Plastics in Buildings and Construction

29  Plastics in Buildings and Construction Sushant Agarwal and Rakesh K. Gupta Department of Chemical Engineering, West Virginia University, Morgantown, WV, United States

29.1 Introduction

29.2 Applications

Modern building construction, for both residential and commercial purposes, is subject to diverse constraints and objectives. Besides the basic concerns of durability, comfort, and cost-effectiveness, building designs also need to take into account energy efficiency and ecological and environmental concerns. In this quest, polymer-based building materials have not only been used as replacements for traditional materials such as brick, cement, concrete, metal, wood, and glass, but they have also been shown to work in a complementary fashion with traditional materials to enhance their performance with unique and innovative applications satisfying the demands of the modern building construction industry. One of the key advantages of plastic materials is their light weight and their ability to be formed into complex shapes. Other features include durability, low maintenance, low cost, availability in a range of shapes and forms, and possession of a wide spectrum of properties. From an aesthetics point of view, plastic materials are available in attractive colors and textures, and they require minimal or no painting. Another selling point of plastics is their inherent resistance to heat transfer and moisture diffusion. Being electric insulators as well, plastic materials do not suffer from problems such as metallic corrosion or microbial attack. From polyurethane foam insulation, which is a thermoset, to transparent polycarbonate glazing, which is a thermoplastic, to wood-plastic composites for decking and railing, polymers are used in innumerable applications in the building industry for both structural and nonstructural applications. Indeed, the building construction industry accounts for about 18% of plastic consumption in the United States [1]. In this chapter, some of the major applications of polymeric materials in the building construction industry are presented and discussed in terms of material usage, important physical properties, method of production, and relative advantages and disadvantages.

29.2.1  Siding or Cladding

Applied Plastics Engineering Handbook. http://dx.doi.org/10.1016/B978-0-323-39040-8.00030-4 Copyright © 2017 Elsevier Inc. All rights reserved.

Siding or cladding forms the outermost layer of a building or a house. Consequently, it must satisfy two important functions. The first one is to form a protective cover around the building to shield it from the outside elements, and the second is to impart aesthetic beauty to the building. polyvinyl chloride (PVC) sidings, popularly known as vinyl sidings, are perhaps the most well-known plastic product used in the building construction industry. Vinyl sidings are popular because of their ease of installation, durability, low maintenance, and low cost. Plastic sidings are lightweight, and they do not require painting. Due to their inherent low thermal conductivity and moisture resistance, plastic sidings offer good protection against weather elements such as heat, cold, rain, and snow. Aluminum, wood, stucco, brick, and fiber cement are other materials that are popular alternatives to plastic sidings. Initially vinyl sidings grew at the expense of aluminum sidings, but with new innovations they are successfully competing against wood and fiber cement sidings [2]. Extruded plastic sidings continue to dominate the market, with about 30% of homes installing them in 2014 compared to 23% brick and stucco, 18% fiber cement, and 5% wood [3]. To enlarge their market share, plastic sidings need improved performance in the areas of appearance (wider color choices and color retention), thickness, and weather-resistance properties. In general, vinyl sidings are available in light color palettes; however, the competition from paintable wood and fiber cement sidings have necessitated the development of darker color ­palettes that retain color over the lifetime of the siding. This requires protecting the vinyl siding from the weather damage that causes fading of colors. To meet this challenge, vinyl sidings are coextruded with a capstock material that is more weather resistant,

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Figure 29.1  Heat resistance factor (R-value) for 5 cm—thick insulation materials [8].

such as PVC with a high loading of TiO2. Another method is the use of more weather-resistant films, such as acrylic films, plasticized PVC, and polyvinylidene fluoride (PVDF) to coat the PVC siding [2]. Yet another issue is the thickness and thermal expansion of vinyl sidings. Generally, vinyl sidings are only 0.05 in. thick, and this gives them a flimsy appearance as compared to the thicker and stiffer wood and fiber cement sidings. Foamed and wood-plastic composite sidings that are thicker and stiffer than solid-state PVC sidings are being developed in various designs, such as hollow, capstocked, and multilayer configurations [4]. A more recent innovation in siding technology is the use of insulated vinyl sidings. These consist of an expanded or foamed polymer layer at the back of a regular vinyl exterior layer. This combination provides an extra layer of insulation and imparts more stiffness and impact strength. The foamed layer can be made from extruded polypropylene (XPP) or EPS [4,5]. The presence of the foamed layer also reduces any problems due to the thermal expansion of vinyl sidings. Glass-fiber reinforced polyester (GFRP) is also used as a cladding material, but for bigger structures [6]. In wall panels it works as a decorative layer on concrete and brick structures, providing various color and texture options [7]. But, GFRP claddings are expensive, and as a result their application is not as widespread as that of thermoplastic-based claddings and sidings.

29.2.2  Insulation: Foundation Insulation, Spray Foam, and Structural Insulated Panels Insulating materials constitute a major application area for polymers in buildings. Plastics are inherently poor conductors of heat, and most of them are hydrophobic as well. This makes them very attractive starting materials for fabricating thermal and moisture barriers. In a building, insulation is applied to the surrounding walls, basement, attic, and roof. It can be used in a variety of forms, including batts or rolls, loose fill, sprayed foam, and foam boards. The insulation is also applied to domestic hot- and cold-water supply lines and to heating/cooling systems. While the main nonplastic insulation systems are fiberglass and mineral wool, the most widespread plastic insulation is made from polyurethane. Also encountered are polyisocyanurate (PIR), polystyrene (PS), and PVC. Plastic insulation has gained popularity because of its ability to form closed-cell foams that trap gases or air inside the bubbles; the result is a material with a very low thermal conductivity and negligible convection heat transfer because the trapped gas is stagnant. Thus, foaming creates a structure that is lightweight and highly resistant to heat transfer. Fig. 29.1 shows the heat resistance factor (R-value) for several materials that are used for insulation. Note that a material with a larger R-value has better heat insulation performance. It can be seen that foamed plastics have superior insulation properties.

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Table 29.1  Typical Thermal and Vapor Barrier Properties of Common Insulation Materials Material Physical Property

Glass Wool

Mineral Wool

XPS

EPS

PUF

13–100

30–180

20–80

18–50

30–80

Thermal conductivity (W/mK)

0.03–0.045

0.033–0.045

0.025–0.035

0.029–0.041

0.020–0.027

Temperature application range (°C)a

–100 to –500

–100 to –750

–60 to –75

–80 to –80

–50 to –120

Water vapor permeance (perm-inch)b

118

116

1.2

2.0–5.8

0.4–1.6

Density (kg/m3)a a

a b

Data from Papadopolous [13]. Data from 2009 ASHRAE Handbook [14].

Foamed PU, PIR, extruded PS (XPS), and expanded PS (EPS) are popular polymer foam insulations. PU and PIR are thermoset foams that are produced by the reaction between a polyol and a polyisocyanate, both of which are in liquid form. Typically, the polyol is part of an aqueous mixture of catalyst, surfactant (foam stabilizers), flame retardants, and blowing agents [9]. When this mixture is combined with the isocyanate, an exothermic reaction takes place, releasing significant quantities of energy that activates the blowing agent and expanding the reaction mixture into a foamed structure as it polymerizes and solidifies. Isocyanates can also react with each other to form a PIR in the presence of a proper catalyst. If this reaction takes place in the presence of polyols, a mixed structure composed of foams of both PU and PIR can be formed [10]. By controlling the relative amounts of catalyst, foam stabilizers, and blowing agents, foams with various morphologies and properties can be obtained. PU and PIR foams are employed in several forms which include sandwich panels for walls and roofs, flexible boards, slabstocks for construction-size pieces, and spray-on foams [10]. To make a preformed rigid PU structure, the reaction mixture is introduced into box-shaped molds where the foam is synthesized and solidified. Panels of various shapes and sizes can then be cut from the stock panels. Prefabricated panels are useful when working with large flat surfaces where discontinuities and joints can be avoided. However, when complicated surfaces and structures are involved, spray-on foam is preferred. In this case, a precursor mixture is formulated with a proper catalyst to ensure fast reaction and curing. In applying such a spray polyurethane foam (SPF), the liquid reaction mixture is directly sprayed on to the surface. As it is applied, it adheres to the surface and expands. Being in liquid form, it easily fills cavities,

cracks, and gaps forming a better barrier against water and air infiltration as well. Closed-cell SPF is also accepted as a roofing system, and it adds to structural strength as well [9]. Extruded polystyrene (XPS) and expanded polystyrene (EPS) are other popular foamed products for insulation. As the name suggests, extruded PS foam boards are produced by an extrusion process in which the resin is fed to an extruder, which melts and pressurizes it. A physical blowing agent, such as pentane or a hydrochlorofluorocarbon, is introduced into the extruder, and the result is a single-phase polymer mixture. When the molten PS exits through the die, the dissolved gas expands, creating foam. A closed-cell rigid-foam structure is obtained as the extrudate cools and solidifies. EPS is made by molding expandable polystyrene beads that have already been saturated with a blowing agent such as pentane or butane [11]. A mold cavity is filled with EPS beads and heated. As the temperature rises, the polymer melts, and foaming occurs. Here again, a closed-cell structure is obtained, and this is preferred because it increases the structural strength of the foam and resists moisture penetration as well. Typical thermal and moisture diffusion properties of various insulation materials are listed in Table 29.1, which shows that plastic foamed materials have much superior waterresistant properties as well. XPS foam, for example, absorbs only 0.3 wt.% moisture [12]. The good thermal and water-resistance properties of plastic foams, combined with their good structural strength, have led to the development of structural panels known as insulated concrete forms (ICFs). The process of making an ICF involves pouring concrete in between the panels of foamed plastics, mostly XPS and EPS. The panels are tied together by metal or plastic ties. The resulting product has the strength and durability of concrete and the barrier properties

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of plastic foams [15]. In addition, ICFs also provide less air leakage and better acoustic protection [16]. Initially ICFs were used in below-grade foundation wall-forming systems. Now they are being used as part of interior walls, noise abatement systems, storm shelters, and structural elements [15]. Foamed plastics are also used to make structure insulated panels (SIPs) in which a sheet of foamed plastic is sandwiched between wood boards or concrete walls. XPS and XPP foam boards are used for this purpose.

29.2.3 Roofing Roofing systems and house wraps together constitute a protective envelope that safeguards a building from weather elements, such as rain and snow. Roofing systems, as the name suggests, protect the roof, while housing wraps or weather-resistance barriers protect the surrounding walls. In addition to guarding against water leakage, these systems also provide insulation against heat transfer to and from a building. This section discusses the use of polymers in roofing, while housing wraps are discussed in the next section.

Applied Plastics Engineering Handbook

Roofing systems are essentially a film or a layer that retards the leakage of water to the concrete or wood roof structure. The membrane must be strong enough to withstand stresses and flexible enough to accommodate any building movement; the expected service life is in excess of 10 years. Traditionally, bitumen and coal tar have been used, and these are still the dominant roofing materials. Layers of molten bitumen are applied to the roof, which is known as built-up roofing. Since the 1960s, though, polymeric sheets have acquired a growing role as roofing materials. Plastic-based roof membranes were first introduced in the 1960s in Europe and in the 1970s in the United States [17]. The main component of this system is a waterproofing membrane that is applied directly to the roof structure or on top of a layer of insulation [18]. Single-ply roofing membranes consist of reinforcing fibers or fabric sandwiched between two sheets of flexible material. The reinforcing material can be short-glass fiber mat, polyester scrim, or nonwoven polyester mat [18]. Polymeric sheets can be either thermoplastic or thermoset. The latter are applied to the roof in a cured state, but it is then necessary to use an adhesive tape for joining and sealing the edges of the membranes [19]. Fig. 29.2 illustrates

Figure 29.2  Plastics used in roofing systems. Adapted from Paroli et al. [18].

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Table 29.2  Solar Heat Reflecting Characteristics of Some Roofing Membranes Roofing Material

Solar Reflectance

Infrared Emittance

Temperature Rise (°C)

Gray EPDM

0.23

0.87

38

White EPDM

0.69

0.87

14

Black EPDM

0.06

0.86

46

Dark gravel

0.12

0.9

42

Light gravel

0.34

0.9

32

White gravel

0.65

0.9

16

Bitumen, smooth

0.06

0.86

46

Bitumen, white

0.26

0.92

35

Asphalt shingles, black

0.05

0.91

46

Asphalt shingles, white

0.25

0.91

36

Siliconized polyester, white

0.59

0.85

21

Data adapted from Sadineni et al. [21] and Cool Roofing Material Database [22], LBNL.

the various polymeric materials that are being used as roofing materials; these include bitumen, modified bitumen, PVC, polyethylene (PE), chlorinated PE, chlorosulfonated PE (CSPE), ethylene propylene diene monomer (EPDM), ketone ethylene ester (KEE), polyisoprene (PI), and polyisobutylene (PIB). Amongst all these choices, PVC sheets were the first thermoplastic to be used as roofing membranes. Flexible thermoplastic polyolefin (FPO) membranes were first introduced in the 1990s in Europe and a little later in the United States, where they are referred to as thermoplastic olefin (TPO) membranes [17]. A typical TPO roofing polymer is a polypropylene (PP) copolymer which provides higher physical strength than PVC or EPDM [19]. One advantage of using polymeric sheets is that large sizes—as wide as 50 ft., can be produced which reduces the need for seams and joints. Secondly, the thermoplastic sheets can be heat welded together without the need for any connectors or adhesives. The welded joints are as strong as the sheet itself. Polymer sheets are produced by calendering, spread coating, lamination, or extrusion. The sheet thickness can vary from 40 to 100 mils. Roofing materials are exposed to harsh conditions, which cause degradation in properties over time. Deterioration occurs due to wind damage, sunlight exposure, rain, snow, hail, and temperature variations [20]. To prevent, or at least slow down these processes, thermal and UV stabilizers, antioxidant materials, and flame retardants are added to the plastic in appropriate amounts. PVC membranes also contain plasticizers for flexibility.

Apart from serving their main function as a barrier against water leakage, the new plastic roofing systems are being required to act as good heat insulators. Energy-efficient building designs require that heat transfer through the roof is minimized. Dark color roofs absorb more radiative heat, and the surface temperature can be several degrees higher than the atmospheric temperature which adds to the cost of air-conditioning. A cool-roof design seeks to minimize the heat absorption and conduction, while maximizing heat reflectance and emissivity of roofing systems. Thermal insulation layers, generally in the form of foamed plastics sheets of PIR or PS, are used under the roofing membrane. To maximize the heat reflectance and emissivity, light color plastic sheets are utilized, and these are made by using light color pigments in place of dark color pigments, such as carbon black. In some cases, when it is not possible to use light color pigments (as in EPDM sheets), light color paint may be used instead. Table 29.2 provides data that can be used to compare solar reflectance properties and temperature rise of some polymer-based roofing membranes and their nonpolymer counterparts. It is evident that light color polymeric membranes provide superior heat insulation performance.

29.2.4  House Wraps, Building Envelopes, and Barrier Films In building design it is critical to protect the structure and interior of a house from the outside weather

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elements while maintaining a comfortable atmosphere inside in an energy-efficient manner. House wraps, building envelopes, and barrier films, collectively referred to as weather-resistive barriers (WRBs), are employed to protect a building from intrusion by water and air by forming a protective envelope around it [23]. Heat transfer to or from a building occurs by means of heat conduction, convection, radiation, and air infiltration. While radiation usually constitutes a small part of the total heat loss, conduction and convection losses can be minimized by the use of proper insulation and design. However, it is estimated that in a typical US household, half the energy used in air-conditioning is used to heat or cool the air that enters the house by infiltration [24] or air leakage. Air infiltration occurs not only via open doors and windows but also through gaps in the joints where various structural elements of the building frame come together. The second issue is to minimize the penetration of water into the building structure. Though claddings or sidings form the first layer of protection against rainwater, water may still leak through various gaps or as the result of an improper drainage system. In addition, accumulating water absorbed by wood may lead to mold formation and rotting of the structure. House wraps prevent the penetration of water and help in drainage of water away from the exterior walls. House wraps can serve these dual functions if they possess a required set of properties. While a housewrap film should form a barrier against penetration by liquid water, it should be permeable to water vapor [25]. Similarly, while it should prevent air leakage, it must be permeable to air at the same time [23]. These characteristics are necessary so that moisture does not build up and a healthy circulation of air is maintained inside the house. It is also necessary to allow the exterior walls to dry out. Fig. 29.3 shows schematic diagrams of WRB installation in structures where brick wall, vinyl siding, and stucco form the external surface. Traditionally, organic fiber felt and kraft paper saturated with asphalt have been used as house wraps. Since the 1980s, however, polymeric films have seen increasing use as house wrapping material [27]. Polymeric house wraps are mostly polyolefin based, with (PP) and high-density PE being the most common. Polymeric house wraps are thin sheets (only few mils in thickness) that can be classified as either woven or nonwoven. Nonwoven sheets are obtained by an extrusion process, while woven sheets are made from fibers that are very fine spun and only

Applied Plastics Engineering Handbook

a few microns thick, which are bonded together by heat and pressure. Sometimes, in order to impart proper water permeability, microscopic holes are perforated through the films. A filler material is also used to make the films opaque, white, or translucent, as required. Polymeric films have several advantages over traditional asphalt films [27]. They are stronger and have better tear resistance. They can be manufactured in large sheet sizes, minimizing joints and seams. They have better air and water permeability performance. On the other hand, they are relatively expensive and can have low UV stability. Various building codes and ASTM standards are employed to test the performance of house wraps. Some of these standards were formulated to evaluate traditional asphalt-based house wraps but have not been modified to accommodate polymeric house wraps [26,27]. For air leakage and porosity, TAPPI T460 and ASTM E 283 tests are performed. For water permeability and transmittance, ASTM D226, ASTM D779, ASTM E96, and AATCC 127 standards are followed. ASTM D1117 is used for tear strength while ASTM D882 is used for tensile strength measurements. Flammability properties are classified according to the ASTM E84 standard.

29.2.5  Electrical Wiring Insulation and Conduits Thermoplastics and thermosets are very good insulators of electricity, as their electrical resistance is in the range of 1012 ohms cm or higher. As a consequence, they are widely used as insulating and sheathing materials for wiring and cables for electrical and data transmission. Besides natural polymers like rubber, phenolic resins (Bakelite) were the first synthetic polymers to be used for electrical insulation; their use started in the 1920s and was followed by PVC in later decades [28]. Many different types of polymers are now used, including PP, low-, medium-, and high-density PE, cross-linked polyethylene (PEX), polyamides, ethylene propylene rubber, polyesters, and fluoropolymers [29]. Electrical cable and wiring are used for underground, residential, and distribution purposes, and each has to satisfy different performance criteria. Electrical properties of interest are dielectric constant, dielectric strength, and surface and volume resistivity [30]. Other distinguishing properties are strength, flexibility, fire and solvent resistance, durability, and cost. Table 29.3 lists the various plastic electrical insulation materials and their relative advantages.

29:  Plastics in Buildings and Construction

Figure 29.3  Weather-resistance barrier installation in a wall structure. Adapted from Hall and Hoigard [26].

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Table 29.3  Polymeric Wire Insulation Materials and Their Advantages Polymer

Advantages

Polyethylene

Good electrical properties; high moisture and chemical resistance; light, flexible, cheap, and readily available

PVC

High outputs possible; property modification by the use of additives; cheap and readily available

Nylon

High strength; heat and abrasion resistance

Polytetrafluoroethylene (PTFE) and blends

High toughness; very good solvent resistance; outstanding electrical properties

Polyester

High temperature resistance; improved adhesion to wires

Thermoplastic rubbers

Good environmental and heat resistance; improved aging characteristics versus PE

Rubbers

EPR: improved heat resistance, easier processing; silicone rubber: very high temperature resistance, very flexible

Adapted from Podolsak and Tiu [31].

Additives, such as plasticizers, fillers, colorants, stabilizers, flame retardants, smoke-suppressants, and lubricants, are added to achieve different performance criteria. In building construction, PVC is the dominant polymer used as a wire insulator because of its inherent flame-resistant properties [32], strength, and low cost. But due to high stiffness, plasticizers are added to make it flexible. However, toxic smoke that is generated on combustion is a major concern in its use, and therefore various smoke-reducing additives are added to minimize this problem. Polyethylene is lightweight and water and solvent resistant. High density PE is preferred over low density PE because it has higher abrasion and tear resistance and higher tensile and shear strengths [33]. Cross-linked PE (PEX) is used because it can withstand higher operating temperatures than PE. In addition, larger amounts of fillers, such as carbon black and flame retardants, can be incorporated into PEX, resulting in a more fire- and abrasion-resistant material [33]. PVC is also the main thermoplastic used to make electrical wire conduits, since it is corrosion free and water resistant. Consequently, it can be easily buried underground and in concrete structures. Other plastics used to make electrical conduits are PE, nylon, and polyester.

29.2.6  Glazing, Windows, and Doors Glazing of window panels, building facades, skylights, or roof domes provide separation from exterior

elements such as hot and cold weather, high winds, rain, and snow, while letting daylight in and allowing outside visibility. Glass has been used as the traditional material for glazing applications. However, the use of plastics in this area has increased steadily over the years, and their application in flat glazing constitutes one of the largest applications for transparent plastics [6]. Acrylics such as PMMA, polycarbonate (PC), glass-fiber reinforced polyesters, and PVC are some of the materials that are being increasingly used to replace traditional glass glazing. Some desirable characteristics of plastic glazing and skylight materials are provided in Table 29.4. A glazing material should be lightweight, inexpensive, UV protective, transparent, a good insulator, and easy to install. In addition, it should have good structural and impact strength, good fire resistance, and reduced smoke generation [34]. Plastic glazing materials have some distinct advantages over glass in terms of these properties. Plastic glazings are much lighter than glass and are self-supporting, so that very large structures, such as stadium roofs, can be engineered easily. They also have much higher impact strength compared to glass. This is especially true for PC, which is significantly more shatter resistant than glass. This makes the installation of plastic glazing much easier, since plastics are not only much lighter than glass but they also do not break easily. Typical properties of plastic glazing materials as compared to glass are provided in Table 29.5. Another major advantage of plastic glazing materials is their superior thermal insulation properties compared to glass. In a building, windowpanes

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Table 29.4  Plastic-Based Glazing and Skylight Materials and Their Desirable Characteristics [36] Material

Desirable Characteristics

GRP

Diffuse light, high UV absorbance, less discoloration, good for industrial and commercial applications

Polycarbonate

High clarity, impact resistant, moldable, functional coatings and additives, lightweight, multipane, multiwall assembly, highly insulating

PMMA

Lightweight, clear, impact resistant, durable, available in colors and coatings

Polyester

Great clarity, easily thermoformed

PVC

Inexpensive, suitable for small domestic applications

Table 29.5  Typical Properties of Plastic Glazing Materials Compared with Glass

Visible Light Transmission

Tensile Strength (ASTM D638), MPa

Impact Strength (Notched Specimen), /m (ASTM D256, Izod test)

Flexural Modulus (ASTM D790), GPa

3.1

91–93

72

21–27

2.4–3.4

1.2

3.8

82–89

62–72

640–860

2.2–2.6

GRP

1.40–1.60

3.4–4.4

76–85

76–117

430–1070

50–100

PVC

1.30–1.40

5.0–10

76–89

38–62

13–64

2.60–3.7

Sheet glass Soda-lime glass

2.46–2.49

0.85

88–90

—

Brittle

—

Glazing Material

Specific Gravity (ASTM D792)

Coefficient of Thermal Expansion (ASTM D696) 10−5/°C

PMMA (acrylic)

1.19

Polycarbonate

Adapted from Blaga [35].

or facades contribute to significant heat losses. With increasing emphasis on energy-efficient building designs, plastic glazings offer a very attractive alternative to glass-based designs due to the fact that the thermal conductivity of plastics is much lower than that of glass. The thermal insulation property of glazing is usually characterized by means of a U-factor (or R-value = 1/U), which encompasses total heat transfer through the window. For energy-efficient solutions, a window must have a low U-factor or a high R-value, indicative of high thermal resistance. A multipane plastic window can have a U-factor as low as 0.16 Btu/ft.2 h °F. For similar U-factor performance, a glass window would weigh much more than a plastic window [34]. Despite having some obvious advantages over glass, plastic glazing materials suffer from problems like yellowing, discoloration, crazing, cracks, and low scratch resistance. However, new technologies and materials are being developed that overcome some of these problems. For example,

glazing sheets can be coated with UV-resistant or scratch-resistant coatings. Plastic glazing sheets are generally produced by processes of extrusion, coextrusion, or casting. These sheets can be a few millimeters in thickness and several feet in width and length. In the case of thermoplastic grades, various shapes can be obtained by thermoforming. Sometimes coextrusion is used to apply a thin film of one polymeric material to another to enhance the UV stability of glazing materials. Fiber-containing glazing sheets are generally produced by a casting process. Another application area of plastics is in the manufacturing of window profiles and doors as a substitute for traditional materials such as wood and metal. In the case of doors, the market is dominated by wood and metals, while plastic doors lag behind. In case of windows, wood and plastic compete closely, while metals still dominate the market [37]. However, plastic doors and windows are expected

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to show growth in the market due to the fact that they have recycling potential. Unplasticized PVC is the main thermoplastic used in this regard. Unfilled and fiber composites both are used to make window profiles and doors. Glass-fiber and woodplastic composites are expected to show about 37% growth rate for use as window materials [38]. Glass-fiber reinforced windows have polyester as the matrix material, whereas in WPC mostly PVC is used. Composite windows are strong, durable, and paintable, and they have low thermal expansion. Acrylonitrile butadiene styrene (ABS) capped with acrylic styrene acrylonitrile is also used as molding material for window profiles [39]. Despite being more expensive than PVC, ABS window profiles offer better impact strength, higher heat-deflection temperature, less shrinkage, and better resistance to weather damage.

29.2.7 Piping Plastic materials have long been used to make pipes and tubing systems. These are categorized as gravity pipes (meant for building and civil engineering) and pressure pipes (for utilities and plumbing). The gravity sector is the larger of the two. The first plastic pipes were made from PVC in the 1930s, and later PE and ABS joined the family of materials for mass production of pipes and tubes. Various other polymeric materials are also used to make pipes, and these include chlorinated PVC (CPVC), chlorinated polyethylene, PEX, polybutylene (PB), PP, PVDF [40,41], and various glass-reinforced thermosets, such as epoxy and polyesters [42]. However, PVC and various grades of PE dominate the plastic piping market. According to a report prepared by the Freedonia Group on the plastic and competitive pipe market, worldwide demand for plastic pipes is going to increase by 8.5% per year to 11.2 billion meters by 2017 and 6.2% per year to 23 million metric tons by weight, indicating increasing usage in larger diameter pipes. PVC will continue to dominate, with about 55% of the market, but newer materials such as molecularly oriented PVC and bimodal PE will show greater growth as well [43]. Note that a variety of additives are normally incorporated into plastics to endow them with specific desirable properties. Some essential additives used in plastics for piping applications include heat and UV stabilizers, antioxidants, lubricants, coupling agents, and colorants. Some of these additives protect pipes that are used outdoors from degradation due to weathering.

Applied Plastics Engineering Handbook

Pipes made from plastic compete with traditional materials (such as metallic pipes made from copper, steel, or aluminum) and also with pipes manufactured from cement and concrete. Plastic pipes offer many advantages over traditional materials. They have good hydraulics (low resistance to flow, high resistance to scale or build-up), and they are lightweight, low cost, and easy to manufacture. Very small to large diameters and long lengths can be extruded and transported. Plastics are flexible and they can bend easily to go around corners and tight spaces without breaking. Long lengths and flexibility minimizes the need for many joints and connectors. Since plastics are nonconductive, they do not suffer from electrochemical degradation, such as corrosion or rusting. They are resistant to chemical and biological degradation also. They are durable, and easy to maintain and replace. One major advantage with plastic piping systems is the variety of joints and connectors that can be used to make leakproof and durable connections. Nonplastic piping systems require flangetype or threaded fittings to make connections, which are prone to leaking and failure. By contrast, thermoplastic piping can be joined by heat welding or solvent cementing, which creates joints that are almost seamless and as strong as the rest of the pipe. A variety of metallic and plastic fittings and connectors are compatible with plastic pipes. However, plastic pipes are limited to low pressure and temperature applications due to their low strength and the tendency of the polymers to soften at elevated temperatures. This is the reason that the drainage and wastewater pipelines from sinks and toilets are made from plastics, but pressurized hot- and cold-water distribution systems in a household are still predominantly made of metal, especially copper. However, with new innovations in plastics technology, the use of plastic piping is being extended to more demanding applications, such as hot-water supply, radiant floor heating, and fire sprinkler systems. Various grades of plastics used in piping systems are described in the material that follows. Polyvinyl chloride (PVC) and chlorinated PVC are the most widely used plastics to make piping systems. In the United States, PVC accounts for twothirds of water distribution systems and about threefourths of sanitary sewer systems [44]. Rigid PVC or unplasticized PVC is preferred, because it has the highest strength of all plastic piping materials, as shown in Table 29.6. It also has excellent long-term strength, high stiffness, and resistance to chemicals. PVC piping is available in a wide range of sizes and wall thicknesses for both pressure and nonpressure

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Table 29.6  Typical Physical Properties of Thermoplastics for Piping Property

ASTM Test Method

ABS

Approximate Values at 24°C PVC

CPVC

PE

PEX

PB

PVDF

PVC

Specific gravity

D792

1.08

1.4

1.54

0.95

0.94

0.92

1.76

Tensile strength (MPa)

D638

48.3

55.2

55.2

22.1

19.3

28.9

48.3

Tensile modulus (GPa)

D638

2.3

2.8

2.9

0.82

1.0

0.38

1.5

Izod impact strength (J/m)

D256

213.6

53.4

80.1

>534

>534

>534

202.9

Coefficient of linear expansion (m/m°C)

D696

108

54

63

162

162

130

126

Nonpressure

80

65

100

70

100

100

150

Pressure

70

55

80

60

95

80

140

Approximate operating temperature limits (°C)

Adapted from McGrath and Mruk [40].

applications. PVC piping is classified based on its tensile strength, impact strength and stiffness. PVC is recommended for temperatures up to 60°C [41] for nonpressure applications. Chlorinated PVC is obtained by adding extra chlorine to PVC, which results in a material that is similar in strength and modulus to PVC but has a higher temperature rating. CPVC can be used at temperatures up to 93°C for pressure and 100°C for nonpressure applications [40], making it suitable for both hot- and cold-water applications. PVC materials have excellent flame-resistant properties due to the presence of halogen atoms in the polymer structure. They therefore are also recommended for household fire sprinkler systems. The other major material for plastic pipe manufacture is PE, a polyolefin. This is the second-most common plastic material after PVC. PE is broadly classified into three types. Low density PE (LDPE) is Type I, and it is soft and flexible with low temperature resistance. Type II is medium-density PE (MDPE), and it is stronger and more temperature resistant. Type III is high-density PE (HDPE); it is much stronger, tougher, and more temperature resistant. HDPE is also the preferred material for piping [41]. PE is less strong as compared to PVC, but, because it has a very low glass transition temperature, it maintains flexibility even at low temperatures. It has better chemical resistance and a smoother surface, which reduces friction losses. It can be easily heat welded to fittings and connectors, ensuring virtually leakproof joints. The main applications of PE piping are in water distribution and in sewage and drain systems. Because of their better crack-resistance

properties, PE pipes are also used for natural gas delivery. HDPE is used for moderate water pressure applications (6.3 MPa), LDPE is used for low-pressure applications (4 MPa), whereas a blend of MDPE with HDPE is used for higher-pressure requirements (8– 10 MPa) [6]. Recently, ultrahigh molecular weight PE pipes have become available, and these have a higher resistance to stress cracking. Cross-linked polyethylene (PEX) is the most widely used thermoset in the piping industry. It is obtained by the process of cross-linking PE molecular chains after the extrusion process, as this creates a stronger molecular structure. Three methods used for cross-linking are peroxide, silane grafting, and irradiation. Compared to PE, PEX has higher heat resistance; at higher temperatures, it becomes flexible but does not melt. The recommended temperature limit for PEX usage is 93°C. It also has better creep resistance, UV stability, and resistance against environmental stress cracking. Other thermosets encountered are mostly reinforced materials, which are used more in industrial applications for more demanding situations than those in building applications. Polybutylene (PB) is also a polyolefin that is flexible but has a much higher long-term strength. In addition, it retains its long-term strength at higher temperatures much better than PE does. That is why it is recommended for use up to 93°C, as compared to 60°C for PE [40], making it suitable for domestic hot-water applications. Note that antioxidants have to be added to both PEX and PB in order for these materials to perform well at 93°C. An equally important member of the polyolefin family used in piping systems is PP. It has more stiffness and strength than

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PE, but less impact strength. It is more temperature resistant and has better chemical and solvent resistance. It is classified as Type I, which is stronger but has less impact strength, and Type II, which is less strong but has higher toughness. ABS is a copolymer in which a rubbery polybutadiene phase is dispersed in a rigid but brittle styreneacrylonitrile (SAN) phase. The presence of rubber particles imparts flexibility and impact strength to the material even at low temperatures. Due to its excellent strength, ABS pipes are also available whose pipe walls are made of foamed core rather than being solid walls, which decreases weight without compromising physical properties. The major use of ABS pipes is in drain, waste, and vent (DWV) applications. The demand for these different types of plastic pipes is expected to remain strong due to the replacement of concrete and metal pipes with plastic piping, and also because of the need for new water-supply and sewer systems to satisfy the needs of a growing global population.

29.2.8  Decking, Fencing, and Railings Decking, fencing and railings are outdoor building applications, and these are generally made from wood. Deforestation and the use of hazardous chemicals such as chromated copper arsenate, which is used as antifungal agent, are the main reasons for seeking alternatives to wood in such applications. Plastic products used in these applications are known as plastic lumber (PL) which include both unfilled and fiber reinforced plastic products. Demand for PL, in addition to environmental concerns, is also driven by product variety, durability, aesthetics and low maintenance that one expects from plastic products. However, neat thermoplastics have much less strength and stiffness compared to wood which is the cause of sagging of decking and railings. By adding wood flour and biofibers, such as cellulose, as reinforcing materials, a significant improvement in these properties can be obtained [45]. Biofibers and wood fibers start to degrade at 200°C, and, therefore only resins that are processable at temperatures less than 200°C are used as matrix polymers for WPCs. Thermoplastics used in these applications are various grades of PE, PP, PS, PVC and ABS [46,47]. About 80% of the market is domi­ nated by polyolefins, but PVC is likely to gain an in­creasing market share. A significant portion of the matrix material in WPCs is post-consumer recycled

Applied Plastics Engineering Handbook

plastic, such as HDPE and LDPE from recycled plastic bags and milk containers. The wood content can vary anywhere from 20 to 80% by weight, but most commercial products contain 50–60% wood by weight. This is because higher loadings are difficult to process due to a sharp increase in melt viscosity which causes problems in extrusion. WPC decking and railing are obtained by the profile extrusion process, but coextrusion is also used to apply capstock for UV protection or to create a solid skin around a foamed core. Profile extrusion can be a single stage or two stage operation. In the single-stage operation, resin, additives, processing aids and wood flour are directly fed to the extruder where melt blending takes place, and the blended product is then extruded through a profile die. In the two stage process, the plastic resin and wood are compounded in the form of pellets in a twin-screw extruder, and then these pellets are used for profile extrusion in a single-screw extruder. PVC and polyolefin-based wood composites are the main materials that are used to make fencing profiles and slats. Due to low maintenance and greater tolerance to heat and moisture degradation, the plastic fencing market has seen rapid growth in recent years, particularly wood plastic composites that have gained wide acceptance. The plastic fencing market has also benefitted from the fact that fencing is not considered to be structural. As a result, building code requirements are not stringent except in some cases, such as pool or ranch fencings or in hurricane affected areas [48]. PVC and WPC fences also have the advantage of being available in various surface and paint finishes; this is achieved by using capstock or by giving the WPCs embossed texture. Plastic fencing can have a foamed core or a solid core structure, and it is produced by a profile extrusion/coextrusion process, similar to the one used in the WPC decking industry. Since recycled PVC, polyolefins, and recycled wood flour are used as raw materials to make plastic fencing, these products can be viewed as a part of green and sustainable building design.

29.3  Plastic Applications in Green Building Design With the rising cost of energy, and concerns regarding global warming related to CO2 emissions, much emphasis is being placed on constructing buildings utilizing materials, designs, and systems that are environmentally friendly, energy efficient, and sustainable. These improvements are sought not only for new construction but in the renovation and repair of

29:  Plastics in Buildings and Construction

existing buildings as well. Federal, state, and local governments are encouraging the use of green technology by providing various incentives in terms of tax rebates, low-interest loans, and subsidies. In the United States, the residential and commercial building sectors taken together, account for 40% of total energy usage. In a typical US household, as much as 45% of the energy use is for heating and cooling [49], and most of this is expended on energy loss due to air infiltration and leakage. The Energy Policy Act of 2005 provides for tax incentives for a reduction of 50% in energy and power cost over that of the International Energy Conservation Code (IECC) for residential buildings and the ASHRAE [14] codes for commercial buildings [50]. Plastic materials are playing a major part in achieving these goals, which involve improving the performance of interior lighting, heating, cooling, ventilation, hot water, and building envelope insulation [51]. Solid foam insulation for walls and roofs, such as SPF, light colored plastic roofing membranes, plastic glazing and skylights with high R-values, plastic piping for hot water and radiant heating, and foam-insulated concrete panels containing XPS are some examples of the applications of polymer-based materials in making the building construction more eco-friendly. The US Green Building Council (USGBC) has developed a program called Leadership in Energy and Environmental Design (LEED) to set standards and certification mechanisms for green building designs. Points are awarded based on sustainable site selection, water efficiency, energy and atmosphere, materials and resources, and indoor air quality. Based on discussions presented in previous sections, one can see that the use of polymeric materials can be very helpful in this regard. Under LEED guidelines, the use of materials that are recycled, recyclable, reusable, and renewable is encouraged; these include WPCs, which are based on recycled and renewable wood and recycled and recyclable thermoplastics. Similarly, the use of plastic piping, which reduces water leakage, or the use of plastic WRBs would help in achieving green building design certification. A recent exciting development is the use of phase change materials (PCMs) that go from solid to liquid at temperature ranges between 0 and 60°C [52]. PCMs are commercially available, and they absorb energy and melt when the indoor temperature goes above the human comfort range. When the temperature falls, they solidify and release energy. When incorporated into building materials, PCMs help to reduce energy costs for heating and cooling. In the coming years, building construction based on green building design will

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continue to increase, and polymer-based materials and systems will constitute a significant part of the construction industry.

29.4 Conclusions Polymeric materials, both thermoplastics and thermosets, have wide applications in the building construction industry. They provide unique and innovative solutions at low cost. Many such applications were described in this chapter. With greater emphasis on energy-efficient and sustainable building construction, the use of polymeric materials will continue to garner a larger share of construction materials [13,31,53].

Acknowledgments Drs. Karl W. Haider of Bayer MaterialScience, Prithu Mukhopadhyay of IPEX, and Tammy Yang of GAF Materials Corporation provided useful suggestions and help during the writing of this manuscript. This is gratefully acknowledged.

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Applied Plastics Engineering Handbook

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