Thesis (M.Eng.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Injection pressures available on commercial injection molding
machines have increased from 10,000 to 20,000 psi with 40,000 psi
in prospect. The pressure during solidification should strongly
influence the crystallinity, and hence mechanical properties, of those
regular polymers which can crystallize when cooled from the melt.
In this study, samples of isotactic polypropylene were solidified
under pressures up to 40,000 psi. In addition to tensile properties,
the resultant density, microstructure and DTA structure were examined.
From all measurements, it was concluded that the degree of crystallinity
decreased with increasing solidification pressure. Spherulites formed
under higher pressure were smaller in size and less branched than those
formed at low pressure. Yield and tensile strengths were reduced as the
solidi fication pressure was increased, the reduction being about 10%
when solidi fication occurred at 40,000 psi.
At first glance, these findings appear to predict strength differences
within a particular molded part depending on the molding pressure
used. It is concluded, however, that the strength variation would be
less in a commercial part. The loss of pressure in the cavity as a
result of freezing off at the in-gate should lead to a reduction in
cavity pressure early in the solidification process, a lower mean
pressure during freezing, and a relatively higher degree of crystallinity. / 2031-01-01
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/35460 |
| Date | January 1968 |
| Creators | Johnson, Lawrence P., Wong, Hasting |
| Publisher | Boston University |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0022 seconds