**3. Crystallization morphologies of iPP nucleated with α/β compounded NAs**

The spherulite size of iPP can be decreased by cooperation with any kinds of NAs. But the morphology of nucleated iPP largely depends on the types of NA. The α NA will only induce α form iPP while β form iPP can be obtained by incorporating with β NA. Then what about the morphologies of iPP nucleated by α/β compounded NAs?

Polarized optical microscope was used to investigate the crystallization morphologies of iPP nucleated with Phosphate/Carboxylate compounded NA, NA40/H-Ba by Xu et al. (Xu et al., 2011). As shown in Fig.1, in nucleated iPP, a large number of nuclei would be produced due to the existence of NAs. Therefore the spherulites cannot grow large enough to overlap, the size of spherulites in nucleated iPP would be much smaller than those in pure iPP. But as to the morphologies of the samples, iPP nucleated with NA40/H-Ba showed no sign of bright and colorful β crystals, appeared much close to the morphology of iPP induced by NA40 individually.

Fig. 1. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 135 °C (Xu et al., 2011)

The crystallization morphologies of pure iPP and iPP induced by Sorbitol/Amide compounded NA, 3988/DCHT were shown in Fig.2 (Zhao & Xin, 2010). From figure, it can be seen that with the addition of the α/β compounded NA, the spherulite size decreased

Controlled Crystallization of Isotactic Polypropylene

Fig. 4. SEM for pure iPP and nucleated iPP samples (Bai et al., 2008)

by Xu, as shown in Fig.6 (Xu, 2010).

However, it was interesting that totally different results could be gained when the DCHT compounded with different α NAs. Zhao et al. found the nucleation effect of NA11/DCHT compounded NA was between that of iPP/NA11 and iPP/DCHT. It can be seen from Fig.5, the spherulites of pure iPP showed the typical characteristic of α crystal, which had a large size and clear boundaries (Zhao & Xin, 2010). By adding compounded NA, the spherulite size greatly reduced, indicating that compounded NA played a role of heterogeneous nuclei during crystallization. The content of bright and colorful β form iPP was less than that of iPP/DCHT, but was higher than iPP/NA40, which means at this condition the crystallization morphology of iPP was affected by both NAs within the compounded NA. The same result was got through the study on crystallization morphologies of iPP nucleated with Phosphate/Amide compounded NA, NA40/NABW

Based on α/βCompounded Nucleating Agents: From Theory to Practice 131

significantly. Different from iPP with NA40/H-Ba, β form iPP became the majority in the morphology of iPP nucleated with 3988/DCHT. It can be considered that DCHT played a leading role during crystallization. The same conclusion was drew by investigating of iPP cooperation with 3988/NABW (Xu, 2010). The morphology of nucleated iPP was close to that incorporation with NABW individually. In addition, Bai et al. directly observed the crystallization morphologies of iPP nucleated with Sorbitol/Amide compounded NA, DMDBS/TMB-5 by SEM (Bai et al., 2008). Pure iPP showed the growth of well developed α spherulites with 30~50um in diameter. The size of iPP spherulites was also reduced with addition compounded NA. Similarly β form iPP dominated in the morphology of PP/0.1DM/0.1TM.

Fig. 2. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 140 °C (Zhao & Xin, 2010) (a) pure iPP, (b) iPP/ (3988/DCHT)

Fig. 3. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 135 °C (Xu, 2010)

significantly. Different from iPP with NA40/H-Ba, β form iPP became the majority in the morphology of iPP nucleated with 3988/DCHT. It can be considered that DCHT played a leading role during crystallization. The same conclusion was drew by investigating of iPP cooperation with 3988/NABW (Xu, 2010). The morphology of nucleated iPP was close to that incorporation with NABW individually. In addition, Bai et al. directly observed the crystallization morphologies of iPP nucleated with Sorbitol/Amide compounded NA, DMDBS/TMB-5 by SEM (Bai et al., 2008). Pure iPP showed the growth of well developed α spherulites with 30~50um in diameter. The size of iPP spherulites was also reduced with addition compounded NA. Similarly β form iPP dominated in the morphology of

Fig. 2. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 140 °C (Zhao & Xin, 2010) (a) pure iPP, (b) iPP/ (3988/DCHT)

Fig. 3. Polarized light microphotographs for pure iPP and nucleated iPP samples

crystallized at 135 °C (Xu, 2010)

PP/0.1DM/0.1TM.

Fig. 4. SEM for pure iPP and nucleated iPP samples (Bai et al., 2008)

However, it was interesting that totally different results could be gained when the DCHT compounded with different α NAs. Zhao et al. found the nucleation effect of NA11/DCHT compounded NA was between that of iPP/NA11 and iPP/DCHT. It can be seen from Fig.5, the spherulites of pure iPP showed the typical characteristic of α crystal, which had a large size and clear boundaries (Zhao & Xin, 2010). By adding compounded NA, the spherulite size greatly reduced, indicating that compounded NA played a role of heterogeneous nuclei during crystallization. The content of bright and colorful β form iPP was less than that of iPP/DCHT, but was higher than iPP/NA40, which means at this condition the crystallization morphology of iPP was affected by both NAs within the compounded NA. The same result was got through the study on crystallization morphologies of iPP nucleated with Phosphate/Amide compounded NA, NA40/NABW by Xu, as shown in Fig.6 (Xu, 2010).

Controlled Crystallization of Isotactic Polypropylene

kinds of nucleating agents?

Phosphate/Amide

Sorbitol/Amide

Phosphate/Carboxylate

Compounded NAs (Xu et al., 2011; Zhao & Xin, 2010)

sign of enhancing the toughness of iPP.

Compounded NA Tensile

Based on α/βCompounded Nucleating Agents: From Theory to Practice 133

The effects of different NAs on the crystallization process of polymer reflect on its mechanical properties finally, which determines on the use value of the polymer. Mentioned in the introduction, the α NA can improve the stiffness and optical properties of iPP while decrease its toughness. The β NA will induce β-iPP during crystallization, which can improve toughness and heat distortion temperature of iPP while decrease its stiffness. Will it come true that we can balance the iPP's stiffness and toughness by compounding two

Xu et al. investigate the effect of Phosphate/Carboxylate α/β compounded NA, NA40/HB on the mechanical properties of iPP (Xu et al., 2011). As shown in Tab.3, tensile strength (ASTM D-638) and flexural modulus (ASTM D-790) of iPP were improved with the presence of NA40 while the impact strength (ASTM D-256) decreased. On the contrary, the impact strength of iPP could increase to 3.4 times to that of pure iPP but tensile strength and flexural modulus was reduced as always by adding HB. Numerically the mechanical properties of iPP nucleated with NA40/HB were close to that iPP/NA40, which showed no

strength /MPa

iPP 29.8 1223 33.8

iPP 29.8 1223 33.8

iPP 33.1 1052 35.6

NA11 (0.1 wt %) 34.5 1770 30.2

DCHT (0.1 wt %) 27.9 1143 74.0

NA11/DCHT (1:1) 34.2 1669 49.7

3988 (0.1 wt %) 31.5 1297 30.9 DCHT (0.1 wt %) 27.9 1143 74.0 3988/DCHT (1:1) 27.6 1108 73.4

NA40 (0.1 wt %) 36.2 1562 33.2 HB (0.1 wt %) 28.8 1025 158.2

NA40/HB (1:1) 36.3 1521 34.2

Table 3. Mechanical Properties of Pure iPP and iPP Nucleated with Individual α, β and α/β

Similar to the effect on crystallization morphologies, different mechanical properties of iPP would be reached when the DCHT compounded with different α NAs. Incorporation with Sorbitol/Amide compounded NA, 3988/DCHT can significantly improve the impact

Flexural modulus /MPa Impact strength /(J/m)

**4. Mechanical properties of iPP nucleated with α/β compounded NAs** 

Fig. 5. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 140 °C (Zhao & Xin, 2010) (a) iPP, (c) iPP/ (NA11/DCHT)

Fig. 6. Polarized light microphotographs for pure iPP and nucleated iPP samples crystallized at 135 °C (Xu, 2010)

All studies showed that the size of spherulites in nucleated iPP appeared much smaller than that of in pure iPP. However, iPP nucleated by different α/β compounded NAs showed different crystallization morphologies. The morphology of iPP nucleated Phosphate/Carboxylate compounded NA, NA40/H-Ba was close to iPP nucleated by NA40 individually, while iPP nucleated by Sorbitol/Amide compounded NA, 3988/DCHT showed the similar morphology of iPP/DCHT. IPP nucleated with Phosphate/Amide NA40/NABW compounded NA presented a crystallization morphology that combined both NAs' within the compound system.

Fig. 5. Polarized light microphotographs for pure iPP and nucleated iPP samples

Fig. 6. Polarized light microphotographs for pure iPP and nucleated iPP samples

All studies showed that the size of spherulites in nucleated iPP appeared much smaller than that of in pure iPP. However, iPP nucleated by different α/β compounded NAs showed different crystallization morphologies. The morphology of iPP nucleated Phosphate/Carboxylate compounded NA, NA40/H-Ba was close to iPP nucleated by NA40 individually, while iPP nucleated by Sorbitol/Amide compounded NA, 3988/DCHT showed the similar morphology of iPP/DCHT. IPP nucleated with Phosphate/Amide NA40/NABW compounded NA presented a crystallization morphology that combined

crystallized at 135 °C (Xu, 2010)

both NAs' within the compound system.

crystallized at 140 °C (Zhao & Xin, 2010) (a) iPP, (c) iPP/ (NA11/DCHT)
