Properties Of Isotactic Polypropylene Nucleated With Compound Nucleating Agents Based On 1,3,5-benzenetricarboxylamides

One of the important methods to improve properties of polypropylene is addition of nucleating agents during processing of polypropylene.Different nucleating agents have different effects in polypropylene.The a nucleating agents can significantly improve the rigidity of polypropylene but will reduce toughness,while the p nucleating agents can significantly improve the toughness of polypropylene,but the rigidity is reduced slightly,so how to balance the relationship between rigidity and toughness of polypropylene by a/p compound nucleating agents becomes one of the key problems in the field of polypropylene modification.In this paper,nucleating agent 1,3,5-benzenetricarboxylic acid tris(cyclohexylamide)(BTA-99)was prepared firstly by using cyclohexylamine and 1,3,5-benzenetricarbonyl trichloride,and the crystallization and melting behaviors of polypropylene nucleated with BTA-99 were studied by differential scanning calorimetry(DSC).The results showed that BTA-99 can obviously increased the crystallization peak temperature of polypropylene,and there was only one melting peak at about 163OC in the melting curves,which indicated that BTA-99 was a typical a nucleating agents.In addition,BTA-99 was compared with three different ? nucleating agents calcium pimelate(CaPi),N,N,-dicyclohexyl terephthalamide(TMB-5)and rare earth compound WBG-?,and the nucleation efficiency of the four nucleating agents was studied by Fillon method.It was found that the order of nucleation efficiency of the four nucleating agents was WBG-?>TMB-5>BTA-99>CaPi.A series of compound nucleating agents(BxTy,BxCy,BxWy)were prepared by mixing BTA-99 with TMB-5,CaPi and WBG-? at a mass ratio of 1:4,1:3,2:3,1:1,3:2,3:1,4:1,respectively.The DSC results showed that the crystallization peak temperature of polypropylene nucleated by compound nucleating agents BxTy and BxWy increased firstly and then decreased with the increase of BTA-99 contents,and at the compound ratio was 1:1 and 2:3,the crystallization peak temperature of nucleated polypropylene reached the highest values of 129.7? and 128.9?,respectively.While the crystallization peak temperature of polypropylene nucleated by BxCy increased continuously with the increase of BTA-99 content.When the compound ratio was 4:1,the crystallization peak temperature of nucleated polypropylene was up to 127.6?.Subsequently,wide angle X-ray diffraction diffraction(WAXD)was used to study the crystal form of polypropylene nucleated by a series of compound nucleating agents.The ?-crystal relative content of the nucleated polypropylene was calculated by the Turner-Jones formula.It was found that the ?-crystal relative content of nucleated polypropylene reached the highest value of 53.6%,10.4%and 47.5%when the compound ratio of BxTy,BxCy and BxWy was 1:1,4:1 and 2:3,respectively,which was consistent with the results of DSC.Thus,it can draw a conclusion that the optimal compound ratio of BxTy,BxCy and BxWy were 1:1,4:1 and 2:3,respectively.The results on mechanical properties of nucleated polypropylene including flexural modulus,tensile strength,impact strength and heat distortion temperature showed that the nucleating agents with t'he optimal compound ratio B1T1,B4C1 and B2W3 all improved the comprehensive property of polypropylene,and achieved the balance between different property to certain extent.Especially B1T1,which increased the flexural modulus,tensile strength and impact strength of polypropylene by 43.78%,9.52%and 27.27%,respectively,and the heat distortion temperature was also increased by 45.15%.The non-isothermal crystallization kinetic parameters of polypropylene nucleated by the compound nucleating agents B1T1,B4C1 and B2W3 were determined by the Caze method.The results showed that the crystallization peak temperature of nucleated polypropylene was higher than that of pure polypropylene at the same cooling rate ?.With the increased of ?,the crystallization peak temperature of polypropylene changed from high to low,and the crystallization peak width increased gradually,The crystallization peak temperature calculated by the Caze method was roughly the same as that obtained by the DSC results,which indicated the effectiveness of the Caze method.The nucleation mechanism of nucleated polypropylene during non-isothermal crystallization process was investigated.The results showed that the addition of compound nucleating agents changed the crystal growth mode of polypropylene,which transformed from homogeneous nucleation of multi-dimensional spherulitic growth to heterogeneous nucleation of two or three-dimensional spherulitic growth.At the same time,the crystallization peak temperature of polypropylene increased obviously,and the semi-crystallization time of polypropylene reduced significantly,but due to the hindrance effect of the compound nucleating agents on the molecular chain of polypropylene,the crystallization activation energy of polypropylene has not been reduced,on the contrary,it has been improved.