| Controlling the crystallization of Polypropylene (PP) to improve the properties of PP through adding nucleating agent (NA) is an effective and practical way. NA for PP can be divided intoα-form N A (αNA) andβ-form NA (βNA) depending on which PP crystal form it can induce,αNA can improve the stiffness and optical properties of PP while decrease its toughness.βphase NA will induceβ-PP during crystallization, which can improve toughness and heat distortion temperature of PP while decrease its stiffness. Thereby, it is well expected to balance the PP's stiffness and toughness.First, substituted aromatic heterocyclic phosphate nucleating agent NA 40 was selected as theαNA. It was compounded with threeβNAs TMB-5, HHPA-Ba and PA-03with different nucleating efficiency. Effects of three a/p compounded NAs NA40/TMB-5, NA40/HHPA-Ba and NA40/PA-03 on the mechanical properties of isotactic Polypropylene (iPP) were investigated systematically with different addition amount and different compounded ratio. The results showed that stiffness and toughness of iPP could be adjusted and enhanced simultaneously by changing the ratio ofαandβnucleating agents. It was foundα/βcompounded NAs like NA40/TMB-5 0.1 wt% (compounded ratio of 1:1), NA40/TMB-5 0.2 wt% (compounded ratio of 2:3), NA40/TMB-5 0.3 wt% (compounded ratio of 3:7), NA40/HHPA -Ba 0.3 wt% (compounded ratio of 3:17), NA40/PA-03 0.1 wt% (compounded ratio of 3:7), NA40/PA-03 0.2 wt% (compounded ratio of 3:7), NA40/PA-03 0.3 wt% (compounded ratio of 3:7), can improve tensile strength, flexural modulus and impact strength of iPP simultaneously.Then, through the analysis of iPP crystallization process, the key factor of affecting threeα/βcompounded NAs NA40/TMB-5, NA40/HHPA-Ba and NA40/PA-03 was summarized and testified, which was ATcp (the crystallization peak temperature of iPP nucleated with NA individually). The NA with higher ATcp would play a leading role in the crystallization process. Consequently the mechanical properties of iPP would appear close to it. Competitive nucleation will occur when the difference of△TCp between two NAs is not pronounced.According to this rule, the optimization method for compoundingαandβNAs was developed. That is to find out the ratio ofαandβNAs with△Tcpα-△TcPβso as to let competitive nucleation occur during crystallization. Rely on it the optimal ratios ofα/βcompounded NAs can be easily determined by calculation ATcpap at different ratios instead of testing them on mechanical properties. The method was then verified validity through the investigation of S20/TMB-5, S20/HHPA-Ba and S20/PA-03α/βcompounded NAs, during which it was found S20/TMB-5 0.2 wt% (compounded ratio of 3:2), S20/TMB-5 0.3 wt% (compounded ratio of 1:1), S20/HHPA-Ba 0.2 wt% (compounded ratio of 2:3), S20/HHPA-Ba 0.3 wt% (compounded ratio of 3:17), S20/PA-03 0.2 wt% (compounded of 1: 1), S20/PA-03 0.3 wt% of (compounded ratio of 2:3), was able to improve the rigidity and toughness of iPP simultaneously achieving the purpose of compounding two kinds of nucleating agents.Crystallization morphologies and non-isothermal crystallization kinetics of iPP modified byα/βcompounded NAs were studied by means of polarized optical microscope (POM) and differential scanning calorimeter (DSC). The results showed the size of spherulites in nucleated iPP appeared much smaller than that in pure iPP. Caze method was used to deal with non-isothermal crystallization kinetics obtained by DSC. Parameters showed addition ofα/βcompounded nucleating agents could greatly raise crystallization peak temperature of iPP and shortened the crystallization half-time. Crystallization morphologies and crystallization behaviors of nucleated iPP also depended on ATcp ofαandβNA. The one with the higher ATcp played a leading role in the crystallization process resulting crystallization morphologies and Avrami exponents of nucleated iPP appeared close to it. Competitive nucleation would occur when the difference of△Tcp between two NAs was not pronounced. At this time the morphology of nucleated iPP presented the one that combined both NAs' within the compound system, while the Avrami exponents revealed the polymer was nucleated in a mixed mode.At last, the nucleation mechanism of a a NA was discussed.2,2'-methylene-bis-(4, 6-di-t-butylphenylene) phosphate lithium (NA03) was synthesized and its crystal structural characterization was obtained by single crystal X-ray diffusion. The crystal data showed geometrically the cell parameter of NA03 matched with a-iPP, the a cell dimension was about two times to the value of cell edge of (010) ipp. The disregistry was 2.89%, which was under the upper limit between the lattice matching spacing of host and guest crystals. Then the epitaxial behavior between iPP and NA03 was confirmed by investigating the crystallization process and lamellar structure of iPP/NA03. NA03 was proved to be a highly effective NA for iPP through studying crystallization behaviors, crystallization morphologies and mechanical properties of iPP nucleated with NA03. The outstanding nucleation efficiency could be attributed to the lattice matching between NA and iPP. Crystallographically lattice matching, e.g., a coincidence of unit-cell dimensions can be regarded as a criterion for seeking a new NA. |
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