The relationship between the impact strength and the filled quantity of nucleating agent is shown in Fig.4. A maximum impact strength exists at the 0.4 wt.% filled quantity of nucleating agent, corresponding to the changing regularity of the crystalline morphology. While the filled quantity of the nucleating agent was below 0.4 wt.%, with the rise of the filled quantity, the spherulite size tended to decrease. The fineness of the crystal grain must, therefore, be beneficial to impact strength.Furthermore, the nucleating agent impelled the degree of orientation of the polymer and improved the crystallization rate, retarding the relaxation of the cooling process of the polymeric melt. This will produce a more tied-molecule structure among the intra- and interspherulite to improve the molecular entanglement between the crystal grain.Therefore, the boundary strength between spherulite increased, thus it will be beneficial to the improvement of the impact strength of the materials w3x.When the filled quantity of nucleating agent was beyond 0.4 wt.%, with the rise of the filled quantity, the spherulite size tended towards stabilization, whilst the crystallinity of the PP still went up. The flexibility of the molecular chain will decrease, at conditions of higher crystallinity. Because of the decline in the active region of the molecular chain, its capability of energy absorption decreases within the process of deformation due to the effect of an external force. Therefore, the phenomenon is unfavorable to impact strength; instead it tended towards a decrease. To sum up, the maximum impact strength was found in the test with the filling of nucleating agent.
For obtaining the quantitative relation between impact strength and crystalline morphology, a series of succeeding heat treatments were carried out on the PP
materials in Table 1, as the process of heat treatment only affected the crystallinity of the materials see Table 2.. Therefore, we can consider the effect of crystallinity and spherulite size separately. As shown in Fig. 5, under different spherulite sizes for spherulite sizes of various materials, see Fig. 1., the variation of impact strength with crystallinity had the same regularity,which can be expressed with a unified type of fitting formula