Classification of Lubricant Varieties – Saturated Hydroxyl “Polyethylene Wax”

2022-04-22   Pageview:15

Saturated hydroxyls are mainly natural and synthetic waxes. Hydroxy compounds are generally less polar than PVC, have poor compatibility with PVC, and are easy to migrate to the surface. Due to their low surface energy, they can better prevent polymerization. Vinyl chloride sticks to metal surfaces. Mainly lubricated outside, non-toxic, low melting point varieties include liquid paraffin and so on. High melting point varieties include polyethylene wax and oxidized polyethylene wax.

Generally, hydroxyl compounds with lower molecular weight and melting point have better initial lubricity, while those with higher molecular weight and melting point have better lubricity in the later period.

Paraffin wax:
straight chain alkane hydroxyl mixture, relative density 0.87-0.92, melting point about 57-63 ℃, soluble in gasoline, chloroform, xylene and other solvents, insoluble in small, no polar groups, and poor compatibility with polyvinyl chloride , is a typical external lubricant.

Due to the low melting point of paraffin wax, easy precipitation, many times of mold cleaning, low melt viscosity and low lubricating efficiency, it can only play a lubricating role in a narrow range, and has an adverse effect on physical properties such as weld fillet strength. In the production of plastic profiles, try not to use paraffin, or use paraffin and stearic acid together, which can reduce volatility and improve lubrication. Generally 0.1-0.8 is used. The optimal dose is 0.05-0.2. In organotin formulations, high-melting paraffin wax, such as Sasol wax or refined wax with a melting point of 75°C, can be used as external lubricants. In the presence of calcium stearate, stearic acid can also be used to replace paraffin to exert external lubrication.

Polyethylene wax:
PE wax, which is a low molecular weight by-product in the production of polyethylene resin, also known as low molecular weight polyethylene.

Foreign products are obtained by direct polymerization of ethylene, and the molecular weight is controlled by the degree of polymerization, such as Honeywell, BASF, Degussa, Mitsui and other companies. Most of the domestic enterprises use the cracking method for production, and the molecular weight is controlled by the cracking temperature and pressure. There are also manufacturers who use Sinopec, PetroChina and other large enterprises to start and stop the production of PE in the process of producing PE. The quality is extremely unstable, and the molecular weight and molecular weight distribution varies from batch to batch. The molecular weight, distribution, structure and lubricating properties of the products prepared by different methods are different.

Polyethylene wax is white powder with an average relative molecular weight of 1500-5000. The relative density is about 0.9, and the softening point is about 100-117 °C. Due to the relatively large relative molecular weight, high melting point and low high temperature volatility, it shows obvious lubricating effect at higher temperature and shear rate. The usual amount is 0.1-0.3 servings. It can effectively improve the fluidity of plastic processing. The spit volume and film release have both strong external lubrication and strong internal lubrication. High softening point, low melting degree, strong thermal stability and good dispersibility. Excellent electrical performance, non-toxic use and low cost.

In view of the domestic production of polyethylene wax melting point is mostly 70 ℃ -80 ℃. The molecular weight of PE wax produced by the cracking method is only about 2000, which cannot meet the requirements of improving the brightness of plastic products. Even the same well-known foreign AC6 molecular weight is only about 2700. Germany BASDE uses the world’s top synthetic method to produce AN wax with a molecular weight of 7000, which is recognized as the best wax in the world. Although the price is high, but because of its large lubricating effect, the amount of addition is small. It is currently used by many companies. Especially due to the increasing production of calcium powder and recycled materials, and the increase of screw and screw mills, the role of this kind of high-grade PE wax is more and more important.

Oxidized polyethylene wax (OPE):
melting point 115℃-125℃, external and internal lubrication. Oxidized polyethylene wax is a partial oxidation product of polyethylene wax, with certain carboxyl and hydroxyl groups on the molecular chain, and the appearance is white or light yellow fluid powder or granules. Although OPEWax contains a small amount of polar groups, it is still incompatible with PVC and has high external lubrication efficiency. However, CPE and ACR are added to the lead salt stabilizer system of the rigid PVC formula, and the oxidized polyethylene wax has great compatibility with CPE and ACR. Oxidized polyethylene wax also acts as an internal lubricant. It can be seen that the oxidized polyethylene wax has both internal and external lubricating functions.

OPE is divided into high density and low density, oxidizing and non-oxidizing. Oxidized polyethylene wax has a certain amount of hydroxyl groups on the molecular chain, and their compatibility with polar lipids is significantly improved, and they have good compatibility with rubber, plastic, paraffin and other materials. The internal and external lubrication effects of PVC are relatively balanced; the lubricity of adding oxidized polyethylene wax to the hard transparent PVC formulation is better than that of non-oxidized polyethylene wax and other lubricants. Those with an acid value greater than 13 can be used as an emulsification type; high-density OPE has very efficient internal and external lubrication, which can accelerate the plasticization process, improve metal detachment, blast body plasticization uniformity, dimensional stability, and high productivity; low density OPE is a high-efficiency external lubricant, which can maintain the best material and performance properties of profiles under high shear operating conditions, and has good metal peeling properties. The lubricating effect of a lubricant is sometimes also characterized by an acid value.

Acid value is the content of inorganic acid and organic acid in lubricating oil, expressed in milligrams of potassium hydroxide required to neutralize LC oil sample, the unit is mgKOH/g, the acid value of lubricating oil can measure the oxidation of lubricating oil during use The degree of deterioration has a great influence on the use of lubricating oil. The larger the acid value, the faster the plasticization and the stronger the internal lubrication. When the OPE acid value is above 15, it is basically completely compatible with gloss improve wax pvc, and is only used for transparent products. If the acid value of the lubricant is too large, it means that its organic acid content is high, which may cause corrosion to mechanical parts, especially when there is water, the corrosion effect is more obvious. If the acid value is too large, the oil should be changed. Low-density non-oxidizing OPE has very low acid value or basically no acid value, poor polarity, and is incompatible with polar resin PC. It mainly plays the role of external lubrication and delayed plasticization. Secondly, high-density OPE also has high viscosity, low acid value and low viscosity, high acid value. OPE with high viscosity and low acid value is very effective in accelerating plasticization and reducing costs; OPE with low viscosity and high acid value has accelerated plasticization, super metal peeling, and excellent dispersion effect. The basic dosage of the above OPE in the processing of plastic products is 0.1-0.3 parts.

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