If you’re in the market for rubber products—especially those for automotive inner tubes, pharmaceutical stoppers, or industrial sealants—you’ve likely worked with butyl rubber for its unrivaled impermeability to gases and resistance to extreme temperatures. But as a butyl rubber supplier, I’ve spent years answering a question that pops up again and again, whether from new product designers or long-time manufacturing partners: what plasticizers are actually used in butyl rubber, and why do they matter for the final product? Butyl Rubber
Let’s start with the basics: butyl rubber (IIR, or isobutylene isoprene rubber) is a synthetic elastomer made from 97% isobutylene and 3% isoprene. Its tightly cross-linked structure gives it that near-zero air permeability, which is why it’s the go-to for tire inner liners and medical vial stoppers. But pure butyl rubber has a major downside: it’s rigid and brittle at room temperature, which makes it hard to mold, extrude, or process on standard industrial equipment. That’s where plasticizers come in—chemical additives that lower the glass transition temperature (Tg) of the rubber, improve flow during processing, and adjust the final product’s flexibility.
Not all plasticizers work for butyl rubber, though. The key here is compatibility: a plasticizer has to bond weakly with the butyl polymer’s non-polar backbone without disrupting its cross-linking, which would kill its core properties (gas barrier, chemical resistance). Over the years, our team has tested dozens of additives, and today we stick to three primary classes of plasticizers that deliver the right balance of processability and performance for butyl rubber products.
First, paraffinic and naphthenic mineral oils are the most widely used plasticizers for general-purpose butyl rubber. Mineral oils are derived from crude oil, with paraffinic oils made of straight-chain alkanes and naphthenic oils containing cyclic alkanes. For many of our customers making low-stress parts like basic inner tubes or gaskets, these are the perfect fit. Why? They’re affordable, readily available, and blend seamlessly with butyl rubber’s non-polar structure. We typically add 5 to 15 parts per hundred rubber (phr) of paraffinic oil for standard processing: too little, and the rubber stays too stiff to extrude evenly; too much, and the rubber becomes soft, loses its shape, and can’t hold air pressure. Naphthenic oils, on the other hand, are slightly more aromatic, so they work better for applications where a touch higher flexibility is needed, like flexible hoses for light industrial use. One thing we always warn customers about: mineral oil plasticizers can leach out over time when exposed to high temperatures or oils, which makes them a no-go for medical or food-grade applications. That’s why we reserve them for non-critical, bulk parts.
Second, polyisobutylene (PIB) resins are a workhorse for our premium butyl rubber lines, especially for products that need consistent flexibility over decades. PIB is a synthetic polymer made from isobutylene monomers, and it’s chemically very similar to butyl rubber itself—so compatibility is near-perfect. Unlike mineral oils, PIB doesn’t leach out; it’s covalently linked to the butyl rubber network during vulcanization, which means it stays in place for the life of the product. That makes it ideal for high-performance parts like tire inner liners, where even a small loss of flexibility could lead to cracks that cause air leaks. We use PIB in blends of 10 to 25 phr for heavy-duty applications, and for some specialized products, we blend different molecular weights of PIB: lower molecular weight PIB (around 10,000 g/mol) acts as a plasticizer, while higher molecular weight PIB reinforces the rubber a bit. The trade-off? PIB is more expensive than mineral oil, so it’s reserved for applications where long-term performance is non-negotiable. A lot of our automotive clients prefer PIB-plasticized butyl inner liners because they don’t need to be replaced as often, even in extreme weather.
Third, for medical and food-grade butyl rubber products, phthalate-free synthetic plasticizers like dioctyl sebacate (DOS) and dioctyl adipate (DOA) are the only acceptable options. Phthalates were once common plasticizers, but they’ve fallen out of favor due to regulatory concerns about potential leaching into foods, pharmaceuticals, or bodily fluids. DOS and DOA are diesters of fatty acids, and they’re non-toxic, odor-free, and highly resistant to extraction by water or alcohol—critical properties for medical stoppers that come into contact with injectable drugs. Our medical-grade butyl rubber line uses 5 to 10 phr of DOS, adjusted based on the specific part: a vial stopper needs just enough flexibility to seal the vial without cracking when punctured by a needle, while a syringe plunger washer needs slightly more flexibility to create a tight seal with the barrel. We also test every batch of plasticized rubber for extractables and leachables, per USP Class VI standards, to make sure it meets FDA and EU requirements. It’s a more involved process than with mineral oils, but for our medical customers, there’s no compromise on safety.
A common mistake we see new rubber manufacturers make is over-plasticizing their butyl rubber. We once had a small startup approach us a few years ago, excited to launch a line of butyl rubber weatherstripping for commercial buildings. They ordered a batch of our butyl rubber and added 20 phr of a cheap mineral oil to make it easier to extrude. The product came out soft and flexible, which looked good at first—but within six months, the oil had leached out, leaving the rubber brittle, cracked, and unable to seal against rain. That’s why we always work with customers to run small-scale test batches first: we’ll mix a few samples with different plasticizer ratios, test their flexibility, cure time, and barrier properties, to find the exact blend that fits their needs.
Another factor to consider is processing temperature. Plasticizer performance changes with heat: at higher extrusion temperatures, plasticizers flow more easily, so you can use a slightly lower ratio, while at lower molding temperatures, you might need a bit more to avoid stiffness. We also keep an eye on how plasticizers interact with other additives in the rubber blend—like fillers (carbon black, silica) or curing agents. For example, too much aromatic mineral oil can interfere with vulcanization, slowing down the curing process and weakening the final product. Our team of application engineers works with every customer to adjust the blend, so they don’t run into these issues down the line.
I should also mention that sustainability is a big topic for our customers now, and we’re investing in bio-based plasticizers for butyl rubber as an alternative to petroleum-derived options. We’ve tested bio-based versions of DOS and PIB, made from plant-derived fatty acids and sugarcane isobutylene, and they perform almost identically to their fossil fuel-based counterparts. A few of our European automotive clients have already switched to these for their electric vehicle tire inner liners, looking to reduce their carbon footprint. While they’re still a bit more expensive, as demand grows, we expect the cost to come down and make them more accessible for all our customers.
As a butyl rubber supplier, our role isn’t just to deliver raw materials—it’s to help customers make parts that work as intended. Choosing the right plasticizer is one of the most critical steps in that process, and it’s not a one-size-fits-all decision. Whether you’re making a low-cost gasket, a high-performance tire liner, or a medical stopper, the right plasticizer will balance processability, performance, and longevity.
If you’re working on a project that uses butyl rubber and need to nail down the right plasticizer blend, or if you’re sourcing high-quality butyl rubber for your products, we’re here to help. Our technical team can walk you through test batches, adjust ratios to meet your specifications, and answer any questions you have about plasticization, vulcanization, or material properties. Don’t hesitate to reach out to start a conversation about your needs.
Butadiene Vinyl-pyridine Latex References
- Coran, A. Y. (Ed.). (2007). Science and Technology of Rubber (4th ed.). Academic Press.
- ASTM D1148-19, Standard Test Method for Rubber Deterioration by Heat Air (Hot Air Oven Method).
- Hofmann, W. (2011). Rubber Technology: Compounding and Testing for Performance (2nd ed.). Hanser Publications.
- European Chemical Agency (ECHA). (2022). Restriction of Phthalates in Rubber and Plastic Products.
- Kawahara, S. (2009). “Compatibility of Polyisobutylene with Butyl Rubber.” Journal of Applied Polymer Science, 112(3), 1567-1574.
Heze Great Bridge Chemical Co., Ltd.
With abundant experience, we are one of the most professional butyl rubber manufacturers and suppliers in China. We warmly welcome you to buy high quality butyl rubber in stock here and get pricelist from our factory. Good service and reasonable price are available.
Address: No.1679 Renmin Road,Heze City,Shandong,China
E-mail: export@greatbridge-chem.com
WebSite: https://www.greatbridgechem.com/
