Thermal and barrier properties of EVOH/EFG nanocomposite films for packaging applications: Effect of the mixing method

Ethylene‐vinyl alcohol copolymer (EVOH)/exfoliated graphite (EFG) nanocomposite films were prepared by precoating EFG on the EVOH surface and conducting a successive melt‐extrusion process. Their physical properties were strongly dependent on the EFG content and the mixing method, which strongly affected the morphology and surface properties of the nanocomposite films. The hydrophobicity and water resistance property of EVOH increased by incorporating hydrophobic EFG and their effects were more pronounced in the precoating method, which is related to good dispersion of EFG in EVOH and an enhanced crystalline structure. The incorporation of EFG into EVOH by the precoating method more effectively diminished the dependence of the relative humidity on the oxygen transmission rate of pure EVOH and increased the oxygen barrier properties of EVOH at a high relative humidity. The incorporation of EFG into EVOH by the precoating method also induced relatively more enhanced thermal stability. These results suggest the feasibility of the application of moisture‐sensitive EVOH resin for food packaging films. POLYM. COMPOS., 37:1744–1753, 2016. © 2014 Society of Plastics Engineers     

Oxygen barrier properties of polyketone/EVOH blend films and their resistance to moisture

Polyketone (PK) has excellent chemical and mechanical properties, but its use in food packaging is limited due to its oxygen barrier properties being insufficient for high-barrier film applications. To improve its oxygen barrier properties, PK has been blended with ethylene vinyl alcohol copolymer (EVOH), which is one of the highest oxygen barrier polymers in use today. The oxygen barrier properties under both dry and humid conditions, as well as the mechanical properties of PK/EVOH blend films were investigated in this study. These novel PK/EVOH blend films exhibited unusually low oxygen permeability values from 0.3 to 0.16 cc 20 μm m⁻² day⁻¹ atm⁻¹ with increasing EVOH content from 30 to 70 wt%, which are even lower than those of the ideal laminar model that expresses the theoretical minimum permeability values attainable for blended barrier films. These high oxygen barrier properties of PK/EVOH blend films can conceivably be attributed to the combination of two dominant effects: a tortuous diffusion path through the EVOH domains in the PK matrix and hydrogen bonding interactions between PK and EVOH. Furthermore, in high-humidity environments with retorting, the PK/EVOH blend films exhibited superior resistance to moisture over EVOH. Immediately after the retorting test, the oxygen permeability of the high-barrier PK/EVOH blend films with an EVOH content of 30–40 wt% increased by less than 3× the pre-retorting value, as opposed to 74× for EVOH. In addition, PK/EVOH blend films displayed superior stretching characteristics, with a breaking strain of over 300%, which are valuable for flexible packaging applications.     

Preparation and properties of hydrophobic layered silicate-reinforced UV-curable poly(urethane acrylate) nanocomposite films for packaging applications

A series of poly(urethane acrylate)/Cloisite 15A (PUA/C15A) nanocomposite films were successfully prepared via a UV-curing system, and their physical and barrier properties were investigated as a function of clay content. The physical properties were strongly dependent upon the chemical and morphological structures originating from differences in Cloisite 15A content. With high clay content, the PUA/C15A nanocomposite films displayed an intercalation/exfoliation combined structure. However, no strong interfacial interactions occurred between the PUA and clay, possibly leading to poor dispersion with relatively high clay content. The thermal stability displayed some enhancement with the introduction of clay into PUA, while the gas and moisture barrier properties showed significant enhancement. The oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) decreased with increasing contents of Cloisite 15A, and varied within the range of 714.0–71.1 cm³/m² day and 29.9–13.9 g/m² day, respectively. Thus the enhanced gas and moisture barrier properties of PUA/C15A nanocomposite films make them promising candidates for food and pharmaceutical packaging applications. However, further studies will be performed to increase the compatibility and dispersion of clay particles in the PUA polymer matrix.     

Melt processing and characterization of polyvinyl alcohol and polyhydroxyalkanoate multilayer films

Multilayer films for food packaging applications composed of polyvinyl alcohol (PVOH) as the core layer and polyhydroxyalkanoate (PHA) as the outer skin layers were produced by the co‐extrusion process. Rheological properties of PVOH and PHA were performed and analyzed before co‐extruding into a cast film. Analysis of the rheological data indicated the processing temperatures and grades of the PVOH and PHA polymers that would produce similar viscosity and melt flow properties. To improve adhesion of the layers, PHA was grafted with maleic anhydride using a dicumyl peroxide initiator to provide a tie layer material, which improved the peel strength of the PHA and PVOH layers by over 2×. Oxygen transmission rate (OTR) testing showed that the multilayer sample provided an OTR of 27 cc/m²‐day at 0% relative humidity (RH) and rates of 41 and 52 cc/m²‐day at relative humidity values of 60% and 90% RH, respectively. This indicates significant barrier performance enhancement over monolayer PVOH that provided an OTR of 60 cc/m²‐day at 0% RH and 999 cc/m²‐day at 60% RH. Biodegradation testing of the films in the marine environment showed that both the unmodified and maleated PHA polymers displayed high levels of mineralization, whereas the PVOH material did not. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Preparation and characterization of poly(propylene carbonate)/exfoliated graphite nanocomposite films with improved thermal stability,mechanical properties and barrier properties

Relatively high aspect ratio exfoliated graphite (EFG) particles with an average size of 7.4 µm and a nanometer sized thickness of 30–50 nm were successfully prepared by thermal treatment at 1050 °C and subsequent ultrasonication for application as a filler to improve the physical properties of eco‐friendly poly(propylene carbonate) (PPC). A series of poly(propylene carbonate)/exfoliated graphite (PPC/EFG) nanocomposite films with different EFG contents were prepared via a solution blending method. The physical properties were strongly dependent upon the chemical and morphological structures originating from the differences in EFG composition. The morphological structures, thermal properties, mechanical properties and barrier properties of the nanocomposite films were investigated as a function of the EFG content. While all of the PPC/EFG nanocomposite films exhibited good dispersion of EFG to some extent, Fourier transform infrared and SEM results revealed that solution blending did not lead to strong interactions between PPC and EFG. As a result, poor dispersion occurred in composite films with a high EFG content. By loading EFG particles, the oxygen permeabilities, moisture permeabilities and water uptake at equilibrium decreased as the EFG content increased. Compared with pure PPC, PPC/EFG nanocomposite films have enhanced molecular ordering. Specifically, the 2% PPC/EFG composite film shows greater molecular ordering than the other composite films, which results in the highest mechanical strength. In future work, the compatibility and dispersion of the PPC matrix polymer and EFG filler particles should be increased by modifying the EFG surface or introducing additives. © 2013 Society of Chemical Industry     

Oxygen barrier and enthalpy of melting of multilayer EVOH films after pressure‐assisted thermal processing and during storage

Pressure‐assisted thermal processing (PATP) is an advanced thermal process involving application of elevated pressures above 600 MPa on a preheated food for a holding time of 3 to 5 min, causing the volumetric temperature of food to increase above 100°C, to inactivate bacterial spores and enzymes. This study evaluated the influence of PATP on two state‐of‐the‐art multilayer EVOH films. Flexible pouches containing water as the food simulant were made from the two films and processed at 680 MPa for 3 min at 105°C and 680 MPa for 5 min at 100°C. Each film was investigated for its oxygen transmission rates (OTRs), melting temperature (T_m), enthalpy of melting (ΔH), and overall crystallinity before (control) and after processing. The changes in OTRs and total ΔH of the two films were also analyzed during a storage period of 240 days in ambient conditions after processing. Results showed a significant (P < 0.05) increase in the OTRs of the two films after PATP. However, PATP did not cause a significant (P > 0.05) change in the T_m and ΔH of the two films. The overall crystallinity of film A decreased, but improved slightly for film B after PATP. A recovery in the OTRs of the two films occurred during storage. The films also showed changes in the total ΔH measured during the storage period, which was used to explain the changes in the oxygen barrier properties. The OTR of both films remained below 2 cc/m² day, which is required in packaging applications for shelf‐stable foods with a 1‐year shelf life. This work demonstrates the advantages of using multilayer films containing EVOH as the barrier layer in PATP applications to produce shelf‐stable foods. This work also highlights the advantage of, DSC analysis for studying the physical ageing of polymers during storage. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Mechanical and barrier properties of carbon nanotube reinforced PCL‐based composite films: Effect of gamma radiation

Carbon nanotube (CNT) reinforced (0.05–0.5% by wt) polycaprolactone (PCL)‐based composites were prepared by compression molding. Addition of 0.2% CNT caused a 131% improvement of tensile strength (TS) of PCL films. The tensile modulus (TM) and elongation at break (Eb) of PCL were also significantly improved with the addition of CNT. The water vapor permeability of PCL was 1.51 g·mm/m²·day but 0.2% CNT containing PCL films showed 1.08 g·mm/m²·day. Similarly, the oxygen transmission rate (OTR) of PCL films was found to decrease with the addition of CNT. But, carbon dioxide transmission rate (CO₂TR) of PCL film was improved due to incorporation of CNT. Effect of gamma radiation on PCL films and CNT reinforced PCL‐based composites were also studied. The TS of the irradiated (10 kGy) PCL films gained to 75% higher than control sample. The TS of the 0.2% CNT reinforced composite film was reached to 41 MPa at 15 kGy dose. The barrier properties of non‐irradiated and irradiated (10 kGy) PCL films and composites (0.2% CNT reinforced) were also measured. Both PCL films and composites showed lower values of WVP upon irradiation and indicated better water vapor barrier. The OTR and CO₂TR of the irradiated (10 kGy) PCL films and composites were decreased compared to their counterparts. Surface and interface morphologies of the composites were studied by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical,barrier, and interfacial properties of biodegradable composite films made of methylcellulose and poly(caprolactone)

Methylcellulose (MC) films were prepared by casting from its 1% aqueous solution containing 0.5% vegetable oil, 0.25% glycerol, and 0.025% Tween^®80. Poly(caprolactone) (PCL) films were prepared by compression molding from its granules. Biodegradable composite films were fabricated using MC film as reinforcing agent and PCL as the matrix material by compression molding. One layer of MC film was reinforced with two layers of PCL films. The MC content in the composites was varied from 10 to 50% by weight. Mechanical, barrier, and degradation properties of PCL, MC, and composite films were evaluated. The values of puncture strength (PS), puncture deformation (PD), viscoelasticity (Y) coefficient, and water vapor permeability (WVP) of the composites (50% MC content) were found to be 124.3 N/mm, 3.2 mm, 31%, and 2.6 g·mm/m²·day·kPa, respectively. Oxygen transmission rate (OTR) of PCL, MC, and composites (50% MC) were found to be 175, 25, 22 cc/m²/d, respectively, which indicated that composite films showed significantly lower OTR than PCL films. Degradation tests of the composite films (50% MC) were performed for 6 weeks in aqueous medium (at 25°C), and it was found that composites lost its mass slowly with time. After 6 weeks, mass and PS of the composites were decreased to 13.4 and 12%, respectively. Composite interface was studied by scanning electron microscopy (SEM). The MC film had good adhesion with PCL matrix during compression molding and suggested strong interface of the composite system. SEM image after 6 weeks of degradation showed some openings in the interface and revealed slow degradation of the MC films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enhanced oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) blended with poly(acrylic acid) for packaging applications

To enhance the oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) (PVA) and expand its food packaging applicability, five crosslinked poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend films were prepared via esterification reactions between hydroxyl groups in PVA and carboxylic acid groups in PAA. The physical characteristics of the blends, including the thermal, barrier, mechanical and optical properties, were investigated as a function of PAA ratio. With increasing PAA content, the crosslinking density was significantly increased, resulting in changes in the chemical structure, morphology and crystallinity of the films. The oxygen transmission rate of pure PVA decreased from 5.91 to 1.59 cc m^?1 day^?1 with increasing PAA ratio. The water resistance, too, increased remarkably. All the blend films showed good optical transparency. The physical properties of the blend films were strongly correlated with the chemical structure and morphology changes, which varied with the PAA content. © 2016 Society of Chemical Industry     

Latex co‐coagulation approach to fabrication of polyurethane/graphene nanocomposites with improved electrical conductivity,thermal conductivity,and barrier property

This study describes a simple and effective method of synthesis of a polyurethane/graphene nanocomposite. Cationic waterborne polyurethane (CWPU) was used as the polymer matrix, and graphene oxide (GO) as a starting nanofiller. The CWPU/GO nanocomposite was prepared by first mixing a CWPU emulsion with a GO colloidal dispersion. The positively charged CWPU latex particles were assembled on the surfaces of the negatively charged GO nanoplatelets through electrostatic interactions. Then, the CWPU/chemically reduced GO (RGO) was obtained by treating the CWPU/GO with hydrazine hydrate in DMF. The results of X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Raman analysis showed that the RGO nanoplatelets were well dispersed and exfoliated in the CWPU matrix. The electrical conductivity of the CWPU/RGO nanocomposite could reach 0.28 S m^?1, and the thermal conductivity was as high as 1.71 W m^?1 K^?1. The oxygen transmission rate (OTR) of the CWPU/RGO‐coated PET film was significantly decreased to 0.6 cm³ m^?2 day^?1, indicating a high oxygen barrier property. This remarkable improvement in the electrical and thermal conductivity and barrier property of the CWPU/RGO nanocomposite is attributed to the electrostatic interactions and the molecular‐level dispersion of RGO nanoplatelets in the CWPU matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43117.     

三层共挤阻透薄膜的加工与性能研究

选用乙烯-乙烯醇共聚物（EVOH）、聚酰胺6（PA6）、茂金属聚乙烯（mPE）和改性线形低密度聚乙烯（PE-LLD）为原料,制备了3种三层共挤阻透薄膜PA6/EVOH/PA6、PA6/PE-LLD/mPE和EVOH/PE-LLD/mPE。通过对原料树脂热性能与流变性能的分析,探讨了三层共挤薄膜的最佳加工工艺。结果表明,所得3种共挤薄膜中以PA6/EVOH/PA6三层共挤薄膜的力学性能和氦气阻透性能最佳。     

Mechanical and barrier properties of nanocrystalline cellulose reinforced poly(caprolactone) composites: Effect of gamma radiation

Nanocrystalline cellulose (NCC) reinforced poly(caprolactone) (PCL) composites were prepared by compression molding. The NCC content varied from 2 to 10% by weight. NCC played a significant role in improving the mechanical properties of PCL. The addition of 5 wt % NCC caused a 62% improvement of the tensile strength (TS) value of PCL films. Similarly, tensile modulus (TM) values were also improved by NCC reinforcement but elongation at break (Eb) values decreased montonically with NCC content. The water vapor permeability (WVP) of PCL was 1.51 g·mm/m²·day·kPa, whereas PCL films containing 5 wt % NCC showed a WVP of 1.22 g·mm/m²·day·kPa. The oxygen transmission rate (OTR) and carbon dioxide transmission rate (CO₂TR) of PCL decreased by 19 and 17%, respectively, with 5 wt % NCC incorporation. It was found that the mechanical and barrier properties of both PCL and PCL‐NCC composites further improved with 10 kGy gamma irradiation treatment. The combination of NCC and radiation significantly increased the TS, TM, and Eb (by 156, 123, and 80%, respectively, compared to untreated PCL). The WVP, OTR, and CO₂TR decreased by 25–35% with respect to untreated PCL. The surface and interface morphologies of the PCL‐NCC composites were studied by scanning electron microscopy and suggested homogeneous distribution of NCC within the PCL matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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。     

Improving the oxygen barrier properties of polyethylene terephthalate by graphite nanoplatelets

Enhancement of the oxygen gas barrier properties of polyethylene terephthalate (PET), used in the packaging industry, is the main objective here. For this purpose, nanocomposites of PET containing graphite nanoplatelets (GNPs) were prepared by melt compounding. The effects of the nanocomposites' structural morphology on oxygen gas permeability were analyzed using a range of thermal, microscopic, and mechanical characterization techniques. The investigated nanocomposite films exhibited GNP exfoliated morphology and good mixing with PET, as well as uniform dispersion within the polymer. All nanocomposite films were shown to possess superior oxygen barrier properties and improved thermal and dimensional stability compared with the plain PET films. In the best case, for 1.5 wt % GNP, the oxygen permeation was reduced by more than 99%. The improved barrier properties are attributed to the direct effect of the GNPs and to their induced increase of degree of crystallinity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of poly(urethane acrylate) (PUA) and tetrapod ZnO whisker (TZnO‐W) composite films

Tetrapod zinc oxide whiskers (TZnO‐Ws) were successfully synthesized via a thermal oxidation method and confirmed using Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy. A series of poly(urethane acrylate) (PUA)/TZnO‐W composite films with various TZnO‐W contents were prepared via a UV curing method and their physical properties were investigated to understand their possible use as packaging materials. The morphological, thermal, mechanical, antibacterial and barrier properties of the PUA/TZnO‐W composite films were interpreted as a function of TZnO‐W content. The thermal stability, barrier properties and antibacterial properties of the composite films, which were strongly dependent upon their chemical and morphological structure, were enhanced as the TZnO‐W content increased. The oxygen transmission rate and water vapor transmission rate decreased from 614 to 161 cm³ m^?2 per day and 28.70 to 28.16 g m^?2 per day, respectively. However, the mechanical strength of the films decreased due to the low interfacial interaction and poor dispersion with high TZnO‐W loading. The enhanced barrier properties and good antibacterial properties of the PUA/TZnO‐W composite films indicate that these materials are potentially suitable for many packaging applications. However, further studies are needed to increase the compatibility of polymer matrix and filler. © 2012 Society of Chemical Industry     

Morphology and properties of polymer/organoclay nanocomposites based on poly(ethylene terephthalate) and sulfopolyester blends

Poly(ethylene terephthalate) (PET) nanocomposite films containing two different organoclays, Cloisite 30B^® (C30B) and Nanomer I.28E^® (N28E), were prepared by melt blending. In order to increase the gallery spacing of the clay particles, a sulfopolyester (PET ionomer or PETi) was added to the nanocomposites via a master‐batch approach. The morphological, thermal and gas barrier characteristics of the nanocomposite films were studied using several characterization techniques such as scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, rheometry and oxygen permeability. PET and PETi were found to form immiscible polymer blends and the nanoparticles were preferentially located in the PETi dispersed phase. A better dispersion of clay was obtained for nanocomposites containing N28E with PETi. On the contrary, for nanocomposites containing C30B and PETi, the number of tactoids increased and the clay distribution and dispersion became worse than for C30B alone. Overall, the best properties were obtained for the PET/C30B nanocomposite without PETi. Higher crystallinity was found for all nanocomposite films in comparison to that of neat PET. © 2012 Society of Chemical Industry     

Effect of Type of Surfactants and Organoclay Loading on the Mechanical Properties of EVOH/Clay Nanocomposite Blown Films

EVOH/clay nanocomposite films were prepared by using four types of surfactants to treat surface of clay because the surfactants were expected to affect the degree of clay dispersion in the EVOH matrix, which would in turn affect the properties of film. The nanocomposite films that contained the single alkyl tail with two repeating units of oxyethylene surfactants or single alkyl tail surfactant showed higher tensile strength, tensile modulus and elongation at break than those with 15 repeating units of oxyethylene surfactants or those with double alkyl tail surfactant.     

Permeation of oxygen and water vapor through EVOH films as influenced by relative humidity

The transport properties of oxygen and water vapor through EVOH films as functions of relative humidity (RH) and temperature were studied. The results of oxygen and water vapor permeation demonstrated that temperature and RH markedly affected barrier properties of these films. In general, the EVOH films had minimal oxygen and water vapor permeabilities at a low RH, attributed to the reduced mobility of the polymer resulting from strong interactions between small water molecules and the polymeric matrix at low RH. Beyond 75% RH, the permeabilities increased considerably. In addition, the barrier performance of the EVOH films was found to be dependent on their ethylene content and orientation. From the experimental data, semiempirical equations describing oxygen transmission rates (O₂TR) as functions of RH and temperature were developed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1866–1872, 2001