The Challenge The most distinctive characteristic of rubber is its elasticity or the ability to stretch and return to its original shape. This property is used to dampen vibrational forces in moving parts. Rubber helps in noise reduction, reduces mechanical stress, and isolates movement to extend the usable life of equipment. Rubber seals and gaskets are used in a variety of applications such as automobiles, electrical motors, fans and blowers, compressors and measuring instruments. In addition to its basic properties, rubber also offers the benefit of lower production costs in terms of material and ease of manufacturing. Rubber components can be readily extruded, molded, or cutout and bonded into desirable shapes and geometries. Rubber parts can wear out with use causing equipment failure and heavy losses due to downtime. Frequent replacement of these components increases maintenance costs and requires regular interruptions in productivity. Additives are used to enhance the durability and physical properties of rubber. Polytetrafluoroethylene (PTFE), a synthetic fluoropolymer of tetrafluoroethylene, is commonly used as an additive to enhance the physical properties of rubber. An essential ingredient used in the production of PTFE is Perfluorooctanoic acid (PFOA). Studies have linked PFOA exposure to serious health issues including cancer, high cholesterol, and hypertension. The EU, in accordance with the UN’s Stockholm Convention on persistent organic pollutants has agreed to a global ban on PFOA. Formulators are, therefore, looking for a suitable PTFE alternative to reformulate their products.
Furthermore PTFE, when used as a rubber additive, often falls short of performance goals. The United Nation’s Sustainability Development Goals (SDGs) call for improvements in durability for responsible consumption and production. The challenge, therefore, is to find a safe alternative to PTFE that delivers enhanced strength and abrasion resistance without compromising on the essential physical properties of rubber.
The Solution Mitsui Chemicals’ MIPELON™ ultra-high molecular weight polyethylene (UHMW-PE) is a very fine polyethylene powder. MIPELON™ enhances the abrasion resistance and lubricity when used as a rubber additive. Additionally, MIPELON™ is safe and environment friendly. MIPELON™ is a highperformance alternative to the use of PTFE in rubber formulation. MIPELON™ XM220, a grade suitable for use as a rubber additive, has an average diameter of 30µm as shown in Figure 1. Due to Mitsui Chemicals’ proprietary production technology, the particles are spherical in shape as compared to other U-PEs. They are also uniformly sized with a narrow distribution around the mean, as shown in Figure 2. Due to its distinctive particle geometry and ultra-high molecular weight, MIPELON™, has excellent abrasion resistance, weather resistance, and chemical resistance properties. MIPELON™ XM-220 (30μm) Other`s U-PE (30μm)
MIPELON™ reduces friction and increases abrasion resistance when used as an additive. Tests were conducted to compare the performance of MIPELON™ with other organic beads used as additives for reducing friction and abrasion in rubber. An SUS board was pulled horizontally on a dry powder sample of the additive. Figure 3 shows the particle size and coefficient of friction for each type of powder tested. MIPELON™ shows the lowest friction coefficient when compared to PTFE, Nylon and Crosslinked PMMA. Figure 1: Comparison of particle size and coefficient of friction between various additives in dry powder form Abrasion resistance is a highly desirable property in rubber components, especially in view of compliance with SDGs. MIPELON™ can be used as an additive in the formulation of EPDM compound for improved abrasion resistance. Being a Polyethylene, it is highly compatible with olefin-based rubbers such as EPDM. Figure 4 shows the typical compounding process for incorporating MIPELON™ in an EPDM rubber formulation. MIPELON™ is added in the ratio 10-40phr along with carbon black and process oil to the EPDM mixture at 100°C. A temperature lower than 130°C is recommended for rubber-MIPELON™ compounding since the melting point of MIPELON is 136°C. At higher temperature, the dispersibility of MIPELON™ in rubber might be poor due to aggregation of particles. Figure 4: Typical compounding process for incorporating MIPELON™ in an EPDM rubber formulation Tests were conducted to compare the effect on abrasion resistance of rubber, upon addition of MIPELON™ XM220 and PTFE. The additives were incorporated into a graft-copolymer of methacrylic ester and polydimethylsiloxane in the range 0-40phr (0-14%). The material produced was tested using an H-18 abrasive wheel loaded with 1kg and rotating at 60rpm for 1000 revolutions. The weight of material lost due to abrasion was recorded. Figure 5 shows the prepared rubber compound with 40 phr of MIPELON™ XM220 added during the compounding process. Figure 5: Rubber compound with 40phr of MIPELON™ XM220
MIPELON™ XM220 (40phr) Figure 6 shows the abrasion loss (in mg) for materials prepared using various amounts of PTFE and MIPELON™ XM220 additives. The abrasion loss is reduced by about 45% upon addition of 40phr of MIPELON™; addition of the same amount of PTFE only reduces the abrasion loss by approximately 7%. The abrasion loss decreases with increasing amount of MIPELON™ XM220 between 10-40 phr. MIPELON™ particles are self-lubricating; this property contributes to enhanced abrasion resistance. Figure 6: Abrasion loss under H-18 abrasive wheel loaded with 1kg and rotating at 60rpm for 1000 revolutions Figure 7 shows the effect of addition of MIPELON™ XM220 on the hardness and density of rubber. The hardness of rubber increases with the addition of MIPELON™. The increase in hardness is greater for MIPELON™ when compared to the increase due to the addition of the same amount of PTFE. The density of rubber decreases with increasing amounts of MIPELON™. Addition of PTFE, on the other hand, leads to an increase in the density of rubber. The lower density allows production of lighter components with greater abrasion resistance. Figure 7: Effect of the addition of MIPELON™ XM220 on the hardness and density of rubber
Figure 8 shows the effect of the addition of MIPELON™ XM220 on the tensile strength and compression set. Addition of MIPELON™ has no detrimental effect on the tensile strength and compression set of rubber. Addition of PTFE, however, shows a decrease in tensile strength. Conclusion MIPELON™ by Mitsui Chemicals is an attractive substitute for PTFE for increasing the abrasion resistance of EPDM rubber. It offers the following benefits when added to rubber formulations: • Improved abrasion resistance • Hardness adjustment • Lighter components • Retention of tensile strength and compression set properties • Complies with health and safety regulations MIPELON™ can be used in the production of industrial rolls such as OA rolls and for reforming conveyors and motorcycle belts. It is ideal for applications that require improved abrasion resistance to enhance the usable life of the component and reliability of equipment. MIPELON™ is an olefin-based substance and conforms to FDA and GB standards. It is harmless to the human body can be used in components for food applications. MIPELON™ also enhances chemical resistance and is suitable for use in the production of medical rubber. (MPa) For an easy selection of the most suitable grade for your formulation, the table below shows the key mechanical properties of various MIPELON™ grades.