Plasticizer

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Plasticizers are additives that increase the plasticity or fluidity the material to which they are added, these include plastics, cement, concrete and clay bodies. Although the same compounds are often used for both plastics and concretes, the desired effect is slightly different. The plasticizers for plastics soften the final product increasing its flexibility. Plasticizers for concrete soften the mix before it hardens, increasing its workability, and are usually not intended to affect the properties of the final product after it hardens.

Plasticizers for plastics

Plasticizers for plastics are additive, most commonly phthalates, that give hard plastics like PVC the desired flexibility and durability. They are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. Plasticizers work by embedding themselves between the chains of polymers, spacing them apart (increasing of 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 plasticiser added, the lower its cold flex temperature will be. This means that it will be more flexible, though its strength and hardness will decrease as a result of it. Some plasticizers evaporate and tend to concentrate in an enclosed space; the "new car smell" is caused mostly by plasticizers evaporating from the car interior.

Dicarboxylic/tricarboxylic ester-based plasticizers

Other plasticisers

  • Polymeric plasticizers

Some other chemicals working as plasticizers are nitrobenzene, carbon disulfide and β-naphthyl salicylate. Plasticizers, such as DEHP and DOA, were found to be carcinogens and endocrine disruptors.

Safer plasticizers

Safer plasticizers with better biodegradability and less biochemical effects are being developed. Some such plasticizers are:

Plasticizers for energetic materials

For energetic materials, especially propellants (eg. smokeless powders), plasticizers based on nitrates are frequently employed. Some such plasticizers are:

Due to the secondary alcohol groups, NG and BTTN have relatively low thermal stability. METN, DEGN, BDNPF and BDNPA have relatively low energies. NG and DEGN have relatively high vapor pressure. [1]

Plasticizers for concrete production

Superplasticizers are chemical admixtures that can be added to concrete mixtures to improve workability. 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, which makes the concrete mixture very unworkable and difficult to mix, necessitating the use of plasticizers and superplasticizers.

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 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. Superplasticizers have generally been manufactured from sulfonated naphthalene formaldehyde or sulfonated melamine formaldehyde, although new generation products based on polycarboxylic ethers are now available. Traditional lignosulfonate based plasticisers and naphthalene and melamine 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. Naphthalene and melamine 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), the new generation of superplasticisers are not only chemically different from the older sulphonated 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.

Plasticisers can be obtained by your local concrete manufacturer

Household washing up liquid may also be used as a simple plasticizer.

External links

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