3.4. Effects of b-nucleating agent on the impact strength of iPP
Table 1 lists the impact strength of the iPP and the iPP modified with b-NA ranging from 0 to 0.50 wt%. At 0.05 wt% nucleator, the impact strength increased slightly as compared with that of the neat iPP. Further addition of the b-NA, particularly by 0.10– 0.20 wt%, improved the impact strength of the b-NA nucleated iPP significantly, presumably this was due to the higher fraction of the tough b-crystal phase in the b-NA nucleated iPP, as was evi- dent in Figs. 3 and 4. The improvement of the impact strength was believed to arise by the increment of the boundary strength be- tween the fine and tougher b-phase spherulites [12] as shown in Fig. 5i and n. With further addition of the b-NA beyond 0.20 wt%, the impact strength started to decline although it was still greater than that of the neat iPP. As demonstrated in Fig. 3, the b-phase crystallization reached its saturation of 0.8–0.81 at the b-NA con- tent of 0.10–0.20 wt%, both the Kb and the Xb tended to drop min- utely and remained stagnate despite the rise of the b-NA content to 0.50 wt%. The impact result is in agreement with the work reported by Xu et al. [42]. They found that the impact strength was con- trolled mainly by the spherulite size; the maximum impact strength was due to the comprehensive result of the spherulite size and the degree of crystallinity.