PVC

PVC Suspension Polymerization Initiators

Match the initiator half-life to the reactor temperature and stripping stage, not to a generic “PVC grade” label.

Overview

PVC suspension polymerization is an initiator-selection problem before it is a purchasing decision. Reactor temperature, stage length and residual-monomer stripping determine which decomposition rate will finish conversion without fish-eyes, yellowing or an uncontrolled exotherm. The process window below starts from those operating conditions and then maps them to LAAP grades.

Process Window

Start with the reactor temperature and stage length. This table shows where an organic peroxide does work in PVC suspension polymerization and what the initiator must do at each stage.

Stage	Temperature	Duration	Initiator requirement
Suspension polymerisation (hot, 55-62 °C)	55-62 °C	4-7 h	An initiator whose 10-hour half-life lands close to the reaction temperature, so conversion stays controlled and the reactor jacket can remove the heat.
Suspension polymerisation (low-temperature, 45-52 °C)	45-52 °C	6-9 h	Faster low-temperature initiators are needed to reach conversion without extending cycle time; these must be stored and dosed cold.
Post-polymerisation stripping	85-100 °C	0.5-1 h	Residual initiator should be essentially consumed; unreacted peroxide here causes fish-eyes and yellowing in the finished resin.

Grade Selection by Stage

Each grade below fits a specific stage of the window above. Half-life and SADT values are the manufacturer figures for the undiluted grade.

Dilauroyl Peroxide (LPO, Lauroyl Peroxide) CAS 105-74-8CAS 105-74-8

Classic hot-process grade; 10h t½ 62 °C sits inside the 55-62 °C window.

1 hour: 79℃
10 hours: 62℃
SADT: 50℃
Typical dose: 0.02-0.06 phr

Bis(3,5,5-trimethylhexanoyl) peroxideCAS 3851-87-4

Lower-temperature acyl peroxide (10h t½ 59 °C) for shorter cycles.

0.1 hour: 96℃
1 hour: 77℃
10 hours: 59℃
SADT: 20℃
Typical dose: 0.02-0.05 phr

Bis(2-ethylhexyl) peroxydicarbonate (EHP)CAS 16111-62-9

Fast peroxydicarbonate (10h t½ 47 °C) for the low-temperature window.

0.1 hour: 83℃
1 hour: 64℃
10 hours: 47℃
SADT: 5℃
Typical dose: 0.03-0.08 phr

Cumyl peroxyneodecanoate (CPND)CAS 26748-47-0

Very fast option (10h t½ 38 °C) for high-VCM-throughput cold processes.

0.1 hour: 75℃
1 hour: 56℃
10 hours: 38℃
SADT: 10℃
Typical dose: 0.02-0.06 phr

Procurement & Handling

HS code: 2909.60 / 2915.90 (confirm per grade)
Transport class: UN 3103-3110, Class 5.2 organic peroxide, self-reactive
Packaging: 20 kg or 25 kg PE-lined drums; 50% phlegmatised grades in 25 kg packs
Storage: Below 20 °C for ester grades; below -10 °C for peroxydicarbonates (SADT as low as 5 °C)
Minimum order: 25 kg trial, 1 t commercial

Common Questions

Which initiator should I use for PVC suspension polymerisation at 57 °C?

Match the initiator 10-hour half-life temperature to the reaction temperature. For 57 °C, LPO (10h t½ 62 °C) or a bis-3,5,5-trimethylhexanoyl peroxide (10h t½ 59 °C) both sit inside the window. Below 52 °C, move to peroxydicarbonates such as EHP (47 °C) or CPND (38 °C) and arrange cold storage.

Why do my PVC resin batches show fish-eyes or yellowing?

Two common causes are residual unconsumed initiator at stripping temperature and uneven initiator distribution from a poorly dispersed liquid grade. Confirm dosing with a pre-dispersed 50% form and verify that the initiator half-life at stripping temperature leaves under 0.1% residue.

Can I run a mixed initiator system?

Yes, and it is standard practice in suspension PVC: a fast low-temperature initiator starts conversion while a slower high-temperature one finishes it, which flattens the exotherm peak. LAAP supplies both components and can advise the ratio for your reactor size.

Our Advantages

LAAP supplies low- and high-temperature initiators for suspension PVC, including peroxydicarbonates for cold processes, with grade-specific half-life data, batch COA/TDS support and cold-chain options for temperature-sensitive grades.