Conductive polymer composites (CPCs) with a positive temperature coefficient (PTC) effect are attractive because of their temperature-dependent electrical response. In this study, an industrial-grade high-density polyethylene (HDPE) film was incorporated into virgin HDPE as a compositionally controlled component in film form to construct an HDPE film/HDPE-based PTC system, with carbon black (CB) used as the conductive filler. Benzoxazine (BZ) network and diatomaceous earth (DE) confinement were introduced to regulate the matrix structure and CB conductive network. The results showed that 2 wt.% BZ increased the PTC intensity to 5.03 and reduced the negative temperature coefficient (NTC) intensity to 0.24. Further addition of 20 wt.% DE substantially suppressed the NTC effect, decreased the room-temperature resistivity from 4.93 to 3.32 Ω·cm (a 32.66% reduction) and significantly improved the cycling stability of the PTC intensity. Microstructural analysis indicated that the BZ-derived network and DE-induced confinement stabilized the CB conductive network and inhibited its high-temperature migration. These findings provide a structural regulation strategy for HDPE film/HDPE-based PTC composites and may serve as a reference for future studies using recycled HDPE films. An industrial-grade high-density polyethylene (HDPE) film was incorporated into virgin HDPE with carbon black as the conductive filler to construct an HDPE film/HDPE-based positive temperature coefficient (PTC) composite. A benzoxazine (BZ)-derived network and diatomaceous earth (DE) confinement stabilized the conductive network and inhibited its high-temperature migration: 2 wt% BZ increased the PTC intensity to 5.03 and reduced the negative temperature coefficient (NTC) to 0.24, while 20 wt% DE further suppressed the NTC effect, lowered room-temperature resistivity by 32.66%, and improved cycling stability.
To improve the flexibility and electrical insulation of poly(phenylene sulfide) (PPS), a candidate insulating material for electric vehicle drive motors under high-temperature conditions, blends with fluoroelastomers (FEPMs) were investigated. Owing to the inherent immiscibility of PPS and FEPM, reactive blending using an iodine-terminated FEPM (mFEPM) was also evaluated to improve interfacial compatibility. The PPS/FEPM blend showed an improved partial discharge inception voltage (PDIV); however, coarse phase separation and poor interfacial adhesion were also observed. In contrast, PPS/mFEPM blends exhibited significant refinement of the dispersed phase and a more uniform morphology, suggesting in situ copolymer formation at the interface. Furthermore, although the incorporation of mFEPM significantly accelerated the crystallization rate of PPS, unlike FEPM, the flexural fatigue resistance improved dramatically. Regarding the PDIV, the PPS/mFEPM blend, like the FEPM blend, maintained high values even at high temperatures of up to 150 °C, demonstrating excellent insulation reliability even under severe operating conditions. These findings demonstrate that PPS/mFEPM blends are highly promising insulating materials capable of simultaneously achieving mechanical flexibility and electrical reliability in high-temperature environments. To improve the flexibility and high-temperature electrical insulation properties of poly(phenylene sulfide) (PPS), a blend with a fluoroelastomer (FEPM) was selected. Since PPS and FEPM are immiscible and simple blending results in a deterioration of physical properties, reactive blending using iodine-terminated FEPM (mFEPM) was employed. This significantly refined the dispersed phase, leading not only to an improvement in the partial discharge inception voltage (PDIV) but also to a marked increase in MIT folding endurance. Improved interfacial adhesion and the refinement of PPS crystals also contributed to these improvements.
Optimizing block copolymer microphase structures to improve mechanical performance remains a challenge in polymer science and the rubber industry. In this study, folded lamellar microstructures of poly(styrene)-block-poly(butadiene)-block-poly(styrene) (SBS) triblock copolymers were demonstrated to increase the compressive modulus. Folded lamellar structures were formed at 120 °C by applying compressive deformation followed by cooling while strain was maintained. The resulting structures and fold angles were characterized using azimuthal profiles obtained by two-dimensional small-angle X-ray scattering (2D SAXS). Two folded structures, namely, chevron and kink-band structures, were identified. The fold angle increased with compressive strain above 20%. With respect to the chevron structure, the interlamellar distance decreased with increasing compressive strain above a fold angle of ~60°, whereas that for the kink-band structure did not clearly decrease. Subsequent compression tests at 23 °C demonstrated that compared with the original lamellar structure, both folded structures exhibited higher compressive stress. The strain-dependent compressive modulus of the chevron structure increased with the fold angle, whereas that of the kink-band structure showed no clear dependence. Notably, the chevron structure with a fold angle of approximately 80° exhibited the highest modulus, which reached 4.3 times that of the original lamellar structure. These results demonstrate that folded lamellar structures can increase the compressive stiffness of SBS without changing the volume fractions of the components. The effect of lamellar folding on the compressive modulus of SBS block copolymer was systematically investigated. Compression at 120 °C followed by cooling under strain induces chevron and kink-band folded lamellar structures. The fold angle increases progressively with compressive strain. Subsequent compression at 23 °C reveals enhanced compressive stress in both folded morphologies. The chevron structure exhibits a strong fold-angle-dependent modulus increase, reaching 4.3× the compressive modulus of the original lamellar structure at ~80° fold angle.
The repetitive region of Bombyx mori silk fibroin is composed mainly of Ala- and Ser-rich sequences but also contains Tyr- and Val-containing sequences with bulky side chains. Although these residues may affect the formation of the fibroin structure, their local structures remain unclear. Here, we analyzed Tyr residues in stable-isotope-labeled fibroin by solid-state NMR. Tyr-specific 13C signals were identified, and 13C-13C dipolar-assisted rotational resonance (DARR) spectra indicated that Tyr Cβ has at least three structural components. Peak deconvolution indicated that Tyr residues are mainly in random coil and/or β-turn conformations in air-dried liquid silk, whereas β-sheets are the major component in fibers. These assignments were supported by 15N and amide 1H chemical shifts and by time-resolved observations of the Silk I-to-Silk II transition under magic-angle spinning. The β-sheet content of Tyr in the Tyr- and Val-containing sequences was estimated to be 78% in the fibers. These results clarify the structural distribution of Tyr residues and support the contribution of minor repeat sequences to the formation of the fibroin structure. Tyrosine residues in Bombyx mori silk fibroin were selectively analyzed by solid-state NMR using stable isotope labeling. Tyr Cβ signals showed multiple structural components, and peak deconvolution revealed that β-sheet structures become dominant in silk fibers. After correction for Tyr residues outside the Tyr- and Val-containing repeats, the β-sheet content of Tyr in these repeats was estimated to be 78%, supporting the involvement of these minor repeats in β-sheet-rich structures.
Polypyrrole (PPy) is an attractive electrically conducting polymer, but its practical use is limited by poor processability arising from the formation of insoluble aggregates during conventional oxidative polymerization. Herein, we report a surfactant-free aqueous route to colloidally stable polypyrrole‒Laponite (PPy‒LAP) nanocomposite particles via oxidative polymerization of pyrrole in the presence of exfoliated Laponite (LAP) nanosheets. LAP effectively suppressed PPy aggregation, yielding discrete nanocomposite particles with hydrodynamic diameters of approximately 120–200 nm. Transmission electron microscopy revealed irregular particles comprising interconnected LAP nanosheets bound by PPy. X-ray diffraction, X-ray photoelectron spectroscopy, and zeta potential measurements indicated that PPy disrupted the ordered stacking of LAP nanosheets, while LAP remained exposed at the particle surface, providing colloidal stability over a wide range of pH values. The particles contained approximately 6–13 wt% PPy and exhibited increasing electrical conductivity with increasing PPy content. Furthermore, these particles effectively stabilized dichloromethane-in-water Pickering emulsions. This surfactant-free approach provides a straightforward route to colloidally stable conducting polymer–clay nanocomposite particles for interfacial and dispersion-based applications. Polypyrrole–Laponite (PPy–LAP) nanocomposite particles were directly prepared by surfactant-free aqueous oxidative polymerization without prior surface modification of LAP. Two-dimensional LAP nanosheets suppressed macroscopic aggregation of PPy and were interconnected through PPy to form colloidally dispersible, irregular nanocomposite particles. The resulting particles combine aqueous colloidal stability, electrical conductivity, and interfacial activity, demonstrating the potential of two-dimensional clay nanosheets as colloidal stabilizers for constructing water-dispersible conducting polymer–clay nanocomposites.
