Buying Antioxidant 168 (Irgafos 168): What Matters
Antioxidant 168 (CAS 31570-04-4) is a commodity-scale polymer additive, but two suppliers offering the same headline assay can differ in the parameters that actually matter — transmittance, free DTBP, acid value and hydrolytic stability. Because the material is a moisture-sensitive phosphite, buying it well means specifying those parameters and protecting the product in storage.
For the chemistry behind these points, see our main article on antioxidant 168 (CAS 31570-04-4).
Step 1: Confirm the Identity
Antioxidant 168 is tris(2,4-di-tert-butylphenyl) phosphite; Irgafos 168 is a trade name for the same substance. Confirm the CAS number (31570-04-4) and that the product is the phosphite, not a phenolic antioxidant or a different phosphite.
Step 2: Read the Specification
| Parameter | Why it matters | Typical value |
|---|---|---|
| Appearance | Confirms a clean white powder | White powder |
| Main content | The active phosphite level | ≥ 99% |
| Melting point range | Identity and purity | 186–187 °C |
| Heating decrement | Volatiles | ≤ 0.3% |
| Transmittance (425/500 nm) | Colour; important for clear/light polymers | ≥ 98% each |
| Acid value | Rises if the phosphite has hydrolysed | ≤ 0.3 mg KOH/g |
| Hydrolysis resistance | Confirms the material is intact | Qualified |
| 2,4-Di-tert-butylphenol (DTBP) | Direct marker of hydrolysis | ≤ 0.2% |
The acid value and DTBP content are the two parameters that most directly reveal whether a batch has taken up moisture. A low assay with a high DTBP is a warning sign.
Step 3: Choose the Form
- Standard powder. The white crystalline powder for conventional dosing.
- One-pack blends. Pre-blended with a phenolic antioxidant (for example Irganox 1010), which simplifies dosing and improves dispersion.
- Low-dust / pre-dispersed. Cleaner, easier dosing in continuous processes.
Step 4: Protect Against Hydrolysis
Phosphites hydrolyse on contact with moisture, so the product’s usefulness depends on how it is packed and stored:
- Insist on moisture-tight inner liners inside the outer bag or drum.
- Store cool and dry, and reseal opened containers promptly.
- Rotate stock so that material does not sit for long periods.
- Check acid value / DTBP on receipt if the material may have been stored poorly.
Supplier Checklist
- Identity. CAS 31570-04-4 and the correct phosphite confirmed.
- Assay and DTBP. Main content ≥ 99% and free DTBP within limit.
- Transmittance. Within specification, especially for light-coloured polymers.
- Acid value / hydrolysis. Within limit, confirming intact material.
- Form and packaging. Powder or one-pack, with moisture-tight packaging.
- Documentation. SDS, per-batch COA and, where needed, food-contact statements.
Common Buying Mistakes
- Buying on assay alone. A high assay with a poor DTBP or transmittance result may not suit clear or light-coloured polymers.
- Ignoring hydrolysis. Poorly stored material can arrive partly hydrolysed, so it underperforms even though the label says 168.
- Confusing it with a phenolic antioxidant. 168 is a secondary antioxidant; if you expected a phenol you have the wrong product.
- Neglecting storage. Moisture uptake after delivery destroys the product’s value.
- Overlooking regulatory limits. Food-contact and other uses set limits on additive levels; confirm the grade and documentation.
How PolyBlueChem Can Help
PolyBlueChem can supply antioxidant 168 (CAS 31570-04-4) as a bulk raw material, with the documentation appropriate to your application. We can provide current specifications and a COA, discuss the grade and form that fit your process, and quote packaging and shipping options. To request specifications, a sample or a quotation, contact the PolyBlueChem team.
Frequently Asked Questions
What should I look for when buying antioxidant 168?
Confirm the identity (CAS 31570-04-4), check the main content, transmittance, acid value and free-DTBP content, choose the right form, and ensure the packaging is moisture-tight.
Why does DTBP content matter?
2,4-Di-tert-butylphenol is the hydrolysis product of antioxidant 168. A high DTBP content means the material has partly hydrolysed and lost antioxidant activity.
Is Irgafos 168 the same as antioxidant 168?
Yes; Irgafos 168 is a trade name for tris(2,4-di-tert-butylphenyl) phosphite.
What documents should come with a shipment?
At minimum a safety data sheet and a per-batch certificate of analysis; food-contact statements where relevant.
How should antioxidant 168 be stored?
Cool and dry in sealed, moisture-tight packaging, with stock rotation, to avoid hydrolysis.