D - Polymer Processing Glossary of Terms

Daylight opening - Clearance between the two platens of the press in the open position.
Decompression - See Suckback
Degradation - A deleterious change in the chemical structure of a plastic.
Degating - The removal of material left on a plastic part formed by the opening through which material was injected into the mold cavity.
Degree of polymerization - The average number of monomer units per polymer molecule, a measure of molecular weight. In most plastics, the molecular weight must reach several thousand to attain worthwhile physical properties.
Density - Mass per unit volume of a substance, exposed in units such as grams per cubic centimeter, pounds per cubic foot or pounds per gallon.
Desiccant - A substance capable of absorbing water vapor from air or other gaseous material, used to maintain low humidity in a storage or test vessel.
Draft - The degree of taper of a side wall or the angle of clearance designed to facilitate ejection of parts from the mold.
Dry coloring - A method commonly used for coloring plastics by tumble-blending uncolored and colored particles of the plastic material with selected dyes and pigments.

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