Morphology of polyethylene foamed crosslinked specimens made by hot mold injection molding

Foamed and crosslinked specimens of polyethylene made by hot mold injection molding were investigated. A combination of PELD, dicumilperoxide and azodicarbonamide was used. The three components were mixed and granulated in an extruder-granulator at temperature 100-120 deg C. The degree of crosslinking was calculated by equilibrium strain epsilon sub r determined at temperature 140 deg C and pressure stress sigma sub p =0.045 MPa. The same parameter was evaluated by thermomechanical curves. The degree of crystallinity was determined by DSC-kinetics of a nonisothermal melting and crystallization. The morphology was investigated by a polarized microscope MIN 8. It is established that a part of polymer crystallizes as spherulites. The spherulites can be observed with crossed polarizers. The samples on the whole are not oriented. There exists only a local orientation around the edge of the bubbles which is proved by the observed bright regions. The number of the spherulites decreases with the increase of crosslinking degree. This also conforms with the degree of crystallinity which decreases with the increase of the crosslinking degree.