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Molten Polymers (molten + polymer)
Selected AbstractsEffect of screw element type in degradation of polypropylene upon multiple extrusionsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2002Sebastião V. Canevarolo Abstract The screw profile of a twin-screw extruder can be designed to contain kneading and conveying elements inducing different levels of degradation in the polymer melt. In this work, the level of degradation in polypropylene has been measured after multiple extrusions,for various screw profiles,using size exclusion chromatography and IR spectroscopy. The average molecular weight and the polydispersity have been reduced and the carbonyl and unsaturation indexes increase as the number of extrusions and the aggressivity of the screw profile increase. The kneading element with 90° caused the greater level of degradation. On the other hand, the addition of left-hand conveying elements reduces the level of degradation because of the extra volume of molten polymer held in the screw, reducing the viability of oxygen inside the barrel. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 243,249, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10028 [source] Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular WeightsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Claudia Stern Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,·,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,·,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source] Disturbance Propagation in the Melt Spinning ProcessPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Anthony McVeigh This work deals with the propagation of a disturbance acting on a fibre in the melt-spinning process, where molten polymer is ejected vertically downwards from an orifice before being drawn onto a wind-up spool. The disturbance may be produced by a sudden horizontal draught of air impinging on a part of the fibre. The flow is modeled as a wave propagating on a moving string under the influence of damping and variable tension. The amplitude of the disturbance is obtained in closed-form along the characteristics which emanate from the boundaries of the localised initial disturbance; the general solution of the damped disturbance is determined numerically. An important aspect of the model is the ability to predict the magnitude of this disturbance close to the orifice, where the extruded polymer is molten and therefore extremely sensitive to disturbances. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Novel synthesis of polyethylene,poly(dimethylsiloxane) copolymers with a metallocene catalystJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Andrés E. Ciolino Abstract Polyethylene,poly(dimethylsiloxane) copolymers were synthesized in solution from an ethylene monomer and an ,-vinyl poly(dimethylsiloxane) (PDMS) macromonomer at 363 and 383 K with EtInd2ZrCl2/methylaluminoxane as a catalyst. The copolymers obtained were characterized with Fourier transform infrared spectroscopy, 1H and 13C NMR, size exclusion chromatography, and differential scanning calorimetry. The rheological properties of the molten polymers were determined under dynamic shear flow tests at small-amplitude oscillations, whereas the physical arrangement of the phase domains was analyzed with scanning electron microscopy (SEM)/energy dispersive X-ray (EDX). The analysis of the catalyst activity and the resulting polymers supported the idea of PDMS blocks or chains grafted to polyethylene. The changes in the rheological behavior and the changes in the Fourier transform infrared and NMR spectra were in agreement with this proposal. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2462,2473, 2004 [source] Role of processing aids in the extrusion of molten polymers,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2002E. C. Achilleos Product quality and, in general, processing windows and rates of production in the extrusion of molten polymers are limited by various flow instabilities (mainly melt fracture) that are observed at high production rates. While there still are unresolved issues in comprehending these phenomena, industry demands for process optimization dictate the employment of processing aids (PAs) for product quality improvement and energy requirement reduction. In this review paper, most commercially used processing aids (PAs) are discussed, namely, fluoroelastomers, stearates, small amounts of polymers blended with the process polymer, and the newly discovered boron nitride as pure and in combination with other fluoroelastomers. This paper focuses on the appropriate and optimum usage of the various PAs as well as on the mechanism that underlies their action for flow enhancement and instability elimination. Finally, numerous experimental observations are discussed, and several examples are illustrated. [source] Effect of melt annealing on the phase structure and rheological behavior of propylene,ethylene copolymersPOLYMER ENGINEERING & SCIENCE, Issue 6 2007Vanesa De La Torre The morphological and rheological properties of a commercial propylene-ethylene copolymer (PEC) and a series of blends with different concentrations of poly (ethylene- co -propylene) are investigated. The blends are prepared mixing PEC with fractions obtained from it by solvent extraction. The phase structure of samples exposed to different thermal and mechanical histories was analyzed using scanning electron microscopy. The linear viscoelastic properties of the molten polymers were measured using different test sequences that include dynamic frequency and time sweeps. The phase structure of most blends changes dramatically with time when the polymers are kept in the molten state due to the coalescence of the domains. For example, the initial morphology of PEC which presents domains of ,1 ,m diameter changes to regions of more than 10 ,m of average diameter after 90 min at 178°C at rest. Coincidentally, the dynamic moduli of the blends change during annealing reaching values that depend on the mechanical history. For example, the elastic modulus of PEC increases ,32% during a dynamic time sweep of 45 min using a frequency of 0.1 s,1, while it decreases ,18% when a frequency of 1 s,1 is applied. Moreover, the modulus measured at 0.1 s,1 of samples annealed at rest during 45 min is ,58% larger than that of the fresh material. POLYM. ENG. SCI., 47:912,921, 2007. © 2007 Society of Plastics Engineers [source] | ||||||||||