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Melt Strength (melt + strength)

Distribution by Scientific Domains

Polymers and Materials Science	64%

Selected Abstracts

The effect of long chain branching on the processability of polypropylene in thermoforming

POLYMER ENGINEERING & SCIENCE, Issue 5 2004
A. D. Gotsis
Linear polypropylene was modified by reaction with peroxydicarbonates in a twin screw extruder to obtain varied degrees of long chain branching. The melt strength and the elasticity of the modified polymers were found to increase with the modification. The processability in foaming and thermoforming processes improved with branching and showed an optimum, beyond which higher degrees of long chain branching appeared not to help any further. The branched PP samples showed distinct strain hardening in the elongational viscosity, which was absent from the original linear melts. Melt strength, elasticity and strain hardening increased with the increase of the number of long chain branches on the main chain. The effect of molecular weight and molecular weight distribution of the precursor on the improvement of the processability of the polymer was examined. Polym. Eng. Sci. 44:973,982, 2004. © 2004 Society of Plastics Engineers. [source]

Melt strength of calcium carbonate filled polypropylene melts

POLYMER INTERNATIONAL, Issue 12 2002
Nhol Kao
Abstract This paper investigates the extensional rheology (through melt strength measurement) of calcium carbonate (CaCO3) filled polypropylene (PP) melts. Different concentrations of CaCO3 filled PP were produced by mixing two master batches of pure PP and 70,wt% CaCO3 filled PP in required proportions in a counter-rotating twin-screw extruder. It was found that the melt strength of the CaCO3,PP melts was independent of CaCO3 concentrations up to 25,vol%. Further increase in CaCO3 concentration led to a severe reduction of melt strength. © 2002 Society of Chemical Industry [source]

Rheology and thermal properties of polypropylene modified by reactive extrusion with dicumyl peroxide and trimethylol propane triacrylate

ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2009
Feng-Hua Su
Abstract Trimethylol propane triacrylate (TMPTA) and dicumyl peroxide (DCP) were used to modify polypropylene (PP) by reactive extrusion in a twin-screw extruder. The effects of TMPTA concentration on oscillatory shear rheology, melt elongational rheology, and thermal properties were comparatively evaluated. Fourier transform infrared spectroscopy indicated that the grafting reaction took place and TMPTA had been grafted onto the PP backbone. Differential scanning calorimetric results showed that the crystallization temperatures of modified PPs were higher than those of the initial and degraded PPs. The rheological characteristics such as higher storage modulus (G,) at low frequency, increased degree of shear thinning, a plateau in tan ,,, plot, and upturning at high viscosity in the Cole,Cole plots proved that the long-chain branches have been added to the linear PP molecule. The melt elongational rheology showed that the modified PPs exhibit improved melt strength and increased elongational viscosity in the presence of TMPTA and DCP, which further confirmed the existence of long-chain branching (LCB) in their backbone. According to the analytical results from oscillatory shear rheology and elongational rheology, it can be inferred that the LCB level in modified samples increases with an increase in TMPTA concentration. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:16,25, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20146 [source]

Rotational foam molding of polypropylene with control of melt strength

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003
Remon Pop-Iliev
Abstract Polypropylene (PP) has not been used extensively in rotational foam molding because it has been traditionally considered as nonfavorable for foaming applications because of its relatively weak melt strength and melt elasticity at elevated temperatures. However, because of the unique end-use properties of PP, PP foams have recently grown in importance. An experimental study was conducted to identify feasible processing strategies for producing PP foams with satisfactory morphologies in dry-blending-based rotational foam molding. The obtained results revealed that cell coalescence plays a key role in the production of PP foams in rotational foam molding. If it is efficiently suppressed, the cell morphology of the PP foams improves dramatically. To suppress cell coalescence, it would be necessary to preserve the melt strength of PP during processing. One way of doing this is maintaining the temperature of the PP melt as low as possible. This can be accomplished by either lowering the decomposition temperature of the chemical blowing agent by using an activator such as zinc oxide and/or reducing the temperature of the oven. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 280,296, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10056 [source]

Quantitative relation between shear history and rheological properties of LDPE

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2001
Masayuki Yamaguchi
The role of the applied processing equipment shear history on the rheological properties of low-density polyethylene was studied in detail. It was found that the shear history depresses the melt strength and the oscillatory shear modulus, especially the storage modulus in low frequency region. This phenomenon is not caused by lowering of the molecular weight, which remained the same as the original, for all shear history samples, indicating absence of mechanical/thermal degradation during processing. Furthermore, annealing the melt processed samples enhances both the melt strength and the oscillatory modulus to the values of the original, unsheared sample. Finally we applied shear history in a cone-and-plate rheometer and found that the growth curve of the storage modulus, which can be expressed by a simple equation, is determined by both the duration of the flow and the magnitude of the applied shear stress. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 261,269, 2001 [source]

Microcellular foaming of PE/PP blends

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
Ping Zhang
Abstract Three different polyethylene/polypropylene (PE/PP) blends were microcellular foamed and their crystallinities and melt strengths were investigated. The relationship between crystallinity, melt strength, and cellular structure was studied. Experimental results showed that the three blends had similar variation patterns in respect of crystallinity, melt strength, and cellular structure, and these variation patterns were correlative for each blend. For all blends, the melt strength and PP melting point initially heightened and then lowered, the PP crystallinity first decreased, and then increased as the PE content increased. At PE content of 30%, the melt strength and PP melting point were highest and the PP crystallinity was least. The blend with lower PP crystallinity and higher melt strength had better cellular structure and broader microcellular foaming temperature range. So, three blends had best cellular structure at PE content of 30%. Furthermore, when compared with PE/homopolymer (hPP) blend, the PE/copolymer PP (cPP) blend had higher melt strength, better cellular structure, and wider microcellular foaming temperature range, so it was more suited to be microcellular foamed. Whereas LDPE/cPP blend had the broadest microcellular foaming temperature range because of its highest melt strength within three blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4149,4159, 2007 [source]

Rheology and melt strength of long chain branching polypropylene prepared by reactive extrusion with various peroxides

POLYMER ENGINEERING & SCIENCE, Issue 2 2010
Feng-Hua Su
Long Chain Branching Polypropylenes were prepared in an extruder by a melt grafting reaction in the presence of various peroxides and a polyfunctional monomer of 1,6-hexanediol diarylate. Fourier Transformed Infrared spectra and the rheological characteristics indicated that the grafting reaction added long branched chains to linear polypropylene (PP). In comparison to the initial PP, the branched samples exhibited higher melt strength, lower melt flow index, and enhancement of crystallization temperature. The branching number of the modified samples agreed well with their melt viscoelasticity and the improved degree of their melt strength. The branching level in modified PPs could be controlled by the property and structure of the peroxide used. Peroxides with lower decomposition temperature and more stable radicals after decomposition promoted the branching reaction, leading to the modified PPs with higher branching level and melt strength. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Molecular, rheological, and crystalline properties of low-density polyethylene in blown film extrusion

POLYMER ENGINEERING & SCIENCE, Issue 12 2007
Khokan Kanti Majumder
The molecular weight and its distribution, degree of long chain branching and cooling rate strongly influence crystallinity during processing, which in turn determines the processability and the ultimate properties of the blown film. Generally a decrease in the number of branches and molecular weight of the polymer and the cooling rate results in an increase of the crystallinity. Length of the main chain and extent of branching in low-density polyethylene (LDPE) are also factors that affect melt rheology and film crystallinity. Long chain branched polyethylene is suitable in the blown film process due to its better melt strength for bubble stability. The objective of this article is to describe the effect of molecular properties (e.g. molecular weight and its distribution, degree of long chain branching etc) of LDPE on film crystallinity at different cooling rates of blown film extrusion. Two different grades of LDPE were selected to investigate molecular characteristics, crystallinity, and rheology. The resins were processed in a blown film extrusion pilot plant using four different cooling rates. Molecular, rheological, and crystalline properties of the resins were key parameters considered in this study. POLYM. ENG. SCI., 47:1983,1991, 2007. © 2007 Society of Plastics Engineers [source]