| Polypropylene(PP)is widely used in daily life for its excellent chemical as well as physical properties.However,the poor toughness of polypropylene severely limit their practical applications fields,thus it is crucial to toughen and modify polypropylene to meet this issue.Among the many possible approaches,adding ?-crystal nucleating agent is attractive as it is a simple and effective method.Recently researches have shown that zinc carboxylate act as an effective ?-nucleating agent whereas there is a lack of systematic understanding on the nucleating efficiency of such nucleating agents as well as its compatibility with acid scavenger served as another important additive agent of polypropylene.In this paper,the nucleation efficiency of dicarboxylates with different carbon chain lengths in polypropylene are systematically studied,and the compatibility and failure mechanism with scavenger calcium stearate are discussed.Firstly,a series of aliphatic dicarboxylic acid zinc salts with different carbon chain lengths were synthesized,and their nucleation efficiency in isotactic polypropylene was investigated.The experimental results show that zinc adipate(ZnAA),zinc pimelate(ZnPA)and zinc suberate(ZnSA)can effectively induce ?-crystal form polypropylene.Compared with pure iPP,the impact strength of nucleated iPP is respectively increased by 238%,224%and 203%;crystallization temperature increased by 4-6? and their ?-crystal contents(kp value)were 0.96,0.94 and 0.86 respectively.Nevertheless,the other six carboxylic acid zinc salts,including zinc acetate,zinc malonate,zinc succinate,zinc glutarate,zinc azelaite and zinc sebacate,can not induce the formation of ?-crystal effectively.These results indicate that the zinc adipate,zinc pimelate and zinc suberate are highly effective ?-nucleating agents for polypropylene.Secondly,zinc adipate and zinc suberate are performed as the template to elucidated their effects on annealing,melting temperature and cooling rate on the properties of nucleated iPP.It was found that annealing treatment greatly improved the mechanical properties of polypropylene,especially the impact strength.In the studied melt temperature range,the melt temperature did not significantly affect the mechanical properties of polypropylene.In addition,the effects of cooling rate on the crystallization and melting behavior of the nucleated iPP was investigated by Flash DSC.The results showed that with the increase of the cooling rate,the intensity of characteristic peak ascribed to the ?-crystal polypropylene gradually decreased,indicating the fast cooling rate was adverse to the formation of ?-PP.Comparatively,ZnAA which exhibited superior nucleating ability is less sensitive to the cooling rate than that of ZnSA.Finally,the compatibility between three zinc dicarboxylates and acid scavenger calcium stearate(CaSt)during the polypropylene nucleating process.And the results revealed that the addition of calcium stearate impaired the ?-nucleating ability of zinc adipate.Futhermore,deactivation mechanism of such issue was also elucidated.According to Fourier infrared spectroscopy(FT-IR)and Differential scanning calorimetry(DCS)results,it was determined that there is no chemical reaction occurred between the acid scavenger and the nucleating agent.The SEM-EDS spectrogram showed that the nucleating agent ZnAA was surrounded by CaSt,and further Polarized Optical Microscopy(POM)experimental observations show that the added CaSt dissolves in the polypropylene melt at high temperature and gathers around the nucleating agent and occupies or shields the nucleation site during the crystallization process,hindering the epigenetic crystallization process of polypropylene on the surface of the nucleating agent causes the nucleating agent ZnAA to lose the ability to induce ?-PP. |
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