This is an editorial article. It has no abstract.
Low molecular weight polyesters were end-functionalized with ammonium and carboxylate salts and used in ionic exchange reactions with respectively cationic (MMT) and anionic (LDH) clays. The hybrid organic-inorganic substrates were structurally analysed to determine the ester oligomers’ modification degree and their thermal behaviour owing to confinement effects. The dispersion of such hybrids in polylactic acid (PLA) matrix was performed and the ultimate structural, morphological and thermal properties of the collected nanocomposites were investigated and correlated to the tailored interfacial properties with the different inorganic substrates. While the composites with MMT proved to be stable under thermo-oxidative conditions, the samples obtained by dispersing the LDH hybrid suffered from poor final thermostability owing to molecular weights decrease. Deeper insights about the effect of the interactions at interface (polymer chain-surfactant and polymer chain- inorganic surface) evidenced that by promoting an intimate contact between PLA chains and LDH surface (through oligoester used as inorganic substrate modifier) a certain extent of PLA hydrolysis triggered by both surfactant and inorganic surface (LDH) occurred and cannot completely avoided.
Electroactive films of thiophene-acrylate polymers were simultaneously photopolymerized by means of ultraviolet (UV) irradiation using diphenyliodonium hexafluorophosphate and acrylate special photoinitiators (PIs) as a mixed photoinitiator. Free radicals from PIs can promote cationic polymerization of thiophenes. Electrical conductivity and transmittance of the electroactive film are high to 10–2 S•cm–1 and >90%. Electroactivity of the photopolymerized polymer film was confirmed by electro-polymerization of aniline on this film in aqueous solution and employed to assemble a full polymer electrochromic device having a superior optical contrast of 36.6%.
Polyhydroxyalkanoate (PHA) composites containing multi-walled carbon nanotubes (MWCNTs) were prepared using a process of melt-blending three-dimensional (3D) printing filaments. Maleic anhydride (MA)-grafted polyhydroxyalkanoate (PHA-g-MA) and chemically modified MWCNTs (MWCNTs-COOH) were used to improve the compatibility and dispersibility of the MWCNTs within the PHA matrix. Structural, morphological, thermal and mechanical characterisations revealed dramatic enhancements in the thermal and mechanical properties of the PHA-g-MA/MWCNTs-COOH composites compared with PHA, because of the formation of ester carbonyl groups through the reaction between MA groups of PHA-g-MA and the carboxylic acid groups of the MWCNTs-COOH. For example, with an addition of 1.0 wt% of MWCNTs-COOH, the initial decomposition temperature and tensile strength at failure increased by 72 °C and 16.0 MPa, respectively. Moreover, MWCNTs or MWCNTs-COOH enhanced the antibacterial activity and static dissipative properties of the composites. Composites of PHA-g-MA or PHA containing MWCNTs or MWCNTs-COOH had better antibacterial activities and antistatic properties.
Using molecular dynamics simulations and a simple model for chain molecules we study the gel formation under different conditions. The main characteristic of the model is the short attractive range of the non-bonding interaction, which leads to the formation of a single percolated cluster trapped in long lived metastable state that resemble the properties of polymeric physical gels. The gels are formed by imposing a sudden quenching on well equilibrated high temperature conformations. In particular, we investigated the effect of concentration and polymer persistence length on the resulting percolated structures. Using a Monte Carlo approach, we characterize the size of the cavities that develop inside the bulk of the gels. The results show that polymers with higher persistence length produce gel structures with smaller cavities.
The paper focuses on a series of blends prepared with different contents of polystyrene-block-poly-(ethylene-ranbutylene)-block-polystyrene (SEBS) and polypropylene (PP) for the purpose of examining the potential as proton exchange membranes. Polymer blends were prepared by twin-screw extrusion and then compressed by means of a hot-press device into thin films of 125 µm and then ionic sides were created by solid state sulfonation in a chlorosulfonic acid solution. Obtained films were characterized by means of water-uptake, mechanical properties, ion-exchange capacities (IEC) and ion conductivities. It was observed that the rigidity of the films increased with rising sulfonation durations. However humidity absorption from the air decreased the rigidity at high sulfonation levels. Improved water uptake values were obtained when compared to previously reported values in the literature. On the other hand ion exchange values showed an increase parallel to the sulfonation duration up to 45 minutes, but a decrease thereafter was observed due to the diffusion of some sulfonated polymer chains into the ion-exchange medium thereby calculated ion exchange values of S-SEBSH45 and S-SEBSH60 were found less than expected. All films showed ion conductivities up to 432 mS/cm at 25 °C. Only S-SEBSH45 and S-SEBSH60 were successful in conducting protons at 80 °C owing to the high water retaining capacity.
A new self-lubricating, wear resistant epoxy resin material (ER+DCi) has been obtained by addition of a 9 wt.% of the room-temperature protic ionic liquid (PIL) tri-[bis(2-hydroxyethyl)ammonium)] citrate (DCi) to the mixture of the prepolymer and the hardener composed of a mixture of amines. The highly polar tricationic protic ammonium carboxylate ionic liquid shows a high contact angle on the resin surface and distributes inside the epoxy matrix as spheres of around 50 µm in diameter, with a mean density of approximately 38 mm2. The presence of the ionic liquid fluid phase inside the cavities has been determined by SEM observation of fracture surfaces and FTIR microscopy. The DCi phase reduces the residual curing enthalpy and the glass transition temperature, as determined by DSC, without significantly changing microhardness or electrical resistivity values. DMA analysis shows that DCi reduces storage modulus, loss modulus and tan δ values. The tribological performance of the new material has been compared with that of the neat epoxy resin under pin-on-disc sliding conditions. ER+DCi shows more than 50% reduction of the friction coefficient with respect to neat epoxy resin, and no surface damage, in contrast with the severe wear that takes place in the case of neat epoxy resin. A self-lubrication mechanism by release of the ionic liquid lubricant under load is proposed.
In the present work, the development and characterization of an intrinsically self-healable material based on butyl imidazole modified bromobutyl rubber (BIIR)/natural rubber (NR) blends, which are filled with carbon nanotubes (CNTs) are reported. It was found that the addition of CNTs and the blending with NR significantly enhance the tensile strength of the BIIR composites. The use of butyl imidazole as physical cross-linker for the BIIR phase provides the blend composites the non-covalent bondings, which are responsible for their self-healing properties. Owing to the increase of the viscosity of the BIIR phase upon its physical crosslinking the island-matrix morphology of the blend changes over to a co-continuous structure. The preferential wetting of the CNT surface by the low-loading NR phase in the NR/BIIR blends can be explained by the good rubber-filler interaction between the linked phospholipids of the NR molecules and the π-electrons of the CNT surface. As a result, the favored localization of the CNTs in the NR phase strongly improves the electrical properties of the blends according to the double percolation theory. On the other hand it does not deteriorate the self-healing of the BIIR phase. The high electrical conductivity provides us a possibility to heat the blend by application of an electrical voltage in order to accelerate the self-healing process.