EPDM Roof Sheeting

ROOF SHEETING

Submitted by: Hamzah Mukhtar

Contents Introduction

Properties Required For Roof Sheeting

Material Selection

Ethylene Propylene Diene Monomer (EPDM)

Properties of EPDM

Recipe

Plasticizers and Processing Aids

Mixing and Compounding

Sheet Production

Recycling

Results

Conclusion

1

EPDM Roof Sheeting Introduction

EPDM roof sheeting offers any homeowner, builder, or roofer the means to reliably and permanently

waterproof low-slope roofs, rooftop decks, and green roofs. In most cases a single sheet is custom fabricated of

the size of each roof, eliminating the risks associated with field seaming. Installation is easy, clean, simple, safe

and time saving: no heating torches or hazardous adhesives are required. Field seaming is usually necessary

due to limited sheet sizes of EPDM. [1] The incorporation of mineral talc coating in the manufacture of this type

of EPDM makes it hard to properly clean the sheets for effective seaming and flashing. EPDM roof sheets have

been used successfully to large commercial buildings.

Properties required for roof sheeting

For roof sheeting, a material might fulfill specific properties required depending on the environmental

conditions in which they are to be used in. Some properties are mentioned below which are required in a

material to be selected for roof sheeting depending on the environmental conditions of subjected areas.

o Ultra violet resistance o Highly Durable and long service life o Thermal resistance (Insulation properties) o Abrasion resistance o Oil resistance o Oxidation resistance o Weathering and ozone resistance o Resistance to Heat ageing o Cold stiffening o Water resistance o Fire resistance o Rebound elasticity in cold and heat o Resistance to cyclic fatigue o Compression set o High Friction o Good bonding to other materials o Easy installation o Easily repairable o Non toxic o Price

Material Selection

Proper material selection is the most common problem encountered by the designer. Among the various

parameters, that must be taken into account for material selection are physical properties, structural strength

specifications, corrosion resistance, fabrication characteristics, thermal properties, composition and structure

of material and the most important is the cost of material. [2]

The requirement of the properties that a material must have largely depends on the environment in which the

material is subjected to be used. Material selection begins from the determination of operating conditions,

pressure, temperature, equipment, and many other factors in the process.

All the required properties cannot be fulfilled by a material. For example, good thermal conductivity and

thermal insulation properties cannot be attained from a single material. A chemical resistant material might

2

have poor physical properties. Also, materials that have good mechanical and chemical properties may be too

expensive.

The initial cost of the material does not provide the whole economic picture. It is possible that the expensive

material may be more favorable than the less expensive material. The difference may lie in the high processing

cost of less expensive material. Any material may possess desirable and nondesirable properties with respect

to the specific application, the selection of materials is reduced to a reasonable compromise.

Ethylene Propylene Diene Monomer (EPDM) Rubber

In 1962 EPDM was first introduced in America and its commercial production started later on in 1963. [3]

EPDM roof membrane has been manufactured over 50 years. It has a proven performance record and quality

control process. EPDM uses less energy to manufacture and is installed on most flat roofing systems. Average

EPDM roof system installation are a safe process as there is no open flame and no extremely heavy machinery

is required. EPDM is also a lightweight single-ply membrane which means less weight on the building structure.

[4]

There are two types of ethylene propylene rubber EPM and EPDM. EPM stands for simple copolymer of

ethylene and propylene and in case of EPDM, the “D” defines the third co-monomer of non-conjugated Diene,

and it causes unsaturation into the molecules. Dienes are so structured that only one of the double bonds gets

polymerized and the other unreacted acts as a site for the sulfur crosslinking and its does not become the part

of the polymer backbone but as a side group. As a result the EPDM retains excellent ozone resistance. [5]

Different dienes are used in order to attain specific vulcanization behavior. Most common ter-monomer used

is ethylidiene norbornene (ENB) because it is very reactive towards sulfur vulcanization and it incorporates

very easily.

[6]

EPDM can be manufactured with different ethylene and propylene ratios. Increasing content of ethylene

increases mixing behavior but also has effects of decreasing low temperature properties. Commercial grades

of EPDM have 50% to 70% of ethylene. [7] There are several other possible variations in EPDM which effect

the resultant properties of the polymer like molecular weight and molecular weight distribution.

[8] Structure of EPDM

3

Properties of EPDM

Some properties of ethylene propylene rubbers are given below. These properties may vary in accordance with

the compounding or composition of the sample, since they are obtained from specific samples. [9]

Elasticity and strength: Good performance under maximum working load.

Multidimensional strain - High resistance to ground movements and settlement.

Puncture resistance

Good flexibility up to the maximum tensile strength even at low temperature.

Lay flat characteristics - adapts to any substrate shape, due to superior stretching properties.

Insensitive to temperature variations.

Thermally seam-able, even by freezing weather.

Optimal surface friction characteristics - soft textured rubber surface provides high interface friction.

Excellent UV and ozone resistance ensuring good service life even in case of severe weathering conditions.

Good resistance to chemicals

Prefabrication of large panels to specified sizes according to site drawings. This allows reducing field seaming and installation time.

Versatility of shape.

Long service life.

Low maintenance.

Recipe

[17]

Typical Recipe for Sheeting

4

Reinforcement

EPDM needs reinforcement to be of practical value as the mechanical properties of the unfilled rubber are very

poor. Carbon black reinforcement causes a partial immobilization of the polymer chain segments.

Reinforcement by carbon black and vulcanization generates a three dimensional viscoelastic network that

converts softs elastomers into an elastic and strong material. Surface area of the carbon black is much

important factor which defines the availability if the surface area for interaction with other materials present

in a rubber compound. [10]

Carbon black has a variable chemical nature. Elastomer of a polar nature will interact more strongly with filler

surfaces having diploes such as OH and COOH groups or chlorine atoms. Carbon blacks are generally conductive

due to their highly conjugated bonding scheme present in the crystalline regions. Increasing the surface area

and structure both cause to enhance electrical conductivity. [11] The large average particle size and low level

of agglomeration can result in the lowest amount of inherent conductivity in the carbon black. [12]

Dispersion of carbon black must be done adequately for obtaining the maximum benefits of carbon black

reinforcement. Breakup of the carbon black pellets is the initial step for mixing into a polymer. Small particle

size carbon blacks show difficulties in incorporation. High-structure blacks contain high void volume to be

penetrated by rubber due to which it takes long time to incorporate. If high-structure carbons are once

incorporated then they disperse more rapidly than low structure carbons. [13]

[14]

Sketch of entanglement of EPDM chains on carbon black

Plasticizers and Processing Aids

EPDM is an elastic polymer which is usually processed without plasticizers and EPDM is generally offered as plasticizer free alternative product but there are some specific applications in which plasticizers are used. The main objective to use plasticizer in a formulation is to increase the flexibility. Plasticizer contributes in the development of surface tack and for EPDM surface tacking property is very important. [15] Most widely used plasticizers for EPDM compounds are Naphthenic Oils because of their reasonable cost and they provide best compatibility as well. For higher temperature applications and for color compounds paraffinic oils are selected because of their good UV resistance and low volatility. Some paraffinic tend to bleed from cured high ethylene EPDM compounds and if such oils must be used then replace 20-25phr part of high ethylene EPDM with EPDM having low ethylene content. As a processing aid stearic acid, zinc stearate and other internal lubricants are often included. [16] For roof sheeting paraffinic oil being low volatile and UV resistant is much suitable to long term aging conditions. [17]

5

Mixing and Compounding

Production of an EPDM membrane is to combine all the raw materials like filler, accelerator, processing aids

and plasticizers into a homogenous mixture. This is achieved by using high shear mixing equipment consisting

of enclosed chambers designed around moving rotors. This mixing equipment is generally known as Internal

Mixers (also called “Banbury mixer” after their inventor, Fernley Banbury). Generally the mixing process will

take about 3 – 4 minutes for each batch and reach a final temperature of 120 – 140 C.

This is generally a batch process, with batch sizes up to 1300 pounds. At the completion of the mixing process

the mixing chamber is opened and on a sheeting mill the final compound is dropped to form 8–15mm slabs or

sheets of compound, cooled and stored prior to the calendaring or rotor die operation process, where these are

converted into the final membrane form and dimension.

Raw material being fed into Banbury

6

Cross linking

The term vulcanization or crosslinking is usually related to rubbers or elastomeric materials. The cross-linked

materials forcibly retain approximately their original shape after a rather large mechanically imposed

deformation. Viscoelastic properties of vulcanizates are largely related to density of crosslinks. Chemically

producing network junctions by the insertion of crosslinks between the polymer chains is called crosslinking.

The process is generally carried out by heating the rubber (mixed with the cross-linker) in a mold under

pressure.

In the following figure the properties as a function of extent of crosslinking are shown

8-15 mm slabs or sheets of compound

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From above figure it can be observed that the static modulus increases with crosslinking to a greater extent than does the dynamic modulus. The dynamic modulus is a composite of viscous and elastic behavior, while the static modulus is a measure of only elastic component of rheological behavior. [18] Hysteresis is the ratio of the rate-dependent or viscous component to the elastic component of the complex modulus. It is a measure of the deformation energy which is not stored but which is converted to heat. Hysteresis is reduced with increasing crosslink formation. Tear strength, fatigue life, and toughness are related to the breaking energy. Values of these properties increase with small amounts of crosslinking but they are reduced by further crosslink formation. Properties related to the energy-to-break increase with increasing both the number of network chains and hysteresis. Since hysteresis decreases as more network chains are formed, the energy to break related properties reach a maximum at some intermediate crosslink density. The properties given in above figure are not only functions of crosslink density, they can also be affected by the type of crosslinks, the type of polymer, and type and amount of filler. [18] The first and by far the most important crosslinking agent is sulfur, which is relatively inexpensive and yet vital to the rubber industry. Efficient vulcanization can be attained by addition of a particular type of accelerator to the

rubber formulation, which avoids using elemental sulfur and has available sulfur atoms in its molecule. In such a case

the accelerator is now more appropriately called a crosslinking agent, which becomes a sulfur donor. [18]

[19]

In above figure the products and reaction mechanism of accelerated sulfur vulcanization of EPDM is shown.

8

Sheet Production

Because of the chance that there could be an imperfection in a single-ply sheet which could undergo some kind

of leak or propagation after installation. Generally EPDM is classified as a « single-ply » membrane, most

actually comprise of two plies of material to make one single ply to prevent an imperfection from occurring

through the sheet. [20]

EPDM roofing material can be produced by two methods, either by Calendaring or through a Roller die

extruder.

[20]

At this point of the process the EPDM is still uncured, which means that it can be molded or formed using heat into other shapes and is very tacky to the touch. EPDM at this stage is similar in consistency and tackiness to taffy. EPDM is then produced into two sheets which are laminated into one which is termed as single ply membrane. Due to space and handling constraints, EPDM is initially produced in maximum sizes of 10’ x 50’. While in its uncured state, the 10’ x 50’ panels can be spliced to each other one after another to produce a « master roll ». This is accomplished by moving the panels along an assembly machine, lapping them 2-3 inches, and then applying pressure to the seam area to splice or fuse the two panels together. [20] This process only takes a matter of a few seconds. Because the EPDM is very tacky and has yet to be cured, without some type of anti-blocking agent it would stick to itself if rolled up. So, a dusting agent is applied immediately after the panels are spliced and just before they are rolled up for curing. General dusting agents are Talc and Mica and in color both are white to silver. [20] After the master rolls are placed on what are called curing mandrels (similar to a cardboard core but made out of steel), they are loaded into an Autoclave. An Autoclave is very similar to a device we use in the kitchen- a pressure cooker. For a pre-determined length of time the uncured EPDM is placed into the autoclave to cure under heat and pressure. The curing process converts the material from an uncured state to a thermoset material, making it extremely durable and resilient to heat, ultraviolet exposure, ozone, rooftop traffic as well as extreme cold and hot temperatures. [20]EPDM can be exposed to temperatures approaching -16°C to over 93°C being the only membrane that can be exposed to these types of extremes without performance consequences.

9

After the EPDM membrane on master rolls is cured, it is slit to pre-determined dimensions. Some panels are as

narrow as 5’ and as wide as 50’ with lengths being up to 200’. [20]

[20]

Recycling

Sulfur vulcanized EPDM can be de-vulcanized by the incorporation of de-vulcanization agent, plasticizer and processing aids. In the reaction zone, high shear rate and elevated de-vulcanization temperature ranging from 230-300 C are applied to the mixture. [21]

Results

Samples taken from the roofs none of the showed visible indications of material damage. [22] All roofing

membranes were still fully performing their task of sealing a roof.

Conclusion

A correctly made EPDM roof sheet can provide long service life. The EPDM membranes have an excellent

elongation power to be able to resist the mechanical and thermal effects of exposure on flat roofs.

Master rolls being loaded into an « Autoclave » for curing [20]

10

References

1. EPDM Roofing Handbook (Conservation technology incorporation)

2. Materials Selection Book Nicholas P. Cheremisinoff, Ph.D.NOYES (P-51)

3. Rubber Technology by Maurice Morton (3rd Edition, P-260)

4. Godfrey Roofing Incorporation (www.godfreyroofing.com)



7. The effect of different nano-fillers on properties and mixing of EPDM (Master’s thesis TUT)


9. Prelasti Rubber Company (www.prelasti.com) 10. Rubber Technology by Maurice Morton (3rd Edition, P-59, 66)


12. THERMAX Article ( MEDIUM THERMAL BLACK N990 IN EPDM)

13. Rubber Technology by Maurice Morton (3rd Edition, P-70, 71, 273)

14. Article on “Effects of carbon blacks with various structures on vulcanization and reinforcement of filled ethylene-propylene-diene rubber” (College of Materials Science and Engineering, Nanjing University of Technology, Nanjing 210009, P. R. China)

15. Handbook of Plasticizers by George Wypych (ChemTec Laboratories, Inc.,Toronto Canada) (Ch-11, P-290)



18. Article on “INVESTIGATION OF PEROXIDE CROSSLINKING OF EPDM RUBBER BY SOLIDSTATE NMR” by Ramona Orza (Ch-1, P-6,7) (Technische Universiteit Eindhoven, 2008)

19. Article on “Chemistry of EPDM crosslinking” by M. Van Duin, Geleen (The Netherlands)

20. EPDM Roofing Association (www.epdmroofs.org) 21. Article on “EPDM Rubber Reclaim from De-vulcanized EPDM” (Chemical Engineering Department,

University of Groningen)

22. Article on “The study Evaluation of the useful life of EPDM roofing membranes” (Commissioned by the Trade Association of the German Rubber Industry, Frankfurt and performed by SKZ – TeConA GmbH, Wurzburg)

http://www.godfreyroofing.com/

http://www.prelasti.com/

http://(www.epdmroofs.org)/

Documents

EPDM Roof Sheeting