Insights into the Improved Gas Barrier Properties of Polyurethane-Clay Nanocomposite-Coated Nylon: A Solid-State NMR Study

Herein, the reason for the improvement in the gas barrier properties of polyurethane (PU)-clay nanocomposite-coated nylon fabric compared to unfilled PU-coated nylon fabric is investigated by probing the changes in relaxation times of PU using solid-state nuclear magnetic resonance (SS NMR) spectroscopy. The interaction of the organically modified montmorillonite (MMT) clay (Cloisite 30B) with polyurethane (PU) in PU-clay (0.5/1/2 wt %) nanocomposites was probed with respect to the change in the spin-lattice relaxation time of protons in the PU chain due to the presence of paramagnetic species in clay (T1H, para). The better the dispersion of the clay in the PU matrix, the lower the T1H, para, due to the interaction between clay and the PU matrix. 0.5 wt % PU-clay has lower T1H, para, (6.4 s) compared to 1 wt % (18.3 s) and 2 wt % (14.3 s) filled systems. The SS NMR findings are in good agreement with field-emission scanning electron microscopy (FE-SEM) analyses. In SEM microscopic images, it is observed that the PU-0.5 wt % clay has better exfoliation of clay compared to the 1 and 2 wt % PU-clay nanocomposites. This is in agreement with improved gas barrier properties of the nanocomposite coated on the nylon fabric for 0.5 wt % clay (2300 mL/m2/day) compared with 1 wt % (2500 mL/m2/day) and 2 wt % clay (2600 mL/m2/day)-incorporated PU-coated fabrics and neat PU-coated nylon fabric (4500 mL/m2/day) at 260 GSM.

Obtaining the Dimensions and Orientation of 2D Rectangular Flakes from Sectioning Experiments in Flake Composites

Recently, we developed and reported the statistical validity of two methods for determining the planar aspect ratios of two-dimensional (2D) rectangular flakes in composites from the statistics of intersection lengths: one method is based on the maximum intersection length, and the other on the average intersection length. In this work, we show that these methods are valid and robust not only for flakes having isotropic, random in-plane orientations, but for the more general situations of planar orientations ranging from unidirectional (misalignment angle ϵ=0), to partially aligned (0<ϵ<π/2), to flakes of isotropic, random-in-plane orientations (ϵ=π/2). We prove, by Monte Carlo simulations and by numerical sectioning experiments, the validity of the proposed methods for characterizing the extent of the partial alignment (the misalignment angle ϵ) of 2D rectangular flakes in composites, based again on the statistics of the intersection lengths; this information can be obtained from cross-sections of composite samples used in optical or electron microscopy or using tomographic imaging techniques. The performance of these techniques was tested using blind experiments in numerically sectioned composites which contained up to 106 individual flakes, and was found to be very good for a wide range of flake aspect ratios.

A Novel Method for the Determination of the Lateral Dimensions of 2D Rectangular Flakes

We present a novel method for the determination of the lateral dimensions of thin rectangular flakes, as they exist randomly dispersed in flake composites. Knowledge of flake size and shape is essential for the correct prediction of the mechanical, electrical, thermal and barrier properties of flake composites. The required information is the distribution function of lengths of the lines representing the intersection of flakes with a sectioning plane, as seen in cross-sections of composite samples used in optical or electron microscopy or obtained using tomographic imaging techniques. The key observation is that the major peak of the distribution function coincides with the short dimension S of the flake while a secondary peak corresponds to its long dimension W. These observations are explained using Monte-Carlo simulations, as well as deterministic, geometry-based modeling and probability analysis. Since the strength of the secondary peak diminishes with increasing flake aspect ratio r=W/S, we develop two additional methods for the determination of W. The first finds W from the maximum intersection length; this procedure is justified by computing the relevant probability fields through Monte-Carlo simulations. The second method finds r from the average intersection length and is valid in the range 1<r<15. The performance of these techniques is tested and found to be very good using blind experiments in numerically sectioned specimens.

Self-Compounded Nanocomposites: toward Multifunctional Membranes with Superior Mechanical, Gas/Oil Barrier, UV-Shielding, and Photothermal Conversion Properties

Nanocomposites combine multiple favorable properties to achieve intriguing functionalities, but the formation of nanocomposites with only one constituent with the inclusion of multiple superior properties is still not known. Herein, novel self-compounded nanocomposite membranes from one single polymer-cellulose cinnamate (CCi)-with multiple outstanding properties are reported. The self-compounded membranes contain two distinct morphologies as CCi nanoparticles (CCi-NPs) and a CCi polymer matrix, while CCi-NPs are either firmly embedded in the CCi matrix or fused with adjacent CCi-NPs. The unique self-compounded nanostructure endows the membranes with a tensile strength of 94 MPa and Young's modulus of 3.1 GPa. The water vapor permeability, oxygen permeability, and oil permeability reach as low as (0.94 ± 0.03) × 10^-11 g m^-1 s^-1 Pa^-1, (8.48 ± 2.39) ×10^-13 cm³·cm/cm²·s·cmHg, and 0.008 ± 0.003 g mm m^-2 day^-1, respectively. Moreover, self-compounded CCi nanocomposite membranes also demonstrate UV-shielding and photothermal conversion properties. UVB and UVC light are entirely blocked, while UVA light is partly blocked. The temperature increases from room temperature to 120 °C within 1 min under UV irradiation. In addition, CCi membranes also show remarkable thermal and humidity resistance. Based on these outstanding properties, CCi membranes are applied as food packaging materials. This work offers a new avenue to construct nanocomposites with multiple superior properties from one constituent, which is promising for diverse applications.

High Oxygen and Water-Vapor Transmission Rate and In Vitro Cytotoxicity Assessment with Illite-Polyethylene Packaging Films

This work reports the preparation of a ceramic hybrid composite film with illite and polyethylene (illite-PE), and the evaluation of the freshness-maintaining properties such as oxygen transmission rate (OTR), water vapor transmission rate (WVTR), tensile strength, and in vitro cytotoxicity. The particle size of the illite material was controlled to within 10 μm. The illite-PE masterbatch and film were prepared using a twin-screw extruder and a blown film maker, respectively. The dispersity and contents of illite material in each masterbatch and composite film were analyzed using a scanning electron microscope (SEM) and thermogravimetric analyzer (TGA). In addition, the OTR and WVTR of the illite-PE composite film were 8315 mL/m2·day, and 13.271 g/m2·day, respectively. The in vitro cytotoxicity of the illite-PE composite film was evaluated using L929 cells, and showed a cell viability of more than 92%. Furthermore, the freshness-maintaining property was tested for a packaging application with bananas; it was found to be about 90%, as indicated by changes in the color of the banana peel, after 12 days.

Filler-Modified Castor Oil-Based Polyurethane Foam for the Removal of Aqueous Heavy Metals Detected Using Laser-Induced Breakdown Spectroscopy (LIBS) Technique

The use of polymeric material in heavy metal removal from wastewater is trending. Heavy metal removal from wastewater of the industrial process is of utmost importance in green/sustainable manufacturing. Production of absorbent materials from a natural source for industrial wastewater has been on the increase. In this research, polyurethane foam (PUF), an adsorbent used by industries to adsorb heavy metal from wastewater, was prepared from a renewable source. Castor oil-based polyurethane foam (COPUF) was produced and modified for improved adsorption performance using fillers, analyzed with laser-induced breakdown spectroscopy (LIBS). The fillers (zeolite, bentonite, and activated carbon) were added to the COPUF matrix allowing the modification on its surface morphology and charge. The materials were characterized using Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and thermal gravimetry analysis (TGA), while their adsorption performance was studied by comparing the LIBS spectra. The bentonite-modified COPUF (B/COPUF) gave the highest value of the normalized Pb I (405.7 nm) line intensity (2.3), followed by zeolite-modified COPUF (Z/COPUF) (1.9), and activated carbon-modified COPUF (AC/COPUF) (0.2), which indicates the adsorption performance of Pb²⁺ on the respective materials. The heavy metal ions’ adsorption on the B/COPUF dominantly resulted from the electrostatic attraction. This study demonstrated the potential use of B/COPUF in adsorption and LIBS quantitative analysis of aqueous heavy metal ions.