Evaluating organic compound migration in poly(ethylene terephthalate): a simple test with implications for polymer recycling.

PurposeThis paper aims to focus on achieving triple-shape memory effect (triple-SME) of a commercial poly (ethylene terephthalate) (PET) film with the thickness of 100 µm.Design/methodology/approachThe thermal characteristics and microstructure of PET film were characterized by differential scanning calorimetry, thermogravimetric analysis and wide-angle X-ray diffraction analysis. The dual-shape memory effect (dual-SME) of the PET film was then systematically investigated, and based on that, triple-SME in thin PET film was achieved.FindingsInvestigation of the dual-SME in PET film revealed the difference between recovery temperature and programming temperature reduced with increasing programming temperature. An obvious intermediate shape shifting between the original and final programmed shape was observed during shape recovery in triple-shape memory behaviors.Research limitations/implicationsCompared with dual-SME in polymer, relatively less work has been done on multi-SME in polymer, especially in thin polymer film. In this study, triple-SME in a PET film was investigated based on the results of dual-SME of the film. The main implication of the study is on how to achieve a watermark between the final programmed pattern and the original pattern, for the application of shape memory polymer in anti-counterfeiting label.Originality/valueDual- and triple-SMEs were achieved in a PET film that is only 100 µm in thickness, and the underlying mechanism for the difference between programming temperature and recovery temperature was discussed. For the novel application of triple-SME in anti-counterfeit label, the watermark during shape recovery in triple-SME can effectively prevent duplication.

In this paper, we demonstrate the humidity-sensing ability and the robustness of our syringe-printed single-walled carbon nanotube–graphene oxide (SWCNT–GO) traces on adhesive and flexible poly(ethylene terephthalate) (PET) thin films. The printed traces, which exhibited humidity sensing by undergoing a change in resistance with the relative humidity, showed a high humidity sensitivity (S, where S can be as high as 1.5%). At the same time, the flexible and adhesive nature of thin PET films ensures that these traces are deployable on surfaces with different curvatures. The humidity sensitivity of our SWCNT–GO traces is over 2 times greater than the pure SWCNT networks: we propose that the hygroscopic swelling of GO flakes under humid conditions is responsible for this enhanced humidity sensitivity. Furthermore, the printed traces demonstrated that even after being subjected to hundreds of hours of long-term stability tests, their humidity-sensing capabilities remained intact. Furthermore, these traces withstood over 2200 cycles of temperature cycling reliability tests without any failures or significant degradation in their electrical performances. Therefore, these SWCNT–GO traces printed on thin, flexible, and adhesive PET films demonstrate excellent potential for being used as highly reliable humidity sensors, which are ultrathin, highly sensitive, and can be deployed on surfaces of various curvatures.

The aim of this work was to study the variations in the oxygen diffusion, solubility, and permeability coefficients of polylactide (PLA) films at different temperatures (5, 23, and 40°C) and water activities (0–0.9). The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for poly(ethylene terephthalate) (PET) films under the same experimental conditions. The water sorption isotherm for PLA films was also determined. Diffusion coefficients were determined with the half‐sorption time method. Also, a consistency test for continuous‐flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Fickian diffusion in the PLA films. The permeability coefficients were obtained from steady‐state permeability experiments. The results indicated that the PLA films absorbed very low amounts of water, and no significant variation of the absorbed water with the temperature was found. The oxygen permeability coefficients obtained for PLA films (2–12 × 10−18 kg m/m2 s Pa) were higher than those obtained for PET films (1–6 × 10−19 kg m/m2 s Pa) at different temperatures and water activities. Moreover, the permeability coefficients for PLA and PET films did not change significantly with changes in the water activity at temperatures lower than 23°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1790–1803, 2004

Barrier Polymers

Barrier polymers are used for many packaging and protective applications. As barriers they separate a system, such as an article of food or an electronic component, from an environment. Barrier polymers limit movement of substances, called permeants. The movement can be through the polymer or, in some cases, merely into the polymer. After crossing the barrier polymer, the permeant moves to the polymer surface, desorbs, and moves away. Permeant movement is a physical process that has both a thermodynamic and a kinetic component. For polymers without special surface treatments, the thermodynamic contribution is in the solution step. The permeant partitions between the environment and the polymer according to thermodynamic rules of solution. The kinetic contribution is in the diffusion. The net rate of movement is dependent on the speed of permeant movement and the availability of new vacancies in the polymer. The traditional definition of a barrier polymer required an oxygen permeability less than \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${2{\hskip0.167em}{\hskip0.167em}{\rm{nmol}}/{(}{\rm{m}} {\hskip-0.167em}{\hskip-0.167em}{\cdot{}}{\hskip-0.167em}{\hskip-0.167em} {\rm{s}}{\hskip-0.167em}{\hskip-0.167em}{\cdot{}}{\hskip-0.167em} {\hskip-0.167em}{\rm{GPa}}{)}}$\end{document} (originally, less than \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{(}1{\hskip0.167em}{\hskip0.167em}{\rm{cc}}{\hskip-0.167em} {\hskip-0.167em}{\cdot{}}{\hskip-0.167em}{\hskip-0.167em}{\rm{mil}}{)}/{(}100{\hskip0.167em}{\hskip0.167em}{\rm{in}} ^{2}{\hskip-0.167em} {\hskip-0.167em}{\cdot{}}{\hskip-0.167em}{\hskip-0.167em}{\rm{d}} {\hskip-0.167em}{\hskip-0.167em}{\cdot{}}{\hskip-0.167em}{\hskip-0.167em} {\rm{atm}}{)}}$\end{document} ) at room temperature. Poly(ethylene terephthalate) (PET), with an oxygen permeability of \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${8{\hskip0.167em}{\hskip0.167em}{\rm{nmol}}/{(}{\rm{m}} {\hskip-0.167em}{\hskip-0.167em}{\cdot{}}{\hskip-0.167em}{\hskip-0.167em} {\rm{s}}{\hskip-0.167em}{\hskip-0.167em}{\cdot{}}{\hskip-0.167em} {\hskip-0.167em}{\rm{GPa}}{)}}$\end{document} , is not considered a barrier polymer by the old definition; however, it is an adequate barrier polymer for holding carbon dioxide in a 2‐L bottle for carbonated soft drinks. Many months are required to lose enough carbon dioxide (15% of initial) to be objectionable. The polymers that are good barriers to permanent gases, especially oxygen, have important commercial significance. Vinylidene chloride copolymers are available as resins for extrusion, latices for coating, and resins for solvent coating. Vinylidene chloride copolymers are marketed under a variety of trade names. Saran is a trademark of The Dow Chemical Company for vinylidene chloride copolymers. Other trade names include Daran (W.R. Grace), Amsco Res (Union Oil), and Serfene (Morton Chemical) in the United States; and Haloflex (Imperial Chemical Industries, Ltd.), Diofan (BASF), Ixan (Solvay and Cie SA), and Polyidene (Scott‐Bader) in Europe. Hydrolyzed ethylene–vinyl acetate copolymers, commonly known as ethylene–vinyl alcohol (EVOH) copolymers, are usually used as extrusion resins, although some may be used in solvent‐coating applications. Copolymers of acrylonitrile are used in extrusion and molding applications. Commercially important comonomers for barrier applications include styrene and methyl acrylate. Polyamide polymers can provide a good‐to‐moderate barrier to permeation by permanent gases. Two often‐used polymers have adequate properties for some applications. Poly(ethylene terephthalate) (PET) is used to make films and bottles. Poly(vinyl chloride) (PVC) is a moderate barrier to permanent gases. Plasticized poly(vinyl chloride) is used as a household wrapping film. In regard to water vapor transmission (WVTR) values, those polymers that are good oxygen barriers are often poor water‐vapor barriers and vice versa. Polymer molecules without dipole–dipole interactions, such as polyolefins, dissolve very little water and have low WVTR and permeability values. The permeation of flavor, aroma, and solvent molecules in polymers follows the same physics as the permeation of small molecules, but with two significant differences. For these larger molecules, the diffusion coefficients are much lower and the solubility coefficients are much higher. Furthermore, the large solubility coefficient can lead to enough sorption of the large molecule that plasticization occurs in the polymer, which can increase the diffusion coefficient. Generally, vinylidene chloride copolymers and glassy polymers such as polyamides and EVOH are good barriers to flavor and aroma permeation, whereas the polyolefins are poor barriers. Several physical factors can affect the barrier properties of a polymer. These include temperature, humidity, orientation, and cross‐linking. Typically, the permeability increases 5 to 10% for every increase of 1°C. When a polymer equilibrates with a humid environment, it absorbs water. This can plasticize the polymer and increase the permeability. The effect of orientation on the permeability of polymers is difficult to assess; diffusion in some polymers is unaffected by orientation; in others, increases or decreases are observed. Cross‐linking has been shown in a few cases to decrease the diffusion coefficient. Reasonable prediction can be made of the permeabilities of low molecular weight gases such as oxygen, nitrogen, and carbon dioxide in many polymers. The diffusion coefficients are not complicated by the shape of the permeant, and the solubility coefficients of each of these molecules do not vary much from polymer to polymer. Reasonable predictions of the permeabilities of larger molecules such as flavors, aromas, and solvents are not easily made. The diffusion coefficients are complicated by the shape of the permeant, and the solubility coefficients for a specific permeant can vary widely from polymer to polymer. The permachor method is an empirical method for predicting the permeabilities of oxygen, nitrogen, and carbon dioxide in polymers. In this method a numerical value is assigned to each constituent part of the polymer. An average number is derived for the polymer, and a simple equation converts the value into a permeability. The model has been modified to liquid permeation with some success. For larger molecules, independent predictions of the diffusion coefficients and the solubility coefficients are required. Predicting the diffusion coefficient for a permeant in a polymer requires knowing one other diffusion coefficient in the polymer. The solubility coefficients are more difficult to predict. Although advances are being made, the best method is probably to use a few known solubility coefficients in the polymer to predict others. Measuring the barrier properties of polymers is important for several reasons. The effects of formulation or process changes need to be known, new polymers need to be evaluated, data are needed for a new application before a large investment has been made, and fabricated products need to have performance verified. Two methods of measuring water‐vapor transmission rates (WVTR) are commonly used. The newer method uses a Permatran‐W (Modern Controls, Inc.). The other method is the ASTM cup method. Measuring the permeation of carbon dioxide occurs far less often than measuring the permeation of oxygen or water. The simplest method uses the Permatran‐C instrument (Modern Controls, Inc.). Many methods are used to characterize the transport of flavor, aroma, and solvent molecules in polymers. Each has some value, and no one method is suitable for all situations. Any experiment should obtain the permeability, the diffusion coefficient, and the solubility coefficient. The primary application for barrier polymers is food and beverage packaging. Barrier polymers are also used for packaging medical products, agricultural products, cosmetics, and electronic components and in moldings, pipe, and tubing. The use of safe materials is vital for barrier applications, particularly for food, medical, and cosmetics packaging. Suppliers of specific barrier polymers can provide the necessary details to ensure safe processing and use of barrier polymers.

The kinetic parameters of disperse dyeing of polyethylene terephthalate (PET) sheets modified by a nanostructured hyperbranched polymer were investigated in terms of dyeing rate constant, time of half-dyeing, diffusion coefficient, and activation energy of the diffusion. The results were compared with those of pristine PET. The surface morphology, surface structure, and thermal properties of modified PET sheets were also studied by atomic force microscopy (AFM), attenuated total reflectance infrared spectroscopy (ATR-FTIR), and differential scanning calorimetry (DSC). Results indicated that the crystallinity and glass transition temperature of modified samples were decreased compared with that of the pristine PET. The diffusion coefficient of dye molecules increased by increasing temperature of dyeing. The highest diffusion coefficient was obtained for the modified PET sample containing 2 wt% hyperbranched polymer while pristine PET sheet showed the lowest one. The activation energy of diffusion of dye into the modified PET sheets was lower than that of the unmodified PET.

The electrochemical impedance spectroscopy (EIS) technique was used to evaluate the water transport (diffusion and equilibrium water uptake) and the dielectric properties of free‐standing poly(ethylene terephthalate) (PET) membranes at 40°C. Permeability and diffusion coefficients were also obtained using the Payne cup method and the MacBain quartz spring balance to assess the reliability of the EIS method when compared to other techniques. In addition, an electromigration (dc) technique was used to estimate the NaCl diffusion coefficient across PET films. Results obtained indicate that PET is highly permeable to water and much less permeable to salt. The water diffusion coefficient, D, varies from 2.11× 10−9 to 9.97× 10−9 cm2s−1 for thicknesses between 22 and 205μm, whereas the equilibrium water uptake, W, varies from 0.54 to 0.95 wt % for the same given range of thicknesses. The average calculated dielectric constant of the free‐standing PET films is 3.6. An estimate of the NaCl diffusion coefficient, Ds, is 9.34× 10−14 cm2s−1. Transport properties results obtained via the electrochemical technique are in reasonable agreement with those obtained with the classical gravimetric method. © 1993 John Wiley & Sons, Inc.

The need of and opportunities for recycling of plastics for food packaging have been recognized, and a lot of work to find meaningful and cost-effective solutions to this issue is in progress. The safety of recycled plastics for food contact use is largely dictated by the ability of post-consumer contaminants to absorb into recycled materials and later diffuse from recycled plastics into the food. The objective of the present study was to establish a suitable analytical approach to identifying and quantifying any chemical substances that derive from the earlier use and remain in the polyethylene terephthalate (PET). A simple gas chromatographic technique using flame ionization detection was developed to allow quantification of solvent extractable compounds in a series of recycled PET samples. Identification of the nature and extent of contaminants in the PET samples was also attempted using GC/MS analysis.

A method for measuring a distribution of contact pressures between ground surfaces using a thin PET, polyethylene terephthalate, film of 0.9 μm thickness has been developed. Punch specimens were made of carbon steel, S45C, and their ends were ground. The PET film was inserted between ground surfaces of the punch specimens and pressed at a given pressure for one minute. The PET film was indented by surface asperities on the ground surfaces at real contact points. Thus if the relationship between the areas of the indented parts and the applied pressures were known, the contact pressures could be determined by measuring the indented areas of the PET film. The indented areas of the PET films were proportional to the applied pressures in the range of zero to 300 MPa. These areas were measured automatically by image processing through an optical microscope which was modified so that its stage was controlled by a microcomputer. The apparent contact area was divided into many small portions with areas of about 0.017 mm2 and the contact pressure was determined in each portion. The measured distributions of contact pressures for circular and square punches were compared with the calculated ones. They were in relatively good agreement with each other.

Characterization of water vapor transport in glassy polyacrylonitrile by combined permeation and sorption techniques

The two most widely used polymers in packaging in recent years are polyethylene terephthalate (PET) and polyethylene (PE). The biggest fractions of these polymers are not re‐utilized, in spite of the fact that they possess excellent properties even after their first application. The ban on using recycled polymers in food packaging applications and the lack of good value outlets for these materials causes them to end up in landfills. The high cost nylon, used in packaging primarily as high gas barrier laminates with PE, also finds its way to landfills. In this case, the reason is the difficulty of recycling different polymers that are incompatible. Thus, the Municipal Solid Waste (MSW) stream transferred to landfills contains many plastic packages. These packages are being blamed as a major pollutant of the environment in spite of the fact that all plastics contribute only a small percentage to the weight of the garbage in landfills. If proper and cost effective applications for the recycled polymers could be developed, the waste related to their disposal could be limited. In addition, the contribution of plastic packages to the environmental problem could be diminished. In the present paper, the possibility of sandwiching a contaminated PET layer between two layers of the virgin material was studied. The aim of the study was to determine whether such an operation could lower the migration level of contaminants from a multilayer structure (containing a recycled layer of PET) to values below the limits required by regulatory agencies. The diffusion coefficients (required to determine migration) of four organic liquids in PET were determined. As a result of the sandwiching operation, the amount of pollutant (toluene) migrating into the food simulant was reduced by two orders of magnitude. The properties of PE/nylon blends were also studied. It was found that the high gas barrier properties of nylon are preserved in the blend when proper processing conditions are used. Therefore, the recycled material could be used as a centre layer in a multilayer structure providing good gas barrier properties to this structure.

Flexible electronics have been recently paid much attention. A flexible substrate (Organic resin film) is indispensable component for flexible devices. Though PET film is low-cost organic film, low heat-resistance of PET film limits its application as a flexible device substrate. We have developed heat-resistant PET which does not deteriorate even at 190°C heat treatment for one hour. An excimer light was irradiated onto a polysi-lazane (PHPS: perhydropolysilane)-coated film to form a dense silicon-dioxide (SiO2) layer on a PET film, and the heat-resistance property of the formed film was examined. Changes of surface state and cross-sectional structure of the formed film due to heat treatment were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Compared to normal PET, which is deteriorated and whitened by heat treatment of about 110°C - 120°C, the SiO2-coated PET film maintains transparency and does not deteriorate after heat treatment at 180°C - 190°C for one hour. This high heat resistance is due to a dense SiO2 film formed on the surface that prevents surface precipitation and crystallization of low-molecular-weight oligomers (which are the cause of thermal degradation of PET). It is expected that enhancing the heat resistance of PET—which has high versatility and low cost—to about 180°C to 190°C will allow SiO2-film-coated PET to be developed as a film substrate for flexible devices.

Polymeric materials can be used as functional barriers to prevent contamination of food from the environment or from other packaging components, e.g. mineral oil hydrocarbons from printing inks. Polyethylene terephthalate (PET) is such a promising barrier material. From permeation studies found in the scientific literature lag times, diffusion coefficients or permeation rates towards organic chemicals could not derived because of the slow diffusion process of the permeants in PET. Knowledge about lag times or diffusion coefficients for different permeants, however, is essential for the evaluation of the barrier properties of PET films towards organic contaminants, e.g. mineral oil hydrocarbons. The aim of the study was to develop automated permeation testing method in order to determine the lag times of high-barrier films. From the lag times, the diffusion coefficients as well as the partition coefficients of the alkanes were calculated. In addition, the permeated amounts were simulated by use of diffusion models. Therefore, the lag times can be predicted under different experimental conditions as used in the current study. The results of this study show that the investigated 12 µm PET film is an effective barrier towards mineral oil hydrocarbons. For example, the predicted lag time for n-octane or n-dodecane at 40°C is 8.8 and 210 years respectively. Copyright © 2014 John Wiley & Sons, Ltd.

The major challenge of plastic electronics is the deposition of gold nanoparticles (AuNPs) on flexible substrates at room temperature. Here, we show fast, single step, room temperature deposition of AuNPs on polyethylene terephthalate (PET) and biaxially oriented PET (BoPET) substrate by employing dielectrophoresis. The deposition has been carried out using two-electrode system, with BoPET (or PET) and metallic (Pt or stain steel) mesh, under an AC signal of 20 kHz and 20 V peak-to-peak (V(pp)) (signal for PET is 6 V(pp) and 6 kHz). In this method, we show how to deposit AuNPs on PET-like insulator by exploiting its polarization capability under an AC signal. The polarization of PET has been confirmed by change in the Raman spectra of the PET film under in situ AC signals. Furthermore, we show that using this dielectrophoretic deposition method, the PET films can be patterned by AuNPs at room temperature without any pre- and posttreatment.

Why was the work done: The Brazilian distilled spirit cachaça has a complex composition. Numerous reactions occur throughout the production chain from fermentation, to distillation and then packaging. During these processes secondary compounds, together with organic and inorganic contaminants, are formed. Among the organic contaminants, carcinogenic and genotoxic polycyclic aromatic hydrocarbons (PAHs) can be introduced into the distillate from packaging such as polyethylene terephthalate (PET). What are the main findings: This study analysed physicochemical properties and quantified PAHs in cachaça packaged in PET stored under different conditions. These included storage in the cold (refrigerator) and ambient under artificial light, continuous sunlight, and protected from light. Physicochemical analyses of cachaça, was performed before and after packaging in PET for a period of twelve months. The methodology was as established by MAPA (Ministry of Agriculture and Livestock), with the quantification of PAHs by HPLC. PET was characterised by thermogravimetric analysis, and changes in its surface were evaluated by Fourier-Transform Infrared Spectroscopy. Why is the work important: Cachaça stored in glass packaging complied with the Normative Instructions for Identity and Quality from MAPA. Cachaça was affected by packaging and storage in PET due to mass transfer, migration of substances, oxidation, and loss of aroma. Storage of cachaça under both laboratory light and sunlight resulted in higher concentrations of benzo[a]pyrene and benzo[a]anthracene compared to storage in glass. The quality of cachaça was also affected by storage conditions, mainly due to the loss of the water-ethanol fraction and the oxidation of some compounds. Why is the work important: The findings highlight that PET packaging, when combined with exposure to light, can facilitate the transfer of PAHs to cachaça. This suggests that packaging of cachaça in PET may be unsuitable in certain situations.