Application of PE (polyethylene) wax in rubber

As a rubber processing aid, it can enhance the dispersion of fillers, increase the extrusion molding rate, boost die flow, facilitate demolding, and improve the surface gloss and smoothness of the finished product after demolding.

Rubber: Protects rubber from the corrosive effects of static electricity and ozone, and enhances the dispersion of carbon black in rubber. The recommended addition level is 2–5 phr.

PE wax used in rubber is a chemical material whose polyethylene wax appears as tiny white beads or flakes, produced through the processing of polymerized rubber. It features a relatively high melting point, great hardness, high glossiness, and a snow-white color.

PE wax, when used in rubber, is a low-molecular-weight homopolymer or copolymer widely employed in coatings. The term "wax" here refers to a polymer that ultimately forms microcrystals floating on the surface of the coating, creating a wax-like appearance similar to paraffin wax yet possessing many additional properties that set it apart from paraffin wax.

The primary functions of PE wax in rubber and solvent-based coatings include: matting, scratch resistance, abrasion resistance, polish resistance, anti-etching, anti-sticking, anti-settling, thixotropy, as well as excellent lubricity and processability. It also exhibits metallic pigment properties.

1. Lubrication and dispersion

Generally, when compounding rubber or silicone, some fillers are added—such as carbon black, calcium carbonate, and talc. For applications with high transparency requirements, fillers like precipitated silica (white carbon black) are often used. Adding polyethylene wax can provide a certain lubricating and dispersing effect.

2. Non-stick and demolding

Most rubbers are relatively sticky and tend to stick to molds! Polyethylene wax can provide a certain degree of external lubrication.

3. Antiozonant—a physical antioxidant for rubber products—that migrates into the rubber to form a protective film, thereby providing antiozonant protection.

4. Proper addition can reduce the Mooney viscosity of the compounded rubber and act as a plasticizer; however, be mindful that excessive amounts may adversely affect the mechanical properties of the rubber compound.

5. The fluidity required for certain product extrusion, calendering, and vulcanization molding processes.

6. Improve the uniformity of the compound: The self-lubricating properties of both inner and outer rubber compounds, combined with their ability to disperse inorganic additives, enhance the uniformity of the compound’s mixing process.

However, most manufacturers don't choose polyethylene wax for the following reasons:

1. Relatively high melting point

Some rubber compounds are mixed at temperatures ranging from 70 to 120℃, whereas polyethylene wax has a high melting point and is difficult to melt, rendering it ineffective. (Generally, polyethylene wax with a softening point around 70–100℃ is chosen.)

2. Prone to precipitation

Rubber is a polymer material, while polyethylene wax has smaller molecules. Adding too much of it can easily cause it to precipitate out, whereas adding too little generally won't achieve the desired effect. (A dosage of 2–4 phr is ideal.)

3. Narrow scope of use

It is mainly limited by the melting point.

4. Affects the transparency of the product

1. Resistance to ozone aging: Polyethylene wax will migrate to the rubber surface, forming a protective film.

2. Plasticization and improved processing performance: Polyethylene wax has a much lower molecular weight than rubber. After addition, its molecular chains can easily intercalate between the rubber molecular chains, making it easier for the rubber molecular chains to slide past one another.

3. Lubrication (internal lubrication + external lubrication) improves extrusion performance and reduces shrinkage: Same as 2;

4. Makes the rubber compound easier to mix uniformly: Polyethylene wax enters between the rubber molecular chains, increasing the distance between them. At the same time, it carries low-molecular-weight compounding agents into the rubber molecular chains, making it easier for other compounding agents to disperse evenly.

Protective waxes are classified according to their intended use; PE wax, paraffin wax, and microcrystalline wax can all be used as protective waxes.

PE wax, also known as polyethylene wax (PE-WAX), is a type of ultra-low molecular weight polyethylene. Polyethylene waxes are generally categorized into four types: oligomeric wax, pyrolytic wax, polymerized wax, and compounded wax. Among these, oligomeric wax is commonly produced domestically, while pyrolytic wax, polymerized wax, and compounded wax are predominantly manufactured overseas. Theoretically, polymerized wax exhibits superior performance compared to pyrolytic wax; however, the specific choice of wax should be based on the compatibility with the intended application. Generally, PE wax is widely used to enhance the flowability of polyolefin plastics and improve the dispersion of fillers and additives. It is also employed as an internal lubricant in rubber and plastic materials.