Effects of α/β Compound Nucleating Agents on Mechanical Properties and Crystallization Behaviors of Isotactic Polypropylene

Sodium 2,2’-methylene-bis (4,6-di-tert-butylphenyl) phosphate (commercial name: Irgastab NA-11) and N,N’-dicyclohexylnaphthalene-2,6-dicarboxamide (commercial name: NU-100) are highly effective nucleating agents for α-isotactic polypropylene (iPP) and β-isotactic polypropylene (iPP) respectively. Effects of a total concentration of 0.2 wt% NA-11/NU-100 compound nucleating agents with different ratios of NU-100 on mechanical properties and crystallization behaviors of iPP were studied in this paper. The results showed that good balance between decreased stiffness and increased toughness of iPP was realized when the ratio of NU-100 was 50 wt%. Compared with those of virgin iPP, tensile strength, tensile modulus, flexural strength, and flexural modulus of iPP nucleated by the compound nucleating agent with 50 wt% NU-100 decreased by only 2.9%, 4.8%, 3.8% and 6.1% respectively, while the notched Izod impact strength of the nucleated iPP was increased by 212.8%. In addition, differential scanning calorimetry analysis results showed that addition of the NA-11/NU-100 compound nucleating agent increased the peak crystallization temperature of iPP significantly, but the crystallization rate of the nucleated iPP decreased with increasing ratio of NU-100 in compound nucleating agents.     

Isothermal Crystallization of Isotactic Polypropylene Nucleated with a Novel Aromatic Heterocyclic Phosphate Nucleating Agent

The incorporation of a nucleating agent into isotactic polypropylene (iPP) is one of the most important and widely used methods to improve performance in the polypropylene industry. Aromatic heterocyclic phosphate salt is a kind of highly effective nucleating agent for iPP and one of the typical products is a compound nucleating agent based on 2, 2-methylene-bis (4, 6-di-tert-butylphenyl) phosphate hydroxyl aluminum (commercial product name: ADK NA-21). In this paper the isothermal crystallization kinetics of iPP nucleated with the α-nucleating agent NA-21, investigated using differential scanning calorimetry (DSC), is described with the crystallization data being analyzed by using the classic Avrami method. During isothermal crystallization the addition of nucleating agent NA-21 dramatically shortened the crystallization half time (t_1/2) of iPP under the same conditions and the crystallization activation energy, ΔE, decreased from 422 kJ/mol for virgin iPP to 369 kJ/mol with the addition of NA-21. Thus, the addition of NA-21 significantly increased the crystallization rate of iPP.     

Synthesis and Effect of Ammonium 2,2′-Methylene-bis-(4,6-di-t-Butylphenylene) Phosphate as Nucleating Agent of Poly(Propylene)

A nonmetallic organophosphate salt, ammonium 2,2′- methylene-bis-(4,6-di-t-butylphenylene) phosphates (An), was synthesized via a simple method, and its application in iPP as a nucleating agent was investigated. Differential scanning calorimetry (DSC) result showed the melting temperature of An was 262°C, and SEM (scanning electron microscopy) observations indicated that its crystallization morphology was lamellar shape with a quite smooth surface. The crystallization behavior of nucleated isotactic poly(propylene) (iPP) containing An demonstrated that An can effectively raise the crystallization peak temperature and reduce the spherulite size, resulting in obviously improved strength and transparency. The tensile and flexural strength of iPP nucleated with An was increased by 11% and 32%, respectively. The haze value of iPP/An was decreased from 36.7% to 15.5%. These results revealed that this organophosphate ammonium salt can be used as an effective nucleating agent of iPP and provides a new organophosphate salt type nucleating agent for polymers.     

Nucleating Efficiency of Organic Phosphates in Polypropylene

Organic phosphates used as nucleating agents can remarkably promote the stiffness and crystallization rate of polypropylene homopolymer and ethylene–propylene copolymer. In this article, the nucleating activity of 2,2′-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid and its derivatives for isotactic polypropylene (iPP) were investigated with a differential scanning calorimeter (DSC) and polarized light microscope (PLM), and their influence on mechanical properties of polypropylene was also studied. The results showed that the sodium salt (NA7) and the glyceride ester (NA8) of the organic phosphoric acid were of high nucleating efficiency. If 0.4 wt% of NA7 or NA8 was added to PP, the crystallization peak temperature of PP was raised 15°C or 11°C, respectively, the amount of crystallinity was increased by 3 to 6%, and the crystallization rate was enhanced significantly. The nucleating activity is thermally stable when the mixture of iPP and a nucleating agent was melted and crystallized repeatedly in the DSC. The nucleating agents mentioned above could increase the modulus of the polymer by 20 to about 30% and could increase the flexural strength by 10 to about 20%. However, a number of other organic phosphates tested have little nucleating effect.     

Properties and Crystallization Behaviors of Isotactic Polypropylene Under Action of an Effective Nucleating Agent

The calcium salt of hexahydrophthalic acid (Hyperform HPN-20E) is an effective nucleating agent for polyethylene which was developed by Milliken Chemical Co., (USA) in recent years. In this paper, the properties and crystallization behaviors of isotactic polypropylene (iPP) in the presence of Hyperform HPN-20E were investigated by using differential scanning calorimetry and polarized optical microscopy. Addition of Hyperform HPN-20E improved the tensile, flexural and optical properties of iPP significantly and increased the crystallization rate of iPP greatly. The nucleation effects were comparable to the nucleation efficiency of a highly effective commercial iPP nucleating agent Hyperform HPN-68. When the addition amount of Hyperform HPN-20E in iPP was 0.2 wt.%, the tensile strength, tensile modulus, flexural strength, and flexural modulus of iPP were increased by 10.81%, 8.65%, 16.67%, and 11.96%, respectively, compared to those of pure iPP; the haze value was decreased by 42.44% and the crystallization peak temperature was increased by 11.2°C. In addition, incorporation of Hyperform HPN-20E in iPP greatly reduced the spherulite size of iPP.     

Nucleation Effects of a Novel Nucleating Agent Bicyclic [2,2,1] Heptane Di-carboxylate in Isotactic Polypropylene

Nucleation effects of a novel nucleating agent, bicyclic [2,2,1] heptane di-carboxylate (commercial product name: HPN-68), in isotactic polypropylene (iPP) were studied by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The results showed that HPN-68 is a typical nucleating agent for α-iPP and has high nucleation efficiency. Crystallization peak temperature and mechanical properties of iPP nucleated with HPN-68 can be greatly increased with only a low concentration of HPN-68. However, increased concentration of HPN-68 has a saturation value and properties of iPP, which tend to plateau when the concentration of HPN-68 exceeds the saturation value. When the concentration of HPN-68 was 0.2 wt%, the crystallization peak temperature was increased by about 15°C, and the tensile strength and flexural modulus of iPP were increased by 13% and 18%, respectively.     

Crystallization Kinetics of Nucleated Polypropylene with Organic Phosphates

The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with two organic phosphates, sodium salt (NA7) and triglyceride ester (NA8) of 2,2'-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid, were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, a modified Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters, such as the Avrami exponent, n, the crystallization rate constant, k, and the half-time of crystallization, τ_1/2, are compared. The results showed that a dramatic decrease of the half-time of crystallization, as well as a significant increase of the overall crystallization rate, were observed in the presence of the organic phosphates. During nonisothermal crystallization, the primary crystallization was analyzed using the Ozawa model, leading to similar Avrami exponents for iPP and iPP/NA7, which means simultaneous nucleation with three-dimensional spherulitic growth. However, for iPP/NA8, the Avrami exponent in nonisothermal crystallization is evidently different from that in isothermal crystallization, which would indicate a different mechanism of crystal growth. Adding the nucleating agent to iPP makes the overall crystallization activation energy increase.     

Effect of Metallic Salts of Phenylmalonic Acid on the Crystallization of Poly(L-lactide)

The effect of the metallic salts of phenylmalonic acid (PMA), as novel nucleating agents, on the melt and crystallization behaviors, spherulitic morphologies, and crystal structures of poly(L-lactide) (PLLA) was studied by means of differential scanning calorimetry, polarized light microscopy, and wide angle X-ray diffraction (WAXD). The results showed that calcium and cadmium salts of PMA are good nucleating agents for PLLA. Lithium, sodium, magnesium, strontium, and zinc salts of PMA are moderate nucleating agents, barium and aluminum salts of PMA are weak nucleating agents, while potassium phenylmalonate is not a nucleating agent for PLLA. The presence of nucleating agents significantly increased the number and decreased the size of the spherulites, but the crystal structures of the nucleated PLLA samples were not changed.     

A Novel Strategy for Achieving High Melt Strength Polypropylene and an Investigation of Its Foamability

A novel and feasible strategy for preparing high melt strength polypropylene (HMSPP) was developed by a melt grafting reaction in the presence of macro-monomer vinyl polydimethylsiloxane (VS), co-monomer styrene (St), and initiator benzoyl peroxide through a one-step reactive extrusion. The rheological behaviors, melt strength, and foaming ability of HMSPP were studied. The results showed that VS and St were successfully grafted onto polypropylene (PP), and the weight average molecular weight, molecular weight distribution, and melt strength of HMSPP were dramatically increased compared with those of the virgin isotactic polypropylene (iPP). Especially, the melt strength of HMSPP increased from 0.022 N for the virgin iPP to 0.29 N, which made the foamability of HMSPP significantly improved when supercritical carbon dioxide was used as the blowing agent. The foaming condition was optimized to 160°C and 14 MPa, for which HMSPP foams with a high expansion ratio of 66 times and a high cell density of about 5.8×10⁷ cell/cm³ were obtained, while the virgin iPP did not yield foams with good cell structure. Moreover, the resultant HMSPP could be foamed in a remarkably wide temperature range from 145°C to 165°C, which would be of great significance for industrial application.     

Polypropylene Nanocomposites Based on Synthetic Organic-Soluble Ag Nanocrystals with Prominent β-nucleating Effect: Quiescent Crystallization and Melting Behavior

Differential scanning calorimetry, x-ray diffraction, and polarized optical microscopy were used to investigate the quiescent crystallization and melting behavior of isotactic polypropylene (iPP) nanocomposites based on synthetic organic-soluble Ag nanocrystals (NCs). The effects of Ag loading and crystallization temperature on the crystallization behavior and crystalline structure were studied. The results showed that the synthetic Ag NCs as a novel effective β-crystal nucleating agent for iPP could promote the overall crystallinity, decrease the size of spherulites, and induce the formation of large amounts of β-crystals in the nanocomposites under quiescent crystallization. The relative content of β-crystals significantly increased with increasing Ag loading, and slightly increased with decreasing crystallization temperature. The quiescent crystallization kinetics was analyzed using the Avrami model. The results showed that the iPP nanocomposites with added Ag NCs had higher crystallization rate constant (k) and lower crystallization half-times (t_1/2) as well as the Avrami exponent (n) than pure iPP, indicating that the presence of Ag NCs acted as heterogeneous nucleating sites and promoted the crystallization rate of iPP.     

Nonisothermal Crystallization Nucleation of In‐Situ Fibrillar and Spherical Inclusions in Poly (Phenylene Sulfide)/Isotactic Polypropylene Blends

Nonisothermal crystallization nucleation and its kinetics of in‐situ fibrillar and spherical dispersed phases in poly (phenylene sulfide) (PPS)/isotactic polypropylene (iPP) blends are discussed. The PPS/iPP in‐situ microfibrillar reinforced blend (MRB) was obtained via a slit‐die extrusion, hot stretching, and quenching process, while PPS/iPP common blend with spherical PPS particles was prepared by extrusion without hot stretching. Morphological observation indicated that the well‐defined PPS microfibrils were in situ generated. The diameter of most microfibrils was surprisingly larger than or equal to the spherical particles in the common blend (15/85 PPS/iPP by weight). The nonisothermal crystallization kinetics of three samples (microfibrillar, common blends, and neat iPP) were investigated with differential scanning calorimetry (DSC). The PPS microfibrils and spherical particles could both act as heterogeneous nucleating agents during the nonisothermal crystallization, thus increasing the onset and maximum crystallization temperature of iPP, but the effect of PPS spherical particles was more evident. For the same material, crystallization peaks became wider and shifted to lower temperature when the cooling rate increased. Applying the theories proposed by Ozawa and Jeziorny to analyze the crystallization kinetics of neat iPP, and microfibrillar and common PPS/iPP blends, both of them could agree with the experimental results.     

Injection Molding Shrinkage and Mechanical Properties of Polypropylene Blends

Polypropylene (PP) blends based on isotactic polypropylene (iPP), propylene-ethylene block copolymer (bPP), and propylene–ethylene random copolymer (rPP) were prepared by melt blending and the effects of content of bPP and rPP on the shrinkage during solidification and storage and mechanical properties of the blends were studied. It was found that the addition of polypropylene copolymer could effectively reduce the processing shrinkage of iPP and the lowest shrinkage of the blends was achieved at a loading of 2 wt% bPP or rPP. The flexural modulus and tensile strength of the blends decreased a little while the impact strength and elongation at break were improved greatly compared with those of iPP.     

Nature of Shear-Induced Primary Nuclei in iPP Melt

Although observations of molecular processes in the formation of primary nuclei prior to actual crystallization are beyond the detection limits of current instrumentation, we attempted to probe the nature of primary nuclei in sheared isotactic polypropylene (iPP) polymer melt. In situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide angle X-ray diffraction) experiments using synchrotron radiation were carried out to evaluate the effects of an addition of a high molecular weight atactic polypropylene (aPP) (5 wt%), which is compatible with the iPP matrix but does not crystallize, on the evolution of oriented structures in the sheared iPP melt and its crystallization kinetics. It is unlikely that the aPP chain segments can be incorporated into iPP nuclei or crystal; hence, its addition effects, if any, would be seen only in the amorphous melt prior to crystallization. The results showed stonger orientation and improved crystallization kinetics in the iPP/aPP blend compared to pure iPP. Observations that the presence of long chains of an amorphous polymer aid in nucleation and crystallization kinetics of iPP, combined with our previous synchrotron results of sheared iPP melts at high temperature (165°C), lead us to conclude that primary nuclei in iPP most likely consist of liquid-crystalline or mesomorphic bundles of aligned chain segments prior to the formation of crystals.     

Influence of the Polymer/Inorganic Filler Interface on the Mechanical,Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups in DP provide flame retardancy.     

Effect of β-Nucleating Agent on the Crystallization,Mechanical Properties,and Heat Resistance of Injection-Molded Isotactic Polypropylene

Injection-molded β-isotactic polypropylene (β-iPP) was prepared with a commercial β-nucleating agent (NT-A). The effect of NT-A on the crystallization, mechanical properties, and heat resistance of β-iPP was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and mechanical and heat deflection tests. DSC and WAXD analysis showed that the content of β-crystals in the nucleated iPP was higher than that of pure iPP, and the content of β-crystals of the core was higher than that of the skin. PLM observations showed that injection-molded iPP had an obvious skin-core structure. NT-A induced abundant β-crystals and resulted in small spherulites which improved the Izod notched impact strength. When the content of NT-A was 0.075wt%, the Izod notched impact strength reached a maximum, 2.6 times more than that of pure iPP. The heat distortion temperature was also improved by NT-A.     

In situ evolution of Ni environment in magnesium aluminosilicate glasses and glass–ceramics–Influence of ZrO2 and TiO2 nucleating agents

The evolution of Ni²⁺ environment has been systematically investigated using optical and in situ X-ray absorption spectroscopy (XAS) to determine the influence of nucleating agents (TiO₂ and/or ZrO₂) during the formation of spinel in magnesium aluminosilicate glass–ceramics. The results were complemented by in situ X-ray diffraction data. According to XAS and optical spectroscopy, the nature of nucleating agents does not modify significantly the Ni environment in initial glasses. However, it has a relatively strong influence in the observed crystallization sequence. Ni²⁺ ions do not enter the Zr-containing crystalline phase of ZrO₂ or ZrTiO₄ but a Ni²⁺ coordination change from the fivefold coordinated sites, with a small amount of tetrahedral sites in parent glasses, to ^[6]Ni²⁺ and ^[4]Ni²⁺ sites in spinel (in glasses nucleated by ZrO₂ and/or TiO₂) or in β-quartz solid solutions (in glasses nucleated by ZrO₂) has been found.     

Formation of β-iPP in Isotactic Polypropylene/Acrylonitrile–Butadiene–Styrene Blends: Effect of Resin Type,Phase Composition,and Thermal Condition

The formation of β-iPP (β-modification of isotactic polypropylene) in the iPP/ABS (acrylonitrile–butadiene–styrene), iPP/styrene–butadiene (K resin), and iPP/styrene–acrylonitrile (SAN) blends were studied using differential scanning calorimery (DSC), wide angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM). It was found that α-iPP (α-modification of isotactic polypropylene) and β-iPP can simultaneously form in the iPP/ABS blend, whereas only α-iPP exists in the iPP/K resin and iPP/SAN blend samples. The effects of phase composition and thermal conditions on the β-iPP formation in the iPP/ABS blends were also investigated. The results showed that when the ABS content was low, the ABS dispersed phase distributed in the iPP continuous phase, facilitating the growth of β-iPP, and the maximum amount of β-iPP occurred when the composition of iPP/ABS blend approached 80:20 by weight. Furthermore, it was found that the iPP/ABS blend showed an upper critical temperature T _c * at 130°C for the formation of β-iPP. When the crystallization temperature was higher than the T _c *, the β-iPP did not form. Interestingly, the iPP/ABS blend did not demonstrate the lower critical temperature T _c ** previously reported for pure iPP and its blends. Even if the crystallization temperature decreased to 90°C, there was still β-iPP generation, indicating that ABS has a strong ability to induce the β-iPP. However, the annealing experiments results revealed that annealing in the melt state could eliminate the susceptibility to β-crystallization of iPP.     

CO2-induced Crystallization of Isotactic Polypropylene by Annealing Near Its Melting Temperature

CO₂-induced crystallization of isotactic polypropylene (iPP) by annealing had been studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The iPP before annealed was in α-form and amorphous states. At lower temperatures by CO₂ isothermal treatments, iPP chains crystallized from the amorphous phase and only one crystal form, i.e., α-form, was observed. At higher temperatures by CO₂ isothermal treatments, both crystallization from the amorphous phase and thickening of existing crystal lamellae were observed. Moreover, light γ-form crystal appeared in the treated iPP. The crystalline lamellar thickness of iPP annealed at different CO₂ pressures had been determined. Using the Gibbs–Thomson plot method, the equilibrium melting temperature was found to be 187.6°C.     

Nucleator-Enhanced Molecular Orientation and Crystallization in Melt-Spun Monofilaments of Syndiotactic Polypropylene

Different from other semi-crystalline polymers, the crystallization of syndiotactic polypropylene (sPP) into helical sequences under flow is largely inhibited due to favorable formation of trans-planar conformations. The results presented in this study, using micro-FTIR, 2D-WAXS, and 2D-SAXS characterization, indicate that molecular orientation and crystallization in melt-spun sPP monofilaments can be dramatically enhanced by a sorbitol-based nucleator. It is suggested that, similar to the oriented crystallization in the nucleated isotactic polypropylene (iPP), the phase-separated nanofibrils, aligned under flow prior to sPP crystallization, act as shish structure (primary nuclei) to mediate the molecular orientation and crystallization of sPP.     

聚丙烯中电树枝生长机理研究

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一.聚丙烯(PP)是典型半结晶聚合物,其复杂的非均匀聚集态结构影响电树枝的生长.本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验,通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响.以相界面自由能的热驱动作用以及放电雪崩理论为基础,对电树枝生长的热力学和动力学机理进行分析,阐明电场分布对电树枝生长的重要作用.根据半结晶材料的结晶相和非晶相的物理性能,建立材料内部电场分布计算模型,模拟针-板电极条件下聚合物材料内部的局域电场分布情况,分析了电树枝通道的动力学生长特征,探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用.