The Relationship Between Crystal Structure Of Nucleating Agent 1,3,5-benzenecarboxyltrisamides And Nucleation Effect In Isotactic Polypropylene

Addition of highly effective nucleating agents in isotactic polypropylene(iPP)during processing plays important roles in improving the comprehensive properties of iPP.Effect of the chemical structure of nucleating agents on the properties and crystallization process of iPP has been diffusely researched in recent decades.There is a significant difference in the nucleation effect of nucleating agents with similar chemical structures.Therefore,it is important to explain the nucleation mechanism of nucleating agents and understand the correlation between crystal structure and nucleation efficiency of a nucleating agent in iPP.The 1,3,5-benzenecarboxyltrisamide derivatives have become known to be novel nucleating agents for iPP.In this work,1,3,5-benzenetricarboxylic acid tris(phenylamide)(BTA-93)was synthesized and the single crystal was cultivated by the vapor diffusion method.The chemical structures of the prepared nucleating agents were characterized by such methods as FT-IR,NMR and melting point test and single crystal structure was obtained by single crystal X-ray diffusion and X-ray diffraction.At the same time,the effects of nucleating agents on the nucleation density and crystallization behaviors of iPP were investigated under controlled isothermal and nonisothermal conditions.Using a combined approach based on FT-IR,1H-NMR and DSC test,we were able to determine the chemical structure of BTA-93.The single crystal of BTA-93 was obtained by vapor diffusion method with methanol and ether as solvents.The SCXRD date and PXRD data allowed to ensure the crystal structural parameters of BTA-93,which had a monoclinicsymmetry.The crystal data indicated geometrically the cell parameter of BTA-93 matched with iPP that the b-direction of BTA-93 crystal was about four times of 0.655 nm which was the cell edge of(010)iPP plane,and the lattice mismatch degree was 2.81%,which is lower than the upper limit of the epitaxial crystallization.It indicates that there is a good lattice matching relationship between BTA-93 and iPP.The nucleus density,crystallization behaviors,crystalline morphologies of neat iPP and iPP nucleated with BTA-93 and 1,3,5-benzenetricarboxylic acid tris(cyclohexylamide)(BTA-99)were studied by the Avrami theory,the calculation model of Lamberti,POM and WAXD.These results show that the crystallization rate constants and the nucleus densities of neat and nucleated iPP were evidently reduced with the increase of crystallization temperature.However,the crystallization rate constants and the nucleus densities of nucleated iPP were higher than those of neat iPP during different crystallization temperatures.Compared with iPP nucleated with HPN-68,the nucleus densities of iPP nucleated with BTA-93 and BTA-99 were a little higher at the same crystallization temperatures.Meanwhile,the spherulite size of iPP was dramatically decreased by addition of nucleating agents BTA-93 or BTA-99 and the crystal form of iPP wasn’t changed.It illustrated that BTA-93 and BTA-99 added in the processing provided more crystal nuclei,leading to obvious increase of the nucleation density,and enhanced the nucleation rate dramatically of iPP.Similar to HPN-68,both BTA-93 and BTA-99 are a nucleating agents for iPP.The nonisothermal crystallization behaviors were evaluated by the Mo method.It turned out that,with the increase of the cooling rate,the crystallization peaks of neat iPP and nucleated iPP shifted from high to low temperature,and peak shapes became wider.At the same cooling rate,the crystallization peak temperature of nucleated iPP was higher than that of neat iPP.When the cooling rate was 10℃/min,the increase degree of crystallization peak temperature of iPP nucleated with BTA-93 and BTA-99 was comparable to that of iPP nucleated with HPN-68.With the increase of the relative crystallinity of iPP,the faster the cooling rate,the smaller the crystallization rate is.It meaned that the cooling rate needed should be higher to achieve a higher degree of crystallinity.The results also showed that,for reaching the same relative crystallization,the cooling rate of neat iPP was the largest and that of iPP nucleated with BTA-93 was the lowest,followed by iPP nucleated with HPN-68 and iPP nucleated with BTA-99,which indicated that iPP nucleated with BTA-93 and BTA-99 crystallized at a relatively faster rate.These results show BTA-93 and BTA-99 are two effective and novel nucleating agents which are comparable to HPN-68.