MACT

Maximum Achievable Control Technology. A technology-based air pollution control standard developed by the U.S. Environmental Protection Agency (EPA) aimed at reducing emissions of hazardous air pollutants (HAPs) from U.S. manufacturing operations.

Mandrel

A form, fixture or male mold used as the base for production of a part in processes such as layup or filament winding.

Mat

An unwoven textile fabric made of fibrous reinforcing material, such as chopped filaments (to produce chopped strand mat) or swirled filaments (to produce continuous strand mat) with a binder applied to maintain form. Available in blankets of various widths, weights, thicknesses and lengths. May be oriented.

Matched metal molding

See compression molding.

Matrix

Material in which reinforcing fiber of a composite is embedded. Matrix materials include thermosetting and thermoplastic polymers, metals and ceramic compounds.

Matrix content

Amount of matrix present in a composite expressed either as a percent by weight or percent by volume. For polymer-matrix composites this is the resin content. (Also see fiber content.)

Metal-matrix composite (MMC)

Continuous carbon, silicon carbide, or ceramic fibers embedded in a metallic matrix material.

Midplane

Plane that is equidistant from both surfaces of the laminate.

Microcracking

Microscopic cracks formed in composites when thermal stresses locally exceed the strength of the matrix.

Mil

The unit used in measuring the diameter of glass fiber strands, wire and so forth (1 mil = 0.0254 mm/0.001 inch).

Milled fiber

Continuous glass or carbon strands hammer-milled into very short fibers.

MMC

See metal-matrix composite.

Modulus

The physical measure of a material's stiffness, equal to the ratio of applied load (stress) to the resulting deformation of a material. May be represented by a number or in descriptive glossary as low, intermediate, high or ultrahigh. A higher modulus indicates greater stiffness. (See stiffness and Young's modulus.)

Moisture absorption

Pickup of water vapor from the air by a material. Refers to vapor withdrawn from the air only as distinguished from water absorption, which is weight gain due to the absorption of water by immersion.

Mold

An enclosed cavity or open form from which a composite component takes its shape, size and exterior surface appearance (also known as a tool).

Mold release agent

A lubricant used to prevent a part from sticking to a mold surface.

Molding

The process of forming composite materials into a solid mass of prescribed shape and size, using a mold or tool.

Monomer

A single molecule that reacts with like or unlike molecules to form a polymer.

Monofilament

Single continuous filament strong enough to function as a fiber in textile or other operations.

Multifilament

Yarn or tow consisting of many continuous filaments (also see yarn and tow).