Almost all commercial plastics are based on fossil carbon resources, mainly oil and gas. The resource base of plastics is thus very limited, energy consuming, heavily polluting and a major source of climate emissions. Refining plastics requires a great deal of energy compared to other materials. In all phases from production to use in the indoor climate and as waste, the majority of plastic products can cause considerable health risks and pollution. This includes a broad spectre of environmental toxins in addition to the greenhouse gas carbon dioxide (see Chapter 9).
Plastic sheeting plays a very important role in water and vapour-proofing of conventional buildings. Durability is therefore a decisive factor. According to existing documentation it is unlikely that plastic products have these qualities to the desired extent. In terms of pollution, products made of polyethylene and polypropylene are unproblem-atic in the user phase. Sheeting and membranes made of polyvinyl chloride can contain softeners (phthalates) and other volatile additives that can cause problems if exposed in the indoor air. In waterproofing membranes for bathrooms, residues of bisphenol A and phosphates of lead have been documented. Products of polyvinyl chloride also often contain the potent heavy metals cadmium or lead as a stabilizer against ultraviolet radiation. Heavy metals are also commonly used in flashings and gutters made of polyvinyl chloride.
Mastics must be applied when still soft. During the hardening process, the indoor climate can be affected by emissions of aromatic, aliphatic and chlorinated hydrocarbons. At the Royal Theatre in Copenhagen, an unpleasant smell (best described as garlic or rotten eggs) occurred after the use of a mastic, which was responsible for the release of sulphur compounds on oxidation with the air (Gustafsson, 1990). There have also been many cases of serious mould growth on polymer mastics in bathrooms. Mastics break down when exposed to weather and wind, becoming powdery. They then fall into or out of the joint and represent a toxic risk both inside the building and for the surrounding soil. This decay progresses much more quickly than was assumed during the 1960s when building methods with precast concrete elements began - these days, a large number of buildings have considerable problems and high maintenance costs as a result. The limited durability of mastics is in sharp contrast to the vital functions they are put to perform: air and wind-proofing and, above all, waterproofing. Mastic joints in construction are also often invisible for later inspection. Their use should be reduced to a minimum.
Sealing strips of plastic are already hardened by the manufacturer and are a lower pollution risk in the indoor environment. However, their durability is much shorter than the products they are built to protect, and they can be difficult to replace after a few years.
Thermal insulation made of polystyrene is always delivered as a ready made product. The same is the case for some types of polyure-thane-based insulation, though it is most often blown into buildings on site, being used in particular for filling around windows and doors. Urea formaldehyde foam is always sprayed in on site. The latter emits fumes during the hardening phase, particularly formaldehyde. Depending upon how the materials are installed, ready made products of polystyrene can emit monomers of styrene. From foamed polyurethane there can be emissions of unreacted isocyanates, which are highly toxic even in small concentrations, as well as amines. Emissions of brominated hydrocarbons have also been registered from polyurethane products. Chlorofluorocarbons and hydrochlorofluorocarbons can be emitted during the whole material lifecycle where these are used as foaming agents. This leakage also reduces the insulating properties considerably.
Plastics-based insulation materials have no moisture buffering capacity.
The re-use of plastics-based climatic products is not particularly appropriate because of their short lifespan. Even material recycling of climatic plastic products is not very practicable, as most of them are fixed to other materials. An exception is products consisting of pure polyethylene, polypropylene and polyvinyl chloride that can often be down-cycled to manufacture a range of more or less useful low quality plastic products.
Most plastics can be transformed to energy by combustion in special furnaces with smoke cleaning systems. One should remember that since these are originally oil products, there are corresponding carbon dioxide emissions. Ashes from the furnaces, and plastic waste that is not recycled, must be disposed of safely to prevent seepage into the ground water or soil. Quite a few plastics, especially where there are additives, pigments, softeners, etc. have to be treated as special waste. Once on the refuse tip most plastic waste is not naturally degraded.
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