1

Higher Tie Layer Adhesion in Machine Direction Oriented (MDO) Barrier Films Chun D. Lee, Jeff J. Strebel, and Joel D. Goudelock Lyondell Technology Center Lyondell Chemical Company Cincinnati, OH, USA ABSTRACT Machine Direction Orientation (MDO) is a post-extrusion process used to enhance film properties such as barrier, stiffness and clarity. Orienting coextruded films containing EVOH or Nylon presents the special challenge of maintaining adhesion at the tie-layer barrier interface after orientation. When conventional tie-layer resins are used, the post-oriented adhesive bond force can decrease by up to 90% of the initial or pre-oriented levels. This decrease is due to a reduction in surface bond population as the interfacial area expands and a loss of interfacial strength as the film is stretched in the solid state below melting temperature. Why does the tie layer, which is primarily PE, lose interfacial strength between the tie layer and barrier materials when the other PE film layers are getting “enhanced film properties?”

To address this challenge, a new tie resin for MDO-processed barrier film has been developed. This paper investigates the effects of orientation on crystalline morphology, clarity, stiffness and adhesion in these coextruded oriented films. Correlations are drawn between the morphological and structural changes occurring during the orientation and the resulting improvements in clarity, stiffness, and interlayer adhesion. 1. Introduction The use of oriented barrier films is growing rapidly in many flexible packaging markets, including meat and cheese wraps and dry food liners. In-line or post-manufacturing orientation of films enables converters to create films with enhanced properties, such as heat shrinkability, dimensional stability, clarity or exceptionally high barrier, impact and tensile properties [1-11]. The term “orientation” has broad meaning in the film industry but generally refers to a process for aligning long polymer chains in one (Machine Direction (MD) only) or two directions (MD and Transverse Direction (TD)). As the polymer chains move from a random arrangement into an aligned and oriented matrix, the physical properties of the film change. In extruded films, polymer chains are oriented in the liquid or melt phase as the polymer extrudate moves through flow channels and exits the die. The degree of orientation can be controlled by the draw rate and, in blown films, the blow-up ratio. The amount of orientation that can be induced during extrusion is limited by the relatively low strength of the polymer in the melt phase. To induce higher degrees of orientation, converters often draw or stretch the film after the polymer has solidified at temperatures between the polymers glass transition and melt temperature. The strength of the film in this solid state is significantly higher than its

2

melt phase strength, allowing for higher chain orientation without film tear. Solid state orientation also increases residual stresses, or film memory, needed to make shrink films. For the remainder of this paper, the term “orientation” will refer to the orientation resulting from solid state processes rather than the orientation that occurs as the polymer exits the die and still in the melt-phase.

Various commercial techniques are used to produce oriented films made from polyesters, polyamides and polypropylenes that are regularly used in packaging, electronics, industrial and other markets. Each process produces unique characteristics in the finished film products. In flexible packaging, three main types of orientation techniques are used commercially:

Double-Bubble Orientation: This is a modified blown-film technique used primarily for shrink bags and films. The process consists of the following basic steps [2,3,7]:

1. A thick polymer extrudate exits an annular die downward with little or no blow-up ratio. The polymer solidifies and goes through collapsing nip rolls.

2. The collapsed film bubble is re-expanded between the two sets of nips using high pressure air. The temperature of the polymer film is typically below the polymer melting point and at or slightly above the polymer softening point as it is re-expanded.

3. The polymer chains are cross–linked, typically by electron beam irradiation. The film is then rolled or converted into shrink bags or sleeves.

The double-bubble process is frequently used to produce shrink bags and films. The biaxial stretching process, along with the chain cross-linking, create inter-chain stresses that can be relieved with low applications of heat. As these stresses are relieved, the film shrinks and conforms to the product’s shape. The biaxial orientation and cross-linked structure create films with high puncture resistance.

Tenter Frame Orientation: The tenter frame orientation process is often part of film casting operation used to orient polyester, polypropylene and nylon films. After the film is extruded, it is oriented in the machine direction by a series of rollers and in the transverse (cross) direction by clamps that grab the film edges and pull outward. The film may then be annealed to prevent shrinkage and improve dimensional stability.

Films oriented in tenter frames are valued for their clarity and dimensional stability. In flexible packaging, they are used in a variety of applications, including reverse printed laminations, lid films and over wraps.

Machine Direction Orientation: The Machine Direction Orientation (or MDO) process is achieved by passing a film or sheet through a series of nip rollers with individual drives and temperature settings. Each set of rollers has a specific function; pre-heating, stretching or orienting, annealing and cooling. The MD orientation process is similar to the tenter frame process without the TD stretching.

3

As the name implies, MDO films are only oriented in the machine direction. Most commercial MDO studies thus far have been with blown film, but the MDO process is also suitable for cast film and sheet processes.

MD orienters are typically small stand-alone units that can be run in-line with film production or as a separate operation and are comparatively lower cost than equipment for double-bubble or tenter frame orientation processes. The low equipment cost and flexibility makes the MDO attractive to converters and small to mid-size polyolefin film producers interested in higher value films. While machine direction orientation improves many physical, optical and barrier properties, MDO films generally have reduced MD tear properties compared to similar tenter frame, double-bubble or even non-oriented films.

CHALLENGES FOR MULTILAYER BARRIER FILM ORIENTATION

Most commercial oriented films are monolayer or 3-layer coextrusions. Until recently, there have been few oriented 5- and 7-layer barrier coextrusions. Orienting coextruded films containing EVOH or nylon presents the special challenge of maintaining adhesion tie layer barrier interface after orientation. Barrier adhesion results from chemical interactions between the tie-layer resin and the barrier material, such as EVOH or nylon. The extent of adhesion depends on the formulation as well as the amount of maleic anhydride functionality. When conventional maleic anhydride functionalized tie-layer resins are used, the post-oriented adhesive bond force can drop to 90% of the pre-oriented levels. This adhesion drop is due to several factors. Fundamentally, the orientation increases the interfacial area, effectively reducing the number of chemical bonds per unit area. Mechanically, certain tie and other resins are subject to strain hardening. As the material becomes less elastic, the ability to absorb and dissipate interfacial stresses is lost. The differences in mechanical/tensile properties of polyolefins and EVOH can also contribute to adhesion loss. As the materials are pulled together, differential stresses are concentrated at the interface between the materials, which can cause bonds to break. As an example, Figure 1 shows adhesion variation due to orientation, using the same layer structure and tie-layer resin. As expected, a coextruded film sample by Killion melt extrusion showed reasonably good adhesion, whereas MDO and other commercial orientation processes led to dramatic reductions in adhesion by 50% to 90% from the Killion data.

Most approaches to maximize post-orientation adhesion have focused on the tie resin rather than EVOH, since physical properties of barrier resins cannot be modified without increasing gas permeability. Lyondell has developed a new tie-layer resin for MDO barrier shrinkage films. This paper investigates the effects of orientation on crystalline morphology, clarity, stiffness and adhesion in these coextruded oriented films. Correlations are drawn between the morphological and structural changes occurring during the orientation process and the resulting improvements in clarity, stiffness and interlayer adhesion.

2. Experimental

4

2.1 Materials Coextruded sheets with a five-layer structure of A (42%)/B (4%)/C (8%)/B (4%)/A (42%) were produced on an Eagan Coextrusion Sheet line. Layer A contained a linear low density polyethylene (LLDPE-A), layer B the tie-layer resin and Layer C an EVOH-A containing 44 mole% ethylene. Basic data of the materials are shown in Table 1. Both tie resins, A & B have almost identical maleic anhydride (MAH) functionality with slightly different formulation in minor component. The final sheet thickness was approximately 0.5 mm. We also prepared a Blend-A for a non-interacting system (50% EVOH-A + 50% LLDPE-A) and a Blend-B for an interacting system (50% EVOH-A + 50% tie-layer resin –A using a Leistritz twin screw extruder at 200 oC (die temperature) and 250 RPM for the rheological measurements. The sheet samples containing the different tie-layer resins were oriented at 115 oC using a lab scale machine direction orienter. All conditions of the MD orientation process were constant with the exception of draw rate, which was 4:1, 5:1 and 6:1 for each sample. Oriented film samples were irradiated with 5 Mrad via e-beam in ambient conditions to investigate the effects of irradiation treatment on adhesion of MDO films. 2.2 Differential Scanning Calorimetry (DSC) Morphological characterization of unoriented and oriented samples was carried out by thermal analysis using a TA Instrument Q1000 DSC unit with a 10 oC/minute heating rates under nitrogen flow. The first melting curves show the thermal behavior of the crystalline domain with unorientation and orientation. We also measured the first melting curves of annealed unoriented coextruded samples for 1, 3 and 5 minutes at 115 oC to simulate the annealing effect during MDO on melting curves. The second melting curves were obtained as follows: after recording the first melting curves, the samples were held at 210 oC for one minute to remove the thermal and mechanical history, followed by cooling to 25 oC, and then rerun for the second melting curves. 2.3 Dynamic Mechanical Analysizer (DMA) Dynamic mechanical experiments were performed using TA Instruments Q800 DMA in film tension mode. Samples were analyzed using a strain amplitude of 20 microns at a frequency of 1 Hz. A dynamic temperature ramp of 3 oC/minute was used for a range of -80 oC to 60 oC. 2.4 Narrow Angle Scattering (NAS) clarity data NAS measurements were conducted using the Zebedee CL-100 clarity meter (ASTM D1746). Unoriented and oriented coextruded film samples were cut into 10 cm X 10 cm

5

squares and adhered to the test unit in front of the light source. A minimum of six specimens were tested for each sample. 2.5 Dynamic rheological and extensional stress growth measurements Oscillatory dynamic rheological measurements were carried out using a TA ARES at 170 oC with parallel plate geometry, a gap of 1.0 mm and a diameter of 25.0 mm. A frequency sweep test from 0.0251 to 389 rad/sec was carried out for each sample, with an amplitude of 10% strain to maintain the response of the material in the linear viscoelastic regime. Extensional stress growth measurements were carried on the SER unit designed for use on a TA ARES. A detailed description and a discussion of the elongational rheometer were given in the references [12-13]. Extensional test specimens were prepared by compression-molding flat polymer samples to a nominal gage of less than 1 mm, and then cutting fixed width strips using a cutter. Specimens were tested at a melt temperature of 180 oC, using constant Hencky strain rates of 1/sec, which is similar to the rate of MDO stretching for 6X orientation. The ends of the specimen were loaded onto the securing clamps and sandwiched between the wind-up drums, thereby securing the ends of the sample for subsequent stretching. Extensional stress growth as a function of time was calculated according to the equation derived in Ref. [13]. 2.6 Adhesion test The peel test was carried out with an MTS Q-test apparatus at ambient conditions. A specimen with dimensions of 25.4 X 230 mm was cut from the midsection of the MDO films for peel test. For adhesion data, a 180o peel geometry was used for coextruded MDO films with a grip speed of 25.4 mm/min. Force versus displacement data were collected during the peel test. 3. Results and Discussion 3.1 Effects of Orientation on Crystalline Morphology

Figure 2 shows the first heating DSC curves of unoriented (1X) and oriented by six times (6X) coextruded film samples. As expected, there are two melting peaks: the LLDPE produces a broad melting point, which peaks at 121.2 oC, while the second peak at 161.8 o

C is reperesentative of the crystalline EVOH. The broad melting peak in LLDPE resin results from melting behavior for a wide range of crystallite sizes associated with broad short chain branching distribution (SCBD) [14-16]. This broad LLDPE melting peak becomes sharper but maintains its 121.2 oC position, and the heat of fusion increases from 88 J/g to 111 J/g, when the film is oriented to 6X. The increased heat of fusion in the LLDPE melting peak, without changing the peak position, represents increased crystallinity without changing lamella thickness of chain axis (c-axis, parallel to MD). The narrowing (sharpening) of the peak indicates the smaller lamellae have recrystallized to the larger size upon orientation. However, the EVOH domain shows shifts of melting

6

position from 161.8 to 163.7 oC with enhanced heat of fusion upon orientation, indicating increased lamellae thickness and higher crystallinity, respectively. Considering the fact that EVOH is a high melting (>160 oC) material, this morphological change in the crystalline domain of the EVOH with orientation at 115 oC can be attributed not to rearrangement of the polymer chains associated melting but to the presence of the α-phase transition at that temperature. The presence of such a transition can account for the activation of molecular mobilities within the crystalline phase, leading to enhanced crystallinity and lamellae size upon orientation [17,18]. It is, however, not clear whether such a crystalline morphological change with MDO process results from an annealing effect at drawing temperature (115 oC) or from the orientation itself. In order to investigate the effect of annealing for the short period of the MDO processing time (less than 3minutes), we annealed unoriented sheet samples at 115

oC for 1, 3 and 5 minutes for DSC data. The annealed samples showed little change in heat of fusion or positions of melting peaks at 121.5 oC for LLDPE and 161.5 oC for EVOH. This result rules out the effect of annealing on crystalline morphological change during MDO run. As a result, the increased crystallinity with orientation can be solely attributed to strain-induced crystallization with higher chain orientation at an elevated temperature (below melting temperature). Figure 3 shows the second heating curve of unoriented and oriented coextruded film samples. As expected, both samples show identical melting behavior due to the elimination of the thermo-mechanical history developed during the MDO process. Also, the unoriented sample shows much sharper melting behavior compared to its first melting curve (Figure 2). The sharpened melting curve for the unoriented sample is a result of the annealing effect during the heating cycle of the DSC run. Based on this DSC investigation, orienting the coextruded film below the polymer’s melt temperature can alter the crystalline morphology dramatically, but annealing above the melt temperature eliminates the thermo-mechanical history of the MDO process. It is interesting to note how the orientation process affects the mechanical strength of the film. Figure 4 shows the DMA results of storage modulus vs. temperature for unoriented and oriented film samples. As expected, modulus decreases with increased temperature for all samples. For a given temperature, oriented samples show much higher moduli than unoriented, and moduli increase with increased orientation. It is well known that high density polyethylene (HDPE) has a much higher modulus than LLDPE, due to the increased crystallinity of HDPE. We can apply the same concept to MDO-oriented coextruded film for enhanced modulus, compared to unoriented film. Increased modulus with increased orientation results from increased crystallinity, which is in line with the DSC results as discussed previously. We also investigated how film clarity was changed with increased orientation. Figure 5 shows film see-through clarity (based on NAS data) of coextruded film samples made of different tie-layer resin as a function of degree of orientation. Film clarity increased with increased orientation, changing film appearance from milky to clear. Both tie-layer resins produced very similar levels of clarity. In general, PE film with higher crystallinity tends

7

to exhibit poorer clarity than that of a lower crystallinity film, based on the fact that the former film tends to form larger crystallite size. However, as discussed previously, increased orientation results in increased crystallinity. An increase in clarity with increased crystallinity is contradictory to the conventional understanding of the relationship between film clarity and crystallinity. It is well understood that distribution of crystallite size in PE film plays a major role to determine a film clarity. Clarity increases with decreased crystallite size. This means that higher MDO orientation tends to form smaller crystallites as indicated by better clarity. The only way of forming smaller crystallites during the MDO process is to develop a lateral breakage of large lamellae without changing lamella thickness. Higher orientation induces more lateral breakage of lamella and thus better clarity. Figure 6 shows a schematic of crystalline morphological change with orientation of a coextruded film sample, based on the results of DSC, DMA and film clarity. It is accepted that unoriented film contains a wide range of lamella sizes with random orientation of each crystallites [Figure 6 (A)] as indicated by a broad DSC melting curve. Orientation leads to two major developments [Figure 6 (B)]: a) breakage of lamella in lateral dimension to form smaller crystallites being responsible for increased clarity with increased orientation, b) strain induced crystallization being responsible for increased crystallinity with increased orientation. In the orientation process, crystallite orientation increases with increased orientation along MD. 3.2 Effects of Orientation on Tie-Layer Adhesion Figure 7 shows the effect of the degree of orientation on tie-layer adhesion in coextruded films. Tie-layer adhesion decreases with increased orientation. A decreased adhesion results from the following combination of effects: a) the orientation increases the interfacial area effectively reducing the number of chemical bonds per unit area, b) as the material becomes less elastic with increased crystallinity, the ability to absorb and dissipate interfacial stresses is lost, c) mechanically, tie-layer resins are subject to strain hardening by interacting with EVOH upon orientation, d) differences in the effect of chain orientation on polyolefins (tie-layer resin) and EVOH, coupled with the presence of a transition at the drawing temperature for EVOH [16,17], might contribute to a reduction of adhesion. The items (a) and (b) described above are well understood for a reduction of adhesion with increased orientation. However, in order to prove the presence of a strain hardening with orientation process in the tie-layer interacting with EVOH, we prepared two samples of Blend-A (a non-interacting material between EVOH and LLDPE) and Blend-B (an interacting blend between EVOH and tie-layer resin-A) and investigated the rheological measurements on them. Figure 8 shows complex viscosity vs. frequency for the blends. As expected, Blend-A shows normal rheological behavior with shear thinning at increased frequency. However, Blend-B shows unusual rheological behavior; a rapid viscosity up-turn in the low frequency region (<1 rad/sec) and normal behavior in the high frequency region (>10 rad/sec). Published works on rubber modified impact PP [19,20], peroxide modified PP/PE blend [21], carbon black filled compound [22] and

8

ABS [23-25] showed similar unusual rheological behavior (i.e., viscosity up-turn at low frequencies/shear rates, which was attributed to some sort of interacting network structure resulting from an interaction between two immiscible blend components or fillers.) The viscosity up-turn shown by Blend-B results from the presence of a network structure created by the interaction between EVOH and the tie-layer resin via MAH functionality. Obviously, there is no interaction between EVOH and LLDPE-A, resulting in normal rheological behavior of the immiscible blend system. It is interesting to note how such an interaction between EVOH and the tie-layer resin leads to uni-axial melt drawing behavior. We investigated the elongational stress growth function using the SER extensional rheometer on Blend-A and Blend-B at 1 sec-1 Hencky strain rate, which is similar to the MDO draw down rate of a 6X orientation. As shown in Figure 9, stress increased with increased time, and then flattened out, followed by decreased stress with further increased time in Blend-A (non-interacting system). This observation of softened stress with further stretching is typical behavior of linear LLDPE without LCB [26]. However, Blend-B shows a similar behavior at an earlier time followed by unusual stress growth with further increased time. A deviation of stress growth from linear viscoelastic (LVE) simple shear results from a presence of strain hardening [27,28] for Blend-B, compared to Blend-A. Thus, the presence of strain hardening, resulting from an interaction between EVOH and tie-layer resin-A via chain entanglements, can be attributed to partial reduction in adhesion after orientation [29]. We also investigated the effects of different tie-layer resins and irradiation treatment on adhesion of oriented MDO films. Barrier film industry uses an irradiation process on oriented films to enhance shrinkage property. As shown in Figure 10, oriented film made with tie-layer resin-B showed higher adhesion than that made with tie-layer resin-A. It has been also accepted that irradiated oriented film tends to reduce adhesion due to enhanced stiffness/hardness associated with an irradiation process, compared to unirradiated film. For a given tie-layer structure of coextruded films, stiffer film tends to reduce interlayer adhesion between tie-layer resin and EVOH, which is analogous to the item (b) as discussed previously. The irradiated oriented film made of tie-layer resin-A shows some reduction in tie-layer adhesion. However, irradiated film made with tie-layer B shows even higher adhesion than unirradiated oriented film. Higher adhesion of irradiated oriented film made of tie-layer resin-B might be due to a different physical/chemical nature in the interface coupled with an irradiation process compared to that of tie-layer resin-A. Additional investigation is necessary to understand what the physical/chemical nature is in the interface between tie-layer resin and EVOH with an irradiation process. 4. Conclusions We investigated the effects of orientation on crystalline morphology, stiffness, clarity and adhesion of MDO process barrier films. It was found that orientation increases crystallinity, stiffness and clarity but decreases tie-layer adhesion. We proposed a crystalline morphological change occurs with orientation to understand the relation between increased crystallinity and clarity. A decreased tie-layer adhesion with increased

9

orientation results from a combination of effects: a) the orientation increases the interfacial area effectively reducing the number of chemical bonds per unit area, b) mechanically, tie-layer resins are subject to strain hardening by interacting with EVOH upon orientation, c) as the material becomes less elastic with increased crystallinity, the ability to absorb and dissipate interfacial stresses is lost. A formulation change in tie-layer resin for a given level of MAH functionality results in improved adhesion with increased orientation. 5. References [1]. Prinsen, B., 2002, “Barrier Films: Machinery Issues and Processing, TAPPI PLACE Conference., Chicago, IL. [2]. Stibie, J. Stibie 2002, “Producing Co-extruded high barrier heat shrinkable packaging films”, TAPPI PLACE Conference, Chicago, IL. [3]. Hatfield, E., Tate, R., William, K., and Todd, W., “New MDO medium Mw HDPE PE films”, J. Plastic Film and Sheeting, 18, No.2, (2002), p 117. [4]. Jabarin, S.A.,, ANTEC, 554(1992). [5]. Schwartz, S. A. and McCullough, M.J., ANTEC, 538 (1992). [6]. Evstatiev, M. et al., Polym. Eng. Sci., 32, 964 (1992). [7]. Bobovitch, A. L. et al, ANTEC, 1757 (2005). [8]. Elyashevich, G. K. et al., Polym. Eng. Sci., 32, 1341 (1992). [9]. Yamada, T., “Production Technologies of Films and Membrane of New Film and Membrane”, Kagaku Kogyu Nippo, Toyyo (1997). [10]. Takashige, M., et al., Intl. Polym Process. 18, 4 (2003). [11]. Takashige, M., et al., Intl. Polym Process., 11, 1 (2004). [12]. Sentmanat, M.L., “Novel device for characterizing polymer flows in unaxial extension, ANTEC, #49 (2003). [13]. Sentmanat, M.L., Rheol Acta, 43 , 657 (2004). [14]. Furumiya, A., Akana, Y., Ushida, Y., Masuda, T., and Nakajama, A., Pure & Applied Chemistry, 57, 823 (1985). [15]. Wlochowicz , A. and Eder, M., Polymer, 25, 1268 (1984). [16]. Hosoda, S., Polymer J., 20, 383 (1988). [17]. Djezzar, K., Penel, L., Lefebvre, J., Seguela, R., and Germain, Y., Polymer, 39, 3945 (1998). [18].Penel, L., Djezzar, K., Lefebvre, J., Seguela, R., and Fontaine, H., Polym, 39, 4279 (1998). [19]. Lee, T. S., Proc. 5th. Intl. Cong. Rheol., 4, 421 (1970). [20]. Lee, Chun D., October 19-23,1997, “Rheology of Visbroken Reactor-produced PP/E-P Copolymer Blends”, Presented in Society of Rheology Annual Meeting, Columbus, OH. . [21]. Lee, Chun D., October 1997, “Rheological Characterization of PP based Extrusion Coating Resins”, Presented in TAPPI, Toronto. [22]. Lee, Chun D., 1998, “Rheology of Semiconductive Black Compounds with Low Carbon Black Content”, Intl. Wire Cable Symp. 47th, p 161. [23]. Zosel, V. A., Rheol. Acta, 11, 229 (1972). [24]. Aoki, Y and Nakayama, K., Polymer J, 14, 951 (1982).

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[25]. Munstedt, H., Polym. Eng. Sci., 21, 259 (1981). [26]. Winter, H. H., Pure. Appl. Chem., 42, 553 (1975). [27]. Fleissner, M., Intern. Polym. Process., 2, 229 (1988). [28]. Meisner, J. et al., Rheol. Acta, 33, 1 (1994). [29]. Chun D. Lee, unpublished data (2007).

Table 1. Basic data of the materials used for the investigation

0.9111.9Tie layerTie Resin-B

(developmental)

0.9131.7Tie layerTie Resin-A

(commercial)

-2.1barrierEVOH-A

0.9181.0skinLLDPE-A

DensityMIlayermaterial

Figure 1. Adhesion data of different coextrusion process for Tie resin -A

1.9

0.73

0.25

2.1

0.87

0.18

0

0.5

1

1.5

2

2.5

Killion MDO commercial

Adh

esio

n, lb

/inch

Tie resin A

Tie resin A-1

(6X)(15X)

11

Figure 2. DSC 1st melting curves of unoriented and oriented by 6X coextruded film samples

Orientation temperature (115 C)

Unoriented(1 X)

Oriented (6 X)

EVOH

Figure 3. DSC 2nd melting curves of unoriented and oriented by 6X coextruded film samples

Unoriented (1X)

Oriented (6X)

12

Figure 4. DMA data of unoriented and oriented coextruded film samples

0

2000

4000

6000

8000

10000

12000

-100 -80 -60 -40 -20 0 20 40 60 80

Temperature, C

Stor

age

mod

ulus

, MPa

Tie resin A (1X)

Tie resin A (4X)

Tie resin A (6X)

Figure 5. NAS data of unoriented and oriented coextruded film samples made of tie layer resins A & B

2.1

9.0

24.6

4.1

9.5

21.4

0.0

10.0

20.0

30.0

Tie-A, 1X Tie-A, 4X Tie-A, 6X Tie-B, 1X Tie-B, 4X Tie-B, 6X

Tie Layer

% N

AS

13

Figure 6. Schematic representation of crystalline morphology forlamellae stacking (top) and crystallites distrubution (bottom) in unoriened

coextruded film (A), and oriented (6X) film (B)

C cMD

(A) (B)c-axis

Orientation

crystallites

amorphous chains

Figure 7. Effect of orientation on adhesion of coextruded film

1.15 0.79 0.73130

0.4

0.8

1.2

1.6

2

1:1 4:1 5:1 6:1

Tie layer A

Tie

Laye

r Adh

esio

n, lb

/in

18 mils 3 mils

14

Figure 8. Dynamic rheological data of blend-A (50% EVOH-A + LLDPE-A) and blend-B (50% EVOH-A + Tie resin-A)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0.01 0.1 1 10 100 1000

Frequency (rad/sec)

50% EVOH-A+LLDPE-A50% EVOH-A + Tie resin A

Figure 9. Extensional stress growth of blend-A (50% EVOH + LLDPE) and blend-B (50% EVOH + Tie Resin A)

1000

10000

100000

1000000

0.010 0.100 1.000 10.000

Time, sec

Exen

. Str

ess

Gro

wth

(Pa-

s)

50% EVOH + Tie resin A50% EVOH + LLDPE

Projected LVE

15

Figure 10. Adhesion data of 6X oriented coexfilms with different tie layer resins A & B

0.76

1.15

0.68

1.39

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Tie Layer A Tie Layer B

Adh

esio

n, lb

-in

6X, MDO/0 Mrad

6X MDO/5 Mrad

2007 PLACE Conference

September 16-20

St Louis, MO

Higher Tie Layer AdhesionHigher Tie Layer Adhesionin Machine Direction Oriented (MDO)in Machine Direction Oriented (MDO)

Barrier FilmsBarrier FilmsChun D. Lee, Jeff J. Strebel, and Joel D. Goudelock

Presented by:Chun D. LeeLyondell Chemical Company

2

Lyondell Laboratory MDO Line

3

What is MDO?

Planner uniaxially drawing of films in the machine direction

Process either in-line or off-line with film fabrication process

Draw ratios typically from 2:1 to 10:1

Output line speeds up to 1,000 ft/min

4

Adhesion Data of Different Orientation Process for Tie-layer Barrier Films

1.9

0.73

0.25

2.1

0.87

0.18

0

0.5

1

1.5

2

2.5

Killion MDO commercial

Adh

esio

n, lb

/inch

Tie resin A

Tie resin A-1

(6X)(15X)(6X)

5

Evaluation of Tie Resins in MD Oriented Barrier Film Coextrusions

Objective: Investigate the effects of MDO orientation on crystalline morphology, clarity, stiffness, and adhesion in a coextruded barrier film.

MD Draw Ratios - 4:1, 5:1, 6:1 @ 115oC

Properties studiedMorphology with Differential Scanning Calorimetry (DSC)

Stiffness with DMA

Interfacial interaction by shear and extensional rheology

Clarity with NAS

Adhesion by T-peel test

6

Basic Data of Materials Used for the Investigation

0.9111.9Tie layerTie-layer Resin-B

(developmental)

0.9131.7Tie layerTie-layer Resin-A

(commercial)

-2.1BarrierEVOH

0.9181.0SkinLLDPE-A

DensityMILayerMaterial

7

Coextrusion Structure Used for MDO Orientation

LLDPE – 42 %

Tie-layer Resin - 4 %

EVOH – 8 %

Tie-layer Resin - 4 %

LLDPE - 42 %

Five layer, 20 mil cast film, 6” wide

8

DSC 1st Melting Curves of Unoriented and Oriented by 6X Coextruded Film Samples

Orientation temperature (115 C)

Unoriented(1 X)

Oriented (6 X)

EVOH

9

DSC 2nd Melting Curves of Unoriented and Oriented by 6X Coextruded Film Samples

Unoriented (1X)

Oriented (6X)

10

DMA Data of Unoriented and Oriented Coextruded Film Samples

0

2000

4000

6000

8000

10000

12000

-100 -80 -60 -40 -20 0 20 40 60 80

Temperature, C

Stor

age

mod

ulus

, MPa

Tie resin A (1X)

Tie resin A (4X)

Tie resin A (6X)

11

NAS Data of Unoriented and Oriented Coextruded Film Samples Made of Tie Layer Resins A & B

2.1

9.0

24.6

4.1

9.5

21.4

0.0

10.0

20.0

30.0

Tie-A, 1X Tie-A, 4X Tie-A, 6X Tie-B, 1X Tie-B, 4X Tie-B, 6X

Tie Layer

% N

AS

12

Schematic representation of crystalline morphology for lamellae stacking (top) and crystallites distribution (bottom) in unoriened coextruded film (A), and oriented (6X) film (B)

C cMD

(A) (B)c-axis

Orientation

crystallites

amorphous chains

13

Effect of Orientation on Adhesion of Coextruded film

1.15 0.79 0.73130

0.4

0.8

1.2

1.6

2

1:1 4:1 5:1 6:1

Tie layer A

Tie

Laye

r Adh

esio

n, lb

/in

18 mils 3 mils

14

Dynamic Rheological Data of Blend-A (50% EVOH-A + LLDPE-A) and Blend-B (50% EVOH-A + Tie resin-A)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0.01 0.1 1 10 100 1000

Frequency (rad/sec)

50% EVOH-A+LLDPE-A50% EVOH-A + Tie resin A

15

Extensional Stress Growth of Blend-A (50% EVOH + LLDPE) and Blend-B (50% EVOH + Tie Resin A)

1000

10000

100000

1000000

0.010 0.100 1.000 10.000

Time, sec

Exen

. Str

ess

Gro

wth

(Pa-

s)

50% EVOH + Tie resin A50% EVOH + LLDPE

Projected LVE

16

Adhesion Data of 6X Oriented Coex Films with Different Tie Layer Resins A & B

0.76

1.15

0.68

1.39

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Tie Layer A Tie Layer B

Adh

esio

n, lb

-in

6X, MDO/0 Mrad

6X MDO/5 Mrad

17

ConclusionsMDO process results in the following observation

Increased crystallinity

Increased stiffness

Enhanced clarity

Decreased adhesion dramatically

Change to the crystalline morphology can result in increased clarity with increased crystallinity

A reduction in adhesion with MDO process can be explained by thenature of interfacial change

A minor change in tie layer formulation results in improved adhesion with increased MDO orientation.

Thank You

PRESENTED BY

Chun D. LeeLyondell Chemical Company

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