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Matrix

The primary functions of the matrix in a composite:

  • Transfering stress between the reinforcements,

  • Binding to hold the fibers together, 

  • Protecting the fibers from mechanical and environmental damage. 

Technically, there are four types of matrices for composites:

  • Polymer Matrix Composites

  • Cement Matrix Composites ​

  • Metal Matrix Composites

  • Ceramic Matrix Composites

  • Carbon Matrix Composites​

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Polymers

Matrix = Resins

There are two major groups of resins that make up what we call polymer materials; thermosets and thermoplastics. These resins are made of polymers (large molecules made up of long chains of smaller molecules or monomers).

In most cases, when you read composite materials this means polymer matrices since, in practice, they have the biggest industrial adoption with the largest market size. 

Thermoset resins

Thermoset resins are used to make most composites. They’re converted from a liquid to a solid through a process called polymerization or cross-linking. When used to produce finished goods, thermosetting resins are “cured” by the use of a catalyst, heat, or a combination of the two. Once cured, solid thermoset resins cannot be converted back to their original liquid form. 

There are five thermoset resin classes:

  • Polyester

  • Epoxy

  • Vinyl Ester

  • Phenolic

  • Polyurethane

​Unsaturated polyester resins (UPR) are the workhorse of the composites industry and represent approximately 75% of the total resins used.

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Thermoplastics

Thermoplastic resins, on the other hand, are not cross-linked and, so, can be melted, formed, re-melted, and re-formed. Thermoplastic resins are characterized by materials such as ABS, polyethylene, polystyrene, and polycarbonate.

These resins are recognized by their capability to be shaped or molded while in a heated semi-fluid state and become rigid when cooled. We are surrounded by everyday household items made of thermoplastics.

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Other Matrices

Cement composites are one of the basic materials in the construction industry but in a traditional definition usually they are classified separately. Other matrix materials are utilized for sophisticated engineering purposes like aerospace. They are small in manufacturing volume but play very critical roles.

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Cement Matrix Composites

Flexible, tough concrete