Utilizing the Polymorphism of Isotactic PP Homo

Crystallinity-Based Product Design: Utilizing the Polymorphism of Isotactic PP Homo- and Copolymers Markus Gahleitner1, a), Daniela Mileva1, René Androsch2, Dietrich Gloger1, Davide Tranchida1, Martina Sandholzer1 and Petar Doshev1 1 2

Borealis Polyolefine GmbH, Innovation Headquarters, St. Peterstr. 25, 4021 Linz, Austria.

Martin-Luther-University Halle-Wittenberg, Institute for Polymeric Materials, Eberhard-Leibnitz-Str. 2, 06217 Merseburg, Germany. a)

Corresponding author: [email protected]

Abstract. The polymorphism of isotactic polypropylene (iPP) in combination with the strong response of this polymer to nucleation can be utilized for expanding the application range of this versatile polymer. Based on three “case studies” related to β-iPP pressure pipes, ethylene-propylene (EP) random copolymers for thin-wall injection molding and transparency and sterilization resistance of cast films we demonstrate ways of combining polymer composition, nucleation and process settings to achieve the desired application performance. The importance of considering interactions between polymer design, nucleation and processing parameters for designing application properties is highlighted.

INTRODUCTION Isotactic polypropylene (iPP) has experienced a massive volume growth since its introduction in the mid-1950s and is nowadays present in an extremely wide range of applications. One of the essential reasons for this development is the flexibility of this polymer in terms of property design and processability. Together with the availability of an initially cheap monomer, this resulted in a rapid growth of the production volume from less than 100*103 t/a in 1960 to more than 53*106 t/a in 2012, making it the most produced single thermoplastic material (Gahleitner & Paulik 2014). The polymorphism of iPP, i.e. its capability to solidify in so far five documented crystal modifications from α to ε (Brückner et al. 1991, De Rosa et al. 2011, Lotz 2014) and in a mesomorphic state (Androsch et al. 2010) is one key element of this flexibility. Varying mechanical and optical performance of singlephase iPP materials is possible for homopolymers by modifying the degree of isotacticity (Paukkeri & Lehtinen

1993), and further by copolymerization with ethylene (Gahleitner et al. 2005) as well as with higher α-olefins like butene (De Rosa et al. 2011), pentene or hexene (Boragno et al. 2013). Next to the comonomer amount, variations of catalyst type (Vestberg et al. 2012) and sequential polymerization resulting in multimodality both in terms of molecular weight distribution (MWD) and comonomer content distribution (CCD) is applied for designing specific materials. This way, lower stiffness in combination with better transparency and improved toughness can be achieved as verified by numerous patents and publications in this field (see e.g. Grein & Schedenig 2007, Potter et al. 2011). The target applications for these materials cover a wide range from cast and blown films and various fibers over injection-molded packaging articles to pressure pipes.

Further modification of the performance of iPP homo- and copolymers can be done by nucleation (Gahleitner et al. 2011). In case of α-nucleation (which can also promote the γ-modification (Foresta et al. 2001) as will be also shown in the present paper), the target of applying the nucleating agent may vary from stiffness increase (Fiorentino et al. 2013) and transparency improvement (Menyhard et al. 2009) to increasing processing speed, meaning higher line speed in continuous conversion processes resp. lower cycle time in discontinuous ones. The common cause for these latter described improvements is an increase in nucleation density and in crystallization temperature, causing thicker lamellae but smaller crystalline superstructures like spherulites (Pukánszky et al. 1997). It should be noted here already that a positive interaction can also be found between flow-induced crystallization and nucleation (Ma et al. 2011), even if different types of nucleating agents – especially soluble vs. particulate systems – will affect the morphology and properties quite differently. In contrast to α-nucleation, specific β-nucleation changes the mechanical performance of iPP towards higher toughness at reduced stiffness and heat resistance (Grein 2005). The crystal morphology is clearly decisive for this different mechanical behavior, with the α-form being stiffer due to its cross-hatched crystalline structure, while βiPP has a “sheaf-like” structure formed by piles of lamellae connected by “tie chains” which gives more ductility to the material. Even if various reasons have been given over time for the higher toughness of β-iPP (Karger-Kocsis 1996, Policianová et al. 2015), its practical relevance as well as its long-term stability is well proven.

The third and frequently decisive factor is the processing history defining the actual crystallinity and crystal superstructure in the final part. Roughly speaking this step is defined by the cooling rate and the deformation rate during processing, even if interactions between both can be decisive and the part geometry needs to be considered as well. Both factors have been studied frequently in recent years, even if mostly for one iPP type only. Studies concerning a variation of cooling rate and polymer composition (Konishi et al. 2005, Housmans et al. 2009a, Cavallo et al. 2010) are rather the exception, but exactly those deliver more insight into the possible interaction between chain structure and processing effects. The same holds for studies relating molecular weight (distribution) effects to flow-induced crystallization phenomena, and especially to the formation of oriented structures like shishkebab crystallites (Phillips et al. 1994, Housmans et al. 2009a). In the end it is also necessary to consider processing effects on polymorphism (van Drongelen et al. 2012) and the interaction between flow-induced crystallization and

nucleating agents (Gahleitner et al. 2002a, Ma et al. 2011), in order to finally being able to simulate industrial materials and processing conditions.

Still unable to give a full account of this complex situation, we will rather present three “case studies” in the present paper, each of these dedicated to one crystal modification of iPP and a specific application case. It will be shown that the interaction between polymer structure, nucleation and processing conditions defines the final performance in all three cases.

THREE CASE STUDIES FOR POLYMER – NUCLEATION – PROCESSING INTERACTION Impact Strength of β-iPP Homo- and Copolymer Pipes High and medium density polyethylene (HDPE/MDPE), the dominant material class for polyolefin pressure pipes, is limited in its thermal resistance and thus operating temperature by the rather low melting point (135°C for HDPE). For hot water, heating and industrial process applications iPP pipes, especially those from random ethylenepropylene (EP) copolymers, are applied frequently. The fact that both impact strength and pressure resistance of these pipe materials are improved by β-nucleation has generated significant research activities in this area (Gedde et al. 1994, Ebner et al. 2002, Grein 2005). The application is facilitated by the fact that the impact improvement and the related shift in the brittle-to-ductile transition temperature are highest for high molecular weight grades typically in use for pipe extrusion (see Figure 1).

A number of critical issues exist, however, for this application. Firstly, it is important to select an efficient nucleating agent for the β-modification (Varga 2002).Next to the well-known γ-quinacridone (Lustiger 1995), calcium salts of aliphatic dicarboxylic acids (Li et al. 2001) have been found to be most effective, while other substances like N,N‘-Dicyclohexyl-2,6-naphthalenedicarboxamide (NJS) present problems due to a dual nucleation capability for both the β- and the α-modification (Varga & Menyhard 2007).

Furtheron, the questions of iPP chain structure and polymer purity effects on the polymorphism, particularly the balance between α- and β-phase formation have been studied. The fact that EP random copolymers with their highly disturbed chain structure are more difficult to β-nucleate was already documented by Varga (2002), while similar homogeneous copolymers with higher α-olefins do not suffer from this limitation (Ebner et al. 2002). Stereodefects are known to affect crystallization of iPP homopolymers in a similar way as comonomer units (Gahleitner et al. 1999), and a certain effect of isotacticity variation on the expression of the β-modification was found in an internal study related to the formation of this polymorph at high processing temperatures but in absence of a nucleating agent was therefore hardly surprising. An earlier study by Kim (2005), in which however homopolymers and random

copolymers had been studied based on xylene cold solubles (XCS) content as a measure for chain irregularity, gave similar results.

Much stronger was, however, the effect of catalyst residues and solid additives as expressed by the total ash content. In order to cover a wide range of ash content, mostly polymer samples from an MgCl2 supported ZieglerNatta (ZN) catalyst produced in pilot or commercial scale polymerisation plants were analysed in as-polymerised granular state, prior to the addition of additives. Testing was done in differential scanning calorimetry (DSC) in the range of 1-100 K min-1. As Figure 2 shows, even at standard DSC cooling at 10 K min-1 a high content of βmodification can be achieved with highly isotactic iPP homopolymers of very low ash content. This is in line with the results of other groups who have found non-specific inhomogeneities, i.e. ash and additive particles, to promote α- or γ-phase formation depending on pressure (Zapala et al. 2012). Competition effects between β- and αnucleation are also known from the combination of β-nucleating agents with talc (Gahleitner et al. 2012), where the β-phase content is reduced from 93% to 0% when replacing calcium carbonate by talc as filler combined with Capimelate as nucleant.

As indicated above, processing conditions play a further role in the final expression of crystal modifications. Quite obviously the crystallization rate of the different crystal modifications not only depends on temperature (Lotz 1998, Housmans et al. 2009b) but also on cooling rate, and here the available data in the literature are still rather incomplete. For the β-modification we studied the effect of chain structure and cooling rate several years ago (Nestelberger et al. 2008) in order to optimize processing conditions for pipe extrusion. Figure 3 shows both the similarity and the significant difference in cooling rate dependence between two identically β-nucleated iPP grades, a homopolymer and a random copolymer with ~ 4 wt% ethylene. A cooling rate of 50 °C/min is sufficient to almost fully suppress the β-growth and favor the development of α-phase in the homopolymer, since the nucleating agent is effective only below such cooling speed (Mollova et al.. 2013). For the EP-random copolymer the situation is even less favorable, and at around 20 °C/min the amount of beta phase becomes negligible. Compared to that, the difference in the “quenching rate” defining the transition to the mesomorphic phase is small (more detailed data for the latter were collected by Cavallo 2010).

Together with extensive numerical simulations these results could be used for optimizing the pipe extrusion process. In case of well-selected processing conditions, an excellent combination of short- and long-term properties can be achieved for β-nucleated EP-random copolymers designated PP-RCT in the respective standards for pressure pipes (ISO 2013). As Figure 4 shows, the shift in brittle-to-ductile transition temperature for both base polymers is 20-25°C for a β-phase content of ~ 85% in both materials achieved by proper processing.

Transparency and Impact Strength Effects in Random Copolymer Nucleation The structural similarity to the α-phase makes a specific nucleation of the γ-phase impossible (Foresta et al. 2001), and generally no specific advantages have been quoted so far for this modification in the literature. The focus of research regarding γ-iPP was mostly on high pressure during crystallization (Kressler 1998, Zapala et al. 2012, Zhang et al. 2015) and iPP grades with an increased content of stereodefects and comonomer (Busse et al. 2000, Gou et al. 2008, Selikhova et al. 2015). Both factors increase the content of γ-phase significantly, but none of the studies considers optical and/or mechanical consequences of this. Extensive studies related to α/γ-nucleation effects in EP-random copolymers, especially when used for blow molding and thin-wall injection molding, allowed us to find some interesting correlations. In the property triangle of stiffness (modulus), toughness (impact strength) and transparency (haze) one would normally assume increasing comonomer content to reduce the former one and increase the latter two (Gahleitner et al. 2005), but nucleation can affect that significantly.

In a first study based on four different EP random copolymers and an organophosphate-type particulate nucleating agent (Sandholzer et al. 2012), it could be shown that the relative content of γ-modification can be significantly increased with this type of nucleating agent. While toughness improvement appeared to be limited to high molecular weights (similar to β-nucleation), transparency was found to positively correlate with the γ-phase content in all cases. As Figure 5 demonstrates, haze values as low as 15% can be achieved at γ-phase contents of nearly 80% with the proper combination of base polymer and nucleation. Processing effects need to be considered however, as higher cooling rates clearly suppress the γ-phase formation (Gou et al. 2008).

A more recent collaboration with the group of Prof. Pukánszky at TU Budapest, Hungary, (Horváth et al. 2014 & 2015) involved five EP random copolymers nucleated with two soluble nucleating agents. The ethylene content ranged between 1.7 and 5.3 wt%, while the nucleating agent content was adjusted according to the solubility of the additive. It varied from 0 to 5000 ppm for the sorbitol (1,2,3-tridesoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]nonitol) (Millad NX 8000, CAS No. 882073-43-0) and from 0 to 500 ppm for the trisamide compound (1,3,5benzene-trisamide) (Irgaclear XT386, CAS No. 745070-61-5). The main structural parameters of the five polymers are listed in Table 1. Starting from an earlier study on processing effects with a “standard” sorbitol-type nucleating agent (Millad 3988, 1,3:2,4-Bis(3,4-dimethylbenzylidene)sorbitol, CAS No. 135861-56-2) where problems with injection speed and melt temperature effects had been found, an additional focus of the present work was on flowinduced morphology development in injection moulding.

Only selected results from this study which delivered extensive insight into the interaction between polymer structure and nucleating agent and also resulted in patent applications (Doshev 2011) shall be highlighted here. Stiffness effects were found to be largely independent of the base polymer type, achieving linear correlations

between crystallization temperature and yield stress as experienced before (Pukánszky et al. 1997). Transparency effects were similar to the first study (Sandholzer et al. 2012).

In contrast to that, the nucleation effect on impact resistance is completely different as shown in Figure 6, effectively also changing the important stiffness-toughness balance. At least for the two polymers with the largest ethylene content (R42 and R53) nucleation results in a significant increase in impact strength. The effect is ~ 200 % for the higher and ~100 % for the lower molecular weight. Impact strength reaches a maximum in a medium concentration range, followed by a slight decrease with further increasing concentration. This is necessarily initiated by changes in crystalline structure, but cannot be directly related to crystallinity or lamellar thickness. Changes in crystalline morphology by nucleation, possibly also related to processing effects, must have induced the profound modification of molecular mobility or phase structure (Salazar et al. 2003).

Fracture mechanics investigations by instrumented impact tests indicated that the molecular weight effect for R42 was clearly related to an increase in crack initiation energy, but the basic effect remained unclear. A look at crystal modification distribution and morphology gave however some indications: At first, both types with higher ethylene content (R53 and R42) showed an increase of the γ-phase content up to ~ 50% in both skin and core parts of the specimens as a result of nucleation (see Figure 7). A closer look at the crystal morphology by scanning electron microscopy (SEM), for which the specimens were cryo-cut and etched with potassium permanganate to reveal the lamellar structure, further showed a massive presence of shish-kebab structures also in the core for the compositions with highest impact strength (see Figure 8). The coincidence of increased shish-kebab formation and γ-phase content is remarkable and has a striking parallel in the work or Roozemond et al.. (2014). In combination, these changes obviously increase crack propagation energy considerably leading to the observed large improvement in impact resistance.

Cast Film Properties and Sterilization Resistance In recent years more attention than earlier has been paid to the mesomorphic phase of iPP, not the least because better calorimetric techniques and instruments had become available, enabling studies at high cooling rate (Piccarolo 1992, Androsch et al. 2010, Cavallo et al. 2010, Mileva et al. 2012, Mollova et al. 2013). In addition to the scientific interest sparked by the availability of novel differential scanning calorimetry (DSC) equipment enabling cooling rates up to 3.000 K/s, the mesomorphic phase also plays an important role in industrial conversion processes for iPP materials. Typical examples involve cast-film extrusion (Hsu et al. 1986, Lamberti & Brucato 2003, Xu et al. 2014), metal or paper coating, fibre spinning (Nadella et al. 1997) and cable insulation. In all these cases, the presence of this phase can be either positive, e.g. for transparency and toughness in case of films, or negative in terms of long-term stability and post-crystallization.

Especially when targeting packaging films for food and medical articles, sterilization resistance is a key factor next to the initial performance of the films. As steam sterilization is predominantly applied, this means a stability towards post-crystallization at temperatures above 120°C which is certainly a safe temperature range for iPP homopolymers but potentially critical for EP random copolymers (Gahleitner et al. 2002b). In an extensive study performed some years ago (Gahleitner et al. 2011b) we checked the effect of comonomer content and distribution (randomness) on the primary performance and sterilization resistance of cast films from EP random copolymers. DSC on as-cast respectively as-sterilized films with an – admittedly difficult – evaluation of the 1st heat was used mainly (as also shown by Caldas et al. 1994), supplemented by WAXD and transmission electron microscopy (TEM) in some cases.

Cast films having 50 µm thickness and produced with a chill roll temperature of 15°C for two series of polymers, A and B both ranging from 0 to 5.2 wt% in ethylene content but produced with two ZN-type catalysts giving different randomness (Grein & Schedenig 2007) were studied. Post-crystallization during the steam sterilization step (121°C / 30 min) increased significantly with increasing ethylene content, but rather by the formation of a secondary crystal structure than by lamellar thickening.

Figure 9 shows the massive effect of comonomer content melting point which is rather comparable for series A and B, but also the striking difference in the optical changes during sterilization. The haze increase from this annealing process remains rather constant up to an ethylene content of about 2,5 wt% and then rises significantly for the polymers based on the conventional catalyst (B) while staying at a lower level (< 100%) for the products with better randomness (A). The high numbers of up to ~ 650% for the relative haze change should be considered together with the absolute values ; only for the materials showing the strongest haze increase the film loses its transparency visibly with an absolute haze value of > 15%. No acceptable correlation between crystallinity change in sterilization which was found to be rather identical for both series and the haze effect could be found, and only a look at the crystallinity distribution between primary and secondary melting peak gave some explanation. In case of series B, the secondary melting peak in DSC at a temperature of 10°C above the sterilization temperature is far more dominant and indicates a “bimodal” crystallinity distribution in the films which can certainly cause more local differences in refractive index and an increased haze (see Figure 10).

In this study the effect of processing conditions was mostly studied for nucleated materials, finding a reduced effect of chill roll temperature (i.e. the effective cooling rate) on crystallinity and haze especially for a particulate nucleating agent (NA-21 as discussed above). Although this approach may seem to be more complicated than just adapting the processing conditions, particularly the chill roll temperature, it was found to be the only way to achieve stability at elevated temperatures as reflected by a low haze even after steam sterilization.

The interaction between comonomer content and processing conditions had not been considered sufficiently, and so we decided to perform an extensive study on this, including the possible consequences on the formation of

biaxially oriented (BOPP) films (Lüpke et al. 2004). Cast films of 50 and 200 µm thickness have been produced from iPP homopolymers of different isotacticity as well as EP random copolymers, using 6 variations of melt temperature, chill roll temperature and line speed / output in both series. Parallel to that, fast scanning calorimetry (FSC) has been performed to relate the films to an average cooling rate in the process. Figure 11 gives a first impression of chill roll temperature effects on film crystallinity (WAXD) for an iPP homopolymer on 200 µm films.

In case of the 50 µm films, the quenching effect is even stronger. Similar effects in terms of mechanical and optical properties were found for the tested homopolymer and random copolymer as shown in Figure 12. The crystallinity effect on tensile modulus is strong but rather comparable for both polymer grades which were selected to have the same MFR and MWD (for details see Gahleitner et al. 2005), the difference being ~ 200 MPa between both series. Effects of the output resp. line speed are small here, but not in case of the film transparency (haze & clarity). At constant chill roll temperature, an increase in output by a factor of 2 results in a haze reduction of ~50%. The reasons for this effect are now being checked further by surface investigations with atomic force microscopy (AFM). Especially one needs to consider that the total haze depends on the surface roughness and bulk superstructure of the film as shown by Resch et al. (2006).

These AFM investigations yielded some interesting results in terms of chill roll temperature effect. In Figure 13 two examples for the surface structures of 50 µm films based on PP homopolymer (HD234CF) are presented, representing the low (15°C) and high chill roll temperature (70°C) versions of the low output rate (60 kg/h). While the higher chill roll temperature (i.e. the lower cooling rate) induces a “spherulitic” surface structure, only rows of small crystalline structures (next to some isolated ones), always arranged in machine (flow) direction, are found at higher cooling rate (lower chill roll temperature). These structures are obviously identical to the ones found in a previous study (Resch et al. 2006) where they were termed “8-shaped superlamellar crystalline structures”. The now available better SFM resolution clearly shows that these are surface imprints of spherulites arranged along row nuclei as postulated e.g. by Lamberti & Brucato (2003). Nodular shaped domains are seen in the vicinity of the ordered rows of crystalline structures, in accordance with the WAXS data showing presence of mesomorphic phase with small inclusions of alpha-crystals of films quenched at 15°C. Further work will still be required in order to check the effect of annealing steps on these structures and the related optical performance.

CONCLUSIONS AND OUTLOOK The polymorphism of iPP is increasingly seen as an opportunity to expand the application range of this versatile polymer. In our paper we demonstrated different ways of combining polymer design, nucleating agents and processing pathways to utilize polymorphism for fulfilling specific application requirements. Several quite diverse applications like hot-water pressure pipes, cast and biaxially oriented (BOPP) film and sterilisable medical packaging all can benefit from this crystallinity based design. Basic research on iPP crystallization is elementary for

achieving the target, as a thorough understanding is required to find suitable combinations of polymer composition, nucleation and process settings. These three factors can and will interact with each other in defining the final application properties. This makes attempts to vary just one performance factor (like haze), while keeping all others (like stiffness and toughness) constant, a rather complex task.

In a new systematic study focussing on iPP cast films and BOPP films derived therefrom we tried to expand the knowledge in this area. In this case a combination of data from standard DSC and fast scanning chip calorimetry (FSC) with results from a laboratory-scale cast-film processing line the possibility to affect the formation of the mesomorphic phase was studied. Modifying iPP crystallinity by copolymerization can clearly be combined with a selection of suitable processing parameters to achieve the desired product performance.

ACKNOWLEDGMENTS Many people have contributed to a bigger or lesser extent to this overview. The authors would especially like to thank Bernard Lotz (CNRS Strasbourg, FR) for his outstanding contributions to understanding nucleation and polymorphism, Christelle Grein (SABIC, Geleen, NL) for her extensive work on the β-modification (see Grein 2005), Gerrit Peters and his team (TU Eindhoven, NL) for many years of inspiring discussions on flow-induced crystallization, and Béla Pukánszky and his team (TU Budapest, HU) for the excellent collaboration on polymer – nucleation interaction.

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FIGURES

FIGURE 1. Double notched impact strengths of β-nucleated and non-nucleated grades in between melt flow rates, MFR, of 0.3 to 40 dg.min-1 at room (a, +23°C) and low (b, -20°C) temperature; adapted from Grein (2005); iPP homopolymer nucleated with Ca-pimelate, injection molded specimens, test speed 3.8 m s-1.

FIGURE 2. Effect of ash content on formation of the β-modification in non-nucleated highly isotactic iPP homopolymer as crystallized in a standard DSC experiment (cooling rate 10 K min-1, evaluation by wide-angle Xray diffraction).

FIGURE 3. α- and β-phase content for an iPP homopolymer (PP-H, left) and an EP-random copolymer (PP-R, right) crystallized in a wide range of cooling rates.

FIGURE 4. Shift of the brittle-to-ductile transition temperature by β-nucleation for an iPP homopolymer (PP-H) and an EP-random copolymer (PP-R); injection-molded specimens tested in Charpy notched impact test.

FIGURE 5. Correlation between γ-phase content and haze on injection-molded plaques for four EP random copolymers nucleated with Adekastab NA-21 (organophosphate, CAS No. 20336-96-3); ethylene content 3.6-5.7 wt%, MFR (230°C/2.16kg) 0.3-12 g/10min.

FIGURE 6. Effect of nucleation on the impact resistance of EP random copolymers; Left: Concentration effect for sorbitol type (NX 8000; symbols: (□) R53, (▲) R42, (◊) R27, (∆) R21, (●) R17); Right: Stiffness / toughness balance of nucleated EP random copolymers.

Intensity (a.u.)

c) b) a) 10

15

20

25

30

Angle of reflection, 2q° FIGURE 7. Increase in the amount of the γ-modification of PP upon nucleation for the R42 copolymer (core of specimen); wide-angle X-ray diffraction (WAXD) curves for a) neat polymer, b) 2000 ppm, c) 4000 ppm sorbitoltype nucleating agent (NX 8000).

FIGURE 8. Crystal morphology effects of PP nucleation for the R42 copolymer (specimen core, SEM images after KMnO4 etching); Left - neat polymer (curve (a) in Figure 7), Right - 4000 ppm sorbitol-type nucl.agt. (NX 8000; curve (c) in Figure 7).

FIGURE 9. Changes in melting temperature and haze change (cast film, 50 µm) in sterilization at 121°C depending on the ethylene content for polymers from series A (high randomness, open symbols) and B (limited randomness, filled symbols); adapted from (Gahleitner et al. 2011b).

FIGURE 10. Partial melting enthalpy for primary (Tm depending on C2 content) and secondary (Tm constant) melting peak for the sterilized cast films from series B; adapted from (Gahleitner et al. 2011b).

FIGURE 11. Effect of chill roll temperature at constant output (90 kg/h), line speed (12 m/min) and melt temperature (270°C) on crystallinity of iPP cast films of 200 µm thickness (note: a certain amount of β-phase is found for higher chill roll temperatures).

FIGURE 12. Effect of chill roll temperature and extruder output at constant melt temperature (230°C) on crystallinity, mechanics (left) and optics (right) of iPP cast films of 50 µm thickness; stars relate to PP homopolymer (HD234CF, MFR 8 g/10min) and circles to EP random copolymer (RD208CF, MFR 8 g/10min, 4.9 wt% C2), materials as in Gahleitner et al. (2005).

FIGURE 13. Effect of chill roll temperature – left 15°C and right 70°C – at constant extruder output (60 kg/h) and melt temperature (230°C) on surface structure of iPP cast films of 50 µm thickness (PP homopolymer, HD234CF, MFR 8 g/10min, machine direction vertical).

TABLES

TABLE 1. Main molecular characteristics of the EP random polymers used in the nucleation study (all polymers based on Ziegler-Natta type catalyst; see Horváth et al 2015 for details). Ethylene cont.

Molecular weight

[wt%]

Mw [kg/mol]

R17

1.7

R21

Polydispersity

MFR (230°C/

[Mw/Mn]

2.16kg) [g/10min]

211

2.7

8.0

2.1

217

5.4

14.0

R27

2.7

195

4.5

15.0

R42

4.2

317

3.7

1.5

R53

5.3

195

3.2

12.0

Polymer