When producing oil-resistant rubber sheets with nitrile rubber, high raw material costs are a major pain point for most rubber product companies. Pure nitrile rubber prices fluctuate significantly, and procurement costs are high. As a result, many manufacturers of oil-resistant rubber sheets have started mixing in recycled nitrile rubber to replace part of the raw rubber, reducing production costs and improving market competitiveness. However, blindly adding recycled nitrile rubber can easily lead to issues such as reduced oil resistance, inadequate tensile strength, surface bubbling, and cracking, which can actually increase rework and waste. Therefore, several key considerations must be taken into account when using recycled nitrile rubber in nitrile rubber sheets.
1. Don’t choose recycled nitrile rubber solely based on price
Recycled nitrile rubber is made from waste nitrile rubber and its products, processed through crushing, desulfurization, refining, and other steps, retaining the basic oil resistance properties of nitrile rubber. When selecting recycled nitrile rubber to cut costs, companies need to focus on factors such as rubber content, Mooney viscosity, plasticity, tensile strength, elongation at break, ash content, and oil resistance performance. For oil-resistant sheets with higher requirements, it’s recommended to prioritize high-quality recycled nitrile rubber with an acrylonitrile content of 36%-42%, high rubber content, and minimal batch variation.
When choosing recycled nitrile rubber, companies should never consider price alone, as performance deficiencies often require additional raw rubber, carbon black, or other additives to compensate, which may not reduce costs but instead increase material costs or unnecessary waste.
2. More recycled rubber isn’t always better
The optimal amount of recycled rubber varies depending on the application of the nitrile rubber sheet. The proportion should be determined based on sheet hardness, tensile strength, oil volume change, compression set, wear resistance, and operating temperature. Ordinary oil-resistant sheets exposed to mineral oils can incorporate 30%-50% recycled rubber, while sheets in constant contact with aromatic solvents should keep the recycled rubber content below 25%, and sometimes add some PVC as needed.
3. Key points in formulating rubber sheets with recycled nitrile rubber
When producing sheets with a mixture of nitrile rubber and recycled nitrile rubber, a common sulfur-accelerator system is used, with sulfur among 1.5-3 parts and CZ accelerators combined with DM or D to prevent scorching while ensuring even curing. Using high-abrasion carbon blacks like N330 can strengthen the rubber and improve wear resistance and can be paired with quick-furnace blacks like N550. However, too much carbon black may increase hardness and make processing difficult. Softening and plasticizing systems can use dibutyl phthalate or aromatic oil, adjusting the amount based on the proportion of recycled rubber to prevent shrinkage and brittleness during calendering.
4. Pay attention to mixing and dispersion
Poor mixing and dispersion when blending nitrile and recycled rubber directly affect processing and finished product quality. Nitrile rubber heats quickly during mixing, while recycled rubber is highly flowable. During combined mixing, it’s important to adjust roller temperature, gap, and mixing time to ensure proper blending with additives and avoid uneven properties.
5. Key points for vulcanization when using recycled rubber
During calendering with nitrile/recycled rubber mixtures, control forming temperature and speed to prevent uneven thickness or surface bubbling caused by changes in material flow. Monitor shrinkage, surface smoothness, and thickness stability throughout calendering. Thicker sheets transfer heat more slowly during vulcanization, so adjust process parameters based on sheet thickness, equipment, and curing curves to prevent under- or over-curing and ensure proper vulcanization.
Rubber sheet manufacturers must choose the right recycled nitrile rubber, control its proportion, redesign rubber formulas based on actual needs—especially reinforcing fillers and vulcanization systems—and adjust mixing, calendering, and vulcanization processes to reduce costs without sacrificing quality.
Exclusive original article [commercial authorization] reprint, excerpt and excerpt in any form are prohibited without written authorization. Focus on Hongyun rubber: learn the process formula and raw material technology of producing rubber products from recycled rubber to help you reduce costs and increase profits