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1、 Petroleum based plasticizer
It is one of the most commonly used plasticizers in rubber processing. Good plasticizing effect, abundant sources, and low cost. Petroleum plasticizers are produced by selecting appropriate crude oil for atmospheric and vacuum distillation. The main varieties include operating oil, three line oil, transformer oil, engine oil, light heavy oil, paraffin, Vaseline, asphalt, and petroleum resin, among which the most commonly used is operating oil.
1. Classification of operating oil
Operating oil is a high boiling fraction of petroleum, composed of complex hydrocarbon compounds with molecular weights ranging from 300 to 600 and a wide molecular weight distribution. According to the different main components in the oil, the operating oil can be divided into the following three types:
① Aromatic oil: Mainly aromatic oil. Brown viscous liquid with the best compatibility with rubber, good processing performance, and fast absorption speed. Suitable for natural rubber and various synthetic rubbers; The disadvantage is that it is polluting and suitable for use in dark colored rubber products.
② Cycloalkane oil: mainly composed of cycloalkanes. Light yellow or transparent liquid, less compatible with rubber than aromatic oil, but less polluting, suitable for NR and various synthetic rubbers.
③ Paraffin oil: also known as paraffin oil, mainly composed of straight or branched chain alkanes. Colorless and transparent liquid, low viscosity, poor compatibility with rubber, poor processing performance, slow absorption rate, mostly used in saturated rubber, with little or no pollution, suitable for use in light colored rubber products.
2. Characteristics of operating oil
(1) The higher the viscosity of the operating oil, the more viscous the oil will be. Operating oil has an impact on the processing performance of the rubber material and the physical properties of the vulcanized rubber. Using low viscosity operating oil has good lubrication effect and improved cold resistance, but there is significant volatilization loss during processing. When the flash point is below 180 ℃, the volatilization loss is greater and special attention should be paid.
The viscosity of the operating oil is closely related to temperature. The viscosity is higher at low temperatures, so the properties of the oil have a significant impact on the low-temperature performance of the vulcanized rubber. Using oil with less viscosity change at low temperatures (dynamic viscosity at -18 ℃) can improve the low-temperature performance of the vulcanized rubber. The viscosity of high aromatic oil is more temperature dependent than that of hydrocarbon oil.
The viscosity of the operating oil is related to the heat generation of the vulcanized rubber, and rubber products using high viscosity oil have higher heat generation. At the same viscosity, aromatic oils have low heat generation. The tensile strength and elongation increase with the increase of oil viscosity, and the flexibility improves, but the tensile stress decreases. If oils of the same viscosity are added in equal volumes, aromatic oils can achieve higher elongation rates than saturated oils.
2) Relative density is usually measured in the petroleum industry at 60 ℃. The relative density of rubber processing oil is crucial when rubber products are sold by weight. Normally, the relative density of aromatic oil is greater than that of alkane oil and cycloalkane oil. Rubber processing oil is often sold by volume, while in rubber processing, it is mixed by weight.
(3) Add 5-10ml of aniline to the test tube, then add the same volume of sample, and heat from the bottom until a uniform transparent solution appears. The temperature at this point is called the aniline point of the oil. The molecular structure of aromatic plasticizers is closest to that of aniline and is easily soluble in it, therefore the aniline point is the lowest. Oils with low aniline point have good compatibility with diene rubber, and when added in large quantities, there is no frost phenomenon. On the contrary, oils with high aniline point need to be miscible with raw rubber at high temperatures, so they are prone to spraying out on the surface when the temperature drops. The high or low operating point of aniline is essentially a marker of the aromatic hydrocarbon content in the oil. Generally speaking, it is more appropriate to operate the oil aniline point within the range of 35-115 ℃.
(4) The pour point (flow point) is the lowest temperature at which flow and tipping can be maintained. This characteristic can indicate the applicability of the operating process temperature to the product.
(5) Flash point refers to the temperature at which a mixture of sufficient steam and air can ignite under standard testing conditions. The flash point of operating oil is directly related to rubber vulcanization, storage, and fire prevention, and can also measure the volatility of operating oil.
(6) Neutrality value is a scale for manipulating oleic acid properties, and high acidity can cause a significant delay in rubber vulcanization rate. The neutralization value can be expressed in milligrams of KOH required to neutralize the acid content of 1 gram of operating oil.
In addition, the refractive index, appearance color, and volatile matter of the oil can also reflect its composition.
3. The influence of operating oil on rubber processing performance
(1) The impact on mixing
The absorption rate of rubber for oil is related to the composition, viscosity, and mixing conditions of the oil: generally low viscosity, high aromatic hydrocarbon content, high temperature, and fast absorption. But the high amount of oil used deteriorates the dispersibility of carbon black in rubber, and it must be added in batches. In addition, adding oil during mixing can reduce heat generation and energy consumption.
(2) The impact on extrusion
Adding an appropriate amount of oil to the rubber material can soften it, resulting in a smooth surface of the semi-finished product, low expansion during extrusion, and fast extrusion speed.
(3) The impact on vulcanization
With the increase of oil filling in the rubber material, the vulcanization rate tends to slow down. The addition of oil reduces the concentration of vulcanizing agents and accelerators in rubber, slowing down the vulcanization rate.
Operating oil with a high content of aromatic hydrocarbons can promote the burning of rubber materials and accelerate vulcanization.
4. Characteristics of using operating oil in several types of rubber
(1) SBR: Aromatic oil is the best, which increases tensile strength and elongation, reduces tensile stress, and improves the flexural flexibility of vulcanized rubber.
(2) BR: Due to the large amount of carbon black filling and the use of more operating oil, the impact on performance is not significant.
(3) CR: Aromatic hydrocarbons are the best choice, followed by cyclohexane oil, and paraffin oil should not be used.
(4) NBR: Generally does not require oil handling, but often uses synthetic plasticizers.
(5) IIR: Use low viscosity oil, cyclohexane oil or paraffin oil, not aromatic oil.
(6) EPDM: Generally does not use aromatic oils, but mostly uses paraffin oil and cyclohexane oil.
2、 Coal tar plasticizer
The main varieties include coal tar, Gumaron, coal tar pitch, and RX-80 resin. Good compatibility with rubber and can improve the aging resistance of rubber. The most commonly used among them is Gumaron resin, which is both a plasticizer and a tackifier, especially suitable for synthetic rubber.
1. Coal tar
Black viscous liquid, odorous, polluting, easily mixed with rubber material, can dissolve sulfur, prevent frosting, improve the aging resistance of products, and increase the adhesion of SBR.
2. Gumaron resin
According to the degree of polymerization, Gumaron resin is divided into liquid Gumaron resin and solid Gumaron resin.
Liquid Gumaron: has plasticizing and thickening effects, better than solid Gumaron, but has low reinforcement and is inconvenient to use.
Solid Gumaron: It has good compatibility with rubber, has plasticizing, tackifying, and reinforcing effects, helps to disperse carbon black, can dissolve sulfur and stearic acid, prevent frosting, improve the adhesion of rubber materials, and enhance the tensile strength and hardness of vulcanized rubber. The dosage is less than 15 parts.
According to the range of softening point of Gumaron, its application also varies. Generally, a viscous liquid with a softening point of 5-30 ℃ belongs to liquid Gumaron, which is used as a plasticizer, adhesive, and rejuvenator in synthetic rubber and natural rubber other than styrene butadiene rubber; Viscous block shaped Gumaron with a softening point of 35-75 ℃ can be used as a plasticizer, adhesive, or auxiliary reinforcing agent; Brittle solid Gumaron resin with a softening point of 75-135 ℃ can be used as a plasticizer and reinforcing agent.
3. RX-80 resin
The reaction activity is very high, which can play a role in plasticizing, thickening, and reinforcing, and can also increase the gloss of colored adhesives.
3、 Pine tar plasticizer
Pine tar is the residual substance obtained by dry distillation of pine roots and pine trunks after removing turpentine oil. The main varieties include pine tar, rosin, rosin oil, tall oil, etc. The most commonly used is pine tar, which can improve the adhesion and cold resistance of the rubber material, help disperse the compounding agent, delay vulcanization, and generate large dynamic heat. Rosin is commonly used in adhesives and adhesives that are bonded to fabrics.
