New Developments in Plexar®Tie-Layer Adhesives

Dr. Maged BotrosLyondell Chemicals

Session: Extrusion MaterialsPaper Number: 7680

7680 – M. Botros 2

New Developments in High-Performance Tie-Layers

Topics:

I. High-Clarity Barrier Films• New Developments

• EVOH Applications• Nylon Skin Layer Application

II. High-performance tie-layer development for PS / HIPS Applications

• Advantages of new development

• Compare Theory to Experimental Results• Developed New Analytical Techniques• Correlation of Macro Scale Performance to Molecular Level

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Global Trend: Increasing Demand for High-Clarity Barrier Films

• Consumer preference for retail display packages with excellent optics

• Films with poor clarity detract from a quality image

• Intense competition in film-converting industry for distinguishing benefits

• Clarity is a “must-have”feature

• Low-clarity films are at a disadvantage

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Transparency Loss in Barrier Coextrusions

Measurement: narrow angle scattering (NAS)

PhenomenaCoextruded barrier films with low optical transparency due to apparent instability at tie-barrier interface- “Ground glass,” “graininess,” “orange peel” appearance

CauseAn uneven interface between tie layer and barrier layer, possibly caused by covalent bonding, that amplifies interfacial stresses that lead to nanometer scale distortions

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Adhesion Versus Clarity in Standard Multi-layer Films With EVOH Barrier

0

1

2

3

4

5

6

2MI LLDPE Adh-A Adh-B

Adhesive

Adhe

sion

(N/1

5mm

)

0

5

10

15

20

25

30

35

40

45

50

NAS Adhesion

NAS Clarity

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Performance of New Tie-Layer Developments in Multilayer Films With EVOH Barrier

7.9

2118.4

28

42

27

05

1015

20

2530

3540

45

Standard-A Tie-Clarity1 Tie-Clarity-2

5X Adh (N/15 mm) NAS

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Key Attributes of New Developments

• LLDPE-based tie-layer: 1.1 MI, 0.92 density

• Specifically designed for EVOH blown film coextrusions where excellent optics and transparency are required

Good viscosity and shear stress matched of most blown film EVOH grades

Optimized anhydride content for adhesion and transparency

Unique structure and graft architecture

Ability to absorb and dissipate interfacial stresses

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New Developments in High-Performance Tie-Layers

Topics:

I. High-Clarity Barrier Films• New Developments

• EVOH Applications• Nylon Skin Layer Application

• Theory versus practice!

– The effect of interfacial shear stress and elasticity ratio at the interface of nylon/tie multilayer film structures were found to be insufficient parameters to explain the optical properties measured experimentally

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Attempt to Correlate Interfacial Elasticity Ratio with Clarity

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New Developments in High-Performance Tie-Layers

Topics:I. High-Clarity Barrier Films

• New Developments• EVOH Applications• Nylon Skin Layer Application

• Theory versus practice!– Theory alone was inadequate in explaining

experimental data– It was predicted that such inadequacy was due to the

neglect of chemical interactions at the Nylon/Tie interface

– A new test was devised to rheologically probe the interaction at the nylon/tie interface

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Rheological Probing of Nylon/Tie Interface:Increase in Elastic Modulus as a Function of Time

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Effect of Outer Nylon Layer Thickness on Film Clarity

59.0

24.6

56.2

0.0

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

High Clarity Tie-A Low Clarity Tie-B4

% N

AS

20% PA10% PA

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New Developments in High-Performance Tie-Layers

Topics:

I. High-Clarity Barrier Films• New Developments

• EVOH Applications• Nylon Skin Layer Application

• Atomic Force Microscopy Study– A closer look at the interface– Additional parameters affecting clarity

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Atomic Force Microscopy Images Showing Crystalline Morphology of Nylon

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AFM Images Using High Clarity Tie Showing Continuous and Undisturbed Tie/Nylon Interface

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AFM Images of Low Clarity Tie in Multilayer Nylon Film. Delamination at the Interface and Interlayer Mixing is Observed

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Summary of High-Clarity Development

• The effect of adhesion on multi-layer film clarity was investigated

–Analysis of current tie-layer grades show that higher adhesion typically leads to lower clarity

–By carefully controlling the reaction kinetics and rheological characteristics of tie-layers, we were able to develop new adhesives that maintained high clarity and high adhesion at the same time

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II- High-Performance Tie-Layer Development for PS/HIPS Applications

Product characteristics

LLDPE-based tie-layer adhesive

Melt index = 3.30 g/10 min (D 1238)

Density = 0.9335 g/cc (D 1505)

Vicat softening point = 88.3°C (D 1525)

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Performance of New Tie-Layer Developments in PS/HIPS Applications

(A) Macro Scale Investigation

Adhesion Performance- Heat Seal- Sheet Co-Extrusion- Effect of Temperature- Thermoforming- Optical Microscopy (Not Shown – Too big to be presented!!)

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Effect of PS/HIPS Blends on Heat Seal Adhesion at 260°C

1.2

0.8 0.8

4.6

4 4

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Adh

esio

n (N

/2.5

4 cm

)

Ref Adh-PX

Tie-Layer

HIPS-1/PS-1

HIPS-2/PS-2

HIPS-3/PS-3

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Adhesion Performance of New Tie-Layer in Co-Extruded Sheet Application

5.1

9

32

0

5

10

15

20

25

30

35

Adh

esio

n (N

/15

mm

)

Ref-1 Ref-2 Adh-PX

Tie-Layer

Coex Sheet

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Effect of Temperature (50 °C) on Adhesion Performance in Co-Extruded Sheet Application

6 5.7

12.3 12.5

0

2

4

6

8

10

12

14

Adhe

sion

(N/1

5 m

m)

Ref-2 Adh-PX

Tie-Layer

3 Min.

5 Min.

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Adhesion Performance of New Tie-Layer After Thermoforming

3.43.8

6

0

1

2

3

4

5

6

7

8

Adhe

sion

(N/1

5 m

m)

Side-Vertical Side-Horizontal Cup Rim

Tie-Layer

Adh-PX

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Performance of New Tie-Layer in PS/HIPS Applications

(B) Micro Scale Investigation

Atomic Force Microscopy- A closer look at the interface- Effect of Tie-Layer- Effect of Thermoforming- Molecular Orientation due to thermoforming

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AFM Images of Low Performance Tie in PS Multilayer Sheet. Large Gap at Tie-PS Interface

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AFM images of New Tie-Layer Exhibiting Excellent Adhesion with No Interfacial Delamination at Tie/PS Interface

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AFM Images of Reference Tie in Thermoformed Cup: Vertical Gap at Tie/PS Interface

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AFM Images of New Tie-Layer in Thermoformed PS Cup Exhibiting Excellent Adhesion in Presence of High Orientation

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Technical Summary for PS/HIPS Applications• 300% – 400% improved adhesion compared to references • Optimized MI for sheet extrusion process• LLDPE-based offer advantages over EVA-based

adhesives– Low odor– Easy thermoform-ability– No Stringing– High temperature applications

• New tie-layer could have a cost/performance advantage upon down gauging

• Enhanced performance at high temperature• Retained high performance after thermoforming

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Conclusions• Developed new tie-layer adhesives for high-performance

applications:– High-clarity, multi-layer film application

• Maintain high clarity and high adhesion at the same time

– High-performance tie-layer development for PS/HIPS applications

• Maintain high adhesion and container integrity after thermoforming

• Applied new analytical techniques in developing high-performance tie-layer adhesives that are targeted for specific applications

• Related performance on macro scale to micro / molecular level

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Acknowledgments

Coauthors: Dr. Harry Mavridis and Dr. Francis Mirabella

The authors would like to thank Mr. Randy McIntosh, Mr. Michael Grubb, Mr. John Leurck, Mr. Daniel Riopell and Mr. William Shumake for their significant contribution and assistance.