Solvents and other chemicals

Light distillates can be used directly as solvents or as a chemical base for other products. Amongst these are the monomers, which constitute essential components of plastics (polymers). Solvents are substances that facilitate mixing and penetration of substances such as

Table 9.4 Hazards of organic solvents used in the building industry

Substance

General hazards

Alcohols1

Irritate mucous membranes; larger doses can damage the foetus

DC

Ethanol

< Û.

Propanol

Methanol

Isopropanol

Butanol

Aliphates

Irritate mucous membranes and skin; can act as promoter for carcinogenic substances

Paraffin

Naphtene

Hexane

Aromates

Irritate mucous membranes and skin; some can damage heart, liver, kidneys, nervous system; some are carcinogens and mutagens

Xylene

Toluene

Benzene

Styrene

Chlorinated hydrocarbons

Highly toxic to most organisms; irritate mucous membranes; liver- and kidney-damage; some are carcinogens and mutagens

Dichloroethane

Trichloroethane

Trichloroethylene

Esters

Irritate mucous membranes and skin; slightly damaging to the nervous system

Butyl acetate

Ethyl acetate

Methyl acetate

Ether alcohols

Irritate mucous membranes

Ethylene glycols

Ketones

Irritate mucous membranes; slightly damaging to the nervous system

Methyl isobutyl keton

Acetone

Terpenes2

Irritate mucous membranes; can damage lungs; toxic to aquatic organisms; some are allergens

Limonen

Turpentine

Effects of selected substances Is detailed In Table 2.5. Emissions of organic solvents will also have a global warming potential GWP of approximately 3 by reacting to carbon dioxide in the atmosphere.

1 Can be produced from plants.

2 Produced from plants.

Effects of selected substances Is detailed In Table 2.5. Emissions of organic solvents will also have a global warming potential GWP of approximately 3 by reacting to carbon dioxide in the atmosphere.

1 Can be produced from plants.

2 Produced from plants.

paints and usually evaporate from a finished product, such as in paint that has dried.

The following substances are directly or indirectly used in the building industry.

Ammonia was originally obtained by distillation of nitrogenous vegetable animal waste product, including cow dung. Today ammonia is produced from natural gas. Ammonia is an important ingredient in ammonia phosphates and sulphates which are much used as fire retardants in plant-based insulation materials.

Aliphatic and aromatic hydrocarbons. Amongst the aliphatic hydrocarbons are paraffins, naphthenes and n-hexane, whilst the aro-matics include substances such as xylene, toluene, benzene, ethyl benzene and styrene. These can be used directly as solvents. Styrene, benzene, toluene and xylene are also necessary chemicals for the plastics industry and the latter two are used in the production of organic pigments. Benzene is the initial source of creosote, which is mixed with coal tar to make the impregnating poison carbolineum.

Chlorinated hydrocarbons are formed when hydrocarbons react with hydrochloric acid. They include important solvents such as trichloroethane, trichloromethane, trichloroethene, dichloroethane and dichloromethane. These substances are used mainly in varnishes, paints and paint removers. Dichloroethane is also an important solvent for synthetic rubber and is often used in mastics with a bituminous base. Polychlorobiphenyls (PCBs) have been used widely in the past but are now very seldom used because of their extreme toxicity. These substances have to a large extent been substituted by the chloroparaffins as softeners and binding agents in putty and mastics and as fire retardants in synthetic rubbers. Chloroparaffins are also used as secondary softener in PVC floor coverings.

Fluorocarbons are chemical compounds that contain carbon-fluorine bonds. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) also contain chlorine atoms and are widely used as a foaming agent to make insulation products of polystyrene and polyurethane. These substances are stable in the lower part of the Earth's atmosphere, but when they reach the stratosphere solar radiation is strong enough to break down their molecular structure, releasing chlorine atoms which react with natural ozone and break down the ozone layer (see Table 9.5). The ozone depleting effects of the HCFCs are only about 10% of the CFCs, which were the major cause of ozone layer depletion and have been phased out fairly successfully since the Montreal Protocol of 1989. Hydrofluorocarbons (HFCs) are fluoro-carbons without this problem, and are now replacing the CFCs and HCFCs in most products. The HFCs are less ozone depleting, but like all fluorocarbons still very potent greenhouse gases (see Table 9.5). Perfluorosulphonates are fluorocarbons much used as flame retarders in carpets.

Brominated hydrocarbons. Hydrocarbons react with bromine to form the brominated hydrocarbons. These are much used as flame retardants in plastics; hexabromocyclododecane (HBCD) in insulation foams

Table 9.5 Fluorocarbons used as foaming agents in the plastic industry, their Ozone Depletion Potential (ODP) and Globa, Warming Potential (GWP)

Substance

CAS No

ODP value

GWP value

CFC-11

75-69-4

1

3800

HCFC-22

75-45-6

0.055

1700

HCFC-141b

1717-00-6

0.11

630

HCFC-142b

75-68-3

0.07

2000

HFC-134a

811-97-2

0

1300

HFC-152a

75-37-6

0

140

HFC- 245

460-73-1

0

950

HFC-365

406-58-6

0

890

Pentane

109-66-0

0

11

Carbon dioxide

124-38-9

0

1

ODP is defined as the relative amount of degradation to the ozone layer compared to CFC 11 = 1. See definition of GWP in Table 2.3. Alternative foaming agents of pentane and carbon dioxide are used for comparison.

ODP is defined as the relative amount of degradation to the ozone layer compared to CFC 11 = 1. See definition of GWP in Table 2.3. Alternative foaming agents of pentane and carbon dioxide are used for comparison.

of polystyrene, tetrabromobisphenol A (TBBPA) in epoxy resin, polyurethane and polycarbonate, and polybrominated diphenyl ethers (PBDE) in polyethylene and polypropylene. In Canada, concentrations of brominated flame retardants indoors have been found to be up to 50 times higher than outdoors, indicating that they are volatile (Schmidt, 2006).

Organophosphates are esters of phosphoric acid. They are used primarily as fire retardants in foamed insulation products made with polyurethane and polyisocyanurate, often together with brominated compounds. They are also used in some products of polyvinyl chloride. The main types are Tris(2-chlorethyl)phosphate (TCEP) and Tris(chlor-oisopropyl)phosphate (TCPP).

Alcohols and aldehydes. The alcohols that are mostly used as solvents, especially in varnishes, are ethanol, propanol, isopropanol, butanol, isobutanol and methanol. Phenol is an important ingredient in different building glues. Through further oxidation of alcohol, formaldehyde (an important glue substance when mixed with phenol and urea) is formed.

Ether alcohols and ketones. Important ether alcohols are glycol ethers such as methyl and ethyl glycol. They are used as solvents and plasticizers; for example, in varnishes. Methyl ethyl ketone and methyl isobutyl ketone are the ketones used as solvents in chloroprene glue.

Amines are produced from hydrocarbons in reaction with ammonia. Amines are most common as additives in plastics, such as silicone and polyester, mainly as a hardener or anti-oxidizer. Amines are the starting point for the production of isocyanate, which is the main constituent of polyurethane. Amines are also used in the production of certain organic paint pigments.

Alkenes (or olefines) is the group name for hydrocarbons with double combinations. Amongst the most important are ethylene and propyl-ene, which are produced from naphtha and function as monomers in the production of polyethylene and polypropylene. Vinyl chloride is produced by chlorinating ethylene and is the main constituent of PVC plastics.

Esters are formed when hydrocarbons react with acetic acid. Butyl acetate, ethyl acetate and methyl acetate are commonly used as solvents in glue, whilst polyvinyl acetate (PVAC), is an important binding agent in certain water-based glues and paints. The acrylates are esters of acrylic acid, oxidized from propylene, and is used as a binding agent in paints and the production of plastics such as polymethyl metacrylate ('plexiglass').

Phthallic acid esters are produced when phthallic acid reacts with alcohols. They are used mainly as plasticizers in a range of plastics and can constitute as much as 50% of the material. Important types are diethylhexylphthalate (DEHP), diisodecyl phthalate (DIDP) and diisononylphthalate (DINP).

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