O2 Barrier Properties Research Articles

Molecular Insights into Antioxidant Efficiency of Melanin: A Sustainable Antioxidant for Natural Rubber Formulations.

N-(1,3-Dimethyl butyl)-N'-phenyl-p-phenylenediamine (6-PPD) is a worldwide antioxidant commonly added to delay the thermo-oxidative degradation of tire rubbers. Unfortunately, 6PPD and its transformation product 6PPD-quinone are toxic to aquatic organisms (e.g., coho salmon). Herein, we explore the free radical scavenging activity and protective mechanism of melanin (MLN) on natural rubber's (NR's) oxidative resistance using molecular dynamics (MD) and quantum mechanical (QM) calculations. The relationship between the molecular structure and the chemical nature of the antioxidant molecules via transition state calculations is explored to unravel the reaction mechanisms of antioxidants interacting with peroxy radicals (ROO·) of NR with the estimation of reaction barriers. Following this, the radical scavenging activity of antioxidants was quantified via a hydrogen atom transfer mechanism and bond dissociation energy calculations. Parallel MD simulations were considered to study the interfacial interactions of antioxidant molecules with polymer chains and fillers with a quantifiable structure-property correlation. Given these results, the nanocomposite (NR-MLN-SiO2) with natural antioxidant melanin manifested outstanding antioxidant properties by preferentially bagging the ROO· radicals, thus improving NR's thermal-oxidative aging relative to 6-PPD. The MD results revealed that the intermolecular interactions at the NR/antioxidant interface benefited the antioxidant MLN to bind tightly to the NR in NR-MLN-SiO2 composite, thus exhibiting improved dispersion, O2 barrier properties, and thermo-oxidative stability, which could extend the service life of NR products (e.g., tires). In addition, as a sustainable antioxidant, MLN could replace toxic antioxidants like 6-PPD. More importantly, the QM/MD simulations provided a fundamental understanding of the mechanistic pathways of antioxidant molecules in NR composites, which are conducive to designing high-performance and sustainable green elastomers.

Resilient high oxygen barrier multilayer films of nanocellulose and polylactide

Nanocelluloses are promising high gas barrier materials for biobased food packaging, but they must be protected from water to preserve high performance. The respective O2 barrier properties of different types of nanocelluloses were compared (nanofibers (CNF), oxidized nanofibers (CNF TEMPO) and nanocrystals (CNC)). The oxygen barrier performance for all types of nanocelluloses was similarly high. To protect the nanocellulose films from water, a multilayer material architecture was used with poly(lactide) (PLA) on the outside. To achieve this, a biobased tie layer was developed, using Corona treatment and chitosan. This allowed thin film coating with nanocellulose layers between 60 and 440 nm thickness. AFM images treated with Fast Fourier Transform showed the formation of locally-oriented CNC layers on the film. Coated PLA(CNC) films performed better (3.2 × 10−20 m3.m/m2.s.Pa) than PLA(CNF) and PLA(CNF TEMPO) (1.1 × 10−19 at best), because thicker layers could be obtained. The oxygen barrier properties were constant during successive measurements at 0 % RH, 80 % RH and again at 0 % RH. This shows that PLA is sufficiently shielding nanocelluloses from water uptake to keep high performance in an extended range of RH and opens the way to high oxygen barrier films which are biobased and biodegradable.

Synthesis of high-Tg fluorinated polyesters based on 2,5-furandicarboxylic acid

The polyesters derived from renewable resources with both high transparency and good heat resistance are urgently desirable. Destroying the crystallization of a material and achieving an amorphous state can ensure high transparency, while good heat resistance can be provided by rigid monomers. Herein, the fluorinated rigid diol 2,3,5,6-tetrafluoro-1,4-benzenedimethanol (TFBDO) was introduced into 2,5-furandicarboxylic acid (FDCA)-based copolyesters to synthesize a series of new bio-based polymers called poly(ethylene-1,4-cyclohexyldimethylene-2,3,5,6-tetrafluoro-1,4-benzenedimethanol 2,5-furandicarboxylate) (PECFF) with different TFBDO contents via a two-step melt polycondensation. The number average molecular weight (Mn) of 24,200 ∼ 46,700 g/mol and the polydispersity index (PDI) of 1.28 ∼ 1.74 for synthesized PECFFs showed the high reaction activity as a rigid diol of TFBDO. As the increasing of tetrafluoro-1,4-benzenedimethanol unit, the Tg was improved from 91 °C for PECFF-15 to 118 °C for PECFF-75, and the thermal stability of Td,5% in nitrogen increased from 371 to 393 °C as well as the hydrophobicity, and gas barrier properties were also improved. When the content of the tetrafluoro-1,4-benzenedimethanol unit was up to 60 %, the copolyester PECFF-60 exhibited the Tg of 113 °C, Td,5% of 421 °C, Young’s modulus of 2460 MPa, and tensile strength of 71 MPa. Moreover, the surface water contact angle increased from 85° to 101° as well as the CO2 and O2 barrier properties improved 43.3-fold and 8.6-fold compared with PET. These studies have shown that the new bio-based polyester could be a potential application in many fields, such as transparent sheet in outdoor, architectural materials or electronic equipment, and non-food contact packaging.

Gas barrier properties of polylactide/cellulose nanocrystals nanocomposites

The development of polylactide (PLA)/cellulose nanocrystals (CNC) nanocomposites in the aim to increase gas barrier properties has been widely studied, but gave rise to conflicting results. To better understand the underlying gas transport mechanisms, PLA/CNC nanocomposites were produced at concentrations between 5 and 50 wt%. The role of the PLA/CNC interface for the permeability was investigated using three different CNC surface grafts, namely lauric acid (slightly interacting with PLA), stearic acid (non-interacting with PLA), and poly glycidyl methacrylate bearing a reactive epoxy end-group (crosslinking with PLA). While PLA/CNC composites contained a large number of aggregates, homogenously dispersed nanocomposites were obtained with surface modified CNCs even at high concentration of CNC (up to 30 wt%). All nanocomposites had better O2 and CO2 barrier properties than PLA. Surprisingly, the nanocomposites prepared with surface grafted CNC did not perform better than the ones prepared with neat CNC. The diffusion coefficient was successfully modeled with Nielsen's law, showing the importance of the shape factor and resulting tortuosity for the barrier performance notwithstanding PLA/CNC surface compatibility. The analysis of the dual-mode O2 sorption isotherm showed the creation of a similar quantity of supplementary sorption sites in nanocomposites prepared with neat or lauric acid grafted CNC. PGMA grafts induced a higher number of sorption sites. The most important advantage of CNC surface grafts was the shielding of CNC against water vapor uptake. As a result, the O2 barrier properties could be maintained constant up to 90% relative humidity.

Bio-based poly(butylene diglycolate-co-furandicarboxylate) copolyesters with balanced mechanical, barrier and biodegradable properties: A prospective substitute for PBAT

Poly(butylene adipate-co-terephthalate) (PBAT) is a flexible aliphatic/aromatic copolyester commercialized for degradable plastics, while the slow degradation rates and poor barrier properties limit its applications. Consequently, it is highly desirable to develop materials with faster degradation rates and enhanced barrier properties. Here, we synthesized poly(butylene diglycolate-co-furandicarboxylate) (PBDF) copolyesters by transesterification and melt polycondensation. The NMR spectra confirmed their structure and composition. Besides, the thermal, mechanical, permeable and degradable properties were characterized thoroughly. It was found that the properties were dependent on chemical composition and crystallinity. Actually, the introduction of diglycolic acid (DGA) comonomer hinders the crystallization and all the copolyesters appear as semicrystalline polyesters except for PBDF80. Among them, PBDF40 possesses outstanding mechanical properties with an elastic modulus of 165 MPa, tensile strengths of 54 MPa, and elongations of break of 654%. Moreover, the CO2 and O2 barrier properties of PBDF40 are 68.6 and 45.9 times higher than those of PBAT. PBDFs also exhibit accelerated rates in hydrolysis and composting degradation, which could be attributed to the enhanced hydrophilicity due to the electronegativity of ether-oxygen atoms in DGA. In particular, the mass loss of PBDF40 reaches 46% and 42% after 28 days of CALB enzymatic degradation and 8 weeks of compost degradation, respectively. These results highlight that the synthesized polyesters, especially PBDF40, demonstrate potential application in food packaging.

Synthesis and properties of poly(ethylene‐co‐diethylene glycol 2,5‐furandicarboxylate) copolymers

AbstractPoly(ethylene 2,5‐furandicarboxylate) (PEF) is a biobased polyester with high gas barrier properties, tensile modulus, and strength. In PEF chain, in addition to ethylene furandicarboxylate repeat unit, there is also a small amount of diethylene glycol furandicarboxylate (DF) unit which is formed by etherification side reactions. However, the effect of DF unit in a wide composition range on polymer properties is still unclear. In this study, random poly(ethylene‐co‐diethylene glycol 2,5‐furandicarboxylate) (PEDF) copolymers were synthesized via melt copolycondensation of 2,5‐furandicarboxylic acid, ethylene glycol and diethylene glycol. The copolymers were characterized and evaluated by intrinsic viscosity, 1H NMR, thermal transition, thermogravimetric analysis, tensile, impact, and O2 penetration tests. The copolymers are amorphous in the full composition range. The presence of less than 58 mol% DF unit in PEDFs neither improves the tensile ductility nor deteriorates the oxygen barrier performance, but reduces the glass transition temperature clearly. In comparison with poly(ethylene terephthalate), the PEDF copolymers containing <58 mol% DF unit have higher tensile modulus, strength, and O2 barrier properties.

Enhanced Polyester Degradation through Transesterification with Salicylates.

Polyesters constitute nearly 10% of the global plastic market, but most are essentially non-degradable under ambient conditions or in engineered environments. A range of degradable polyesters have been developed as more sustainable alternatives; however, limitations of practical degradability and scalability have hindered their viability. Here, we utilized transesterification approaches, including in situ polymerization-transesterification, between a salicylate and a polyester to incorporate salicylate units into commercial polyester backbones. The strategy is scalable and practically relevant given that high molar mass polymers can be obtained from melt-processing of commercial polyesters using common compounders or extruders. Polylactide containing sparse salicylate moieties shows enhanced hydrolytic degradability in aqueous buffer, seawater, and alkaline solutions without sacrificing the thermal, mechanical, and O2 barrier properties of the parent material. Additionally, salicylate sequences were incorporated into polycaprolactone and a derivative of poly(ethylene terephthalate), and those modified polymers also exhibited facile degradation behavior in alkaline solution, further expanding the scope of this approach. This work provides insights and direction for the development of high-performance yet more sustainable and degradable alternatives to conventional polyesters.

Polyvinyl Alcohol-Few Layer Graphene Composite Films Prepared from Aqueous Colloids. Investigations of Mechanical, Conductive and Gas Barrier Properties.

Quasi all water soluble composites use graphene oxide (GO) or reduced graphene oxide (rGO) as graphene based additives despite the long and harsh conditions required for their preparation. Herein, polyvinyl alcohol (PVA) films containing few layer graphene (FLG) are prepared by the co-mixing of aqueous colloids and casting, where the FLG colloid is first obtained via an efficient, rapid, simple, and bio-compatible exfoliation method providing access to relatively large FLG flakes. The enhanced mechanical, electrical conductivity, and O2 barrier properties of the films are investigated and discussed together with the structure of the films. In four different series of the composites, the best Young’s modulus is measured for the films containing around 1% of FLG. The most significant enhancement is obtained for the series with the largest FLG sheets contrary to the elongation at break which is well improved for the series with the lowest FLG sheets. Relatively high one-side electrical conductivity and low percolation threshold are achieved when compared to GO/rGO composites (almost 10−3 S/cm for 3% of FLG and transport at 0.5% FLG), while the conductivity is affected by the formation of a macroscopic branched FLG network. The composites demonstrate a reduction of O2 transmission rate up to 60%.

Wearable transcutaneous oxygen sensor for health monitoring

We present a wearable bandage-like photoluminescence (PL)-based transcutaneous oxygen (tcpO2) sensor consisting of a photoluminescent oxygen (O2)-sensing film, a polyvinylidene chloride (PVDC) film as an encapsulation layer, an indium tin oxide (ITO) thin-film heater, an array of micro-light-emitting diodes (μ-LED) as a light source, red cellophane paper as an optical filter, an organic photodiode (OPD) as a PL detector, and an optical isolation layer. All the components of the tcpO2 sensor were designed to be flexible and thus can be attached anywhere on the curved skin of the human body. The PVDC film with excellent O2 barrier properties and visible light transmittance was a significant additional component of the wearable sensor that improved the sensitivity of the photoluminescent O2-sensing film by minimizing the PL quenching effects of ambient atmospheric O2. Furthermore, the ITO thin-film heater increases the skin temperature, changing the structure of the stratum corneum and allowing O2 to more effectively diffuse from the skin toward the tcpO2 sensor. Therefore, the thin-film heater allows the accurate measurement of the tcpO2 variation from human skin to facilitate the determination of the severity of O2-deficiency related diseases in the tcpO2 range from 0 to 80 mmHg. The μ-LED array embedded into a polydimethylsiloxane (PDMS) film not only maintained its mechanical flexibility but also had stable light emission performance under ambient air conditions, allowing tcpO2 measurements over several cycles for as long as 60 min, which we could not previously achieve with ambient air-unstable flexible organic light-emitting diodes (f-OLEDs). The effects of the heat from the ITO thin-film heater and the skin color of the sensor user on the PL emitted by the sensing film and detected by the OPD were factored out from the tcpO2 measurements by defining two correction coefficients. The performance of the wearable tcpO2 sensor was tested using the leg elevation protocol to induce tcpO2 variation at the skin of the ankles of test volunteers. According to the experimental results, the sensing performance of our wearable bandage-like PL-based tcpO2 sensor proved to be superior to that of a commercially available tcpO2 sensor, as our wearable PL-based tcpO2 sensor demonstrated faster response times to tcpO2 variation and smaller measurement deviations between tcpO2 detection cycles.

In situ fibre-reinforced composite films of poly(lactic acid)/low-density polyethylene blends: effects of composition on morphology, transport and mechanical properties

This study aimed to investigate the effects of blend compositions on packaging related properties of poly(lactic acid) (PLA) and low density polyethylene (LDPE) blown films. Blend films with PLA contents of 5–20 wt% were produced and compared. SEM micrographs of cross-sectional cryofractured surfaces of the blend films revealed that in situ fiber-reinforced composites were obtained. Viscosity ratio of the polymer components of ~ 1 confirmed that fiber formation was favorable for this blend system. PLA microdomains dispersed throughout the film in forms of long fiber (L/D > 100) and ribbon. Number of fibers and ribbons increased with an increase of PLA content. Critical content of PLA was found to be 20 wt% to effectively improve both moduli and gas barrier properties. Incorporation of PE-co-MA compatibilizer showed minimal effect on PLA structure. It, however, did improve moduli and O2 barrier properties when sufficient amount of 1.5 pph was used in 10 wt% PLA/LDPE. In short, flow behavior, ratio of the polymer components, and degree of compatibility together played intricate roles on the morphology and hence mechanical and transport properties of the PLA/LDPE immiscible blend.

Effect of humidity on mechanical, thermal and barrier properties of EVOH films

The moisture content sensitivity of Ethylene-Vinyl Alcohol (EVOH) copolymers is a major problem for food packaging applications. Thus, the relationship between the hydration mechanism at molecular scale and the properties is a critical issue for barrier properties improvement of EVOH films. The aim of this study was to determine material structure-functional property relationships and inter-property correlations.Firstly, mechanical, thermal, water sorption and oxygen barrier properties were determined for a wide range of water activity. The water sorption isotherm modelling with GAB equation, the evolution of the glass transition temperature applying Gordon-Taylor equation as well as the mechanical and O2 barrier properties were studied. The results underlined the plasticization effect of water leading to a decrease of the cohesive energy density and a drastic loss of O2 barrier properties of the EVOH copolymer from a critical point occurring when water activity was close to 0.5.Secondly, an analysis of the experimental water sorption isotherm, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the evolution of polymer chains mobility allowed to establish a relationship between the hydration mechanism at molecular scale and the properties. It was determined that the amount of water sorbed molecules dramatically increased at a critical point, corresponding to the moment from which one water molecule was linked in average every nine amorphous PVOH units. This point corresponded to the saturation of the monolayer and the beginning of the clustering phenomenon.

Effect of montmorillonite (MMT) content on the mechanical, oxygen barrier, and thermal properties of rice husk/MMT hybrid filler-filled low-density polyethylene nanocomposite blown films

Montmorillonite (MMT)/rice husk (RH) hybrid filler-filled low-density polyethylene (LDPE) nanocomposite films, containing 0, 2, 3, 4, 5, and 6 wt% MMT (based on the total weight) were prepared by extrusion blown film. The films were characterized by morphological, mechanical, oxygen (O2) barrier, and thermal properties. The delamination of MMT layers evidenced from X-ray diffraction results suggests an increase in the interlayer distance and shows intercalated structure of the nanocomposites. Adding MMT did not adversely affect the interfacial morphology, as confirmed by scanning electron microscopy. Addition of MMT into the LDPE/RH system improved the mechanical and O2 barrier properties. For instance, tensile strength, tensile modulus, and tear strength increased by 8, 10, and 5%, respectively, with the addition of 3 wt% MMT. Further, the O2 barrier of the composite films improved more than twofold by adding 4 wt% MMT. Initial degradation temperature of LDPE/RH composites increased with the incorporation of MMT suggesting that the nanocomposites are more thermally stable than LDPE/RH composites.

Enhancing polymer/graphene oxide gas barrier film properties by introducing new crystals

A transparent, gas barrier film comprised of poly(vinyl alcohol) (PVA) and graphene oxide (GO) is synthesized through combined methods of solution blending and isothermal recrystallization. The recrystallized PVA/GO film with only 0.07vol% GO gives an O2 transmission rate <0.005ccm−2day−1 and an O2 permeability <5.0×10−20cm3cmcm−2Pa−1s−1; hence, it is far superior to other blend polymer/inorganic composites. The excellent O2 barrier properties are attributed to a unique hybrid of PVA crystals and GO sheets. PVA crystals form around the GO during isothermal recrystallization, indicating that a GO sheet can act as a nucleating agent. The newly formed PVA crystals fill in the spaces between the GO sheets, and together they become ultra-large impermeable regions, which can prevent the passage of O2. The hybrid film has potential applications in flexible electronics, pharmaceuticals, and food packaging.

Comparison of Cellulose, Talc, and Mica as Filler in Natural Rubber Composites on Vibration-Damping and Gas Barrier Properties

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR was mixed with vulcanizing agents in an internal mixer. And then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O2 barrier properties.

Preparation and Performance of High-Barrier Low Density Polyethylene/Organic Montmorillonite Nanocomposite

Montmorillonite (MMT) was first modified with dodecyl dimethylbenzyl ammonium (DDA) salt and octadecyl trimethyl ammonium (OTA) salt. Then low density polyethylene (LDPE)/organic montmorillonite (OMMT) nanocomposites were prepared by twin-screw extruder and hot-press. Transmission electron microscopy (TEM) results showed that OMMT layers were homogeneously intercalated into the LDPE matrix. In terms of MMT, the modification effect of OTA is superior to that of DDA. CO2 and O2 barrier properties of nanocomposites were increased by 7 times and 4 times with 0.5 wt.% OTA-MMT loading, respectively. At 2 wt% OTA-MMT loading, water vapor permeability of LDPE has also decreased about 2.5 times. Compared with pure PE film, 49.5% and 178% improvement of tensile strength of nanocomposites films were obtained by addition of only 4 wt.% DDA-MMT and OTA-MMT, respectively. In addition, with only 0.5 wt.% OMMT loading, the onset degradation temperature of nanocomposites increases by 23°C and 26°C for LDPE/DDA-MMT and LDPE/OTA-MMT, respectively.

Ecological Approach to Graphene Oxide Reinforced Poly (methyl methacrylate) Nanocomposites

Graphene oxide (GO) possesses the desirable characteristic of aqueous solution processability attributed to the oxygen-containing functional groups on the basal planes and edges of graphene. To provide an alternative to conventional procedures for fabricating poly (methyl methacrylate) (PMMA)/GO nanocomposites, which use organic solutions and/or surfactants, we have developed an environmentally friendly technique in which PMMA is polymerized by soap-free emulsion polymerization and incorporated with GO using water as a processing medium. Experimental results showed that the fabricated PMMA/GO nanocomposites had excellent mechanical, thermal, and O2 barrier properties with the nanodispersion of GO.

Resistance of lipid films to oxygen transmission

AbstractVarious lipids, mounted on a polar filter paper matrix, were evaluated as barriers to O2 transmission Among those lipids tested, stearyl alcohol was most resistant to oxygen transmission, the most likely reason being its ability to crystallize as compactly overlapping platelets with their planes normal to the direction of O2 diffusion. Tristearin, beeswax, and acetylated monoglycerides were, respectively, 39, 43 and 61% less resistant to O2 transmission than the fatty alcohol. Activation energies of O2 transport were. 7.0, 7.5, 15.0 and 27.5 kcal/mole, respectively, for stearyl alcohol, tristearin, beeswax, and acetylated monoglycerides. Stearic acid was substantially less resistant to O2 flux than the above four lipids. In addition, the fatty acid was unique among the, lipids tested in its temperature dependence, i.e., resistance to O2 transmission increased with elevation of temperature yielding a negative activation energy of −17.2 kcal/mole. This was attributed to the presence of small interplatelet channels in the stearic acid film, which presumably act as the principal route for gas transport. Hexatriacontane displayed poor O2 barrier properties compared to the other lipids, a consequence of relatively large pores in the alkane film.