Is it a polymer or is it a plastic? While it is tempting and sometimes common to use “plastic” and “polymer” interchangeably, the term polymer is generic and refers to a large molecule. Plastics, while occurring naturally, are mostly synthetic and have their origins in petroleum. Common synthetic plastics include polyethylene, polypropylene and polyester. Research is likewise advancing in the area of bio-plastics or plastics made from renewable material resources. The PS or polystyrene hanger (top) is a common plastic found in consumables. The ETFE foil (bottom) is an emerging plastic material applicable as pressurized cushions in roof and wall applications.

A monomer of ethylene can be thought of as a “molecular unit”. Through synthesis or polymerization, ethylene monomers are added together to form polyethylene.


Polyethylene, a plastic with low moisture-vapor transmission, is commonly found in building and construction as a vapor barrier.


A micro-structural diagram for each group of plastic, thermosets (top) and thermoplastics (bottom), reveals the reason for the often cited “spaghetti analogy”. But, notice the links between the chains of the thermosets. Thermoplastics, such as polyethylene, polypropylene and polystyrene, are tangled but independent macromolecules. Thermosets, such as phenolic resin and polyurethane, are tangled and attached to each other through “cross linking”.

 

PLASTIC TERMINOLOGY

Plastic terminology is inherently cryptic. Often affiliated with polymer chemistry, such terminology deployed in the context of building and construction provides information about a plastic’s physical and chemical properties. But, often comprehension of plastic and affiliated terminology requires further decoding or research. The nineteen terms listed below are really subject headings providing a methodology for naming and defining plastic types found in any architectural project. These subject headings are subsequently used to summarize the Plastics Found in each of our case study projects.

Plastic Performance and Building System Affiliation

Plastic Type

Plastic Acronym

Thermoset

Thermoplastic

Properties

UV Resistance

Useful Life

Building Products - Size and Installation Method

CSI Master Format Number

International Building Code References

Fire Testing/Rating

Year Invented

Natural Resources

Processing

Health and Safety Concerns

End of Life Options

Alternative Plastic Products

Emerging Plastic Technologies

 

Plastic Performance and Building System Affiliation
An indication of plastic's performance and where it is found in the assembly of each architectural project.


Plastic Type
A plastic is a polymer, a macromolecule or a very large molecule resulting from the addition of very small units (monomers) into large chains. Saying that something is made from plastic is typically too general of a description. There are literally hundreds of plastic types all resulting from one of three processes: polymerization, polyaddition or polycondensation. And, mostly resulting from one of five monomers: methane, ethylene, propylene, butylene, and benzene. The diversity of plastic types is then largely dependent on processes of differentiation both at the scale of a chemist's work bench and the scale of a petrochemical processing facility. See our discussion with chemist Tat Tong for further insight into monomers, polymers and processing.
Interview with chemist Tat Tong


Plastic Acronym
Given their long chemical names such as poly diphenylmethanediisocyanate, plastics are typically recognized by an acronym such as pMDI. American Society for Testing and Materials (ASTM) publishes an official list of polymer abbreviations to be used in the building and construction industry.


Thermoset
Thermoset is a term used to describe plastics that become permanently hardened when heated or cured. The curing process of thermosets causes a chemical reaction that creates permanent connections between the material’s molecular chains. Due to their molecular bond, thermoset plastics have superior durability and will not change shape due to extreme thermal and chemical conditions, thus often outperforming other building materials.


Thermoplastic
Thermoplastic is a term used to describe plastics that become soft and pliable, but do not set when heated. Thermoplastics have the ability to harden into a particular mould but because there is no chemical change that occurs during the curing process the material is able to be reprocessed numerous times. The major advantage of thermoplastic materials is their ability to be recycled, though continual recycling may adversely affect the quality of the polymer.


Properties
Once formed, plastics have distinct attributes dependent on their molecular structures and the methods by which they were processed. An individual plastic’s physical properties determine its most appropriate use. In building in construction plastics are detailed or specified for the optical, thermal, corrosion resistive or adhesive qualities.


UV Resistance
Ultra violet (UV) light resistance is an important weather resistive characteristic, especially when a plastic is part of the building envelope. Ultraviolet light can initiate a chemical change in an exposed plastic and alter its color, strength and durability. Plastics today largely control UV-initiated degradation with additives that can be added in various stages of a plastic’s processing or a product's manufacture.


Useful Life
Plastics do weather and can degrade overtime through chemical change initiated by several environmental factors including UV light, pollutants, and moisture. Detailing of assemblies with weather-exposed plastics should account for weathering characteristics and the manufacturer's stated useful life of the plastic.


Building Products - Size and Installation Method
Plastics come as various types and various unit forms: sheets, rolls, tiles and liquids. Plastic is a general description for a vast array of materials used in building and construction, each having its own properties and installation methods. For instance, polycarbonate and acrylic, which are typically used for their optical qualities in a transparent/translucent wall or roof application, significantly expand under thermal loading and require attentive detailing to account for expansion.


CSI Master Format Number
The Construction Specifications Institute is largely a volunteer organization that promotes technical communication within the construction industry. It publishes MASTER FORMAT, a numbering system organizing the technical data or specifications for all building materials and systems. Specifications for materials and their methods are organized into three parts: general, products, and execution. Plastics are specified under Division 06 along with wood and composites. But plastics can actually be specified in multiple divisions because they are functional companions to multiple materials. For instance, in Division 03: Concrete, one might find polyethylene listed under part II products as a vapor barrier in a concrete slab assembly.


International Building Code References
The IBC is mostly concerned with a plastics flame spread index (FSI), smoke-developed index (SDI) and combustibility. The FSI indicates the ability of a flame to travel across the surface of a material in a given amount of time. The SDI indicates how much smoke is created when a material is burned. A low SDI number corresponds to a smaller volume of smoke. The combustibility of a plastic, or its ability to contribute to the fuel load of a fire, varies significantly across the range of plastics available. Some plastics are highly flammable and combustible; others can not sustain flaming once the source of the flame is removed. Some plastics, and the compound they contain, will produce toxic gases when burned. Chapter 26: Plastics of the IBC is organized to address both types of plastic (insulating or light transmitting), and their location in the building (interior finish, exterior wall, glazing and roof). Chapter 26 must also be used in conjunction with IBC chapters and most notably Chapter 8 which addresses Interior Finishes.


Fire Testing/Rating
As a method for evaluating the quality and performance of building materials several organizations develop standard testing procedures to provide certifications for the materials being tested. Some of the major testing organizations include UL (Underwriter’s Laboratories, ASTM (American Society for Testing and Materials), DIN (German Institute for Standardization), and BSL (BS Testing Laboratory).


Year Invented
That plastics were invented is the perception, but more often than not they were “found” in a chemical experiment based in a process of trial and error and searching for an entirely other material.


Natural Resources
Polymers and polymer manufacturing rely mostly on crude oil and natural gas for their production. In this process oil is “cracked” and distilled into a range of products such as kerosene, diesel and gasoline. Naphtha, also a product of the cracking process, is further distilled into hydrocarbon compounds such as ethylene, propylene, butylenes, and benzene, forming the monomer for the polymerization process.


Processing
Processing is a term used to describe the method by which polymers are manufactured from monomers. Selected procedures are dependent on monomer type and the desired physical and chemical properties. While there are literally hundreds of plastic types all resulting from one of three processes: polymerization, polyaddition or polycondensation, methods of working with these three processes are constantly reinvented, allowing for new plastic performance to emerge. Further, processing can take place in many settings and at many scales. For instance, mixing a two-part epoxy, a plastic available at any hardware store, initiates the polymerization process at one’s fingertips. See our discussion with chemist Tat Tong for further insight into customization of plastic properties through processing. Interview with chemist Tat Tong


Health and Safety Concerns
Most plastic materials are inert in common usage. Past health and safety concerns have arisen when plastics reach temperatures that are untenable to the microstructure. For instance, some plastics, if incinerated without proper control can emit smoke and produce noxious gas. Today plastics commonly used in buildings meet or exceed codes and standards for fire resistance and can be used as fire blocks to prevent drafts and ‘combustion venting.’ Foams used to insulate homes and offices today do not contain formaldehyde, or harmful ozone-depleting blowing agents and must pass stringent OSHA testing requirements to assure that the foam is inert, resisting ‘off-gassing’ even before becoming sealed inside a wall.


End of Life Options
Many plastics at the end of life can be reused, recycled or recovered, thereby extending the life of the original material input. The ability to reuse, recycle or recover a plastic is largely dependent on the type of plastic, thermoset or thermoplastic, and the presence or absence of additives in the plastic. Consumables made from plastic are typically marked with a resin identification code, identifying the plastic type and affiliated recycling protocol. Plastics used in building and construction may be in the form of recycled or recovered plastic content or first-use plastics which may be later recycled.

Alternative Plastic Products
Plastic products that may be substituted for the product used without degradation in performance. Alternative products are typically used in cases where budget or availability becomes a problem.


Emerging Technologies
Polymer processing and manufacturing is still a relatively new technology, having its earliest origins in the mid 19th century. As such, material evolution and discoveries are still rapidly emerging.

 

 


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