Characterization of ExxonMobil Escorene and

Achieve Polypropylene Melt Blown Nonwovens

Stephen R. Whitson

Summer 2011

Abstract

The purpose of this research was to analyze the differences in properties of Exxon

Mobile’s Escorene polypropylene resin and their new polypropylene resin Achieve. Both resins

were run through and Industrial Melt Blowing Line at an air pressure of 10 psi, DCD (Die-To-

Collector) distance of 20 cm, and Air Temp of 500 ᵒF to produce non-woven webs. As well as

this, three different Achieve webs were produced and tested, by running the resin at different air

pressures (10 psi – 5 psi) and DCD distances (20 cm – 35 cm). After thickness and fiber diameter

was found (avg. thickness = 1 mm, avg. fiber diam. = 2 μm) each web was tested using ASTM

D737 air permeability method, ASTM D5035 tensile test method, ASTM D5734 Elmendorf tear

test method. A TGA was also performed on both Escorene and Achieve pellets and resins; all

materials lost the majority of weight at around 300 ᴼC. Tensile tests showed that the Achieve

web had a higher average peak load and elastic modulus than the Escorene web. It also showed

that accordingly named PC3 web was had the greatest average peak load (1732 gms) and elastic

modulus (1296194 gms/in²) in the cross direction, while the PC2 web had the greatest average

peak load (2759 gms) and elastic modulus (3576177 gms/in²) in the machine direction.

Introduction

Background

Polypropylene is an isotactic thermoplastic polymer; a crystalline material it is noted for

its high strength-to-weight ratio, excellent chemical resistance and high performance in

thermoforming and corrosive environments. It is a versatile polymer that can be used for a

variety of plastic applications including containers, tools, mechanical parts, and textiles. Both

ExxonMobil’s Escorene and Achieve resins are polypropylene homopolymers designed for melt-

blowing applications. Achieve is the next generation having a higher MFR (1550 g/10 min) and

larger resin particles. It is also free of the peroxides, which the Escorene resin contains to control

rheology (flow). The melt flow rate (MFR) is an indirect measure of the molecular weight of a

thermoplastic polymer. The measure helps to determine how easily the molten raw material will

flow during processing.

Melt blowing is a process for producing fibrous non-woven webs from polymers or

resins. “Melt-blowing is a one-step process and one of the most practical processes for producing

microfiber nonwovens directly from thermoplastic polymers, in which hot/high velocity air

blows the extruded filament from a die tip towards a moving conveyer belt or a cylinder.” [1] In

a melt-blowing line the resin is heated to melting temperatures as it is extruded through a screw

(or screws). The extruded polymer, is then suctioned through a metering pump in order to control

flow rate. The resin is then discharged to the melt-blow die; the die contains holes through which

the molten resin is pushed. The resin is then immediately hit with high velocity hot air coming

from both top and bottom (at various angles) of the die assembly. This extenuates and tangles

fibers unto a conveyor belt which is then fed to a rolling assembly. Schematics of process are

shown below.

Figure 1. Hopper and screw extruder [2] Figure 2. Die To Collector [2]

Figure 3. Schematic of MB process [2]

Testing

To discover how well air flows through a fabric or web an air permeability test is done.

Air permeability is the rate of air flow passing perpendicularly through a known area under a

prescribed air pressure. According to ASTM D737 ten samples are tested to produce at least 4

samples that have values within 5% of one another.

Figure 4. TexTest FX 3300 Air Permeability Tester Figure 5. EJA Tensile Tester

A tensile tester was used to produce a load vs elongation graph. According to ASTM

D5035 8 (1” gauge) samples are tested in the cross direction and 5 (1” gauge) samples are tested

in the machine direction. All 8 cross direction samples must be within 50% of one-another for all

values; all 5 machine direction samples must be within 50% of one-another for all values.

Machine direction is defined as the direction that the fibers are blown onto the conveyor belt; the

cross direction is transverse to the machine direction. A tensile testing instrument will apply an

increasing amount of tensile load on a material, in a specified direction, measuring the elongation

along the direction of the tensile force until the sample fractures. A load vs. elongation curve can

then be mapped from the data. From this curve we can deduce many different aspects of the

particular materials properties. At the beginning of the curve is linear with an even slope. This

slope represents what is called the modulus of elasticity, which can be thought of as the stiffness

of the material; the resistance to permanent deformation. At a certain point the slope ends and the

curve begins to bend, going slowly upward until it reaches its maximum point, the tensile

strength or peak load. Past this point the material can no longer maintain structure, will begin to

break down and eventually fracture. Because the process of breaking down often decreases the

cross-sectional area of the specimen the load-elongation curve will begin to bend downwards as

the area decreases faster than the force of the load increases. It will continue until the fracture

point the maximum load that the sample was able to handle until breaking; at which point data

can no longer be recorded.

The Elmendorf tear “test method covers the measurement of the average force required to

propagate a single-rip tear starting from a cut in a nonwoven fabric using a falling-pendulum

(Elmendorf) apparatus.” [3] It is a measurement of how much resistance a fabric provides against

tearing. According to ASTM D5734 5 samples (2.5” by 4”) are tested in the cross direction and 5

samples (2.5” by 4”) are tested in the machine direction.

Figure 6. TexTest FX 3750 Tear Tester Figure 7. Mettler Toledo TGA/SDT 851

To determine the amount of weight loss that materials undergo under certain

temperatures a TGA test is performed. Thermal gravimetric analysis (TGA) is a type of testing

performed on samples that measures and graphs changes in weight in relation to change in

temperature.

Experimental

Melt-Blowing

An industrial melt blowing line with Haake twin screw extruder, Zenith metering pump,

Ingersol-Rand air compressor, colletor, and 6 in. (120 hole) die were used to melt blow non-

woven webs from ExxonMobil Escorene and Achieve resins.

Table 1. Initial MB processing conditions for ExxonMobil Polypropylene Resins

Parameters Escorene® PP3546 Achieve® 6936G1

Air Pressure: 10 psi 10 psi

DCD: 20 cm 20 cm

Colllector Speed: 137 rpm (4.9 m/min) 137 rpm (4.9 m/min)

Extruder Speed: 57 rpm 69 rpm

Extruder Pressure: 160-180 psi 370-380 psi

Pump Pressure: 11 psi 14 psi

Pump Speed: 8.5 rpm 8.5 rpm

Air Temp: 500 ᵒF 500 ᵒF

In order to maintain a basis weight of 100 grams for each web, extruder speed and the pressure

the of extruder and pump were adjusted. Air temperature and pressure, DCD (Die-To-Collector

distance), and collector speed were kept the same when processing both webs. The Achieve resin

was also run at three different processing conditions. The extruder speed and pressure, pump

pressure, and collector speed shown below were kept constant. However DCD and air pressure

were changed to produce three different Achieve webs (PC1, PC2, PC3).

Table 2. Achieve MB processing conditions

Extruder Speed: 69 rpm

Extruder Pressure 350-380 psi

Pump Pressure: 15 psi

Collector Speed: 137 rpm (4.9 m/min)

Table 3. Achieve MB processing conditions

Sample DCD (cm) Air Pressure

(psi)

PC1 20 10

PC2 20 5

PC3 35 5

Thickness and Fiber Diameter

Tests were conducted under ASTM D5729 standard for Escorene and 3 types of Achieve

web. Web thickness was measured using TMI 49-70, 10 times per web in accordance with

ASTM standard D5729. Fiber diameter was calculated by examining microscopic images of each

web and using ImageJ to measure the average fiber diameter for each web. 6 images were

examined for each web, and 10 measurements were made per image.

Figure 8. Escorene Web Microscope Image Figure 9. Achieve/PC1 Web Microscope Image

Figure 10. PC2 Web Microscope Image Figure 11. PC3 Web Microscope Image

Air Permeability

Tests were conducted using TexTest FC 3300 Air Permeability Tester under ASTM

D737 standard for Escorene and 3 types of Achieve web. 10 samples larger than 5.93 in² of each

web were prepared from the center of the web reel. Each sample was secured in the crosshead

and test run. Values were recorded in cfm (Cubic Foot per Minute).

Tensile Test

Tests were conducted using EJA Tensile Tester (10 lb load cell) under ASTM D5035

standard for Escorene and 3 types of Achieve web. 8 samples 1” wide and 6” along cross

direction were loaded into tensile tester and then tensile test was run. Following this, 5 samples

1” wide and 6” along machine direction were loaded into tensile tester and then tensile test was

run. Peak load, Peak Elongation, and Modulus values were recorded for each run.

Elmendorf Tear Test

Tests were conducted using TexTest FX 3750 Elmendorf Tear Tester under ASTM

D5734 standard for Escorene and 3 types of Achieve web. 5 samples 4” wide and 2.5” along

cross direction were loaded into tensile tester and then tensile test was run. Following this, 5

samples 4” wide and 2.5” along machine direction were loaded into tensile tester and then tensile

test was run. Values were recorded in cN (CentineNewton).

TGA

Tests were conducted using Mettler Toledo TGA/SDT A851 and results were evaluated

using Star-e vs. 8.10. Four tests were run, one each for Escorene pellets, Achieve pellets,

Escorene web, and Achieve web. Samples were loaded into a ceramic crucible, which had been

previously tared, and weighed. The crucible containing the sample was then loaded into the TGA

and temperature program run. The temperature program ran from 25 ᴼC to 650 ᴼC at 10 ᴼC/min.

Results and Discussion

Table 4. Web Properties of Escorene and Achieve

Polymer Fiber Diam. (µM) Thickness (mm) Air Perm (cfm)

Escorene® Mean 1.95 1.15 27.57

Std. Dev. 0.60 0.10 1.02

Achieve® Mean 2.28 1.31 24.59

Std. Dev. 0.67 0.07 0.89

Figure 12. Escorene Fiber Diam. Distributio Figure 13. Achieve Fiber Diam. Distribution

As we can see from these results, under the exact same processing conditions the Achieve

resin produced a thicker web most likely due to the larger fiber diameter. Both the Achieve and

Escorene web attained the same basis weight of 100 grams however, which shows that the

Achieve resin is slightly less dense than the Escorene resin. The Escorene contains peroxide

which breaks down the polymer chains into shorter units in order to control flow rate. The

Achieve being peroxide free “achieves” better flow rate, while retaining the longer polymer

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chains. This lack of peroxide however, makes the Achieve less dense since the longer polymer

chains don’t pack as tight. Being thicker the Achieve web was slightly less permeable than the

Escorene web.

Figure 14. Load vs. Elongation in MD and CD for Escorene and Achieve Webs

Table 5. Tensile and Tear Properties of Escorene and Achieve

Polymer Peak Load (gms)

Peak Elongation (% in)

Modulus (gms/in²)

Elmendorf (cN)

Machine Direction

Escorene® Mean 1403.0 5.40 1,283,755 51.7

Std. Dev. 164.3 0.90 288,090 15.8

Achieve® Mean 1894.6 5.07 1,758,291 49.4

Std. Dev. 228.7 0.42 158,099 11.9

Cross Direction

Escorene® Mean 605.6 18.45 244,525 79.6

Std. Dev. 39.4 2.55 14,633 18.8

Achieve® Mean 619.7 8.39 347,856 68.6

Std. Dev. 17.3 0.8 18,948 6.6

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400

600

800

1000

1200

1400

1600

1800

2000

-0.2 0 0.2 0.4 0.6 0.8

Load (gms)

Elongation (in)

Escorene MD

Achieve MD

Escorene CD

Achieve CD

From the graph and table you may notice the large difference in curves between the

machine and cross directions. When a non-woven web is formed, the majority of the fibers

usually fall into place in the machine direction, which means when a tensile test is run in this

direction we are looking at the strength of the fibers until they break apart. In the cross direction

however, we are looking at the strength of the horizontal bonds between the individual fibers as

they break apart from one-another. This means that as a rule fabrics will have better tensile

strength in the machine direction. The trend we see from the load vs. elongation graph is the

Achieve web is stronger and stiffer (having a higher modulus). This is mostly due the difference

in length of polymer chains within each resin. Because the Achieve is peroxide free, it contains

longer polymer chains that give it it’s larger tensile strength in the machine direction (along the

fibers). This is further proven by lack of a noticeable difference in tensile strength in the cross

direction since, as discussed, this is a measure of bonds between the individual fibers.

In the Elmendorf tear test, fabrics tear much easier in the machine direction since the tear

will propagate along the length of the fibers. In the cross direction however, the tear goes

through the fibers and therefore there is much more resistance. In the case of the Achieve web

vs. the Escorene web, we find that the Escorene, while being the thinner fabric, was much more

resistant to tearing in the cross direction than the Achieve web. This once again may be due to

the Escorene having shorter polymer chains and as the tear propagates in the cross direction it

will have a much less linear pathway as it diverges more frequently, between polymer chains.

When weight loss under high temperatures was tested, both Escorene and Achieve (resins

and webs) performed about the same. As can be seen in table and graph below, both resins

(pellets) lost around 99% of their weight, beginning at around 300 ᴼC. The nonwoven webs

perform very slightly different losing slightly less weight at slightly higher temperatures. As we

can see from the graph all samples loss their weight very quickly once reaching the threshold.

Table 6. TGA Data for Escorene and Achieve

Initial Weight (mg)

Weight Loss %

Weight Loss (mg)

Onset (ᴼC)

Escorene Pellets

7.26 -99.0% -7.20 309

Achieve Pellets

7.39 -99.3% -7.34 290

Escorene Web

7.59 -97.8% -7.43 304

Achieve Web

7.31 -97.2% -7.11 326

Figure 15. TGA Curve for Escorene and Achieve

( Temperature ᴼC along horizontal axis; % Weight along vertical axis)

Table 7. Web Properties of Achieve Variants

Fiber Diam. (µM) Thickness (mm) Air Perm (cfm)

PC1 Mean 2.28 1.31 24.59

Std. Dev. 0.67 0.07 0.89

PC2 Mean 1.95 0.89 19.46

Std. Dev. 0.4 0.06 0.94

PC3 Mean 2.28 0.96 25.61

Std. Dev. 0.75 0.03 1.18

Figure 16. PC1 Fiber Diam. Distribution Figure 17. PC2 Fiber Diam. Distribution

Figure 18. PC3 Fiber Diam. Distribution

The only differences between the three Achieve webs are processing conditions. Namely

PC1 was processed at an air pressure of 10 psi while the other two were processed at 5 psi; and

PC3 was processed with a DCD of 35 cm while the other two webs were processed with a DCD

of 20 cm. Since all three webs are the made of the same resin, the fibers should therefore be the

same density. The drop in air pressure between PC1 and PC2 (10 to 5 spi) seems to have

produced a smaller fiber diameter and therefore a thinner fabric. However the PC3 was also

processed at 5 psi yet produced the same fiber diameter as the PC1. This is interesting since it

would seem that the DCD, having to do with the process after the die, would not affect fiber

diameter. No web was as thick as the PC1 at 1.31 mm nonetheless. While the thinnest, the PC2

was the least permeable, which implies that the smaller fibers packed more closely creating a

denser, thinner fabric.

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Figure 19. Load vs. Elongation in MD for Achieve Web variants

Figure 20. Load vs. Elongation in CD for Achieve Web Variants

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1200

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Elongation (in)

PC1

PC2

PC3

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Table 8. Tensile and Tear Properties of Achieve Web Variants

Polymer Peak Load (gms) Peak Elongation (% in)

Modulus (gms/in²)

Elmendorf (cN)

Cross Direction

PC1 Mean 619.7 8.39 347,856 68.6

Std. Dev. 17.3 0.80 18,948 6.6

PC2 Mean 877.0 3.90 1,137,186 68.6

Std. Dev. 29.6 0.34 42,429 6.6

PC3 Mean 1732.4 16.02 1,298,194 53.1

Std. Dev. 56.4 1.89 42,891 5.5

Machine Direction

PC1 Mean 2019.9 5.28 1,841,227 49.4

Std. Dev. 244.7 0.51 113,385 11.9

PC2 Mean 2758.9 3.04 3,576,177 40.7

Std. Dev. 147.8 0.13 141,961 4.6

PC3 Mean 2338.5 11.97 2,079,719 55.6

Std. Dev. 402.0 2.44 279,292 4.2

As we can see from the graph and table, the PC3 web had the most tensile strength and

stiffness in the cross direction. This is most likely due to the increase in the distance from die to

collector the fibers tend to become more entangled and randomly laid creating more resistance to

the individual fibers breaking apart from one-another. The fibers in the PC3 web being more

randomly laid means that the direction of the fibers did not as often lie in the direction of the

collector belt. This means that the properties in the cross and machine direction are going to be a

lot closer together than when compared with PC1 and PC2 webs (which were processed at

shorter DCD’s). Unusually the PC2 web was the strongest and stiffest in the machine direction.

This is most likely due to the better bonding between the “thinner” fibers, which were more

densely packed (see air permeability of PC2 web). Surprising these more densely packed fibers

were not more resistant to tearing in the cross direction than the other webs. The PC3 also, while

having the greatest tensile strength in the cross direction was not as resistant to tearing as the

other webs. This may show that there is a correlation between the Young’s Modulus (stiffness)

and the tear resistance; as the webs that were the stiffest tended to tear the easiest.

Conclusion

When melt blown under the same processing conditions the Achieve resin produced a

web that was stronger, had a higher elastic modulus, and was slightly less dense. This is largely a

result due to the lack of peroxide, which the Escorene resin contains. The TGA showed that both

Escorene and Achieve resins (and webs) lose the majority of their weight at around 300 ᴼC.

After running the Achieve resin under three different processing conditions we found that

decreasing air pressure produces a stronger and stiffer nonwoven web. We also found that

increasing the DCD distance produces a web with fibers more entangled and more laid in more

random directions. This in turn produces a web that is comparable in both machine and cross

direction.

References

1. Dr. Lee, Youn Eung and Dr. Wadsworth, Larry C. “Process Property Studies Of Melt

Blown Thermoplastic Polyurethane Polymers For Protective Apparel” Knoxville, TN:

University of Tennessee Department of Materials Science and Engineering, 2005. Print.

2. Kotra, Ramaiah and Rong, Haoming. “Melt Blown Technology” Knoxville, TN:

University of Tennessee Department of Materials Science and Engineering, 2004. Print.

3. ASTM Standard D5734, 2001, "Standard Test Method for Tearing Strength of Nonwoven

Fabrics by Falling-Pendulum (Elmendorf) Apparatus," ASTM International, West

Conshohocken, PA, 2003, DOI: 10.1520/C0033-03, www.astm.org.