Morphological Origin of the Multistep Relaxation Behavior in Semicrystalline Ethylene/Methacrylic Acid Ionomers

Flexible Composite Films Made of EMAA-Na+ Ionomer: Evaluation of the Influence of Piezoelectric Particles on the Thermal and Mechanical Properties

Studies that aim to produce flexible films of composite materials based on ionomers-PZT, and volume fractions lower than 10% PZT, in order to monitor damage in aeronautical structures are seldom investigated. The growing emphasis on the use of polymers capable of self-healing after damage or activation by heating has motivated the application of self-healing ionomers as polymeric matrices in composites with piezoelectric particles aiming to monitor damage. Flexible composite films were developed based on the self-healing polymer matrix Surlyn^® 8940 ionomer (DuPont^TM—Wilmington, DE, USA) and PZT particles (connectivity 2–3) in volume fractions of 1, 3, 5 and 7%, with thickness around 50–100 µm. The choice of PZT volume fractions followed the preliminary requirement that establishes a final density, which is lower or at least close to the density of the materials used in aeronautical structures. Since the application of composites based on epoxy resin/carbon fibers has been increasing in the aeronautical segment, this material (with density lower than 1500 kg/m³) was chosen as a reference for the present work. Thus, due to self-healing (a characteristic of the matrix Surlyn^® 8940) combined with recyclability, high flexibility and low thickness, the flexible composite films showed advantages to be applied on aeronautical structures, which present complex geometries and low-density materials. The manufactured films were characterized by SEM, XRD, DMA and mechanical tensile tests. The results were discussed mainly in terms of the volume fraction of PZT. X-ray diffraction patterns showed coexistent rhombohedral and tetragonal phases in the PZT particles-dispersed composite, which can potentialize the alignment of ferroelectric domains during polarization under strong electrical field, enhancing dielectric and piezoelectric properties toward sensing applications. DMA and tensile testing results demonstrated that the addition of PZT particles did not impair either dynamic or quasi-static mechanical performance of the flexible composite films. It was concluded that the PZT volume fraction should be lower than 3% because, for higher values, the molecular mobility of the polymer would suffer significant reductions. These findings, combined with the high flexibility and low density of the ceramic particle-filled thermoplastic polymer, render the developed flexible composite film a very promising candidate for strain and damage sensing in aeronautical structures.

Mechanical Properties of Poly(ethylene-co-methacrylic acid) Reinforced with Carbon Fibers

The capability of poly(ethylene-co-methacrylic acid) (E/MAA) to self-heal is well known, however, its mechanical properties are weak. In this study, composites with single and double layers of unidirectional (UD) carbon fibers were prepared by compression molding. Even a low mass fraction of fibers substantially improved the polymer. The flexural and tensile properties were tested at 0°, 45° and 90° fibers direction and compared to those of the matrix. The mechanical properties in the 0° direction proved superior. Flexural properties depended on the reinforcement distance from the stress neutral plane. The tensile modulus in the 0° direction was 13 times greater despite only a 2.5% mass fraction of fibers. However, both tensile modulus and strength were observed to degrade in the 90° direction. Dynamic mechanical analysis showed the dependence of both structure and properties on the thermal history of E/MAA. Tensile tests after ballistic impact showed that the modulus of the self-healed E/MAA was not affected, yet the strength, yield point, and particularly the elongation at break were reduced. A composite with higher fiber content could be prepared by mixing milled E/MAA particles in fibers prior to compression.

Temperature and Time Dependence of the Solvent-Induced Crystallization of Poly(l-lactide)

The role of organic solvents in governing the crystallization and morphology of semi-crystalline poly-l-lactide (PLLA) sheets was systematically investigated. Three different organic solvents; ethyl acetate (EA), o-dichlorobenzene (ODCB), and nitrobenzene (NB), with a solubility parameter analogous to PLLA and with a high capability of swelling, were chosen. It has been witnessed that the degree of crystallization and crystal morphology depends highly on the degree of swelling and evaporation rate of the solvent. Besides, the temperature and time of treatment played a significant role in the crystallization of polymers. The effect of different solvents and curing times are reflected by the measured X-ray diffraction (XRD) peaks and the differences are best shown by the unit cell size. The largest variation is observed along the c-axis, indicating shorter bonds, thus, showing better conformation after NB and ODCB treatment. The percentage of crystallinity calculated using the classical relative crystallinity index of XRD shows closer values to those calculated with differential scanning calorimetry (DSC) data, but a huge variation is observed while using the LeBail deconvolution method. The strong birefringence of polarised optical micrograph (POM) and the crystal morphology of scanning electron micrograph (SEM) also evidenced the orientation of polymer crystallites and increased crystallinity after solvent-supported heat treatment.

A High Barrier and Sustained Release Oxygen-Absorbing Ionic Polymer for Food Packaging Applications

Development and utilization of oxygen absorbing materials for food and beverage packaging are important to protect the oxygen-sensitive foods. In this study, we developed a kind of ionic polymer with excellent oxygen absorbing ability based on reacting ethylene-acrylic acid copolymer (EAA) and sodium sulfite (Na₂ SO₃ ). By virtue of the hydrophilicity of the ionic polymer, the sulfite in Na₂ SO₃ is easily hydrolyzed and ionized. The oxygen inhalation reaction was gradually initiated and started, whereas achieved a slow and controllable oxygen absorption process. The oxygen absorbing agent can be directly added in the form of an auxiliary agent, which greatly simplifies the preparation process of the oxygen absorbing material. Furthermore, the ionic structure of the EAA/Na₂ SO₃ composites were destroyed and mechanical properties of the material did not decrease after oxygen absorption. More importantly, it can effectively prevent the entry of external oxygen because the ionic polymer itself has better barrier properties. PRACTICAL APPLICATION: Typical oxygen-sensitive objects include: beer, coffee, canned food, meat products, dairy products, and so on. The presence of oxygen in the package can cause microbial growth, odor generation, color change and nutrient loss, resulting in a significant reduction in food shelf life. Therefore, controlling the oxygen content of the food package is important to limit the rate of these spoilage and spoilage reactions in the food. Materials with active oxygen scavenging and good barrier properties and packaging performance are highly economically viable in terms of improving product quality and reducing packaging costs.

Structural, Thermal, and Gas-Transport Properties of Fe3+ Ion-Exchanged Nafion Membranes

The physical and gas-transport properties of Fe³⁺ cross-linked Nafion membranes were examined. Wide-angle X-ray diffraction results revealed a lower crystallinity for Nafion Fe³⁺ but showed essentially no changes in the average chain spacing upon cation exchange of Nafion H⁺. Raman and Fourier transform infrared spectroscopy techniques qualitatively measured the strength of the ionic bond between the Fe³⁺ cations and sulfonate anions. Thermal gravimetric analysis indicated that the incorporation of Fe³⁺ adversely affected the thermal stability of Nafion due to the catalytic decomposition of perfluoroalkylether side chains. Gas sorption isotherms of Nafion Fe³⁺ measured at 35 °C up to 20 atm exhibited a linear sorption uptake for O₂, N₂, and CH₄ following Henry's law and slight concave behavior for CO₂. Pure-gas permeation results showed reduced gas permeability but higher permselectivities compared to Nafion H⁺ with αN₂/CH₄ = 4.0, αCO₂/CH₄ = 35, and αHe/CH₄ = 733 attributable to the strong physical cross-linking effect of Fe³⁺ that caused chain stiffening with enhanced size-sieving behavior. Gas mixture permeation experiments using 1:1 molar CO₂/CH₄ feed demonstrated reduced CO₂ plasticization for Nafion Fe³⁺. At 10 atm CO₂ partial pressure, CO₂/CH₄ selectivity decreased to 28 from the pure-gas value of 35, which was a significant improvement compared to the performance of a Nafion H⁺ membrane.

Nanoscale Aggregation in Acid- and Ion-Containing Polymers

In this review we summarize recent efforts in understanding nano-aggregation in acid- and ion-containing polymer systems. The acid and ionic groups have specific interactions that drive aggregation and alter polymer behavior at the nano-, micro-, and bulk length scales. Advancements in synthetic methods, characterization techniques, and computer simulations have enabled researchers to better understand the morphologies and dynamics, particularly at the nanoscale. This overview of recent advancements in nano-aggregated polymer systems highlights the current understanding of the field and presents promising directions for future investigations and new applications.

Molecular relaxation and dynamic rheology of “cluster phase”-free ionomers based on lanthanum(iii)-neutralized low-carboxylated poly(methyl methacrylate)

La(iii)-neutralized low-carboxylated poly(methyl methacrylate)-based ionomers free of cluster phase exhibit a fluid-to-solid transition assigned to an interconnected multiplets network.

Nanoscale morphology in precisely sequenced poly(ethylene-co-acrylic acid) zinc ionomers

The morphology of a series of linear poly(ethylene-co-acrylic acid) zinc-neutralized ionomers with either precisely or randomly spaced acid groups was investigated using X-ray scattering, differential scanning calorimetry (DSC), and scanning transmission electron microscopy (STEM). Scattering from semicrystalline, precise ionomers has contributions from acid layers associated with the crystallites and ionic aggregates dispersed in the amorphous phase. The precisely controlled acid spacing in these ionomers reduces the polydispersity in the aggregate correlation length and yields more intense, well-defined scattering peaks. Remarkably, the ionic aggregates in an amorphous, precise ionomer with 22 mol % acid and 66% neutralization adopt a cubic lattice; this is the first report of ionic aggregate self-assembly onto a lattice in an ionomer with an all-carbon backbone. Aggregate size is insensitive to acid content or neutralization level. As the acid content increases from 9.5 to 22 mol % at approximately 75% neutralization, the number density of aggregates increases by approximately 5 times, suggesting that the ionic aggregates become less ionic with increasing acid content.