Plastic Materials

Basic info is found in Chapter 9.

Many plastics have high thermal insulation properties when foamed and good water and vapour-proofing properties when used as paint, sheeting, sealing strips and mastics.

Sheets and membranes. Several plastics are used for sheeting and membranes. Most important are polypropylene, polyethylene, polyvinyl chloride and synthetic rubbers.

Vapour retarders are often made of spun high-density fibres of polyethylene or polypropylene. These products are also often used as air and wind barriers. Polyethylene is the most frequently used plastic sheeting for vapour barriers, either alone or as coating on paper sheeting. Polyvinyl chloride sheeting is not as vapour proof as polyethylene, but it is still used for this purpose when higher strength is required.

Polyvinyl chloride and the synthetic rubbers polyisobutylene (PIB) and styrene butadiene (SBR) are much used as waterproofing membranes in bathroom floors and walls.

External moisture proofing on foundations (geomembranes) are often done with profiled sheeting made of polyethylene or polypropylene, usually with carbon as ultraviolet stabilizer. In some products polyester fibres are used as reinforcement. Polyvinyl chloride and synthetic rubbers are much used as roofing membranes, especially on flat or nearly flat roofs.

Flashings and gutters. The most common plastic for use in flashing and gutters is polyvinyl chloride. Products are often coloured and stabilized with cadmium or organic tin compounds.

Mastics and sealants. Apart from linseed oil based putty, most mastics available on the market today are plastic or bitumen based. A mastic has to fulfil conditions of constant elasticity and high durability. The plastics commonly used are polysulphide, silicone, polyurethane and various acrylic substances. These compositions are complex, the binders being mixed with fillers, organic solvents, drying agents, softeners and biocides. Some products also have pigments and fibres added, the latter usually fibreglass. Pure silicone is easy prey for mould in damp situations, and therefore often has isothiazoli-nones, carbendazim or organic tin compounds added, about 0.05% by weight. Organic arsenic compounds are also used as a biocide in some products. Polyurethane mastics contain 10-60% phthalates. Other products can contain chloroparaffins as softeners. Mastics of polysulphide, polyurethane and polyacrylates can contain brominated or chlorinated hydrocarbons as fire retardants. Up to the end of the 1980s highly toxic polychlorinated biphenyls (PCBs) were an important part of mastics for sealing between modules in prefabricated buildings, as well as in sealants between glass layers in insulating windows.

Sealing strips are used mainly between the sheets of glass in windows and in window and door reveals. Important plastics used include polyurethane, polyamide, polyvinyl chloride, ethylene-propyl-ene rubber (EPDM), choloprene rubber (CR) and silicone. The products include different additives such as fire retardants, stabilizers and pigments.

Thermal insulation. Various insulation materials are produced from foamed polystyrene (EPS, XPS, MEPS) and polyurethane. Polyiso-cyanurate and polyicynene are recent alternatives with similarities to polyurethane. Foamed polyvinyl chloride, polyethylene and phenolic products are also used, but to a lesser extent. A fairly new product group is based on the recycling of plastic bottles made of polyethylene which are shred, and are produced as matting. The other materials are foamed up using hydrofluorocarbons, pentane or carbon dioxide as foaming agents. As fire retardents brominated and chlorinated hydrocarbons are often used, the largest portions in polyurethane products.

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