Plastics and rubber degrade in two predictable ways: during high-temperature melt processing, and slowly over years of heat, light and oxygen exposure. Both paths run through the same chemistry — free-radical chain oxidation of the polymer backbone. Antioxidants do not stop oxidation by magic; they interrupt it at specific steps. Picking the right stabilizer means matching the antioxidant mechanism to the failure mode, and almost always using more than one type together.
The two jobs: kill radicals and destroy hydroperoxides
Thermal oxidation starts with a radical (R·), reacts with oxygen to form a peroxy radical (ROO·), then abstracts hydrogen from the polymer to create a hydroperoxide (ROOH) and a fresh carbon radical. That hydroperoxide is the real time-bomb: when it decomposes, it generates two new radicals and accelerates degradation.
- Primary antioxidants donate a hydrogen atom to ROO·, converting it to a harmless hydroperoxide and yielding a stable, non-propagating phenoxy radical. They stop the chain. Hindered phenols are the dominant class.
- Secondary antioxidants decompose ROOH into stable, non-radical products before it can split. Phosphites and thioesters are the main classes; they extend the life of the primary antioxidant and protect the polymer during processing.
In practice, a durable compound almost always pairs a primary phenolic antioxidant with a phosphite (processing protection) and/or a thioester (long-term heat aging). The three classes regenerate each other in a genuine synergy.
Primary hindered phenolic antioxidants
Phenolic antioxidants differ mainly in molecular weight, volatility, compatibility and extraction resistance. Higher molecular weight means lower volatility during compounding and longer service life, but it can reduce mobility in the polymer matrix.
BHT (butylated hydroxytoluene, CAS 128-37-0)
Antioxidant BHT is the small-molecule reference standard. It is inexpensive, globally approved for food contact and widely used in lubricants, waxes and low-stress plastics. Its weakness is volatility and migration: at typical processing temperatures for polyolefins it can sublime out of the melt or bloom to the surface, so it is rarely the right choice for long-term heat aging or thin sections. Use it where cost dominates and the service temperature stays moderate: adhesives, sealants, some rubber goods and indirect food-contact applications. Typical use level: 0.05–0.5%.
Antioxidant 1010 (CAS 6683-19-8)
Antioxidant 1010 is the workhorse high-molecular-weight hindered phenol — pentaerythrityl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. With four phenolic groups on a compact core, it offers very low volatility, excellent extraction resistance and broad regulatory acceptance. It is the default choice for long-term thermal stabilization of PP, PE, EVA, ABS, POM, polyesters, elastomers and adhesives. Typical use level: 0.1–0.5% on its own, or 0.05–0.3% when paired with a phosphite.
Antioxidant 1076 (CAS 2082-79-3)
Antioxidant 1076 is the long-chain octadecyl ester of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid. Its single phenolic group gives it lower intrinsic activity per gram than 1010, but the C18 chain makes it more compatible with polyolefins and gives outstanding extraction resistance in thick sections, wire & cable insulation and geomembranes. It is often preferred when the compound will sit in hot water or oil. Typical use level: 0.1–0.5%, frequently co-stabilized with a phosphite.
Secondary phosphite antioxidants
Phosphites react with hydroperoxides to give phosphate esters and alcohols, sparing the phenolic antioxidant from being consumed by ROOH. They are indispensable during extrusion and injection molding, where transient hydroperoxide concentrations are highest.
Antioxidant 168 (CAS 31570-04-4)
Antioxidant 168 — tris(2,4-di-tert-butylphenyl) phosphite — is the most widely used processing stabilizer in the polymer industry. It is non-discoloring, low in volatility and highly effective at protecting the polymer during melt processing. It is almost never used alone; the classic pairing is with 1010 or 1076 in polyolefins, styrenics and engineering plastics. Typical use level: 0.1–0.5%, often at roughly 1:1 to 2:1 with the phenolic antioxidant by weight.
Antioxidant 626 (CAS 26741-53-7)
Antioxidant 626 is a diphosphite (bis(2,4-di-tert-butylphenyl) pentaerythrityl diphosphite) with higher phosphorus content per gram than 168. That translates to better hydroperoxide decomposition efficiency at lower loadings and improved resistance to gas-fade discoloration in polyolefins exposed to combustion gases or NOx. It is widely used in PC, PA, styrenics, PVC and coatings. Typical use level: 0.05–0.3%.
Thioester synergists for long-term heat aging
Thioesters decompose hydroperoxides through a sulfur-mediated redox cycle, consuming multiple ROOH molecules per thioester molecule. They are the standard route to long-term heat stability at elevated temperatures, especially in polyolefins and lubricants.
Antioxidant DLTP (CAS 123-28-4)
Antioxidant DLTP (dilauryl thiodipropionate) is the cost-effective thioester. It is non-staining and works well in white and bright-colored goods. Its shorter alkyl chains make it somewhat more mobile and slightly less extraction-resistant than its heavier cousin DSTP. Typical use level: 0.2–1.0%, usually paired with 1010 or 1076.
Antioxidant DSTP (CAS 693-36-7)
Antioxidant DSTP (distearyl thiodipropionate) has longer C18 alkyl chains, giving lower volatility, better compatibility with polyolefins and superior extraction resistance compared with DLTP. It is the preferred thioester for long-term service in hot environments and for FDA food-contact applications. Typical use level: 0.2–1.0%.
Antioxidant 1035 (CAS 41484-35-9)
Antioxidant 1035 is a sulfur-containing hindered phenol with both primary and secondary activity in one molecule. It is especially valued in XLPE wire & cable insulation, carbon-black-filled compounds and peroxide-crosslinked systems where conventional phosphites can interfere with the crosslinking chemistry. It also performs well in PU flexible foams and synthetic elastomers. Typical use level: 0.1–0.5%.
Ready-made blends: B215 vs. B225
Blends simplify weighing, improve dispersion and give a balanced phenolic/phosphite ratio for general-purpose polyolefins.
- Antioxidant B215 (CAS 6683-19-8; 31570-04-4) is a 1:2 blend of 1010 and 168. The higher phosphite content favors processing stability and is the go-to for high-shear compounding of PP, PE and EVA.
- Antioxidant B225 (CAS 6683-19-8; 31570-04-4) is a 1:1 blend of 1010 and 168. The higher phenolic content gives better long-term heat aging, making it suitable for compounds that will see sustained elevated temperature in service.
Typical use level for either blend: 0.1–0.5%. For severe long-term aging, supplement the blend with a thioester such as DSTP.
Side-by-side comparison
| Product | CAS No. | Class | Main role | Best for | Typical use level |
|---|---|---|---|---|---|
| BHT | 128-37-0 | Hindered phenol | Low-cost primary | Waxes, adhesives, lubricants, low-heat plastics | 0.05–0.5% |
| Antioxidant 1010 | 6683-19-8 | Hindered phenol | Long-term primary | PP, PE, ABS, POM, elastomers, adhesives | 0.1–0.5% |
| Antioxidant 1076 | 2082-79-3 | Hindered phenol | Long-term primary, extraction resistant | Wire & cable, thick sections, hot-water/oil exposure | 0.1–0.5% |
| Antioxidant 168 | 31570-04-4 | Phosphite | Processing stabilizer | Polyolefins, styrenics, engineering plastics | 0.1–0.5% |
| Antioxidant 626 | 26741-53-7 | Diphosphite | Processing + gas-fade resistance | PC, PA, styrenics, PVC, coatings | 0.05–0.3% |
| Antioxidant DLTP | 123-28-4 | Thioester | Long-term heat synergist | White/bright PE, PP, ABS, PVC | 0.2–1.0% |
| Antioxidant DSTP | 693-36-7 | Thioester | Long-term heat synergist, extraction resistant | Polyolefins, rubber, lubricants, food contact | 0.2–1.0% |
| Antioxidant 1035 | 41484-35-9 | Sulfur-containing phenol | Dual primary/secondary | XLPE cable, carbon-black compounds, PU foams, elastomers | 0.1–0.5% |
| Antioxidant B215 | 6683-19-8; 31570-04-4 | Blend | Phenolic + phosphite, processing biased | General polyolefin compounding | 0.1–0.5% |
| Antioxidant B225 | 6683-19-8; 31570-04-4 | Blend | Phenolic + phosphite, aging biased | General polyolefin compounding | 0.1–0.5% |
Practical formulation recipes
- General-purpose PP/PE injection molding: 0.1% 1010 + 0.2% 168, or 0.2–0.3% B215. Handles multiple heat histories during regrind.
- PP/PE pipe or geomembrane (50 °C service): 0.2% 1076 + 0.2% 168 + 0.3% DSTP. The thioester is the key to passing long-term oxidation induction time (OIT) tests.
- White appliance ABS/HIPS: 0.15% 1010 + 0.15% 626 + 0.3% DLTP. 626 reduces gas-fade yellowing; DLTP keeps cost down in non-extractive applications.
- XLPE peroxide-crosslinked cable: 0.2–0.4% 1035, with no conventional phosphite to scavenge radicals from the peroxide initiator. Carbon black adds further stabilization.
- Wire & cable oil/water exposure: 0.2% 1076 + 0.2% 168 + 0.3% DSTP. The C18 chain of 1076 and DSTP improves retention in the compound.
Specs to check when sourcing
- Assay / purity — ≥ 98% is typical for premium grades; lower values mean diluents or impurities that affect color and processing.
- Melt range or pour point — critical for thioesters and for liquid antioxidant systems; off-spec melting points indicate contamination or wrong chain length.
- Phosphorus content (for phosphites) — confirms the active content and molecular identity; compare against theoretical values.
- Hydrolytic stability (for phosphites) — phosphites can hydrolyze to acidic species during storage; ask for acid value and moisture content, and keep containers sealed.
- Color (APHA or Gardner) — high color in a nominally white antioxidant is a warning for yellowing in white or transparent compounds.
- Heavy metals and ash — important for electrical-grade and food-contact compounds.
Shanghai Better Chemical supplies the full polymer antioxidant portfolio above — BHT, 1010, 1076, 168, 626, DLTP, DSTP, 1035, B215 and B225 — China origin, with TDS/COA/MSDS on request. Tell us your polymer, processing temperature and end-use environment, and we will recommend a stabilizer package and current pricing.