Application guide

Resin for Pultruded FRP Profiles

How continuous pultrusion cures resin in a heated die, and the terephthalic grade the catalogue lists for pultruded profiles and sections.

A die-heat cure: no MEKP or cobalt in production.

Pultrusion makes FRP profiles continuously: reinforcement is pulled through resin and then through a heated die, where the resin cures, and the profile is cut to length as it emerges. Unlike a room-temperature process, the cure is triggered by the heat of the die. Pultrusion Grade Resin (SPR 401 PT) is the terephthalic grade the catalogue lists for this process, explained in What Is Pultrusion Grade Resin?. Where the service calls for vinyl ester instead, the vinyl ester pultrusion guide covers that route.

What manufacturers build

Pultruders make constant cross-section profiles — angles, channels, I-sections, rods, tubes and flat bars — in continuous lengths. The catalogue lists continuous pultrusion processing and pultruded FRP profiles and structural sections as the uses of SPR 401 PT. Profile design, reinforcement layout and any load or service requirement are the pultruder’s and the designer’s responsibility. How a pultrusion resin differs from a winding resin is covered in Filament winding vs pultrusion resin.

Why this material suits the work

The catalogue describes SPR 401 PT as a high-strength terephthalic grade with strong mechanical properties for continuous pultrusion, run on a heat-activated peroxide system. It is a clear, light-straw to amber liquid of 300–600 cPs at 25 °C, non-thixotropic, with a specific gravity of 1.10–1.14 and 36–42% styrene by weight. Its hot-die gel time is 40–80 seconds at 130–140 °C. Production runs on a heat-activated peroxide blend at a total dosage of 1.0–2.0%, with 0% MEKP and 0% cobalt. The ambient gel time of 15–25 minutes at 25 °C is a quality-control figure, not the production cure. The grade belongs to the terephthalic polyester family.

Required resin characteristics

A cure triggered by die heat — a heat-activated peroxide blend, with no MEKP or cobalt in production
A hot-die gel time matched to line speed and die length (typical 40–80 seconds at 130–140 °C)
Non-thixotropic flow, typical 300–600 cPs at 25 °C, to wet the reinforcement as it is pulled through
An ambient gel figure for quality control (typical 15–25 minutes at 25 °C), kept separate from the production cure
Non-accelerated supply, since no cobalt accelerator is used on the line

Process context

In general practice continuous rovings and mat are drawn from creels through a resin bath or injection box, guided into shape and pulled through a heated steel die, where the resin gels and cures. A puller draws the cured profile continuously and a saw cuts it to length. For SPR 401 PT the production cure is a heat-activated peroxide blend at a total dosage of 1.0–2.0%, added separately during processing, with 0% MEKP and 0% cobalt; the catalogue gives a hot-die gel time of 40–80 seconds at 130–140 °C. The ambient gel time of 15–25 minutes at 25 °C is a quality-control test, not the way the line cures. The specific peroxide blend, die temperature profile, line speed and any filler are set by the pultruder on its own trials.

Advantages

A grade the catalogue lists specifically for continuous pultrusion and pultruded profiles
A published hot-die gel range and production cure to plan line trials from
Non-thixotropic, with a typical 300–600 cPs at 25 °C, for wetting reinforcement on the line
Described in the catalogue as high strength with strong mechanical properties

Common products

Angles, channels and I-sections
Rods, tubes and flat bars
Pultruded structural sections
Profiles for gratings, ladders and cable trays

Common questions

Can SPR 401 PT be cured with MEKP and cobalt on the line?

The production cure the catalogue gives is a heat-activated peroxide blend at 1.0–2.0% total, with 0% MEKP and 0% cobalt. The die heat does the curing.

What is the ambient gel time for, then?

The 15–25 minutes at 25 °C figure is a quality-control test for the resin. It is not the production cure and does not describe how the line runs.

Should I pultrude with polyester or vinyl ester?

Decide by the service. If the profile specification or its service conditions call for vinyl ester, follow the vinyl ester pultrusion guide; otherwise SPR 401 PT is the polyester grade the catalogue lists for the process.

What load can a profile made with it carry?

None is published for the resin. Load capacity belongs to the finished profile — its design, reinforcement and testing — not to the resin data.

Running a pultrusion line?

Tell us the profiles you pull, the service they go into and the quantity you expect to take. Nepal price, packaging and lead time are confirmed on enquiry.

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