Shares of global plasticizer consumption in 2014 (8 million metric tons)
For plastics
Plasticizers for plastics are additives, most commonly phthalate esters in PVC applications. Almost 90% of plasticizers are used in PVC, giving this material improved flexibility and durability. The majority is used in films and cables. It was commonly thought that plasticizers work by embedding themselves between the chains of polymers, spacing them apart (increasing the "free volume"), or swelling them and thus significantly lowering the glass transition
temperature for the plastic and making it softer; however it was later
shown that the free volume explanation could not account for all of the
effects of plasticization.
For plastics such as PVC, the more plasticizer added, the lower their
cold flex temperature will be. Plastic items containing plasticizers can
exhibit improved flexibility and durability. Plasticizers can become
available for exposure due to migration and abrasion of the plastic
since they are not bound to the polymer matrix. The "new car smell" is often attributed to plasticizers or their degradation products.
However, multiple studies on the makeup of the smell do not find
phthalates in appreciable amounts, likely due to their extremely low
volatility and vapor pressure.
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.
Antiplasticizers
Antiplasticizers
exhibit effects that are similar, but sometimes opposite, to those of
plasticizers on polymer systems. The effect of plasticizers on elastic modulus
is dependent on both temperature and plasticizer concentration. Below a
certain concentration, referred to as the crossover concentration, a
plasticizer can increase the modulus of a material. The material's glass
transition temperature will decrease however, at all concentrations. In
addition to a crossover concentration a crossover temperature exists.
Below the crossover temperature the plasticizer will also increase the
modulus. Antiplasticizers are any small molecule or oligomer additive
which increases the modulus while decreasing the glass transition
temperature.
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Bis(2-ethylhexyl) phthalate is a common plasticizer.
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 the move away
from classified substances to non-classified which includes high
molecular weight ortho-phthalates and other plasticisers, especially in
Europe.
For concrete
In the concrete technology, plasticizers and superplasticizers are also called high range water reducers. When added to concrete mixtures, they confer a number of properties including improve workability
and strength. Unless the mix is "starved" of water, the strength of
concrete is inversely proportional to the amount of water added, i.e.,
the 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 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. 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 consumed
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 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. Both of 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. 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.
Migration
of plasticizers out of their host plastics leads to loss of
flexibility, embrittlement, and cracking. This decades-old plastic lamp
cord crumbles when flexed, due to loss of the plasticizers.
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 HTPB, a synthetic rubber, as a non-energetic secondary fuel.
Effect on health
Substantial
concerns have been expressed over the safety of some plasticizers,
especially because some low molecular weight ortho-phthalates have been
classified as potential endocrine disruptors with some developmental toxicity reported.
Compounds used as 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
- Bis(2-propylheptyl) phthalate (DPHP), used in cables, wires and roofing materials
- Diisononyl phthalate (DINP), used in flooring materials, 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
- Dioctyl 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.
- 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
- Trimellitates
are used in automobile interiors and other applications where
resistance to high temperature is required. They have extremely low
volatility.
- Trimethyl trimellitate (TMTM)
- Tri-(2-ethylhexyl) trimellitate (TEHTM)(TOTM)
- Tri-(n-octyl,n-decyl) trimellitate (ATM)
- Tri-(heptyl,nonyl) trimellitate (LTM)
- n-octyl trimellitate (OTM)
Adipates, sebacates, maleates
- Adipate-based plasticizers are used for low-temperature or resistance to ultraviolet light. Some examples are:
- Bis(2-ethylhexyl)adipate (DEHA)
- Dimethyl adipate (DMAD)
- Monomethyl adipate (MMAD)
- Dioctyl adipate (DOA)
- Dibutyl sebacate (DBS)
- Dibutyl maleate (DBM)
- Diisobutyl maleate (DIBM)
Other plasticizers
- Azelates
- Benzoates
- Terephthalates such as dioctyl terephthalate/DEHT (Eastman Chemical Company Trademark: Eastman 168).
- 1,2-Cyclohexane dicarboxylic acid diisononyl ester (BASF trademark: Hexamoll DINCH).
- Alkyl sulphonic acid phenyl ester (ASE).
- Sulfonamides
- N-ethyl toluene sulfonamide (o/p ETSA), ortho and para isomers
- N-(2-hydroxypropyl) benzene sulfonamide (HP BSA)
- N-(n-butyl) benzene sulfonamide (BBSA-NBBS)
- Organophosphates
- Tricresyl phosphate (TCP)
- Tributyl phosphate (TBP)
- Glycols and polyethers
- Triethylene glycol dihexanoate (3G6, 3GH)
- Tetraethylene glycol diheptanoate (4G7)
- Polymeric plasticizers
- Polybutene
Bio-based plasticizers
Plasticizers with better biodegradability and presumably lower environmental toxicity are being developed. Some such plasticizers are:
- Acetylated monoglycerides; these can be used as food additives
- Alkyl citrates, used in food packagings, medical products, cosmetics, and children's 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
- Methyl ricinoleate
- Green plasticizers
- Epoxidized soybean oil (ESBO)
- Epoxidized vegetable oils
- Epoxidized esters of soybean oil
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.
