Moisture Barrier Properties Research Articles

Printed and Laser-Scribed Stretchable Conductors on Thin Elastomers for Soft and Wearable Electronics

As printed electronics is evolving toward applications in biosensing and wearables, the need for novel routes to fabricate flat, lightweight, stretchable conductors is increasing in importance but still represents a challenge, limiting the actual adoption of ultrathin wearable devices in real scenarios. A suitable strategy for creating soft yet robust and stretchable interconnections in the aforementioned technological applications is to use print-related techniques to pattern conductors on top of elastomer substrates. In this study, some thin elastomeric sheets—two forms of medical grade thermoplastic polyurethanes and a medical grade silicone—are considered as suitable substrates. Their mechanical, surface, and moisture barrier properties—relevant for their application in soft and wearable electronics—are first investigated. Various approaches are tested to pattern conductors, based on screen printing of 1) conducting polymer [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)] or 2) stretchable Ag ink and 3) laser scribing of laser-induced graphene (LIG). The electromechanical properties of these materials are investigated by means of tensile testing and concurrent electrical measurements up to a maximum strain of 100%. Performance of the different stretchable conductors is compared and rationalized, evidencing the differences in onset and propagation of failure. LIG conductors embedded into MPU have shown the best compromise in terms of electromechanical performance for the envisioned application. LIG/MPU showed full recovery of initial resistance after multiple stretching up to 30% strain and recovery of functionality even after 100% stretch. These have been then used in a proof-of-concept application as connectors for a wearable tattoo biosensor, providing a stable and lightweight connection for external wiring.

Effect of H2 addition during PECVD on the moisture barrier property and environmental stability of H:SiNx film

AbstractA hydrogenated silicon nitride (H:SiNx) film with enhanced moisture barrier property and environmental stability was developed using plasma‐enhanced chemical vapor deposition (PECVD) with the addition of H2 gas at 100°C. The moisture barrier property and film density of the 100‐nm‐thick H:SiNx film were ameliorated by increasing the H2 gas flow rate during PECVD. X‐ray photoelectron spectroscopy and Fourier‐transform infrared spectroscopy studies demonstrated that the improved performance was a result of an increase in the amount of Si–N bonds compared to hydrogen‐terminated bonds with an increase in the H2 gas flow rate. It is believed that H2 gas assisted the formation of aminosilane, which contributed to the condensation of silicon nitride by lowering the activation energy for radicalization reactions of silane and ammonia. After the 85°C/85% RH test, the optimized H:SiNx film maintained a water vapor transmission rate lower than 5 × 10−5 g/m2/day owing to the suppression of oxidation. The optimized H:SiNx film was rarely oxidized owing to the decrease in hydrogen‐terminated bonds and increase in the film density. The results indicated that the introduction of H2 gas during the PECVD process strengthened the environmental stability of the H:SiNx film.

Effects of genipin as natural crosslinker on barrier and mechanical properties of chitosan‐astaxanthin film

The aim of this research was to study the effect of genipin crosslinking (0.5, 1.0, and 1.5% (w/w of chitosan)) on moisture barrier property and mechanical strength of chitosan-astaxanthin film. The film functional properties including transparency, tensile strength (TS), elongation at break (EB), water transmission rate (WVTR), and oxygen transmission rate (OTR) were investigated. The results showed that genipin crosslinking was significantly decrease the film transparency and %EB while OTR slightly increased. Fourier transform infrared observation on the chemical-crosslinking structure showed the shifted peak at 1,720 and 1,569 cm−1, indicating the forming covalent linkage between chitosan and genipin. The morphology characterization of the film was evaluated by scanning electron microscopy and found that the crosslinked film was a rougher surface than non-crosslinked film. Chitosan-astaxanthin film with crosslinking of 1% (w/w) genipin significantly improved WVTR and TS compared to other samples. Novelty impact statement Active biodegradable packaging made from chitosan, such as chitosan film incorporated with natural antioxidants, is preferred but lack the water barrier and strong mechanical properties necessary for high moisture food application. In this study, genipin-crosslinking is not only a promising technique to improve the performance and applicability of our developed chitosan-astaxanthin film, but genipin is also a natural crosslinker and an alternative to most chemical crosslinkers which cause undesirable changes and cytotoxicity.

Preparation and characterization of whey protein isolate/chitosan/microcrystalline cellulose composite films

AbstractA bio‐based composite film was prepared using whey protein isolate (WPI), chitosan (CS) and microcrystalline cellulose (MCC). The effects of film‐forming material concentration ratio, pH value and glycerin addition on the mechanical properties, water vapour permeability and transmittance of the composite film were investigated using response surface methodology. Optimum film‐forming process conditions were obtained, including a CS/MCC concentration ratio of 1.5:1, pH 3.6 and 30% glycerin addition. Scanning electron microscopy and atomic force microscopy images showed that the surface of the WPI/CS/MCC composite films was flat, uniform and smooth. Fourier‐transform infrared spectroscopy analysis indicated that hydrogen bonds occurred between the film‐forming materials. The film‐forming materials were concluded to have good compatibility, while the WPI/CS/MCC composite film showed better mechanical properties and moisture barrier properties, which will provide a good application prospect and foundation for the food packaging industry.

Preparation and evaluation of starch-based extrusion-blown nanocomposite films incorporated with nano-ZnO and nano-SiO2

The effects of nano-ZnO and nano-SiO2 nanoparticles on the properties of starch-based films prepared by extrusion blowing were investigated in this study. New hydrogen bonds between hydroxypropyl starch (HS) and nanoparticles during the extrusion process were formed as shown by Fourier transform infrared spectroscopy (FTIR). The diffraction patterns of nanocomposite films reinforced with nano-ZnO were similar to those of nano-ZnO, except that the peak intensity decreased, whereas, the addition of SiO2 nanoparticles decreased the intensity of the main characteristic peaks, regardless of the HS and nano-ZnO reinforced films. The thermal stability, tensile strength, moisture barrier property, and surface hydrophobicity of nanocomposite films were improved with the incorporation of nano-ZnO and nano-SiO2, the finding that could be attributed to a strong interplay between nano-ZnO, nano-SiO2, and the starch matrix during the extrusion film blowing process. Similarly, the nano-ZnO/nano-SiO2 composite-reinforced films showed smooth, flat, and uniform appearances by scanning electron microscopy (SEM) and atomic force microscope (AFM) tests. In sum, Nano-ZnO and nano-SiO2 nanoparticles can be used as composite reinforcing agents for preparation of starch-based films through extrusion blowing.

Surface energy modification of graphene oxide film by silanization co-functionalized with fluorine to maximize the moisture barrier property

There is a driving necessity for moisture barrier to be flexible as organic-based optoelectronics such as organic photovoltaic devices and organic light emitting diode display devices are opting towards flexible configuration. Most as-reported researches have been focused on increasing the diffusion path of water molecule by adding filler materials in the polymer matrix to improve the water barrier property. However, the surface energy of the barrier film is also an important factor to determine the water barrier property as it controls the degree of water molecule adsorption on the barrier film surface. Herein, surface energy of the graphene oxide (GO) film was varied from 56.7 mN m−1 to 26.3 mN m−1 by combination of removing hydrophilic functional groups by fluorine-silanization and thermal reduction. Altering the surface energy successfully reduced the water permeability value of the bare GO film from 1.86 × 10−2 g mm m−2 day−1 to 6.31 × 10−3 g mm m−2 day−1 which corresponds to improvement of about 70%. Furthermore, the surface energy and the water permeability value showed the linear correlation indicating that required water permeability value can be easily manipulated by controlling the surface energy of the GO film.

Facile fabrication of thermoplastic starch/poly (lactic acid) multilayer films with superior gas and moisture barrier properties

Multilayer films comprised of thermoplastic starch (TPS) and poly (lactic acid) (PLA) were fabricated via a reactive extrusion, compression molding, and dip coating processes. Maleic anhydride (MA) modification of TPS was employed to improve the interfacial adhesion between TPS and PLA layers of the film. The level and effect of TPS modification were evaluated using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (H NMR), titration, and thermogravimetric analysis (TGA). Nanoclays were incorporated in the TPS and maleated TPS (MTPS) matrices to further enhance the physico-mechanical properties of the multilayer films. The optimized multilayer film fabricated in this study, which was the nanoclays-filled maleated thermoplastic starch and PLA multilayer film (MTPS-3C/PLA) displayed good transparency and tensile properties, and excellent moisture and oxygen barrier properties. This multilayer film assembly provided 1300% improvement in moisture barrier compared to TPS films, and 3300% improvement in oxygen barrier properties as compared to PLA films adjusted for thickness. Moreover, these multilayer films are composed of compostable, food-grade, inexpensive, and bio-based ingredients and as such they are expected to be compostable with great cost structure and environmentally friendly.

Structural and gas barrier properties of hydrogenated silicon nitride thin films prepared by roll-to-roll microwave plasma-enhanced chemical vapor deposition

Hydrogenated amorphous silicon nitride films (a-SiNx:H) have attracted attention as barrier layers to prevent the diffusion of water vapor and other gases into electronic devices. Herein, the chemical composition and physical properties of a-SiNx:H films prepared using a roll-to-roll microwave plasma-enhanced chemical vapor deposition (MW-PECVD) process at low temperatures and variable NH3/SiH4 flow-rate ratios (R) were analyzed. This study was performed to identify the factors affecting the gas permeability of these films as represented by their water vapor transmission rate (WVTR) values. The films fabricated under SiH4-rich conditions (R < 2.75) were oxidized during storage in air to produce silicon oxynitride (SiOxNy), whose properties differed from those of silicon nitride (SiNx). It was found that gas barrier properties were affected by both the film and the Si–H bond densities. Under optimal conditions, the WVTR of a 100-nm-thick SiNx single layer was as low as 7 × 10−3 g m−2 d−1, and the Si–H bond density was 6.71 × 1021 cm−3. The compressive and tensile stresses of the SiNx:H films depended on the values of R, with excellent mechanical stability and moisture barrier properties having been obtained for R = 2.75–3.00.

Self-Standing Lignin-Containing Willow Bark Nanocellulose Films for Oxygen Blocking and UV Shielding

Developing the bio-based barrier material to substitute the petroleum-based one is the trend in functional packaging applications. Utilization of the abundantly underappreciated bark biomass is attractive from the sustainability point of view; however, an upgraded approach is required to maximize the performances of the lignin-containing cellulose nanofibril (LCNF) films from willow bark. Herein, hot water extraction (HWE) and microfluidization were studied for their effect on the yield of LCNF and its film performance after treatment of aqueous p-toluenesulfonic acid. The resultant HWE films were superior to the nontreated ones regarding yield, moisture, and oxygen barrier properties. In particular, the HWE films achieved an oxygen permeability of 3 cm3·μm/m2·kPa·day at 50% relative humidity, which is among the lowest achieved for single bio-based materials and comparable to commercially available synthetic barrier films. The LCNF films attained complete blocking of UV light transmission within the wavelength range of 290–400 nm. Overall, this study shows that HWE pretreatment not only allows the recovery of high-value extracts, but also significantly improves the yield of LCNF and its barrier performances. The biocompatible, lignin-containing, and self-standing hydrophobic nanocellulose films show promise as a barrier layer against UV radiation and oxygen permeation in food packaging and other applications.

Development and properties of bacterial cellulose, curcumin, and chitosan composite biodegradable films for active packaging materials

To deal with serious environmental damage resulting from plastic packaging materials, biodegradable films using natural products have gained considerable attention. Here, we provide a simple, fast, and environmentally-friendly route to construct a biodegradable film using chitosan (CS), bacterial cellulose (BC), and curcumin (Cur). Composite films (CSn-BC-Cur) using CS with different molecular weights were investigated, and their water moisture content (MC), water solubility (WS), contact angle (CA), mechanical properties, barrier properties, and antioxidant properties were compared. The obtained films were characterized by SEM, XRD, and TGA. The results showed that chitosan with a higher molecular weight presented higher contact angles and mechanical properties, along with a lower moisture content, water vapor transmission rate, and oxygen transmission rate. Furthermore, when the composite film was placed in 95 % ethanol, it released active substances. The results suggest that these composite films can be used as promising materials for food packaging.

Epoxidised sesame oil as a biobased coupling agent and plasticiser in polylactic acid/thermoplastic yam starch blends

This work aims to improve the physicochemical properties of polylactic acid (PLA) and thermoplastic yam starch (TPS) blends using epoxidised sesame oil (ESO). We used epoxidised sesame oil from two Colombian Caribbean crops: Dioscorea rotundata and Sesamum indicum, with an oil substitution of 58.4 %. Films were obtained through extrusion and compression moulding processes. Moisture content, solubility, contact angle, and mechanical, barrier, and structural properties were determined using optical and scanning electron microscopy, infrared Fourier transform spectroscopy. Thermal analyses were also performed using thermogravimetry and differential scanning calorimetry techniques. The results suggest that the PLA and TPS interactions can be improved with the addition of ESO as coupling agent, enhancing the interfacial adhesion between the polymers, and favouring the smoothness of the film surface. Furthermore, the ESO addition led to increased thermal stability while restricting molecular mobility, indicating a coupling agent effect. In conclusion, the use of epoxidised oil for preparing films based on high PLA content and TPS allows obtaining enhanced interfacial adhesion. Considering the above, the developed materials have potential application in semi-rigid food packaging.

P‐6.4: Enhanced Moisture Barrier Properties by the Use of Clay Nanoparticle‐embedded Nanocomposite

Organic electronic devices, such as organic light‐emitting diodes (OLEDs), are very sensitive to air environment, so it is necessary to encapsulate these devices to increase the service life[1−2]. In this study, we report a high transparent inorganic /organic multilayer barrier film, in which the inorganic layer is a high‐quality SiNx layer and the organic layer is clay nanoparticle‐embedded organic—inorganic hybrid (C—H) nanocomposite.

Moisture Barrier Properties of Silicone Rubber Surface Layers Fluorinated at Different Temperatures

In this study, direct fluorination is used to modify the surface of silicone rubber. Moisture barrier properties of the SIR surface layers fluorinated at different temperatures are evaluated by moisture absorption experiments at a temperature of 30 or 60°C and at a relative humidity of 75 or 97%. Physicochemical characteristics of the fluorinated SIR surface layers are investigated on the basis of ATR-IR, XPS and SEM techniques. The moisture absorption measurements show that the fluorinated surface layer has a distinct moisture barrier to the entry of water into the interior of SIR at each humidity and temperature condition, and a close association of the barrier properties with fluorination temperature or physicochemical characteristics of the fluorinated layer. The barrier is particularly significant for such a surface layer fluorinated at a lower temperature, which has higher fluorine content and compactness although a small thickness, compared to the surface layer fluorinated at higher temperatures. In addition, fitting analysis of the experimental data further shows a lower apparent diffusivity of the surface fluorinated samples than the unfluorinated sample.

Environmental reliability and moisture barrier properties of silicon nitride and silicon oxide films using roll-to-roll plasma enhanced chemical vapor deposition

The moisture barrier properties and long-term reliability of flexible thin barrier films under harsh environmental conditions are crucial parameters to consider for the real-world applications of flexible electronics. In this study, we fabricated flexible barrier films of single-layer silicon nitride (SiNx) and silicon oxide (SiOx) on a polyethylene terephthalate substrate using plasma enhanced chemical vapor deposition. We investigated the stability and degradation mechanism of SiNx and SiOx barrier films at high temperature and under high humidity using water vapor transmission rate (WVTR) measurements and cyclic bending tests. The changes in chemical composition, film density, surface roughness, and WVTR were analyzed after environmental reliability tests. It was found that high temperature and high humidity induced oxidation of the SiNx and SiOx films, resulting in an increase in the surface roughness and decrease in the film density. The SiOx film was oxidized faster than the SiNx film and formed large hillocks on the surface. The WVTR values of both films increased as the reliability test time increased, especially under environmental conditions of 85 °C/85% relative humidity, with the barrier performance of the SiOx film degrading more than the SiNx film. The SiNx film displayed stable barrier performance during 10,000 cycles bending test at a fixed bending radius of 10 mm, even after harsh environmental reliability tests.

Effects of ultrasonication on the properties of maize starch/stearic acid/ sodium carboxymethyl cellulose composite film

Ultrasonic treatment can improve the compatibility between a hydrophobic material and a hydrophilic polymer. The light transmittance, crystalline structure, microstructure, surface morphology, moisture barrier, and mechanical properties of a composite film with or without ultrasonication were investigated. Ultrasound increases the film’s light transmittance, resulting in a film that has good transparency. Ultrasonication did not change the crystalline structure of the polymer film, but promoted V-type complex formation. The surface of the film became smooth and homogeneous after the film-form suspension underwent ultrasonic treatment. Compared to the control film, after ultrasonication at 70% amplitude with a duration of 30 min, the average roughness and maximum roughness declined from 212 nm to 17.6 nm and from 768.7 nm to 86.5 nm, respectively. The composite film with ultrasonication exhibited better tensile and moisture barrier properties than the nonsonicated film. However, long-term and strong ultrasonication will destroy the polymer structure to some extent.

Strategic biorefinery platform for green valorization of agro-industrial residues: A sustainable approach towards biodegradable plastics

The production of cellulose reinforced bio-composites has emerged as an efficient bio-sustainable alternative for high-quality functional polymeric materials to replace the presently dominated petroleum-based plastics. Also because, lignocellulose biorefinery from waste agro-industrial residues has attracted widespread attention for combating increasing environmental pollution caused by incineration of such wastes. In this prospect, the fractionation of tender coconut husks (TCH) to yield cellulose, hemicellulose and lignin fractions has been investigated by different pretreatment methodologies using conventional and novel reaction media. Excellent outcomes were obtained with the use of the deep eutectic solvent composed of choline chloride and oxalic acid dihydrate that led to the dissolution of 95.5% of the initial lignin in TCH to yield a cellulose fractional recovery of 87.5% at the optimal conditions attained by parametric variations. Interestingly, the same eutectic mixture also functionalized the obtained cellulose to cellulose nanocrystals (CNC) with 69% yield, crystallinity index of 88.6% and average particle size of 146 nm. Further, isolated starch from waste tamarind seeds was used as the polymer matrix wherein the CNC was added as a suitable bio-filler to cast bioplastic films using biodiesel byproduct glycerol as a plasticizer. The characterization of the biodegradable films revealed a tensile strength of 21.8 MPa along with outstanding thermal and moisture barrier properties. The results elucidate that the huge dependence for petro-plastics could be reduced with the integrated valorization of solid wastes that can aid wide-ranging industries and align with the rising motto of a bioeconomy.

Impact of heating and drying temperatures on the properties of konjac glucomannan/curdlan blend films

The impact of preparation conditions including heating temperature (from 60 °C to 90 °C) and drying temperatures (from 25 °C to 90 °C) on the properties of pure curdlan film and konjac glucomannan (KGM) and curdlan blend films were analyzed. Microstructure analysis indicated the KGM addition could significantly improve the relatively poor film-forming property of curdlan. FTIR and X-ray analysis showed that at high heating temperature 90 °C, molecular interaction might be enhanced in the films due to the stretched structure of curdlan and dissociation of curdlan bundles or triple-helix structure. This was supported by the changes in the mechanical property, surface hydrophobicity, moisture barrier, and moisture tolerance property. The impacts of drying temperature were some different for the curdlan film and KGM/curdlan blend film, and were explained from the molecular hydrophilicity-hydrophobicity, compactness of the films, curdlan conformation, and molecular interaction. This work guided biodegradable film production especially with curdlan added.

Assessment of moisture barrier, mechanical, and thermal property of base/nanophased carbon-epoxy composites in seawater

Polymeric composites absorb moisture by quick surface absorption followed by slow diffusion through the matrix in humid environment. Moisture absorption damages the matrix and interface of fiber reinforced polymer (FRP) composites and consequently, weakens their mechanical and thermal properties. Effects of seawater on mechanical and thermal behavior of base and nanophased carbon fiber reinforced epoxy polymer (CFRP) composites were investigated in this study. It was observed that moisture barrier property of carbon/epoxy composites can be improved by adding a small amount (1 to 3% by weight) of nanoclay as filler. Base and nanophased carbon/epoxy composite panels were fabricated by the vacuum assisted resin transfer molding (VARTM) process and samples were prepared from these panels for mechanical and thermal testing according to ASTM standards. Some of these samples were exposed to seawater for 180 days. Moisture intake by the samples was measured every 10 days for 90 days by which time samples reached a saturated state. Mechanical and thermal behavior of base and nanoclay-infused carbon/epoxy composites with exposure to seawater for 180 days were compared with those with no exposure to seawater for 180 days. Mechanical characterization was performed by compression test. Thermal characterizations were carried out by dynamic mechanical analysis, thermo-gravimetric analysis, and thermo-mechanical analysis tests. Results showed that the 2 wt% nanoclay loading is optimum in terms of moisture barrier capability, compression, and thermal properties. After 90-day exposure to seawater, the 2 wt% nanophased composite absorbed 0.39% moisture compared to 0.67% moisture absorption by the base carbon/epoxy composite. Compressive strength and modulus were decreased by 8.20% and 7.11% respectively, for 2 wt% nanophased composites submerged in seawater for 180 days compared with identical samples with no exposure to seawater. Corresponding data from thermal characterization tests indicate storage modulus and glass transition temperature to be 6.59% and 6.1 °C lower respectively, and the coefficient of thermal expansion to be increased by about 6% for the 2 wt% conditioned sample. SEM study revealed that the nanophased composites exhibited a better bonding between the fiber and matrix compared to the base one even after exposure in the seawater. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for enhanced durability of the nanophased carbon/epoxy composite in seawater compared to the base one in the same condition.

Sustainable atmospheric-pressure plasma treatment of cellulose triacetate (CTA) films for electronics

Surface treatments of cellulose triacetate (CTA) films via atmospheric pressure plasmas containing helium and either O2 or C3F6 as plasma reactive gas were performed to study their effects on moisture barrier, transmittance, thermal, surface chemistry, and morphological properties. Plasma treated CTA films were characterized using X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy analytical techniques. Both surface chemical and morphological changes were correlated with water vapor transmission rates (WVTRs) and contact angle measurements. XPS spectra showed that the relative chemical composition of the C 1s spectra after O2 plasma treatments exhibits an increase in the relative amount of C—C bonds, which may be due to a change in surface cross-linking. ToF-SIMS spectra showed the depth of treatment of atmospheric plasma treatment of CTA films at about 100 nm. The WVTR of the CTA film was reduced up to 20% after sustainable atmospheric O2/helium plasma, while no significant changes were observed in light transmittance. Thus, the use of sustainable atmospheric plasmas to enhance moisture barrier while maintaining other critical properties such as light transmittance, thermal stability, and morphology of a CTA film could provide significant benefits to the electronics industry.

Evaluation of beeswax coated coconut shells for packaging of set-type dahi: an Indian fermented product.

An attempt was made to develop coconut shell-based eco-friendly packaging material for the packaging of set-type dahi. Beeswax was used to improve the moisture barrier properties of coconut shell (CS). UV treatment for 60min showed complete disinfection of the coconut shell surface. The top open side of the coconut shell was sealed with aluminium foil using pectin solution as adhesive. Set-type dahi was prepared and packaged in beeswax coated CS (BCCS) and evaluated for physico-chemical, textural, sensorial and microbiological quality changes for a period of 21days at 6 ± 1°C. The rate of increase in acidity was found slower in BCCS as compared to dahi packaged in polypropylene cups (control). There was no whey separation, consequently water-holding capacity and firmness of product were better in dahi packaged in BCCS. The sensorial analysis revealed better body and texture properties for dahi packaged in BCCS. However, the flavour score of dahi packaged in BCCS decreased comparatively after 12days due to the absorption of coconut flavor by the product. These findings demonstrated the potential of coconut shell based eco-friendly packaging material for packaging set-type dahi and thereby aim to reduce the use of non-biodegradable plastics.