Yu Zheng

Poly(vinylidene fluoride) (PVDF) possesses a high dielectric constant (εr), but its large dielectric loss (tan δ) and low breakdown strength (Eb) restrict its application in film capacitors. Herein, by adopting blending modification and biaxial stretching, PVDF/poly(methyl methacrylate) (PMMA) blend films with enhanced dielectric and energy storage performance were prepared. The microstructural evolution of the films was explored, and the corresponding structure‐property relationship was clarified. As PMMA content ≤ 30 wt%, biaxial stretching induced fragmentation, α‐to‐β phase rearrangement, recrystallization and orientation of PVDF crystals; α‐crystal size declined continuously whereas β‐phase crystals developed. As PMMA content ≥ 40 wt%, PMMA significantly inhibited PVDF crystallization and weakened the strain-induced crystallization, lowering the crystallinity and molecular orientation. Although the relative β-phase fraction further elevated, both the size and content of β-phase crystals decreased. Benefiting from the balance among crystallinity, β-phase content, orientation degree and crystal size, the blend film with 30 wt% PMMA exhibited the optimal comprehensive dielectric properties with an ultrahigh Eb of 1060.7 kV/mm, a large εr of 6.2 at 103 Hz, and a very low tan δ. It also exhibited excellent energy storage performance with an energy density of 19.5 J/cm3 at 1000 kV/mm while maintaining a charge-discharge efficiency of 63%. Moreover, the addition of PMMA decreased the tensile strength (σ) yet increased the elongation at break (ε). The 30 wt% PMMA sample achieved a desirable strength‐toughness balance with σ above 100 MPa and ε approaching 70%. This study offers an efficient route to developing high-performance PVDF‐based dielectrics.

A sustainable strategy integrating reactive compatibilization with biaxial stretching was developed to produce high-performance polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blend films. Pentamethylene diisocyanate (PDI) served as a reactive compatibilizer to enhance the interfacial compatibility of PLA/PBAT blends, while the thermo-mechanical field generated by biaxial stretching was utilized to tailor microstructure and properties. It was revealed that PDI significantly improved the stretchability of blends and affected the film surface quality. At low PDI contents, interfacial debonding between PLA and PBAT phases readily occurred, whereas excessive PDI contents promoted fragmentation and cavitation of the dispersed PBAT domains, both of which deteriorated the film quality. In contrast, the blend with 1.5 phr PDI exhibited balanced stress transfer and superior film-forming performance. Increasing the stretching rate further promoted molecular orientation and crystallinity while reducing surface roughness, thereby optimizing the comprehensive properties. The 7.0 × 7.0 biaxially stretched film fabricated with a stretching rate of 60%/s achieved a tensile strength of 113.9 MPa, representing a 172.5% improvement over the unstretched counterpart, while maintaining a high elongation at break of 176.0%. Owing to its dense surface structure and oriented microcrystals, the film exhibited low water vapor and oxygen permeability coefficients of 1.18 × 10–14 g cm/(cm2 s Pa) and 3.72 × 10–16 cm3 cm/(cm2 s Pa), respectively, while retaining high optical transparency of 86%. This work provides valuable insights into the development of PLA/PBAT biodegradable films with simultaneously enhanced mechanical and barrier properties, demonstrating considerable potential for industrial applications.

Polylactide (PLA) films were fabricated via sequential biaxial stretching under non-crystalline conditions to explore the correlation between mesophase-driven structural evolution and film-forming behavior. Visual contour analysis verified the deformation uniformity of the film throughout the stretching process. Uniaxial stretching along the machine direction induced the formation of locally ordered mesophase and oriented amorphous molecular chains. Subsequent transverse stretching significantly increased the mesophase content and further enhanced its degree of ordering. Meanwhile, the molecular orientation gradually evolved from being dominated by the machine direction to being dominated by the transverse direction. The synergistic effects of mesophase-induced physical crosslinking, slow chain relaxation, and sustained chain orientation enabled uniform macroscopic film formation. Owing to the absence of crystallization and mesophase-mediated suppression of interchain slippage, a yield-free and stepwise linear response was observed during stretching. Consequently, a monotonic increase in the stress–strain curve, especially in the strain-hardening regime, directly correlated with enhanced film uniformity, demonstrating that the mechanical response is a reliable indicator for film-forming quality. Moreover, the high mesophase content and oriented structure impart a superior strength-toughness balance and excellent optical transparency to the PLA film. This work provides useful guidance for the preparation of high-performance PLA films and also holds significance for the production of other biaxially oriented polymer films.

Incorporating high-dielectric fillers into polymer matrices can enhance the dielectric constant (εr) of films, but it inevitably compromises the electric breakdown strength (Eb), thereby limiting the improvement in energy density. Herein, poly(vinylidene fluoride) (PVDF)-based composite dielectric films featuring ultrahigh Eb and energy density are fabricated via high-ratio biaxial stretching. High-dielectric BaTiO3 was grafted with fluorosilane and subsequently incorporated into PVDF to enhance the polymer/filler interfacial compatibility. This approach suppressed the premature fracture caused by modulus mismatch during film stretching, enabling the composites to realize a biaxial stretching ratio up to 4 × 4. The orientation and fragmentation PVDF crystals caused by stretching not only reduced the leakage current but also increased the Young’s modulus of films, achieving an ultrahigh Eb of 795 kV/mm. Meanwhile, the stretching-induced α-to-β crystal phase transition in PVDF, together with the high-dielectric BaTiO3 fillers, synergistically enhanced the polarization capability of films, yielding a remarkable εr of 19.0. The successful decoupling and synchronous enhancement of Eb and εr endowed the composite film with a superior energy density of 21.1 J/cm3. Moreover, this biaxial stretching strategy is compatible with scalable capacitor film manufacturing, offering a promising route toward high-performance dielectric films.

The switching temperature (T _s) of polylactide/thermoplastic polyurethane (PLA/TPU) shape-memory blend is much higher than the body temperature, which is regarded as the key obstacle for it to realize biomedical applications. In this study, PLA was first blended with the plasticizer of poly(ethylene glycol) (PEG) and then laminated with TPU into the bilayer and sandwich structured shape-memory polymeric materials. Unlike that PEG would migrate from PLA into TPU during direct blending, PEG was totally confined in PLA of the layered structures, which significantly optimized the plasticization effect and successfully adjusted T _s to the body temperature range. Then, the body temperature-triggered shape-memory effect (SME) was researched and the related shape-memory mechanism was deeply discussed. It was revealed that the layered structures had a much better SME than that of blend because the totally continuous phase and two-dimensional interfaces maximally promoted stress transferring and load distribution. Moreover, a spiral-like stent made of sandwich sample with the best SME showed excellent self-expanding performance in 37 °C water bath, providing a great support within the ureter mimicked by silicone tube. Besides, the cytocompatibility testing results evidenced the good biocompatibility of sandwich sample, further demonstrating the great potential of the prepared material for development of biomedical applications such as the ureter stent.

Sustainable poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends were compatibilized by the environmentally friendly epoxidized soybean oil (ESO) through the chemical reaction of epoxy functional groups on ESO with the terminated carboxyl and hydroxyl groups of PLA/PPC. The compatibilization effect of ESO was confirmed by Fourier transform infrared spectroscopy, rheological property testing, differential scanning calorimetry, and morphological observations. It was revealed that the molecular chain entanglement between PLA and PPC was significantly enhanced and the dispersed PPC phase size was decreased, which endowed the blend with high viscosity modulus, low tan δ, and great stretchability, especially for the blend containing 1.0 wt % ESO. The compatibilization effect dramatically reinforced the toughening modification of PPC on PLA, resulting in a great ductility with a fracture strain up to 187.3%, more than 20 times that of the pristine PLA, while maintaining a high strength of 44.5 MPa. Compared to the neat PLA and the PLA/PPC blend, the compatibilized blend showed a much larger draw ratio of up to 6.5 × 6.5 during biaxial stretching, producing a uniform film with balanced mechanical properties, high optical transparency, and good oxygen barrier performance. This work will be of vital importance for guiding the preparation of PLA-based films with superior comprehensive properties.