Plasticizers (UK: also plasticisers) or dispersants are additives that increase the plasticity or fluidity of a material. The dominant applications are for plastics, especially polyvinyl chloride (PVC). The properties of other materials are also improved when blended with plasticizers including concrete, clays, and related products. The worldwide market for plasticizers in 2000 was estimated to be several million tons per year.
For plastics 
Plasticizers for plastics are additives, most commonly phthalate esters in PVC applications. Almost 90% of the market for plasticizer is for PVC, giving this material improved flexibility and durability. Plasticizers work by embedding themselves between the chains of polymers, spacing them apart (increasing the "free volume"), and thus significantly lowering the glass transition temperature for the plastic and making it softer. For plastics such as PVC, the more plasticizer added, the lower its cold flex temperature will be. This means that it will be more flexible and its durability will increase as a result of it. Plasticizers evaporate and tend to concentrate in an enclosed space; the "new car smell" is caused mostly by plasticizers evaporating from the car interior.
Plasticizers make it possible to achieve improved compound processing characteristics, while also providing flexibility in the end-use product. Ester plasticizers are selected based upon cost-performance evaluation. The rubber compounder must evaluate ester plasticizers for compatibility, processibility, permanence and other performance properties. The wide variety of ester chemistries that are in production include sebacates, adipates, terephthalates, dibenzoates, gluterates, phthalates, azelates, and other specialty blends. This broad product line provides an array of performance benefits required for the many elastomer applications such as tubing and hose products, flooring, wall-coverings, seals and gaskets, belts, wire and cable, and print rolls. Low to high polarity esters provide utility in a wide range of elastomers including nitrile, polychloroprene, EPDM, chlorinated polyethylene, and epichlorohydrin. Plasticizer-elastomer interaction is governed by many factors such as solubility parameter, molecular weight and chemical structure. Compatibility and performance attributes are key factors in developing a rubber formulation for a particular application.
Plasticizers also function as softeners, extenders, and lubricants, and play a significant role in rubber manufacturing.
Ester plasticizers 
Plasticizers used in PVc and other plastics are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. These compounds are selected on the basis of many critieria including low toxicity, compatibility with the host material, nonvolatility, and expense. Phthalate esters of straight-chain and branched-chain alkyl alcohols meet these specifications and are common plasticizers. Ortho-phthalate esters have traditionally been the most dominant plasticizers, but regulatory concerns have led to pressure to change to non-phthalate plasticizers, especially in Europe.
For concrete 
Plasticizers or water reducers, and superplasticizer or high range water reducers, are chemical admixtures that can be added to concrete mixtures to improve workability. Unless the mix is "starved" of water, the strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is added (without "starving" the mix), which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants. 
Plasticizers are also often used when pozzolanic ash is added to concrete to improve strength. This method of mix proportioning is especially popular when producing high-strength concrete and fiber-reinforced concrete.
Adding 1-2% plasticizer per unit weight of cement is usually sufficient. Adding an excessive amount of plasticizer will result in excessive segregation of concrete and is not advisable. Depending on the particular chemical used, use of too much plasticizer may result in a retarding effect.
Plasticizers are commonly manufactured from pop lignosulfonates, a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, although newer products based on polycarboxylic ethers are now available. Traditional lignosulfonate-based plasticisers, naphthalene and melamine sulfonate-based superplasticisers disperse the flocculated cement particles through a mechanism of electrostatic repulsion (see colloid). In normal plasticisers, the active substances are adsorbed on to the cement particles, giving them a negative charge, which leads to repulsion between particles. Lignin, naphthalene and melamine sulfonate superplasticisers are organic polymers. The long molecules wrap themselves around the cement particles, giving them a highly negative charge so that they repel each other.
Polycarboxylate ether superplasticizer (PCE) or just polycarboxylate (PC), work differently from sulfonate-based superplasticizers, giving cement dispersion by steric stabilisation, instead of electrostatic repulsion. This form of dispersion is more powerful in its effect and gives improved workability retention to the cementitious mix.
For gypsum wallboard production 
Plasticizers can be added to wallboard stucco mixtures to improve workability. In order to reduce the energy in drying wallboard, less water is added, which makes the gypsum mixture very unworkable and difficult to mix, necessitating the use of plasticizers, water reducers or dispersants. Some studies also show that too much of lignosulfonate dispersant could result in a set-retarding effect. Data showed that amorphous crystal formations occurred that detracted from the mechanical needle-like crystal interaction in the core, preventing a stronger core. The sugars, chelating agents in lignosulfonates such as aldonic acids and extractive compounds are mainly responsible for set retardation. These low range water reducing dispersants are commonly manufactured from lignosulfonates, a by-product from the paper industry.
High range superplasticizers (dispersants) have generally been manufactured from sulfonated naphthalene condensate, although polycarboxylic ethers represent more modern alternatives. These high range water reducers are used at 1/2 to 1/3 of the lignosulfonate types.
Traditional lignosulfonate and naphthalene sulfonate based plasticisers disperse the flocculated gypsum particles through a mechanism of electrostatic repulsion (see colloid). In normal plasticisers, the active substances are adsorbed on to the gypsum particles, giving them a negative charge, which leads to repulsion between particles. Lignin and naphthalene sulfonate plasticizers are organic polymers. The long molecules wrap themselves around the gypsum particles, giving them a highly negative charge so that they repel each other.Kirby, Glen H.; Jennifer A. Lewis (2002). "Rheological property evolution in concentrated cement-polyelectrolyte suspensions". Journal of the American Ceramic Society 85 (12): 2989–2994. doi:10.1111/j.1151-2916.2002.tb00568.x. Retrieved 2008-03-27.
Plasticizers for energetic materials 
Energetic material pyrotechnic compositions, especially solid rocket propellants and smokeless powders for guns, often employ plasticizers to improve physical properties of the propellant binder or of the overall propellant, to provide a secondary fuel, and ideally, to improve specific energy yield (e.g. specific impulse, energy yield per gram of propellant, or similar indices) of the propellant. An energetic plasticizer improves the physical properties of an energetic material while also increasing its specific energy yield. Energetic plasticizers are usually preferred to non-energetic plasticizers, especially for solid rocket propellants. Energetic plasticizers reduce the required mass of propellant, enabling a rocket vehicle to carry more payload or reach higher velocities than would otherwise be the case. However, safety or cost considerations may demand that non-energetic plasticizers be used, even in rocket propellants. The solid rocket propellant used to fuel the Space Shuttle solid rocket booster employs a non-energetic plasticizer/binder/secondary fuel: HTPB. HTPB is a synthetic rubber.
Substantial concerns have been expressed over the safety of some plasticizers, especially because several ortho-phthalates have been classified as potential endocrine disruptors with some developmental toxicity reported.
Appendix: various specific plasticizers 
Dicarboxylic/tricarboxylic ester-based plasticizers 
- Phthalate-based plasticizers are used in situations where good resistance to water and oils is required. Some common phthalate plasticizers are:
- Bis(2-ethylhexyl) phthalate (DEHP), used in construction materials and medical devices
- Diisononyl phthalate (DINP), found in garden hoses, shoes, toys, and building materials
- Di-n-butyl phthalate (DnBP, DBP), used for cellulose plastics, food wraps, adhesives, perfumes, and cosmetics - about a third of nail polishes, glosses, enamels, and hardeners contain it, together with some shampoos, sunscreens, skin emollients, and insect repellents
- Butyl benzyl phthalate (BBzP) is found in vinyl tiles, traffic cones, food conveyor belts, artificial leather, and plastic foams
- Diisodecyl phthalate (DIDP), used for insulation of wires and cables, car undercoating, shoes, carpets, pool liners
- Di-n-octyl phthalate (DOP or DnOP), used in flooring materials, carpets, notebook covers, and high explosives, such as Semtex. Together with DEHP it was the most common plasticizers, but now is suspected of causing cancer
- Diisooctyl phthalate (DIOP), all-purpose plasticizer for polyvinyl chloride, polyvinyl acetate, rubbers, cellulose plastics, and polyurethane.
- Diethyl phthalate (DEP)
- Diisobutyl phthalate (DIBP)
- Di-n-hexyl phthalate, used in flooring materials, tool handles, and automobile parts
- Trimellitates are used in automobile interiors and other applications where resistance to high temperature is required. They have extremely low volatility.
Adipates, sebacates, maleates 
- Adipate-based plasticizers are used for low-temperature or resistance to ultraviolet light. Some examples are:
Other plasticizers 
- Terephthalates such as Dioctyl terephthalate/DEHT (Eastman Chemical Company Trademark: Eastman 168).
- 1,2-Cyclohexane dicarboxylic acid diisononyl ester (BASF trademark: DINCH).
- Epoxidized vegetable oils
- alkyl sulphonic acid phenyl ester (ASE).
- Polymeric plasticizers
Biodegradable plasticizers 
Safer plasticizers with better biodegradability and fewer biochemical effects are being developed. Some such plasticizers are:
- Alkyl citrates, used in food packagings, medical products, cosmetics and children toys
- Triethyl citrate (TEC)
- Acetyl triethyl citrate (ATEC), higher boiling point and lower volatility than TEC
- Tributyl citrate (TBC)
- Acetyl tributyl citrate (ATBC), compatible with PVC and vinyl chloride copolymers
- Trioctyl citrate (TOC), also used for gums and controlled release medicines
- Acetyl trioctyl citrate (ATOC), also used for printing ink
- Trihexyl citrate (THC), compatible with PVC, also used for controlled release medicines
- Acetyl trihexyl citrate (ATHC), compatible with PVC
- Butyryl trihexyl citrate (BTHC, trihexyl o-butyryl citrate), compatible with PVC
- Trimethyl citrate (TMC), compatible with PVC
Plasticizers for energetic materials 
- Nitroglycerine (NG, aka "nitro", glyceryl trinitrate)
- Butanetriol trinitrate (BTTN)
- Dinitrotoluene (DNT)
- Trimethylolethane trinitrate (TMETN, aka Metriol trinitrate, METN)
- Diethylene glycol dinitrate (DEGDN, less commonly DEGN)
- Triethylene glycol dinitrate (TEGDN, less commonly TEGN)
- Bis(2,2-dinitropropyl)formal (BDNPF)
- Bis(2,2-dinitropropyl)acetal (BDNPA)
- 2,2,2-Trinitroethyl 2-nitroxyethyl ether (TNEN)
Due to the secondary alcohol groups, NG and BTTN have relatively low thermal stability. TMETN, DEGDN, BDNPF and BDNPA have relatively low energies. NG and DEGN have relatively high vapor pressure. 
- David F. Cadogan and Christopher J. Howick "Plasticizers" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a20_439
- Cement Admixture Association. "CAA". www.admixtures.org.uk. Retrieved 2008-04-02.
- Cemex Mortars, p. 6
- Plasticisers Information Centre
- Glass transition
- DIDP, DINP, and DBP - Risk Assessment Reports by the European Chemicals Bureau (ECB).
- Medscape: Alternative Materials for Flexible PVC and DEHP