Efficient approach to high barrier packaging using microfibrillar cellulose and shellac

This paper presents an investigation on the enhancement of the barrier properties of paperboard and paper. Microfibrillar cellulose (MFC) and shellac were deposited on the fibre based substrates using a bar coater or a spray coating technique. The air, oxygen and water vapour permeability properties were measured to quantify the barrier effect of the applied coatings. In addition, the mechanical properties were determined and image analysis of the structure was performed to examine the coating adhesion. The air permeance of the paperboard and papers was substantially decreased with a multilayer coating of MFC and shellac. Furthermore, for the MFC and shellac coated papers, the oxygen transmission rate decreased several logarithmic units and the water vapour transmission rate reached values considered as high barrier in food packaging (6.5 g/m² 24 h). The analysis of mechanical and morphological properties indicated good adhesion between the coating and the base substrate.     

O-acetyl galactoglucomannan esters for barrier coatings

A major enhancement of grease and water vapor barrier properties was accomplished with a 1–10 g/m² coating of O-acetyl galactoglucomannan (GGM) ester or with GGM coatings applied as water dispersions on cartonboard. GGMs were esterified with phthalic and benzoic anhydrides, respectively. The novel phthalic esters of GGM (GGM-Ph) were characterized with HPLC, NMR, and matrix-assisted laser desorption/ionization with mass spectrometry (MALDI-TOF-MS). The degree of substitution of GGM-Ph was obtained by ¹H NMR, ¹³C NMR, and HPLC. The GGM esters and GGM were coated onto cartonboard, and they demonstrated good moisture and very good grease resistance even with thin 1–3 g/m² coatings. The time for penetration of 0.1 % rapeseed oil was 54 h with the 2.4 g/m² coating thickness. The lowest water vapor transmission value was 39 g/m²/24 h with 9.7 g/m² coating. The GGM esters had clearly higher water resistance and slightly higher grease barrier values than native GGM. High-molar-mass-based GGM (50 kg/mol) and GGM-Ph rendered better water vapor and grease barrier properties than low-molar-mass GGM (9 kg/mol) and GGM-Ph. The GGM-based coatings can be safely used on an industrial scale as water was used as a solvent. As obtained from non-food-based side-stream wood-based resources, GGM and GGM esters project a sustainable and modern conception for barrier purposes in food packaging.     

Multi-functional coating of cellulose nanocrystals for flexible packaging applications

In this paper, we systematically address the performance of cellulose nanocrystals (CNs) coated flexible food packaging films. Firstly, the morphology of CNs from cotton linters and homogeneity of its coating on different substrates were characterized by transmission electronic microscopy and atomic force microscopy. Then, the 1.5 μm thick CNs coating on polyethylene terephthalate (PET), oriented polypropylene, oriented polyamide (OPA), and cellophane films were characterized for their mechanical, optical, anti-fog, and barrier properties. CNs coating reduces the coefficient of friction while maintaining high transparency (~90 %) and low haze (3–4 %) values, and shows excellent anti-fog properties and remarkable oxygen barrier (oxygen permeability coefficient of CNs coating, P’O₂, 0.003 cm³ μm m^?2 24 h^?1 kPa^?1). In addition, the Gelbo flex test combined with oxygen permeance (PO₂) measurements and optical microscopy are firstly reported for evaluating the durability of coatings, revealing that the CNs coated PET and OPA provide the best performance among the investigated coated films. CNs are therefore considered to be a promising multi-functional coating for flexible food packaging.     

Properties of nitrocellulose‐coated and polyethylene‐laminated chitosan and whey films

Chitosan (chitosan acetic acid salt) and whey (65% protein) films were coated with a nitrocellulose lacquer or laminated with polyethylene to enhance their water resistance and gas barrier properties in humid environments. The barrier properties were measured by the Cobb₆₀ test and water‐vapor (100% relative humidity) transmission and oxygen (90% relative humidity) permeability tests. Mechanical properties were obtained with tensile tests. Packaging properties were studied with crease and folding tests. The Cobb₆₀ test revealed that the coated films were resistant to liquid water, at least for a short exposure time, if the coating thickness was at least 10–17 μm. Water‐vapor transmission rates comparable to those of polyethylene‐laminated films were obtained for coated chitosan at a coating thickness of 5–7 μm. The coated films possessed low oxygen permeability despite the high humidity. Coated films dried for 3 weeks showed oxygen permeabilities at 90% relative humidity that were similar to values for dry ethylene‐co‐vinyl alcohol at 0% relative humidity. The lacquer partly penetrated the whey films, and this led to excellent adhesion but poor lacquer toughness. The lacquer coating on chitosan was tougher, and it was possible to fold these films 90° without the coating fracturing if the coating thickness was small. The coated whey films were readily creasable. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 985–992, 2001     

Graphene oxide-modified polyaniline pigment for epoxy based anti-corrosion coatings

In the present work, a set of polyaniline–graphene oxide (PANI–GO) nanocomposites which exhibit superior properties in terms of shelf life, processability and conductivity due to the synergistic effect of GO and PANI, have been synthesized by varying the concentration of highly non-conducting GO with respect to aniline. The obtained materials were characterized by UV–Vis, FTIR, XRD, Raman, TGA as well as FESEM, TEM analysis. The results reveal that nanocomposites show better dispersibility, crystallinity, thermal stability, and conductivity. Further, the synthesized composites have been tested for their anti-corrosion properties. The potentiodynamic results reveal that PANI nanocomposites with 1% GO exhibited long-term anti-corrosion behavior with a corrosion rate of 6.5 × 10^?5 mm year^?1, which is much lower than its individual components and commercial-grade red oxide. Also, it possesses highest impedance modulus ~33 kΩ cm² and real impedance ~32 kΩ cm², maximum coating resistance ~14.81 × 10³ Ω cm² and minimum coating capacitance after 96 h of immersion in 3.5% mass NaCl than those exhibited by all other coated samples. Higher concentration of GO could not retard the corrosion rate confirming that hydrophilicity of GO play an important role in the redox mechanism of PANI.     

Improved water resistance of SrAl2O4: Eu2+, Dy3+ phosphor directly achieved in a water-containing medium

In this paper, a heterogeneous precipitation method utilizing urea hydrolysis was adopted to coat a SiO₂ layer on the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ long persistence phosphors. To avoid phosphor hydrolysis in a water-containing coating medium, the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) were concerned and carried out. The crystal phases, surface morphologies, hydrolysis stability and water resistance on afterglow properties of coated phosphors were investigated. Scanning electron microscopy, energy dispersive spectrum analysis, transmission electron microscope and Fourier transform infrared spectrum results confirmed that a continuous, uniform and compact SiO₂ coating layer was successfully obtained on the phosphors surface. A theoretical coating amount of 5% or higher was found to be good for hydrolysis stability. Photoluminescence results revealed the coated phosphors showed much better water resistance on afterglow properties than the uncoated phosphor. We also discussed and proposed the hydrolysis restriction mechanism of SrAl₂O₄:Eu²⁺, Dy³⁺ in the water-containing coating medium.     

Water vapor adsorption equilibria and mass transport in unmodified and modified cellulose fiber-based materials

Water vapor adsorption isotherms of different unmodified and coated paper samples were studied to determine their suitability as water barrier packaging materials. The sorption behavior of these samples was compared with commercially available paper. The experimental data were analyzed using the Hailwood–Horrobin (H–H), Guggenheim–Anderson–De Boer (GAB) and BET models for extraction of isotherm parameters and determination of monolayer moisture contents. The H–H and GAB models were found to provide good fits to the experimental data. The monolayer moisture content of modified papers was less than 3.0 % (dry basis) as compared to unmodified paper samples (4.20 %), at saturation. It was also observed that the sorption behavior of modified paper samples differed with substrate type. Water vapor permeability (WVP) of unmodified and coated paper samples at the temperatures of 25 and 38 °C were also measured for a wide range of vapor partial pressure gradients. The permeabilities of the modified samples were found to be generally low compared to the unmodified (reference) paper sample. Among the investigated samples, PLA and PHBV coated paper samples showed higher mass transfer resistance to water vapor transport. Furthermore, the water vapor permeabilities of different samples were found to be relatively constant up to the modest relative humidity levels; however, at the higher humidity levels they showed increasing trend with the further increase in relative humidity. Results of this study confirmed that blocking of active surface sites by coating with PLA and PHBV is the most effective way to increase the water vapor barrier properties of modified papers, thus making them the appropriate candidates for green-based food packaging materials.     

Crosslinked poly(ethylene oxide) fouling resistant coating materials for oil/water separation

Potential fouling reducing coating materials were synthesized via free-radical photopolymerization of aqueous solutions of poly(ethylene glycol) diacrylate (PEGDA). Crosslinked PEGDA (XLPEGDA) exhibited high water permeability and good fouling resistance to oil/water mixtures. Water permeability increased strongly with increasing the water content in the prepolymerization water mixture, going from 10 to 150 L μm/(m² h bar) as prepolymerization water content increased from 60 to 80 wt.%. However, molecular weight cutoff decreased as water content increased. These materials were applied to polysulfone (PSF) UF membranes to form coatings on the surface of the PSF membranes. Oil/water crossflow filtration experiments showed that the coated PSF membranes had water flux values 400% higher than that of an uncoated PSF membrane after 24 h of operation, and the coated membranes had higher organic rejection than the uncoated membranes.     

Structure,hydrophilicity and corrosion resistance of sol–gel derived Ag-containing TiO2 film on plasma nitrided 316L stainless steel

Pure and Ag-containing TiO₂ films (Ag/Ti = 3.3 at.%) are coated on plasma nitrided 316L stainless steel by sol–gel method for biomedical applications. The addition of Ag does not cause obvious change in TG–DSC curves of the dried gels. The rough surface generated by plasma nitriding and the addition of Ag improve structural integrity of the TiO₂ films. X-ray diffraction reveals N loss and oxidation of the nitride layer during calcination treatment, and peaks of Ag or its oxides are not detected. X-ray photoelectron spectroscopy analysis indicates that Ag presents as metallic state in the film. Water contact angles of the coating samples decrease with UV irradiation treatment. The potentiodynamic polarization tests in a Ca-free Hank’s balanced salt solution show that the TiO₂ coated samples have decreased corrosion resistance due to N loss and oxidation of the nitride layer. The methods for crystallization of TiO₂ gel layers with minimized or avoided structural changes of the nitride layer will be tried in order to improve corrosion resistance of the duplex treated 316L stainless steel.     

Low degree of substitution cellulosic textile coatings with improved physiological parameters

To further improve the physiological properties of textiles, solutions of low degree of substitution cellulose derivatives, i.e. carbamates and acetates, containing finely dispersed sub-micron scaled NaCl particles (d₁₆ = 269 nm, d₅₀ = 275 nm, d₈₄ = 283 nm) serving as templates were coated on textiles. By wet milling of NaCl particles in a 12.5 wt% solution of polyvinylpyrrolidone in dimethylacetamide (DMAc) as dispersing agent, a stable, processable dispersion was obtained, which could be diluted with LiCl/DMAc without any flocculation. For the preparation of the coating solution, the NaCl/DMAc dispersions were diluted with LiCl/DMAc and added to the DMAc-swollen cellulose derivatives. After application onto the textiles, the NaCl particle-containing coating had to be coagulated directly after application in a solvent bath, otherwise slow replacement of hygroscopic DMAc by water lead to the dissolution and recrystallisation of NaCl on the surface of the coating, thereby changing particle distribution and diameter. The solvent for the coagulation bath was chosen in a way that it allows for a high coagulation speed for the cellulose derivative matrix while possessing a low solubility product for NaCl (e.g., 2-propanol) in order to prevent any loss of the NaCl particles. Due to the highly porous structure created, increased water retention values and increased water vapour permeabilities were observed under preservation of the number of accessible hydroxyl groups of the cellulose derivatives. Both the templated and non-templated coatings could be processed on various textile substrates (e.g., on PET and PP). An important feature of these new materials, i.e. the possibility to apply an antibacterial finish, is discussed within the context of a potential use in the medical sector.     

Substrate role in coating of microfibrillated cellulose suspensions

Interest in nanocellulose-based coatings for packaging applications has been growing due to their excellent oil and gas barrier properties combined with their sustainable, recyclable, biodegradable, and non-toxic nature. Coating of nanocellulose materials such as microfibrillated cellulose (MFC) on paper/paperboard is challenging compared to traditional paper coating materials due to excessively high viscosity and yield stress of MFC suspensions at rather low solids content, typically below 5%. Possessing large amounts of water and a distinct rheological behavior such suspensions set tough demands on the substrate to be coated. It is important to understand and quantify substrate requirements in order to coat these suspensions successfully and achieve a satisfactory coating quality. A custom-built slot geometry is used herein to enable coating of highly viscous MFC suspensions on different paper-based substrates in a roll-to-roll process. The impact of substrate properties, such as surface chemistry and surface energy, surface roughness and surface porosity, and water absorption capacity on MFC coatability and coating quality is reported. Coating adhesion to the substrate was quantified with surface strength testing of MFC coated substrates. Various techniques, such as Scanning Electron Microscopy, IGT print penetration tests, and air permeability tests were employed for measuring coating coverage and surface porosity. MFC coating was found to adhere best to a highly hydrophilic surface, whereas the most uniform and defect-free film at low coat weights was formed on a smooth surface. It was also found that the MFC coat weight needed for full coverage, and therefore potentially good barrier, needs to exceed the surface roughness volume of the substrate. Water absorption capacity of the substrate also determines the final MFC coating quality obtained. The results clearly highlight the role of paper-based substrate for successful and effective coating of the micro and nanocellulose suspension.     

The maleimide modified epoxy resins for the preparation of UV‐curable hybrid coatings

In the present study, maleimide‐modified epoxide resin containing UV‐curable hybrid coating materials were prepared and coated on polycarbonate substrates in order to improve their surface properties. UV‐curable, bismaleimide‐modified aliphatic epoxy resin was prepared from N‐(p‐carboxyphenyl) maleimide (p‐CPMI) and cycloaliphatic epoxy (Cyracure‐6107) resin. The structure of the bismaleimide modified aliphatic epoxy resin was analyzed by FTIR and the characteristic absorption band for maleimide ring was clearly observed at 3100 cm^?1. Silica sol was prepared from tetraethylorthosilicate (TEOS) and methacryloxy propyl trimethoxysilane (MAPTMS) by sol–gel method. The coating formulations with different compositions were prepared from UV‐curable bismaleimide‐based epoxy oligomer and sol–gel mixture. The molecular structure of the hybrid coating material was analyzed by ²⁹Si‐CP/MAS NMR spectroscopy techniques. In the ²⁹Si CP/MAS NMR spectrum of the hybrid coating, mainly two kinds of signals were observed at ?68 and ?110 ppm that correspond to T³ and Q⁴ peaks, respectively. This result shows that a fully condensed structure was obtained. The thermal and morphological properties of these coatings materials were investigated by using TGA and SEM techniques. Hardness and abrasion resistance properties of coating materials were examined and both were found to increase with sol–gel precursor content of the coating. The photopolymerization kinetics was investigated by using RT‐IR. 70% conversion was attained with the addition of 15 wt% of BMI resin into the acrylate‐based coating formulation. It was found that the UV‐curable organic–inorganic hybrid coatings improved the surface properties of polycarbonate. Copyright © 2009 John Wiley & Sons, Ltd.     

Microstructural and Thermal properties of Plasma Sprayed YSZ Nano-Clusters Thermal Barrier Coatings

In the present study, a novel durable three layered thermal barrier coating (TBCs) were prepared using atmospheric plasma spray (APS) on Ni718 superalloy substrate consisting of the YSZ nano-clusters. In order to develop a functionally graded coating system, the non-transformable (t′) tetragonal YSZ nano-clusters (40 nm) were synthesized by a sol–gel process and characterized at the temperature 1200 °C for 100 h. NiCrAlY was used as bond coat. The developed coating system introduces a protective top layer of MoSi₂ (top coat) for preventing diffusion of oxygen, oxidation of the bond coating, provides thermal insulation and protection against corrosion and high temperature erosion. Microstructural, thermal oxidation resistance, thermal shock and adhesion strength of TBCs were analyzed. Different properties of as-sprayed TBCs have no significant effect on thermal oxidation property. The TBCs have shown better thermal shock resistance but lower adhesion strength than the TBCs made of without MoSi₂ layer.     

Superhydrophilic and superoleophobic chitosan-based nanocomposite coatings for oil/water separation

To overcome easy oil fouling and poor efficiency of traditional oil/water separation materials, superhydrophilic and superoleophobic coatings were fabricated by spray casting chitosan (CTS)-based nanocomposites. The molecular rearrangement of hydrophilic and oleophobic constituents, combined with the hierarchical rough surface structures, enabled a coating with a water contact angle of 0° and a hexadecane contact angle of 157° ± 1°. Hexadecane droplets can easily slide off the dried and water-wetted coating without leaving any obvious oily trailing stains. When the superhydrophilic and superoleophobic CTS-based nanocomposite coatings were applied to oil/water separation, they exhibited excellent anti-fouling capacity, high separation efficiency and easy recyclability. The superhydrophilic and superoleophobic CTS-based coating would be a good candidate for the treatment of industrial oil-polluted water and the cleanup of oil spills.     

Robust superhydrophobic surface fabrication by fluorine-free method on filter paper for oil/water separation

Robust superhydrophobic surface exhibiting anti-fouling and self-cleaning ability were successfully fabricated by nano TiO2 modified by γ-aminopropyltriethoxysilane (KH550) and polydimethylsiloxane (PDMS) via wire rod coating. Due to the lower surface energy of PDMS and the hierarchical structure caused by the different aggregation sizes of TiO2 nanoparticles, the contact angle of the resulting superhydrophobic coating was 154.5° and the rolling angle was 3.5°. And the coated paper still had good non-wettability under water immersion. In addition, the coated paper was tolerant to mechanical damage and various temperature conditions. Even after 40 sandpaper wear cycles, the coating can still maintain good mechanical stability and superhydrophobicity. The superhydrophobic paper was used for oil-water separation, the separation efficiency was about 98% even after used 10 times. Furthermore, the prepared superhydrophobic paper exhibited excellent self-cleaning and anti-fouling properties, as well as demonstrated superb resistance to various water solutions owing to its high hydrophobicity. Moreover, the prepared superhydrophobic paper has application prospects in the industry of special wetting materials.     

A Study on Liquid Hybrid Material for Waveguides—Synthesis and Property of PSQ‐Ls for Waveguides

Silicate‐based inorganic‐organic hybrid polymer systems have many unique properties including thermal stability and photo‐stability, chemical resistance with the combination of tunable optical properties. Two kinds of new UV‐patternable hybrid materials PSQ‐Ls were synthesized by a sol‐gel process at room temperature, which can be used for low cost fabrication of optical waveguides. Thick films (up to 8.31 µm) can be coated by a single spin‐coating process without any cracking and the average surface roughness (Ra), detected by atomic force microscopy (AFM), is below 0.5 nm. The optical properties (refractive index, birefringence, and optical loss at 1310 nm and 1550 nm, respectively) of the PSQ‐Ls films are investigated by a prism coupler. The refractive index of PSQ‐Ls can be exactly tuned from 1.4483 to 1.5212 by blending PSQ‐LH (n_TE=1.5212 @ 1310 nm) and PSQ‐LL (n_TE=1.4483 @ 1310 nm). The maximum refractive index contrast is about 4.8%. After post‐baking, birefringences of the films are below 0.0005 and optical losses are about 0.2 dB · cm^?1 at 1310 nm, 0.7 dB · cm^?1 at 1550 nm, respectively. Furthermore, the PSQ‐Ls films also show outstanding thermal stability in air atmospheres.     

Optical, mechanical, and dielectric properties of Bi1/2Na1/2TiO3 thin film synthesized by sol–gel method

The Bi_1/2Na_1/2TiO₃ (BNT) thin film has been researched as an excellent candidate of lead-free ferroelectric materials. We synthesized BNT thin film on Si wafers or quartz glass by sol–gel spin coating method. The homogeneous and crack-free BNT thin film was synthesized by cost effective solution sol gel coating method. The main crystal phase of the film was identified as Bi_1/2Na_1/2TiO₃. The BNT thin film which was coated 3 times and heat-treated at 700 °C had about 70% of transmittance in the ultra-violet visible (UV–VIS) light wavelength region. The calculated band gap energies from the UV transmittance spectra were 3.0 and 3.5 eV for indirect and direct transition, respectively and the refractive index of BNT thin film was 2.16 at 898 nm of wavelength. The hardness and elastic modulus of the film were about 9 and 136 GPa at 10 mN load, where the penetration depth was about 220 nm. BNT thin film showed the diffuse type of dielectric properties due to its Na⁺ and Bi³⁺ ions in A′_1/2A″_1/2BO₃-type perovskite structure and the dielectric constant was about 10 until 300 °C and showed maximum value at 550 °C, 450 at 1 kHz.     

Water vapour barrier performance of corn-zein coated polypropylene (PP) packaging films

The novel film structure of corn-zein coated on polypropylene (PP) synthetic film for packaging industry was developed to examine the feasibility of resulting coated films as an alternative water barrier performance for food packaging. The effects of coating formulation (solvent, corn-zein, plasticizer concentration and plasticizer type) on final properties of films were observed. Corn-zein is the most important protein of corn and has good film forming property. Composites structures of PP films coated with corn-zein were obtained through a simple solvent casting method. Polyethylene glycol (PEG) and glycerol (GLY) were used as plasticizer to increase film flexibility. Statistical analysis based on full factorial design was performed to observe coating formulation effects. The high water vapour barriers were obtained for films coated with coating formulation consisting of higher amounts of corn-zein plasticized by GLY. The lower glass transition temperatures (T _g) of films were obtained by plasticization of films and T _g decreased by increasing plasticizer content. The statistical analysis defined the key parameters of coating formulation that had major effects on the final properties of coated PP films as corn-zein, plasticizer concentration and plasticizer type. In conclusion, corn-zein coatings could have potential as an alternative to conventional synthetic polymers used in composite multilayer structures for food packaging applications.     

Inorganic-Organic Polymers as Migration Barriers Against Liquid and Volatile Compounds

In addition to the barrier properties against water vapor and oxygen, inorganic-organic polymers can also function as protection layers against unwanted migration of chemical substances in two ways. First, hybrid polymers prevent components from migrating out of polymer substrates. This is of special interest for polymeric materials containing substances like plasticizing agents, unreacted monomers or catalysts. Thus the olfactory nuisance and the toxicological emission are decreased. The plastics are also prevented from becoming prematurely brittle. Second, the coated materials are also protected against the interaction of dyes or dirt staining the material.These functions can be achieved by thermally or UV curable coating materials, synthesized by the sol-gel technique. Since several polymer materials show only a low heat resistance (e.g. PVC, polyolefines), this publication is focussed on the development of new migration barriers based on photochemically curable sols.Another advantage of the UV process in comparison to thermal treatments are the short curing times and low power consumption which make this process even more attractive for industrial applications. The coatings were characterized by IR and solid state NMR spectroscopy. The migration barrier properties were tested according to industrial standards.Due to the choice of specific functional groups, these hybrid polymers can be further modified in order to combine the migration barrier function with additional properties: scratch and abrasion resistance, hydrophobicity, antistatic effects. Examples of feasible combinations of properties are also given.