Morphology and barrier properties of oriented blends of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate) with poly(ethylene-co-vinyl alcohol)

Morphology and oxygen permeability studies were carried out for blends of poly(ethylene terephthalate), PET, and poly(ethylene 2,6-naphthalate), PEN, with poly(ethylene-co-vinyl alcohol), EVOH. PET/EVOH blends are seen as a possible substitute for poly(vinylidene chloride)-coated PET packaging films. The effects of several processing parameters such as draw temperature and draw ratio on blend morphology and barrier properties suggest that the morphology of the EVOH phase dictates to a large extent the oxygen permeabilities of these blends. The relationships between morphology and oxygen permeability and explained are explained by consideration of two-phase conduction models. The model of Fricke is found to be a good predictor of the barrier properties of the PET/EVOH system. The oxygen permeability of PET was reduced by a factor of 4.2 with the addition of 20 wt% EVOH and that of PEN by a factor of 2.7 with the addition of 15 wt% EVOH. Water vapor permeabilities and mechanical properties of PET and PEN were only slightly affected by the addition of 15 wt% EVOH.     

Barrier property by controlled laminar morphology of LLDPE/EVOH blends

Using the extrusion blown film process, we obtained linear low density polyethylene (LLDPE)/ethylenevinyl alcohol copolymer (EVOH) blends with an improved barrier property by generating a laminar structure of the dispersed phase in the matrix phase. This laminar morphology induced by drawing and blowing was found to result in a significant decrease in toluene permeability with only 10 wt% EVOH. Effects of compatibilizer content and processing parameters such as blending sequence, screw configuration, and stretch ratio on the toluene permeability and morphology of the blends were investigated. It was revealed that the optimum amount of compatibilizer, maleic anhydride grafted LLDPE, should be used to improve the barrier property of the LLDPE/EVOH blends with a well developed laminar structure. The blending sequence had a significant influence on the permeability of the blends. The blend films exhibited a more pronounced laminar structure when all blend components were simultaneously melt blended in a single screw extruder. In addition, the screw configuration designed to impart a low shear stress and the balanced stretching in the machine and transverse directions were more favorable processing conditions in obtaining high barrier blends.     

Morphological, Thermal, Barrier and Mechanical Properties of LDPE/EVOH Blends in Extruded Blown Films

We have investigated the morphological, thermal, barrier, and mechanical properties of low-density polyethylene/ethylene–vinyl alcohol blend (LDPE/EVOH; 85/15 wt%) in highly and biaxially oriented blown films. Maleic anhydride-grafted linear low-density polyethylene (LDPE-g-MAH) in various concentrations (from 0 to 10 phr) was used as the compatibilizer for the immiscible system. Thermal analysis of the blend films shows that their melting temperatures, crystallization temperatures, and heats of fusion stay almost constant upon varying the amount of compatibilizer. The addition of the compatibilizer did not adversely affect the inherent properties of the blends, especially their barrier properties, through constraint effects of the grafted EVOH (EVOH-g-LD). The heat of fusion of EVOH obtained during the first heating is much higher than that of the second as a result of stress-induced crystallization during the blown film process. Oxygen permeation measurements show that the oxygen barrier properties of both highly and biaxially oriented blown films decrease upon increasing the amount of compatibilizer, although morphological analysis showed that the blends exhibit better laminar dispersion of the EVOH phase in the LDPE matrix when LDPE-g-MAH is added. The increase in oxygen permeability results from the presence of microvoids at the interface between the two phases during the process. Mechanical measurements showed that there exists an optimal amount of LDPE-g-MAH for maximizing both the tensile and tear properties in both the machine and transverse directions.     

新型EVOH/PE⁃RT合金包覆PE⁃RT双层阻氧管的制备及性能研究

针对市场上常见的阻氧管存在难以热熔回收再用的问题,制备了新型乙烯?乙烯醇共聚物（EVOH）/耐热聚乙烯（PE?RT）合金包覆PE?RT双层阻氧管,其内层工作管为PE?RT材质,外层为EVOH/PE?RT合金阻隔材料;研究了EVOH和相容剂含量对EVOH/PE?RT合金阻隔膜阻氧性能的影响,并对新型双层阻氧管的氧气透过量和热熔回收情况以及新型双层阻氧管回收料的力学性能进行了测试。结果表明,EVOH/PE?RT合金阻隔膜的氧气透过量随EVOH含量的增加而降低,随相容剂含量的增加而上升;含30 %（质量分数,下同）EVOH、64 % PE?RT和6 %相容剂的新型双层阻氧管的氧气透过量接近市售3层、5层阻氧管,并且能够实现热熔回收,回收料具有较好的力学性能。     

High oxygen barrier materials from paper to regenerated cellulose films

A transparent, bendable, high oxygen barrier cellulose-based film was prepared, which has far better oxygen barrier properties than conventional polyethylene, polypropylene and cellophane materials. A series of regenerated cellulose films (RCs) were prepared from filter paper lacking oxygen barrier properties under different cellulose concentrations and gelation times. It was shown that the cellulose concentration and gel time had a greater effect on the oxygen barrier properties of RCs. When the cellulose concentration was 4 wt% and the gel time was 3 h, the RCs obtained the lowest oxygen permeability coefficient (OPC) down to 2.21 × 10⁻¹⁷ cm³ cm cm⁻² s⁻¹ Pa⁻¹. The films have a tensile strength of 109.5 MPa, an elongation at break of 27.3% and a light transmission rate of 89%. In further, molecular dynamics simulations showed that when the filter paper was converted to RCs, the increase in hydrogen bonding and the decrease in free volume between cellulose chains caused a decrease in the diffusion coefficient of oxygen. As a novel biobased high oxygen barrier material, the film has broad application prospect in packaging and chemical industry.     

Bio-inspired cross-linking with borate for enhancing gas-barrier properties of poly(vinyl alcohol)/graphene oxide composite films

The demand for flexible and transparent barrier films in industries has been increasing. Learning from nature, borate ions were used to cross-link poly(vinyl alcohol) (PVA) and graphene oxide (GO) to produce flexible, transparent high-barrier composite films with a bio-inspired structure. PVA/GO films with only 0.1 wt% GO and 1 wt% cross-linker exhibited an O₂ transmission rate <0.005 cc m⁻² day⁻¹, an O₂ permeability <5.0 × 10⁻²⁰ cm³ cm cm⁻² Pa⁻¹ s⁻¹, and a transmittance at 550 nm >85%; thus, they can be used for flexible electronics. Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy indicated that the outstanding barrier properties are attributed to the formation of chemical cross-linking involving borate ions, GO sheets, and PVA, similar to the borate cross-links in high-order plants. Comparing our experimental data with the Cussler model, we found that the effective aspect ratio was significantly increased after cross-linking, suggesting that cross-linking networks connected GO with each other to form ultra-large impermeable regions. A feasible green technique, with potential for commercial production of barrier films for flexible electronics was presented.     

High oxygen barrier property of polyethylene composite films with bilayer polyvinyl alcohol coating for emergency foods in high-humidity environments

The limited oxygen barrier of polyethylene (PE) films has restricted their further application in food packaging, like emergency foods. Although its oxygen barrier property can be improved by applying a polyvinyl alcohol (PVA) coating, the application of PVA/PE composite films in high-humidity environments is still challenging. Hence, this study aimed to enhance the oxygen barrier properties of PVA/PE composite films in high-humidity environments. Specifically, PVA coatings were modified by the itaconic acid (IA) and magnesium-aluminum layered double hydroxides (LDH), and then applied to PE films as bilayer coating. Because of the unique bilayer coating on the PE surface, the oxygen barrier property of PVA/PE composite film (IA/LDH-p) in high-humidity environments has been further improved. The results confirmed that IA/LDH-p had an oxygen permeability coefficient of 1.92 ± 0.16 × 10⁻¹⁶ cm³ cm/(cm² s Pa) under a high-humidity environment test, 82.42% better than that of single-layer coating coated on PE surface. After being stored at RH 90% for 36 h, the tensile strength and elongation at break values of IA/LDH-p were 27.20 MPa and 919.63%, respectively. Overall, this obtained PVA/PE composite films showed great potential for application in emergency foods packaging, particularly in high-humidity environments.     

High performance structured polymer barrier films obtained from compatibilized polypropylene/ethylene vinyl alcohol blends

The effects of different functionalized polypropylene (PP) and diethyl maleate (DEM) combined with styrene–ethylene–butene–styrene copolymer (SEBS) on various properties of extruded-stretched films of polypropylene/ethylene vinyl alcohol (PP/EVOH) blends were studied. The stretched films of the original PP/EVOH blends and those of the polymer-g-DEM modified blends showed lamellar-type morphology, whereas their maleic anhydride (MAH) functionalized counterparts showed fibrillar morphology. Such peculiar morphology resulted in a dramatic decrease of oxygen permeability as compared with the unmodified or MAH modified PP/EVOH blends. These spectacular improvements in barrier properties were obtained without much altering thermal and mechanical properties of the blend. POLYM. ENG. SCI., 47:1114–1121, 2007. © 2007 Society of Plastics Engineers     

EHA/PE复合薄膜的力学性能和阻透性能

分别使用氧气透过率分析仪、水蒸气透过率分析仪、拉伸试验机、紫外可见分光光度计以及差示扫描量热仪测试了乙烯乙烯醇共聚物(EVOH)、聚酰胺6(PA6)、EVOH/PA6(EHA)等薄膜以及EHA/聚乙烯(PE)复合薄膜的力学性能和阻透性能。结果表明,EVOH与PA6有较好的相容性,所制成的薄膜EHA与PE复合后的EHA/PE复合薄膜对氧气和水蒸气有良好的阻隔性,并且对可见光有很好的透过性,比较适合作食品包装材料。     

EVOH nanocomposite films with enhanced barrier properties under high humidity conditions

To improve the oxygen and water vapor barrier properties of ethylene vinyl alcohol, EVOH/EFG nanocomposite films under high humidity conditions, we successfully prepared highly exfoliated graphite (EFG) containing a monolayer or a few layers of graphene via rapid heating treatment and ultrasonication as confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), elemental analysis (EA), and nitrogen adsorption–desorption analysis. Six different EVOH/EFG nanocomposite films containing as‐prepared EFG were prepared via a solvent blend method and their physical and barrier properties at different relative humidities were investigated as a function of EFG content. Depending on the EFG content, oxygen transmission rate (OTR) decreased from 3.7 to 0.1 cc/m²/day at dry condition, and the difference in OTR between dry condition and humid condition decreased from 6.5 to 2.3 cc/m²/day. Barrier properties of the EVOH/EFG nanocomposite films were strongly dependent on their chemical structure and morphology. Crystallinity, tortuous path length, and hydrophobicity of EVOH/EFG nanocomposite films were enhanced by the addition of EFG. However, the thermal stability and glass transition temperature of the nanocomposite films were not improved by incorporation of EFG due to the weak interaction between EVOH and EFG. To maximize the performance of EVOH/EFG nanocomposite films, the compatibility of the polymer matrix and fillers needs to be improved. POLYM. COMPOS., 35:644–654, 2014. © 2013 Society of Plastics Engineers     

Biobased Polyester-Amide/Cellulose Nanocrystal Nanocomposites for Food Packaging

The worldwide plastic waste production is steadily increasing, since the use of polymeric materials continues to rise. One area of particular high plastic consumption is food packaging. Flexible and rigid packaging films are typically made from petrochemical-sourced polymers, which are utilized because of their low cost, ductility, melt-processability, and gas barrier properties, but a major downside is their inability to biodegrade in a reasonable time. Packaging-relevant properties of nanocomposites based on polyester-amides (PEAs) are reported, which are chosen on account of their tunable crystallinity, biobased starting materials, and biodegradability. These polymers are synthesized via melt polycondensation of a building block made from caprolactone and 1,4-diaminobutane, with the addition of 1,4-butanediol and dimethyl adipate. The fraction of the amide segment is varied between 25 and 75 mol%. The oxygen transmission rate (O₂TR) drops upon increasing the amide content from 1.6 × 10⁵ to 2.9 × 10⁻⁴ cm³ m⁻² d⁻¹ on account of increasing crystallinity. In order to improve the gas barrier properties further, nanocomposites of the PEAs and 1–10 wt% cellulose nanocrystals (CNCs) are prepared. These nanocomposites have indeed lower O₂TR values than the neat PEAs, with reductions of as much as 50% for a CNC content of 10 wt%.     

Reverse exfoliation in a polymer nanocomposite by blending with a miscible polymer

An investigation of the permeability to methanol of blends of a PA-6 nanocomposite and ethylene-vinyl alcohol copolymers (EVOH), containing approximately 32 mol% ethylene, has been conducted. Blends were prepared by melt compounding and permeation measurements were performed by gravimetric uptake methods. The nanocomposite polyamide exhibited significantly reduced permeability compared to the unmodified polymer. The blends exhibited permeability that was non-linear with blend composition. The nanoscale filler in a blend containing up to 50 wt% EVOH remained fully exfoliated, however, in a blend containing 75 wt% of EVOH there was little or no exfoliation and the blend had a measured permeability lower than that of either of the pure components. Electron microscopy and X-ray analysis has indicated a reversal of exfoliation of the nanocomposite filler particles to be responsible.     

Effect of gamma irradiation on the oxygen barrier properties in ethyl-vinyl acetate/ethylene-vinyl alcohol/ethyl-vinyl acetate multilayer film

The potential changes of single-use plastic materials (EVA/EVOH/EVA multilayer film in this study) used in biopharmaceutical and food-packaging industries are investigated after several gamma irradiation doses: 30, 50, 115, and 270 kGy, and for nonsterilized samples (0 kGy) from a point of view of mechanical properties, thermal properties and permeability properties. Tensile tests, differential scanning calorimetry (DSC), oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) are performed on the multilayer film. For irradiation doses below 50 kGy, thermal and water vapor barrier properties are not altered. For higher doses (50 to 270 kGy), mechanical, thermal and water vapor barrier properties are slightly altered whereas oxygen barrier property decreases from 13 to 27 cm³.m⁻².day⁻¹. This slight change is shown not to happen due to chain entanglement or chain mobility loss in the amorphous phase of the different polymers. It rather comes from a change of the chemical environment of the EVOH layer.     

Thermal,mechanical, and gas barrier properties of ethylene–vinyl alcohol copolymer‐based nanocomposites for food packaging films: Effects of nanoclay loading

For the application of single‐layer food packaging films with improved barrier properties, an attempt was made to prepare ethylene‐vinyl alcohol (EVOH) copolymer‐based nanocomposite films by incorporation of organically modified montmorillonite nanoclays via a two‐step mixing process and solvent cast method. The highly intercalated tactoids coexisted with exfoliated clay nanosheets, and the extent of intercalation and exfoliation depended significantly on the level of clay loadings, which were confirmed from both XRD measurements and TEM observations. It was revealed that the inclusion of nanoclay up to an appropriate level of content resulted in a remarkable enhancement in the thermal, mechanical (tensile strength/modulus), optical, and barrier properties of the prepared EVOH/clay nanocomposite films. However, excess clay loadings gave rise to a reduction in the tensile properties (strength/modulus/elongation) and optical transparency due to the formation of clay tactoids with a larger domain size. With the addition of only 3 wt % clay, the oxygen and water vapor barrier performances of the nanocomposite films were substantially improved by 59 and 90%, respectively, compared to the performances of the neat EVOH film. In addition, the presence of clay nanosheets in the EVOH matrix was found to significantly suppress the moisture‐derived deterioration in the oxygen barrier performance, implying the feasibility of applying the nanocomposite films to single‐layer food packaging films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40289.     

Effect of blend rheology on the transport property of oriented poly(ethylene terephthalate) blends

Rheological studies were performed to delineate appropriate stretching windows, and poly(ethylene terephthalate)/poly(ethylene-co-vinyl alcohol) blend films were extruded biaxially within such processing windows. The morphology and oxygen permeability properties of these films, with and without a compatibilizer, were characterized. The intent of this study was to achieve a blend oxygen permeability value (OPV) of less than 1. At a fixed draw ratio and draw temperature, appropriate rheological matching could lead to an increase in the aspect ratio of the EVOH phase and, thereby, of oxygen barrier properties. This study concludes that by melt viscosity matching it is not possible to obtain blends with OPV of less than 1. The model of Fricke, used to predict blend permeability, was found to be more accurate at the higher draw temperatures, with the measured values deviating increasingly negatively from the predicted values as the draw temperature is decreased. © 1995 John Wiley & Sons, Inc.     

Laminar morphology development and oxygen permeability of LDPE/EVOH blends

Morphology and oxygen barrier properties of LDPE/EVOH blends have been studied. Laminar dispersion of ethylene-vinyl alcohol copolymer (EVOH) with high oxygen barrier properties was obtained in the matrix of low density polyethylene (LDPE) when extruded through an annular blown film die. Various laminar morphologies were observed and the main factors determining the morphology of the blends were viscosity ratio of the components, processing conditions, and compatibilizer level. Oxygen permeation tests have shown that thinner and longer EVOH layers in larger numbers were more effective in reducing the oxygen permeability. The oxygen permeability of the compatibilized blend having 6 phr of LLD-g-MAH was reduced by a factor of 740. The correlation between morphology and oxygen permeability was explained as a function of the EVOH layer size (L × R) and the number of EVOH layers (N), which were closely related to the predeformed domain size (L_o × R_o). The high Weber number (resulted from large L_o × R_o and low interfacial tension) and low viscosity ratio yielded large L × R. However, small L_o × R_o produced high N. Experimental results of oxygen permeability were well correlated with (L × R) × N.     

Design and mechanism of controllable respiration polyamideamine-epichlorohydrin modied sugarcane bagasse pith hemicellulose film

The major challenge in hemicellulose blend films for food packaging is to overcome the inferior wet strength and hydrophilic properties of hemicellulose-based films. Inspired by the principle of wet strength of paper, novel bio-based packaging film with high barrier and strength properties was designed via bagasse pith hemicellulose as main substrate materials and polyamideamine-epichlorohydrin (PAE) as strengthening agent. The chemical characterization showed that the mechanical and barrier properties of the blend films were found to be strongly dependent upon the amount of PAE added in the films. Compared with the film without PAE, the tensile strength of PAE-containing film with optimal amount of 1% PAE increased by 100.25%, the water vapor permeability decreased by 23.25%, and the oxygen permeability decreased by 87.18%. The results showed that the new ester bond formed between PAE and hemicellulose caused the more excellent mechanical and barrier properties of films.     

Laminar morphology development using hybrid EVOH–nylon blends

Properties of blends having two types of hybrid dispersed phases as laminar morphology were investigated. The hybrid dispersed phases were prepared by preblending nylon and ethylene–vinyl alcohol (EVOH) in solid state (E + N) and in melt state (E/N). Oxygen and toluene barrier properties through the hybrid-dispersed phases in low-density polyethylene (LDPE) matrix were analyzed considering the morphological changes (number and size of layers). Oxygen barrier properties of the blends of LDPE–E + N hybrid dispersed phase having separate domains of nylon and EVOH were found to be linearly dependent on EVOH composition in the blend, but toluene barrier properties of the blends exhibited negative deviation. The other hybrid dispersed phase (E/N) in LDPE matrix, having comingled dispersed phase of nylon and EVOH, exhibited positive deviations in both oxygen and toluene barrier properties. Tensile properties also showed positive deviation. Basic studies on the melt blend (E/N) of EVOH and nylon 6 showed some miscibility, which was revealed from melting point depression, and positive deviation in complex viscosity and tensile properties of the blend. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2001–2014, 1998     

Preparation of biaxially oriented polyamide 6/polyketone/graphene oxide films with enhanced barrier and mechanical behaviors

In this study, biaxially oriented polyamide 6/polyketone/graphene oxide (PA6/PK/GO) films were prepared by melt blending then simultaneously biaxially stretched process, with the aim of obtaining high barrier properties films and improvements in their mechanical properties. The oxygen transmission rate of biaxially oriented PA6/PK/GO film significantly decreased with addition of polyketone and GO. It is surprising that the biaxially oriented process can excellently improve the barrier properties of biaxially oriented PA6/PK/GO film. For example, there was 94.7% OTR reduction of the film containing 20 wt% PK and 0.08 wt% GO compared with PA6 film at a stretching ratio of 3.3 × 3.3. It is due to more tortuous permeation path of oxygen molecule owing to molecular orientation during biaxially stretching, and higher relative crystallinity with addition of GO. The tensile strength of film was remarkablly improved by stretching orientation and increase GO concentration. However, the elongation at break of film was considerably reduced by increase of stretching ratio. Although addition of GO may slightly improve the elongation at break of film at low stretching ratio, there was dramatic decline of elongation at break with increasing the content of GO at a stretching ratio of 3.3 × 3.3.     

Tailoring morphology to improve the gas‐barrier properties of thermoplastic polyurethane/ethylene‐vinyl alcohol blends

The morphology and helium‐barrier properties of thermoplastic polyurethane (TPU)/ethylene‐vinyl alcohol (EVOH) blends with and without dicumyl peroxide (DCP) were investigated by melting blending. A lamellar dispersion of EVOH with good helium‐barrier properties was observed in the TPU matrix with DCP. The evolution of the morphology of the blends is mainly related to the variation of the viscosity ratio between the dispersed phase and the matrix phase. Compared with pure TPU, lamellar morphology increased the helium‐barrier properties of the TPU/EVOH (60/40) blend by as much as 10‐fold. We also explored the effects of composition, DCP content, and blending sequence on the morphology and helium‐barrier properties of the TPU/EVOH blends. The morphology of the blends ranged from a droplet‐matrix to a lamellar structure. We determined the optimum amount of DCP to improve the helium barrier of the blends. The helium‐barrier properties of the blends prepared by direct blending were superior to those of the blends prepared by two‐segment blending, and the blends prepared by direct blending exhibited a well‐developed lamellar morphology. We compared the permeability of the samples with the theoretical results to explain the relationship between morphology and helium‐barrier properties. POLYM. ENG. SCI., 56:922–931, 2016. © 2016 Society of Plastics Engineers