The Influence Of Novel Nucleating Agent On The Properties Of Isotactic Polypropylene

Polypropylene (PP), which belongs to the rank of thermoplastic semi-crystalline polymer materials, is of considerable value in use and market in our life and industries. However, some drawbacks, such as unsatisfactory impact strength at low temperatures, large shrinkage-rate, and poor resistance to weathering, have impeded its further promotion and wider range of using. So far, a variety of kinds of methods and means have been used to improve the performance of PP so as to increase its durability and broaden its application scope. Adding a nucleating agent is an effective method which brings to modification of PP from changing its microstructures, for example, crystal structure, crystalline morphology, crystallinity, and so on. Most important, this approach is low dosage, efficient and simple.From the perspective of preparation novel nucleating agent, three categories of eight kinds of nucleating agents were synthesized in the paper: four kinds of N-benzoyl glycine acid salts (PGCa, PGMg, PGZn and PGBa), a nove1β-crystalline nucleating agent CMH, a nucleating agent with analogous planar molecular structure (OXIPA1), and two semi-crystals (Glycine zinc sulphate salt:GZS, and calcium dibromide bis(glycine) tetrahydrate:GCB). Thermal stability of them was individually characterized by using thermogravimetric analysis technology (TGA). The influences of nucleating agent on crystal form, crystalline morphology and crystallization behavior of isotactic polypropylenes (iPP) were investigated with the aid of X-ray diffraction (XRD), polarized light microscopy (PLM) and differential scanning calorimetry (DSC) respectively. Moreover, mechanical properties of samples were also tested, so that the influence of nucleating agent on the properties of PP was studied comprehensively.The results indicated that all the nucleating agents PGCa, PGMg, PGZn and PGBa could efficiently induce to the generation of β-iPP. Especially after adding PGCa, the relative content of β-crystalline in iPP was up to73.27%. These four kinds of nucleating agents significantly affected the melting and crystallization behavior of iPP. In particular, the crystallization temperature (Tc) of iPP improved by13.36℃by nucleator PGCa, while the difference between the initial crystallization temperature (Tonset) and the crystallization temperature (Tc) was reduced to2.18℃and the crystallinity (Xc) was increased by2.82%through the addition of PGBa. Meanwhile, the spherulite size was miniaturized after adding the four kinds of nucleators, particularly PGCa and PGMg at a higher degree of refinement. The addition of them played a role in improvement of tensile and impact strength of iPP to some extent, while made a slight decrease in flexural strength. The largest increment of impact strength of iPP/PGCa was183.33%, and the maximum tensile strength of iPP/PGMg was increased by10.80%.TGA demonstrated that under the experiment processing temperature of PP, CMH remained stable without decomposition basically. The results also showed that CMH could be an efficient β-crystalline nucleating agent that enabled the relative content of β-crystalline in iPP increase to55.03%. The increment of crystallinity (Xc) of iPP was as much as7.56%, the Xc value being up to60.05%. CMH played little in spherulite refinement. After adding CMH, the impact strength of iPP was enhanced by36.25%. At the same time, the tensile strength and flexural strength was raised by5.48MPa and1.22MPa, respectively.Under the experiment processing temperature of PP, OXIPA1decomposed slightly. XRD manifested that OXIPA1could serve as effectively a-crystalline nucleating agent. The increase of the crystallization temperature (Tc) and the reduce of the difference between the initial crystallization temperature (Tonset) and the crystallization temperature (Tc) were respectively13.26℃and4.48℃with adding OXIPA1. Thus, it would contribute to effectively accelerating crystallization and shortening processing cycles’time of polypropylene. In addition, OXIPA1refined spherulites of iPP remarkably. When the content of OXIPA1was0.3wt%, the flexural strength was as highly as50.89MPa, which manifested that the flexural performance of iPP/OXIPAl was much better than that of iPP/TMA-3.Semi-crystal GZS and GCB had little effect on induction of transition to β-crystalline and a slight influence on grain refinement. The increase of crystallization temperature (Tc) of were by3.84℃and3.15℃, and increment in crystallinity (Xc) were1.48%and1.67%, respectively. GCB enhanced the tensile strength of iPP by18.96%at most. GZS improved the impact strength of iPP by51.29%. The two kinds of semi-crystals brought to little improvement in flexural performance of iPP.