This is an editorial article. It has no abstract.
Based on atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) analysis of the rubber-filler gel (wetting concept) the kinetics of selective wetting of carbon nanotubes (CNTs) in ternary styrene butadiene rubber (SBR)/butadiene rubber (BR)/natural rubber (NR) blends was qualitatively and quantitatively characterized. Almost all CNTs are found to be wetted by the non-polar NR but not by the other non-polar rubber like BR or weakly polar SBR. It was proposed that phospholipids, which are linked to the α-terminal of NR can interact with the CNT surface through cation-π interactions forming strong bonding between NR and CNTs. Using the corrected surface tension value of NR, which involves the effect of phospholipids found in our previous work the selective wetting of CNTs in ternary rubber blends can be well predicted using the Z-model for a thermodynamic equilibrium state. By replacing the non-polar BR by a polar rubber like nitrile butadiene rubber (NBR) as a blend component CNTs are wetted by NBR slightly more than by NR thanks to the strong interaction between CNTs and nitrile groups of NBR. SBR remains unbound to CNTs in both blends.
A series of novel random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) (PPCE) containing neo -pentyl glycol sub-unit (P(PCExNCEy)) were synthesized and characterized in terms of molecular and solid-state properties. In addition, biodegradability studies in compost have been conducted. The copolymers displayed a high and similar thermal stability with respect to PPCE. At room temperature, all the copolymers appeared as semicrystalline materials: the main effect of copolymerization was a lowering of crystallinity degree (χc) and a decrease of the melting temperature compared to the parent homopolymer. In particular, Wide Angle X-Ray diffraction (WAXD) measurements indicated that P(PCExNCEy) copolymers are characterized by cocrystallization, PNCE counits cocrystallizing in PPCE crystalline phase. Final properties and biodegradation rate of the materials under study were strictly dependent on copolymer composition and χc. As a matter of fact, the elastic modulus and the elongation at break decreased and increased, respectively, as neopentyl glycol cyclohexanedicarboxylate (NCE) unit content was increased. The presence of a rigid-amorphous phase was evidenced by means of Dynamic Mechanical Thermal Analysis (DMTA) analysis in all the samples under investigation. Lastly, the biodegradation rate of P(PCExNCEy) copolymers was found to slightly increase with the increasing of NCE molar content.
Materials with macroporous architecture were prepared in a template-free system using linear oligo(phenylsilsesquioxanes) (Ph-LPSQ), obtained in a two-step, one-pot, acid/base sol-gel method. The spontaneous self-assembly of silsesquioxane chains is governed by π-π interactions between side substituents and facilitated by the backbone rigidity of the polymer. The porous structure of the material can be changed on adjusting the processing conditions (concentration of Ph-LPSQ solution, the ratio solvent/nonsolvent and rate of stirring during precipitation). Ph-LPSQ oligomers can be also used for modification of silica particles and preparation of interesting macro-mesoporous materials of narrow pore size. Morphology and properties of the polymer and self-assembled particles were characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies, wide angle X-ray scattering (WAXS), scanning electron microscopy SEM, mercury intrusion porosimetry, fluorescence spectroscopy and dynamic light scattering.
A novel diamine monomer α,α'-bis(2-aminophenoxy)-p-xylene (2APX) was synthesized and condensed with four different dianhydrides to prepare a series of polyimides. Aminopropyl terminated polydimethylsiloxane (PDMS) was incorporated within the backbone of polyimides for the preparation of poly(imide siloxane) copolymers. Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopic studies accompanied by elemental and single crystal X-ray analysis were performed for structure elucidation of 2NPX and 2APX. The crystal system of the 2NPX was found to be monoclinic, belonging to space group P21/n while 2APX was triclinic with space group P1. The structural elucidation of polymers was carried out by FTIR and 1H NMR spectroscopy and their properties were studied by solubility testing, wide angle X-ray diffraction (WAXRD), thermogravimetric analysis (TGA) and viscosity measurement along with laser light scattering technique (LLS). WAXRD pattern showed the semicrystalline nature of polyimides which was decreased in case of copolymers. The poly(imide siloxane) copolymers displayed slightly lower temperature resistance but improved solubility as compared to polyimides. Maximum degradation temperature (Tmax.) of polyimides was in the range of 523–570°C while that of copolyimides, ranged between 483–525°C. Similarly, a decline in inherent viscosities and increase in molecular weight was noticed while moving from polyimides to copolyimides.
Microwave devulcanization is known to be a promising and an efficient rubber recycling method which makes possible for the rubber to regain its fluidity, and makes it capable of being remolded and revulcanized. The focus of this work is to understand the physical and chemical changes that occur in the ground tire rubber after different microwave exposure periods. For this purpose chemical, thermal, rheological and morphological analyses were performed on the tire rubber, which contains natural rubber (NR) and styrene-butadiene rubber (SBR) as polymeric material. The results showed that the microwave treatment promoted the breaking of sulfur cross-links and consequently increased the rubber fluidity. However, long periods of exposure led to degradation and modification of some properties. At nanoscale, the deformation of the devulcanized NR domain under stress was observed, and the morphology obtained appears to be a droplet dispersion morphology. The most exposed samples presented only one glass transition temperature, and from this it was concluded that the treatment may have played an important role in the compatibilization of the elastomeric blend. Based on the results, it is required to control the microwave exposure time and polymeric degradation in order to achieve a regenerated rubber with satisfactory properties.
Two novel side-chain conjugated polymers, PTBT-TID and PTBT-TTID, based on the new synthetic thiophene-benzne-thiophene (TBT) unit, side-chain isoindigo (ID) unit, and the introduced thiophene π-bridge, have been designed and synthesized. The photophysical, electrochemical and photovoltaic properties of the two polymers have been systematically investigated. The two polymers possess relatively good solubility as well as excellent thermal stability up to 380°C, and all of the polymer solar cell (PSC) devices based on the two polymers obtain high open circuit voltage (Voc) of about 0.8 V. The polymer solar cells based on the polymer PTBT-TID show relatively higher efficiencies than the PTBT-TTID-based ones, due to the broader absorption spectrum, a relatively higher hole mobility, a lower HOMO (the highest occupied molecular orbital) energy level, a stronger IPCE (the incident photon to current conversion efficiency) response and a better microphase separation, Consequently, the device based on PTBT-TID:PC61BM (1:2, by weight) gives the best power conversion efficiency (PCE) of 2.04%, with a short-circuit current density (Jsc) of 5.39 mA·cm–2, an open-circuit voltage (Voc) of 0.83 V, and a fill factor (FF) of 0.45.
The metallic effect obtained by incorporation of metal particles in polymers by injection molding has the advantage of eliminating post-processing techniques reducing production cost and time. Nevertheless, undesired defects in the final appearance of parts are common. In this work PP/aluminum pigments were obtained by direct injection molding and the influence of metallic particles on the aesthetic, morphological and mechanical properties of the parts was assessed. Aesthetic aspects could be improved by manipulating processing conditions: high melt temperatures diminished differential shrinkage and made weld lines less noticeable. Also at high melt temperatures Al particles increased thermal conductivity of PP generating a thicker skin, which combined with an inherent gradient temperature and typical shear stresses developed during injection molding, induced the formation of β-PP phase. Mechanical performance of parts showed to be dependent on PP morphology. Distinct deformation behaviors were seen according to the presence of PP polymorph, β-PP counteracting the detrimental effect of not bonded Al flakes, and making PP-Al moldings to have similar toughness as PP moldings with the added value of metallic looking.