abstract - · pdf filea separate 5% crodamide er erucamide masterbatch was used to vary the...

SURFACE STRUCTURAL CHARACTERIZATION OF ANTIBLOCK FILMS CONTAINING ERUCAMIDE Authors: John W. Catino, Specialty Minerals Inc.

Donald R. Deutsch, Specialty Minerals Inc. John L. Gardiner, Specialty Minerals Inc.

9th European PLACE Conference May 12-14, 2003, Rome, Italy ABSTRACT Antiblocking efficiency of mineral additives in Polyethylene film has long been associated to the performance of the particles relative to their size, distribution, placement in the film, and optical performance. The effectiveness of the antiblock is directly related to the roughness they impart on the film while minimizing loss in optical properties. New hybrid clarity antiblocks provide the necessary roughness and optical quality required in today’s high clarity films when compared to alternative synthetic and natural silica. Erucamide is added to improve film slip. Erucamide does not act as an organic antiblock, but works in harmony with antiblocks especially talc, as it aids in the migration process to the surface. Because of the high surface area and pore volume with synthetic silica, amides work less efficiently in this combination. Polyethylene films containing antiblock mineral additives and 1000 ppm erucamide were characterized with the Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), and Scanning White Light Interference Microscope (SWLIM). The AFM and SWLIM provide quantitative surface topography data that is used to compare the roughness and surface morphology among LLDPE films containing several types of mineral antiblocks. AFM phase yields information about the film chemical differences supported by surface analysis. INTRODUCTION Polyolefin films are generally tacky and possess a high coefficient of friction, properties that are not desired for processing and handling of blown films. Mineral and organic additives are incorporated as an effective method to control blocking and slip. Mineral additives increase the film’s roughness and reduce the tendency to block. Fatty acid amides are added to modify slip of polyoelfin films [1,2]. The level of slip and antiblock addition is a balance between desired blocking, friction and optical properties. Common antiblock mineral fillers are amorphous or synthetic silica, diatomaceous earth, and talc. Associated with these three basic antiblock mineral types is a fourth category, or Hybrid Clarity Antiblock additives, such as zeolites and specialty processed mineral blends. Figure 1 shows SEM micrographs of synthetic silica, diatomaceous earth and Hybrid Clarity Antiblock “A”. The tendency to block is significantly reduced as the level of inorganic mineral filler is increased. However, increased loading levels of mineral antiblock will have negative effects on optical properties such as haze and clarity. Highly efficient antiblocks, however, will have the least negative impact on the intrinsic optical properties of the film. Optical properties were related to AFM surface roughness measurements of unfilled [3] and mineral filled [4] polyoelfin film. Fatty acid amides are functional organic additives used to reduce the frictional properties of film by migrating to the film surface [1,2,5]. Common amides such as oleamide and erucamide work in harmony with antiblocks especially talc, as it aids in the migration process [1]. Because synthetic silica has high surface area and pore volume, amides work less efficiently in this combination believed associated with additive absorption by silica [1]. The objective of this study is to study physical and optical properties of polyolefin films containing antiblock minerals and erucamide. Previous investigations used AFM to study optical properties of unfilled films [3] and AFM to visualize slip migration to the surface [5]. Through AFM and other surface characterization tools, we will attempt to establish a topographic and chemical “map” that distinguishes surface structure between films with different additives.

The antiblock minerals and slip additive used in this study are commercially available and are designed for polyethylene film applications. LLDPE film formulations were designed as a comparison of the Hybrid Clarity Antiblock “A” at loading levels equal to and greater than the loading level of synthetic silica. This paper summarizes surface structural properties of the system typically used in blow films: LLDPE, mineral additive for antiblock and erucamide for friction control. EXPERIMENTAL Materials OPTIBLOC 10 clarity antiblock is a grade of commercially available antiblocks, produced by Specialty Minerals Inc., a division of Minerals Technologies Inc. They are designed to provide the optimum in antiblock efficiency along with the added benefits of maximum clarity. Referred to as a Hybrid Clarity Antiblock “A” for this paper, it has the added benefit of minimal additive interaction and improved dispersibility. The comparative antiblock tested in this paper is referred to as Synthetic Silica. The synthetic silica used in this study was W. R. Grace’s SYLOBLOC® 45. The slip additive is a conventional grade of erucamide, Crodamide ER produced by Croda Universal, added at 1000 ppm. The polyethylene resin is a 1.0 MI Butene copolymer LLDPE (0.918 density). Extrusion Conditions All formulations are laboratory prepared masterbatch at 20% concentration except for the commercially available 5% concentration masterbatch for synthetic silica. A separate 5% Crodamide ER erucamide masterbatch was used to vary the slip loading. The compounding is completed on a Leistritz counter-rotating twin screw extruder with 34mm screws and a L/D ratio of 30:1. Final die temperature during extrusion was 215°C. Blown Film The final films are prepared on a Killion blown film line consisting of a Killion extruder with a L/D ratio of 30:1 and a multi-stage temperature profile from 177°C to 204°C at the die. The blown film die diameter is 2½ inches with a .035 inch die gap. Output is 15 pounds per hour with a lay-flat of 8 inches. The final thickness for all films is 0.001 inches (1.0 mil). Test Methods – Film Performance The induced reblock data reported here follows the parallel plate method of ASTM D3354 to determine the degree of blocking. In preparing the samples, 4” X 8” pieces are cut from the lay-flat tubing. The double film layer is separated, passed slowly over a grounded bar to remove static charges, and then reunited so that the inside surfaces of the original bubble is in direct contact with each other. All films are first conditioned under a top load of 1.0 psi for 24 hours using a recirculating forced air oven set at 40°C or 60°C before being measured for induced reblock force (in grams). Slip performance, as measured by static coefficient of friction (COF), follows the test procedure of ASTM D 1984. Haze and clarity are measured according to ASTM D1003 test method, and gloss is measured using ASTM D2457. Surface Structure Characterization Atomic Force Microscopy (AFM) TappingMode™ images collected with a Digital Instrument Dimension 3000 AFM. TappingMode™ collects two simultaneous images for the Height and Phase. The Height is the Z-direction displacement and the Phase yields contrast based on dissipation of energy (modulus) during tip-sample contact [6] and should not be confused with actual material phase images. Differences in adhesive or mechanical properties of different components in a heterogeneous sample, such as crystallinity or material, may affect the energy dissipation . Scan lengths of 10µm, 20µm and 80µm are acquired on films attached to steel planchetes with double-sided tape. Films separated immediately before imaging to expose a fresh surface. Five areas are scanned at 10µm, four areas at 20µm and one area at 80µm. Average roughness values calculated with manufacturer software. Typical images of “average” samples are included in this paper. Scanning White Light Interference Microscopy (SWLIM) images collected on films at five areas with at 25X equivalent to a 250 µm scan length. Films attached to a glass slide and separated prior to imaging.

RESULTS AND DISCUSSION Film Performance Evaluations Performance comparison of synthetic silica versus the Hybrid Clarity Antiblock “A” are summarized in Tables I and II. The Hybrid Clarity Antiblock “A” shows equal optical properties as Synthetic Silica, even at a higher loading level of 3000 ppm. Hybrid Clarity Antiblock “A” yields better blocking at 23°C compared to Synthetic Silica and equivalent reblock at 60°C. At 60°C the polymer physical properties control reblock with negligible contribution of mineral additive. Synthetic Silica and Hybrid Clarity Antiblock “A” at 3000 ppm yield similar reblock at 40°C. A possible explanation of the significant reduction of reblock at 40°C for Synthetic Silica is increased surface migration of erucamide at elevated temperature that may help inhibit blocking. Such migration is not as important with Hybrid Clarity Antiblock “A” films since migration appears to occur at ambient temperature.

Table I Optical Properties

Antiblock ppm Haze Clarity 45° Gloss Synthetic Silica 2000 6.3 95.4 76 Hybrid Clarity Antiblock “A” 2000 5.2 97.0 77 Hybrid Clarity Antiblock “A” 3000 6.0 95.9 76

Table II

Blocking Properties Antiblock ppm Blocking (g)

23°C Reblock (g)

40°C Reblock (g)

60°C COF

Synthetic Silica 2000 121 55 140 0.31 Hybrid Clarity Antiblock “A” 2000 86 86 139 0.19 Hybrid Clarity Antiblock “A” 3000 86 61 140 0.16

The Hybrid Clarity Antiblock “A” gives lower Coefficient of Friction at both antiblock-loading levels. The lower COF is consistent with silica absorption of slip additive due to its pore and high surface area whereas talc type additives work synergistically with slip additives. Surface Structural Characterization SEM micrographs of film surface are shown in Figure 2. Clearly, surface roughness increases as mineral is added. AFM and SWLIM techniques are used to measure roughness. Figures 3-6 show 10 µm scan Z Height (left) and Phase (right) images. Phase images show LLDPE lamellae structure along with localized regions of antibloc filler or erucamide if present on the surface. Figure 7 is composite image of height projection to illustrate representative surface roughness. Average roughness measurements of 10 µm scans suggest no significant differences among films (Table III). Barefoot values are consistent with literature values reported for unfilled blown LLDPE [3]. Both Hybrid Clarity Antiblock “A” filled samples yield a greater variability (larger standard deviation) in RMS Roughness, Rq, Average Roughness, Ra, and Z-Range, suggesting greater variation in film topography. Barefoot AFM Phase image shows uniform surface modulus (Figure 3). Fine structure is described as “cauliflower” pattern of polymer lamellae associated with aggregates of stacked lamellar [3]. Dark regions correspond to soft amorphous and light regions to crystalline lamellae. There is no significant MD (vertical) orientation to the lamellae. Corresponding high areas of Z height image suggest a smoothing or disruption of the lamellae structure, possibly due to contact between the top and bottom film surface.

Table III. Average (Standard Deviation) AFM Roughness 10 µm Scan Length, nm

Sample Z-Range Rq Ra Barefoot LLDPE 120 (12) 16 (1.3) 13 (1.0) Synthetic Silica, 2000 ppm 110 (12) 15 (1.5) 12 (1.0) Hybrid Clarity Antiblock “A”, 2000 ppm 120 (25) 15 (2.3) 12 (2.1) Hybrid Clarity Antiblock “A”, 3000 ppm 120 (22) 15 (2.1) 12 (1.8)

Synthetic Silica 2000 ppm images shown in Figure 4 are similar to Barefoot with less rounding at the high spots. Discrete bright regions associated in Phase image is attributed to silica or erucamide crystals. Hybrid Clarity Antiblock “A” 2000 ppm images shown in Figure 5 are similar to Synthetic Silica with less rounding at the high spots. Height image shows higher frequency of raised regions. The Phase image shows mineral enrichment or erucamide crystals. Surface enrichment of additives does not necessarily correlate with surface height. Hybrid Clarity Antiblock “A” 3000 ppm images shown in Figure 6 is similar to Synthetic Silica with less rounding at the high spots. More regions of Hybrid Clarity Antiblock “A” surface enrichment or erucamide crystals are present. Surface additive enrichment areas correspond directly to elevated regions of Height image. AFM Phase images Hybrid Clarity Antiblock “A” show structures similar to erucamide crystal formation on the surface of films without antiblock mineral [5]. The enhanced erucamide surface concentration on Hybrid Clarity Antiblock “A” is consistent with reported synergistic relationship between slip and talc additives. Enhanced surface migration of erucamide yields a lower COF as noted in Table II. Erucamide surface enrichment was verified by XPS that shows nitrogen enrichment for Hybrid Clarity Antiblock “A” compared to Synthetic Silica ( Table IV.)

Table IV. XPS Surface Elemental Concentration (atom %)

Sample C O F N Barefoot LLDPE 99.7 0.07 0.19 ND Synthetic Silica, 2000 ppm 99.7 0.13 0.10 0.03 Hybrid Clarity Antiblock “A”, 2000 ppm 99.5 0.21 0.26 0.08 Hybrid Clarity Antiblock “A”, 3000 ppm 99.2 0.28 0.37 0.15

AFM scan size was increased to understand the larger roughness variability noted in 10 µm scan of filled films. Table V shows roughness measurements for 20 µm scan length yields similar trends as observed for 10 µm scans. Barefoot film still maintains the lowest variability and roughness, but now the average roughness values for filled samples are larger than barefoot. Roughness data for single 80 µm scan for each sample is shown in Table VI.

Table V. Average (Standard Deviation) AFM Roughness 20 µm Scan Length, nm

Sample Z-Range Rq Ra Barefoot LLDPE 160 (20) 19 (1.6) 15 (0.8) Synthetic Silica, 2000 ppm 250 (110) 23 (6.7) 17 (7.6) Hybrid Clarity Antiblock “A”, 2000 ppm 350 (180) 30 (14.5) 21 (8.2) Hybrid Clarity Antiblock “A”, 3000 ppm 725 (210) 31 (10.6) 20 (4.1)

Table VI.

Average AFM Roughness 80 µm Scan Length, nm Sample Z-Range Rq Ra

Barefoot LLDPE 174 19 15 Synthetic Silica, 2000 ppm 1060 65 43 Hybrid Clarity Antiblock “A”, 2000 ppm 640 49 35 Hybrid Clarity Antiblock “A”, 3000 ppm 1023 87 56

SWLIM images collected over a 250 µm scan region to overcome limitation of the AFM scans are shown in Figure 8. Multiple regions are scanned and measured roughness values are shown in Table VII. Both SWLIM and AFM values at the largest scan length are similar. Plots of Roughness Average, Ra, versus optical and block values are shown in Figures 9 – 11. Haze increases with roughness while clarity decreases with roughness. Blocking tendency does not show a consistent dependence on roughness of original film. Reblock at 60°C is independent on initial roughness and 40 °C reblock decreases with initial roughness. Generally, 23 °C block decreases with surface roughness except for 2000 ppm Hybrid Clarity Antiblock “A”, where a lower blocking value than expected is observed. A possible explanation for the low blocking value is surface erucamide acting as an antiblock.

Table VII. Average SWLIM Roughness 250 µm Scan Length, nm

Sample Rt Rq Ra Ra (AFM) Barefoot LLDPE 570 35 27 15 Synthetic Silica, 2000 ppm 3290 99 54 43 Hybrid Clarity Antiblock “A”, 2000 ppm 2700 71 46 35 Hybrid Clarity Antiblock “A”, 3000 ppm 2350 88 58 56 CONCLUSIONS In a LLDPE film formulation, performance data shows the Hybrid Clarity Antiblock “A” can replace synthetic silica at a replacement ratio at 1:1 or above. With a loading level greater than synthetic silica, induced reblock was equal to synthetic silica with equal haze suggesting a reduced antiblock loading level would significantly improve optical properties. Generally, no significant differences noted among sample average roughness measurements, except for a greater variability (larger standard deviation) in the filled samples compared to the barefoot at 10 µm scan length. As scan length increases, filled samples yield larger average roughness and peak range values. Filled samples have a greater average and maximum Range than barefoot. The average Z-Range increases from Barefoot < Hybrid Clarity Antiblock “A” 2000 ppm < Synthetic Silica < Hybrid Clarity Antiblock “A” 3000 ppm. Barefoot roughness is consistent at each scan length indicating a uniform surface topography. Phase images show polymer lamellae structure, filler and erucamide crystals present on the surface. Lower filler level does necessarily correspond to a height increase, but suggests lamellar structure at high regions are disrupted due to contact between the two films. Increased filler loading, 3000 ppm, of Hybrid Clarity Antiblock “A” shows a direct relationship between film roughness (height) and additive location in the film. Hybrid Clarity Antibloc “A” films show erucamide surface enrichment consistent with lower COF. Haze increases and clarity decreases as the film roughness increases. Initial film roughness generally correlates with 23 °C blocking and 40 °C reblock, suggest a blocking decrease as roughness increases. Hybrid Clarity Antiblock “A” at 2000 ppm yields a lower blocking value than expected for the roughness believed associated with erucamide acting as an antiblock. The 60 °C reblock is independent of initial film roughness.

REFERENCES 1. Coupland, K., and A. Maltby, Plastic Film & Sheeting, 13 (4) 142 (1997).

2. Maltby, A. and P. Ruxton, ADDCON Asia, 1999 – RAPRA.

3. Smith, P. F., I. Chun, G. Liu, D. Dimitrievich, J. Rasburn and G. J. Vansco, Poly. Eng. Sci, 39, 2129 (1996).

4. J. W. Catino, D. R. Deutsch, and J. L. Gardiner, TAPPI Place, Boston, MA 2002.

5. Ramirez, M. X., D. E. Hirt and L. L. Wright, Nano Letters, 2 (1) 9 (2002).

6. Cleveland, J. P., B. Anczykowski, A. E. Schmid and V. B. Elings, Appl. Phys. Lett., 72 2613 (1996). ACKNOWLEDGEMENTS Thanks to Ali Bashey of Specialty Minerals for XPS analysis and Dr. Wendy Chang of International Paper for use of the AFM.

Diatomaceous Earth Synthetic Silica Hybrid Clarity Antiblock Figure 1. SEM images of common mineral antiblocks.

Figure 2. SEM images at low and high magnification of LLDPE films. Filler Level noted on images.

Figure 3. AFM images of Barefoot LLDPE.

Figure 4. AFM images of LLDPE filled with 2000 ppm Synthetic Silica.

Figure 5. AFM images of LLDPE filled with 2000 ppm Hybrid Clarity Antiblock “A”.

Figure 6. AFM images of LLDPE filled with 3000 ppm Hybrid Clarity Antiblock “A”.

Barefoot LLDPE 2000 ppm Synthetic Silica

2000 ppm Hybrid Clarity Antiblock “A” 3000 ppm Hybrid Clarity Antiblock “A” Figure 7. AFM Height images shown as projections.

Barefoot LLDPE 2000 ppm Synthetic Silica

2000 ppm Hybrid Clarity Antiblock “A” 3000 ppm Hybrid Clarity Antiblock “A”

Figure 8. SWLIM images of LLDPE films.

Figure 9. Relationship between SWLIM measured Ra and Haze.

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Ra, µm

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Figure 10. Relationship between SWLIM measured Ra and Clarity.

Figure 11.. Relationship between SWLIM measured Ra and Blocking.

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Surface Structural Characterization of Antiblock Films containing Erucamide

John W. CatinoDonald R. DeutschJohn L. Gardiner

Specialty Minerals, Inc.640 N. 13th StreetEaston, PA 18042

[email protected]

TAPPI European Place 2003Rome, Italy

May 14, 2003

Overview• Background

• Optical and Blocking Properties

• Surface Structural CharacterizationSEMAtomic Force MicroscopySWLIMXPS

• Summary

Mineral Filler to Control Blocking

Benefits:• Mineral additives used as an effective means of

producing roughness on the film’s surface.

• The tendency to block is significantly reduced asthe level of inorganic mineral filler is increased

Limitation:• Negative effects on optical properties such as haze

and clarity

BALANCE OPTICAL and PHYSICAL PROPERTIES

Mineral Filler Morphology

Diatomaceous Earth Synthetic Silica Hybrid Clarity “A”

Objectives• To understand the relationship between mineral fillers as

antiblock additives, relative to the effect they impart to the film

• To develop understanding of the effect between mineral and slip additives

• To better understand ways to characterize relative performance:

- Optical and antiblock efficiency testing- Relate surface structure and chemistry to physical

properties

Optimize Properties

Particle Size Distribution: • Refine the particle size distribution to produce a

Very tight distribution Scatter minimal light

Hybrid Clarity Antiblock • Target Refractive Index (RI) of PE

Minimizing oversize and fine particles Match mineral with RI of Polyethylene

• Hybrid Clarity Antiblock “A” RI = 1.53 - 1.54 RI Minimal negative effect to the film’s optical properties Allows for greater flexibility in antiblock loading levels

Refractive Indices forCommon Media

Substance Refractive Index (RI)1

Air 1.00Water 1.33Polyethylene low

medium high

1.511.521.54

Polypropylene – unmodified 1.49Calcite 1.64Amorphous silica – material 1.44Amorphous silica – synthetic 1.4 – 1.5Diatomaceous Earth (DE, SiO2) 1.44Hybrid Clarity Antiblock” “A 1.53 – 1.54Talc 1.571 literature values ideal particle size (25 – 60 microns)

Experimental MaterialsAntiblocks

Hybrid Clarity Antiblock “A”OPTIBLOC® 10 Clarity Antiblock

Produced by Specialty Minerals Inc. a division of Minerals Technologies Inc.

Synthetic SilicaSYLOBLOC ® 45 Synthetic Silica

Produced by W. R. Grace Inc.

Experimental Materials, Conditions, and Test Methods

Resin - 1.0 M.I. Butene LLDPE Slip Agent - 1000 ppm Crodamide ER erucamideBlown Film - Killion extruder - L/D ratio 30:1Die diameter - 2 1/2 inch ( 64mm) with a .035 inch (0.875 mm) die gapFinal Film - 1.0 mil (25.4 µm)

Test MethodASTM D3354 - Induced reblock - parallel plate 40°/60° C conditioningASTM D1984 - COF (coefficient of friction)ASTM D1003 - Haze and ClarityASTM D2457 - Gloss

Optical ComparisonAntiblock ppm Haze Clarity 45° Gloss

SyntheticSilica

2000 6.3 95.4 76

Hybrid ClarityAntiblock “A”

2000 5.2 97.0 77


3000 6.0 95.9 76

1.0 M.I. Butene LLDPE with 1000 ppm Erucamide

Blocking ComparisonAntiblock ppm Blocking

(g) 23°CReblock(g) 40°C

Reblock(g) 60°C

COF

Synthetic Silica 2000 121 55 140 0.31


2000 86 86 139 0.19


3000 86 61 140 0.16

Barefoot(no erucamide)

0 181 136 145 --

1.0 M.I. Butene LLDPE with 1000 ppm Erucamide

Barefoot

2000 ppm Synthetic Silica

2000 ppm Hybrid Clarity Antiblock “A”

3000 ppm Hybrid Clarity Antiblock “A”

AFM: Barefoot

AFM: Synthetic Silica, 2000 ppm

AFM: Hybrid Clarity Antiblock “A” 2000 ppm

AFM: Hybrid Clarity Antiblock “A” 3000 ppm

Barefoot Synthetic Silica, 2000 ppm

Hybrid “A”, 2000 ppm Hybrid “A”, 3000 ppm

Summary of 10 µm ScanRoughness Measurements, nm

Sample Z-Range Rq Ra

Barefoot, LLDPE 120 16 13

Synthetic Silica, 2000 ppm 110 15 12

Hybrid Clarity Antiblock “A”, 2000 ppm 120 15 12


XPS

Elemental Concentration (atom %)Sample C O F N

Barefoot LLDPE 99.7 0.07 0.19 NDSynthetic Silica, 2000 ppm 99.7 0.13 0.10 0.03Hybrid Clarity Antiblock “A”, 2000 ppm 99.5 0.21 0.26 0.08Hybrid Clarity Antiblock “A”, 3000 ppm 99.2 0.28 0.37 0.15

SWLIM

Barefoot 2000 ppm Synthetic Silica

2000 ppm Hybrid Clarity “A” 3000 ppm Hybrid Clarity “A”

Summary of 250 µm SWLIM Roughness Measurements, nm






Optical Properties and Roughness

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Conclusions• Blocking performance data shows the Hybrid Clarity

antiblock “A” can replace synthetic silica at 1:1 or above.

• AFM average roughness measurements yield greater variability in filled samples compared to the barefoot.

• As scan length increases, filled sample roughness increases compared to barefoot and becomes almost constant above 80 µm scan length showing good correlation between AFM and SWLIM roughness.

• Phase images show polymer lamellae structure, filler and erucamide crystals present on the surface

• Slip values, AFM phase images and XPS indicate erucamide surface enrichment for Hybrid Clarity Antiblock “A” consistent with the synergy between the two additives.

• Blocking Properties:60 C Reblock is independent of initial roughness40 C Reblock decreases with initial roughness23 C Blocking generally decreases with roughness. Anomalies may be due to surface erucamide enrichment indicted.

• Haze increases and Clarity decrease with surface roughness.

Conclusions

Acknowledgements

Ali Bashey of Specialty Minerals for XPS analysis Dr. Wendy Chang of International Paper

abstract - · pdf filea separate 5% crodamide er erucamide masterbatch was used to vary the...

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