Plasticizers are additives that increase the plasticity or fluidity of the material to which they are added, these include plastics, cement, concrete, wallboard and clay bodies. Although the same compounds are often used for both plastics and concretes, the desired effect is slightly different. In 2004, the worldwide market for plasticizers had a total volume of around 5.5 million tons, which led to a turnover of about 7 billion Euro.[1]
Plasticizers for concrete soften the mix before it hardens, increasing its workability or reducing water, and are usually not intended to affect the properties of the final product after it hardens.
Plasticizers for wallboard increases fluidity of the mix, allowing lower use of water and thus reducing energy to dry the board.
The plasticizers for plastics soften the final product increasing its flexibility.
Superplasticizers or high range water reducers or dispersants are chemical admixtures [2] 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 very unworkable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants.
Superplasticizers 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% superplasticizer per unit weight of cement is usually sufficient. However, note that most commercially available superplasticizers come dissolved in water, so the extra water added has to be accounted for in mix proportioning. Adding an excessive amount of superplasticizer will result in excessive segregation of concrete and is not advisable. Some studies also show that too much superplasticizer will result in a retarding effect.
Plasticizers are commonly manufactured from lignosulfonates, a by-product from the paper industry. High Range Superplasticizers have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, although new-generation 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 ethers (PCE) or just polycarboxylate (PC), the new generation of superplasticisers, are not only chemically different from the older sulfonated melamine and naphthalene-based products, but their action mechanism is also different, 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. Furthermore, the chemical structure of PCE allows for a greater degree of chemical modification than the older-generation products, offering a range of performance that can be tailored to meet specific needs.
In ancient times, the Romans used blood as a superplasticizer for their concrete mixes.[citation needed]
Plasticisers can be obtained from a local concrete manufacturer.
Household washing up liquid may also be used as a simple plasticizer.
Superplasticizers or dispersants, are chemical additives that can be added to wallboard 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.
Adding about two pounds per thousand square feet of 1/2 inch wallboard (15 g/m² of wallboard) of dispersant is usually sufficient. 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.
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 new generation products based on polycarboxylic ethers are now available. Traditional lignosulfonate and naphthalene sulfonate based superplasticisers 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.
