What Is Low-Viscosity Isophthalic Resin? SPR 301 LV for Jute Explained

Why jute is harder to wet than glass

Glass fibres are solid and non-absorbent; resin only has to flow between them. Jute fibres are natural, hollow-structured and absorbent, and jute mats are typically thicker and bulkier than glass mats of similar use. A resin at ordinary laminating viscosity can coat the outside of a jute mat and leave dry fibre in the middle.

A dry core is a weak core. It also traps air and moisture, which show up later as delamination and poor durability.

What the low viscosity buys

SPR 301 LV is the catalogue’s low-viscosity isophthalic grade designed for jute reinforcement, with a typical viscosity of 80–180 cPs at 25 °C. At that viscosity the resin penetrates a thick mat far more readily than a general laminating grade such as GP Clear Resin, published at 350–450 cPs.

It is paired with a long typical gel time — 40–90+ minutes at 25 °C — which gives time for impregnation to finish before the resin begins to gel.

Moisture is the hidden variable

Natural fibres carry water, and how much depends on storage and humidity. Water on the fibre interferes with wetting and with the resin’s cure at the fibre surface. Conditioning jute to a consistent, low moisture level before impregnation, and trialling at production moisture, is part of making jute composites repeatable.

Cure and handling notes

The catalogue’s reference cure is MEKP 1.5% with cobalt octoate 0.2% — half the cobalt level used by most SPR 301 grades — each added separately. Styrene content is 42–50% by weight typical, higher than general laminating grades, so ventilation and control of styrene exposure deserve particular attention.