Search

[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 [...]

The effect of the addition of polyvinylpyrrolidone (PVP) to polyamide resins was studied using polyamide 6 (PA6) and an amide copolymer with a low melting point (PA-L). For the PA6/PVP blends, the crosslinking reaction occurred during rheology measurements in the molten state. The blends did not show a phase-separated structure. Furthermore, the crystallization of PA6 was greatly inhibited by PVP addition. These results suggest that the PVP chains were dissolved in PA6 in the molten state, although the effect of the crosslinking reaction on the structure development is unknown. In the case of the PA-L/PVP blends, melt-mixing and the rheology measurements were performed at low temperature to avoid the crosslinking reaction. It was found that PVP was miscible with PA-L in the molten state when the PVP content was 10 and 15 wt%. The intermolecular interaction between the polyamide resins and PVP was detected from the peak shift of the infrared absorbance. PVP addition enhanced the moisture content in both polyamide resins and decreased the contact angle with water droplets. These results suggested that the surface properties and mechanical properties of polyamide resins, which are affected by the moisture content, are modified by PVP addition. [ABSTRACT FROM AUTHOR]

Polybenzimidazole (PBI) is a high-performance polymer known for its excellent thermal stability, mechanical strength, and chemical resistance, attributes that are derived from its unique structure comprising repeated benzene and imidazole rings. However, limitations such as relatively low thermal stability and moisture sensitivity restrict its application as a super engineering plastic. In this study, amide groups are incorporated into the PBI backbone to synthesize the copolymer poly(BI-co-A), effecting a structural modification at the molecular level. Additionally, silica nanospheres were composited into the poly(BI-co-A) film to further enhance its thermal performance. The resulting composite films exhibited remarkable thermal stability, with the temperature for 10% weight loss reaching as high as 761 °C. To address increased water absorption due to the high hydrophilicity of hydroxyl groups on the silica nanospheres' surface, a dehydration treatment was applied in an electric furnace. This treatment produced a highly thermoresistant poly(BI-co-A) nanocomposite film with reduced wettability, making it suitable for applications in humid environments. [ABSTRACT FROM AUTHOR]

We studied the rheological properties under both shear and elongational flow and crystallization behaviors after shear history for binary blends of poly(lactic acid) (PLA) and ethylene–vinyl acetate copolymer (EVA) with a slightly lower shear viscosity. EVA was immiscible with PLA and dispersed in droplets in the blend. The addition of EVA significantly reduced the shear viscosity, which is attributed to the interfacial slippage between PLA and EVA. In contrast, under elongational flow, the addition of EVA provided strain hardening in the transient elongational viscosity. Consequently, the degree of neck-in behavior in T-die extrusion, i.e., a decrease in the film width, was reduced with the high orientation of the PLA chains. Furthermore, it was found that the addition of EVA accelerated the shear-induced crystallization of PLA, although EVA showed no nucleating ability without a flow field. Because the EVA addition can improve the mechanical toughness, this modification technique is attractive for various industrial applications of PLA. [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 [...]

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 [...]