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β-crystal formation of isotactic polypropylene under the combined effects of acid-corroded glass fiber and preshear
β-crystal formation of isotactic polypropylene under the combined effects of acid-corroded glass fiber and preshear
The acid-corroded glass fiber (GF)/isotactic polypropylene
(iPP) composite was injection molded by mixing–
injection molding (MIM). Through this method,
preshear can be imposed on melt during mix–plasticization
process. The crystalline structure across the
thickness direction of the injection-molded bars was
investigated by wide-angle X-ray diffraction and differential
scanning calorimetry (DSC). It was unexpectedly
found that, in core region, the acid-corroded GF/iPP
sample has the highest content of b-form crystals, followed
by uncorroded GF/iPP and neat iPP. Additionally,
the crystalline morphology was investigated by polarized
optical microscopy (POM) and scanning electron microscopy,
and the results showed that b-transcrystallization
is preferably present in the acid-corroded GF/iPP system.
Confirmed by POM and DSC, the acid-corroded GF
shows strong b-nucleation ability to iPP under static
condition. Combined with the main features of MIM,
three b-nucleation origins in the acid-corroded GF/iPP
system under injection molding condition are proposed:
(1) precursors induced by preshear in the barrel, (2) rownuclei
induced by local shear, and (3) the acid-corroded
GF nuclei.
