytical protocol was suitable to study the influence of (multiple) recycling on the food safety of plastic materials. The protocol can be applied to other plastic food contact materials and provides valuable information on the food safety of the recycling process and the resulting recycled food contact materials in addition to challenge testing.     

Fingerprinting of bottle-grade poly(ethylene terephthalate) via matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) has been shown to provide a valuable technique to study the thermomechanical degradation of poly(ethylene terephthalate) (PET). MALDI-MS has been tested to monitor both the admixture of post-consumption bottle-grade PET (PET_pc-btg) with virgin bottle-grade PET (PET_v-btg) and the thermomechanical degradation effects on the chemical properties of PET_v-btg. Principal component analysis of MALDI-MS data classify the samples into groups with specific features: a) PET-btg with intrinsic viscosities of 0.80 or 0.65-0.60 dL g⁻¹); b) processed or virgin PET with the same intrinsic viscosity; c) PET_v-btg from PET containing PET_pc-btg; and d) PET_v-btg from different manufacturers. MALDI-MS data is therefore able to reveal the quality of PET-btg resins preventing frauds and illegal use of recycled PET-btg.     

Thermal analysis as a quality tool for assessing the influence of thermo-mechanical degradation on recycled poly(ethylene terephthalate)

Mechanical recycling of poly(ethylene terephthalate) (PET) was simulated by multiple processing to assess the effects of thermo-mechanical degradation, and characterized using rheological and thermal analysis techniques. Thermo-mechanical degradation under repeated extrusion induces chain scission reactions in PET, which result in a dramatic loss in the deformation capabilities and an increase in the fluidity of the polymer under reprocessing, reducing its recycling possibilities after four extrusion cycles. Multiple reprocessing severely affects the storage modulus and the microstructure of recycled PET, both in the amorphous and crystalline regions. Multimodal melting behavior is observed for reprocessed PET, indicating heterogeneous and segregated crystalline regions. A deconvolution procedure has been applied to individually characterize each crystalline population in terms of lamellar thickness distribution and partial crystallinity. Thermal analysis techniques such as differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA) have proved to be suitable techniques for the quality assessment of recycled PET, giving unequivocal information about its degree of degradation compared to the common technological measurements of melt-mass flow rate (MFR) or oxidative stability (T_Ox).     

Determination of intrinsic viscosity of poly(ethylene terephthalate) using infrared spectroscopy and multivariate calibration method

A methodology was developed to determine the intrinsic viscosity of poly(ethylene terephthalate) (PET) using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and multivariate calibration (MVC) methods. Multivariate partial least squares calibration was applied to the spectra using mean centering and cross validation. The results were correlated to the intrinsic viscosities determined by the standard chemical method (ASTM D 4603-01) and a very good correlation for values in the range from 0.346 to 0.780 dL g⁻¹ (relative viscosity values ca. 1.185-1.449) was observed. The spectrophotometer detector sensitivity and the humidity of the samples did not influence the results. The methodology developed is interesting because it does not produce hazardous wastes, avoids the use of time-consuming chemical methods and can rapidly predict the intrinsic viscosity of PET samples over a large range of values, which includes those of recycled materials.     

Monitoring the extraction of additives and additive degradation products from polymer packaging into solutions by multi-residue method including solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry analysis

The use of polymer materials in industry for product packaging is increasing. The presence of additives in the polymer matrix enables the modification or improvement of the properties and performance of the polymer, but these industries are concerned regarding the extractability of these additives. The quantification of these additives is particularly challenging because of the presence of these substances as contaminants in all the analytical equipment and the diversity of their physicochemical properties. In this context, a multi-residue analytical method was developed for the trace analysis of the twenty main additives (and their degradation products) authorized in plastic products such as pharmaceutical packaging (e.g., antioxidants, release agents, and light absorbers). This analytical method consisted of a solid phase extraction (SPE) followed by an analysis using ultra-high performance liquid chromatography coupled to a tandem mass spectrometer (UHPLC-MS/MS). A comparison of two ionization interfaces and the optimization of the extraction procedure were discussed. The influence of the quality of the solvent type (distilled versus not distilled) and the nature of the SPE cartridges (Polypropylene versus Teflon^®) were demonstrated. The optimized method exhibited a quantification limit lower than 20 ng mL^?1 and recoveries between 70 % and 120 % for all compounds. Finally, the method was validated according to the ICH directive and was subsequently applied to the extraction of polymers under different pH conditions and storage temperatures. To the best of our knowledge, this study presents the first methodology allowing the simultaneous quantification of 24 additives at low ng mL^?1.     

The effects of gamma irradiation on the fate of hindered phenol antioxidants in food contact polymers. Analytical and 14C-labelling studies

The extractable levels of two hindered phenol antioxidants (Irganox 1076 and Irganox 1010) present in PVC, polyethylene and polypropylene, have been monitored by HPLC techniques following progressive exposure of the polymers to ⁶⁰Co γ radiation. There is a gradual diminution in the extractable levels of each antioxidant as irradiation progresses as a result of transformation of the antioxidants in the oxidation reactions ensuing during irradiation. Experiments involving the use of a ¹⁴C-labelled sample of Irganox 1076 in polyolefins have provided evidence of covalent binding of antioxidant degradation products to the polymer following gamma irradiation. However, there is also evidence of the formation of extractable degradation products, the identity of which is as yet unknown.