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Geotextiles and Geomembranes 29 (2010) 360e362

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Geotextiles and Geomembranes

journal homepage: www.elsevier .com/locate/geotexmem

Technical Note

Puncture resistance of polyester (PET) and polypropylene (PP) needle-punchednonwoven geotextiles

George R. Koerner a,*, Robert M. Koerner b

aGeosynthetic Institute, Folsom, PA, USAbDepartment of Civil, Architectural and Environmental Engineering, Drexel University, Philadelphia, PA, USA

a r t i c l e i n f o

Article history:Received 25 November 2009Received in revised form17 September 2010Accepted 16 October 2010Available online 10 December 2010

Keywords:PunctureGeotextileGeosyntheticIndexLaboratoryTest

* Corresponding author. Tel.: þ1 610 522 8440; faxE-mail addresses: gkoerner@dca.net (G.R. Koerner

edu (R.M. Koerner).

0266-1144/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.geotexmem.2010.10.008

a b s t r a c t

It is common practice to use needle-punched nonwoven geotextiles as puncture protection for geo-membranes against sharp objects like gravel or stones in either the soil above or the underlying soil/rockbelow. There are several design and experimental methods available for geotextile selection in thisregard. None, however, directly address the type of resin or fiber from which the geotextile is made. Thispaper does exactly that insofar as a direct comparison of similar mass per unit area polyester (PET) versuspolypropylene (PP) geotextiles are concerned. Furthermore, two types of PP geotextiles are evaluated;one made from continuous filaments and the other from staple fibers. Three different size and shapedpuncture probes are used in the testing program. All three are ASTM Standards, i.e., D4833, D5495 andD6241.

The test results clearly indicate that geotextiles made from PP fibers outperform those made from PETfibers at all masses evaluated. Clearly, the present trend of using PP resin for heavy nonwoven protectiongeotextiles seems justified on the basis of these test results. In addition, the continuous filament PP andstaple fiber PP geotextiles performed equivalently over all mass ranges for the three different types ofpuncture tests.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Over the past 15e20 years there has been a major shift in thetype of polymer used in the manufacturing of needle-punchednonwoven geotextiles. In the past, themajority were frompolyester(PET) resin whereas presently polypropylene (PP) resin is usedalmost exclusively. That said, the geotextile manufacturing processitself has continued to be similar at least for the relatively thickneedle-punched nonwoven fabrics used in this study.

One of the major uses for high mass per unit area (or simply“mass”) geotextiles of this type is for puncture protection of geo-membranes when used as barriers for geoenvironmental andhydraulic engineering applications. Some of the major applicationsare as follows; Koerner (2005);

� landfill liner systems,� landfill cover systems,� waterproofing of all types of dams,� liner systems for reservoirs and surface impoundments, and� liner systems for canals and tunnels.

: þ1 610 522 8441.), robert.koerner@coe.drexel.

All rights reserved.

In this paper we present a laboratory study of using equivalentmasses of needle-punched nonwoven fabrics made from either PET(continuous filament) or PP resins. For the PP geotextiles bothcontinuous filament and staple fiber are used. All of the tests areevaluated in-isolation, i.e., without an accompanying geomem-brane, using three different ASTM puncture test methods.

2. Properties and test methods

Since the mass of the geotextiles to be evaluated is the majorvariable in this series of tests, differences in the intrinsic polymerproperties of the two resin types should be kept in mind in viewingthe results. Table1presents variousproperties ofpolyester (PET) andpolypropylene (PP) fibers from the perspective of the basic resin.

Using fabrics of different mass per unit area (from 135 g/m2 to1220 g/m2) in this laboratory study, each was evaluated for theirpuncture resistance using three different standardized puncturetests. The tests are as follows:

(i) ASTM D4833, the “pin” puncture test (there is no ISO equiv-alent test)

(ii) ASTM D5494, the “pyramid” puncture test (there is not ISOequivalent test)

Table 1Selected properties of polyester and polypropylene resins, Shreve and Brinks (1977).

Property PET(high-tenacity)

PP(cont. and staple)

Breaking tenacityStandard g/denier 2.5e5.0 4.8e7.0Wet (g/denier) 2.5e5.0 4.8e7.0

Specific gravity (g/cc) 1.38 0.91Static moisture regain (%) 0.8 3.0Coef. thermal expansion

(� 10�5 per �C)4e5 6

Melting temp. (�C) 250e290 160e170Glass trans. temp (�C) 60e85 �7

Fig. 1. Different probe shapes and sizes; see Table 2 for dimensions.

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G.R. Koerner, R.M. Koerner / Geotextiles and Geomembranes 29 (2010) 360e362 361

(iii) ASTM D6241, the “CBR” puncture test (this is equivalent to ISO12236)

Table 2 presents the relevant differences in the testmethods andFig. 1 shows the different puncturing probe sizes and shapes.

3. Test results and discussion

Five fabric masses of 135, 270, 406, 813 and 1220 g/m2 ofcontinuous filament PET (it was never available from staple fibers)and both continuous filament and staple fiber PP needle-punchednonwoven geotextiles were evaluated in the three test methodsmentioned previously.

The results of the PET continuous filament fabric are given inFig. 2(a). Note the near linear behavior of all three responses. Herethe ordering of the puncture resistances is as follows:

� Pyramid puncture is greater than pin puncture by a factor ofapproximately two.

� CBR puncture is greater than pin puncture by a factor ofapproximately nine.

These trends are relatively constant throughout the range of PETfabric masses evaluated.

The results of the PP continuous filament fabric tests are given inFig. 2(b). Note the essentially linear behavior of all three curves.Here the ordering of the puncture resistances is as follows:

� Pyramid puncture is only marginally greater than pin puncture.� CBR puncture is greater than pin puncture by a factor ofapproximately seven.

These trends are relatively constant throughout the range of PPcontinuous filament fabric masses evaluated.

The results of the PP stable fiber fabric tests are given in Fig. 2(a).Note the essentially linear behavior of all three curves. Here theordering of the puncture resistance is as follows:

Table 2Selected differences in the three puncture tests used in this study.

Item or property Pin (D4833) Pyramid (D5494) CBR (D6241)

Probe puncturing tip 8.0 mm dia. Point 50 mm dia.Chamfered point

or edge45�; 0.8 mm 0.5 � 0.01 mm 2.5 � 0.5 mm

Specimen containment 50 mm dia. 150 mm dia. 150 mm dia.Probe advancement rate 300 � 10 mm/min 1 þ 0.1 mm/min 50 mm/minNo. of replicate tests 15 10 10Lab temperature 21 � 2 �C 21 � 2 �C 21 � 2 �CLab relative humidity 65 � 5% 50e70% 50e70%Test conclusion Break Puncture via

electric contactBreak

Value reported Max. resistance Max. resistance Max. resistance

� Pyramid puncture is only marginally greater than pin puncture.� CBR puncture is greater than pin puncture by a factor ofapproximately seven.

These trends are relatively consistent throughout the range ofPP staple fiber fabric masses evaluated.

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Pyramid; D5495

Pin; D4833

Legend

Fig. 2. (a). Puncture resistance curves of PET continuous filament geotextiles. (b).Puncture resistance curves of PP continuous filament geotextiles. (c). Puncture resis-tance curves of PP staple fiber geotextiles.

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Fig. 3. (a). Pin puncture resistance curves of three geotextiles evaluated. (b). Pyramidpuncture resistance curves of three geotextiles evaluated. (c). CBR puncture resistancecurves of three geotextiles evaluated.

G.R. Koerner, R.M. Koerner / Geotextiles and Geomembranes 29 (2010) 360e362362

Regarding a direct comparison of puncture resistance behaviorof geotextiles made from PET resin (continuous) versus PP resin(continuous and staple) at the same weights, Fig. 3 is offered.

The results of the pin puncture testing, according to ASTMD4833, are given in Fig. 3(a). Here it is seen that both PP geo-textiles (continuous filament and staple fiber) give approximatelysimilar responses. Both, however, are significantly higher than thePET geotextile (continuous filament) by approximately 100%. Aswill be seen these results have the largest scatter of all puncturetests.

The results of the pyramid puncture testing, according to ASTMD5494, are given in Fig. 3(b). Again it is seen that the two PP

geotextiles (continuous filament and staple fiber) give approxi-mately the same results. Both are higher than the PET geotextile(continuous filament) by approximately 35%. Interestingly, this isthe same percentage increase as is the ratio of PET/PP specificgravity values; recall Table 1.

The results of the CBR puncture testing according to ASTMD6241, are given in Fig. 3(c). The two PP geotextiles (continuousfilament and staple fiber) are again close to one another and bothare higher than the PET geotextile (continuous filament). Theamount of increase is about 25%.

4. Conclusion

This study indicates that the puncture resistance of needle-punched nonwoven geotextiles has been measurably increased bychanging the fiber’s base resin from PET-to-PP at an equivalentmass per unit area. The approximate puncture resistance increasesof the PP geotextiles over the PET geotextiles are 100% for pinpuncture, 35% for pyramid puncture, and 25% for CBR puncture.Certainly part of the improvement comes from polypropylenebeing a significantly lower specific gravity polymer than PET thusmore fiber mass is in an equivalent weight; recall Table 1. In itself,this lower specific gravity could account for up to a 34% increase inthe amount of fibers when using PP resins. There are, however,many other factors between the two resin types and their respec-tive geotextiles which are much more difficult to isolate. They areprocessability differences, needling behavior, breaking tenacity,fiber frictional characteristics, polymer state (glassy versusrubbery), and possibly others.

The conclusion, however, stemming from this study is thatneedle-punched nonwoven fabrics used for protection (or cush-ioning) of geomembranes is better provided by geotextiles madefrom polypropylene (PP) fibers than those made from polyester(PET) fibers.

References

ASTM D4833-07, Standard test method for index puncture resistance of geotextiles,geomembranes and related products, ASTM,West Conshohocken, Pennsylvania.

ASTM D5494-06, Standard test method for the determination of the pyramidpuncture resistance of unprotected and protected geomembranes, ASTM, WestConshohocken, Pennsylvania.

ASTM D6241-04, Standard test method for the static puncture strength of geo-textiles and geotextile related products using a 50-mm probe, ASTM, WestConshohocken, Pennsylvania.

ISO 12236, Geotextiles and geotextile-related products e Static puncture test (CBRtest).

Koerner, R.M., 2005. Designing with Geosynthetics, fifth ed. Pearson Prentice Hall,Englewood Cliffs, New Jersey.

Shreve, R.N., Brink Jr., J.J., 1977. Chemical Process Industries, fourth ed. McGraw-Hill,New York, New York.