Amine Functional Specialty Polymers as Adhesives in Multilayer Film

Chapter 14

Amine Functional Specialty Polymers as Adhesives in Multilayer Film Composite Structures C. Chappell, Jr., E. L. Mason, and J. A. Siddiqui

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Tech/R&D Laboratory, DuPont Polyester Films, P.O. Box 411, Hopewell, VA 23860

This chapter will provide an overview on the applications of amine functional polymers as coating materials in the preparation of multilayer composite film structures. In this study, amine functional polymers such as poly(ethylene imine), PEI, polyvinylamines, PVAm, polyvinylalcoholamines, PVAA, and Starburst® dendrimer, polyamidoamine (PAMAM) generation-2, were evaluated as interlayer adhesion promoting polymers between poly(ethylene terepthalate), and ionomeric polyethylene, Surlyn®. With the exception of Starburst dendrimer, all amino-functional polymers were found to be excellent adhesion promoters as tie coat adhesive layers between PET and Surlyn®. Using near infrared spectroscopy, NIRA, peel strength, and scanning electron microscopy data, we have shown that in the "PET-PEI-Surlyn®" composite structure, there is an amide bond between PET, and PEI interface, and metal-amine complexation at the PEI-Surlyn® interface. Experiments also suggest ways for making strong interfaces in the "PET-PEI-Surlyn®" composite structures. The "PET-PEI-Surlyn®" interface integrity is very sensitive to the molecular weight, solution pH, chain conformation, side chain of the grafted poly(ethylene imine), and heat seal temperatures during the preparation of laminate composite structures.

In the flexible packing industry, composite film laminate structures of poly(ethylene terepthalate), (PET), with Surlyn®, and polyethylene are common. The laminate film structures combine the good properties of each individual substrate and maximize benefits from the standpoint of oxygen barrier, moisture barrier, flavor, heat seal, printing, gloss and aesthetics of a composite package. Without surface modifications, PET film doesn't adhere to Surlyn® or polyethylene. In order to promote adhesion between PET film and Surlyn ® or polyethylene (PE), amine functional polymers such as poly(ethylene imines), (PEI), grafted poly(ethylene imine) (g-PEI),

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© 2000 American Chemical Society

In Specialty Monomers and Polymers; Havelka, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

187


polyvinylalcohol amines (PVAA), and polyvinylamine (PVAm) are used as a tie-eoat adhesive layer in the preparation of composite film laminate structures (1,2,3,4). The amine functional polymers are applied as thin polymeric coatings on the PET film surface and molten polyethylene or molten Surlyn® is extruded as thin film on the amine functional modified PET. The "PET-PEI-Surlyn®" laminate can also be prepared by first coating the PET film surface with the amine functional polymer, followed by drying, and then finally heat sealing the coated PET film with Surlyn® or polyethylene film. In this study, we used Surlyn®, or polyethylene films in the preparation of the laminate composite structures. An understanding of the structure, property relationship in the "PET-PEISurlyn®" interface is necessary in order to facilitate the design of laminate structure with desirable performance properties. Therefore, we wish to characterize the chemical nature of the poly(ethylene imine), and polyvinylamine in the tie coat layer between polyethylene terepthalate) and Surlyn®. Our approach involves the selection of several types of commercially available amino functional polymers. In this study, we selected linear and branched poly( ethylene imine) functional polymers as a "tie coat layer" in the "PET-PEI-Surlyn®" composite laminate. It is our goal to correlate the peel strength in the "PET-PEISurlyn®" interface with the molecular characteristics of amino functional polymers. Experimental A) Materials: Several grades of poly(ethylene imines), trade name Lupasol P, and Lupasol SK were obtained from BASF Corporation; polyvinylalcoholamine (PVAA) and polyvinylamine (PVAm) were purchased from Air Products, Inc.; Starburst® dendrimer polyamidoamine was purchased from Dendritech Corporation. Poly(ethylene terepthalate) film , grade, Melinex® 800/48 and coextruded 850/48 films, and Surlyn®, grade 1702, were from DuPont Films. B) Coating Method: 0.3%, 05%, 0.7% and 1.0% amine solutions were used for coating the PET films. The coating solutions were applied using Meyer bar, the coated surface was dried atl80°C for one minute; the dry coating thickness range was between 0.01 micron to 0.05 micron. C) Laminate Preparation: The PEI coated PET film was laminated with Surlyn® 1702 (200 gauge thick) at various temperatures between 290 to 450°F for one minute. The peel strength curves were obtained using Instron, and the plane of fracture was obtained using scanning electron microscopy(5). Near infrared spectra (NIRA) were obtained to study the surface amidation reaction of PET with PEI. The laminate structures are shown in figures 1 and 2. In figure 1, the PEI coating is on the semicrystalline surface of the PET film (Melinex® 800/48) whereas in figure 2, the PEI coating is on the amorphous side of the coextruded PET film (Melinex® 850/48). Both sides of the PET film (amorphous and crystalline) surface produce strong "PETPEI-Surlyn®" interface.



188

Figure 1: Poly (ethylene terepthalate) film, both sides are semi-crystalline semicrystalline and the seeond side is amorphous.

Figure 2: Poly (ethylene terepthalate) film, one side is semicrystalline and the second side is amorphous.


189 (D) Instrumentation • • •

Instron peel test was performed on an Instron, Instru-Met Model 1101. Heat seal laminates were prepared using a laminator, Seneorp System 12ASL Fourier transform infrared spectroscopy ( FTIR) was performed on Nicolet Magna-IR/550.


Results and Discussion In this section, we wish to describe: a) synthesis of PEI, PVAm, and P V A A using various monomers, b) effect of molecular weight on the bond strength of the PET-PEI-Surlyn interface, c) effect of coat weight on adhesion, d) effect of polymer composition on the bond strength at the PET-PEI-Surlyn interface and finally e) characterization of the PET-PEI-Surlyn® interface. Experiments suggest that polyvinylamines (PVAm) behave in a similar manner to PEI, whereas dendrimeric polyamidoamine has very poor tie-coat properties between PET and Surlyn®, In our discussions, we will refer to the composite laminated as "PET-PEI-Surlyn®" structure for the sake of simplicity.

A) Synthesis of PEI, PVAm, and PVAA In figures 3, 4, and 5, commercial synthesis of poly(ethylene imine), polyvinylamine, and polyvinylalcohol amine are described (6,7).

B) Effect of Molecular weight on PET-PEI-Surlyn® Laminate Structures In figure 6, the peel strength of the PET-PEI-Surlyn® interface as a function of molecular weight of PEI is shown. Clearly, data suggest that as the molecular weight of PEI increases, the peel strength also increases (8,9). For example, the low molecular weight PEI (M. wt. ~ 600 Daltons) gave a peel strength of 130 gms/inch whereas the higher molecular PEI (M.wt - 50,000 Daltons) gave a peel strength of 580 gms/inch Interestingly, the polyvinylalcohol amine copolymer follows a trend similar to that of PEL The hyper-branched, low molecular weight dendrimer behaves very much like a very low molecular weight PEI, and produced a weak interface between PET and Surlyn® films. 2

2

C) Effect of Coat Weight on the Peel Strength of PET-PEI-Surlyn® Interface Several concentrations of PEI solutions (0.15%, 0.20%, 0.60% and 1.00%) were applied to the PET film surface. The coated film was dried at 180°C for 60 seconds. After coating and drying, the coated PET film was laminated with Surlyn® 1702, and the bond strength was measured using the Instron peel test method. Data suggest that as the coat weight increased; the bond strength at the PET-PEI-Surlyn® interface also increased. However, at higher PEI concentration levels (exceeding 1.0% PEI solution)


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HOCH CH NH Downloaded by UNIV OF GUELPH LIBRARY on September 7, 2012 | http://pubs.acs.org Publication Date: March 27, 2000 | doi: 10.1021/bk-2000-0755.ch014

2

2

H S0 2

S0 OCH NH

4

3

2

2

3

NaOH

V

H Ethylenimine Aziridine)

H

+

CH CH NH 2

2

2

—(CH CH NCH CH2t% 2

2

2

;H CH NH CI2

2

2

Figure 3: Synthesis of Poly (ethylene imine), primary: secondary: tertiary Nitrogen ratio: 1:1:0.75



HOO

I

NH

Initiator

VINAMER EF

2

H C=CH

HC=0

NH

ΌΗ/Η*

Figure 4: Synthesis of Polyvinylamine

PEF

Poly(N^thenylformamide)

2

•H C-CH

I

2

NH

PVAm

Poly(vinylamine)

2

HC —CH -


192

H C=CH 2

HOMOPOLYMERS

COPOLYMERS >/

-H C—CH

HC=0

3-

2

H C— C H -

H C — CH • 2

2

I

I

NHCHO

NHCHO


^

HYDROLYSIS

HYDROLYSIS

"H C 2

•H C

-H C — C H -

CH-

2

2

I

NH2

NH,

CH X

X= OAc, OH ,C I ,H, COOK COOR, CN.CONH2

Figure 5: Synthesis of Polyvinylalcohol Amines (PVAA)

Effects of Molecular Weight on the Peel Strength of Surlyn - PEI - PET Interface & Other Amines 600

103

1000

10000

100000

1000000

10000000

Molecular Weight »

enrpty

PEI

PVAA

& DENDRIMER

•

P R O T O N A T E D PEI

Figure 6: Effect of Molecular Weight on the Peel Strength of PET-PEI-Surlyn® Interface


193 the bond strength begins to level out. Figure 7 shows the effect of coat weight on the peel strength of PET-PEI-Surlyn® interface. D) Effect of PEI Composition on the Peel Strength of PET-PEI-Surlyn® Interface


In Figure 8, effect of PEI composition on the PET-PEI-Surlyn® interface is shown. Clearly, data suggest that protonated PEI (below pH = 7), (Figure 9) gives a very poor adhesive bond strength, whereas partially acylated PEI, (Figure 10), maintains good adhesive characteristics between PET and Surlyn® 1702. E) Characterization of the Interfacial Bond between Poly(ethylene terepthalate) and Polyethylene imine): In Figure 11, the near infrared (NIRA) data of the PEI coated PET is plotted. Clearly the presence of-CONH2 group suggests an amidation reaction between the surface carboxylic group of PET and the amino functional groups of PEI during the curing process. In Figure 12, the effect of heat seal temperature on the peel strength is plotted. Interestingly, as the heat seal temperature increases, the peel strength also increases, suggesting an increase in the population density of amido groups. Additional experiments are in progress to quantify the increase in amido functional group concentration as a function of temperature. The peel strength data also suggest that as the lamination temperature increased above 400° F, the peel strength started to deteriorate This decrease in the peel strength is due to the degradation of PEI, resulting in the cohesive failure in the PEI region of the PET-PEI interface (Figure 10). A yellowing of the laminate was also observed above 400°F. Based on the peel strength, NIRA, and heat-seal data at different temperatures, we propose a chemical interface between PET and PEI via amidation reaction. The schematic of the interface is shown in Figure 13. F) Characterization of the "Surlyn®-Poly(ethyIene imine)" Interface. Surlyn® is an ionically crosslinked thermoplastic derived from ethylene/methacrylic copoloymer; the ionically crosslinking metal ions are zinc and sodium. To investigate the nature of bonding between PEI and Surlyn®, several laminates were prepared using PEI under acidic and basic conditions. In Figure 8, data on the effect of pH on peel strength is plotted. Clearly, protonated PEI (pH below 5) has practically no bond strength, suggesting an "amine-metal" complexation reaction at the "Surlyn-PEI" interface. Since the protonated PEI prevents metal complexation, the interfacial bonding fails completely. In Figure 13, the schematic of the PEI-Surlyn® interface in the PET-PEI-Surlyn® interface is proposed. Conclusions High molecular weight amine functional polymers, such as PEI, P V A m and P V A A are excellent adhesion promoters and serve as a strong "tie-coat" in the preparation of multi-layer composite structures between poly(ethylene terephthate) and ionomeric Surlyn®. Using near infra-red spectroscopy, peel strength and heat seal data, we have



194

Effects of C o a t Weight on Surlyn - PEI - P E T Interlace Molecular W e i g h t 5 0 K - 1 0 0 K Heat S e a l Temperature = 380 F

0

ι

ι

ι

ι

ι

ι

0

0.2

0.4

0.6

0.8

1

ι 1.2

% PEI( High Molecular Weight) M e y e r R o d =#0rod (4 microns Wet)

Figure 7: Effects of Coat Weight on PET-PEI-Surlyn® Interface, MolecularWeight: 50,000 -100,000 (Heat Seal Temperature =300°F)



195

Figure 8: Effects of Composition on PET-PEI-Surlyn® Interface, Molecular Weight: 50,000 (Heat Seal Temperature = 380°F)

Figure 9: Effect of Composition on Peel Strength, Structure of Protonated Poly (ethylene imine), Poor Peel Strength.



196

TERTIARY AMINE -[--NH

CH2—CH2

N~

CH2

CH2

]

CH2

CH2 NH—CH2—CH2—NHCOCH3

A

A

SECONDARY AMINE AMIDO GROUP Figure 10: Acylated Poly (ethylene imine), Lupasol SK, Lupasol Ρ has no · COCHj Groups. See Peel Strength Data in Figure 8.


197

Near Infrared Spectrum of PET - PEI Interface


0.060

1000

1010

1020

1030

1040

1050

W A V E L E N G T H (cm-1) ·••- Untreated PET Film

PEI Treated Film

PEI Treated Film

PEI Treated Film

Figure 11: Near Infra-red Spectrum of the PET-PEI-Surlyn® Laminates

600 500 400 LU

300

-1 LU LU CL

200

i

100

285

315

375

450

TEMPERATURE DEGREES F - * - 0 . 3 % P E I - - - 1 . 1 % PEI

* 1.1%PEI&H3P04

Figure 12: Peel Strength as a Function of Heat Seal Temperature



198

Figure 13:

Schematic Representation of PET-PEI-Surlyn® Interface


199


shown that in the "PET-PEI-Surlyn®" composite structure, there is an amide bond formation between poly(ethylene terepthalate) and poly(ethylene imine) interface, whereas a strong "metal-amine" complexation occurs between polyethylene imine) and Surlyn® interface. The "metal-amine" complexation theory was substantiated by using protonated poly(ethylene imine) as a coating layer on the PET surface. Interestingly, use of protonated PEI on the PET surface has no peel strength with Surlyn®, resulting in a very poor PET-PEI-Surlyn® laminate structure. Additionally, the PEI coat thickness control at the PET-PEI-Surlyn® is very important. Initially, as the coat thickness increases, the peel strength increases, followed by leveling out of the heat seal strength, and finally the interface weakens due to the cohesive failure. Acknowledgement We would like to express our sincere thanks to the management of the E.I. DuPont de Nemours Company for giving us the permission to publish this work.

Literature Cited 1. Siddiqui, J.A., 1995, U.S. Patent #5, 453, 326 2. Siddiqui, J.A. Proceedings of the Seventh International Conference on Web Coating, Miami, Florida, November 10-12, 1993, Vol. 7, pp. 43-53 3. Siddiqui, J.A.; Mason, E.L., Chappell, Jr., C., Polymer Preprint, 1998, pp. 39, 111, 658-659 4. Siddiqui, J.A.; Mason, E.L.; Chappell, Jr., C.; Polymer Preprint, 1998 39(2), pp. 348-349 5. Kinloch, A. J.; Lau, C. C.; Williams, J. G., Int. J. Fract. 1994, 66, 45 nd

6. DeRoo, A. M., Handbook of Adhesives, 2 Edition, Editors Skiest, I., Van Nostrand, Rheinhold Company, 1977, pp. 592-596, Chap. 36 7. Winnik, A. M., Bystryak, M, S.: Liu,Z.;Siddiqui, J.A.; Macromolecules 1998, 31, 6855-6864 8. Lee, L, Fundamentals of Adhesion; Plenum Press, N.Y., 1991, Chaps. 1-4 9. Mittle, K. L., Pure and Applied Chem. 1980, Vol. 52, 1295 10. Belton, D. J.; Joshi, A, Molecular Characterization of Composite Interface, Marcel Dekker, Inc., N . Y . Edited by Ishida, H. and Kumar, G., 1988, p. 187


Amine Functional Specialty Polymers as Adhesives in Multilayer Film

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