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It is widely believed that [beta]-nucleating agent is beneficial for effectively toughening isotactic polypropylene (iPP). However, for the injection molding process, the shearing and thermo-mechanical conditions make the nucleation and crystallization process complicated. In this paper, the effects of injection rate on crystallization of [beta]-nucleated iPP were studied by scanning electron microscope (SEM), two-dimensional wide-angle X-ray diffraction and differential scanning calorimetry (DSC). It is observed that with increasing injection rate, the content of [beta]-crystals exhibits different tendencies in the skin, intermediate layers, and core zone. Specifically, for the intermediate layer, the [beta]-crystals content first increases with increasing injection rate to 85 cm [s.sup.-1], and begins to decrease afterward. By simulating the injection process, the most likely explanation for the [beta]-crystal change is the comparatively high shear rate and low shearing time that the melt experienced. Variations in [beta]-form content are mainly responsible for the mechanical properties of [beta]-nucleated iPP. The results of this study provide a valuable way to control the iPP toughness in the injection molding process., INTRODUCTION Isotactic polypropylene (iPP) is one of the most widely used thermoplastic materials [1]. However, low impact toughness has limited its extensive application, especially at low temperatures. To overcome the [...]

A review of nucleating agent (NA) types and their effect on crystallization in high-density polyethylene (HDPE) is presented. The focus is on methods to improve the physical properties of HDPE due to its widespread use in commercial applications and high volume use in typical industrial processes including extrusion, injection molding, and blow molding. The crystallization process in HDPE significantly affects its final optical, mechanical, and thermal properties. The addition of NAs affects the physical properties of HDPE by controlling the crystallization from the melt state. Specific NAs improve properties such as clarity, cycle time, and modulus. NAs are more widely developed for polypropylene (PP) than HDPE as its slower crystallization rate allows greater control in achieving property improvements. While certain NAs are effective in improving property characteristics in HDPE, greater control over the crystallization process would achieve further improvements in specific properties. Research has progressed in identifying effective NAs for HDPE, though the magnitude of the effects remains lower than those generally observed in PP. Inorganic and organic NAs are reviewed with an emphasis on the mechanisms by which they function. Fundamentals of polymer crystallization and modeling kinetics during both isothermal and nonisothermal studies provide the necessary framework for characterizing the effects of a NA in HDPE. Finally, the interactions between HDPE, NA, and industrial processing conditions as related to practical applications are discussed., INTRODUCTION In industrial applications, polymers are melted in processing steps such as extrusion and molding and the size, dimension, and distribution of crystalline domains, or crystallites developed upon cooling determine [...]

Viscoelasticity was applied to monitor the early stage of the crystallization process of poly(lactic acid). The evolution of the storage modulus in the process was divided into three stages with the help of optical microscopy. A simple model, combining the kinetics of embryo population and the Palierne Equation for suspension, was proposed to describe the evolution of the storage modulus along the process. The model was extremely successful in portraying the rheological behavior. Rate constants related to the nucleation and the formation and dissociation of the embryo, as well as the Avrami parameter, could therefore be determined by the rheological tool. Although linear viscoelasticity is frequency dependent, the rate constants were found to be essentially independent of the frequency applied. The Avrami parameter was found to have a threefold change over a frequency range of more than two orders of magnitude, which could be an important reference for the frequency selection when implementing the rheological tool in the investigation of polymer crystallization., INTRODUCTION The crystallization behavior of semicrystalline polymers is crucial in the final mechanical properties of the plastic products. Crystallization commonly occurs in industrial processing such as fiber spinning, die extrusion, [...]

Two semicrystalline poly(3-hydroxybutyrate) (PHB) and polylactic acid (PLLA) blends with and without poly (vinyl acetate) (PVAc) were prepared by dissolving different ratios in hot chloroform at 50 °C to obtain promising alternative biodegradable materials for eliminating plastic waste. The miscibility, crystallization, melting behavior and vibration modes of the prepared samples were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FTIR), and wide angle X-ray diffraction (WAXD) techniques. DSC analysis showed that only one crystallization temperature for blends with PVAc (single homogeneous phase) and two crystallization temperatures for blends without PVAc (immiscible blends) were obtained. The POM results indicated that the morphological structures of B38I B551, and B83i samples consist of two types of spherulites (fibrils and banded) which created at different crystallization temperatures. The irrelevant interaction between PHB and PLLA structures was detected from FTIR spectra. The addition of PVAc caused an obvious decrease in the peak position of the carboxyl group C=0 from 1752 to 1724 cm'1 due to dipoledipole interactions. WAXD indicated that the lattice parameters are changed in blends with PVAc and unchanged without PVAc-Our results indicated that, the PVAc can be used as compatibilizer and improved the compatibility between PHB and PLLA. POLYM. ENG. SCI., 51:2191-2202, 2011. ©2011 Society of Plastics Engineers, INTRODUCTION The quantities of plastic waste are increasing in all places of the world as the production and consumption of plastic materials. Most of these plastic materials are produced from [...]

This study proposes an experimental method to quantify the molecular orientation of the crystalline phase of isotactic polypropylene from polarized Raman spectroscopy measurements. The method is based on the intensity sensitivity of two Raman scattering bands located at 973 (C-C stretching mode) and 998 c[m. sup -1] (C[H. sub 3] rocking mode) to laser light polarization. The first part of this article is devoted to the validation of the method by comparing Raman and Wide Angle X-ray Scattering (WAXS) results obtained on postmortem test samples uniaxially deformed at growing levels. Second, the method is applied to follow the molecular orientation in situ during a tensile test by combining a video-controlled test machine and a Raman spectrometer. Postmortem results show a quantitative agreement between Raman and WAXS measurements. In situ results mainly evidence the ability of the Raman method to characterize molecular orientation in real-time with less than 5 s time resolution. POLYM. ENG. SCI., 51:1607-1616, 2011. ©2011 Society of Plastics Engineers, DOI 10.1002/pen.21944 INTRODUCTION To gain a better understanding of the mechanical properties of solid polymers, it is fundamental to understand the mechanisms of deformation which take place at the microstructure [...]

Poly(phenylene sulfide)/ferrosoferric oxide composites (PPS/[Fe.sub.3][O.sub.4]) with various loading levels were prepared by melt compounding. The crystallization, thermal, and viscoelastic properties were characterized respectively by the DSC, DMA, TGA and parallel plate rheometer. The results reveal that the well-dispersed [Fe.sub.3][O.sub.4] particle restricts the segmental motion of polymer chain, leading to a remarkable increase of the glass transition temperature and thermal stability of the PPS due to the strong physical association and interactions between particles and matrix. The presence of the [Fe.sub.3][O.sub.4] particles, however, can not facilitate crystallization of PPS, because the particles only play the role of inert filler and have no heterogeneous nucleating effect. The crystallization kinetics, as a result, decreases with increasing particles loadings due to the increasing restriction of the chain mobility and high viscosity. In addition, the rheological percolated network of the [Fe.sub.3][O.sub.4] particles is very sensitive to the steady shear deformation, and also to the temperature. The network structure is easily broken by the steady shear flow due to the sharply reduced particle-particle interactions. However, the percolation threshold reduces with increase of temperature, because those interactions are temperature-dependent. POLYM. ENG. SCI., 48:966-975, 2008. © 2008 Society of Plastics Engineers, INTRODUCTION Poly(phenylene sulfide) (PPS) is a high-performance semicrystalline polymer that has been utilized in a variety of market segments such as electrical, electronic, automotive, appliance, industrial, and chemical sectors due [...]

Byline: T.J. Makriyannis, M.Z. Saghir, D. Labrie The travelling solvent method known as TSM is a process used to produce pure and homogeneous crystals. The TSM process has been tested on many alloys producing uniform and uncontaminated crystal products. A three-dimensional numerical simulation for the fluid flow, heat and mass transfer in the solvent during the growth of Ge1-xSix by the travelling solvent method under axial rotation has been modelled. The full Navier-Stokes equations together with the energy, mass transport and continuity equations were solved numerically using the finite element technique. The application of crucible rotation to the travelling solvent method is an attempt to control the buoyancy induced convection throughout the melt and to suppress the three-dimensional characteristics of unsteady heat flow. The application of rotation was shown to have a considerable effect on the buoyancy-induced flow. An optimal rotational speed was found that lessened the convective flow, provided a uniform concentration along the growth interface, and gave symmetrical characteristics to the three-dimensional buoyancy-induced flow.