POLYPROPYLENE-RICH BLENDS WITH ETHYLENE/

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1 POLYPROPYLENE-RICH BLENDS WITH ETHYLENE/ -OLEFIN COPOLYMERS COMPATIBILIZED WITH INTUNE POLYPROPYLENE-BASED OLEFIN BLOCK COPOLYMERS Jeff Munro, Yushan Hu, Ray Laakso, Lisa Madenjian, Steve Werner, Gary Marchand The Dow Chemical Company, Freeport, TX 77541, USA Abstract Polypropylene (PP) is one of the most commonly used thermoplastics due to its low cost and excellent properties, such as stiffness and heat resistance. However, PP is a relatively brittle material and is frequently modified with elastomers and other thermoplastics to impart toughness. Ethylene/ -olefin copolymers, including ethylene-propylene rubbers produced in the impact copolymer polypropylene (ICP) process and polyolefin elastomers (POEs) made in a solution process, are commonly used to impact modify isotactic polypropylene. While blends of polyethylene (PE) and polypropylene often have poor properties due to the incompatibility of the two resins, INTUNE Polypropylene-based Olefin Block Copolymers (PP- OBCs) were recently introduced as a means to compatibilize PE and PP resins. The design flexibility of these novel OBCs allows for a variety of ethylene-based polymers to be compatibilized with PP, from high-density PE (HDPE) to low density POEs, such as ethylene-octene elastomers. As with any immiscible blend, controlling the dispersion of the minor phase is critical to achieving the desired mechanical properties. Compatibilization can reduce the size of the domains in the blends and improve properties. Three cases of PP-rich blends will be used to illustrate the capability of novel PP-OBC compatibilizers to improve the dispersion and properties of ethylene-based copolymers dispersed in a PP matrix: injection molded ICPs, injection molded thermoplastic polyolefin blends (TPO PP/POE/talc blends), and slowcooled compression molded PP/POE blends. Introduction INFUSE Olefin Block Copolymers (OBCs) were commercialized by Dow Elastomers in These OBC elastomers contain two types of ethylene-based blocks: high-crystallinity hard segments with melting temperatures similar to high-density polyethylene and semi-crystalline-to-amorphous soft segments that are elastomeric. The crystalline hard-segment domains provide the physical cross-links between the elastic softsegment chains, resulting in an elastic network. The block structure of these polymers results in an advantaged performance balance of flexibility and heat resistance versus random polyolefin copolymers [1, 2]. In 2013, another generation of OBCs was introduced. INTUNE Polypropylene-based OBCs (PP-OBCs) are designed as compatibilizers rather than elastomers. They contain propylene-rich blocks compatible with polypropylene and ethylene-rich blocks compatible with polyethylene. The block compositions can be tuned to compatibilize a range of propylene and ethylene-based thermoplastics. As shared in previous papers, these compatibilizing OBCs can be used in a range of applications, such as tie layers between PP and PE films and in PE/PP recycle blends [3 5]. More recently, the composition of the PP-OBCs have been tuned to enable compatibilization of ethylene/α-olefin elastomers with PP. Ethylene/a-olefin elastomers, including EP rubbers produced during the manufacture of impact copolymer polypropylenes (ICPs) and ethylene/1-octene or ethylene/1-butene polyolefin elastomers (POEs) used TPO compounds, can be compatibilized using these novel PP-OBCs. In this paper, three cases will be used to demonstrate the efficacy of PP-OBCs in reducing the size of dispersed elastomer domains in a PP matrix: injection molded ICPs; injection molded TPO compounds (PP/POE/talc blends); and slow-cooled compression molded PP/POE blends. In addition to elastomer domain size reduction, the resulting mechanical properties of the materials will be discussed, including stiffness and Izod impact toughness. Materials Materials and Methods A range of PP resins were used in this work. For the ICP work, 12 commercial ICP resins with melt flow rates ranging from 0.3 to 100 dg/min (2.16 kg, 230 C) were used. For the TPO injection molding work, a 35 MFR ICP and 65 and 52 MFR homopolymer PPs (hpps) were used. For the PP/POE slow cooled blends work, a 35 MFR hpp was used. Two POEs were used: POE_1 was a g/cc, 1 MI (2.16 kg, 190 C) ethylene/1-octene random copolymer and POE_2 was a g/cc, 0.3 MI (2.16 kg, 190 C) ethylene/1-octene random copolymer, both from The Dow Chemical Company. In all of the studies presented, the PP-OBC resin used had a density of g/cc, melt flow rate of Trademark of The Dow Chemical Company ( Dow ) or an affiliated company of Dow SPE ANTEC Anaheim 2017 / 961

2 6.5 (2.16 kg, 230 C), and DSC melting temperature of about 135 C, which was produced by The Dow Chemical Company. JetFil* 700C talc from IMERYS was used in some blends. Sample Preparation All blends and neat resins were compounded on a Coperion ZSK-25 mm twin screw extruder (TSE) at approximately 200 C and 300 rpm. Neat ICP resins were also processed on the TSE at the same conditions to ensure equivalent mixing and heat history for the neat ICP and ICP/PP-OBC blend samples. Approximately 2000 ppm Irganox** B225 from BASF was added to each blend. All components were added to the main feed throat. The extrudate was cooled in a water bath and pelletized using a strand cutter. All materials were dried overnight with a nitrogen purge. ICP and TPO samples were injection molded on a Krauss-Maffei KM /390 CL injection molding machine equipped with an Axxicon mold base. ASTM D638, Type I tensile bars were molded with an injection barrel temperature of approximately 225 C and a mold temperature of 32 C. For slow cooled samples, pellets were compression molded on a Carver ASTM press at 230 C for about 5 min and slow cooled to room temperature at approximately 5 C/min. Testing The stiffness of the materials was measured either by flexural testing or uniaxial tensile testing. For the slowcooled PP/POE blends, flexural modulus, 1% secant modulus, was measured on specimens cut from compression molded plaques according to ASTM D790 at a test speed of 1.3 mm/min. For ICP and ICP/PP-OBC blends, tensile modulus, 2% secant modulus, was measured on injection molded ASTM D638, Type I tensile bars with a test speed of 50 mm/min. Impact toughness of the samples was assessed using notched Izod impact testing. Specimens were cut from injection molded ASTM D638, Type I tensile bars or were cut from compression molded plaques. Samples were tested according to ASTM D256 at test temperatures ranging from 23 to -40 C. In some cases, the ductile-tobrittle transition temperature (DBTT) was determined by plotting the Izod strength versus temperature and determining the midpoint between the ductile and brittle plateaus (approximately equivalent to 20 kj/m 2 Izod impact strength). Morphology The morphology of the PP/POE blends was assessed using atomic force microscopy (AFM). Specimens were taken from the core of injection molded tensile bars or compression molded plaques. For injection molded samples, specimens were prepared for analysis by cutting 1 cm x 1.5 cm pieces from the linear center of the injection molded tensile bar sample to reveal a view parallel with injection direction. A block face was established at the center of the thickness using a razor blade then cryogenically polished to produce a planarized surface. A Leica UC6/FCS ultramicrotome fitted with diamonds knives was operated at -120 C. A Brüker Dimension ICON AFM was operated in tapping mode for phase detection. A NanoScope V controller was operated with NanoScope v8.15 operating software. Tips used for all scans were Mikro Masch #16 NSC without Al backside coating. Tips had a resonance frequency of ~170 khz and a force constant of ~40-45 N/m. Image post-processing was done using Image Analysis SPIP v Quantitative particle size data was obtained by using Image Metrology SPIP v6.4.1 image analysis software to identify and quantify the discrete particles. Four 20 µm x 20 µm phase images were used to generate data for particle size (dispersed rubber domain size). Image thresholding was manually conducted for each image using the image histogram. To suppress image noise an 80 nm equivalent diameter-based filter cut-off was imposed on all data. To control the effects of image artifacts manual image editing was done as necessary. Average particle size was calculated as an area-weighted average of particle equivalent diameters. Injection Molded ICPs Results and Discussion PP-OBC was blended with a range of ICP resins with melt flow rates ranging from 0.3 to 100 dg/min (2.16 kg, 230 C). These ICP resins represented an array of different ICP manufacturing processes and had a range of EP rubber contents and compositions. As shown in Figure 1, in all but the very lowest and highest MFR ICPs, the addition of 5 wt% PP-OBC to the ICP resins resulted in a significant reduction in the average EP rubber domain size in injection molded parts. Across the 12 ICP resins evaluated the average reduction in EP rubber domain size was 25%, with as high as a 55% reduction in the case of the 28 MFR ICP, which had exceptionally large EP rubber domains in the neat ICP. One example of the morphology change upon addition of the PP-OBC to an ICP resin is shown in Figure 2, where AFM phase images are provided for one of the 50 MFR ICP resins without and with addition of 5 wt% PP-OBC. Rubber domain size SPE ANTEC Anaheim 2017 / 962

histograms are also provided for each image. With addition of the PP-OBC to the ICP, the distribution of EP rubber domain sizes was significantly reduced.

In addition to the effect on morphology, the effect of addition of PP-OBC on the physical properties of the ICP resins was also evaluated.

In all cases, addition of 5 wt% PP-OBC compatibilizer resulted in an increase in the notched Izod impact strength of the materials, consistent with the reduced EP rubber domain size.

Nonetheless, incorporation of the PP-OBC increased the Izod impact strengths of the ICPs by about 1 to 4 kj/m 2.

Though optical properties are not discussed in this paper, the clarity of ICP is expected to improve by better dispersing EP rubber in PP matrix. 50 MRR ICP 50 MFR ICP +5 wt% PP-OBC Figure 2.

3 histograms are also provided for each image. With addition of the PP-OBC to the ICP, the distribution of EP rubber domain sizes was significantly reduced. In particular, EP rubber domains larger than approximately 1.8 µm were practically eliminated. In addition to the effect on morphology, the effect of addition of PP-OBC on the physical properties of the ICP resins was also evaluated. The room temperature Izod strength and tensile modulus for some of the ICP resins are shown in Figure 3. In all cases, addition of 5 wt% PP-OBC compatibilizer resulted in an increase in the notched Izod impact strength of the materials, consistent with the reduced EP rubber domain size. While not an elastomer, the PP-OBC compatibilizer is softer than the PP matrix itself, so addition of 5 wt% of the PP-OBC did result in some decrease of the tensile modulus as well. Nonetheless, incorporation of the PP-OBC increased the Izod impact strengths of the ICPs by about 1 to 4 kj/m 2. Further studies on the addition level of PP-OBC to ICP resins could be conducted to optimize the EP rubber domain size reduction, melt flow characteristics, and stiffness-toughness property balance. Though optical properties are not discussed in this paper, the clarity of ICP is expected to improve by better dispersing EP rubber in PP matrix. 50 MRR ICP 50 MFR ICP +5 wt% PP-OBC Figure 2. AFM phase images and EP rubber domain size histograms for an injection molded 50 MFR ICP without and with addition of 5 wt% PP-OBC. The light, continuous areas in the images are the rigid PP matrix and the darker regions are the softer EP rubber domains. The lighter areas within the EP rubber domains are more rigid ethylene-rich EP inclusions. Figure 1. Average EP rubber domain diameter (areaweighted average) for a range of ICP resins without and with addition of 5 wt% PP-OBC. Figure 3. Izod impact strength at room temperature versus 2% secant tensile modulus for injection molded tensile bars. The solid symbols are data for the neat ICP resins and the unfilled symbols are data for ICP with 5 wt% PP-OBC. SPE ANTEC Anaheim 2017 / 963

Injection Molded TPO Compounds In the second scenario, POE impact modifiers were compounded with either an hpp or ICP with and without talc.

$According to well-established fracture models, such as the Wu model, at a given elastomer volume fraction, impact strength should improve with a reduction in elastomer particle size [6].$ Similar to the case of the injection molded ICP samples, addition of a PP-OBC to TPO compounds resulted in improved dispersion of the POE elastomers in TPO compounds without and with talc, as

Similar to the case of the injection molded ICP samples, addition of a PP-OBC to TPO compounds resulted in improved dispersion of the POE elastomers in TPO compounds without and with talc, as

Addition of talc can also improve dispersion of the elastomer by helping to breakup and disperse the elastomer domains during compounding and by impeding phase coalescence in the polymer melt state.

4 Injection Molded TPO Compounds In the second scenario, POE impact modifiers were compounded with either an hpp or ICP with and without talc. POE impact modifiers are frequently used in TPO compounds in order to achieve low temperature toughness requirements. According to well-established fracture models, such as the Wu model, at a given elastomer volume fraction, impact strength should improve with a reduction in elastomer particle size [6]. Thus, the use of PP-OBC compatibilizers were studied in TPO compounds. Similar to the case of the injection molded ICP samples, addition of a PP-OBC to TPO compounds resulted in improved dispersion of the POE elastomers in TPO compounds without and with talc, as illustrated in Figure 4. Addition of talc can also improve dispersion of the elastomer by helping to breakup and disperse the elastomer domains during compounding and by impeding phase coalescence in the polymer melt state. But, at the 10% talc level shown, there is still further reduction in the POE domain size with addition of PP-OBC compatibilizer. The Izod impact toughness of the injection molded TPO compounds was assessed across a range of talc levels in two different PP/POE systems. As shown in Figure 5, the Izod ductile-to-brittle transition temperature was a function of the talc level in the TPO compounds (formulations provided in Table 1). Talc addition can help to disperse the POE in the TPO compound, resulting in lower DBTT at higher talc levels. In both cases shown in Figure 5, without the use of the PP-OBC compatibilizer, the Izod DBTT decreases significantly when talc is added to the compounds. The PP-OBC compatibilizer was effective at decreasing the elastomer domain size in the TPO compounds even in the absence of talc filler. In both cases shown, addition of a few wt% PP-OBC to the TPO compounds without talc resulted in a dramatic improvement in Izod impact toughness, decreasing DBTT by as much as 25 C. In the first case shown, addition of 10 or 20% talc enabled good dispersion of POE_1, a relatively compatible, moderate molecular weight elastomer, resulting in lower DBTT. Addition of PP-OBC compatibilizer in these talc-filled blends did not further improve Izod impact toughness. On the other hand, when a POE that was more difficult to disperse was used, the PP-OBC compatibilizer was still beneficial at 10 wt% talc level, but not at 20 wt% talc. In this case, POE_2 was significantly higher molecular weight and more difficult to disperse. While not shown here, the stiffness and melt flow rate of the TPO compounds did not change significantly with the addition of wt% PP-OBC compatibilizer. higher molecular weight POEs were used in the TPO blend. Optimization of the PP-OBC level would be required depending on a number of formulation parameters, including elastomer and talc level, elastomer type (i.e. molecular weight and density), PP melt flow rate, and mixing conditions. 65 MFR hpp % POE_1 65 MFR hpp + 35% POE_ % PP-OBC 52 MFR hpp + 36% POE_1 52 MFR hpp + 31% POE_ % talc + 10% talc + 5% PP-OBC Figure 4. AFM phase images of injection molded PP/POE (top) and PP/POE/talc (bottom) blends without and with PP-OBC. The light, continuous areas in the images are the rigid PP matrix and the darker regions are the softer POE elastomer domains. In the bottom images, the bright, platelet-like features are the talc particles, which reside primarily in the hpp matrix. Table 1. TPO Formulations* Component 65 MFR hpp wt% 35 MFR ICP POE_1 + PP-OBC POE_2 + PP-OBC Talc *Corresponding to data shown in Figure 5 The PP-OBC was most beneficial to improving impact properties in either unfilled TPO blends or in cases where more incompatible (i.e. higher density) POEs or SPE ANTEC Anaheim 2017 / 964

Izod ductile-to-brittle transition temperature versus talc level for TPO compounds prepared with different PP/POE combinations: top) 65 MFR hpp and POE_1; and bottom) 35 MFR ICP and POE_2.

5 35 MFR hpp + 35% POE_1 35 MFR hpp + 40% POE_1 + 5% PP-OBC Figure 6. AFM phase images of slow-cooled, compression molded PP/POE blends without and with PP- OBC. The light, continuous areas in the images are the rigid PP matrix and the darker regions are the softer POE elastomer domains. Figure 5. Izod ductile-to-brittle transition temperature versus talc level for TPO compounds prepared with different PP/POE combinations: top) 65 MFR hpp and POE_1; and bottom) 35 MFR ICP and POE_2. Slow Cooled PP/POE Blends Injection molded parts were analyzed in both of the previous examples. In injection molding, the samples underwent high shear during the injection step followed by quench cooling in the mold. This combination helped to preserve the relatively small elastomer dispersed domain size in the PP/elastomer compounds. In other fabrication processes, for example rotational molding, the shear forces are much lower and the cool times can be on the order of min, which can allow significant phase coalescence to occur in immiscible polymer blends. Blends similar to those studied in the unfilled, injection molded TPO case were evaluated using a slow-cooled (~5 C/min) compression molding fabrication method. The morphology of a few slow-cooled PP/POE blends is shown in Figure 6. As compared to the blends shown in Figure 4, the POE level is slightly higher, which contributed to the more continuous elastomer domains. However, considerable phase coalescence also occurred due to the low shear and long time in the melt state, resulting in very large POE domains. Addition of 5 wt% PP-OBC significantly reduced the amount of phase coalescence. As in the injection molding cases, the improved elastomer dispersion with the PP-OBC resulted in significantly improved mechanical properties, as shown in Table 2. In this case, both notched Izod impact strength and stiffness were improved with the addition of PP-OBC. The improvement in this case was quite significant as compared to the improvements observed in the injection molded blends. Table 2. Properties of PP/POE Blends after Compression Molding (Cooling Rate ~ 5 C/min) Property PP/POE (60/40 wt%) PP/POE/PP- OBC (60/35/5 wt%) Flexural Modulus, 1% secant, kpsi Notched Izod Impact Strength, kj/m 2 23 C C C Conclusions PP-OBCs are effective at reducing the domain size of ethylene/α-olefin elastomers dispersed in a polypropylene matrix. Significant domain size reductions were observed in a variety of blend systems, including injection molded impact copolymer polypropylene resins that contain EP rubber domains, injection molded TPO compounds that contain PP, polyolefin elastomers, and talc, and in slowcooled compression molded PP/polyolefin elastomer blends. The elastomer domain size reduction resulted in improved toughness, particularly Izod impact toughness. References 1. K. Swogger, E. Carnahan, W. Hoenig, A. Frencham, "The Development of a New Generation of Novel High Performance Olefin," Proceedings of SPE ANTEC, H. Wang, A. Hiltner, E. Baer, A. Taha, S. Chum, "Comparison of Block and Random Ethylene-Octene Copolymers based on the Structure and Elastomeric Properties," Proceedings of SPE ANTEC, SPE ANTEC Anaheim 2017 / 965

6 3. G. Marchand, K. Walton, Y. Hu, C. Li Pi Shan, R. Barry, E. Carnahan, E. Garcia-Meitin, "Polypropylene Based Olefin Block Copolymers as Compatibilizers for Polyethylene and Polypropylene," Presentation at Polyolefins Conference, Y. Hu, J. Bonekamp, E. Garcia-Meitin, G. Marchand, K. Walton, R. Patel, " Polypropylene Based Olefin Block Copolymers as Tie Layers for Multilayer Packaging," Proceedings of SPE ANTEC, Y. Hu, G. Marchand, R. Patel, M. VanSumeren, E. Garcia-Meitin, S. Baker, F. Camacho-Hadad, X.B. Yun, "High Performance PP/PE Multilayer Films Enabled by PP Based OBC," Proceedings of SPE ANTEC, Wu, S. Phase Structure and Adhesion in Polymer Blends: A Criterion for Rubber Toughening, Polymer 1985, 26, SPE ANTEC Anaheim 2017 / 966

Polypropylene Based Olefin Block Copolymers for Clear Cold Tough Application

Polypropylene Based Olefin Block Copolymers for Clear Cold Tough Application Jihean Lee, Colin Li Pi Shan, Ray Laakso, Lisa Madenjian, Eddy Garcia-Meitin, Michael White The Dow Chemical Company, Freeport,