5. novel processing aids in extrusion
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Novel Processing Aids in Extrusion
The Use of ThermoplasticThe Use of Thermoplastic ElastomersElastomers as Novelas Novel
Processing Aids in Extrusion of PolyethyleneProcessing Aids in Extrusion of Polyethylene
M.H. Wagner1
, M. Mller1
, O. Kulikow2
, K. Hornung2
1 Technische Universitt Berlin, Polymertechnik/-physik2 Universitt der Bundeswehr der Mnchen, Luft- und Raumfahrttechnik
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Outline
Introduction
Motivation
Background
Additives
Mode of action
Benefits
Outlook
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Motivation
Polyolefins (Polyethylene, Polypropylene and copolymers) are the
world's fastest growing polymer family:
Cost / performance: modern polyolefins cost less to produce andprocess than many other plastics. In addition, continuous improvementin strength and durability enables manufacturers to use less of them.
Extremely low environmental impact: The processes that are usedto produce them are considered to be the cleanest and most efficient inthe industry. At the end of their useful life polyolefins are inert productsthat lend themselves to a multitude of safe, efficient waste disposal
processes, including recycling.
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Metallocene Polyethylene
mPE is a new development which is of special interest because of
narrow molar mass distribution:
Polyethylene made from metallocene catalysts is tougher, stronger andcleaner than resin made from conventional catalysts
The film manufactured with metallocene PE offers downgaugingopportunities to reduce costs and environmental pollution
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Problems with Polyethylene
LLDPE and metallocene PE are
especially subject to variousflow instabilities (so called meltfracture) during extrusion andblown film production.
LDPE low density polyethylene
LLDPE linear low density PE
m-LLDPE metallocene PE
Ref.:ExxonMobil
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Appearance of melt-fracture during extrusion
Extrusion at 165 C
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Mechanism of sharkskin
Strain stress near the die rim.
Swelling of the extrudate.
Eruptive detachment of moltenpolymer from the die exit.
detachment
point oscillates
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The use of Polymer Processing Aids
Aim
By postponing the onset of these instabilities to higher rate it becomespossible to enhance both the processing efficiency and the finalproduct quality
Solution A solution for a better processability of LLDPE and m-PE is the use of
Polymer Processing Aids (PPA), i.e. additives designed to improve theprocessing of polymers
A typical amount of PPA is 500 to 1,000 ppm Market size for PPA nowadays is 100 Mio Euro per year and it is
increasing
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Available Polymer Processing Aids (PPA)
Available PPA on the market are mostly fluorinated:
"VitonFreeFlow" - DuPont,
"Dynamar" - Dyneon (3M),
"Kynar" - Atofina Chemicals,
"Metablen A" - Mitsubishi Rayon Co., Ltd.
Disadvantages:
Expensive Environmentally harmful
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Alternative Polymer Processing Aids
Use of < 500 ppm of thermoplastic elastomers (TPE-U) based on block
copolymers of diisocyanates, i.e. urethanes and polyols
Elastollan" Elastogran
Baymod Bayer
Use of < 500 ppm Silicone Elastomers
TPSE Wacker Chemie
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Action of processing aids
Traditional (fluorinated) PPA
Molecules of fluorinated PPA flow along the wall
Conception is based on the use of materials with low surface energy(lubrication layer)
Novel PPA (TPE-U)
TPE-U are immiscible with PE resins but adhere well to metals andoxides
Molecules of novel PPA are strongly bonded to the die wall
The additives accumulated at the wall (coating of the die) slowly flowalong the wall to the exit of the extrusion die so that the product surfaceis enriched by the additives.
Hypothesis: Polyethylene slips on PPA-film
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Extrusion (film blowing)
outside appearance as
result of film blowing ofm-LLDPE
Comparison of filmprocessed with and
without novel PPA atthe same processingvelocity
Results: less opacity,less pressure at thedie exit
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Appearance of flow instabilities during extrusion
Extrusion of m-PE-LLD at 165 C
averaged product velocity [mm/s]
pressure
[ba
r]
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Extrusion with additive (postponing of flow instabilities)
Extrusion of m-PE-LLD & Baymod at 165 C
pressure
[bar]
averaged product velocity [mm/s]
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Benefits of novel PPA
Delay of melt flow instabilities
Faster extrusion (increase in processing velocity)
Positive impact on printability and adhesion (presence of polar
molecules at the product surface)
TPE-U which is entrapped inside a PE film also acts as an antiblockingagent
Cheaper then traditional additives Lower environmental impact
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Outlook
TPE-U and TPSE offer a great potential to substitute fluorinated PPA
because of their additional benefits
Challenge and potential for optimizing:
choosing the right Polymer Processing Aid (PPA) for a particular
application (e.g. regarding FDA compliance or stability under heating) Research has to be done to understand the specific mode of action and
physical origin how the sharkskin effect is postponed to a higherprocessing velocity
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Thank youfor your attention!
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