Mechanical and Crack-Sensing Capabilities of Mode-I Joints with Carbon-Nanotube-Reinforced Adhesive Films under Hydrothermal Aging Conditions

The fracture behavior and crack sensing of mode-I joints with carbon nanotube (CNT)-reinforced adhesive films were explored in this paper under hydrothermal aging conditions. The measured fracture energy of CNT-reinforced joints in grit blasting conditions is higher for non-aged samples than for neat adhesive joints (around 20%) due to the nanofiller toughening and crack bridging effects. However, in the case of brushed surface-treated adherents, a drastic decrease is observed with the addition of CNTs (around 70%) due to the enhanced tribological properties of the nanofillers. Hydrothermal aging has a greater effect in the CNT-reinforced samples, showing a more prevalent plasticization effect, which is confirmed by the R-curves of the specimens. The effects of surface treatment on the crack propagation properties was observed by electrical resistance monitoring, where brushed samples showed a more unstable electrical response, explained by more unstable crack propagation and reflected by sharp increases of the electrical resistance. Aged specimens showed a very uniform increase of electrical resistance due to slower crack propagation, as induced by the plasticization effect of water. Therefore, the proposed adhesive shows a high applicability for crack detection and propagation without decreasing the mechanical properties.

Axial Orientation of Co-Crystalline Phases of Poly(2,6-Dimethyl-1,4-Phenylene)Oxide Films

Films exhibiting co-crystalline (CC) phases between a polymer host and low-molecular-mass guest molecules are relevant for many applications. As is usual for semi-crystalline polymers, axially oriented films can give relevant information on the crystalline structure, both by Wide Angle X-ray diffraction fiber patterns and by polarized Fourier-transform infrared spectroscopy. Axially oriented CC phases of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with 1,3,5-trimethylbenzene (mesitylene) can be simply obtained by the stretching of CC PPO films. In fact, due to the plasticization effect of this highly boiling guest, PPO orientation can occur in a stretching temperature range (170–175 °C) nearly 50 °C lower than that generally needed for PPO films (220–230 °C). This low stretching temperature range allows avoidance of polymer oxidation, as well as formation of the mesomorphic dense γ PPO phase. Axially oriented CC phases of PPO with toluene, i.e., with a more volatile guest, can be instead obtained by the stretching (in the same low temperature range: 170–175 °C) of CC PPO blend films with polystyrene.

Plasticization Effect of Bio-Based Plasticizers from Soybean Oil for Tire Tread Rubber

Modified soybean oil (MSO) is synthesized from soybean oil (SO) and sulfur, aiming to reduce the double bond quantity of SO and avoid harmful effects on the crosslink density and mechanical properties of rubber. MSO modified with different weight percentages of sulfur is then used to plasticize tire tread rubber (TR). It is found that the crosslink density and modulus of MSO- plasticized rubber are significantly improved compared with that of SO-plasticized TR. MSO modified with 6 wt % sulfur (MSO-6%) exhibits the best plasticization effect on TR, thus, the plasticization effect of MSO-6% on TR was further studied by adjusting its additive content. Thereafter, the Mooney viscosity, Payne effect, mechanical property of different amount of MSO-6% plasticized TR are studied to investigate their plasticization effect. At the same additive content of plasticizer, the plasticization effect of MSO-6% and a commonly used aromatic hydrocarbon plasticizer (AO) is compared to determine the potential application of MSO on tire tread rubber. It is found MSO shows similar plasticization effect on TR compared with AO. More important, the aging resistance property and wear resistance property of MSO-6% plasticized rubber are better than those of AO-plasticized rubber. Therefore, MSO-6% is a promising bio-based plasticizer for tire tread rubber.

Thermoplastic Starch (TPS) Films Added with Mucilage from Opuntia Ficus Indica: Mechanical, Microstructural and Thermal Characterization

Opuntia cladodes are a typical vegetable waste, from which mucilage in gel form can be extracted. This work proposes blending it with a self-produced thermoplastic starch (TPS), originating from potato starch with a high content in glycerol (ca. 30%). Three methods were compared for extraction, bare maceration (MA), mechanical blending (ME) and mechanical blending following maceration (MPM) to produce films with an approximate thickness of 150 μm. For the comparison, tensile testing, differential scanning calorimetry and scanning electron microscopy were used. The MPM process proved the most effective, not only for extraction yielding, but also to obtain a larger deformation of the samples with respect to the one allowed by the pure TPS films. A considerable plasticization effect was observed. Despite this, the mechanical performance is still not completely satisfactory, and the expected effect of the calcium and magnesium salts contained in the mucilage to improve the rigidity of the TPS film was not really revealed. Prospected improvements would concern the fabrication process and the investigation of other possible loading modes and sample geometries.

Self-plasticization of neoprene rubber via click chemistry from environmentally sustainable cardanol

The sustainable biomass cardanol grafting onto neoprene (CR) rubber was carried out successfully at room temperature by covalently binding to CR via click chemistry to realize the internal plasticization of CR rubber. The structure of the synthesized product was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and differential scanning calorimetry and thermogravimetric analysis demonstrate a lowering of the glass transition temperature of the CR-propargyl ether cardanol as compared to CR. This confirms the plasticization effect of the cardanol when grafted onto CR. The cardanol as an internal plasticizer also has a good thermal stability and almost near-zero migration.

Optimization of Maleinized Linseed Oil Loading as a Biobased Compatibilizer in Poly(Butylene Succinate) Composites with Almond Shell Flour

Green composites of poly(butylene succinate) (PBS) were manufactured with almond shell flour (ASF) by reactive compatibilization with maleinized linseed oil *MLO) by extrusion and subsequent injection molding. ASF was kept constant at 30 wt %, while the effect of different MLO loading on mechanical, thermal, thermomechanical, and morphology properties was studied. Uncompatibilized PBS/ASF composites show a remarkable decrease in mechanical properties due to the nonexistent polymer‒filler interaction, as evidenced by field emission scanning electron microscopy (FESEM). MLO provides a plasticization effect on PBS/ASF composites but, in addition, acts as a compatibilizer agent since the maleic anhydride groups contained in MLO are likely to react with hydroxyl groups in both PBS end chains and ASF particles. This compatibilizing effect is observed by FESEM with a reduction of the gap between the filler particles and the surrounding PBS matrix. In addition, the Tg of PBS increases from −28 °C to −12 °C with an MLO content of 10 wt %, thus indicating compatibilization. MLO has been validated as an environmentally friendly additive to PBS/ASF composites to give materials with high environmental efficiency.