This is an editorial article. It has no abstract.
In the current research, to develop the morphology and improvement of electrical conductivity at low levels of graphene nanoplates (GNPs); the effect of polyolefin elastomer (POE) and graphene content on morphology, mechanical and electrical properties of polylactic acid (PLA) was investigated. Different Blends with and without compatibilizer were prepared via melt mixing process in an internal mixer through masterbatch approach. Co-continuous morphology was obtained at the ratio of 60/40 (wt%/wt%) of PLA/POE. By considering the wetting coefficient, it was predicted that graphene nanoplates have more affinity to the POE phase than PLA, which was confirmed by microscopic observations. The electrical percolation threshold was seen at 0.5–1 wt% of graphene, while the rheological percolation threshold was obtained at 0.2–0.5 wt%. The addition of POE and graphene to PLA led to balancing elongation at break and tensile strength of final products.
A series of novel shape memory and self-healing composites of natural rubber (NR) and polycyclooctene (PCO) were designed using a simple physical blending method. These two polymers were selected with the intent of introducing network flexibility and mobility into the prepared blends. The mechanical, curing, thermal, shape memory, and thermally assisted self-healing properties of the NR/PCO composites were investigated in this study. In these composites, the crosslinked network generated in both the NR and PCO portions acted as a fixed phase, while the crystalline regions of the PCO portions acted as a reversible phase in the shape memory behavior. The composites showed self-healing properties at an elevated temperature (90 °C), which was attributed to molecular chain interdiffusion processes. Shape memory and thermally assisted self-healing properties were improved by increasing polycyclooctene content. The NR/PCO showed superior mechanical, shape memory, and self-healing properties (Rf = 94.57%, Rr = 98.92% and healing efficiency = 19.03%) when the blending ratio was 50/80. Due to these superior properties, this kind of natural rubber-based composites may have the potential to be used in intelligent and thermal-response shape memory fields.
The role of entanglement of polymer chains in the merging and consolidation of polypropylene (PP) powder grains was elucidated. The entanglement density was varied by the dissolution of PP and precipitation. The differently entangled powders were sintered, without melting, applying severe plastic deformation by equal channel multiangular extrusion (ECMAE). Compaction by ECMAE resulted in healing of the interparticle pores, as well as the formation of a fibrillar structure, more significant in the case of disentangled PP. Lower entanglement density also led to the formation of thicker interfaces and to new crystals due to the strain-induced crystallization of slacks between entanglement knots. The consolidation of disentangled powder was drastically better than entangled PP powder: the yielding in compression occurred via crystallographic slips in the sintered disentangled powder while in the entangled PP powder through a series of weak elements and defects, due to much poorer compactness and cohesion. It was suggested that better consolidation of disentangled PP powder is due to reptation of longer slacks between entanglement knots and also due to sideway motions of their loops.
Grafted poly(vinylidene fluoride) (PVDF)-based copolymers attract great attention due to their tunable ferroelectric and dielectric characteristics, which gives great perspectives for electronic applications. In this work, two strategies for polyacrylonitrile-grafted PVDF-based copolymers synthesis, namely single electron transfer radical polymerization (SET-LRP) and photoinduced Cu(II)-mediated reversible deactivation radical polymerization (RDRP) were investigated, their advantages and shortcomings are discussed. Using these methods two series of poly(vinylidene fluoride-co-chlorotrifluoroethylene)-grafted-polyacrylonitrile p(VDF-co-CTFE)-g-PAN and poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene)-grafted-polyacrylonitrile p(VDF-co-TrFE-co-CTFE)-g-PAN with different PAN content were prepared. Important characteristics of the grafted PVDF-based copolymers such as phase behavior, thermal stability, and dielectric properties were investigated, and impacts of the macromolecular backbone type, as well as the content of grafted PAN on these properties, are discussed. It was shown that PAN incorporation leads to significant dielectric properties change since the dielectric permittivity of PAN-grafted copolymers is twice higher in comparison to the pristine copolymers. The crucial impact of PAN grafting onto PVDF-based copolymers backbone on their phase, thermal and dielectric behavior is demonstrated.
The present research aims to clarify the friction and wear behavior, the transfer layer formation, and the wear mechanism of mono-filled polytetrafluoroethylene (PTFE). A well-known limitation of PTFE is the low wear resistance, which can be surpassed with the use of micro- or nanoparticles. The applied fillers were graphene, alumina (Al2O3), boehmite alumina (BA80), and hydrotalcite (MG70). The samples were produced by room temperature pressing – free sintering method. All specimens were tested with a pin-on-disc tribo-tester in dry contact condition against 42CrMo4 steel disc counterface with 3 MPa contact pressure and 0.1 mm/s sliding speed. PTFE filled with 4 wt% Al2O3 achieved the highest wear resistance; the increase was more than two orders of magnitude compared to the neat PTFE. This improvement comes from the protective transfer layer formation due to the Al2O3 and the iron-oxide accumulation on the polymer contact surface. Significant wear-induced crystallinity was also registered, which originated from the mechanical chain scission of the PTFE molecular chains during the wear process.
The production of poly(lactic acid) (PLA) biodegradable blends with other biopolymers, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and the introduction of carbon nanotubes (CNT) are promising solutions for electrical and electromagnetic application. PHBV has a great potential to improve the processing and toughness of PLA. The addition of CNT contributes to the electrical and electromagnetic properties of polymeric nanocomposites. PLA/PHBV blend (80/20) and PLA/PHBV blend-based nanocomposites with 0.5 and 1.0 wt% of CNT were produced. Morphology images showed the homogeneous dispersion of PHBV domains in PLA, and that CNTs are preferably dispersed in the PHBV phase. The CNT acted as a nucleating agent for the crystallization of PHBV and did not affect the thermal stability of the nanocomposites. CNT reduced the Izod impact strength; however, flexural properties were not affected. The addition of 1.0 wt% CNT resulted in better electrical properties (2.79・10–2 S/m) and an excellent result as electromagnetic interference shielding material (attenuation of approximately 96.9% of the radiation in X-band). Biodegradable nanocomposite based on PLA/PHBV blend reinforced with 1.0 wt% CNT presented interesting properties for possible applications in electronic device and military sectors.
Carbon fibers (CFs) are commonly applied reinforcement material in various composites to improve their mechanical, thermal, or electrical properties. The physical and chemical state of the interface, the chemical bonds, and adhesion between the fiber and matrix have a great influence on certain properties of the composite, including the mechanical ones. The originally low adhesion between the CFs and the matrix material can be improved by employing non-equilibrium plasma for surface treatment of the fiber. In the present study, we compared the effect of an atmospheric dielectric barrier discharge (DBD) and a low-pressure radio frequency (RF) plasma processing on poly(acrylonitrile) based and sized CFs in terms of surface chemistry, morphology, and adhesive properties of the treated fibers. It was found that atmospheric DBD plasma treatment induced greater changes in the surface properties of the CFs as compared to RF plasma. The DBD treated CF surface became more oxidized, increasing the O/C ratio by 30%, while reaching a twofold increase in the roughness. Surface adhesion improved after both plasma treatments, but it was significantly higher after the atmospheric DBD process.