The specialist composite prepreg producer, GMS Composites, has developed a new, high performance flame retardant (FR) epoxy prepreg with increased toughness and a significantly shorter gel time, which passes the UL94 V0 flammability rating.

The new FR grade, GMS EP-540 is a non–halogenated epoxy resin matrix prepreg, replacing EP-530, a previously developed FR grade which had an average 16-minute gel time at a 120^oC mould temperature.

The new EP-540 grade has a significantly faster gel time down to only 6 minutes at 120^oC for thinner laminates, with parts fully cured within 2 hours, the company reports.

Feedback

“We developed this improved performance FR prepreg in direct response to feedback about our old FR grade from design and process engineers working for two leading OEM automotive companies producing motorsport super cars,” commented Sam Weller, Managing Director.

“With this automotive application, certification to UL94 V0 was the critical factor, so meeting this demanding fire specification whilst balancing and improving both the mechanical and processing properties of the prepreg system was a real challenge, but we persevered.”

Faster cycle time

Having a faster cycle time was a critical objective to appeal to motorsport OEMs, which is a key automotive target market, as well other sectors needing high FR rated prepregged composite parts, such as powerboat racing, aerospace, defence, rail and hazardous goods vehicles, the manufacturer reports.

According to the company, having a fast cure epoxy prepreg which meets UL94 V0 has opened the door for GMS Composites to trial its new FR epoxy prepreg for carbon fibre (CF) composites parts in GT3, GTE, rally cross and similar racing car classes, as UL94 V0 is one of the critical fire standards required by FIA (Federation International de L’automobile).

The UL94 standard rates the ignition characteristics of plastic materials. To achieve the highest V0 flammability resistance rating for UL94, test samples are placed vertically with a specified test flame applied from below directly on the bottom of the sample; all flaming combustion must extinguish within 10 seconds, and without burning to the top clamp or dripping molten material.

Technical properties

According to GMS Composites test data++ in its published datasheet, the new EP-540 epoxy prepreg has a tensile strength of 460 MPa, flexural strength 578 MPa, with an Izod Impact strength of 230 J/m. Fire performance data provided shows that the UL94 V0 rating is comfortably achieved in the most demanding vertical flame test, recording an average burning time of only 3 seconds, which is 7 seconds less than the maximum allowable combustion time to meet the V0 rating, and 2 seconds less than the old EP-530 grade it replaces.

The resin formulation of GMS EP-540 also aims to provide a high degree of processing versatility, with a range of cure cycles, pressures and ramp up rate options possible depending on the part being produced; the tack can also be varied. The curing cycle for GMS EP-540 can be as low as 80^oC up to a maximum of 150^oC, offering moulders processing flexibility to precisely suit the specific production parameters.

The grade is compatible with all standard sandwich core materials, as well as carbon, glass and aramid fibre reinforcements. GMS EP-540 prepreg has a shelf life in excess of 6 weeks at a 23^oC ambient temperature and 12 months in -18^oC cold storage conditions.

www.gmscomposites.com