Development and oxygen scavenging performance of three‐layer active PET films for food packaging

Polymeric active materials represent an innovative food packaging concept that has been introduced to improve the quality of foods and to enhance their shelf life. In this article, the effect of the inclusion of an oxygen scavenger in a polymeric matrix, realizing multilayer active polyester films by coextrusion process, is analyzed. In particular, three layer active films, at different mass ratios of the layers, were produced to form symmetrical "ABA" structures comprising polyethylene terephthalate (PET) with a polymeric oxygen scavenger (OS) as core layer and pure PET as external layers. Oxygen scavenging tests conducted on the multilayer active structures have pointed out the role of the relative layer thickness in controlling the scavenging capacity, the activity time and the oxygen absorption rate. A modeling of the scavenging phenomena, which combines a quasi steady‐state distribution in the skin layers with a flat profile of O₂ content in the active core layer, can explain the experimentally observed oxygen absorption rate at short times. Moreover, steady state oxygen transport measurements, performed when the scavenger reactive capacity is exhausted, have shown that the presence of the active phase slightly reduces the O₂ permeability, compared with the neat PET. The effect, which progressively increases with the amount of active phase in the film formulation, was related to the different morphological state developed on processing. Finally, preliminary shelf life tests on fresh‐cut untreated apples suggest that the developed three layer active films have a significant potential in the shelf‐life extension of oxygen sensitive food products. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41465.     

Optimized design of multilayer barrier films incorporating a reactive layer. III. Case analysis and generalized multilayer solutions

In part III of this series of articles, we present the analysis of transient permeation through two‐layer reactive–passive (RP) film designs, the analysis extension to multilayer structures, and optimized design solutions for multilayer barriers incorporating immobile noncatalytic oxygen scavenger within one of the layers. The reduction of oxygen ingress into a package within a certain timeframe depends on two factors: extension of the scavenger exhaustion time and reduction of the transient transmission rate through the film during that time. The optimal design for the scavenger exhaustion time involves exposure of the reactive layer to the package contents and its protection from high levels of environmental oxygen by the best possible passive barrier layer. The film barrier properties can be further optimized by the selection of the matrix material to place the scavenger in. Reducing the initial transmission rate requires the placement of the scavenger within a layer with the lowest diffusivity of the matrix polymer. When one chooses between two layers with different material transport properties in which to put the scavenger, the optimal solution for the ingress depends on the desired time to provide an improved barrier. The lifetime of the scavenger in the RP film is shortened for design 1, when the diffusivity of the reactive layer is smaller than that of the passive layer, compared to RP design 2, with the layer matrix sequence reversed, but the transient transmission rate is greatly reduced on average for the former. If the desired time to provide a barrier does not exceed the scavenger exhaustion time for RP design 1, the lowest diffusivity material should be used as a matrix for the innermost layer loaded with the scavenger. Otherwise, the highest possible passive barrier should be placed into the film external layer to minimize the total ingress during longer times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1966–1977, 2006     

Optimized design of multilayer barrier films incorporating a reactive layer. I. Methodology of ingress analysis

A new method for the analysis of oxygen ingress into packages and optimized design solutions for multilayer barrier films incorporating an immobile noncatalytic oxygen scavenger within one of the layers are presented in this three‐part series. The results are based on the theoretical framework of transient permeation through a dense reactive medium with a finite solute scavenging capacity. The target application was flexible and rigid plastic packaging for oxygen‐sensitive products, and the goal was the minimization of oxygen ingress into the package within a predetermined timeframe. A predictive model for oxygen ingress was developed, and practical recommendations for the selection of layer material properties, layer sequencing, and placement of the scavenger within a layer to achieve this goal are provided. Part I introduces the concepts of reference and steady‐state lag times for passive barriers to gas permeation. These concepts are expanded to include the scavenger exhaustion lag time for noncatalytic reactive barriers with an instantaneous scavenging reaction. The steady‐state lag time concept is applied to the characterization of noncatalytic reactive barrier solutions with finite rates of the scavenging reaction using transient effective flux dynamics and the model of solute ingress into the package. The model is based on the semipermeable reaction wavefront concept, which we developed. The corresponding passive‐to‐reactive film transition and its effect on the lag times are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1940–1951, 2006     

Thermoformable high oxygen barrier multilayer EVOH/LDPE film/foam

The effect of the number of layers on oxygen transmission and thermoformability of novel multilayer film/foam materials was investigated. Ethylene-vinyl alcohol copolymer/low-density polyethylene multilayered film/foam composites having 16, 32, and 64 alternating layers were developed using continuous multilayer coextrusion process, and the morphology, density, oxygen transmission, and mechanical properties of the as-extruded film/foams were characterized. Tensile properties of the film/foams at elevated temperatures were used to optimize thermoforming conditions. Uniaxial orientation was discovered as an efficient approach to evaluate the potential for thermoforming. Oxygen transmission showed a strong correlation with the thickness reduction which could be used as an indicator for barrier properties of the packaging materials. Film/foam materials with 32 layers demonstrated optimum performance with low oxygen transmission along with high drawing capability. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48903.     

Linking morphology changes to barrier properties of polymeric packaging for microwave‐assisted thermal sterilized food

It is a priority to develop polymeric packaging that can withstand microwave‐assisted thermal sterilization (MATS) and maintain the quality of low‐acid foods during long‐term storage. In this study, we explored changes in the morphology of pouch films with two multi‐layer structures. The films are based on barrier layers of metal oxide‐coated poly(ethylene terephthalate) (PET) (film A) and ethylene vinyl alcohol (EVOH) (film B). A 8‐oz model food in pouches was processed with MATS (F₀ = 9.0 min) and stored at 23, 35 and 45 °C for up to 12 months. Findings reveal that the oxygen barrier of film A was influenced by the coating and crystallinity of PET. The oxygen barrier of film B was primarily affected by the moisture content of the EVOH polymer. Results also show that changes in barrier properties depended on storage temperature. Recrystallization in polymer might be an important morphological change that occurs during storages. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45481.     

Modification of poly(ethylene terephthalate) (PET) using linoleic acid for oxygen barrier improvement: Impact of processing methods

Poly(ethylene terephthalate) (PET) is commonly used in the packaging industry; however, there is considerable interest in reducing the rate of oxygen permeation through PET to extend product shelf life. One method being employed to improve oxygen barrier is the introduction of reactive compounds to bind the oxygen permeating through the polymer. This work investigates a naturally occurring oxygen scavenger, linoleic acid (LA), which was incorporated within blown PET bottles using two different processing schemes. The LA was incorporated within PET at 0.5% by weight using both by blending and reaction of carboxyl end of LA and hydroxyl end of PET. The effect of LA on the thermal, mechanical properties, and oxygen permeation were determined. There was a decrease in oxygen permeability for the PET/LA samples with little change in physical properties relative to base PET. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45023.     

Influence of the environment during a photodegradation of multilayer films

The influence of different stratosphere parameters on the degradation of a multilayer film was investigated. The selected multilayer was a three polymeric layers film, a polyamide 6 film inserted between two poly(ethylene terephthalate) (PET) films. Samples were exposed for several ageing under ultraviolet radiations (filtered at 270 nm), varying the atmosphere at 55 mbar pressure (atm, atm + ozone, N₂, and T = ?55 °C or +23 °C). Evolution of it mechanical properties defined by uniaxial tractions, thermo‐optical properties defined by spectrophotometry UV–vis‐NIR, chemical properties defined by FTIR‐ATR, and thermal and dielectric properties defined, respectively, by differential scanning calorimetry (DSC) and dynamical dielectric spectroscopy (DDS), were investigated. Our results showed that UV irradiation causes multilayer films degradations, that is, principally decrease of UV transmittance and stress and strain at break (?50%). An increase of the ageing temperature causes an acceleration of these degradations. Degradations principally occur on the PET side of the multilayer exposed to UV radiation. Moreover, the DDS analysis shows a plasticization effect of the primary mode in the polyamide 6 due to photo‐oxidation. Oxygen diffusion is the principal element for this plasticization, indeed it not occurs in a nonoxidative environment (nitrogen), or at low ageing temperature (?55 °C). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44075.     

Hydrogen gas barrier property of polyelectrolyte/GO layer‐by‐layer films

Different types of ultrathin multilayer composite membranes adsorbed on polyethylene terephthalate (PET) substrates are fabricated by the layer‐by‐layer (LBL) self‐assembly technique. The hydrogen gas barrier performances of these membranes are measured using a pressure permeation instrument. Polyethylenimines/graphene oxide (PEI/GO) are chosen as the optimal system; the multilayer film reduces the hydrogen transmission rate of the uncoated PET film from 1357 to 24 cm³/(m² 24 h 0.1 MPa). The membrane assembly process for the PEI/GO system is analyzed with UV–Visible spectroscopy, and the flat morphology of the ultrathin film is observed by scanning electron and atomic force microscopies. Moreover, in order to fully characterize the PEI/GO multilayer film system, we investigate the effects of multiple variables on the hydrogen resistance performance. These include the molecular weight of PEI, concentrations of PEI and GO, number of bilayers, soaking time, and drying methods. The film thickness is found to increase linearly during the LBL assembly process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41973.     

High oxygen barrier multilayer EVOH/LDPE film/foam

High oxygen barrier film/foam system had been developed using multilayer coextrusion technology. The film/foams contained alternating ethylene–vinyl alcohol (EVOH) copolymer film layers and low‐density polyethylene (LDPE) foam layers. To ensure good adhesion and layer integrity, the LDPE was preblended with LDPE grafted maleic anhydride. The layered structure of film/foam was characterized by scanning electron microscopy. The film/foams showed adjustable density, oxygen permeability, and mechanical properties by changing the film and foam composition. Film/foam with 10% EVOH film layer was successfully thermoformed at room temperature. The cells in the foam layer were observed to deform during the mechanical forming process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46425.     

Development of a melt‐extrudable biobased soy flour/polyethylene blend for multilayer film applications

Monolayer and multilayer films from biobased linear low‐density polyethylene and milled soy flour were produced through cast film coextrusion processes using conventional thermoplastic processing equipment. Films containing 10 and 20% by weight of soy flour milled to maximum particle sizes of 8, 11, and 22 µm were extruded and characterized as a packaging film material. Water resistance, tensile properties, and gas permeability were measured on each film and analyzed with respects to the soy particle size, soy loading, and layer configuration in the multilayer film structure. Mechanical properties results indicated that ultimate elongation of the soy‐containing films decreased by as much as 14% compared to the control, while tensile strength and maximum load testing did not reveal any identifiable trends. Monolayer soy‐containing film showed high moisture sensitivity, as measured by contact angle and absorption testing, while the multilayer films demonstrated a more hydrophobic nature as indicated by higher contact angle measurements. This increase in hydrophobic properties is due to protective polyolefin skin layers, which are more hydrophobic. Oxygen transmission rates of the multilayer films decreased by 38% due to the presence of soy flour as compared to the control that did not contain any soy flour. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40707.     

Development of active barrier systems for poly(ethylene terephthalate)

Copolymers of Poly(ethylene terephthalate) (PET) were synthesized by the melt polymerization of terephthalic acid (TPA) with ethylene glycol (EG) and with each of the active oxygen scavengers; monoolein (MO) and 3‐cyclohexene‐1,1‐dimethanol (CHEDM) in separate compositions. Proton nuclear magnetic resonance spectroscopy (¹H NMR) and 2D correlation spectroscopy (COSY) indicated that PET had reacted with both MO and CHEDM at their hydroxyl end groups. Oxygen barrier properties of the MO and CHEDM copolymers exhibited improvements of up to 40%, in comparison to an unmodified commercial PET. Effects of the oxygen scavengers on the copolymers' physical properties were investigated in terms of their crystallization, melting, and rheological behaviors. Both types of copolymers showed decreases in peak melting temperatures with increased scavenger concentrations and also crystallized more slowly as the scavenger concentrations increased. The PET/MO copolymer showed non‐Newtonian rheological behavior with higher MO concentration; while the PET/CHEDM copolymers showed Newtonian behavior within the studied range of CHEDM concentrations. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Construction of multilayer coatings for flame retardancy of ramie fabric using layer‐by‐layer assembly

Complex multilayer coatings composed of α‐zirconium phosphate (ZrP), polyethylenimine (PEI), and ammonium polyphosphate (APP) were constructed via layer‐by‐layer assembly method for flame retardant ramie fabric. Bicomponent PEI/ZrP layers served as insulating barrier coating, and bicomponent PEI/APP layers served as intumescent coating. The flame retardancy of the coated ramie fabric was strongly dependent on the nature of the coatings and the layer‐by‐layer assembly patterns. The coated ramie fabric with inside PEI/ZrP layers and outside PEI/APP layers possessed the most uniform and consistent coating surface morphology, as well as the highest content of N and P elements, resulting in an excellent improvement in flame retardancy of ramie fabrics. When this kind of coated ramie fabric was heated, the inner PEI/ZrP layer effectively prevent oxygen and heat from penetrating into the substrate, and the outer PEI/APP layer exposed to air with good expansion during combustion. The synergistic effect was formed during the combustion process and could impart ramie fabrics with high flame retardancy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45556.     

Inhomogeneous distribution of platinum and ionomer in the porous cathode to maximize the performance of a PEM fuel cell

A proton exchange membrane (PEM) fuel cell model, accounting for the combined water transport mechanism, ionomer swelling, water phase‐transfer, two‐phase flow and transport processes, is developed. The inhomogeneous distributions of Pt and ionomer inside the catalyst layer (CL) are numerically studied to achieve an optimal cell performance for two types of oxygen reduction reaction catalysts at different loadings. Results indicate that the optimal variation in loading through the thickness of the electrode (slopes) of Pt catalyst and ionomer vary with conditions of operation. An optimal platinum slope increases the agglomerate effectiveness factor and decreases the second Damköhler number near the CL‐membrane interface. An optimal ionomer slope increases the CL porosity near the GDL‐CL interface and decreases the mass transport resistance of reactant through the ionomer film. Their interaction shows that the optimal platinum slope is a tradeoff between the electrochemical active surface area and porosity at high current densities. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Self‐cleaning,titanium dioxide based,multilayer coating fabricated on polymer and glass surfaces

A photocatalytic self‐cleaning titanium dioxide (TiO₂) coating was prepared as a multilayer coating structure by the spin‐coating method. Three substrate materials (two thermoplastics and one ceramic) were used: (1) high‐density polyethylene (HDPE), (2) poly(vinyl chloride), and (3) borosilicate glass (BK7). The multilayer structure consisted of a polyurethane protective layer on the substrate, two layers of photocatalytic TiO₂ on the protective layer, and finally immobilized TiO₂ particles bound in a diluted polyurethane dispersion. Photocatalytically active surfaces were achieved by reactive oxygen‐plasma surface etching of the fabricated coatings. The structure and properties of the coating surfaces were characterized with scanning electron microscopy and contact‐angle measurements. The coatings on HDPE and BK7 were rendered superhydrophilic by an oxygen‐plasma treatment. The photocatalytic activity and self‐cleaning properties of the prepared surfaces were studied with palmitic acid (model soil), the degradation of which was confirmed by contact‐angle measurements and gas chromatography analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

纳米晶硅多层薄膜的低温调控及其发光特性

采用单-双靶交替溅射法低温沉积了纳米晶硅多层薄膜（nc-SiO_x/a-SiO_x）,通过改变a-SiO_x势垒层的厚度和化学成分比例,实现了纳米晶硅多层薄膜的低温过程控制。透射电子显微镜（TEM）结果显示,a-SiO_x层太薄,不能有效阻断纳米硅生长,导致多层周期结构在后期沉积过程中受到破坏;增加a-SiO_x层厚度,周期性结构生长得以实现,但仍有部分纳米硅穿透a-SiO_x势垒层;傅里叶变换红外光谱（FTIR）分析表明,薄膜中的氧化反应以及活性氢对物相分离过程的促进作用均对纳米硅生长有影响。进而增加a-SiO_x层氧含量,纳米硅的纵向生长被成功阻断。在此基础上,通过调整nc-SiO_x层厚度实现了薄膜光学带隙调整和纳米硅粒度控制。光吸收谱分析显示,随nc-SiO_x层厚度的增加,薄膜光学带隙逐渐减小;光致发光谱表明,多层周期结构实现了纳米硅尺寸的调控,粒子尺寸为几个纳米的纳米硅表现出了较强的发光,发光机制为量子限制效应-缺陷态复合发光。     

Cellulose nanofibrils in biobased multilayer films for food packaging

The aim of this study was to evaluate a thin, TEMPO‐oxidized (2,2,6,6‐tetramethylpiperidine‐1‐oxyl–mediated oxidation) cellulose nanofibril (CNF) coating as a barrier layer in multilayer packaging films together with biobased polyethylenes. The purpose was also to explore the possible interactions between food products and the biobased films, and to evaluate the feasibility of these films for packaging of dry foods. CNF provided the biobased multilayer films with an oxygen barrier suitable for both demanding food products and modified atmosphere packaging (MAP). The MAP pouches made of these multilayer films retained their atmosphere and shape and protected ground hazelnuts from further oxidation for the storage time used in this study. However, irradiation used to sterilize packed foods and aroma compounds from clove in particular impaired the oxygen barrier property of the CNF layer, while the water vapor barrier property of the multilayer films remained unaffected. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44830.     

Optimized design of multilayer barrier films incorporating a reactive layer. II. Solute dynamics in two‐layer films

Extending the model of transient permeation through the reactive barrier film presented in part I of this series to two‐layer reactive–passive barrier structures, we devote part II to the analysis of the evolution of interfacial solute concentrations between the layers. The concepts developed earlier are applied to the transient ingress analysis of two‐layer films where one of the layers contains a noncatalytic solute scavenger. In particular, we show that for reactive–passive films, the averaging approximation of the transient interfacial solute concentration provides good agreement with numerical results for the transient effective flux. The applicability range of this averaging and the error introduced by it are quantified. For the passive–reactive films, the same averaging fails to predict the effective flux dynamics. A new method of ingress analysis is presented for such structures to correct the situation. The method is based on the effective flux dynamics in the homogeneous reactive membrane and the dynamic reactive to the passive–reactive flux scaling between the initial and final solute concentration profiles corresponding to the scavenger activation and scavenger exhaustion times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1952–1965, 2006     

Study of the interfacial adhesive strength of a heat-shrinkable multilayer film

A heat-shrinkable multilayer film is widely employed as labels of plastic bottles. A new heat-shrinkable multilayer film without an adhesive layer was designed in this study. The interfacial adhesive strength between the layers was controlled to avoid layer separation. We assumed a polyethylene terephthalate glycol-modified (PETG)/styrene-co-butadiene block copolymer/PETG shrinkable film substitute as the general poly(ethylene terephthalate) (PET)/polystyrene/PET shrinkable film. The interlayer adhesive strength between the layers was retained for industrial utilization even after drawing. Additional polybutadiene (PB) infiltrated the butadiene layer in the microphase-separated structure. Further addition of PB could not infiltrate the butadiene layer. The excessive PB contents coexisted with the interface between the layers, as observed by transmission electron microscopy (TEM). The segregated PB enhanced the interfacial adhesive strength. We concluded that the selective distribution of adhesive functional materials along the interface could appropriately retain its adhesive strength.     

Layer‐by‐layer self‐assembly of a lignin–poly(vinyl alcohol) based polyelectrolyte with a conductivity method

In this study, we made a new attempt to examine the relationship between the conductivity and the concentration of a polyelectrolyte solution and to prepare multilayer films with cationic lignin and polyanions through layer‐by‐layer self‐assembly. The nitrogen content of trimethyl lignin quaternary amine salt (TLQA) was 3.56%, and the carboxyl content of carboxymethylated poly (vinyl alcohol) (CMPVA) was 0.62 mmol/g. Attenuated total reflectance spectra confirmed that TLQA and CMPVA were fabricated and assembled successfully. The concentration of TLQA had a polynomial correlation with the conductivity [correlation coefficient (R²) = 0.9953], and the concentration of CMPVA was linear with the conductivity (R² = 0.9819). The electrostatic sequential adsorption process was monitored with a UV–visible spectrophotometer, and the morphology of the (TLQA/CMPVA)_n (where n is the number of double membranes) multilayer film was observed by atomic force microscopy and scanning electron microscopy. When the absorbance of the (TLQA/CMPVA)_n multilayer film increased linearly, the linear equation was y = 0.0267x + 0.07453 and R² was 0.9735. When five layers of TLQA and CMPVA were assembled, the surface root mean square roughness of TLQA and CMPVA were 21.07 and 65.28 nm, respectively. When the number of layers increased, the film surface roughness increased. The stability of the multilayer films in aqueous solution was determined by a conductivity meter. The (TLQA/CMPVA)_n multilayer film was stable in water. The results of the research demonstrate for the first time that TLQA and CMPVA could be assembled and successfully driven by electrostatic forces. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44416.     

Actual air separation across multilayer composite membranes

Multilayer composite membranes are fabricated from six types of thin films as selective layers, an ethyl cellulose (EC) thin film as a flexible spacer, and poly(ether sulfone) (PES) with 15–45 nm pore size or 100–120 μm thickness as a porous support layer. The effects of the thin‐film type and its layer number, operating temperature, and transmembrane pressure difference, as well as the operational time on the actual air‐separation properties through the composite membranes, are investigated by a constant pressure‐variable volume method. The results show that a pure polystyrene thin‐film composite membrane exhibits poor actual air‐separation performance due to its brittleness, although it has a higher ideal oxygen over nitrogen separation factor. The oxygen‐enrichment air (OEA) flux through all of the composite membranes tested increases significantly with increasing operating temperature and pressure difference. The oxygen concentration in the OEA increases slightly with an increase in operating temperature, and the oxygen concentration through the polystyrene/cholesteryl oleyl carbonate blend, top layer composite membrane exhibits the maximal value. As the transmembrane pressure difference increases, the oxygen concentration in the OEA also exhibits the maximal value. The maximum oxygen concentration can reach 39.1%, which is achieved by the multilayer composite membrane consisting of a polystyrene/cholesteryl oleyl carbonate (95/5) monolayer, an EC single flexible spacer, and a PES support at 35°C and a transmembrane pressure difference of 550 kPa. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2396–2403, 2000