Graphite oxide-driven miscibility in PVDF/PMMA blends: Assessment through dynamic rheology method

Melt Rheological Behavior and Morphology of Poly(ethylene oxide)/Natural Rubber-graft-Poly(methyl methacrylate) Blends

The influence of morphology on the rheological properties of poly(ethylene oxide) (PEO) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) blends in the melt was investigated. The blends were prepared at different blend compositions by a solution-casting method. Linear viscoelastic shear oscillations measurements were performed in order to determine the elastic and viscous properties of the blends in the melt. The rheological results suggested that the blending of the two constituents reduced the elasticity and viscosity of the blends. The addition of an even small amount of NR-g-PMMA to PEO changed the liquid-like behavior of PEO to more solid-like behavior. Morphological investigations were carried out by optical microscopy to establish the relationship between morphology and melt viscosity. Depending on the blend compositions and viscosities, either droplet-matrix or co-continuous morphologies was observed. PEO/NR-g-PMMA blends exhibited a broad co-continuity range, and phase inversion was suggested to occur at the PEO/NR-g-PMMA blend with a mass ratio of 60/40 (m/m), when NR-g-PMMA was added to PEO as a matrix.

Preparation of polyimide films via microwave-assisted thermal imidization

A series of polyimide (PI) films based on aromatic heterocyclic monomers of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), p-phenylenediamine (p-PDA) and 4,4′-oxydianiline (ODA) were prepared via a microwave-assisted thermal imidization and conventional thermal imidization method at different temperatures. The effects of microwave irradiation on the imidization degree, microstructures, mechanical and thermal properties of PI films were investigated. The imidization degree of the PI films treated with microwave-assisted heating reached a relatively high value at 250 °C, which was twice as much as those treated with traditional thermal imidization. The tensile strength and modulus of PI films treated with microwave-assisted imidization at 300 °C were 187.61 MPa and 2.71 GPa respectively, which were 30% higher than those of PI films treated with thermal imidization. Moreover, the order degree of polymer chains was improved by the microwave-assisted imidization method. The PI films prepared by the microwave-assisted imidization method showed excellent thermal stability with a 5% weight loss temperature of 573 °C under N₂. The microwave-assisted thermal imidization proved to be a rapid and efficient way to prepare high-performance polyimide materials.

A series of polyimide films were prepared via a microwave-assisted thermal imidization and conventional thermal imidization method at different temperatures.

Rheology⁻Microstructure Relationships in Melt-Processed Polylactide/Poly(vinylidene Fluoride) Blends

In this study, small amplitude oscillatory shear tests are applied to investigate the rheological responses of polylactide/poly(vinylidene fluoride) (PLA/PVDF) blends and to correlate their viscoelastic properties with the morphological evolutions during processing. Although the analysis of the elastic moduli reveals some changes as a function of blend composition and processing time, the weighted relaxation spectra are shown to be more useful in detecting changes. The analysis demonstrates that when PVDF, i.e., the more viscous phase, is the matrix, the blend relaxes cooperatively and only a single relaxation peak is observed. By contrast, blends with highly concentrated morphologies do not fully relax, showing instead an upward increasing trend at longer times. This outcome is attributed to the broad distribution of highly concentrated droplets with a high probability of droplet⁻droplet contacts. Dynamic mechanical analysis (DMA) reveals that crystalline segmental motions attributed to the α-relaxation of PVDF at around 100 °C are restricted by the highly concentrated morphology of the 50/50 PLA/PVDF blend processed for 10 min. Relaxation analyses of the blends via dynamic oscillatory shear tests and DMA are shown to be powerful tools for investigating small microstructural changes in immiscible polymer blends.