Polypropylene Melt Research Articles

유변학적 물성을 이용한 폴리프로필렌의 분자량과 분자량 분포를 결정하는 방법

The rheological measurement of polypropylene (PP) has been performed using a rheometer, an intrinsic vis- cometer, and an MI machine to predict the molecular weight and the molecular weight distribution. Also, GPC has been used for the determination of the molecular structure. The distribution broadness parameter using modified Carreau model has been used to make the correlation between the rheological parameter and the molecular structure instead of the rheo- logical PI (polydispersity index) which is determined from the cross of modulus from the dynamic oscillatory mea- surement. Even though the rheological PI is useful to determine the molecular weight distribution of the PP using controlled rheology, which has narrow and uniform molecular weight distribution, but not suitable to determine the molecular weight distribution of the PP made from direct polymerization which has broad and various molecular weight distribution. However the distribution broadness parameter which determined from the index of the shear thinning of the PP melt well predicts the molecular weight distribution of PP.

Cellulose nanocrystal/polyolefin biocomposites prepared by solid-state shear pulverization: Superior dispersion leading to synergistic property enhancements

Cellulose nanocrystals (CNCs), a class of renewable bionanomaterials with excellent mechanical properties, have gained major interest as filler for polymers. However, challenges associated with effective CNC dispersion have hindered the production of composites with desired property enhancements. Here, composites of polypropylene (PP) and low density polyethylene (LDPE) with 5–10 wt% unmodified CNC are produced for the first time via a solventless process. In particular, we employ solid-state shear pulverization (SSSP). Optical and electron microscopy reveals excellent CNC dispersion with strongly suppressed degradation relative to composites made by melt mixing. Effective dispersion leads to major increases in Young's modulus, including a 69% increase in 90/10 wt% LDPE/CNC composites relative to neat LDPE, the highest modulus enhancement ever reported for polyolefin/CNC composites. The composites also exhibit superior creep performance with modest increment in yield strength compared to neat polymer. The LDPE/CNC composites retain elongation at break values that are equal to that of neat polymer while a decrease is observed with PP/CNC composites. The CNC thermal degradation temperature in air is close to that of PP melt processing conditions. We hypothesize that during melt-processing CNCs undergo preferential thermo-oxidative degradation in LDPE and simultaneous degradation in PP. Thus, CNC incorporation results in impaired thermal stability in LDPE and, especially, PP. Care must be taken in selecting the post-SSSP melt processing temperature and residence time in order to suppress degradation. Taking that into account, this study has produced polyolefin/CNC composites with superior dispersion and property enhancements and shown that CNC is an attractive filler for green polymer biocomposites.

Analysis of non-isothermal crystallization during cooling and reorganization during heating of isotactic polypropylene by fast scanning DSC

Crystallization, reorganization and melting of isotactic polypropylene (iPP) were analyzed by DSC and fast scanning DSC. The cooling and subsequent heating DSC curves are measured at scanning rates between 0.1K/min and 30,000K/s. We study the formation of the mesophase and the α-phase during cooling. Using subsequent heating measurements the formation of the mesophase during cold crystallization and the kinetics of the reorganization are analyzed. From the cooling rate dependence of the glass transition and the melting behavior we discuss relations between the crystalline fraction (CF), the mobile amorphous fraction (MAF), the rigid amorphous fraction (RAF) and the influence of these fractions on the reorganization processes. Furthermore, we use the heating rate dependence of the melting behavior for stability analyses of the related crystals and propose the Illers-plot as a simple analysis tool. Using this technique the melting temperature of the mesophase is determined to about 86°C.

Structure and properties of low-isotacticity polypropylene elastomeric fibers prepared by sheath-core bicomponent spinning: effect of localization of high-isotacticity component near the fiber surface

Abstract Sheath-core type bicomponent melt-spun fibers were produced by extruding the melts of low-isotacticity polypropylene (LPP) as the core component and the blend of LPP and high-isotacticity PP (IPP) as the sheath component. IPP content in the sheath was changed from 8 wt% to 40 wt% while sheath/core composition was varied from 50/50 to 10/90. Accordingly overall IPP content was kept constant at 4 wt%. Even though the overall IPP content was intact, bicomponent fibers with lower contraction ratio after spinning, higher elastic recovery and slightly higher modulus and strength were obtained by increasing the IPP content in the sheath and decreasing the sheath layer composition, i.e., localizing the IPP to the region near the surface in the fiber cross-section. Structure analysis of the as-spun fibers suggested the suppression of crystallization of LPP in the sheath by blending IPP. By contrast, enhancement of molecular orientation and crystallization of the sheath component were found to occur by localizing the IPP to the region near the fiber surface. It was speculated that this behavior was caused by the kinematic mutual interaction of the sheath and core components in the melt spinning process.

Reactive extrusion processing of polypropylene/SiO2 nanocomposites by in situ synthesis of the nanofillers: Experiments and properties

The concept of a lab-scale developed in situ sol–gel batch process for fabrication of polypropylene (PP)/silica nanocomposites based on a solvent-free silica precursor polymer, a hyperbranched polyalkoxysiloxane (PAOS), has been transferred to a continuous industrially applicable extrusion process. To achieve a suitable process set-up for the continuous in situ synthesis of nanofillers in the PP melt, process parameters are varied. The influence of process parameters on precursor conversion, size and distribution of the formed silica particles and the mechanical properties of the resulting PP nanocomposites is determined. In addition, these materials are compared to conventional silica composites based on melt mixing process. It was found, that a PAOS conversion to silica particles of more than 90% could be realised using a hexadecyl-modified PAOS of 12.5% degree of modification (C16(12.5%)-PAOS) at the given process set-up. Well distributed, small silica particles without any agglomeration were yield in the resulting composites in comparison to application of silica powder.

Synthesis of a New Liquid Crystalline Polymer as a Highly Active β-Nucleator and Its Effect on Melting and Crystallization Behaviors of Isotactic Polypropylene

A new nematic liquid crystalline polymer as a highly active β-nucleator (LCP-N) of isotactic polypropylene (iPP) was synthesized and characterized. The effect of LCP-N on thermal behavior of the iPP was investigated with differential scanning calorimetry. LCP-N showed a melting transition at 85.0°C and a nematic to isotropic phase transition at 278.0°C. The incorporation of LCP-N could lead to substantial changes in the thermal behavior of the iPP. The nucleating activity of LCP-N mainly depended on its content, mesogenic molecular structure, and thermal history of processing. A high content of β-form could be obtained by the combined effect of the optimum LCP-N concentration and crystallization temperature and time. The Φβ reached 77% when the LCP-N content, crystallization temperature, and crystallization time were 0.4 wt.%, 125°C, and 1 h, respectively.

Flow-Induced Precursors of Isotactic Polypropylene: An in Situ Time and Space Resolved Study with Synchrotron Radiation Scanning X-ray Microdiffraction

Shear-induced precursors obtained by fiber pulling with high shear rate in undercooled melts of isotactic polypropylene (iPP) at a wide temperature range were investigated by highly time and space resolved synchrotron radiation scanning X-ray microdiffraction (SR-μSXRD). X-ray diffraction patterns in spot area of 4.9 × 5.3 μm2 were obtained by scanning proximities around the fiber with step size of 7 μm immediately after shear and during the sequent crystallization process. The crystallinity derived from SR-μSXRD indicates that the structure of precursors was determined by shear temperature, providing a high shear rate was imposed. At shear temperatures around or below the melting temperature, the presence of crystal diffraction immediately after shear indicates the formation of crystalline precursors with reduced density by increasing shear temperature. At shear temperatures in between melting and equilibrium melting temperature, the formation of noncrystalline precursors is supported by three evidence: (i) formation of shear-induced ordered structure indicated by preference of crystallization on fiber surface; (ii) absence of crystal signal immediately after shear; (iii) induction time necessary for transforming noncrystalline precursor into crystal. The experimental results suggest that the structure of noncrystalline precursors probably is aggregates of partially ordered chain segments which orient along the shear direction.

Effect of cellulose nanocrystals (CNC) particle morphology on dispersion and rheological and mechanical properties of polypropylene/CNC nanocomposites.

Polypropylene (PP) nanocomposites containing spray-dried cellulose nanocrystals (CNC), freeze-dried CNC, and spray-freeze-dried CNC (CNCSFD) were prepared via melt mixing in an internal batch mixer. Polarized light, scanning electron, and atomic force microscopy showed significantly better dispersion of CNCSFD in PP/CNC nanocomposites compared with the spray-dried and freeze-dried CNCs. Rheological measurements, including linear and nonlinear viscoelastic tests, were performed on PP/CNC samples. The microscopy results were supported by small-amplitude oscillatory shear tests, which showed substantial rises in the magnitudes of key rheological parameters of PP samples containing CNCSFD. Steady-shear results revealed a strong shear thinning behavior of PP samples containing CNCSFD. Moreover, PP melts containing CNCSFD exhibited a yield stress. The magnitude of the yield stress and the degree of shear thinning behavior increased with CNCSFD concentration. It was found that CNCSFD agglomerates with a weblike structure were more effective in modifying the rheological properties. This effect was attributed to better dispersion of the agglomerates with the weblike structure. Dynamic mechanical analysis showed considerable improvement in the modulus of samples containing CNCSFD agglomerates. The percolation mechanical model with modified volume percolation threshold and filler network strength values and the Halpin-Kardos model were used to fit the experimental results.

Elongational flow properties of thermoplastic polyvinyl alcohol/polypropylene from the melt spinning method

In this investigation, the blend melts of thermoplastic polyvinyl alcohol (TPVA) and polypropylene (PP) were prepared through melt blending with various blending ratios. The melt spinning method was then adopted to determine and analyze the uniaxial elongational flow properties of the blend melts. First, a melt with a fixed blending ratio (TPVA/PP = 60/40) was selected as the sample to examine the effects of drawing ratios and spinning temperatures on the flow behavior. Experimental results demonstrate that the drawing ratio is the major determinant of elongational flow behavior, while temperature variation exerts little influence on flow behavior. Furthermore, the drawing ratio can also be altered through melt throughputs. The major differences between the samples with different melt throughputs were in the variations of thinning ability and the alteration of melt solidification points, leading to completely different elongation rate ranges. However, the elongation rate ranges increased with the drawing ratio. In addition, the elongation rates were initially close to each other, since the drawing ratio is changed by take up speed with same throughput. Moreover, the experimental data indicate that the elongational flow behavior of blend melts is also influenced by blending ratios. As the blending ratios converged, the elongational resistance decreased, and the elongation rate increased, suggesting a high deformation rate. Conversely, as the differences between blending ratios rose, the elongation rate decreased and the elongational resistance increased, such that the TPVA blending proportion was 20% or 80%. The elongational resistance of TPVA that increases with concave downward, and TPVA/PP blend melts exhibited an inflection in the profile of the elongational resistance versus the elongation rate.

Simulation of the Flow-Induced Crystallization of Polypropylene Based on Molecular Kinetic Model

A model for the isothermal flow-induced crystallization (FIC) of polypropylene melt in a simple shear flow is developed. The model is based on the molecular kinetic theory. The first normal stress difference of the stress tensor, calculated according to a molecular model, is assumed as the driving force of the flow-induced nucleation. Crystallization is described as a spherulitical nucleation and growth process. The theoretical predictions of the evolution of the viscosity in steady shear flow of iPP are in agreement with the experimental findings. The relative influence of the mechanical and thermal phenomena on the crystallization development is then analyzed as a function of the shearing intensity in terms of nucleation density. The results show the enhancement of the crystallization kinetics due to the shearing.

Preparation of Nano-Filled Polypropylene Microfibers

The effects of carbon nanotubes (CNT) and CNT-compatibilizer additives on the flow characteristics of melts of polypropylene—copolyamide (PP—CPA) mixtures were studied. It was shown that the elasticity of the melts and the longitudinal deformation increased in the nano-filled mixtures. It was found that combining CNT with a compatibilizer improved PP fiber formation in a CPA matrix by decreasing the surface tension at the interface of the components. This stabilized the PP liquid streams. Nano-filled PP microfibers with increased specific surface area and hygroscopicity were obtained.

Optimization of Manufacturing Parameters for Melt Spun Yarns Using Taguchi Method

In melt spinning process, evenness of polypropylene melt spun yarns affects the appearance, hairiness, strength and productivity of yarns, as well as product production and profits, causing rejection due to nonconformity. The research is to find optimal manufacturing parameters of melt spun yarns. Firstly, to proceed the parameter design by Taguchi method, then to select a manufacturing parameter which will affect the quality of melt spun yarns as controllable factors. Also to choose a suitable orthogonal arrays. Meanwhile, according to variation of analysis, to decide optimal manufacturing parameters of melt spun yarns and its remarkable factor. Finally, using 95% confidence interval to proof the experiment’s reliability and repeatability.

Comparison of superimposed effects in high-shear-rate capillary rheology of polystyrene, polypropylene, and linear low-density polyethylene melts

Polymer melts exhibit unique rheological behaviors at high shear rate up to 106 s−1, which is a common phenomenon in micro-injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low-density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 105, 8.0 × 105, and 2.8 × 106 s−1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 105 s−1 for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers

Multi-Component Composites Based on Polypropylene, Ethylene-Octene Copolymer and Zinc Oxide

Multi-component blends of polypropylene (PP), ethylene-1-octene copolymer (EOC) and zinc oxide (ZnO) are prepared by melt mixing using two-roll mill. Samples prepared by compression moulding have been investigated by using differential scanning calorimeter (DSC). It is found that addition of ZnO particles decreases PP melting point and increases crystallinity degree of PP. ZnO works as nucleation agent for PP by increasing quantity of crystallization centers, but at the same time decreasing structure quality. Because of the structure change mechanical properties are affected. At lower nanoparticle concentration some reinforcement effect I observed, while at higher particles concentration brittlening occurs. Crystalline structure and particles nature increases thermal stability of PP and PP/EOC blends.

Solid-state shear pulverization as effective treatment for dispersing lignocellulose nanofibers in polypropylene composites

Lignocellulose nanofibers (LCNFs) were prepared by the wet-disk milling of wood flour and were subsequently used as a reinforcing filler for a polypropylene (PP) polymer matrix. The specific surface area and the smallest fiber width of the LCNFs were found to be 106 m2/g and 20 nm, respectively. Solid-state shear pulverization (SSSP) using a batch-type kneader was performed at a temperature lower than the PP melting point in order to improve the dispersion of the LCNFs in the PP matrix, which also contained 5 wt% maleic anhydride-grafted PP. The SSSP treatment improved LCNF dispersion; this was determined through optical and scanning electron microscopy observations. The improvement in LCNF dispersion after the SSSP treatment increased the Young’s moduli, yield strengths, and toughnesses of the resulting composites. The composites showed higher Young’s moduli and yield strengths that those of the neat PP matrix; this was true in the case of both the tensile and the bending tests. However, the impact strengths of the composites were not significantly different from that of the neat matrix. Finally, the crystallization rate of the PP matrix also increased with the increase in LCNF dispersion.

A comprehensive 3D analysis of polymer flow through a conical spiral extrusion die

Several restrictions which are related to extruder machinery and nature of process material exist in the design of plastic extrusion dies. To this respect, it is very important to consider design criteria and limitations in order to operate extrusion dies at desired production rate and temperature. In the current study, flow field characteristics through a conical spiral mandrel die are analysed in detail by 3D Computational Fluid Dynamics (CFD) simulations. The effects of operating conditions such as production rate and temperature on pressure drop through the spiral mandrel die and the occurence of melt fracture are investigated. The temperature dependent viscosity versus shear rate data for grade QB79P (CarmelTech) polypropylene (PP) melt under study are measured by use of rotational and capillary rheometers. Stress terms in the momentum equations are modeled by Generalized Newtonian Fluid (GNF) Model. For this, Bird-Carreau Model is employed as the viscosity model for the polymer melt. 3D CFD analyses provide comprehensive data and understanding with regard to flow behaviour through complex extrusion dies.

In–line Ultrasonic Melt Flow Measurement of Polypropylene with Different Fillers

Pulsed Wave Velocimetry (PWV) is an ultrasonic technique for measuring velocity profiles in flowing liquids. We already demonstrated that PWV can be used to obtain velocity profiles of polypropylene melt, flowing in capillary dies with channel depths less than 2mm. The required ultrasound transducer with large bandwidth (which is restricted to operating temperatures below 50°C) is coupled to the hot melt using a temperature buffer, which serves as acoustic waveguide, but decouples transducer and melt thermally. In this contribution, we show results obtained in-line during the extrusion of glass-fiber-filled polypropylene as well as talcum-filled polypropylene at various feed rates.

Effect of stereochemical sequence on the dynamics of atactic polypropylene melt

Dynamic Monte Carlo (DMC) simulation was used to study the dynamics of a series of coarse-grained atactic polypropylene (aPP) model chains (C192H578) in the melt state at 473 K. Model chains with meso diads factions, P m , set at 0.25, 0.5, and 0.75 but with different meso and racemo diads sequences were studied. It was observed that aPP chains with an alternate meso and racemo diads sequence exhibited the highest mobility (or diffusivity) among all stereochemical sequences studied. Additionally, chains with long consecutive sequences of diads of the same type exhibited lower mobility than those with more random stereochemical sequences. The differences in the intramolecular and intermolecular interactions resulting from differences in diad sequences contributed to the observed differences in dynamics. In particular, intramolecular interactions play a more dominant role for aPP chains containing low fractions of meso diads or none at all (i.e., all racemo diads (P m =0.0) or syndiotactic chains). On the other hand, in the cases of P m values close to 1.0 (i.e., isotactic chains), intermolecular interactions play a more dominant role than the intramolecular interactions.

Short-Term Flow Induced Crystallization in Isotactic Polypropylene: How Short Is Short?

The so-called “short-term flow” protocol is widely applied in experimental flow-induced crystallization studies on polymers in order to separate the nucleation and subsequent growth processes [Liedauer et al. Int. Polym. Proc. 1993, 8, 236–244]. The basis of this protocol is the assumption that structure development during flow can be minimized and the rheological behavior, i.e., the viscosity, does not change noticeably. In this work we explore the validity of this assumption for short but strong flows and reveal the structure formation during the early stages of crystallization. Viscosity and structure evolution of an isotactic polypropylene (iPP, Mw ≈ 365 kg/mol and Mw/Mn = 5.4) melt at 145 °C are measured during the short-flow period (0.2–0.25 s) using the combination of a slit rheometer and fast X-ray scattering measurements. For high enough (apparent) shear rates (≥240 s–1) a viscosity rise during flow is observed; i.e., the condition for “short-term flow” is not satisfied. With a time delay with respect to the viscosity rise, the development of shish is observed at a position halfway the length of slit, along the flow direction, by means of ultrafast time-resolved SAXS measurements. Depending on the shear rate, these shish are detected during (shear rates ≥ 400 s–1) or after flow (240 s–1 ≤ shear rates < 400 s–1). For even lower shear rates of 160 and 80 s–1, the viscosity does not change significantly, and instead of shish, oriented row nuclei (X-ray undetectable) are generated. These two shear conditions qualify as short-term flow. A full understanding of the coupled flow and crystallization phenomena requires that the transient and nonhomogeneous behaviors, both in flow and in flow gradient direction, have to be taken into account. This can only be done by a full numerical model, and therefore, the results presented in this paper also provide a valuable data set for future numerical studies.

Detecting extensional viscosity of polypropylene melt using the Rheotens test: A comparison between standard and steady state test modes

The Rheotens test was used to determine the extensional viscosity of a polypropylene (PP) melt at three different extrusion velocities and using two capillaries with different length-to-diameter ratios. Results showed that, in the standard Rheotens test, the extensional viscosity curves determined under different testing conditions exhibit an obvious difference, especially under low extensional strain rates. This is attributed to the pre-orientation of macromolecular chains taking place in the capillary. Hence, a steady state Rheotens test was tentatively proposed. It was demonstrated that the extensional viscosity curves determined under most of the testing conditions by this test mode almost overlap, which is attributed to the fact that the pre-orientation of chains relaxes sufficiently near the capillary exit. This implies that equivalent extensional viscosities can be obtained under a wider range of extrusion velocities and capillary length-to-diameter ratios. Moreover, the equivalent extensional viscosities determined in the steady state Rheotens test exhibit good agreement with the extrapolated extensional viscosity curve determined using the Cogswell convergent flow method.