Crystallinity

The degree to which a polymer's molecular chains pack into ordered, crystalline regions. Higher crystallinity generally increases stiffness, chemical resistance and melting point but also raises moulding shrinkage, as in semi-crystalline thermoplastics such as polypropylene and PEEK.

Also known as: degree of crystallinity, semi-crystalline

Related terms

Amorphous polymer

A polymer whose molecular chains have no long-range order. Amorphous polymers soften gradually above their glass transition temperature rather than melting sharply, and many, such as polycarbonate and acrylic, are naturally transparent.

Materials science (general)AerospaceAutomotiveConstructionMarineGreen energyIndustrial

Glass transition temperature

The temperature region over which an amorphous or partly amorphous polymer changes from a rigid, glassy state to a softer, rubbery one. It sets a practical upper service temperature for resins and adhesives and can be reduced by absorbed moisture or incomplete cure.

Resins & adhesivesMaterials science (general)Composites & laminatesAerospaceAutomotiveConstructionMarineGreen energyIndustrial

Thermoplastic

A polymer that softens when heated and hardens again on cooling without chemical change, so it can be reshaped, welded or recycled. Thermoplastics range from commodity materials such as polypropylene and PVC to high-performance matrices such as PEEK used in advanced composites.

Resins & adhesivesMaterials science (general)Composites & laminatesAerospaceAutomotiveConstructionMarineGreen energyIndustrial

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