A plasticizer is an additive to polymeric materials widely used in industrial production, also known as a plasticizer. Any substance added to a polymer material that can increase plasticity of a polymer is called a plasticizer. The use of plasticizers makes it possible to improve operational characteristics of polymeric materials, reduce cost of production and increase production efficiency. This is an important class of additives to chemical products. As an additive, it is widely used in plastic products, concrete, gypsum, cement, gypsum, cosmetics and cleaning products, especially PVC products. To increase plasticity of plastics And to increase strength of plastics, phthalates must be added, and their content can sometimes reach 50% of product.
There are many types of plasticizers, mainly aliphatic diacid esters, phthalates (including phthalates, terephthalates), benzoate esters, benzoate classes, polyol esters, chlorinated hydrocarbons, epoxy resins, citric acid esters, polyesters, etc. e. Plasticizers in narrow sense mainly refer to phthalates, which is a general term for about 30 esters formed by phthalic acid. At present, this is main part of plasticizers, mainly consisting of 1 rigid planar aromatic ring and 2 consisting of plastic non-linear fatty acids. chains. Different types of plasticizers affect product performance in different ways. In real production, one plasticizer is rarely used alone, and several plasticizers are often mixed to achieve a good plasticizing effect.
The function of plasticizer is mainly to weaken secondary bonds between resin molecules, increase mobility of resin molecular bonds, reduce crystallinity of resin molecules, increase plasticity of resin molecules, improve its flexibility and be easy to process. Plasticizers usually have a polar or partially polar structure and are liquids or low-melting solids with a high boiling point, low volatility and good miscibility with polymers. The plasticizer is distributed between macromolecular chains, which can reduce intermolecular force, lower melting point and viscosity of polymer melt, thereby lower its molding temperature, and make polymer product soft, elastic and resistant to low temperatures.
Plasticizers fall into two categories: primary plasticizers and secondary plasticizers. The role of primary plasticizers is to be well compatible with resins, with low permeability and low volatility, which can improve plasticization efficiency. The most commonly used basic plasticizers are phthalates and phosphates. Secondary plasticizers are also called co-plasticizers. Their main function is to use them together with basic plasticizers to reduce costs. Commonly used secondary plasticizers include cold-resistant esters of aliphatic dibasic acids and cyclic ether plasticizers.
When a small amount of plasticizer is added, effect on mechanical strength of material is not obvious, and when a small amount of plasticizer is added to material, mechanical strength is highest, which is most called anti-plasticization phenomenon. It is generally believed that anti-plasticization phenomenon is effect of adding a small amount of plasticizer to increase mobility of macromolecular chains, causing molecules to form microcrystals. The impact strength of solid products with a small amount of plasticizer is less than without addition of a small amount.plasticizer properties, but after increasing a certain amount, impact strength increases with increasing amount, which is in accordance with universal law. In addition, when plasticizers are added, heat resistance and corrosion resistance of product will decrease. Therefore, no plasticizers are usually added to solid products, or fewer plasticizers are added. Sometimes several plasticizers are added to improve fluidity of processing. In soft products, it is necessary to add a large amount of plasticizer, larger amount of plasticizer, softer product. The total amount of plasticizer should be different depending on softness requirements of product and use environment, process and use.
When a plasticizer is used in a resin, its polarity is different from that of resin, and its mechanism of action is also different. There are basically two effects in organic mechanism.
1. Volume Effect
This effect is mainly characteristic of non-polar plasticizers. Its mechanism of action is to penetrate into middle of molecular chain of resin, increasing distance between molecules, thereby weakening force between molecules and reducing viscosity of melt. , to increase flexibility of molecular chain, more such plasticizers are added, greater volume effect, and volume effect of long-chain plasticizers is greater than that of ring-shaped plasticizers.
2. Screening effect
This effect is characteristic mainly of polar plasticizers by replacing polar attraction between polymer molecules with interaction between polar plasticizer and polar polymer, thereby weakening force between molecules. This plasticizing effect is called screening effect.
Plasticizers mainly have following properties: plasticizing efficiency, compatibility, frost resistance, durability, heat resistance, insulation, fire resistance and hygiene.
Plasticizing efficiency: The plasticizing ability of a plasticizer to a polymer, or plasticizing effect is good or bad. The plasticizing efficiency of various plasticizers is a relative concept. The efficiency of plasticization is usually evaluated by amount of added plasticizer to change quantitative indicator of flexibility. The less plasticizer is added, higher efficiency of plasticization. Common molecular weight plasticizers, together with higher molecular weight plasticizers, have higher plasticizing efficiency for PVC, but as plasticizer molecule polarity increases, degree of alkyl branching and increase in aromatic ring structure reduce plasticizing efficiency.
The order of plasticizing efficiency of commonly used plasticizers is as follows:
Compatibility: refers to compatibility between plasticizer and polymer. The same plasticizer has different compatibility with different polar polymers.
Order of compatibility between commonly used plasticizers and PVC:
Cold resistance: refers to cold resistance of products plasticized with a plasticizer. The cold resistance of a plasticizer is related to its structure. An aliphatic dibasic acid ester with methylene (-CH2-) as main body has best frost resistance and is most commonly used frost-resistant plasticizer. Branched plasticizers have excellent frost resistance, as they are difficult to move in polymer at low temperatures. temperatures.
The order of frost resistance of widely used plasticizers:
Durability: refers to ability of plasticizers to persist in plasticized products. Mainly include migration resistance, extraction resistance and volatility resistance.
Migration resistance Migration of plasticizers involves two aspects: one is exudation of plasticizer from inside of product to outer surface, and other is transfer of plasticizer to solid upon contact with it. The migration of a plasticizer is related to its compatibility, worse compatibility, greater migration. In addition, plasticizers with large molecular weight, branched chain or ring structure have good resistance to migration.
Resistance to extraction: Refers to tendency of a plasticizer to diffuse into liquid medium with which it comes into contact. The medium mainly includes water, solvent, detergent and lubricating oil. In terms of oil resistance and resistance toFor solvents, plasticizers with a large proportion of non-polar alkyl groups have poor extraction resistance, plasticizers with phenyl, ester groups and a high degree of branching have good extraction resistance, and poor water resistance. to above, polyesters are plasticizers with excellent extraction resistance.
Evaporation resistance: refers to tendency of a plasticizer to diffuse from surface of a product into air when heated. The volatility of a plasticizer is related to its molecular weight: as a rule, lower molecular weight, higher its volatility. In terms of molecular structure, linear alkyl plasticizers have better volatility than branched alkyl plasticizers; plasticizers that contain large bulky groups, such as rings, have best volatility. In general, plasticizers such as polyester, epoxy, DIOP, TCP, and pentaerythritol have good volatility.
Insulation: The insulation of plasticizer is not as good as PVC resin. As amount of plasticizer added increases, electrical insulation of PVC decreases. When choosing a plasticizer for PVC insulation products, attention should be paid to its insulation.
Insulation order of commonly used plasticizers:
Hygiene: refers to toxicity of plasticizers. Most plasticizers are non-toxic or have low toxicity. Epoxy esters and citric acid esters are non-toxic plasticizers, phthalates and dicarboxylic acids are low-toxic plasticizers, but DOP and DOA are suspected to cause cancer; most phosphate plasticizers are toxic, with exception of diphenyl-2-ethylhexyl phosphate; chlorinated paraffin is also a toxic plasticizer.
Combustion temperature. Phosphoric esters and chlorinated paraffins are flame retardant plasticizers and order of fire resistance is: