Design And Nucleation Mechanism Study Of Novel Nucleating Agent For Polypropylene Based On The Arrangement Of Phosphate

Isotactic polypropylene(iPP)has been widely used in various fields because of its excellent mechanical properties,good chemical stability,and simple processing.In 2019,Chinese apparent consumption of iPP reached 28.58 million tons.At the same time,with the change of economic development model and the adjustment of the downstream industry structure,the requirements for iPP products are also increasing.So,we need vigorously adjust the product structure and actively develop high value-added products.For iPP,its macroscopic properties are often closely related to the microcrystalline structure,so it is more and more important to control the crystallization of iPP.Adding nucleating agent is the simplest and most effective way to control the crystallization behavior of iPP.Therefore,in this paper based on the mechanism of organophosphate metal salts controlling the dispersion of phosphate esters through metal ions and affecting their nucleation performance in iPP.a stearate-phosphate and phosphate-zeolite nucleation system is designed to control the high performance iPP.Firstly,the effects of different stearates and their synergistic system with phosphate(stearate-phosphate)on the crystallization properties,mechanical properties and optical properties of iPP were studied.It is found that different stearates have different effects on iPP crystallization temperature and macroscopic properties.Among them,sodium stearate has the best comprehensive improvement on iPP performance,which can increase the crystallization temperature of iPP by 5.0℃,the bending modulus by 23.7%,and the impact strength by 11.1%,tensile strength by 5.4%and haze by not changed compared to blank iPP.Different stearatephosphate have different effects on iPP crystallization temperature and macroscopic performance,except stearate calcium salt,lithium salt,sodium salt,potassium salt,zinc salt and the phosphate can synergistically improve the crystallinity and macroscopic performance of iPP.Among them,sodium stearate-phosphate has the most significant effect on iPP performance.The flexural modulus can reach 169 7 MPa,the tensile strength can reach 38.0 MPa,the haze reached 35.2%.Compared to the blank iPP,the flexural modulus increases by 42.8%,the tensile strength increases by 13.1%,and haze decreases by 56.9%.Secondly,the nucleation performance and nucleation mechanism of the synergistic system composed of different ratios of sodium stearate and phosphate in iPP were studied.It is found that when the total addition amount is 0.2wt%,the addition of sodium stearate and phosphate alone has a weak nucleation effect on iPP.When sodium stearate and phosphate are added together,the crystallization temperature and macroscopic performance of iPP could be greatly improved,and as the ratio of sodium stearate to phosphate ester increases,the overall performance shows a trend of increasing first and then decreasing.Especially when the mass ratio of sodium stearate to phosphate is 4:6,the crystallization temperature of iPP can reach 132.4℃,and the flexural modulus can reach 2061 MPa,the tensile strength can reach 40.4 MPa and the haze can reach 25.3%,which can increase by 11.7%,41.2%,13.8%and 64.6%compared to the blank iPP,respectively.In addition,research on the mechanism of the nucleation system shows that this system has the effect of "in situ self-salt formationdegradation promoting nucleation".It means that "in situ" reaction occurs between sodium stearate and phosphate,which generats phosphate sodium salt and stearic acid.The generated phosphate sodium salt can promote the nucleation of the surrounding iPP matrix,and iPP can also inhibit excessive growth of phosphate sodium salt,therefore,which can improve the nucleation efficiency.At the same time,stearic acid can promote the degradation of iPP,which promotes the low-molecular-weight iPP to preferentially adhere to the surface crystallization of the nucleating agent formed,thereby promoting crystallization of iPP.Then,a phosphate-zeolite self-assembly nucleation system was prepared by solution impregnation.The zeolite controls the arrangement of phosphate,which in turn affects the nucleation performance of the self-assembly system in iPP.The researchs on the influence of this self-assembly system on crystallization properties,mechanical properties and optical properties of iPP show that although the addition of zeolite alone has basically no nucleation effect on iPP and the addition of phosphate alone has only a weak nucleation effect on iPP at low addition levels,but the self-assembly nucleation system has a significant effect on iPP nucleation performance,which makes the crystallization and macroscopic properties of iPP show a trend of increasing first and then decreasing as the ratio of phosphate to zeolite increases.Especially when the mass ratio of phosphate to zeolite is 4:6,the crystallization temperature of iPP can reach 127.6 ℃,the flexural modulus can reach 1485 MPa,the tensile strength can reach 35.1 MPa,the impact strength can reach 54.5 J/m,the haze can reach 72.8%.Compared to the blank iPP,the flexural modulus increases by 29.1%,the tensile strength increases by 10.4%,the impact strength increases by 13.1%and the haze decreases by 14.8%.That is to say,the self-assembly nucleation system can not only improve the rigidity of iPP but also significantly improve the toughness to a certain extent,so that iPP can reach the balance of rigidity and toughness.Finally,in order to reveal the mechanism of the phosphate-zeolite nucleation system,the morphology,component distribution,interaction force and crystallization kinetics of the nucleation system were characterized by corresponding characterization methods and compared with the calculation results of DFT based on intermolecular forces.it is found that the phosphate sample has an irregular shape,a size of 20-40 μm,and is accompanied by agglomeration.While the phosphate-zeolite self-assembly system has a regular shape,a size of 5μm,and the phosphate is evenly distributed around the Z13X,indicating that the zeolite has a good promotion effect on the distribution arrangement of phosphate.That can make the phosphatezeolite system effectively reduce the crystallization activation energy and promote crystallization of iPP.DFT calculation shows that the binding energy between the phosphate and zeolite is 35.6 kcal/mol,while the binding energy between the phosphate itself is only 6.5 kcal/mol,that is to say,the zeolite inhibits phosphate agglomeration by combining with the phosphate.The hydrogen bonding between the zeolite and phosphate proved by infrared analysis promotes the easier binding of the phosphate and the zeolite,thereby suppressing the aggregation of the phosphate itself and achieving a certain degree of regular arrangement,which is consistent with the result of the unit cell size of iPP.In short,as far as phosphate is concerned,the arrangement of their molecules can be controlled by in-situ self-salt formation and self-assembly,thereby improving their nucleation performance in iPP,in order to achieve iPP performance control.