LDPE

LDPE High-Pressure Polymerization Initiators

Select the initiator package by reactor zone, peak temperature and residence time for tubular or autoclave LDPE.

Overview

LDPE is produced under high pressure in either a tubular or an autoclave reactor. The initiator package is selected by zone and residence time, not by a single “LDPE grade” label: the entry zone needs fast initiation, the peak zone needs decomposition that tracks the ethylene concentration gradient, and the finishing step needs the radical flux to fall away cleanly. The process window below separates those duties before recommending a grade.

Process Window

Start with reactor type and the temperature at each injection point. This table separates the initiation, peak and finishing zones and the peroxide duty in each one.

Stage	Temperature	Duration	Initiator requirement
Tubular reactor, peak zone	250-330 °C (peak)	Seconds	Very fast initiator that decomposes almost entirely at peak temperature, so the radical flux tracks the ethylene concentration gradient.
Autoclave reactor	150-220 °C	30-60 s residence	Initiator half-life tuned to residence time; too slow leaves residual peroxide, too fast causes local hot spots and gel formation.
Initiation at entry zone	130-170 °C	Continuous	A fast initiator to start the reaction as the feed reaches temperature, typically a peroxydicarbonate or low-temperature peroxyester.

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.

tert-Butyl peroxy 2 ethylhexanoate (TBPEH)CAS 3006-82-4

Medium-temperature ester (10h t½ 73 °C) widely used in autoclave initiator systems.

1 hour: 100℃
10 hours: 73℃
SADT: 35℃
Typical dose: 0.01-0.05 wt% on ethylene

tert-Butyl peroxy-3,5,5-trimethylhexanoate (TBPMH)CAS 13122-18-4

Standard LDPE tubular grade (10h t½ 94 °C).

0.1 hour: 135℃
1 hour: 114℃
10 hours: 94℃
SADT: 55℃
Typical dose: 0.01-0.04 wt%

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

Low-temperature starter (10h t½ 47 °C) for the entry zone.

0.1 hour: 83℃
1 hour: 64℃
10 hours: 47℃
SADT: 5℃
Typical dose: 0.005-0.02 wt%

Di-tert-butyl peroxide (DTBP)CAS 110-05-4

High-temperature finishing initiator (10h t½ 121 °C) for the peak zone.

0.1 hour: 164℃
1 hour: 141℃
10 hours: 121℃
SADT: 80℃
Typical dose: 0.01-0.05 wt%

Procurement & Handling

HS code: 2909.60 / 2915.90 (confirm per grade)
Transport class: UN 3103-3110, Class 5.2
Packaging: Diluted grades in 20-25 kg HDPE drums; bulk ISO tank options for repeat volume
Storage: 10-25 °C for esters; peroxydicarbonates below 0 °C with temperature logging
Minimum order: 25 kg trial, 1 t commercial

Common Questions

How do I choose between tubular and autoclave initiators?

Tubular reactors need initiators that decompose within seconds at peak temperature, usually a very fast peroxide in the peak zone plus a starter at entry. Autoclave reactors have long residence times and use slower, medium-temperature esters such as TBPMH or TBPEH.

What causes gel or crosslinking in my LDPE?

Local peroxide concentration spikes are the usual cause: an initiator that decomposes faster than the mixing scale creates hot spots, and the radicals then abstract hydrogen and crosslink adjacent chains. Moving to a slower grade or improving injection-point dispersion fixes most cases.

Do you supply initiators as pumpable solutions?

Yes. Low-temperature grades are supplied in odourless mineral spirit solutions (typically 75% or 50%) so they can be pumped and metered into a high-pressure reactor; undiluted grades are available where the injection system is designed for them.

Our Advantages

LAAP has supplied high-pressure polyethylene initiators since 1966, including peroxyesters and dialkyl peroxides for tubular and autoclave systems, with half-life tables and batch documentation to support initiator-system changes.