Evaluation of Thermoplastic Olefin (TPO) Roofing Membranes

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Evaluation of Thermoplastic Olefin (TPO) Roofing Membranes

http://irc.nrc-cnrc.gc.ca

Eva luat ion of T he r m opla st ic Ole fin (T PO)

Roofing M e m bra ne s

S i m m o n s , T . R . ; P a r o l i , R . M . ; L i u ,

K . K . Y . ; D e l g a d o , A . H . ; I r w i n , J . D .

I R C - I R - 7 6 8

June 1998

EVALUATION

OF

THERMOPLASTIC OLEFIN

( P O )

ROOFING MEMBRANES

ABSTRACT: As part of a five-year investigation, rnechanicd (strength and elongation)

and chemical (thermogravimetry and dynamic mechanical analysis) methods of

evaluation are used in this paper to characterize in-service thermoplastic olefin (TPQ)

roof membranes. AIF the nun-reinforced membranes meet the minimum thickness and

tensile strength requirement as specified in the proposed ASTM standard. The poIyester scrim reinforced membranes were superior in tensile strength and elongation as compared

to those reinforced with random mat of short glass fibers. The standard should consider

defining the breaking strength in terms of "stress" instead of load, This would allow for a

fairer and easier comparison of strength between reinforced and zlnreinforced TPOs. Also,

the term TPO is confusing and very vague. The standard should consider differentiating

the different types

of

on

KEYWORDS:

thermoplastic poly~lefin, TPO, poIyethylene, polypropylene, flexible polyolefin,

P O ,

mechanical analysis, DMA, thermal analysis, themogravimetry

1. Introduction

TPO

md the use of this

family

with

any

has

curve associated

with the installation and maintenance of TPOk. Also, little information is available to the

general public r e g d i n g their durabiIity.

The objective of this study is to investigate the long-term performance of in-

service thermoplastic olefin or polyolefin (TPO) roofing membranes. A range

of T O

membranes with different reinforcements, weave styEes and polymers is covered. ms

paper

is

analysis) properties of the year-0 membranes. The techniques used in this study were

chosen because they

allow

any,

results will form a baseline for the weathered membranes to be compared against in the

subsequent stages.

1.1 Background

Thermoplastic olefin or polyolefin (TPO) membranes have been available and in-

use for several years. The focus of this paper will be TPO products available in the United

States. At first, only n couple manufacturers produced a hand-full of products. Within the

last few years, other manufacturers have come on-line with new product offerings.

IRC-IR-768 Evaluation of Thern~oplastic Olefin (TPO) Roofirlg Membranes

There are essentially two classes of polymer-based

roofing

rhemzosets ('I3) and thermoplastics (TI'). Thermosets include EPDM, chIorosrrlphonated

polyethylene (CSPE) and neoprene, Thermoplastics include a wider variety of systems

such as TPO's, poly[vinyl chloride],

(PVC);

W E ) ,

thermoplastics share some

of

have very different chemical and physicaVmechanica1 properties.

It is beyond the scope

TP

label dl of these products simply as

TP

The term olefin i s an old chemical name for any molecule contaidng carbon-

carbon double bonds. The modern name for

this

There

are

than

polymer; and, Type 2 contains between 50 and 95% ((mass percenlt) TPO polymer. The

polymer itself is

not

AIE

is

shall

contain the "appropriate" polymers. Using this definition in combination with the definition of olefin, there is an endless list of chemicals which would fit in this standard

(e.g., polyethylene, polypropylene, isobutyIene, etc., as well as their derivatives) There are a few papers written

on

UnfortunateIy, they do not provide specific details on the chemical composition

(although, reference 3 does menti on that acetates, acry lates or octenes are blended together). In fact, these references are somewhat confusing because of the terminology they

use.

are

one

po1yethyIene-based

(FPO-A) [1,3] while the other process known

as

FPO-A is alloyed with polypropylene. Manufacturers of either system report similar

mechanical and chemical properties. However, to date, there is insufficient information to determine the durability of the two types.

TPO membranes, in general, have the potentid to fulfill many of the reqvirements

that are desirable in the roofing

rnarketpIace.

to adhesives, and no external plasticizers added to the compounding.

I.I.1 Field Observations

The last several years have provided insight into the application of TPO

membranes. What became apparent immediately was that the TPO membranes do nut

have the same feel (e.g. flexibility, texture, etc.), handling, and application as the other thermoplastEc membranes

on

The

than some other comparable products. While flexible, the TPO membrane has a rather

rigid feel. The

TPO

not

attributes of

TPO

*

than

IRC-IR-768 Evalrratinn of Thernt onlastic Oldin f TPO 1 Roofirla Menthrones

Lower cost than some other hot-air welded membranes;

Mechanically fastened systems work well in recover applications;

Non-reinforced membrane is easy to form for detailing;

Cold welds frequentIy occur; the start and stop positions of the robotic welder arc especially critical, as well as t-seams;

N m o w welding window between coId welds and scorchhurn-through; Stiff membrane that does not relax well;

Failure of bonding adhesive which will not stick to the membrane;

Noticeable changes in look (color variance) and feel of membrane (texturelfmish), as

manufactured, over time;

Membrane, at times, requires soIvent wipe before welding;

Black membranes are more difficult to weld than white membranes;

Black membranes are hot to the touch after exposure to the sun;

Membrane caulk a problem; on hot days caulk would be runny;

Cigarettes burn holes in membrane easily, noted to be more severe than other

themeplastic membranes;

Problems with re-welding membrane after exposure to sun to make repairs.

In

'tontractor-friendIy." Some of these items may be attributed to the natural learning curve associated with new products, however, for some applicators, ease and satisfaction with the TPO membranes has yet to reach a comfort level.

Aside from the installation issues, there nre what appear to be performance issues as well. Some of the potentially problematic performance attributes that have been

observed include:

Cold welds frequentIy occur resulting in seam voids that leak; Burn-through of membrane during welding results in voids; Failure of bonding adhesive, flashing membranes delaminate/sag;

Color change noted in light-colored

membranes after exposure

sun;

Cigarettes burn holes

in

membrane easiIy

-

users not

respectful of membrane;

Problems with re-welding membrane after exposure to sun to make repairs.

In

instances, adhesive was

required

repairs,

The first appearance of a "TPO-type" roofing product in the W.S. was in ca. 1987

13.

The

from

EPDM

a

hewn as dynamic vulcanization. h the generic classification of thermoplastic

elastomers, the manufacturer reports that the proprietary EPDM polymer is considered

okfinic. The membrane reportedly contained ne fillers or plasticizers.

The

[a.

remained on the

until late 1990, when the company and Ithe product reportedly left the market.

IRC-IR-768 Eval~iarion of Thern~oplasfic Olefin ( P O ) Roofing Membranes

h 1991, another company with a new product entered the market that reportedly had the benefits of EPDM and hot air weIded

seams.

membrane as being EP elastomeric, thermoplastic alloy (ETA), containing no plasticizer

[q.

h

weatherability of rubber with the heat weldability s f a thermoplastic [PI. Listed as an ethylene propylene rubber ('EP), "the base product is made

by

polymerization

of

[IO].

The most current thermoplastic alefin into the market appeared in 1996 with an

ethylene propylene rubber

(EPR)

1.

The marketing

of this

P O

the EPDM-lik characteristics of being rubber with the benefits of welded seams. Another focus has been on the chemical resistance attributed to the olefin side of the

polymers. Unfortunately,

some

regarding the use of the term rhermoplastic (TP). It is important to remember that

TPOs

are

but

thermoplastic non-TPO single-ply membranes (e. g., blends and alloys) market their

product as

TP

2. Experimental

Ten

(see

three

(F2)

for these

J02-S02-MI and J09-SO1

-OK).

Figure 1 Definition of dinerent regions in a membrane sample with a seam.

TABLE 1 Description of TPO sulnples.

*Full Receives sunlight all day. Shade Receives sunlight to varying degrees due to

adjacent trees/structures. Covered Receives very little sunlight. Note: The slope on all projects was noted to be 114" per foot or Iess.

The machine and

cross

no

on

directions were assigned arbitrarily. Specimens were taken in both the machine and cross

directions. When there was a lack of membrane, priority was given to specimens in the machine direction.

Visual examination indicated that the =inforced sanzpIes consisted of fiber

reinforcements bonded in different weave styles and sandwiched in several types of TPO

sheets. A summary of the components in the membranes is shown in Table 2.

2.2 Tension Testing of M e ~ n bmne Satnples

2.2.1 Specimen Preparation

Although method A (grab test method) of ASTM

D751

proposed TPO

standard)

amounts

some

the samples were not sufficient to prepare the necessay number of replicate specimens.

To

A hydraulic die press was used to cut dumbbell shaped specimens from the non-

reinforced membranes using die C as specified in ASTM D412. Ten specimens were

prepared in each of the machine and cmss directions for each test temperature. The

thickness of each specimen was measured, taking an average of five points measured

along the length of the specimen, using a digital micrometer.

TABLE 2 Summary of the cotnpanents in the TPO roofing membranes.

N/A Not Applicable C1 Yellowish brown coating

NC Not Coated

C2 Clear coating

Strip specimens were cut fiom the reinforced

membrane

dimensions

was, where possible, prepared in the machine direction (and where possible, also in the cross-machine direction) for each test temperature. The thickness af the specimens

was

measured using a digital micrometer. The width of the specimens was measured using a

digital calliper, taking an average

of

AII samples were tested using an hstron 4502 Automated Materials Testing System. The room was kept at a constant temperature of 23

+

humidity of 50 f 5%. Pneumatic grips were used for the non-reinforced specimens while

hydraulic grips were used for the reinforced specimens at room temperature. However,

the grips could not be used for low temperature testing. Instead, as shown in

Fig.

pair

with

This

mounted on the testing machine. An Instrwn environmental chamber was used

for

conducted at -40°C

2

The non-reinforced specimens were tested at a constant crosshead speed of 500

rnmlmin using a I-kN capacity load cell.

The

capacity load cell. The gage length was 75 mrn. Specimen ends were also folded in the

grips to prevent reinforcement slippage during testing (Figure 2).

An hsmn

XE

specimens at room temperature. However, crosshead displacement was used to

approximate the specimen dongation at -4U°C due to limited space in the environmental

chamber. Crosshead displacement was

also

data acquisition system. The sampling rates were 25 and 50 points per second for the

room temperature and the cold ternperature tests, respectiveIy.

2.3 Dynamic mechaaicul analysis

@MA)

A Rheometrics Solid Analyzer RSAII equipped with a control computer, a

mechanical cooler and environment controller was used to measure the glass transition

temperature of the samples.

Two

samples (A and B), placed an the dual cantilever fixture and coaled to -70 "C. After

allowing the temperature to stabilized for about 1 minute, the temperature program was

started. The samples were run in duplicate. Test type, dimensions of the specimens and

experirnen tal parameters are summarized below.

Geometry: Specimen dimensions: T a t Frequency: Temperature range: Ramp rate: Soak time:

Time pet measurement: Strain:

Auto Tension Adjustment:

Au tostrain:

Dual cantilever

Length: 36.6 mm (fixed)

Width: 4.9 mrn

-

-

mm

Dynamic temperature ramp 1

Hz

-70 'C to +30 or +I0 "C

2 "Clmin

30 sec

60

0.02-0.2% (depending

on

OFF

XRC-IR-768 Evaluation of Tltennopfastic Oleifin (TPQ) Roofirrg Membraria~ LOAD 4 SCREW - . STEELTAB

+

Figure

2

A Seiko simultaneous thermal analyzes (STA) (TGDTA320) equipped with a

HP

workstation model 712160 was used to determine the thermal stability of the samples. A sample mass of

E

pan containing the sample was placed on the sample holder of the STA and the balance

was allowed ea stabilize before starting the program. The temperature was increased at a

rate of 20 "Urnin, from room temperature to 1000 "C using 150 mL,min of ultra high

purity nitrogen.

IRC-IR-768 Evaiuarion of ThermopEasfic Olefin (TPO) Roofing Membranes

3. Results

Typical force-displacement curves of the membranes are shown in Figures 3-4.

The non-reinforced specimens (Figures 3 - 4) behaved in an elastic manner at 23°C. They

yielded and stretched extensively before they finally broke. At

-40°C,

brittle. The specimens yielded and necked, and broke with little stretching

(Figure

On

-IA

For

J05,

J08,

J09 & JIO), the load went through a peak and a sudden drop before reaching a plateau which was about 15 - 20% of the maximum load (an example,

JO

Figure 5). Except for J08-SO1-DC which was relatively brittle, all samples behaved elastically at 23°C with yielding and stretching exceeding 300%. They became brittle at -

40°C and broke cleanly cross the width with stretching not exceeding 30%.

For the specimens reinforced with random short glass fibers mat (506-501-IA and

J07-SDl-DCS, the

load

and

(Figure 6 ) . The load drop (5 - 10%) was not significant compared to that of the sarnpIes

reinforced with continuous polyester fibers (80 - 85%).

In

again

before

The tensile strength and the ultimate elongation of the non-reinforced membranes were determined. The tensile strength is defined as the maximum tensile force divided by

the cross-sectional area (i-e., width x thickness)

of

while

percentage as measured by the extensiorneter. For the reinforced specimens, the breaking

strength and the elongation at break were determined. The breaking strength is defined as

the breaking force of the reinforcement divided by the cross-sectional area while the elongation at break is the ratio between the gage separation at break and the initial gage length in percentage. Note that the breaking strength

in this paper

in

stress instead of h a d as In the standard. This definition eliminates effect of the difference

in thickness variation of the non-reinforced

membranes. These

parmeters

and

of

at the two test temperatures (Table 5).

MAXIMUM

0 50 1Q3 150 200 250 300

DISPLACEMENT (mm)

Figure 3 Typical force-displacenaen f curves for J03-SO J-IA.

0 50 100 150 200 250 300

DISPLACEMENT (mm)

Figure 4 Typical force -displacement curves for J#-,901 -IA.

IRC-IR-768 Evahation of Thermop!astic Olejin (TPO) Roofing Membranes 100 200 300 DESPLACE~MIENT (mm) BREAKING FORCE M, -40°C M, 23°C y 23°C

Figure 5 Typical force-dkp Lacement curves for 'JOI -501

-GO.

. . -u_---.I I 0 0 100 200 300 4M) 500 600 ₇₀₀ DISPLACEMENT (mm)

-

-.

!

t

Figure 6 Typical force-displacement curves for

JM-SO1

-DC.

'FABLE 3 Mechanical properties of rhe non-reinforced

TF

0

For the non-reinforced specimens, the proposed ASTM specification requires a

minimum thickness far the overall sheet of 1.0 mm. It also specifies a minimum tensile strength and ultimate elongation of 12.0 MPa and 500%, respectively at 23 "C. All of the

samples meet the minimum thickness, elongation and tensile strength requirements at this temperature.

Membrane J03-SOI-IA performed better than JM-Sol-IA at room temperahre,

with higher

smngt'h

(Figures

-

40°C,

tensile strength

both

membranes doubled.

J03-Sol-IA

almost zero - a drop of more than

100 times

JM-Sol-IA

by about 30% only.

For the reinforced membrane samples, the draft ASTM specification requires a

minimum thickness for the overaIl sheet of 1.0 rnrn. Only membranes J06-S01-IA, JOT-

Sol-DC, 908-Sol-DC and J10-Sol-IA meet that specification. The mernbranes reinforced

with the polyester

scrims

and elangation

values

reinforced

with

random

short

mat

as

T h e

MPa while that of the pdyester scrims reinforced

ones

(Figure 7). The elongation at break was less than 10% for the short fiber glass mat reinforced membranes but that of the polyester scrim reinforced ones was at least 20% at

23°C pigure 8).

TABLE 4 Mechanical properties of the re irxforced TPO roofing membranes.

p u p 9 9

n r r

pi;;

d d D d d ;--

IRC-IR-768 Evaluation of Thermoplastic Olefln {TPO) RoofSng Membranes

ULTIMATE ELONGATION

I

ELONGATION AT

BREAK

(%)

Figure 8 Ultimate elongation Iclongation at

break

IRC-R-768 EvaIua r ion of Themoplasric OlejTn (TPO) Rooflng Membranes

TABLE 5 Listing of TPO membranes irz order of decreasing elongafion af diflererrt resr

temperatures.

The polyester scrim reinforced membranes were stronger (10 -

30%)

machine than in the cross direction at both test temperatures. The elongation at break in

the cross direction was at least

as

On

random short glass fiber reinforced membrane JOB-Sol-IA was stronger in the cross than

in the machine direction. The elongation at break was the same for both directions. At -40°C, the increase in the breaking strength of the polyester scrim reinforced membranes

and the decrease in elongation were statistically significant.

-..--..--- I 3.

Three types of polyester reinforcements were used in these membranes, nameIy, a

coated scrim in a plain weave style, an uncoated scrim with intersecting tows held together by fine polyester fibers and a coated scrim in undetermined weave style (Table 2). The membranes reinforced with the coated scrim i n plain weave

(JOI,

J05

J09)

reinforced

with

fibers

(JIO-Sol-Lk)

around

types was the membrane reinforced with the coated scrim (J08-Sol-DC) which had n

breaking strength of 20 ma.

JOS-SO 1-SD

J09-Sol-OK

- - - " " * - - -

J08-Sol-DC

- - - 2 - . . . - - . - m - - - L . . - - -

After the reinforcement broke

(break

polymer matrix only. The polymer stretched and thinned down a great deal before final

failure at 2 3 T . The ultimate elongation, as defined by the ratio between the final and the

initid grip distances, is a measure of stretching ability of the polymer matrix. This

property can

be

by

curves divided by the initial grip distance of 35

mm.

used in the short glass fiber reinforced membranes (506 and 107) was especially high in

the machine direction [over 600%). However, the same colored TPO used in the

membrane J08-Sol-DC had

an ultimate

note

-

or about 4

-

IRC-Building Envelope Program Roofing Sub-Program Page 16

4. J06-Sol-IA

All membranes but the polyester

scrim

membrane J1OSO1-LA

a similar manner in both the machine and cross directions. Unlike the others, when

membrane J10-Sol-IA was stressed in the machine direction, small holes started to

develop on the white polymer sheet at the intersection of the perpendicular tows after the

fiber tows in the loading direction broke. More holes were developed as the specimen was

stretched. Those located along the fiber tows in the cross direction coalesced until the

white polymer sheet broke across the specimen width,

The

direction, then exposed, started to unravel and finally fell off the polymer sheet. At this point, the black poIymer sheet, which was usually still intact, continued to stretch and separated the white polymer sheet into small pieces. The specimen stretched and thinned down to a high degree

such

polymer did not stretch as much after the fibers tows in the loading direction broke. The

polymer sheets findly broke and the polyester scrim delaminated almost completely h r n

the polymer sheets.

3.3 Dynamic mechanical analysis (DMA)

A typical DMA plot is shown in Figure 9. The

T,,

Hz, was obtained from the intercept of two tangents on the storage moduIus (E') and the maximum of loss rnoduIus (E"). The glass transition for all samples ranged from 4 6 "C

to -42 "C using E' and

-37

E".

_-W,

which showed a T, of -58

"C

-54

Table 6).

$ (Bottom)

IO3-SO1IA JWS01-IA

The samples show from one to four weight losses in

the

full

range

analysis (see Table 73. Some display a small weight loss (4%) in the 25 - 340 "C region. This may be due to the loss of stabilizers. The second weight loss (6595%). resulting

fmm

weight loss shows two DTG maxima. One between 330 "C and 430 "C and the other JOS-SO 1 -DC

J09-SO1-OK

J 10-Sol-IA

IRC-Building Envelope Program Roofing Sub-program Page 17

5.05 5.15 5.11 5.14

1

1

I R C - W 6 8 EvaCuarion of ThcrrnopIrastic Olefin (TPOJ Roofing Membranes

TABLE

TABLE 7b Two resolved w e i g h losses.

TABLE 7c. Three (one resolved and two unresolved) weights losses. Sample

m

JWSO1-IA JOS-Sol-DC

' ~ o t e : the 340 to 1000 OC region confains two distinct but unresolved weight losses

TABLE 7d Four (two resolved and

two

Loss

*NOW: the 340 to 550

"C

Residae

947

IRC-Building Envelope Program Roofing Sub-program Page 18

I 25-417 "C 33.2

-

-

I R C-I R-768 El~uiualio~ of Tllernmplas~ic OIejir~ (TPO) Rnojirlg Mernbrarr es

Figure

9

Figure 10a Typical

TG

1 R C-I R-768 E ~ ~ a h t a r i o ~ of Tlrern~nplastic OleJt~ (TPO) R o o m MentBmtrcx

NRC-IRC

Figure lob Typical TG plotfor TPOs showing three weight losses.

I 1 -20.0

-51

0 200 4 0 0 50 0 BOO 1000 1206

T e m p . C

Figure

PRC-IR-768 Evaluation of T!termoplas~ic Olefin (TPO) Roolfing Men1 bmmes

between 430 "C and _{600 ' C , except for J03-SOI-IA and J08-S01-DC samples, which}

shows only one weight loss between 340 "C and 600 "C. The third weight loss (1-8%) occurs in the 600-4000

"C

occurred in the 25 - 417 'C (33%) and 417-600 "C regions (61%). Typical plots nse

shown in Figure 10.

4. Discussion

For the non-reinforced membranes tested at -40°C, J03-Sol-LA was 30% stronger

than JW-SOI-IA, but had almost no ductiIity (Figure 3). The strain energy of J03-S01-IA

(the area under the force-displacement curve) is low. On the other hand, the swain energy remained high for membrane J04-301-L4 at -40°C (Figure 41, perhaps making it more suitable than 503-501

-L4

As expected, the membranes reinforced with continuous

fibers

breaking strength than those reinforced with random short fiber mat. The

membranes

reinforced with the coated scrim in plain weave style were stronger than those reinforced

with the other two polyester scrims. To find out if the difference in strength was due to

the difference in reinforcement strength or the

amount

different weave styles, the number of fiber tows across the width of the specimen was determined. The strength per fiber tow was found to be roughly the same (Table 8). As a result, the variations in the breaking strength were due to the difference in weave style.

TABLE 8 Determination of

rhe

Breaking tows across Strength per

Reinforcement Strength width of fiber tow

Types Membranes (MI%) specimen (MPa)

JO 1 -SO 1 -CO

Coated (yellow) scrim J02-501-MI

J02-S02-MI 36+5

9-

+

in plain weave style

JO5-Sol-SD

J09-SO 1 -OK Uncoated scrim with

intersecting tows held

B

together by fine

polyester fibers

Coated (clear) scrim of

undetemi ned weave

IRC-IR-768 Evaluation of Themsplosric Ole fin (TPO) Roefinn Membranes

TOP VIEW

$prnVrn?%

END VIEW OF MD

Figure 1 1 Deformation of the reirf~rcerneaC sbr~ciure during l'ensil e testing of membrane JIO-$01-IA.

The difference in

an

510-Sol-IA

together by fine, continuous polyester fibers

(Figure

in the machine dimtion, the fine fikrs stretched and tightly held onto the tows in the

cross direction. This created high localized stresses at the intersections. As a result, holes

were

these points. They

membrane

failed.

On

localized stress points were formed

since

direction by sandwiching instead of pulling them.

For the spechens reinforced with continuous polyester fibers, except membrane

J08, the load first went through a peak and a sudden drop, which corresponded to the

breaking

of

reinforcement, The

stretching. It is interesting to note that the load at the plateau region of the force- displacement curves was between 100 - 200 N, or about 4 - 8 ma, for every membrane,

continuous fibers or short fibers alike, tested at 23OC. Since reinforcement sliding should be a function of interfacial adhesions and reinforcement structure, this constant

force

The breaking strength of the polyester scrim reinforced membranes increased by about 20

-

-40°C.

membrane

became brittle and the ultimate dongation (Figure 5 ) reduced more than 15 times. Since

IRC-ZR-368 Evaluation of Themnplasfic Olefit1 (TP 0) Roof~rrg Mer~lbranes

the ductility of the matrix governs that of the membrane, it is recommended that polymers with superior cold temperature mechanicallchemicaI properties (e.g., higher elongation) be used in membranes intended for cold temperature applications. The glass transition

temperature

polymer.

For

fiber reinforced membranes,

onIy

were sandwiched between the two

polymer

themselves with the polymer in the direction of the applied stress. As a result the breaking load

(for random

breaking) is only slightEy higher than the load in the plateau region. Although the cold temperature mechanical behavior was not tested due to the I i d t e d membrane samples, it is expected that the membrane properties at cold temperatures will be dominated by the cold temperature properties of the polymer.

It is necessary to

stress

testing. Preliminary tests performed en specimens without folding the ends (with exposed

fiber ends) in the grip were not successful. Cracks were initiated at the grips due to high stress concentration and there was almost no stretching of the membrane. The piece of

polymer sheel under one set of the grips was pulIed away from the rest of the specimen,

sliding dong the fiber rows. This force represented localized breaking of the polymer

sheets and sliding of the reinforcement only, which is far from the true tensile strength of the material, By folding the ends of the specimens in the grips, localized reinforcement

slippage under the grips was eliminated. The load was therefore transferred to both the

reinforcement and the matrix in a uniform fashion. The breaking strength is a h e

representation

sf

the fieid

may involve some

of

values reported here. Therefore, it is necessary to understand that the results reported reflect the "best" scenario

only.

Thermogravimetq clearly shows that there are at Ieast four different types

sf

TPOs

based

TPO is

generic

lass

useful in

atlempting to interpret the mechanical results. For example, both 503 and 5 0 4 are non-

reinforced, yet

as can

seen

Figure

JQ4

properties than J03. As can be seen from the

TG

different for these two products.

Perhaps the proposed ASTlVI standard should address the different types

of

Although this may seem like a nuisance, there is the risk that should a particular type of TPD encounter problems (e.g., shortened life cycle) then it is possible that all the TPOs

will be seen

as

on the durability of these membranes and more research is required in this area.

Cold temperature flexibility was, essentially, monitored by using the glass

transition temperature. The

E

The one exception is the 504 specimen, which had a

Tg

JQ4

rncrnbrane also had the highest elongation at 4 0

"C.

retained much

of

exposure,

5. Conclusions

1. All the non-reinforced membranes meet the minimum thickness, elongation and

tensile strength requirement as specified in the draft ASTM standard. 2. The term TPO is confusing and

vague.

3. Non-reinforced membrane J03-SO 1 -IA had higher strength and elongation than

membrane 504-SO I -IA at room temperature. At

4O0C,

JWSO1-IA remained relatively ductile. Due to its high strain energy, J04-Sol-IA

could be a better choice for cold temperature applications.

4. Reinforced membranes JOG-SO I

-1A,

-IA

5. The polyester scrim reinforced membranes were superior in tensile strength and

elongation

as

This was to be expected because the function of the glass fiber is to dimensionally

stabilize the membrane and reinforce the polymer while the role of the polyester scrim is to reinforce the membrane for mechanical attachment.

6 . The polyester scrim reinforced membranes had a breaking strength of 20

-

increased

machine than the cross direction at both test temperatures.

7. The number of fiber tows per unit area appears to govern the breaking strength of the

polyester-reinforced membranes. The strength per polyester fiber tow was roughly

estimated to be 3.2 - 4.3

ma.

The

a

8. The membranes reinforced with random short glass fiber mats (J06-Sol-IA and J07-

SO1

-DC)

than

10%. Those of the polymer mainly govern the tensile properties of these membranes. The membrane was about 20% stronger in the crass direction.

9. The results reported assumed minimal reinforcement dippage, thus representing the

"best" tensile performance where all the fibers were uniformly stressed. However,

some

6. Recommendations

I. The proposed ASTM standard should consider defining the breaking strength in terms

of "stress'Yinstead of

load.

This would eliminate

of

should consider incorporating strain energy requirements at low temperatures (e-g.,

-40 C ) in the standard.

2. The proposed ASTM standard should consider using thermogravimetry and glass transition temperature to differentiate the different types of TPOs.

For example,

3. If the ASTM standard task group insists on using the term uiefzn in the standard's name, then the task group shouId consider using the name Flexible or T h e m p h s t i c PoEjol~flrr in the title. This would be in-line with the terminology used in Europe (i-e., flexible polyoIefin, P O ) . Furthermore, perhaps manufacturers should clearly state if

their product is a polypropylene- or polyethylene-based system,

7.

Future

This is the first part o f a multi-year research project on thermoplastic polyolefin

membranes. Research currently being investigated by the authors includes:

1 . Comparison of different polymeric membranes for competitive specifications is becoming more commonplace especially considering the multitude

of

selecting comparable thermoplastic membranes of different polymeric composition.

Mile physicd property test methods are somewhat common among the single-ply

ASTM standards (e,g.,

PVC,

for the conditioning

(e.g., aging or weathering) of the samples. Thus, as a means of assisting the users of

these

helpful

a) The heat aging testing criteria would be standardized between the various

thermoplastic membrane standards to compare the stability of the compound.

Currently, the range in temperature between standards

is

70

"C

duration

of

from

standardize at one temperature and preferably one exposure period

(e.g.,

for 28 days).

b) The artificial weathering testing criteria would be standardized between the

various polymeric membrane standards

for

range in temperature between various ASTM standards is from 63

OC

In

some cases, the bulb type is different between standards (UVA-340 vs. W-

313), along with duration of exposure (4000 h to 5000 h). ?'he recommendation

would be to standardize at one bulb and preferably one exposure condition.

2. Once the weatherindaging program has been established the allowable change in

Ts

and weight loss needs to be determined. The proposed standard would then be able to

incorporate these values as a means of monitoring agingweathering of membranes.

IRC-IR-768 Evuhariotlr oaf Thenrtoplasric OEcfin (TPO) Rwfing Membranes

8. Acknowledgment

The authors wish to thank those contractors, building owners, and Benchmark

staff who collected or sent in samples of projects for this research,

9. References

[I] Beer, Hans-Rudolph, "Flexible Polyolefin Roofing Mernbrmes Properties and Ecological Assessment," Proceedings of Warerproolfing Technology & The

Environment, gth International Waterproofing Association Congress, Amsterdam,

1995, pp. 8 1-89.

[2] de Palo, Roberto, "Flexible Polypropylene Alloys: A New Generation of Materials for Waterproofing Applications ," Proceedings of Waterproofing Technology d 7 h e Environmenr, 9Ih International Waterproofing Association Congress,

Amsterdam, 1995, pp. 309-320.

[3] Beer, Hans-Rudolph, "Longevity and Ecology of Polyolefin Roof Membranes,'" Proceedings of the Fourrh Inremational Symposium on Roofing T e c h ology ,

Gaithersburg,

MD,

141

K.,

Int~rface

(Journal

[5] NRCA Rouftng Muterials Guide, Vol. 1 1, August 1987, National Roofing

Contractors Association, p. 92.

6 Mark

IV

FIex Shield InternationaI, 1987.

171 Versiweldm Roofing Sysfem, product literature, Goodyear, 199 1. [8] Versiweld

Roofing

/

[l 11 GenFlex TPO, product literature, GenCorp, 1997.