Composite processing - Methods and materials

The specific processing methods used for reinforced plastics have contributed to the evolution of the terms used to designate these materials since their origin some fifty years ago.

The term laminates has long been used to refer to the very constitution of the material: "strata", or successive layers of glass fibers or other sheet products (paper, cotton fabric, etc.) and thermosetting resin.

The name low-pressure laminates was then preferred to distinguish the processes used to produce these materials from those used for high-pressure laminates. Indeed, these low-pressure laminates were obtained by molding without pressure (manual molding or winding) or by molding at very low pressures (a few megapascals) between mold and counter-mold.

The glass reinforcement used at the time was mainly in the form of felt (mat), fabric or roving (stratifil or roving).

Evolving needs have gradually necessitated the use of other methods involving other matrices, new presentations of glass fiber and other fibers or hybrids.

The highest tonnages are still obtained with glass/UP (unsaturated polyester). However, we would like to point out the extent to which the techniques presented are applicable or applied to other matrices or reinforcements.

Today, reinforced plastics or composites have come of age, and can be obtained by a wide range of processes described here. These processes require the use of certain polymeric matrices and different presentations of reinforcements, which will be described in greater detail as we go along; but, generally speaking, reinforced plastics are always made up of two main materials: the reinforcement and the matrix, to which various additives are added.

The reinforcement consists of a fibrous material. Most often glass fibers, but also carbon fibers, aramid fibers, silica fibers, boron fibers, etc., are used. It comes in the form of mats (felts made of chopped threads or long fibers), fabrics, rovings or chopped threads.

The matrix is either a thermosetting resin (unsaturated polyester, epoxy or formophenolic resin, polyimide, polyurethane, etc.) or a thermoplastic resin (polyamide, polycarbonate, saturated polyester, polypropylene, etc.).

Additives are products required for cross-linking or polymerizing resins (gas pedals, catalysts, etc.), or for obtaining specific characteristics (fire behavior, resistance to aging, coloring, etc.).

Fillers (calcium carbonate, talc, etc.) are also used for economic reasons or,...