Strain rate and temperature dependence of the mechanical properties of polymers: A universal time-temperature superposition principle

Electromagnetic Interference Shielding Properties of Highly Flexible Poly(styrene-co-butyl acrylate)/PEDOT:PSS Films Fabricated by Latex Technology

As the use of stretchable electronic devices increases, the importance of flexible electromagnetic interference (EMI) shielding films is emerging. In this study, a highly flexible shielding film was fabricated using poly(styrene-co-butyl acrylate) (p(St-co-BA)) latex as a matrix and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a conductive filler, and then the mechanical properties and EMI shielding performance of the film were examined. Styrene and butyl acrylate were copolymerized to lower the high glass transition temperature and increase the ductility of brittle polystyrene. The latex blending technique was used to produce a shielding film in which the aqueous filler dispersion was uniformly dispersed in the emulsion polymerized resin. To determine the phase change in the copolymer matrix with temperature, the storage modulus was measured, and a time-temperature superposition master curve was constructed. The drying temperature of water-based copolymer resin suitable for film fabrication was set based on this curve. The glass transition temperature and flexibility of the blends were determined by evaluating the thermomechanical analysis and tensile tests. The EMI shielding effectiveness (SE) of the films was analyzed at frequencies from 50 MHz to 1.5 GHz, covering the VHF and UHF ranges. As the filler content increased, the SE of the blend film increased, but the elongation increased until a certain content and then decreased. The optimal content of PEDOT:PSS that satisfied both the ductility and shielding performance of the film was found to be 10 wt%. In this case, the elongation at break reached 300%, and the SE of a 1.6 mm thick film was about 35 dB. The film developed in this study can be used as an EMI shielding material that requires high flexibility.

Characterizing the shear response of polymer-grafted nanoparticles

Grafting polymer chains to the surface of nanoparticles overcomes the challenge of nanoparticle dispersion within nanocomposites and establishes high-volume fractions that are found to enable enhanced material mechanical properties. This study utilizes coarse-grained molecular dynamics simulations to quantify how the shear modulus of polymer-grafted nanoparticle (PGN) systems in their glassy state depends on parameters such as strain rate, nanoparticle size, grafting density, and chain length. The results are interpreted through further analysis of the dynamics of chain conformations and volume fraction arguments. The volume fraction of nanoparticles is found to be the most influential variable in deciding the shear modulus of PGN systems. A simple rule of mixture is utilized to express the monotonic dependence of shear modulus on the volume fraction of nanoparticles. Due to the reinforcing effect of nanoparticles, shortening the grafted chains results in a higher shear modulus in PGNs, which is not seen in linear systems. These results offer timely insight into calibrating molecular design parameters for achieving the desired mechanical properties in PGNs.

Hybrid and Synthetic FRP Composites under Different Strain Rates: A Review

As a high-demand material, polymer matrix composites are being used in many advanced industrial applications. Due to ecological issues in the past decade, some attention has been paid to the use of natural fibers. However, using only natural fibers is not desirable for advanced applications. Therefore, hybridization of natural and synthetic fibers appears to be a good solution for the next generation of polymeric composite structures. Composite structures are normally made for various harsh operational conditions, and studies on loading rate and strain-dependency are essential in the design stage of the structures. This review aimed to highlight the different materials’ content of hybrid composites in the literature, while addressing the different methods of material characterization for various ranges of strain rates. In addition, this work covers the testing methods, possible failure, and damage mechanisms of hybrid and synthetic FRP composites. Some studies about different numerical models and analytical methods that are applicable for composite structures under different strain rates are described.

Antibacterial Textile Based on Hydrolyzed Milk Casein

Antimicrobial textile structures are developed based on polypropylene (PP) and a natural material, hydrolyzed casein. The casein, from bovine milk, is subjected to acid hydrolysis in aqueous media, then blended into the PP matrix in the melt phase by extrusion. The obtained blend, containing 5 wt.% of hydrolyzed casein, is then processed by a melt spinning process to get multifilaments, leading to the production knitting structures. Thanks to the addition of the hydrolyzed casein, the obtained textile showed a strong antibacterial activity towards both Gram (+) and Gram (−) bacterial strains. The addition of 5 wt.% hydrolyzed casein does not significantly impact the mechanical properties of PP in the dumbbells form, but a small decrease was observed in the tenacity of the filaments. No moisture retention was observed after the addition of hydrolyzed casein, but the rheological behavior was slightly affected. The obtained results can contribute to addressing concerns regarding nonrenewable antibacterial agents used in textile materials, particularly their effects on the environment and human health, by offering antibacterial agents from a biobased and edible substance with high efficiency. They are also promising to respond to issues of wasting dairy products and recycling them, in addition to the advantages of using melt processes.

Phase manipulation of topologically engineered AB-type multi-block copolymers

Recent advances in the fundamental understanding of the ordered phases of multi-block copolymers (MBCPs) at the molecular level have attracted considerable scientific interest in recent years. Herein, by employing molecular dynamics simulation, we focus on the four typical systems: linear alternating, branch-like, star-like AB-type MBCPs and linear copolymers filled with nanoparticles (NPs). First, we establish the phase diagram for the linear tetrablock copolymers (ABAB) as a function of the composition ratio between A- and B-block, exhibiting six typical phase states. Furthermore, increasing the mutual repulsive interaction strength, the temperature and the periodic dynamic shearing cycle result in the merging of spheres, presenting a clear beginning of the order-to-order transition (OOT) behavior. Second, we examine the branch-like and star-like copolymers and find that increasing branch density significantly leads to the occurrence of phase transition. Particularly, we illustrate that the sphere configurations of the MBCPs can be described in terms of tail, loop and bridge conformations. Increasing the number of distinct blocks in linear alternating copolymers results in an enhancement of the bridge conformation, in which case some spheres are separated to smaller ones. Furthermore, for the tail conformation, we present a unified theoretical framework to rationalize the topological state of the chain arrangements of spheres and infer that the entanglements within the internal reaction layer between different A-blocks result in the inhomogeneous distribution of the spheres sizes even with controlled molecular weight and composition ratio between each block. Finally, we find that the ABAB tetrablock copolymers filled with moderate spherical NPs exhibit a clear OOT from spheres to double gyroid or cylinders. We infer that the maximum amount of the B-block within the second and/or third layers for the filled spherical NPs connects different NPs effectively, leading to the complicated OOT behavior. Generally, this fundamental study could provide some guidelines for designing and fabricating high performance BCPs by manipulating the formation of the ordered phases.