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REFERENCES [1] Molenaar J, Koopmans RJ: Modeling polymer melt-flow instabilities. J. Rheology 38 (1994) 99-109. [2] Georgiou GC, Crochet MJ: Time-dependent compressible extrudate-swell problem with slip at the wall. J. Rheology 38 (1994) 1745-1755. [3] Venet C, Vergnes B: Experimental Characterization of Sharkskin in Polyethylenes, J. Rheology 41 (1997) 873-892. [4] Graham MD: The sharkskin instability of polymer melt flows. Chaos 9 (1999) 154-163. [5] Denn MM: Extrusion instabilities and wall slip. Annu. Rev. Fluid Mech. 33 (2001) 265-297. [6] Barone JR

1 Introduction Sharkskin swimming suits have been forbidden in the Olympic Games and other competitions since 2010 in order to guarantee fairness (Stefani 2012), which potentially implies that the drag reduction effect of sharkskin has been exactly recognized in the practical fluid engineering. Since last century, the superiorities of sharkskin on drag reduction, anti-wear, water-repellent, and anti-fouling properties have been explored, validated, and utilized for several decades, with the result that different drag-reducing functions have been acquired in

DOI 10.1515/polyeng-2011-0157   J Polym Eng 2012; 32: 335–341 Mateusz Barczewski *, Roman Barczewski and Tomasz Sterzynski Dynamic pressure analysis as a tool for determination of sharkskin instability by extrusion of molten polymers Abstract : Increasing requirements which extruded polymeric products should accomplish are imposed to quantitatively characterize the factors which have a con- siderable effect on extrusion stability. Investigation has been realized by means of a rheological measurement device including a single screw extruder, as

C H A P T E R 4 Of Eyelashes and Sharkskin Since 1972, allergy doctors had relied on a list of symptoms to deter- mine if a child had an allergic disease. These symptoms included dark rings under the eyes due to poor sleep, creases on the nose due to fre- quent rubbing, and “long silky eyelashes.” This latter feature had no explanation, although along with the other symptoms, it had been used in medical practice for years. In 2004, Israeli allergy doctors decided to put it to the test. They measured the eyelash length of patients that were having allergic

hun- dred and twenty years after crime was first used to give scientific racism cred- ibility, still play a crucial role in defining the meaning of race in the early twenty-first century.  Reviewed by: Balthazar Becker (City University of New York, Graduate Center)  Lagnado, Lucette. The Man in the White Sharkskin Suit. A Jewish Family’s Exo- dus from Old Cairo to the New World. New York: Harper, 2008. Naggar, Jean. Sipping from the Nile. My Exodus from Egypt. New York: Stony Creek, 2008. Zonana, Joyce. Dream Homes. From Cairo to Katrina, an Exile’s Journey. New

REFERENCES [1] Costas GG, Bainian Q, Todd DB: Melt Flow Instability Studies of Metallocene Catalyzed LLDPE in Pelletizing Dies, SPE ANTEC (2002) 112-116. [2] Venet C, Vergnes B: Stress Distribution Around Capillary Die Exit: an Interpretation of the Onset of Sharkskin Defect, J. Non-Newtonian Fluid Mech. 93 (2000) 117-132. [3] Migler KB, Son Y, Qiao F, Flynn K: Extensional Deformation, Cohesive Failure, and Boundary Conditions During Sharkskin Melt Fracture, J. Rheol. 46 (2002) 383-400. [4] Denn MM: Issues in Viscoelastic Fluid-Mechanics, Annu. Rev. Fluid Mech

1 Introduction Sharkskin is usually defined as high frequency, small amplitude, and fine scale distortions or surface roughness that happen upon extrusion [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ]. It can affect the mechanical and optical properties of the extrudate, so it is significant scientific and commercial motivation to study sharkskin and possible solutions to reduce it. Numerous studies on sharkskin were undertaken during the past 60 years with experimental evidence indicating that sharkskin’s instability originated at the die exit and not inside it [ 6 ], [ 7

). Results revealed that the above mentioned properties are strongly dependent on the presences of kaolin and MAH in both composite systems. Observation on scanning electron microscopy (SEM) analysis showed that the kaolin books (stacks of kaolin particles) were successfully delaminated thus lead to a well dispersed of kaolin particles in PP and UPVC matrix. Key words: polypropylene, unplasticised poly(vinyl chloride), kaolin, maleic anhydride, extrudate swell, melt fracture, sharkskin, flexural behaviour. Introduction The widespread use of polymer materials

”, University of Huelva, 21071 Huelva (Spain); fax: +34 959 219983; email: imgarcia@uhu.es (Received: 16 May, 2007; published: 7 November, 2007) Abstract: A metallocene catalysed linear low density polyethylene (mLLDPE) was mixed with very low amounts of bitumen (1-2%) as an additive. Bitumen interacts with mLLDPE giving rise to a dying effect, which turns the originally white mLLDPE extrudates into black. No slippage is observed during extrusion and sharkskin is postponed as bitumen is added. “Melt strength” values of the blends, determined in melt spinning