PET Membranes Research Articles

The behaviour of wine aroma compounds related to structure and barrier properties of virgin, recycled and active PET membranes

Virgin PET, 100% recycled PET and PET containing an oxygen scavenger have been compared for their thermal properties and gas and aroma compound permeability. Thermal properties were slightly different between virgin and recycled PET, which exhibited the same degree of crystallinity but also strong heterogeneity in dispersion and size of crystals. However, glass transition was higher in the presence of oxygen scavenger because of its nature. Similar oxygen and carbon dioxide permeability were measured for virgin, recycled and PET with 1% of oxygen scavenger, whereas with 3% of oxygen scavenger gas barrier properties increased. Water barrier properties of PET were not influenced either by recycling or by the presence of oxygen scavenger and a plasticization effect was evidenced for all films. Concerning volatile organic compounds such as ethanol and aroma compounds, virgin PET was the best barrier. Permeability was strongly affected by the affinity of the compound for the material. Sorption of pure or diluted solution of ethanol induced changes in thermal properties with a slight decrease in Tg and a marked decrease of crystallinity. In contrast, the oxygen permeability after contact with the diluted solution of ethanol was increased, suggesting a reduction of free volume by sorption. Finally, the impact of film barrier properties on three aroma compounds of wine was evaluated and confirmed the inertness of PET concerning aroma compounds and the positive effect of active packaging.

The long-term differentiation of embryonic stem cells into cardiomyocytes: an indirect co-culture model.

BackgroundEmbryonic Stem Cells (ESCs) can differentiate into cardiomyocytes (CMs) in vitro but the differentiation level from ESCs is low. Here we describe a simple co-culture model by commercially available Millicell™ hanging cell culture inserts to control the long-term differentiation of ESCs into CMs.Methodology/Principal FindingsMouse ESCs were cultured in hanging drops to form embryoid bodies (EBs) and treated with 0.1 mmol/L ascorbic acid to induce the differentiation of ESCs into CMs. In the indirect co-culture system, EBs were co-cultured with epidermal keratinocytes (EKs) or neonatal CMs (NCMs) by the hanging cell culture inserts (PET membranes with 1 µm pores). The molecular expressions and functional properties of ESC-derived CMs in prolonged culture course were evaluated. During time course of ESC differentiation, the percentages of EBs with contracting areas in NCMs co-culture were significantly higher than that without co-culture or in EKs co-culture. The functional maintenance of ESC-derived CMs were more prominent in NCMs co-culture model.Conclusions/SignificanceThese results indicate that NCMs co-culture promote ESC differentiation and has a further effect on cell growth and differentiation. We assume that the improvement of the differentiating efficiency of ESCs into CMs in the co-culture system do not result from the effect of co-culture directly on cell differentiation, but rather by signaling effects that influence the cells in proliferation and long-term function maintenance.

Assessment of the Gas Permeation through Thin Coated Polymeric Membranes; Improvement of the Gas Barrier Ability for Hydrogen Storage

We investigate and simulate the permeation behavior of PET membranes on which thin coatings are deposited. Depending on the parameters of deposition and on the thin coating thickness, we assume this alteration could make it possible to decrease by one order of magnitude the permeation coefficient. Some specific developments have been necessary, all the more not only a decrease of permeation is expected but also the mechanical strength of the thin coating during severe mechanical loadings. We consequently design devices dedicated to the permeation test but also to the bulge and blister tests which permit to check the mechanical properties of the film and its adhesion on the PET surface. This paper focuses on the permeation test.

Selective biological response of human pulmonary microvascular endothelial cells and human pulmonary artery smooth muscle cells on cold-plasma-modified polyester vascular prostheses

The aim of this work was to improve the hemocompatibility and the selectivity according to cells of non-woven poly(ethylene terephthalate) (PET) membranes. Non-woven PET membranes were modified by a combined plasma-chemical process. The surface of these materials was pre-activated by cold-plasma treatment and poly(acrylic acid) (PAA) was grafted by the in situ free radical polymerization of acrylic acid (AA). The extent of this reaction and the number of carboxylic groups incorporated were evaluated by colorimetric titration using toluidine blue O. All samples were characterized by SEM, AFM and thermogravimetric analysis, and the mechanical properties of the PAA grafted sample were determined. A selective cell response was observed when human pulmonary artery smooth muscle cells (HPASMC) or human pulmonary micro vascular endothelial cells (HPMEC) were seeded on the modified surfaces. HPASMC proliferation decreased about 60%, while HPMEC proliferation was just reduced about 10%. PAA grafted samples did not present hemolytic activity and the platelet adhesion decreased about 28% on PAA grafted surfaces.

Probing mechanical properties of thin film and ceramic materials in micro- and nano-scale using indentation techniques

In this study, we report on the mechanical properties, failure and fracture modes in two cases of engineering materials; that is transparent silicon oxide thin films onto poly(ethylene terephthalate) (PET) membranes and glass-ceramic materials. The first system was studied by the quazi-static indentation technique at the nano-scale and the second by the static indentation technique at the micro-scale. Nanocomposite laminates of silicon oxide thin films onto PET were found to sustain higher scratch induced stresses and were effective as protective coating material for PET membranes. Glass-ceramic materials with separated crystallites of different morphologies sustained a mixed crack propagation pattern in brittle fracture mode.

Ion guiding through capillaries in uncoated Al2O3 membranes

We made an experimental study on ion guiding through capillaries in uncoated Al2O3 membranes using a variety of ions such as O1+, O3+, and O6+. The incident energy was varied within the range of 30-150 key. The results were compared with others using coated PET and Al2O3 capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q(infinity) seems to exist in our experiment. (c) 2010 Elsevier B.V. All rights reserved.

Electrokinetic study of etching latent tracks of accelerated heavy ions in poly(ethylene terephthalate) and polyimide

The etching of latent tracks and pore formation in track membranes are studied. It is shown that the incorporation of K+ and Ba2+ ions into alkaline solutions accelerates the etching of poly(ethylene terephthalate) (PET) and latent tracks in it. The etching is accelerated due to a decrease in the negative surface charge of PET surface and the pores in track membranes. Isoelectric points are determined for PET and polyimide track membranes and it is established that they depend on pore diameter. As the pore diameter is enlarged from 30 to 70 nm, the magnitude of the negative surface charge rises seemingly due to the increase in the concentration of carboxyl groups on the pore surface. It is assumed that this effect is due to either a high mobility of carboxyl groups in a gel, which is formed on pore walls as a result of etching latent tracks, or a displacement of the slipping plane caused by a decrease in the thickness of the gel layer.

Advancing Towards a Tissue-engineered Tympanic Membrane: Silk Fibroin as a Substratum for Growing Human Eardrum Keratinocytes

Human tympanic membrane cells (hTMCs), harvested from tympanic membrane (TM) explants, were grown in culture and then seeded on membranes prepared from silkworm (Bombyx mori) silk fibroin (BMSF) and on tissue-culture plastic membranes (PET). Fibroin was isolated from silk cast into membranes with a thickness of 10-15 microm. The hTMCs were cultured on both materials for 15 days in a serum-containing culture medium. The cells grown on both substrata were subjected to nuclear staining (DAPI) and counted. Further, the cultures were immunostained for a number of protein markers related to the epithelial/keratinocyte phenotype and cell adhesion complexes. The BMSF membranes supported levels of hTMC growth higher than that observed on the PET membranes. The immunofluorochemical analysis indicated unequivocally that BMSF is a more suitable substratum than PET with respect to the growth patterns, proliferation, and cell-cell contact and adhesion. BMSF appear as a promising substratum in the tissue-engineered constructs for the replacement of TM in case of nonhealing perforations.

MEASUREMENT OF AVERAGE ETCHED PORE RADIUS IN ION TRACK MEMBRANES THROUGH CONDUCTOMETRIC TECHNIQUE

In the present work, average pore radius in etched PC and PET membranes, exposed to various heavy ions, has been determined using the conductometric technique. The average pore radius, measured directly through optical microscope, has been found to be higher (15%) than the values determined using the conductometric method.

NICKEL/CARBON NANOSTRUCTURED ELECTRODES SYNTHESIZED USING TEMPLATE METHOD

ABSTRACT Nuclear track-etched PET membranes, with a thickness of 20 μm and pore diameters of 200, 400, and 1000 nm, were used as hard templates for the electrodeposition of Ni micro-wires. Galvanostatic deposition of Ni in pores has been investigated using two-electrode electrochemical cell, and the optimal deposition parameters, temperature and electrolyte solution. After removal of the template using KOH, the free standing Ni micro-wires were modified with carbon paste (containing CMS, carbon black, PVDF, NMP). Electrochemical properties of the composite were elucidated using cyclic voltammetry and electrochemical impedance spectroscopy.

Formation of composite films of ion-track membranes embedded with oblique Cu nanowires for anisotropic infrared absorption

Composite films of poly(ethylene terephthalate) (PET) embedded with Cu nanowires were prepared by electroplating ion-track PET membranes. PET films were irradiated with 450 MeV 129Xe 23+ ions with a direction of 45° from the film normal, and then etched with sodium hydroxide solution to form thin pores of 1 μm diameter. Cu was filled into the pores by electroplating in a copper sulfate solution to form Cu nanowires embedded in a direction tilted from the film normal. The composite membrane showed anisotropic infrared absorption in the in-plane direction, having the transmission axis in the direction normal to the ion incidence.

SEM Analysis of Cell Colony growth on PET Membranes

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Synergist Immobilization Method for Photo‐Grafting: Factors Affecting Surface Selectivity

AbstractThe surface‐selectivity of photo‐grafting has been used as a crucial parameter to evaluate the ‘grafting‐from’ efficiency of the synergist immobilization method developed in our recent work. The factors that affect surface‐selectivity of photo‐grafting have been further investigated. It was shown that the competition of solvent with the membrane surface towards the generation of starter radicals led to a decrease in the degree of grafting and surface‐selectivity of photo‐grafting. High UV intensity made the functionalization mechanism more complicated, due to the generation of a new type of starter radical at the membrane surface with immobilized synergist in the absence of BP and because it could lead to cross‐linking in the grafted layer. An appropriately low photo‐initiator concentration was also required in order to achieve the ideal surface‐selectivity of photo‐grafting. In addition, this method has been successfully applied to the track‐etched PET membranes. Pore size distributions as well as ethanol and water permeability of the membranes were used to retrieve information about the effective thickness of the grafted polymer layers.magnified image

Improving Membrane Staining of Cultured Cells Using Ferrocyanide as a Post-Fixative

Abstract Lack of contrast is a common problem encountered when doing TEM of cultured cells, especially of membranes. Using ferrocyanide as a post-fixative can greatly improve membrane fixation and staining. This protocol has been used to study Caco-2 cells grown on PET membranes (the “Caco model”). Caco-2 is a colon cancer cell line that differentiates upon reaching confluency. This allows permeability studies on a cell model, which is reasonably similar to the human intestine. Basically, the protocol is classical, the only peculiarity consisting in including ferrocyanide in post-fixation. I describe how I prepare and embed the membrane in order to obtain transverse sections of a cell monolayer because I find this is the only way to obtain regular sections with the cells sticking to the membrane (otherwise the ultrathin section splits between the cell and membrane).

Surface modification of PET membrane by ion implantation

Semicrystalline poly(ethylene terephtalate) (PET) foils were irradiated with N 5+, O 7+ and C 3+ ions. Ions beams of 50 keV N 5+, 70 keV O 7+ and 30 keV C 3+ were produced from the ECR ion source. The induced effects and wettability of ion-implanted membranes were investigated by means of the Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and by the contact-angle methods. FTIR measurements of the virgin and irradiated samples show the scission processes of main chains at the ethylene glycol residue. Various degradation processes known from photochemical degradation were also observed. The AFM observation revealed that the surface topography changes after irradiation. The contact-angle measurements showed that the PET membranes became significantly more hydrophilic after the ion irradiation.

Permeability and Electrokinetic Characterization of Poly(ethylene terephthalate) Capillary Pore Membranes with Grafted Temperature-Responsive Polymers

Poly(ethylene terephthalate) (PET) track-etched membranes with average pore diameters of 692 and 1629 nm were functionalized using the monomer N-isopropylacrylamide (NIPAAm) and a photoinitiated "grafting-from" approach in which a surface-selective reaction has been most efficiently achieved by combinations of the unmodified PET surface with benzophenone and, alternatively, of an aminated PET surface with benzophenone carboxylic acid. Consistent estimations of the pore diameters of the base PET membranes and of the effective grafted polyNIPAAm layer thicknesses on the PET pore walls were possible only on the basis of the permeabilities measured with aqueous solutions of higher ionic strength (e.g., 0.1 M NaCl). However, the permeabilities measured with ultrapure water indicated that the "electroviscous effect" was significant for both base membranes. The influences of membrane pore diameter, surface charge, and solution ionic strength could be interpreted in the framework of the space-charge model. Functionalized membranes with collapsed grafted polymer hydrogel layer thicknesses of a few nanometers exhibited almost zero values of the zeta potential estimated from the trans-membrane streaming potential measurements. This was caused by a "hydrodynamic screening" of surface charge by the neutral hydrogel. Very pronounced changes in permeability as a function of temperature were measured for PET membranes with grafted polyNIPAAm layers, and the effective layer thickness in the swollen state--here up to approximately 300 nm--correlated well with the degree of functionalization. The subtle additional effects of solution ionic strength on the hydrodynamic layer thickness at 25 degrees C were different from the effects for the base PET membranes and could be explained by a variation in the degree of swelling, resembling a "salting-out" effect. Overall, it had been demonstrated that the functionalized capillary pore membranes are well suited for a detailed and quantitative evaluation of the relationships between the synthesis, the structure, and the function of grafted stimuli-responsive polymer layers.

Photoreactive Functionalization of Poly(ethylene terephthalate) Track‐Etched Pore Surfaces with “Smart” Polymer Systems

AbstractSummary: Poly(ethylene terephthalate) (PET) track‐etched membranes with a pore diameter of ca. 700 nm, optionally surface‐functionalized to create a “carboxyl” or “amino” surface, were used for heterogeneous graft copolymerizations. Grafted poly(acrylic acid) acted as a pH responsive, “smart” polymer. To evaluate the surface‐specific initiation of graft copolymerizations unmodified and primary functionalized membranes were systematically combined with three differently charged benzophenone derivatives as photoinitiators, which were adsorbed on the PET surface prior to the reaction. The functionalized membranes thus obtained were characterized for chemical structure and permeability as a function of pH. The pore structure with a narrow size distribution and the resulting high sensitivity of the membrane permeability to the grafting functionalizations made the track‐etched PET membranes a very useful tool for analyzing structure and function of responsive grafted polymer layers. The primary functionalization of the base polymer with a molecular layer of a multifunctional alkylamine (“amino” surface) enhanced the efficiency of the subsequent graft copolymerization via photoinitiated hydrogen abstraction considerably because a high density of well accessible reactive groups had been introduced. The preadsorption of the photoinitiator on the base polymer surface was significantly improved by ionic interactions between the respective functional groups of the surface and the photoinitiator. Such a photoinitiator preadsorption, especially when combined with a reactive layer from the primary functionalization, enabled a very efficient and surface selective functionalization because a better control of grafting density and a reduction of photoinitiated side reactions along with a more efficient use of the photoinitiator were possible.Water permeabilities (pH 2 and pH 7) of unmodified and functionalized PET membranes for identification of optimal synthesis and evaluation conditions.magnified imageWater permeabilities (pH 2 and pH 7) of unmodified and functionalized PET membranes for identification of optimal synthesis and evaluation conditions.

Gas-Permeation Control by PET Membranes with Nanosized Pores

Gas-Permeation Control by PET Membranes with Nanosized Pores

A spectroscopic ellipsometry study of PET membranes from IR to Vis‐FUV

AbstractA detailed study of Spectroscopic Ellipsometry (SE) spectra of uniaxially stressed, 12μm thick poly(ethylene terephthalate) (PET) membranes were realized in both IR (900‐3500 cm−1) and Vis‐FUV (1.5 to 6.5 eV) spectral regions and in various orientation angles ∅︁ between the plane of incidence and the machine direction (MD) of the PET membranes. In the IR spectra, the three main modes of the ester group at ∼1126, 1256 and 1721 cm−1 are observed. The first two of these peaks show identical polarization dependence, with preferential orientation ∅︁≈0° (i.e. the plane of reflection parallel to the MD), while the peak at ∼1721 cm−1 is excited in the perpendicular direction, ∅︁≈90°. In the Vis‐FUV SE spectra, the dependence of the characteristic electronic absorption bands on the orientation angle ∅︁ is studied. Besides the well known benzene band centered at ∼5 eV, a doublet of less intense peaks appear just above the absorption edge between 4.1 and 4.3 eV with the most striking characteristic that they show polarization selection rules opposing to that of the benzene band. The above characteristics of the electronic Vis‐FUV spectra of PET are discussed in a manner comparative to the corresponding IR spectra. The discussion becomes in the context of determining the molecular orientation of PET using a non‐destructive technique such as SE.

Nanomechanical and optical studies on polymeric membranes

AbstractThe nanomechanical properties of poly(ethylene terephthalate) (PET) membranes, were examined in light of nanoindentation experiments under conditions of maximum contact load in the range of 0.5‐12 m?. Spectroscopic Ellipsometry (SE) from 1.5 to 6.5 ev (Vis‐FUV range) was also applied to probe the dielectric function (ϵ(ω) of the industrially supplied membranes, as well as their geometrical structure. Mechanical stretching (uniaxial or biaxial) procedures are usually applied for the elongation of the polymeric membranes, their thickness reduction and enhancement of their mechanical and optical performance, causing a preferable orientation of the macromolecules close to the surface. Nanoindentation and se testing have revealed the existence of a two‐layer geometrical structure of the pet membranes, consisting of a thick amorphous pet layer and a thin crystalline‐like pet overlayer, with increased hardness (elastic modulus). The analyses of the experimental dataprovides quantitative information on the formed overlayer, which is ascribed to the processing history of the membrane.