Blends were prepared from isotactic polypropylene (iPP) along with its b-nucleated form and poly(vinylidene-fluoride) (PVDF).
Melting, and crystallization characteristics as well as structure of the blends were studied by polarized light microscopy
(PLM) and differential scanning calorimetry. According to PLM studies, the phase structure of these blends is heterogeneous
in the molten state. The temperature range of crystallization of PVDF during cooling is higher than that of iPP. PVDF has
a strong α-nucleating effect on iPP. The crystallization of iPP starts on the surface of dispersed PVDF droplets and an α-transcrystalline
layer forms on the surface of the crystalline PVDF phase. The iPP matrix crystallizes predominantly in a-form in spite of
the presence of a highly active b-nucleating agent.
Crystallization, melting and structure of three different commercial types of isotactic polypropylene (iPP) grafted by maleic
anhydride (PP-g-MAH) with different maleic anhydride content (AC) and their β-nucleated versions were studied by X-ray diffractometry
(WAXS), differential scanning calorimetry (DSC), polarised light microscopy (PLM) and scanning electron microscopy (SEM).
The presence of maleic anhydride units disturbs the chain regularity, hereby decreases the crystallization tendency of iPP
in general and the β-crystallisation ability in particular. β-modification of iPP (β-iPP) forms only in β-nucleated PP-g-MAH
polymers studied if the anhydride content is not larger than 0.5 mass%. The influence of AC of PP-g-MAH on the feature the
spherulitic structure is demonstrated by PLM and SEM micrographs. The β-nucleated iPP/PP-g-MAH blends containing 10 mass%
PP-g-MAH crystallise predominantly in β-form independently of AC of the latter. The β-nuceated blends of iPP and PP-g-MAH
with lowest AC crystallise in β-form in whole concentration range. The interaction parameter between iPP and PP-g-MAH polymers
calculated by Nishi-Wang equation indicate limited interaction between the components.
The nucleating efficiency and selectivity of different
β-nucleating agents was characterised and compared by differential scanning
calorimetry, (DSC) and temperature-modulated DSC (TMDSC). The nucleating agents
were the calcium salts of pimelic and suberic acid (Ca-pim and Ca-sub), linear trans-γ-quinacridone (LTQ), a commercial nucleator
NJ Star (NJS) and an experimental product (CGX-220). The efficiency and the
selectivity of Ca-sub and Ca-pim are extremely high. NJS is efficient above
a critical concentration, which is connected with its partial dissolution
in polypropylene melt. LTQ and CGX-220 possess strong overall nucleating ability
and moderate selectivity. Using TMDSC, we found that three consecutive processes
take place during the heating of β-nucleated samples cooled down to room
temperature: reversible partial melting of the β-form, irreversible βα-recrystallisation,
and the melting of the α-modification formed during βα-recrystallisation
or being present in samples prepared with non-selective β-nucleators.
Melting of the α-phase contains both reversible and irreversible components.