B5: polymer matrix composites

IA-based unsaturated polyester resins for polymer matrix composites

The polymer matrix glass fiber composites are constituted by two parts : fibers and resins. The fiber type is mostly dependant on two factors – weave type and thickness. The thickness of a particular fiber is dependent on the chosen application. For structural applications, the most cost effective solution is to use the thickest possible fiber. Thicker fibers are cheaper than multiple layers of thinner fibers, although thinner fabrics will generally conform better to complex curves than thicker fabrics.

The cheapest and most common types of resin are unsaturated polyesters. These were used exclusively in the early days of fiberglass boatbuilding, tanks and are still the most popular today. When a peroxides is added to polyester resin, the curing reaction does not start at room temperature in absence of an accelerator (usually purple cobalt octanoate). Common polyester resins are based on either orthophthalic or isophthalic acids diluted mainly with styrene and in some cases with methacrylated monomers. These reactive diluents are rheological modifiers imparting low viscosity properties which are necessary for lamination and dispersing resins on glass fibers and mats. Ortho-polyester resins are the weakest and most brittle. They are also the most vulnerable to chemical attack and are the least water resistant. Iso-polyester resins are slightly less brittle and are considerably more chemical and water resistant. Therefore commonly use iso-polyesters in the gelcoat and external layers of a laminate and cheaper ortho-polyesters in the internal layers. Iso-polyester resins are just strong enough to support most sophisticated glass fibers, though they are probably not quite strong enough to be used effectively with exotic fiber.

Vinylester resins (well known also as epoxydimethacrylates) are another very important resins used for glass fiber composites. They are similar to polyester resins and utilize the same catalysts, but are markedly stronger. A vinylester resin, by comparison, can elongate up to 5 percent of its length before fracturing and has a tensile strength of about 45 MPa. Vinylester is also much more water resistant than both ortho- and iso- polyester resins, thus is less prone to blistering.

The easiest way to lay up a fiberglass hull is by hand in an open mold. The resin itself can be applied in different ways. The crudest method is to simply slap it on with brushes from buckets of catalyzed resin, but now airless spray guns or special resin-fed rollers are also applied. Though it takes a long time to cure completely (unless post-cured at higher than room temperatures), resin only remains “wet” in any meaningful sense for a few hours. 

The IA-based unsaturated polyester resins (bioUPR), diluted with commercially available aliphatic mono- or multi-acrylated monomers or with IA-based monomers giving styrene free resins. The diluted resins will be applied on the glass fiber mats creating a composite structure with four/five jointed layers. The thermo-initiated crosslinking reactions (curing) of polymer matrix can occur at room temperature within 24 h in presence of a catalyst (cobalt octanoate). The post-curing process will be applied with a thermal treatment at 110 °C for 2 h. Thermal and mechanical characterization will be applied to prototypes with IA based resins.

 

Beneficiary responsible for implementation: POLYNT

advanced polymer materials