Processability and Film Performance of Single Site sLLDPE / LDPE Blends

Paul Tas(*), Sarah Marshall, Trevor Swabey

NOVA Chemicals Corporation

Abstract To improve the bubble stability of Linear Low Density PolyEhtylene (LLDPE) in blown film, it is common to blend in long chain branched Low Density PolyEthylene (LDPE). For Ziegler Natta (ZN) catalyzed LLDPE typical LDPE levels range from 10% to 30%. With the introduction of single site catalyzed LLDPE produced in dual reactor mode (sLLDPE), blend strategies have been revisited. It appears that addition of 10% or less LDPE to sLLDPE results in high performance films with superior bubble stability. The good compatibility of sLLDPE with LDPE results in a great advantage for film converters in the form of a new tool to design films, based on the selection of the LDPE blend partner. It is demonstrated how film properties of sLLDPE/LDPE blends can be fine-tuned by varying the type of LDPE and the amount added. Introduction The combination of NOVA Chemicals’ Advanced SCLAIRTECHTM dual reactor technology and NOVA Chemicals’ propriety single-site catalyst provides unique opportunities for resin design. This results in sLLDPE products that overcome processability issues encountered with traditional metallocene catalyzed LLDPEs (high extruder pressures, more energy consumption and decreased bubble stability), while maintaining the enhanced physical property performance. Each of the two reactors can be independently controlled to yield different molecular weights, molecular weight distributions and comonomer placements. This allows tremendous flexibility in product development and the ability to tailor products according to customers’ needs. Figure 1 illustrates the degrees of freedom associated with the dual reactor design. A new family of single-site catalyzed products has been commercialized since 2003 under the tradename SURPASS . Attributes of these products have been described in detail elsewhere, see e.g. Aubee (1), Goyal (2) and Dobbin (3). For blown film it is common to blend LLDPE with LDPE to enhance bubble stability. It is well documented that adding LDPE to LLDPE gives enhanced melt strength and thus better bubble stability, see e.g. Ghijssels et al. (4) and Ho et al. (5). Blending percentages typically range from 10 to 30%. Recently, Ajji (6) et al. proposed that 10 to 20% LDPE should be sufficient for enhanced bubble stability. Blending LDPE generally comes at the price of loss of performance. This makes the choice of LDPE and the level of LDPE to be added a matter of finding the right balance between processability and performance. Some attributes regarding the effect of blending LDPE in sLLDPE on processability and film performance have been reported by Tas et al. (7-9). In this paper it is demonstrated how the balance between processability and film performance can be controlled and optimized by proper selection of the LDPE blend partner and the amount added. In order to do so, the following lead questions will be answered: 1. How does addition of LDPE affect bubble stability? (Bubble stability study) 2. How does addition of LDPE affect film performance? (Performance study) 3. What is the optimum LDPE as blend partner for sLLDPE? (Combination of 1 and 2) The blends of sLLDPE/LDPE will be positioned versus a benchmark High Performance ZN LLDPE. (*)Author to whom correspondence should be addressed: phone: (403) 250-4559, fax (403) 250-0621 e-mail: taspa@novachem.com

Experimental and procedure Materials Resins selected for this study comprise sLLDPE, ZN LLDPE and LDPE. All resins used are manufactured by NOVA Chemicals Corporation (Calgary, Canada) and are listed in Table 1.

Table 1. Description of Base Resins Reference name

Melt index I2

(g/10 min)

Base resin density (kg/m3)

Polydispersity

sLL 1.0 0.917 3.2 ZN LL 1.0 0.920 3.5 LD0.3 0.25 0.920 5.2 LD0.8 0.75 0.9205 4.5 LD2.0 2.3 0.919 6.2 LD0.8n 0.75 0.924 3.3 LD2.0n 2.0 0.924 2.9

The LDPEs were chosen such that the study included non-clarity LDPE (LD0.3, LD0.8 and LD2.0) and clarity LDPE (LD0.8n and LD2.0n). Note that the clarity grades are narrower than the non-clarity grades. Film Processing All experiments were run on a Macro blown film line, equipped with a general purpose 3.5 inch (88.9mm) single screw with barrier design, L/D=30. A general-purpose spiral die was used; the die diameter was 8 inch (203.2 mm) and the die gap 50 mil (1.27 mm). The cooling unit consisted of a dual lip air ring in combination with Internal Bubble Cooling (IBC). All films were run at blow-up ratio (BUR) 2.0. Die temperatures were set such that the melt temperature was between 420 F (215 C) and 440 F (227 C). Bubble stability study. The output and film gauge depended on the question to be answered. For the study on the effect of LDPE on bubble stability, maximum output experiments were performed. It is assumed that improved bubble stability results in higher maximum output. The definition of maximum output that was followed in this study reads: maximum output is achieved when bubble instability leads to fluctuation in frost line height and/or fluctuation in lay flat width. After all, both of these criteria will lead to non-uniform films and thus inconsistent film quality. Film gauge was kept at 1 mil (25.4 micron) for all maximum output experiments. Blends run for the bubble stability study are given in Table 2.

Table 2. Blends run for bubble stability study. 100% sLL 95% sLL + 5% LD0.3 90% sLL + 10% LD0.8 100% ZN LL 95% ZN LL + 5% LD0.3 90% sLL + 10% LD0.8

Performance study. To reflect common practice films for the performance study were run at 14 pound per hour per inch of die circumference (14 lbs/hr/inch-c). In SI units that translates into 2.50 kg per hour per centimeter of die circumference (2.50 kg/hr/cm-c). In absolute values this is 350 lbs/hr or 158.9 kg/hr. Film gauge was kept at 2 mil (50.8 microns). Products run for the performance study are listed in Table 3.

Table 3. Blends run for performance study.

LD0.8 LD2.0 LD0.8n LD2.0n 100% ZN LL 100% sLL sLL + 10, 20, 30% 10, 20, 30% 10, 20, 30% 10, 20, 30%

Base Resin Testing Melt index testing was done on a Tinius Olsen melt indexer, according to ASTM D1238. Melt strength tests were done using a Rosand Capillary, D=2 mm and L/D=10 mm. The distance the die exit to the haul-off unit was 415 mm, and the acceleration of the haul-off unit was 54 m/min2. The piston speed was such that the apparent shear rate in the die was 2.5 s-1. Measurements were done at 374 F (190 C). The polydispersity was determined by measuring the molecular weight distribution using a Waters Model 150 GPC apparatus, equipped with a differential refractive index detector. Differential Scanning Calorimetry (DSC) was done on a Perkin Elmer apparatus. The samples were heated from –20 C to 200 C at a heating rate of 10 C/min, subsequently cooled at a rate of 10 C/min. Film Testing The secant moduli were measured on a Instron Model 4204 Universal Testing Machine, according to a company test method (adaptation of ASTM D 882). Tear was measured using a ProTear Electronic Elmendorf Tearing Tester, according to the test method (adaptation of ASTM D1922). ASTM procedure D 1709-01 Method A was used for the measurements of the dart impact strength using a phenolic dart head. Finally, haze was measured according to ASTM D1003 and gloss45 according to ASTM D2457. Results and Discussion How does Addition of LDPE Affect Bubble Stability? In Figure 2 the results for the maximum output study are given in terms of output per hour per cm of die circumference. In the text here, these numbers are translated into absolute values. If no LDPE is added, sLL and ZN LL have similar maximum output at 400 lbs/hr (182 kg/hr). If 5% of the fractional LDPE LD0.3 is added, the maximum output for the sLL/LD blend increases by 50% indicating superior bubble stability. The bubble stability for the ZN LL/LD blend is only marginally better than for the 100% ZN LL, as demonstrated by the small increase in maximum output: from 400 (182 kg/hr) to 450 lbs/hr.(204 kg/hr). A similar trend is seen when 10% of LD0.8 is added. Maximum output for the sLL/LD0.8 blend is 580 lbs/hr (263 kg/hr), while the maximum output for the ZN LL/LD0.8 blend stays behind at 500 lbs/hr (227 kg/hr). The same data as plotted in Figure 2 are listed again in Table 4, along with the measured melt index and melt strength for the blends. From the second column it is seen that no big changes in melt index are present. The 100 % sLL and 100% ZN LL are both at 1.0 dg/min, while the blends of sLL with LD and ZN LL with LD are all at 0.9 dg/min. The melt strength for 100% sLL is slightly lower than for ZN LL, yet both products have the same maximum output. At a loading of 5% LD0.3 the melt strength for the sLL/LD blend is nearly identical to the melt strength of the ZN LL/LD blend. However, the maximum output for the sLL/LD blend is much higher than for the ZN LL/LD blend. Apparently, melt strength is not uniquely related to the maximum output and hence is not necessarily a good measure for bubble stability.

This statement is supported by the results for the 10% LD0.8 blends. For sLL/LD0.8 and ZN LL/LD0.8 similar melt strength is reported, yet the maximum output for the sLL/LD0.8 is significantly higher. Apparently, there is a synergetic effect between sLLDPE and LDPE not seen for ZN LL and LDPE.

Table 4. Melt index, melt strength and maximum output for sLL/LD and ZN LL/LD blends. Product Melt Index I2

gram/10 min Melt strength at 190 C

cN Maximum output

Kg/hr/cm-c (Lbs/hr/inch-c)

SLL 1.0 2.8 2.9 (16) SLL + 5% LD0.3 0.9 6.4 4.3 (24) SLL + 10% LD0.8 0.9 9.1 4.1 (23) ZN LL 1.0 3.6 2.9 (16) ZN LL + 5% LD0.3 0.9 6.2 3.2 (18) ZN LL + 10% LD0.8 0.9 9.1 3.6 (20)

A possible explanation for this observed synergy between sLLDPE and LDPE can be found in the DSC cooling curves. A representative illustration of the cooling curves is given in Figure 3. This figure shows the cooling curves for sLL, ZN LL and LD0.8. The ZN LL has its crystallization peak at a higher temperature than the sLL and the LD0.8. The crystallization temperatures for sLL and LD0.8 are nearly equivalent. For crystallization during film blowing this could mean that for the sLL/LD0.8 blend there is one single position at which both the sLL and the LD0.8 start crystallizing. For the ZN LL/LD0.8 blend there might be two positions at which solidification starts. Closest to the die the ZN LL might start crystallizing followed by the LDPE. Or, in other words, It is very well possible that sLLDPE and LDPE co-crystallize, while ZN LDPE and LDPE don’t. The question posed in the introduction was “How does addition of LDPE affect bubble stability?” The answer reads: Addition of LDPE to sLLDPE results in a significant improvement in bubble stability, more so than found for ZN LLDPE. When adding LDPE with MI 0.75 the LDPE concentration can be reduced to 10%. For a LDPE with MI 0.25 levels as low as 5% are possible. How does Addition of LDPE Affect Film Performance? In this section physical and optical properties of the sLL/LD blends are reported. Comparisons will be made with films made of 100% ZN LL, even though the base resin density is higher (0.917 for sLL, 0.920 for ZN LL). The reason for this comparison is explained in the section on stiffness below. Stiffness. It is common to compare products at equal density. However, what is really important is to compare films at equal stiffness. After all, the final thickness of the film depends on the stiffness of the film and not on the density of the base resin. Adding LDPE to LLDPE increases the stiffness. An example for the stiffness of sLL/LD films and for 100% ZN LL is given in Table 5. As can be seen, the stiffness in the MD direction for the sLL/LD0.8 blend is only slightly lower than that of the ZN LL film. The stiffness in the TD direction for both films is nearly identical. So, even though the base resin density of the sLL is 0.917 and the base resin density of the ZN LL is 0.920, the stiffness of sLL/LD blends falls in the same range as 100% ZN LL. Consequently, comparing sLL/LD blends with 100% ZN LL is a proper approach. Table 5. Secant moduli for 100% ZN LL and for sLL + 10% LD0.8

1% secant modulus

MD (MPa)

2% secant modulus

MD (MPa)

1% secant modulus

TD (MPa)

2% secant modulus

TD (Mpa)

ZN LL 211 185 245 196 sLL + 10% LD0.8 186 170 245 205

Dart. Figure 4 depicts the dart for the sLL/LD blends as function of percentage LDPE. Different lines represent the different LDPEs and the single dot represents ZN LL. It is clear that the dart value drops significantly when LDPE is blended in sLL. A value close to 700 grams for 100% sLL drops to around 400

grams at 10% LDPE loading. Interestingly, the type of LDPE (clarity or non-clarity) and the melt index of the LDPE do not have any effect on the dart value at a 10% LDPE loading. Even at 20% loading there is no significant difference in the dart values. Only at 30% LDPE loading the dart values depend on the type of LDPE. It appears that at this high loading, the non –clarity melt index 0.75 LDPE (LD0.8) has the highest dart. The clarity LDPEs (LD0.8n and LD2.0n) have the lowest dart. In the comparison of the sLL/LD blends with the 100% ZN LL film, it is seen that at 10% LDPE loading the dart values of the blends are still slightly higher than for the 100% ZN LL. This result, along with the findings in the section on bubble stability, leads to two major consequences. If the dart value is of importance for a given application and ZN LLDPE is used in this particular application, 1. one could either downgauge by switching to a 100% sLLDPE film, or 2. one could switch to a sLLDPE/LDPE blend that can be run at higher rates because of the improved

bubble stability. Tear MD. Figure 5 shows the tear MD versus the percentage LDPE. Since the tear TD is generally much higher than the tear MD, it was chosen to plot the weakest direction. Contrary to the results for dart, the tear MD does depend on the type of LDPE. It appears that the clarity MI 2.0 LDPE (LD2.0n) has the least effect on the tear MD, followed closely by the clarity MI 0.75 LDPE (LD0.8n). Blending in non-clarity LDPEs (LD0.8 and LD2.0) result in lower tears. So, if for a certain application a high tear is desired it is recommended to blend in clarity LDPE. If a low tear is desired, e.g. consumer packaging where too high a tear might be detrimental since the packaging might be too hard to open, a non-clarity may be advised. From Figure 5 it is also seen that for 100% sLL the tear MD is slightly higher than for the 100% ZN LL. This is typical for dual reactor sLLDPE. At 10% clarity LDPE the tear MD values for the sLL/LD blends are slightly lower than for the ZN LL. Yet, the differences are small and the same strategy as given in point 2 in the discussion on dart can be applied here. If the tear value is of importance for a given application and ZN LLDPE is used in this particular application, one could switch to a sLLDPE/LDPE blend that can be run at higher rates because of the improved bubble stability. Balance of dart and tear MD. In the discussions on dart and on tear MD, the approach was taken that either dart or tear MD was important. However, in many applications both tear MD and dart are equally important. A plot like Figure 6, dart versus tear MD, facilitates the discussion in that case. Here are two cases how to read this figure. Case 1. A certain application requires high dart, high tear and good bubble stability. In that case one will have to look in the top right corner of Figure 6 to find the high dart and the high tear MD values. This leads to a selection of ZN LL, sLL+ 10% LD2.0n or sLL+10% LD0.8n. Given the desire for good bubble stability one would revert to a sLLDPE with LDPE blended. Either the combination of sLL+10% LD2.0n or sLL+10% LD0.8n would do.

Case 2. A certain application requires high dart for impact and has to be opened easily, i.e. low tear. In that case one will have to look in the top left corner of Figure 6. A good candidate would be any of the sLL/LD0.8 blends. Depending on the tear value desired one could go for anywhere between 10 and 30%.

Most important conclusion from this Figure 6 is that it enables the film converter to design film properties by blending in different LDPEs at various percentages. Optics. A similar approach as discussed above for dart and tear is taken for haze and gloss. Figure 7 shows the haze versus the percentage LDPE and Figure 8 the gloss versus the percentage LDPE. Figure 9 is a combination of the two: gloss is plotted versus reversed haze. The reason to plot reversed haze on the horizontal axis is that this way the highest optical performance is again in the top right corner. Some interesting conclusions can be drawn from these figures. First of all, at 10% LDPE, the haze is lowest and the gloss is highest for the sLL/LD blends with the non-clarity LDPEs. Apparently, having a high clarity when run at 100% LDPE does not necessarily lead to high clarity in blends where the LDPE is the minor component. At 20% LDPE all blends perform more or less the same, the only exception being the

LD0.8 exhibiting a slightly lower gloss value. At 30% LDPE the roles of the clarity LDPE and the non-clarity LDPEs are reversed to the 10% results. Now the clarity LDPEs give a better optical performance than the non-clarity ones. It appears that the type of LDPE, clarity or non-clarity dominates the effect of LDPE on the optical properties. So, the optical properties of the sLL/LD blends can be divided in two groups, the group with clarity LDPE and the group with non-clarity LDPE. Within each group a moderate effect of the melt index on the optical properties can be discerned. It seems that a higher melt index (2.0) gives slightly higher gloss and slightly lower haze values than the lower melt index (0.8). The best optical performance as seen in the top right of Figure 9 is obtained for a sLL/LD2.0n blend. This is obtained for a loading of 30% LDPE. Close to that product are the 10% LD2.0 blend, 10% LD0.8 and 30% LD0.8n. Now, from the previous discussion on dart and tear it was seen that 10% LDPE gives better physical performance than 30% LDPE, regardless the type of LDPE. Thus, if one wants to select a product with high optical performance and with high physical performance, one would choose the 10% LD2.0 or the 10% LD0.8. Which of the two latter has preference depends on whether dart is more important (LD0.8, see Figure 6) or tear (LD2.0, see Figure 6). A final remark on the optical performance concerns the comparison with the 100% ZN LL. From Figure 9 it becomes immediately clear that the haze for the ZN LL is much higher than for all the sLL/LD blends and the gloss is much lower. Thus for any sLLDPE with LDPE blended in at levels of 10 to 30%, the optical performance is much better than for ZN LLDPE. Hot tack. A last advantage of using sLLDPE/LDPE blends versus 100% ZN LLDPE is shown in Figure 10. Here the hot tack curves are given for sLL, ZN LL and for the sLL + 10% LD0.8 blend. Only one blend is shown since it is believed that the trend shown is representative for all blends. The maximum hot tack force for sLL is similar to the maximum hot tack force for ZN LL. Since the maximum hot tack force somehow correlates to the melt strength (see Table 4) this is expected. The hot tack range for the ZN LL seems a little broader than for the sLL. This coincides with the broader melting trajectory for ZN LL, as shown in figure11. This Figure 11 depicts the heating curves for sLL, ZN LL and LDPE (LD0.8). As was the case for the cooling curves, the DSC heating traces for sLL and LDPE follow each other closely right to the peak. ZN LL has a broader melting trajectory and a double peak, causing the hot tack range to broaden as well. For the sLLDPE + 10% LD0.8 the hot tack range is even broader than for the ZN LLDPE. Also the maximum hot tack force is much higher. A broad range and a high force are beneficial for VFFS applications. The fact that the maximum hot tack force is highest and the range broadest for the sLLDPE + 10% LD0.8 must be attributed to the higher melt strength for the blend (see Table 4). Optimization of maximum hot tack force and range certainly is possible, though it was not part of the current study. CONCLUSION What is the optimum LDPE as blend partner for sLLDPE? From the discussion above it is obvious that this question cannot be answered unequivocally. The correct answer would be: it depends. Figures like dart versus tear or gloss versus haze or any other combination are helpful tools to answer the question. More important than finding a straightforward answer to the question is that in the process of trying to find an answer a couple of new findings have been reported:

Using sLLDPE at 100% gives the opportunity to downgauge films when compared to ZN LLDPE. Using sLLDPE/LDPE blends gives the opportunity to run at higher rates while maintaining a high level of film performance.

To obtain improved bubble stability in sLLDPE only 10% (or less) LDPE is needed. This ensures that film physicals like tear and dart stay at a high level at the same time.

To improve optical performance of sLLDPE, 10% of non-clarity LDPE (MI 0.75 or 2.0) is a good choice.

Though these findings are important on themselves, the most valuable finding is depicted in Figure 12. Here the overall performance is plotted versus the processability. Overall performance is a combination of optical performance, dart, tear and hot tack performance. Processability is a combination of maximum output, bubble stability and gauge control. In the figure it is seen that for 100% sLLDPE the processability is ranked similar to that of ZN LLDPE, the performance is ranked better. This is supported by the findings in this paper: similar maximum output for sLLDPE and ZN LLDPE, the tear MD is slightly higher for sLLDPE and the dart is much higher. Blending in LDPE into sLLDPE gives an enormous improvement in processability, yet the physical performance stays at a high level. For 10% LDPE levels it has been shown that the physical performance of sLLDPE/LDPE blends is even better than for 100% ZN LLDPE: dart and tear values are similar, hot tack and optics are much better. Finally, it has been shown that physical properties like dart and tear can be controlled by varying the type of LDPE and the amount added. This gives the film converter a new dimension in designing films. Using one base resin sLLDPE, a wide variety of film performance can be achieved while ensuring superior bubble stability. ACKNOWLEDGEMENT The authors acknowledge the support from NOVA Chemicals and from the members of the technical community at NOVA Chemicals Research Centre and NOVA Chemicals Technical Centre for their assistance in this study LITERATURE (1) Aubee, N., Dobbin, C., Marshal, S., Swabey, T., TAPPI Place Conference, 2004, Indianapolis,

Aug. 30-Sep. 2, 2004 (2) Goyal, S., Marshall, S., Dobbin, C., Boparai, M., Marler, J., Swabey, T., SPE ANTEC 2005, Boston,

May 1-5, 2005 (3) Dobbin, C., Brown, S., Swabey, J., Yamashita, G., PPS, 17th Annual Meeting (PPS17), Montreal 2001 (4) Ghijssels, A., Ente, J., Raadsen, J., Intern. Poly. Process., 4, 284 (1990) (5) Ho, K., Kale, L., Montgomery, S., J. Appl. Polym. Sci., 85, 1408 (2002) (6) Ajji, A., Sammut, P., Huneault, M., J. Appl. Polym. Sci, 88, 3070 (2003) (7) Tas, P., Nguyen, L., Marshall, S., Kashanian ,M., TAPPI Place conference, 2004, Indianapolis,

Aug. 30 – Sep. 2, 2004 (8) Tas, P., Nguyen, L., The, J., Kashanian, M., Polymer Films and Fibers conference, Montreal,

Sep. 27-29, 2004 (9) Tas, P., Swabey, T., Marshall, S., Kashanian, M., SPE ANTEC 2005, Boston, May 1-5, 2005

Advanced SCLAIRTECH™ is a trademark of NOVA Chemicals. NOVAPOL® is a registered trademark of NOVA Brands Ltd.; authorized use. SURPASS™ is a trademark of NOVA Chemicals Corporation in Canada and of NOVA Chemicals (International) S.A. elsewhere.

Figure 1. The multi-reactor technology provides independent control of molecular weight, concentration and density of each of the components making up the final

polymer

Figure 2. Maximum output for sLL and its blends with LDPE and ZN LL and its blends with LDPE.

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Figure 3. DSC cooling curves for sLL, ZN LL and LD0.8

Figure 4. Dart for sLL/LD blends as function of percentage LDPE. Parameter is the type of LDPE and as benchmark the dart for ZN LL is plotted.

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Figure 5. Tear MD for sLL/LD blends as function of percentage LDPE. Parameter is the type of LDPE and as benchmark the tear MD for ZN LL is plotted.

Figure 6. Dart vs. Tear MD for sLL/LD blends. Parameter is the type of LDPE and as benchmark the dart

and tear for ZN LL is plotted.

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Figure 7. Haze for sLL/LD blends as function of percentage LDPE. Parameter is the type of LDPE and as benchmark the haze for ZN LL is plotted.

Figure 8. Gloss for sLL/LD blends as function of percentage LDPE. Parameter is the type of LDPE and as

benchmark the gloss for ZN LL is plotted.

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Figure 9. Gloss vs. haze (reversed) for sLL/LD blends as function of percentage LDPE. Parameter is the

type of LDPE and as benchmark the data for ZN LL are plotted. The higher up in the top right corner the better the optical performance.

Figure 10. Hottack curves for sLL, ZN LL and sLL + 10% LD0.8.

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Figure 11. DSC heating (2nd) curves for sLL, ZN LL and LD0.8

Figure 12. Schematic diagram of how performance relates to processability for ZN LLDPE, LDPE,

sLLDPE and sLLDPE/LDPE blends. The higher up in the top right corner the better.

Processability (maximum output, bubble stability, gauge control)

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/g)

sLL ZN LL LD0.8

Paul Tas, Sarah Marshall and Trevor SwabeyTAPPI Europe 2005

Vienna, May 23-25, 2005

Processability and Film Performance of

Dual Reactor Single Site sLLDPE / LDPE blends

0

0.1

0.2

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0.4

0.5

0.6

0.7

0.8

0.9

2.5 3 3.5 4 4.5 5 5.5 6 6.5

Log (Molecula r W eight)

dW/d

Log(

mw

)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

dens

ity o

r br

anch

es/1

000

C.

Reactor 1 Component

Reactor 2 Component

Comp osite Resin Product

Oc tene Dist ribution

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0.1

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0.5

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0.7

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0.9

2.5 3 3.5 4 4.5 5 5.5 6 6.5

Log (Molecula r W eight)

dW/d

Log(

mw

)

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5.0

10.0

15.0

20.0

25.0

30.0

dens

ity o

r br

anch

es/1

000

C.

Reactor 1 Component

Reactor 2 Component

Comp osite Resin Product

Oc tene Dist ribution

Dual Reactor single site catalyzed LLDPE

Dual reactor products are made in the Advanced SCLAIRTECH™ plant in Joffre, AB

ZN LLDPE like processability Balanced properties

Typical film properties

Yet, blending LDPE for monolayer film is still common practice

Dual Reactor single site catalyzed LLDPE

Shear Viscosity versus Shear Rate at 190oC

100

1000

10000

100000

0.01 0.10 1.00 10.00 100.00 1000.00

Shear Rate [1/s]

Visc

osity

[Pa.

s]

sLLDPEZ/N LLDPEmLLDPE

HighLowZN LLDPE

LowHighmLLDPE

HighMediumsLLDPE

Tear MDDartProduct

Revisiting LLDPE/LDPE blend concepts for dual reactor single site catalyzed LLDPE (sLLDPE)

• How does addition of LDPE affect bubble stability?

• How does addition of LDPE affect film performance?

• What is the optimum LDPE as blend partner for sLLDPE?

Materials

6.20.9192.3LD2.0LF-0219-D

2.90.9242.0LD2.0nLF-0225-B3.30.9240.75LD0.8nLF-Y824-D

4.50.92050.75LD0.8LF-Y819-C5.20.9200.25LD0.3LF-Y320-C

NOVAPOL®, tubular LDPE3.50.9201.0ZN LLFP120-C/D

SCLAIR, single reactor Ziegler Natta LLDPE3.20.9171.0sLLFPs117-C/D

SURPASS™, dual reactor single site LLDPE

PDBase resin density

Melt indexReference name

Product

Processing

• Macro Engineering blown film line• 3.5” single screw, L/D: 30/1• General purpose (GP) screw with barrier design• 8” die diameter; GP spiral• 50 mil die gap • Dual lip air ring and internal bubble cooling (IBC)• BUR 2• Film gauge

– 1 mil for bubble stability study– 2 mil for physical properties

• Output– Maximum for bubble stability study– 14 lbs/hr/inch-c (350 lbs/hr) for physical properties study

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5M

axim

um o

utpu

t in

kg/h

r/cm

-c

100% sLL

100%ZN LL

90% sLL

+ 10%LD0.8

90% ZN LL

+10%

LD0.8

95% sLL

+ 5%

LD0.3

95% ZN LL

+ 5%

LD0.3

16 lbs/hr/inch-c

20 lbs/hr/inch-c

18 lbs/hr/inch-c

16 lbs/hr/inch-c

23 lbs/hr/inch-c

24 lbs/hr/inch-c

1. How does addition of LDPE affect bubble stability?Maximum output for sLL/LD and for ZN LL/LD blends

19.69.10.9ZN LL + 10% LD0.8

18.46.20.9ZN LL + 5% LD0.3

16.03.61.0ZN LL

22.89.10.9sLL + 10% LD0.8

24.06.40.9sLL + 5% LD0.3

16.02.81.0sLL

Maximum output

Melt strengthMelt indexProduct

How does addition of LDPE affect bubble stability?

Maximum output and melt strength for sLL/LD and for ZN LL/LD blends

-0.5

0

0.5

1

1.5

2

2.5

30 50 70 90 110 130 150 170

Temperature (C)

Hea

t flo

w (W

/g)

sLL ZN LL LD0.8

How does addition of LDPE affect bubble stability?

DSC crystallization curves for sLL, ZN LL and LDPE

1. How does addition of LDPE affect bubble stability?

• Addition of low amounts (≤ 10%) of LDPE to sLLDPE has a pronounced effect on bubble stability

• There is no unique correlation between Melt strength and maximum output

• With respect to bubble stability, LDPE and sLLDPE appear to have a increased synergetic effect, when compared to ZN LLDPE and LDPE blends.

2. How does addition of LDPE affect film performance?

Secant moduli

205245170186sLL + 10% LD0.8

196245185211ZN LL

2% secant modulus TD (MPa)

1% secant modulus TD (MPa)

2% secant modulus MD (MPa)

1% secant modulus MD (MPa)

Product

0

100

200

300

400

500

600

700

0 10 20 30

% LDPE

Dar

t (gr

am)

sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

How does addition of LDPE affect film performance?

Dart versus % LDPE

0

100

200

300

400

500

600

700

800

900

0 10 20 30

% LDPE

Tear

MD

(gra

m)

sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

How does addition of LDPE affect film performance?Tear MD versus % LDPE

0

50

100

150

200

250

300

350

400

0 100 200 300 400 500 600 700 800

Tear MD (gram)

Dar

t (gr

am)

sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

30%

20%

10%

How does addition of LDPE affect film performance?Dart versus Tear MD for sLL/LD blends

How does addition of LDPE affect film performance?Haze versus % LDPE

0

5

10

15

20

25

30

0 10 20 30

% LDPE

Haz

e (%

)

sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

How does addition of LDPE affect film performance?Gloss versus % LDPE

0

10

20

30

40

50

60

70

80

0 10 20 30

% LDPE

Glo

ss (%

)sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

40

45

50

55

60

65

70

75

80

68101214161820

Haze (%)

Glo

ss (%

)

sLL + LD2.0 sLL + LD2.0n sLL + LD0.8 sLL + LD0.8n ZN LL

How does addition of LDPE affect film performance?Gloss versus haze (reversed) for sLL/LD blends

0

0.5

1

1.5

2

2.5

3

3.5

80 90 100 110 120 130 140 150

Temperature [C]

Hot

tack

forc

e [N

per

inch

sam

ple

wid

th]

sLL ZN LL sLL + 10% LD0.8

How does addition of LDPE affect film performance?Hot tack curves

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

30 50 70 90 110 130 150 170

Temperature (C)

Hea

t flo

w (W

/g)

sLL ZN LL LD0.8

How does addition of LDPE affect film performance?DSC melting curves and melt strength

9.1sLL + 10% LD0.8

3.6ZN LL

2.8sLL

Melt strength (cN)

Product

3. What is the optimum LDPE as blend partner for sLLDPE

• BubbleStability Only 10% (or less) is required.

• Dart: Keep levels low, preferably ≤ 10%. • Tear MD Keep levels low, preferably ≤ 10% and use of

narrow (clarity) LDPE is advised. • Optics High optical performance for all LDPE levels.• Hot tack Significant improvement in maximum hot tack

force and hot tack range at 10% LDPE

Conclusions

Processability (maximum output, bubble stability, gauge control)

Ove

rall

perf

orm

ance

(com

bina

tion

of

optic

s, d

art,

tear

, pun

ctur

e, s

eala

bilit

y &

hot

tack

)

low

low

high

high

\

sLL / LDPE blends

sLL

ZN LL

LDPE

Conclusions

Properties of dual reactor single site catalyzed sLLDPE / LDPE blends can be fine-tuned by the choice of LDPE and the level of LDPE.

To achieve maximum benefit, 10% LDPE in sLLDPE gives film performance better than 100% ZN LLDPE films and superior bubble stability.