Thermoplastic Polyolefin (TPO) Roofing Membranes Minneapolis Commercial & Town home Roofing

Thermoplastic Polyolefin (TPO) Roofing Membranes Minneapolis Commercial & Town home Roofing

Commercial TPO Single Ply Roofing System

This Update reviews their characteristics and performance to date and clarifies some misunderstandings related to terminology.

A typical low-slope roofing system consists of three components: a structural deck, a thermal insulation barrier and a waterproofing membrane, which consists of reinforcing fibres or fabric sandwiched between two sheets of flexible matrix. The matrix material is either asphalt- or polymer-based (Figure 1). In single-ply membranes, the matrix is made of flexible polymer. The reinforcement provides dimensional stability for the membrane as well as strength to resist stresses in service. It is generally made of chopped short glass fibre strands packed in a mat, or continuous polyester fibre arranged in a grid or in a non-woven mat (Figure 2).

Figure 1. Categories of low-slope roofing membranes

Figure 2. Reinforcement commonly used in roofing membranes: (a) random short glass fibre mat; (b) polyester scrim; (c) non-woven polyester mat

There are essentially two classes of polymer based roofing membranes: thermosets (TS) and thermoplastics (TP) (see Text Box A). Thermoplastics soften when heated (this process is reversible) but thermosets do not. Thermosets include the commonly used ethylene propylene diene monomer [also known as ethylene propylene diene terpolymer] (EPDM), while thermoplastics encompass a wider variety of roofing membranes, including thermoplastic polyolefins (TPOs). All thermoplastic roofing membranes share certain characteristics, e.g. seaming can be done by heat welding. However, for the most part, they have very different chemical, physical and mechanical properties. It is impossible to explain these differences here, but there are different ASTM material-based standards for various TP products. To avoid confusion, one should not just label all of these products simply as TP products. TPOs differ from other TPs in several respects, and thus must be handled and applied differently.

Text Box A

Thermoplastics (TP) vs Thermosets (TS)

Schematic molecular configurations of (a) a thermoplastic and (b) a thermoset

A polymer is a long-chain molecule consisting of many (poly) small repeating units (mer) (

10 3 – 10 6 ) joined end to end. These molecules are tangled in a random manner analogous to cooked spaghetti.

Polymers can be classified into thermoplastics (TPs) and thermosets (TSs) depending on their mechanical behaviour on heating and cooling. TPs comprise long-chain molecules held together by weak bonds (Figure a). When heat is applied, the molecules slide past one another and the polymer softens. On cooling, the molecules cannot slide past each other easily and the polymer hardens. TS longchain molecules, however, are linked together by small molecules via strong chemical bonds, a process sometimes referred to as vulcanization (Figure b). This three- dimensional network is so rigid that the molecules cannot move very much even when the polymer is heated. Thus, TSs do not soften when heated.

Because of these differences, TP and TS membranes are bonded differently when applied. TPs can be bonded using heat welding: the hot air melts the polymer at the seam and the two strips of membrane become fused. TS membranes are usually bonded using adhesives or tapes.

Definition of TPO

Defining thermoplastic polyolefin is difficult. Thermoplastic is a generic term in polymer science; it encompasses a class of polymers that, as mentioned above, soften when heated in a reversible process. The term olefin is even more generic, being an old chemical name for any molecule containing carbon-carbon double bonds (the modern name for this family of molecules is alkenes). Any polymer formed by chemically linking up many olefin molecules is termed polyolefin.

According to the latest draft ASTM standard for TPOs, the composition is very non-specific. The standard states that TPOs must contain more than 95% by mass of TPO polymer. The polymer itself is not defined within the standard, which states only that the sheet shall contain the appropriate polymers. Because of this loose definition, there is an endless list of chemicals that would fall under this standard (e.g. polyethylene, polypropylene, and isobutylene, as well as their derivatives). Ideally, manufacturers would specify the exact polymer in terms of marketing and labeling.

There are a few published papers that attempt to explain the different types of TPOs [ 1 — 4 ]. One point is clear, however: unlike plasticized thermoplastic membranes, TPOs do not contain plasticizers (small molecules added during compounding to increase the flexibility of the product). Therefore, the problem of plasticizer loss associated with some plasticized membranes is eliminated.

Confusion in the Market Place

TPO roofing membranes have been in service in Europe for approximately ten years. The first appearance of a TPO-type roofing product in the United States was around 1987. As yet, little is known about their durability.

The confusion associated with TPOs comes from both the chemical terminology and the product marketing. The latter has promoted mainly the EPDM-like characteristics of TPOs, i.e. it being like rubber with the added benefits of welded seams (which EPDMs do not have). Also promoted has been the chemical resistance attributed to the olefin component of the polymers. Unfortunately, some confusion has occurred, especially regarding the use of the term thermoplastic (TP). It is important to remember that TPOs are thermoplastic (i.e. TPs) but only some TPs are TPOs.

Benefits of TPOs

In general, TPO membranes are being marketed as a product that combines the properties of EPDM and PVC, without the associated drawbacks that the latter two materials have. In other words, they are supposed to be as UV-resistant and as heat-resistant as EPDM, and as heat-weldable as PVC.

The following benefits and characteristics have been reported for TPOs [ 1-3 ]:

environmentally friendly and recyclable

Commercial TPO Single Ply Roofing System

This Update reviews their characteristics and performance to date and clarifies some misunderstandings related to terminology.

A typical low-slope roofing system consists of three components: a structural deck, a thermal insulation barrier and a waterproofing membrane, which consists of reinforcing fibres or fabric sandwiched between two sheets of flexible matrix. The matrix material is either asphalt- or polymer-based (Figure 1). In single-ply membranes, the matrix is made of flexible polymer. The reinforcement provides dimensional stability for the membrane as well as strength to resist stresses in service. It is generally made of chopped short glass fibre strands packed in a mat, or continuous polyester fibre arranged in a grid or in a non-woven mat (Figure 2).

Figure 1. Categories of low-slope roofing membranes

Figure 2. Reinforcement commonly used in roofing membranes: (a) random short glass fibre mat; (b) polyester scrim; (c) non-woven polyester mat

There are essentially two classes of polymer based roofing membranes: thermosets (TS) and thermoplastics (TP) (see Text Box A). Thermoplastics soften when heated (this process is reversible) but thermosets do not. Thermosets include the commonly used ethylene propylene diene monomer [also known as ethylene propylene diene terpolymer] (EPDM), while thermoplastics encompass a wider variety of roofing membranes, including thermoplastic polyolefins (TPOs). All thermoplastic roofing membranes share certain characteristics, e.g. seaming can be done by heat welding. However, for the most part, they have very different chemical, physical and mechanical properties. It is impossible to explain these differences here, but there are different ASTM material-based standards for various TP products. To avoid confusion, one should not just label all of these products simply as TP products. TPOs differ from other TPs in several respects, and thus must be handled and applied differently.

Text Box A

Thermoplastics (TP) vs Thermosets (TS)

Thermoplastic Polyolefin (TPO) Roofing Membranes Minneapolis Commercial & Town home Roofing

Schematic molecular configurations of (a) a thermoplastic and (b) a thermoset

A polymer is a long-chain molecule consisting of many (poly) small repeating units (mer) (

10 3 – 10 6 ) joined end to end. These molecules are tangled in a random manner analogous to cooked spaghetti.

Polymers can be classified into thermoplastics (TPs) and thermosets (TSs) depending on their mechanical behaviour on heating and cooling. TPs comprise long-chain molecules held together by weak bonds (Figure a). When heat is applied, the molecules slide past one another and the polymer softens. On cooling, the molecules cannot slide past each other easily and the polymer hardens. TS longchain molecules, however, are linked together by small molecules via strong chemical bonds, a process sometimes referred to as vulcanization (Figure b). This three- dimensional network is so rigid that the molecules cannot move very much even when the polymer is heated. Thus, TSs do not soften when heated.

Because of these differences, TP and TS membranes are bonded differently when applied. TPs can be bonded using heat welding: the hot air melts the polymer at the seam and the two strips of membrane become fused. TS membranes are usually bonded using adhesives or tapes.

Definition of TPO

Defining thermoplastic polyolefin is difficult. Thermoplastic is a generic term in polymer science; it encompasses a class of polymers that, as mentioned above, soften when heated in a reversible process. The term olefin is even more generic, being an old chemical name for any molecule containing carbon-carbon double bonds (the modern name for this family of molecules is alkenes). Any polymer formed by chemically linking up many olefin molecules is termed polyolefin.

According to the latest draft ASTM standard for TPOs, the composition is very non-specific. The standard states that TPOs must contain more than 95% by mass of TPO polymer. The polymer itself is not defined within the standard, which states only that the sheet shall contain the appropriate polymers. Because of this loose definition, there is an endless list of chemicals that would fall under this standard (e.g. polyethylene, polypropylene, and isobutylene, as well as their derivatives). Ideally, manufacturers would specify the exact polymer in terms of marketing and labeling.

There are a few published papers that attempt to explain the different types of TPOs [ 1 — 4 ]. One point is clear, however: unlike plasticized thermoplastic membranes, TPOs do not contain plasticizers (small molecules added during compounding to increase the flexibility of the product). Therefore, the problem of plasticizer loss associated with some plasticized membranes is eliminated.

Confusion in the Market Place

TPO roofing membranes have been in service in Europe for approximately ten years. The first appearance of a TPO-type roofing product in the United States was around 1987. As yet, little is known about their durability.

The confusion associated with TPOs comes from both the chemical terminology and the product marketing. The latter has promoted mainly the EPDM-like characteristics of TPOs, i.e. it being like rubber with the added benefits of welded seams (which EPDMs do not have). Also promoted has been the chemical resistance attributed to the olefin component of the polymers. Unfortunately, some confusion has occurred, especially regarding the use of the term thermoplastic (TP). It is important to remember that TPOs are thermoplastic (i.e. TPs) but only some TPs are TPOs.

Benefits of TPOs

In general, TPO membranes are being marketed as a product that combines the properties of EPDM and PVC, without the associated drawbacks that the latter two materials have. In other words, they are supposed to be as UV-resistant and as heat-resistant as EPDM, and as heat-weldable as PVC.

The following benefits and characteristics have been reported for TPOs [ 1-3 ]:

environmentally friendly and recyclable


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