Definitions /Dictionary/Glossary - nptel

Glass Transition: Reversible change in an amorphous polymer or amorphous regions of a
partially crystalline polymer from or to a viscous, rubbery, or hard and relatively brittle
condition.
Glass Transition Temperature (Tg): The appropriate midpoint of the temperature range over
which glass transition takes place.
Good Side: Side of molding in contact with a mold surface.
Graphite Fiber: Fiber made from a precursor by oxidation, carbonization and graphitization
process (which provides a graphitic structure).
Green: Resin, which has not completely cured and is still rather soft and rubbery.
Green Strength: That ability of the material, while not completely cured, to undergo removal
from the mold and handling without tearing or permanent distortion.
GRP: A derivation commonly used in Europe referring to glass-reinforced plastic, polymer or
polyester.
Glint: A visual defect in a fiberglass reinforced cured organic (usually corrosion- resistant resin)
panel. The defect appears as many small visible unwet or foreign substances similar to a saltand-pepper
effect. The defect is not visible before cure but appears at the panel’s exotherm.
Guide Pin: A pin which guides mold halves into alignment on closing.
Hand: Fabric softness as determined by touch (individual judgment).
Hand Lay-up: The process of placing (and working) successive plies of reinforcing material or
resin-impregnated reinforcement in position on a mold by hand. It is a method of molding room
temperature curing thermosetting polymers, mainly epoxies and polyesters, in association with
glass, mineral, or fiber reinforcements. Catalyzed resin mixtures are sprayed, brushed, or
spatulated on a mold. A precut reinforcing layer is laid on the wet resin. After the resin soaks
into the reinforcement, subsequent layers are built up to the required thickness and are cured,
removed from the mold and trimmed. Some variations of hand lay-up techniques are bag
molding, drape molding, vacuum molding and spray-up molding. Typical parts are custom auto
bodies and boat hulls.
Hardener: A substance or mixture added to a plastic composition to promote or control curing
by taking part in it.
Hard Glass: A roving product that is not very soluble in acetone or styrene, causing individual
bundles to retain their integrity (hardness) and not filamentize in the matrix resin. Hard glass is
often stiff and brash. The size is generally less than 40% soluble in acetone. see Soft Glass