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Metastable region of phase diagram: optimum parameter range for processing ultrahigh molecular w eight polyethylene blends
Metastable region of phase diagram: optimum parameter range for processing ultrahigh molecular w eight polyethylene blends
Numerous studies suggest that two-phase morphology and thick interface
are separately beneficial to the viscosity reduction and mechanical property
maintainence of the matrix when normal molecular weight polymer (NMWP) is used
for modification of ultrahigh molecular weight polyethylene (UHMWPE).
Nevertheless, it is very difficult to obtain a UHMWPE/NMWP blend which may demonstrate
both two-phase morphology and thick interface. In this work, dissipative
particle dynamics simulations and Flory-Huggins theory are applied in
predicting the optimum NMWP and the corresponding conditions, wherein the melt
flowability of UHMWPE can be improved while its mechanical properties can also
be retained. As is indicated by dissipative particle dynamics simulations and phase
diagram calculated from Flory-Huggins theory, too small Flory-Huggins
interaction parameter (χ)
and molecular chain length of NMWP (NNMWP)
may lead to the formation of a homogeneous phase, whereas very large interfacial
tension and thin interfaces might also appear when parameters NNMWP
and
χ are
too large. When these parameters are located in the metastable region of the
phase diagram, however, two-phase morphology occurs and interfaces of the
blends are extremely thick. Therefore, metastable state is found to be
advisable for both the viscosity reduction and mechanical property improvement of
the UHMWPE/NMWP blends.
