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[alpha]-form crystalline isotactic polypropylene (PP) was prepared by two methods: quenching from the melt state at slow or high crystallization rates. The mechanical properties of the resulting PP samples were evaluated using tensile and stress-relaxation tests to investigate the influence of nodular or spherulite morphologies. PP samples with different morphologies had almost the same crystallinity after annealing at 100[degrees]C for 5 h. The yielding stress, strain-hardening modulus, and strength of the nodular PP were higher than those of the spherulite PP, although the crystallinity was almost the same for both PP samples. Furthermore, the relaxation time during the stress-relaxation process at [epsilon] = 4.0 was longer for the nodular PP than for the spherulite PP. The lamellar structure of a spherulite morphology comprises parent and daughter lamellar crystals, whereas that of a nodular morphology prepared via a mesophase structure comprises only parent lamellar crystals. The formation of the daughter lamellae reduces the number of tie chains. Therefore, the nodular PP has more tie chains than the spherulite PP. This transformation from a spherulite to a nodular morphology improved the mechanical properties of the PP. Highlights * Influences of morphology on mechanical properties of polypropylene (PP). * Tensile properties were higher for nodular PP than spherulite PP. * Relaxation time of nodular PP was longer than spherulite PP. * Nodular PP has more tie chains, resulting in improvements of tensile properties. KEYWORDS isotactic polypropylene, tensile property, tie chain, 1 | INTRODUCTION Polypropylene (PP) has excellent properties and is therefore one of the most widely used semicrystalline polymers. The mechanical properties of PP strongly depend on the tacticity of [...]

Magnetic resonance (MR) imaging is a powerful imaging modality for obtaining anatomical information with high spatial and temporal resolution. In the drug delivery system (DDS) framework, nanoparticles such as liposomes are potential candidates for MR imaging. We validated that RGD peptides are possible targeting molecules for pancreatic cancer with αvβ3 integrin expression. This study aimed to evaluate RGD-modified liposomes loaded with ferrioxamine B for pancreatic cancer imaging. We synthesized four types of RGD-modified liposomes encapsulated with ferrioxamine B (SH-, H-, M-, and L-RGD-liposomes). The binding affinity of RGD-modified liposomes was evaluated in a competitive inhibition study using 125I-echistatin. To investigate the pharmacokinetics of RGD-modified liposomes, a biodistribution study using RGD-liposomes labeled with 111In was carried out in a human pancreatic cancer PANC-1 xenograft mouse model. Finally, MR was performed using ferrioxamine-B-loaded liposomes. RGD-liposomes inhibited the binding of 125I-echistatin to RGD. The biodistribution study revealed that 111In-RGD-liposomes accumulated significantly in the liver and spleen. Among the 111In-RGD-liposomes, 111In-H-RGD-liposomes showed the highest tumor-to-normal tissue ratio. In the MR study, H-RGD-liposomes loaded with ferrioxamine B showed higher tumor-to-muscle signal ratios than RKG-liposomes loaded with ferrioxamine B (control). We successfully synthesized RGD-liposomes that can target αvβ3 integrin. [ABSTRACT FROM AUTHOR]

In the present study, a novel crystalline nucleating agent for isotactic polypropylene (PP) comprising the calcium salt of 4‐methyl‐cyclohexane‐1,2‐dicarboxylic acid (MHPA‐Ca) is developed. The performance of the nucleating agent is evaluated by determining the crystallization temperature and isothermal crystallization period of the PP by differential scanning calorimetry, and comparing them with those obtained using the calcium salt of cyclohexane‐1,2‐dicarboxylic acid (HHPA‐Ca), which is one of the most effective nucleating agents for PP. The results demonstrate that the nucleating ability of MHPA‐Ca is much stronger than that of HHPA‐Ca. Consequently, an injection‐molded plate containing MHPA‐Ca has a high degree of chain orientation. [ABSTRACT FROM AUTHOR]

The rheological behavior under pressure-driven shear flow was studied using binary blends with a sea-island structure. The addition of a low-viscosity dispersion having a high interfacial tension with the continuous phase greatly reduces the shear viscosity, for example, the addition of atactic polystyrene (PS) with a low viscosity to isotactic polypropylene (PP) and the addition of PP with a low viscosity to PS. The interfacial slippage occurs because of the poor adhesive strength with the enlarged interfacial area and is responsible for the viscosity decrease. When the dispersion has a similar viscosity to the continuous phase, the viscosity decrease is barely detected. This is because the deformation of dispersed droplets is restricted, which creates a small interfacial area. The interfacial tension between the continuous and dispersed phases plays a crucial role on the shear viscosity. In the case of PP, the addition of linear low-density polyethylene with a relatively low interfacial tension to PP has almost no impact on the shear viscosity. This is despite the polyethylene having a low viscosity. KEYWORDS Interface, polymer blend, shear viscosity, 1 I INTRODUCTION Interfacial slippage between immiscible polymer pairs during multilayered film extrusion is widely recognized from the pioneering works performed by Macosko et al. [1-5] The phenomenon was also [...]

The rheological properties of a polyamide (PA) resin with low crystallinity were modified by melt-mixing it with a small amount of an alternative α-olefin–maleic anhydride copolymer as a reactive compound. Because PA has a low melting point, rheological characterization was performed over a wide temperature range. Owing to the reaction between PA and the alternative α-olefin–maleic anhydride copolymer, the blend sample behaved as a long-chain branched polymer in the molten state. The thermo-rheological complexity was obvious owing to large flow activation energy values in the low modulus region, i.e., the rheological time–temperature superposition principle was not applicable. The primary normal stress difference under steady shear was greatly increased in the wide shear rate range, leading to a large swell ratio at the capillary extrusion. Furthermore, strain hardening in the transient elongational viscosity, which is responsible for favorable processability, was clear. Because this is a simple modification method, it will be widely employed to modify the rheological properties of various polyamide resins. [ABSTRACT FROM AUTHOR]

In this study, polypropylene (PP) films containing the [beta] nucleating agent, N.N'-dicyclohexyl-2,6-naphthalenedicarboxamide, were prepared using PP with three different molecular weights (low, medium, and high) by extrusion process with T-shaped die. The structure and morphology of the films were studied after stretching. It was found that a unique molecular orientation, in which both the c-axis and crystalline lamellae were oriented perpendicular to the flow direction, was formed in all undrawn film samples, irrespective of the molecular weights of the PP. In the PP sheets stretched in the machine direction, the low-molecular-weight sample containing the nucleating agent exhibited brittle properties owing to a lack of tie chains in the stretching direction. In contrast, cavitation was prominent in the medium (M-PP)- and high (H-PP)-molecular-weight samples. Notably, M-PP containing the nucleating agent, with a high degree of molecular orientation, promoted the formation of a large number of voids. In H-PP containing the nucleating agent, the presence of numerous tie chains inhibited cavitation, resulting in fewer voids. The experimental results demonstrated the influence of the molecular weight on the void structure, which will be useful in the field of microporous membranes. KEYWORDS cavitation, molecular orientation, morphology, nucleation, polypropylene, 1 | INTRODUCTION With an increased demand for high-performance and specialized polymeric materials, polypropylene (PP)--which is one of the most versatile polymers for various applications owing to its good cost [...]