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Synthetic plasticizers are mainly used in rubber or plastics with strong polarity, such as NBR, CR.
The synthetic plasticizer can give the adhesive softness, elasticity and processing properties.
It can also improve cold resistance, oil resistance and flame resistance.
Synthetic plasticizers can be classified into the following types by structure:
Phthalate esters, fatty dibasic esters, fatty acids, phosphates, polyester, epoxy, chlorine and others.
The structure formula is as follows: R is alkyl, aryl, cyclohexyl, etc.
Dibutyl phthalate (DBP) : can improve the flexibility, adhesion and low temperature resistance of the adhesive, but has poor durability.
Dioctyl phthalate (DOP) : it has good comprehensive performance, good compatibility with rubber, good cold resistance, heat resistance and electrical insulation.
Generally, R group is small, good compatibility with rubber, but high volatility and poor durability.
The R group is large, and its volatility, durability and heat resistance are improved, but its plasticization and cold resistance become worse.
Fatty dibasic ester
The formula is as follows:
Mainly used as cold resistance plasticizer, the main varieties are:
Dioctyl adipate (DOA) : excellent cold resistance, but not good enough oil resistance, high volatility.
Dioctyl nonadiate (DOZ) : it has excellent cold resistance, low volatility, heat resistance, light resistance and electrical insulation.
Dioctyl sebacate (DOS) : excellent cold resistance, low volatility and excellent electrical insulation, but poor oil resistance.
Dibutyl sebacate (DBS) : good cold resistance, but high volatility, easy to migrate, easy to extract.
Fatty acid esters
Cold resistance is very good, the main varieties are oleic acid ester, pentaerythritol fatty acid ester, citrate ester.
Commonly used varieties include butyl oleate (BO), which has superior cold resistance and water resistance, but poor weather resistance and oil resistance.
In the structural formula, R1, R2 and R3 represent alkyl, chloroalkyl and aryl.
Mainly used as flame-resistant plasticizer, the higher the dosage, the better the flame resistance, the less alkyl components in the molecules, the better the flame resistance.
Common varieties are: trimethylphenyl phosphate (TCP) : good fire resistance, heat resistance, oil resistance and electrical insulation, poor cold resistance.
Trioctyl phosphate (TOP) : good cold resistance, low volatility, but easy to migrate, poor oil resistance.
Polyester with a molecular weight of 1000~8000 is mainly used as oil resistant plasticizer with little volatility, migration, oil resistant, water resistant and heat resistant.
Main varieties: sebacic acid series, adipic acid series, phthalic acid series.
Among them sebacic acid series of plasticizing effect is good, phthalic acid series of plasticizing effect is poor.
These ester synthetic plasticizers have high polarity and are mostly used in polar rubber.
With the increase of dosage, the physical and mechanical properties of rubber decreased, but the elongation and resilience increased.
Using straight - chain fatty acid esters can improve the cold resistance of vulcanizate, but easy to extract.
In NBR commonly used DOP, DBP, TCP, etc. can be used for cold-resistant products, such as DOA, DOZ, DBS, etc., and polyester plasticizer can be used for oil resistance.
CR usually USES 5~10 petroleum plasticizers, but ester plasticizers should be used for cold-resistant products, polyester plasticizers can be used for oil resistant products.
SBR: use petroleum plasticizer to improve processing performance;
To improve cold resistance, use fatty acids and fatty diacid ester plasticizers.
IIR: DOA and DOS plasticizers can be used to improve cold resistance, and polyester plasticizers can be used to improve oil resistance.
Such plasticizers include epoxidated oil, epoxidated fatty acid single ester and epoxidated phthalate ester.
Epoxy plasticizers contain epoxy structures in their molecules and have good heat and light resistance.
Epoxidated oils, such as epoxidated soybean oil and epoxidated linseed oil, have higher epoxidation values, generally ranging from 6% to 7%. They have good heat resistance, light resistance, oil resistance and volatile resistance, but poor cold resistance and plasticizing effect.
Epoxy value of epoxidated fatty acid monesters is mostly 3% ~ 5%, with good cold resistance and better plasticizing effect than DOA.
The common mono-ester of epoxidated fatty acids are epoxy butyl oleate, octyl ester and tetrahydrofuryl alcohol ester.
Epoxidated tetrahydrophthalic ester has a lower epoxy value, generally only 3% ~ 4%, but they have both epoxy structure and phthalic ester structure, thus improving the poor solubility of epoxy oil. They have the same comprehensive performance as DOP, and their thermal stability is better than DOP.
Chlorine-containing plasticizers are also flammable plasticizers.
Such plasticizers mainly include chlorinated paraffin, chlorinated fatty acid ester and chlorinated biphenyls.
Chlorinated paraffin contains about 35% ~ 70% chlorine, and generally contains 40% ~ 50% chlorine.
In addition to flame resistance, chlorinated paraffin has good electrical insulation and can increase the gloss of products.
With the increase of chlorine content, the flame resistance, mutual solubility and mobility of chlorine increased.
The main disadvantages of chlorinated paraffin are poor cold resistance, heat resistance stability and weather resistance.
Chlorinated fatty acid ester plasticizers are mostly single ester plasticizers, so their mutual solubility and cold resistance are better than chlorinated paraffin.
With the increase of chlorine content, the flame resistance increases, but the tensile stress increases and the cold resistance decreases.
Chlorinated biphenyls have no corrosion effect on metal except fire resistance, do not decompose when exposed to water, have little volatility, good mixture and electrical insulation, and are resistant to bacteria.
8. New plasticizer
Physical plasticizers are volatile, easy to transport, easy to extract, volume shrinkage of products, development of new plasticizers direction:
Reactive plasticizer: plasticizer molecules may react with rubber macromolecules at the curing temperature, or polymerize themselves, such as isoprene oligomers with a terminal group containing an acetate group with a molecular weight of less than 10000.
Liquid rubber also has a certain plasticizing effect, mutual solubility good, difficult to take out, not volatile, such as liquid NBR.
Low molecular weight CR: it can be used as CR plasticizer. It is not easy to be drawn out.
Styrene oligomer synthesized by CCl4 and CHBr3 as regulator can be used as plasticizer for IR, NBR, SBR and BR.
Fluorine waxes (low molecular weight vinylidene fluoride and hexafluoropropene polymers) are used as plasticizers for fluorine rubber.