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Types and application of polyethylene wax

Types and application of polyethylene wax

2021-11-16

Polyethylene wax in a narrow sense is a kind of homopoly polyethylene with low relative molecular weight; Broadly speaking, polyethylene wax also includes modified polyethylene wax and copolymerized polyethylene wax. Generally, if a polyethylene polymer can not provide a certain strength and toughness like resin, and can not be processed as a single material into products with certain functions, we can classify it as polyethylene wax.

Polyethylene wax is divided into many kinds, which can be divided into polymerization, thermal cracking and by-products according to its source. Polymerization polyethylene wax refers to polyethylene wax polymerized by ethylene monomer. According to different polymerization methods, it is divided into several categories: free radical polymerization, Ziegler Natta polymerization, metallocene catalytic polymerization and proprietary polymerization technology. Thermal cracking refers to high-temperature cracking with PE resin as raw material by screw extrusion or reactor, and cracking polyethylene resin or recycled polyethylene plastic into polyethylene wax with low relative molecular weight. Compared with polyethylene wax by polymerization, the relative molecular weight distribution is wide, and the taste from low relative molecular weight is difficult to be completely eliminated, Sometimes it is difficult to avoid black spots. The by-product polyethylene wax comes from the by-product of the synthesis of high-density polyethylene resin. It is an oligomer, usually a mixture of several oligomers with different polymerization degrees. It is difficult to control the quality stability. If the distillation cutting method is adopted, polyethylene wax with different melting processes can be divided into polyethylene wax. 

Polyethylene wax is widely used in plastics, such as pigment dispersant, lubricant for PVC mixture, flow modifier and compatibilizer in PE and PP modifier, etc.

1. polyethylene wax is classified according to production route

1.1 synthetic polyethylene wax

Polyethylene wax polymerized by high-pressure free radical has a number average relative molecular weight of 1000 ~ 6000, a relative molecular weight distribution of 2 ~ 5, a Brookfield viscosity of 100 ~ 3000cps, a high degree of branching, generally soft and diverse products. It belongs to low-density polyethylene wax.

Polyethylene wax polymerized by low-pressure Ziegler Natta has a number average relative molecular weight in the range of thousands, a relative molecular weight distribution of 3 ~ 4, Brookfield viscosity from hundreds to thousands, and a high molecular regularity. It is generally high-density polyethylene.

The metallocene catalyzed polyethylene wax has a number average relative molecular weight in the range of thousands, a relative molecular weight distribution of 1 ~ 3, and Brookfield viscosity from tens to thousands. It can be designed for molecular regularity. It is generally high-density polyethylene with less catalyst residue. It is the latest method for polyethylene wax production at present.

Polyethylene wax produced by Baker Hughes proprietary technology (special catalyst) has a number average relative molecular weight of 400 ~ 3000 and a relative molecular weight distribution of 1.0 ~ 1.1. It has high crystallinity, good heat resistance and is insoluble in most solvents.

1.2 pyrolysis polyethylene wax

Polyethylene wax produced by polyethylene resin cracking technology is more domestic and popular in Thailand and South Korea. This wax usually has a Brookfield viscosity of hundreds to more than a thousand. Compared with the synthetic polyethylene wax, this polyethylene wax has wide relative molecular weight, wide viscosity range and medium temperature resistance. It is popular in middle and low-end applications, especially in polyolefin color masterbatch.

1.3 by product polyethylene wax

The by-product produced in the polymerization of high-density polyethylene has a wide melting point range and the viscosity is lower than 0.1pA · s. It usually needs to be cut into products with different melting point ranges before use.

2. Polyethylene wax is classified according to chemical structure

2.1 homopoly polyethylene wax

Homopoly polyethylene wax is polymerized from ethylene monomer. The physical properties of products are slightly different with different polymerization processes.

2.2 oxidized polyethylene wax

Oxidized polyethylene wax is obtained after the double bond on polyethylene is oxidized. It is divided into different grades according to different acid value. At the same time, the physical properties of oxidized polyethylene are different according to different polyethylene raw materials. It should be selected according to specific application in the process of use.

2.3 ethylene vinyl acetate copolymer wax

Ethylene vinyl acetate copolymer wax is synthesized by copolymerization of ethylene monomer and vinyl acetate monomer. It is divided into different brands according to the content of vinyl acetate. Generally, it is easy to synthesize ethylene vinyl acetate copolymer wax by free radical polymerization technology, and the VA content can reach 6% ~ 25%.

2.4 oxidized ethylene vinyl acetate copolymer wax

The double bond on ethylene vinyl acetate copolymer is oxidized to obtain oxidized ethylene vinyl acetate copolymer.

2.5 ethylene acrylic acid copolymer wax

Ethylene acrylic acid copolymer wax is obtained by copolymerization of ethylene and acrylic acid. With the increase of acrylic acid content, the product becomes softer and softer.

2.6 maleic anhydride grafted polyethylene wax

Grafting maleic anhydride on the side chain of polyethylene can greatly enhance the polarity of polyethylene wax, and the grafting rate of maleic anhydride will be much greater than that of maleic anhydride grafted polyethylene resin.

3. Application of polyethylene wax in plastics

Polyethylene wax is widely used. It can disperse pigments and fillers in color masterbatch, provide lubrication balance in PVC mixing ingredients, provide demoulding in engineering plastics, and provide interface compatibility in filling or reinforcing modified materials.

3.1 application of polyethylene wax in Color Masterbatch

Homopolyethylene wax is mainly used in polyolefin Color Masterbatch, including polyethylene Color Masterbatch, polypropylene color masterbatch and EVA color masterbatch. Due to the large amount of pigment or filler in the color masterbatch, and the particle size of these pigments and fillers is very small, ranging from 0.01 to 1.0 μ M level, easy to reunite. By adding homopoly polyethylene wax, the polyethylene wax melts within a certain temperature range to wet the surface of pigment or filler, reduce the agglomeration between pigment or filler particles, and increase the compatibility between pigment or filler and matrix resin. With the help of the shear force of twin-screw extruder or internal mixer, Thus, the pigment and filler are evenly dispersed in the resin melt.

There are also some differences in the application of homopolyethylene wax from different production routes in color masterbatch. Polyethylene wax from by-products generally has low viscosity. Although it has good wettability to pigments and fillers, it is likely to precipitate in terminal application due to its small relative molecular weight, complex components and poor batch stability.. The polyethylene wax produced by cracking method may produce black spots due to the limitation of the process route. It has high requirements for the quality control of the back end. At the same time, the relative molecular weight distribution is wide. It contains high relative molecular weight parts that are ineffective for wetting and low relative molecular weight parts that are easy to produce taste. It also has the risk of precipitation in terminal application.  Polyethylene wax produced by polymerization has narrow relative molecular weight distribution, so it has higher efficiency of dispersing pigments and fillers and lower risk of precipitation. Compared with the three polymerization processes of free radical polymerization, Ziegler Natta and metallocene, the polyethylene wax of free radical polymerization contains long branched chains and double bonds, so it generally has low crystallinity, soft and good wettability to pigment fillers, but it will have a certain aromatic smell due to the presence of chain terminator. Ziegler Natta polymerization is low-pressure polymerization, with higher purity and higher temperature resistance, However, due to the need to remove catalyst and solvent in the process, the operation cost is high. Polyethylene wax synthesized by metallocene polymerization technology is a more advanced polymerization technology. The catalyst has high reaction activity and less residue in the final product, so more diversified products can be designed. The temperature resistance test of polyethylene wax with three polymerization methods in 200 ℃ air shows that the degree of color yellowing from light to deep is metallocene polymerization, Ziegler Natta polymerization and free radical polymerization.

In general, customers can choose different types of polyethylene wax according to the end application. If the color masterbatch is used in low-end applications, such as garbage bags, garbage cans, mulching films, etc., customers can choose by-product wax or pyrolysis wax. If the color masterbatch is used in mid-range applications and has dispersion and taste requirements, synthetic polyethylene wax should be selected. If the color masterbatch is used for special applications with harsh taste and temperature resistance, Ziegler Natta or metallocene polymerized polyethylene wax should be selected. At this time, users should not only choose polyethylene wax as a dispersant, but also consider other requirements from end applications.

3.2 Application of polyethylene wax in PVC

PVC is fully known as polyvinyl chloride. Its viscous flow temperature is very close to the degradation temperature, so it is easy to degrade in various forms during processing, so it will lose its performance. Therefore, heat stabilizers and lubricants must be added to the formulation of PVC mixed ingredients. The former improves its thermal stability, and the latter reduces the friction between PVC molecular chains and the film removal force between PVC melt and metal, so as to improve the convenience of processing PVC into various products. Polyethylene wax and oxidized polyethylene wax are common lubricants in PVC.

In the processing of PVC, there is no pure melt, only secondary particles (100 μ M, composed of primary particles and nodules) split into small balls (1) under the action of thermal and mechanical shear μ The process of spherule splitting into 100nm (m) is usually referred to as gelation or plasticization. In order to achieve better mechanical properties, surface and processability, the gelation degree is more suitable between 70%~85%. Suitable polyethylene wax can delay or accelerate the gelation process. 

3.3 Application of polyethylene wax in engineering plastics

Common engineering plastics PA6, PA66, pet, PBT and PC also need to add lubricants to demould and improve the effect of flow or compatibilizer. At this time, when we choose polyethylene wax, we can't choose homopoly polyethylene wax, because according to the principle of similarity and compatibility, these engineering plastics have strong or weak polarity, so we need to choose polyethylene wax with certain polarity, such as oxidized polyethylene wax, ethylene acrylic acid copolymer wax, maleic anhydride grafted polyethylene wax, etc, We will further filter according to the functional needs. For example, in PA6, if it is necessary to improve the injection molding filling of the material, it needs an internal lubricant, which can significantly improve the fluidity of the material, and then combined with a certain release agent, such as ethylene acrylic acid copolymer wax, this function can be realized. If you need to improve the surface properties of PC products, you need external lubricants, such as oxidized polyethylene wax, which can improve the demoulding properties of products during injection molding. If you want to eliminate the problem of floating fiber on the surface of glass fiber reinforced PA66, you can achieve this effect by adding maleic anhydride grafted polyethylene, because the - Oh affinity between maleic anhydride and the surface of glass fiber is very good, which can increase the interfacial compatibility between glass fiber and PA66. 

Of course, when choosing different polyethylene wax varieties, we should also take into account the characteristics of temperature resistance, particle morphology and so on.

Qingdao Sainuo Chemical Co., Ltd. We are manufacturer of  PE wax, PP wax, OPE wax, EVA wax, PEMA, EBS, Zinc/Calcium Stearate…. Our products have passed the REACH, ROHS, PAHS, FDA testing.

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