5. Novel Processing Aids in Extrusion

8/12/2019 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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17.06.2008 Novel Processing aids in Extrusion 2

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!

5. Novel Processing Aids in Extrusion

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