PP-Blends with Tailored Foamability and Mechanical
`
`Properties
`
`Norbert Reichelt, Manfred Stadlbauer, Rick Folland. Chul B. Park*
`
`and Jin Wang*
`
`Borealis GmbH, St.-Peter-Str. 25, A4021 Linr, Austria
`'Microcellular Plastics Manufacturing Laboratory, Department ofMechanical and
`Industrial Engineering, University of Toronto, Toronto, Ontario, Canada M5S 3G8
`
`Received: 9 July 2003 Accepted: 1 August 2003
`
`ABSTRACT
`
`The optimisation ofphysical foaming of branched Daploy""‘ WB]30IBlS
`polypropylene foam resin and corresponding blends with a Polypropylene
`Blockcopolymer are described in thispaper. The resultingfoam morphologies
`ofblends consisting oflinear and branchedpolypropylene materialsproduced
`at variousprocessing temperatures were studied using a single—screw tandem
`foam extrusion system and their volume expansion behaviours were compared.
`Ihree diflerent die geometry 's were testedforphysicalfoaming ofPP-blends
`using 5 and I 0 wt% ofbutane. A correlation between extensional rheology and
`lower limit offoam densityfor blends wasfound. Depending an die geometry
`the use of diflerent concentrations of branched polypropylene resin in the
`blends was required to achievefoam densities < 50
`The influence offoam
`density and blend ratio on mechanicalproperties offoams will be discussedon
`a model and representative samples.
`
`1. INTRODUCTION
`
`Polypropylene foams are considered as a substitute for other thermoplastic
`foams in industrial applicafions due to several reasons beyond its lower costs.
`They have a higher rigidity compared to other polyolefins, offer higher
`strength than polyethylene, better impact strength than polystyre, and they
`provide higher service temperature range and good temperature stability
`compared to both classes of materials.
`
`However, since standard linear polypropylene shows low melt strength, low
`extensibility and thus poor foamability, another class ofpolypropylenes must be
`
`Footnote: An earlier version of this paper was presented at Blowing Agents and Foaming
`Processes 2003, 19-20 May 2003, Munich, Germany
`
`Cellular Polymers, Vol. 22, No. 5, 2003
`
`315
`
`PAGE 1 OF 14
`
`BOREALIS EXHIBIT 1014
`
`

`
`Narbm Reichelt, Manfied Stadlbauer, Rick Folland, Clml B. Park and Jin Wang
`
`used. Technologies were established for the production oflong-chain branched
`polypropylene which led to the high-melt-strength polypropylene resins for the
`production of low density foams. Reasons for their better performance in
`foaming are their enhanced extensional flow properties. i.e. increased melt
`strength and increased extensibility of the melt. I-IMS-PP materials can be
`foamed either in its pure form yielding rigid foams. or as a blend with other
`polyolefins in order to tailor the mechanical properties of the foams.
`
`This publication investigates the influence of blending HMS-PP with a
`polypropylene block-copolymer. The interrelations of blend ratio on the
`extensional rheology. on foamability, and on the mechanical properties of
`final polypropylene foams are discussed.
`
`2. EXPERINIENTAL
`
`2.1 Materials
`
`Two Borealis polypropylenes were used in the present work. One of them.
`Daploym WB 1 30HMS is a branched homopolymerwith highmelt strength and
`high extensibility. The second material. BC250MO, is a standardPolypropylene
`Block-copolymer with ethylene commonly used for injection molding.
`
`Table 1 Material data
`
`PP Block Copolymer
`
`Borealis
`
`BC250MO
`
`2-"w
`
`g,\'l0min
`n2
`
`2 E
`
`e\°
`
`I—| ‘
`
`Q‘?
`
`Melt Strength
`
`Extensibility
`Tensile Modulus
`
`Tensile at Yield
`
`‘‘E
`
`longation at Break
`
`2.2 Testing of Material Properties
`
`The extensional flow properties of the melt and the mechanical properties of
`injection molded test specimen were investigated with the Rheotens test, and
`
`315
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`PAGE 2 OF 14
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`

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`PP—Blends with Tailored Foarnabiliiy and Mechanical Proprmics
`
`the tensile test according to ISO527, respectively. The Rheotens experiment
`simulates industrial spinning and ext:rusion processes. In principle a melt is
`pressed or extruded through a round die and the resulting strand is hauled off.
`The stress on the extrudate is recorded, as a fimction of melt properties and
`measuring parameters (especially the ratio between output and haul-otfspeed,
`practically a measure for the extension rate).
`
`For the results presented below, the materials were extruded with a lab
`extruder HAAKE Polylabsystem and a gear pump with cylindrical die (L/D =
`6.0/2.0 mm). The gear pump was pre—adjusted to a strand extrusion rate of
`5 mm/s, and the melt temperature was set to 200°C. The Giittfert Rheotens
`tester was operated at constant acceleration of the pulleys (120 mm/s2). The
`end points ofthe Rheotens curve (force versus pulley rotary speed) is taken as
`the melt strength and extensibility values.
`
`2.3 Experimental Setup for Foaming
`
`This setup is intended to determine the processing window of the selected
`materials and its blends with butane as a foaming agent in a broad range ofmelt
`temperatures with diiferent die geometries. The achieved minimum densities
`are around 30 kg/m3.
`
`A tandem foam extrusion setup was used for this purpose. It consists ofa 5-hp
`extruder drive with a speed control gearbox (Brabender, Prep Center), a first
`3/4” extruder (Brabender, 05-25-000) with a mixing screw (Brabender, 05-00-
`144) of30: 1 IJD ratio, a second 1 1/2” extruder (Killion, KN- 1 50) with a built-
`in 15-hp variable speed drive unit with a 18:1 IJD ratio. The other systems
`include a positive displacementpump forbutane injection. a diffusion enhancing
`device containing static mixer (omega, FMX-84441-S), a gear pump (Zenith,
`PEP-H 1.2 cc/rev) where the volumetric displacement is properly controlled
`by the motor, a heat exchanger for cooling the polymer melt that contains
`homogenizing static mixers (Labcore Model H-04669-12), a cooling sleeve
`for the precise control of die temperature. The first extruder is used for the
`plastication ofthe polymer resin while the second extruder is responsible for
`mixing and initial cooling of the polymer melt. The gear pump controls the
`polymer melt flow rate and the heat exchanger further homogenizes and cools
`the melt. Three different dies(1)L/D=0. 1”/0.018”, (2) I./D=0.3”/0.040”, and
`(3) L/D = 0.5”/0.040”) were used in this study.
`
`The polypropylene material pellets blended with 0.8 wt% talc as cell nucleating
`agentwere first fed into the barrel through the hopper andwere completely melted
`by the screw rotation. Then a metered amotmt of butane was injected into the
`
`Cellular Polymers, Val. 22, Na. 5, 2003
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`

`
`Narbm Reichnlt, Manfied Stadlbmrcr, Rick Folland, Clml B. Park and Jin Wang
`
`extrusion barrel by a positive displat pump and mixed intensively with the
`polymer melt stream. The single-phase polymerlgas solution passed through the
`gearprmlpandwas fedintotheheat exchangerwhere itwascooledtoadesiguated
`temperature. The cooled polymer/gas solution tered flie die and foaming
`occurredatthe die exitthrough a process ofthermodynamic instability inducedvia
`rapid pressure drop. The melt and die temperatures were synchronized for
`
`
`simplicity in this study. While optJnnnng'' '
`all the parameters, the melt and die
`temperature were loweredgraduallyand samples were randomly collected at each
`designated temperature when no fimher change was observed in the pressure.
`
`2.4 Characterization of the Foams
`
`The density ofthe foams was determined by measuring the weight and volume
`of the sample.
`
`For representative samples made from defined blends of WBl30I-IMS and
`BC250MO with industrial foaming lines, tensile tests according to ISO527
`and falling dart tests were performed.
`
`3. RESULTS AND DISCUSSION
`
`3.1 Mechanical Properties of Blends
`
`Daploym WB l30HMS is a homopolymer based material. Although it enables
`the production of very low density foams, these tend to be rather stiff.
`However, because it is pure PP material, it can be blended with the full range
`of other standard P0 materials to modify the final foam properties to fit the
`requirements of the particular end-use application (see Table 2).
`
`As with all polymer blends, the final blend properties depend on the proper1ies
`of the individual materials and the blend ratio.
`
`For our particular system, tensile tests have been performed with the pure
`materials, as well as with a 50/50 blend of WB130I-[MS and BC250MO. It
`shows, that the block-copolymer has lower tensile modulus with l250NIPa,
`while the pure HMS-PP homopolymer has a tensile modulus of2000lvfPa. The
`blends show tensile modulus right between the two pure materials. In terms of
`elongation at break, the pure block-copolymer has an elongation at break of
`450%, while the HMS-PP homopolymer shows elongation at break values of
`12%. No linear relationship ofelongation at break and blend ratio was found.
`This is indicated in Figure 1.
`
`313
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`Cellular PoI_ymarx, Vol. 22, Na. 5, 2003
`
`PAGE 4 OF 14
`
`

`
`PP—Blends with Tailored Faainability and Mechanical Properties
`
`Table 2 Effect of Blend Partners to Daploym VVB130HMS
`
`Blend Partner
`
`Foam Property Modifications
`
`Block Copolymer
`
`- Improved Low Temperature Impact
`0 Reduced Stifiiess
`
`Random Copolymer
`
`Borsoftm PP‘s
`
`0 Increased Toughness
`
`- Softer Foams
`- Improved Toughness
`- Soft Foam
`
`0 Good Low Temperature Impact
`
`- Very Soft Foams
`' Good Low Temperature Impact
`
`
`_/
`
`Tensile Test ISO 527
`Injection molded specimen
`Blends iiith nc2§0Mo
`
`r
`
`-
`
`1
`
`-
`
`500
`
`22
`«E
`5.
`O
`:1
`{J
`
`Ea
`a
`7?
`53
`A
`<:
`5*
`
`2500
`
`2c
`
`»
`3 2000
`2
`.:‘
`:3
`‘D
`
`°
`2
`._
`3 I500
`w
`'=
`0)
`P
`
`0
`
`'20
`
`40
`
`60
`
`80
`
`I00
`
`Daploy WB I 301-[MS (\vt‘7z=)
`
`Figure 1 hlechanieal properties of HMS-PP blends
`
`3.2 Extensional Rheology of Blends
`
`The most important consideration for foam production is the eflect ofthe blend
`partner on the achievable foam density at a given production set up. In this
`respect the linearblendpartnerwill have a “diluting” eflect on the benefits ofthe
`pure HIVIS and reduce its effectiveness. The reason for this is a changed
`
`Cellular Polymers, Vol. 22, Na. 5, 2003
`
`319
`
`PAGE 5 OF 14
`
`

`
`Narbm Reichnlt, Manfied Stadlbaucr, Rick Folland, Clml B. Park and Jin Wang
`
`extensional rheology of the blend due to lower conctration of long chain
`branches. An example ofthe eflect on the Rheotens results with difierent levels
`of standard block copolymer blded with Daploy‘ WBl30HMS is shown in
`Figure 2. For the pure standard block copolymer (0% I-IIVIS content, low melt
`strength, low extensibility), it is diificult to achieve densities below 500 kg/m3.
`By adding HMS to the block copolymer, it is possible to increase melt strength
`and extensibility towards the range of high performance foam resins. As a
`consequence very low foam densities (< 1 00 kg/m3) canbe achievedwithblds
`of Daploym HIVIS, as will be demonstrated in the next section in more detail.
`
`3.3 Foaming Behaviour
`
`In this section, the foaming behaviour ofpine I-IIVIS-PP and its blends with the
`block-copolymerare discussed. The performance ofdifferent resins in foaming
`depends very much on the processing conditions. In particular, the die
`geometry and thus the pressure drop in the die plays a dominant role. In the next
`figures there are compared two different dies, yielding absolutely difierent
`results for linear resins. With die 1
`pressure drop) both, linear and
`branched material can be foamed to reasonably low densities. However, the
`die pressure exceeds 100 bar (in particular for the linear resin), which is
`currently seen as a practical limit for industrial foam extrusion lines.
`
`Rheotens 200°C 120 mm/s
`
` 5
`
`30
`
`3
`
`;
`
`1oo%1‘ WB130H s
`..._...-_..1..-....-....._...
`70%WB13OHMS
`5o%wEl13oHMs
`
`
`
`
`
`MeltStrength(c.\I)
`
`()
`
`50
`
`100
`
`150
`
`200
`
`250
`
`300
`
`Extensibility (mm/s)
`
`Figure 2 Rheotens curves of HIVIS-PP blends
`
`320
`
`Cellular Polymers, Vol. 22, No. 5, 2003
`
`PAGE 6 OF 14
`
`

`
`PP—Blends with Tailored Foamabiliiy and Mechanical Prapenic:
`
`With die 2 (lower pressure drop), there is a remarkable difference between a
`linear resin with low melt strengfll, and a branched resin with high melt
`strength. When the die pressure is below 100 bar, the resin with high melt
`strength can be foamed to densities lower than 30 kg/m3, whereas with the
`linear resin hardly densities lower than 150-2001-Kg/m3 can be achieved. Please
`refer to Figure 3.
`
`F0
`-1
`Z‘
`'5
`5 IO!)
`1
`
`E
`5
`LL H1
`WI
`
`E
`-'3
`3
`2 701!
`5/)
`
`3 Illll
`at
`.2
`D II
`
`Die 1: 1/D=1/0.018
`
`'-‘ I II
`'~;__ Die 2: L/D=0.3/0.040"
`Po
`'-3.‘,
`2*
`'5
`'5 mo
`1::
`
`E
`'8
`L If!
`300
`
`E
`-3
`D
`8 264)
`LI:
`
`I00
`
`:2.
`.9
`5 I)
`
`I20
`
`‘Ht’!
`4
`If-"
`N”
`_
`Die Temperature (“U
`
`nn
`
`my
`:50
`u:u
`Die Temperature (°C)
`
`
`
`
`H
`
`.
`'
`1.‘
`gm Die 3. L/D=0.5/0.040
`(:0
`
`i3
`
`*
`‘<73:0
`-c:
`
`E 8
`
`LL.
`
`ta
`:9
`2 .
`:a(I)
`
`§13..
`.2
`D
`
`III’!
`
`ISFI
`I60
`I-10
`.
`Du: Temperature (°C)
`
`Figure 3 Foaming of linear vs. branched resin for three dies with high and low
`pressure drop with 10% butane
`
`Cellular Polyrnws, Val. 22, Na. 5, 2003
`
`32]
`
`PAGE 7 OF 14
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`

`
`Narbm Reichnlt, Manfied Stadlbaucr, Rick Folland, Clml B. Park and Jin Wang
`
`As it may be expected from the Rheotens results, blends which are rich in
`I-IIVIS-PP show better foamability due to their higher melt strength. Indeed,
`looking at the lowest achievable density at a die temperature of 1 20°C, forpure
`block-copolymer densities lower than 400 kg/m3 (5% butane), or 150 kg/m3
`(10% butane), respectively, cannot be reached. With increasing amount of
`HMS-PP, the lower limit of foam density drops to less than 70 kg/m3 (5%
`butane), or 30 kg/m3 (10% butane), respectively.
`
`Additional to this, the foaming window that enables the production of foam
`density < l00kg/m3 is getting larger with increased HlVIS—PP ratio. This can be
`seen from Figure 5, where the achieved foam density is plotted against the die
`temperature. It shows, that the range oftemperatures, where low density foams
`can be produced is much broader for blends which are rich in HMS—PP,
`compared to the temperature range for blends with less HMS-PP. The
`advantage of such HMS-blends simplifies the production of low density PP
`foams in terms of production stability.
`
`Reason for this is found in the extensional flow properties ofthe blends. With
`adding HNIS-PP both, melt st:rgth and extensibility of BC250M0 are
`improved.
`
`Boreulis BCZSOMO + Daploym WB I SOHMS
`
`Source:
`_..._.__.-.t....._.....__...
`
`Daploym WBl30HMS (wt%)
`
`Figure 4 Achieved foam density with HMS—PP blends
`
`322
`
`Cellular Polymers, Vol. 22, Na. 5, 2003
`
`PAGE 8 OF 14
`
`

`
`PP—Blends with Tailored Foamability and Mechanical Properties
`
`Borealis BCZSOMO + Daploym WB|30HMS
`
`Density
`
`(kg/m3)
`
`1()()
`
`II()
`
`120
`
`l3()
`
`l4()
`
`IS()
`
`160
`
`l7()
`
`l8()
`
`Die Temperature (°C)
`
`Figure 5 Achieved foam density with HMS-PP blends versus die temperature
`(10% butane, die geometry 0.30”/0.040”)
`
`3.4 Mechanical Properties of Foams
`
`According to the model ofGibson and Ashby, the mechanical properties, i.e.,
`the tensile moduli of foams are determined by three factors:
`
`a) Density of the foam
`
`b) Tensile modulus of the bld used, and
`
`c) Foam structure
`
`The model of Gibson and Ashby describes the tensile modulus of isotropic
`foams
`
`5- 2&2
`_
`.&
`Eu_<p[pu)+(1 «p)[pu]
`
`(1)
`
`with E as the tensile modulus, p the density, and the indices M and S refer to
`the matrix and specimen of the foam, respectively. The fitting parameter (D
`corresponds to the portion ofopen cells. Open-celled foams have lower tensile
`modulus compared to foams with closed cell structure.
`
`Cellular Polyrnws, Val. 22, Na. 5, 2003
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`323
`
`PAGE 9 OF 14
`
`

`
`Norbcrl Reichclt, Mmyfiad Stadlbawr, RickFolland, Chul B. Part and In Wang
`
`
`
`Figure 6 Influence factors for mechanical properties of foams
`
`So, the approach how to tailor the mechanical properties of PP foams has
`become clear: One must get control over the three influence variables, i.e.,
`foam density, tensile properties of the blend, density of the blend, and foam
`structure.
`
`First, the density ofthe foam can be varied. This is achieved with the amount
`of either chemical foaming agent for foams in the higher range of densities
`(higher than around 400 kg/m3), or physical foaming agent for low density
`foams (down to around 30 kg/m3). It shouldbe mentioned, that the prerequisite
`for production of low density foam is the resin’s high melt strength and high
`extensibility. Figures 7 and 8 show the eflect offoam densityon the mechanical
`properties offoams made by physical and chemical foaming with butane, and
`chemical foaming agent based on citric acid It shows that the modulus ofthe
`foam decreases with reduced foam density. Depending on the tensile modulus
`ofthe 1m-foamed resin, different levels oftensile modulus can be adjusted by
`density variation.
`
`Secondly, the tensile properties ofthe foam can be varied by the use ofblds.
`With adding, for example block-copolymer to the matrix of I-IMS-PP, the
`tensile modulus is reduced, while the elongation at break is increased. This has
`implications to the several properties of the foam, like impact strength, heat
`resistance and compression strength. The lower the tensile modulus of the
`
`324
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`Cellular Polymers, Vol. 22, No. 5, 2003
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`

`
`PP—Blends with Tailored Foamabiliiy and Mechanical Properties
`
`Tensile Test
`
`Foamcd sheets made from nC250M0/WB I 30nMs (50/50)
`
`Full potential ot blond
`
`(injection mouldung)
`
`
`
`2000
`
`A
`E’ 1500
`
`1000
`
`500
`
`0
`
`5 §
`
`22 E
`
`,’
`
`0
`
`200
`
`400
`
`600
`
`800
`
`Density (kg/m3)
`
`Figure 7 Tensile Modulus vs. Density for blends of WB130lIMS with 50 wt%
`block-copolymer
`
`blend, the higher becomes the impact strength and the softness of the final
`foam product. In the case of blends of HNIS-PP with block-copolymer, the
`tensile modulus of the un-foamed resin decreases, and therefore also the
`modulus of the foamed sheets is lower.
`
`In terms of energy absorption as measured with the falling dart test, the pure
`HMS foam shows values <l00 N/mm over the whole density range. A blend
`containing 50 wt% of block-copolymer offers significantly increased energy
`absorption compared to pure HMS foams.
`
`Other options aside blending to increase energy absorption of PP foams are
`seen in cooling speed in foam production and increased number of cells per
`unit volume. These ways are under investigation, but not fully explored at the
`time being.
`
`4. CONCLUSIONS
`
`Prerequisite for the production of low-density polypropylene foam is the use
`of a resin with high melt strength and high extensibility. Blends of standard
`linear PP with branched HMS-PP allow tailoring extensibility and melt
`
`Cellular Polymers, Val. 22, Na. 5, 2003
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`325
`
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`
`

`
`Norbm Reichnlt, Manfied Stadlbmrcr, Rick Folland, Chul B. Park and Jin Wang
`
`Falling Dart Test
`
`5()()
`
`
`
`.
`so’/.oapIor'wa13oHus
`50%BomaIls aczsouo
`
`300
`
`A 400
`
`E E E
`
`5
`Q
`._
`
`
`
`*
`2.45";
`:
`
`1 oo%oapIu;5" war301-ms
`5‘ __’,t3-—'
`
`
`i
`
`/4
`
`/"’i///
`
`55>‘) 200
`.3
`
`E
`
`O
`
`200
`
`400
`
`600
`
`800
`
`Density (kg/m-‘)
`
`Figure 8 Damage load from the falling dart test vs. density of pure WBl30IIMS
`and its blend with 50 wt% block-copolymer
`
`strength ofblends, as measured with the Rheotens setup. With adding HMS-
`PP to linear PP, one can achieve blends with excellent foaming behaviour.
`
`The mechanical properties of foams, as measured with falling dart test and
`tensile test, can be pre-adjusted by controlling foam density, foam structure,
`and mechanical properties of the resin. Regarding the mechanical properties
`ofthe resins, the concept ofblending I-IIVIS-PP with linear PP has been proven
`successful. Promising PP blend partners are available in a wide property range
`from sofi to stifl allowing to tailor the mechanical properties of foams.
`
`Note: ‘Daploy’ and ‘Borsoft’ are trademarks of Borealis A/S.
`
`REFERENCES
`
`1. M. Ratzsch. M. Arnold. E. Borsig. H. Bucka and N. Reichelt. "Radical reactions
`on polypropylene in the solid state." Progress in Polymer Science. Volume 27.
`Issue 7. pp. 1195-1282 September 2002.
`
`325
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`Cellular Polymers, Vol. 22, Na. 5, 2003
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`PAGE 12 OF 14
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`

`
`PP—Blends with Tailored Foamabiliiy and Mechanical Prapanic:
`
`2. H.E. Naguib and C.B. Park. U. Panzer. andN. Reichelt. “Strategies forAchieving
`Ultra Low-Density PP Foams." Polymer Engineering and Science. Vol. 42. No.
`7. pp.. July 2002.
`
`3. H.E. Naguib. J.X. Xu. C.B. Park. A. Hesse. U. Panzer. and N. Reiehelt. “Eflects
`ofBlending ofBranched and Linear Polypropylene Resins on the Foamability."
`SPE. ANTEC. Technical Papers. Vol. 47. pp. 1623-1630. 2001.
`
`4. H.E. Naguib. C.B. Park. A. Hesse. and N. Reichelt. “Efiect ofRecycling on the
`Rheological Properties and Foaming Behaviors of Branched PP." Blowing
`Agents and Foams 2002. Rapia conference. Heidelberg Geimany. 27.285. 2002
`
`5.
`
`L.J. Gibson. M.F. Ashby. Cellular Solids. Cambridge University Press.
`Cambridge. 1997
`
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`Narbm Reichelt, Manfied Stadlbauer, Rick Folland, Clml B. Park and Jin Wang
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`323
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`Cellular Polymers, Vol. 22, Na. 5, 2003
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`PAGE 14 OF 14