Blending Novapol® Tubular LDPE in Autoclave LDPE for Extrusion Coating Applications Authors: Jim Auger and Paul Tas NOVA Chemicals Corporation Abstract In general autoclave LDPE outperforms tubular LDPE with respect to neck-in. The draw down limit for tubular LDPE on the other hand is higher than for autoclave. The work presented here provides technical details of the benefits of blending tubular LDPE with autoclave LDPE for extrusion coating applications. For a lab scale line, it is shown that at 30 to 50% tube resin content, a blended product performs at least equivalent to a 100% autoclave resin in that the blends showed acceptable neck-in performance but had higher drawdown speed and improved adhesion. This only holds true if the proper selection of blend components is made. A guideline is suggested as to how to make this blend selection. Introduction To be useful in extrusion coating applications, ethylene polymers should have a balance of low neck-in, high drawdown and strong adhesion properties. Low density polyethylene (LDPE) resin, which typically has a density range from about 0.915 to 0.935 g/cc and is prepared by free radical polymerization in either a tubular reactor or an autoclave reactor, is often used for extrusion coating applications because of its good neck-in and drawdown properties. Broad residence time distributions and reactor “zoning” in autoclave reactors produce polyethylene with a larger proportion of high molecular weight polymer and long chain branching.(1) Because of this broader molecular weight distribution, autoclave LDPE generally has superior neck-in properties. In contrast, tubular reactors provide LDPE with a broader crystallinity distribution and higher processability. The tubular process produces LDPE with a shorter reactor residence time and more heterogeneous reactor conditions. Although tubular LDPE is also used at 100% in some extrusion coating applications, a more ideal product for this application would be a positive combination of the two sets of advantages. Attempts have been made historically to combine the best properties of both types of resins. In United States Patent 4,496,698 a process is described in which ethylene is polymerized in an autoclave reactor, passed through a heat exchanger and then further polymerized in a tubular reactor. Alternatively, high drawdown rates and good neck-in values can be achieved by co-extrusion of LDPE with linear low density polyethylene (LLDPE). U.S. patents such as 5,863,665, 5,582,923 and 4,339,507 are examples of extrusion coating polymer blends which are useful for application in extrusion coating processes. The work presented here provides polymer blend characterizations that have a variety of neck-in and adhesion properties over a range of drawdown rates. These polymer blends are prepared by physically blending an ethylene homopolymer produced in a tubular reactor with an ethylene homopolymer produced in an autoclave reactor. Ultimately, it is suggested that blending tubular and autoclave LDPE resins with the “right” characteristics should provide improvements in drawdown and adhesion without sacrificing neck-in properties.

Materials and Experiments Materials The materials used in this study are listed in Table I. The autoclave products are commercial products obtained from a variety of sources. The tubular products were produced by NOVA Chemicals at the Moore facility in Ontario, Canada. Table I: NOVAPOL® Tubular and Competitor Autoclave LDPE Resins Used in This Study

LDPE Nomenclature MI Density Autoclave 1 A1 6.6 0.918 Autoclave 2 A2 4.2 0.924 Autoclave 3 A3 6.8 0.917 LC-0517-A T1 4.6 0.916 LC-0522-A T2 4.2 0.92 LC-0717-A T3 7.2 0.916 NOVAPOL® is a registered trademark of NOVA Brands Ltd.; authorized use/utilisation autorisée. Experiments Physical blends of the autoclave and tubular reactor grades A1/T1, A2/T2 and A3/T3 were prepared by tumble blending pellets of the resins at the desired concentrations then coating the mixture on kraft paper using a 1.5 inch (38.1 mm) extrusion coating line. The extrusion coating line was equipped with a standard screw and barrel, a barrel heater with three 600 watt heating zones and air cooling, a Dynisco pressure indicator, a die plate with a 20-mesh screen pack and a 10 hp General Electric drive capable of up to 50 lb./hour, (22.7 kg/hr). The die assembly consisted of a 12 inch, (30.48 cm), slit Flex LD-40 die with a 0.20 inch, (5.08 mm) die gap and three heating zones totaling 7000 Watts and a laminator coater. The adaptor was equipped with nine heating bands with a total of 4450 Watts, a melt thermocouple located near the outlet of the adaptor and extending into the resin channel with a valve located in the front end of the adaptor to adjust barrel pressure. The laminator/coater consisted of two 15 inch x 15 inch, (381 mm x 381 mm), main rolls, (one chilled chrome roller and one rubber coated chilled pressure roll) powered by a 10 horsepower DC General Electric drive capable of producing chill roll speeds to 2000 ft/min, (610 m/min). A paper roll, equipped with a pneumatic brake system adjustable with a pressure regulator, a wind-up unit with speed control via a magnetic clutch and a speed indicator capable of measuring line speed to 5000 ft/min, (1524 m/min) were also used. Neck-in was recorded as a function of line speed. Adhesion was measured for samples collected at 150 ft/min. Adhesion was measured using the Mullen Burst test, (e.g. ASTM D774). Drawdown was carried out to the point of web breakage. Results Selected analytical and rheological properties for the autoclave and tubular LDPE resins used in this study are listed in Table II. The autoclave resins are commercial products obtained from a variety of sources. Figures 1 through 6 show the molecular weights and distributions, along with comparisons of the capillary flow properties of the resin pairs A1/T1, A2/T2 and A3/T3. All testing was carried out with the intentions of the appropriate ASTM procedures.

Neck-in versus line speed, along with adhesion and drawdown results for extrusion coated paper produced using the pilot scale line described above for 30, 50 and 70% blends, along with their pure components, appear in Figures 7 through 15. Table II: LDPE Blend Resin Analytical and Rheological Properties

ID MI (g/10 min)

Density(g/cm3)

MFR (I21/I2)

PD (MW/MN)

*Br. Cont.

Wt%<104

Mol Wt. Melt Str. @ 190oC(cN)

±Stretch Ratio

A1 6.6 0.918 38.9 22.22 0.56 13.3 5.21 140 A2 4.2 0.924 42.8 12.84 0.60 14.2 6.82 120 A3 6.8 0.917 41.3 19.8 0.51 10.7 6.59 118 T1 4.6 0.916 48.3 9.43 0.52 12.9 6.72 141 T2 4.2 0.92 53.8 7.79 0.58 14.9 5.23 228 T3 7.2 0.916 45.5 12.86 0.56 16.8 4.26 206

* Branch content is the weight average branch index based on differential refractive index and viscometry measurements in molecular weight determinations where the weight average g’ where g’ = [ηb]/[ ηl]). (1) ± Stretch ratio is defined as the ratio of the angular velocity of the extrudate on an accelerating take-up wheel divided by the velocity of that extrudate exiting the die orifice of the capillary rheometer. The results for each of the pairs of resins will be discussed below in detail regarding their performance during coating, the physical properties of neck-in and adhesion and their processability (i.e. drawdown). In the next section an attempt is made to interpret the coating behavior based on the analytical and rheological properties. A1/T1 In the evaluation of these blends it became apparent that not all tubular autoclave blends perform equally well relative to their pure components. A comparison of A1 and T1 molecular weight distributions suggest that while A1 has a significant high molecular weight shoulder, the low molecular weight side of the two profiles is very similar, (Figure 1). As a result, while the MI is measurably different, (A1 = 6.61 and T1 = 4.64), the viscosity in the shear rate range for an extrusion coating process range, (400 – 1000 sec-1), is quite similar, (Figure 4). This behavior appears to be reflected in neck-in performance as an antagonistic response to any amount of tubular resin in the blend, (Figure 7). Although there may be a small improvement in adhesion, (Figure 10), with the addition of tubular resin, there is no improvement in drawdown, (Figure 13). A2/T2 A2/T2 appears to have a more closely matched molecular weight distribution, with A2 having a much less pronounced high molecular weight shoulder than either A1 or A3, (Figure 2). While the MI of these resins is similar, at 4.2 g/10 min., the rheology of this pair is more dissimilar than that seen for the A1/T1 pair in the region of interest, (Figure 5). The neck-in versus line speed profile for these blends suggest this pair is even more antagonistic in that even a small amount of T2 in the blend worsened neck-in beyond what is seen for either A2 or T2 in their pure form. There is no apparent change in adhesion and drawdown appears to be only slightly improved with this blend, (Figures 11 and 14 respectively). A3/T3

Finally, it appears that the A3/T3 blend is most successful in terms of improving coating properties. The molecular weight distributions of these 7 MI resins suggest that while A3 has a large high molecular weight shoulder, T3 provides a significant amount of low molecular weight material, (Figure 3). This in turn provides a rheology profile illustrating the most dissimilar materials in this study, (Figure 6). When the blends are coated, (Figure 9), compositions containing, arguably, up to 70% tubular resin do not significantly increase neck-in, while exhibiting markedly improved adhesion, (Figure 12), and drawdown, (Figure 15) relative to 100% A3. Discussion In a discussion of LDPE extrusion coating resins, it is important to understand some of the differences between tubular and autoclave resins, both in general terms and those specific to extrusion coating. Using Figures 1-3 as examples, it is clear that autoclave resins contain a high molecular weight shoulder. The amount of resin made in each zone is variable, as is evidenced by comparison of the size of the high molecular weight shoulders in the three autoclave resin molecular weight distributions (Figures 1 to 3) and their polydispersity values (PD) as seen in Table II. The low molecular weight side of the resins’ profiles is also of interest. Integration of the area under the curve for content less than 10,000 molecular weight shows that there are almost equal amounts for the A1/T1 (13.3%/12.9%) and A2/T2 (14.2%/14.9%) pairs. The A3/T3 pair shows that T3 has about 6% more low molecular weight material than A3 (16.8% vs.10.7%). This low molecular weight material is thought to contribute to increased processability, as seen by the higher stretch ratio value for T3 (206) vs. A3 (118). This low molecular weight component is also thought to oxidize more readily and promote improved adhesion. The inherently different molecular architecture for tube resins relative to autoclave resins is seen in an increase in stretch ratio for these products. A higher stretch ratio appears to be related to improved drawdown. However, a higher stretch ratio alone is not enough to improve all extrusion coating properties. For example, the A2/T2 pair has stretch ratios of 120 and 228 respectively and drawdown appears to improve with increasing amounts of T2. However, due to an apparent lack of low molecular weight material, adhesion is not improved and neck-in worsens. Tubular resins also tend to shear thin to a greater degree than autoclave resins. This is primarily due to the type of long chain branching (LCB) present in tubular resins. An easy way to discern the differences in the resin types is through their capillary viscosity profiles, (Figures 4 through 6), along with measurement of melt strength and stretch ratio, (Table II). It can be seen from the slopes of the viscosity profiles in Figures 4 and 5 that the resin pairs A1/T1 and A2/T2 display a similar difference in their degree of shear thinning. The A3/T3 resin pair, while being of almost identical MI, has the greatest difference in shear thinning. The three comparisons above suggest that a tubular resin with the same melt index (MI) can have a lower melt strength and higher stretch ratio, (as seen with the A2/T2 and A3/T3 pairs). It is also possible to match melt strength and maintain the same level of processability with a lower MI tubular resin, (as seen with the A1/T1 pair). For extrusion coating applications, these differences become important in several ways. The increase in low molecular weight polymer with higher branch content present in tubular resins suggests that it:

• Improves processability through a higher degree of shear thinning • Should oxidize more readily to provide better adhesion • Should coat at higher speeds due to improved drawdown.

The tubular resin by itself, due to a lack of very high molecular weight material, will neck-in to a greater extent than an autoclave resin of similar MI. Conclusion Overall, it is known that autoclave resins have less neck-in than tubular resins. However, the results of this work suggest that a 30/70 blend of the right tubular and autoclave LDPE resins can overcome the neck-in disadvantages of the tubular resin alone while improving the adhesion properties of the autoclave grade by itself. While the details may vary for other extrusion coating lines or at higher line speeds, it appears that at least some amount of an appropriate tubular resin had a positive effect on the coating operation by managing neck-in and improving adhesion. There may also be opportunities to optimize run conditions and observe improvements in draw down. The justification for the improvements seen with the A3/T3 blend appears to be based on the following two observations

1. For the A3/T3 pair, the viscosity curves are dissimilar in shear thinning. Where shear thinning of the A1/T1 and A2/T2 pairs is quite similar, the A3/T3 pair appears to be more different. This is due to the size of the high molecular weight shoulder for A3.

2. For the A3/T3 pair, 6% more of the component below 10,000 molecular weight for T3 proved to be sufficient to observe improvements in adhesion with little change in neck-in on the pilot line.

If those observations are generalized, the following guidelines could be applied in selecting blend components.

• First choose an autoclave grade with the desired MI (and density) for the desired coating process. • Match a tubular resin of similar MI that has rheology somewhat dissimilar in the region of interest. • Ensure the tubular resin contains an appropriate amount of low molecular weight material.

The above criteria may provide a starting point to begin evaluations to improve overall coating properties of a blended material over that of the pure autoclave resin alone. Acknowledgements The authors would like to thank Ms. Lan Nguyen for all her work in collaboration and running these blends. They would also like to thank the people in the NOVA Chemicals analytical and physical testing labs for their efforts in testing the resins, blends and coated products. References

1. Maraschin, N., Ethylene Polymers, LDPE, Encyclopedia of Polymer Science and Technology, Part 2, (2001), pp 417

2. Yu. Y., DesLauriers P., & Rohlfing, D., Polymer, 46, (2005), pp. 5165 - 5182

Figure 1: Molecular Weight Distribution Profiles for Resins A1 and T1

Figure 2: Molecular Weight Distribution Profiles for Resins A2 and T2

Figure 3: Molecular Weight Distribution Profiles for Resins A3 and T3

Figure 4: Apparent Viscosity vs. Shear Rate for A1 and T1 @190oC.

(L/d=20, dd=0.06")

Figure 5: Apparent Viscosity vs. Shear Rate for A2 and T2 @190oC. (L/d=20, dd=0.06")

Figure 6: Apparent Viscosity vs. Shear Rate for A3 and T3 @190oC.

(L/d=20, dd=0.06")

Figure 7: Coating Line Speed vs. Neck-in for A1/T1 Blends

Figure 8: Coating Line Speed vs. Neck-in for A2/T2 Blends

Figure 9: Coating Line Speed vs. Neck-in for A3/T3 Blends

Figure 10: Adhesion @ 150 ft/min for A1/T1 Blends

Figure 11: Adhesion @ 150 ft/min for A2/T2 Blends

Figure 12: Adhesion @ 150 ft/min for A3/T3 Blends

Figure 13: Maximum Drawdown Speed for A1/T1 Blends

Figure 14: Maximum Drawdown Speed for A2/T2 Blends

Figure 15: Maximum Drawdown Speed for A3/T3 Blends

Blending NOVAPOL® Tubular LDPE in Autoclave LDPE for Extrusion Coating

Applications

Presented by:

Jim AugerResearch ScientistNOVA Chemicals Corp.

Introduction Materials and ExperimentsResults and DiscussionConclusionsQuestions

OverviewOverview

IntroductionIntroductionAn extrusion coating LDPE needs a balance of

Neck-inAdhesionDrawdown

Autoclave LDPE has good neck-in properties

Tubular LDPE has good draw down

What happens if tubular and autoclave LDPE are blended?

Materials and ExperimentsMaterials and ExperimentsTable I: NOVAPOL® Tubular and Competitor

Autoclave LDPE Resins Used in ThisStudy

NOVAPOL® is a registered trademark of NOVA Brands Ltd.; authorized use/utilisation autorisée.

LDPE Nomenclature MI DensityAutoclave 1 A1 6.6 0.918Autoclave 2 A2 4.2 0.924Autoclave 3 A3 6.8 0.917LC-0517-A T1 4.6 0.916LC-0522-A T2 4.2 0.92LC-0717-A T3 7.2 0.916

Materials and Experiments, (cont.)Materials and Experiments, (cont.)Resins were paired:

A1/T1, A2/T2 and A3/T3

Dry blends of each pair at 30:70, 50:50 and 70:30 were prepared and coated along with 100% of each component resin.Coated on untreated kraft paper on a 12”(30.48 cm.) extrusion coating line with a 0.2” (5.08 mm) die gap.

Results and DiscussionResults and Discussion

Table II: LDPE Blend Resin Analytical andRheological Properties

ID MI (g/10 min)

Density (g/cm3)

MFR (I21/I2)

PD (MW/MN)

Br. Cont. Wt%<104 Mol Wt.

Melt Str. @ 190oC(cN)

Stretch Ratio

A1 6.6 0.918 38.9 22.22 0.56 13.3 5.21 140A2 4.2 0.924 42.8 12.84 0.60 14.2 6.82 120A3 6.8 0.917 41.3 19.8 0.51 10.7 6.59 118T1 4.6 0.916 48.3 9.43 0.52 12.9 6.72 141T2 4.2 0.92 53.8 7.79 0.58 14.9 5.23 228T3 7.2 0.916 45.5 12.86 0.56 16.8 4.26 206

Results and Discussion (cont.)Results and Discussion (cont.)Molecular Weight Distribution Profiles for Resins A1 and T1

Results and Discussion (cont.)Results and Discussion (cont.)Coating Line Speed vs. Neck-in for A1/T1 Blends

Results and Discussion (cont.)Results and Discussion (cont.)Adhesion @ 150 ft/min for A1/T1

Results and Discussion (cont.)Results and Discussion (cont.)Maximum Drawdown Speed for A1/T1 Blends

Results and Discussion (cont.)Results and Discussion (cont.)Molecular Weight Distribution Profiles for Resins A2 and T2

Results and Discussion (cont.)Results and Discussion (cont.)Coating Line Speed vs. Neck-in for A2/T2 Blends

Results and Discussion (cont.)Results and Discussion (cont.)Adhesion @ 150 ft/min for A2/T2

Results and Discussion (cont.)Results and Discussion (cont.)Maximum Drawdown Speed for A2/T2 Blends

Results and Discussion (cont.)Results and Discussion (cont.)Molecular Weight Distribution Profiles for Resins A3 and T3

Results and Discussion (cont.)Results and Discussion (cont.)Coating Line Speed vs. Neck-in for A3/T3 Blends

Results and Discussion (cont.)Results and Discussion (cont.)Adhesion @ 150 ft/min for A3/T3

Results and Discussion (cont.)Results and Discussion (cont.)Maximum Drawdown Speed for A3/T3 Blends

ConclusionsConclusions

As expected, auto LDPE resins neck-in less than tube LDPE resins.Judicious choice of tube resins in blends with autoclave can provide benefits in

Increased adhesionIncreased drawdown through optimizationMinimal impact on neck-in relative to 100% auto

AcknowledgementsAcknowledgementsThe authors would like to thank:

Ms. Lan Nguyen for all her work, both in collaboration and in running these blends.

The people in the NOVA Chemicals applications, analytical and physical testing labs for their efforts in coating and testing the resins, blends and coated products.

Please remember to turn in your evaluation sheet...

Thank you

PRESENTED BY

Jim AugerResearch ScientistNOVA Chemicals Corp.augerja@novachem.com