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.     

Comparison of Nucleation Effects of Organic Phosphorous and Sorbitol Derivative Nucleating Agents in Isotactic Polypropylene

Organic phosphorous and sorbitol derivatives are two types of very effective nucleating agents for isotactic polypropylene (iPP). The effects of two kinds of organic phosphorous nucleating agents, Irgastab NA-11 and ADK NA-21, and two kinds of sorbitol derivatives, Irgaclear DM and Millad 3988, on mechanical properties and crystallization behaviors of iPP are compared in this paper. The organic phosphorous nucleating agents had better effects on mechanical properties of iPP than sorbitol derivatives, whereas the latter had better effects on transparency of iPP than the former. At the same time, the organic phosphorous nucleating agents and sorbitol derivatives had similar effects on the crystallization peak temperature (Tc) of iPP. When the concentration of nucleating agents was 0.2 wt%, compared to those of virgin iPP, the tensile strength and flexural modulus of iPP nucleated with Irgastab NA-11 and ADK NA-21 were increased by 19.35% and 17.67%, and 29.48% and 24.84%, and the haze value was decreased by 43.58% and 44.01%, respectively. On the other hand, the tensile strength and flexural modulus of iPP nucleated with Irgaclear DM and Millad 3988 were increased by 7.03% and 7.46%, and 7.20% and 11.96%, and the haze value was decreased by 51.03% and 52.23%, respectively. When the cooling rate was 10°C /min, the Tc of iPP nucleated with these four nucleating agents was increased from 118.74°C of virgin iPP to about 130°C. Meanwhile, the morphology study showed that addition of both organic phosphorous and sorbitol derivative type nucleating agents could decrease the spherulite size of iPP significantly and that sorbitol derivatives have greater effects.     

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.     

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.     

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.     

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.     

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.     

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.     

Isothermal Crystallization and Miscibility of Isotactic Polypropylene/Poly(cis-butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. Isothermal crystallization and miscibility for neat iPP and blends of iPP/PcBR were investigated by differential scanning calorimetry. The presence of PcBR remarkably affected isothermal crystalline behaviors of iPP. An addition of PcBR caused shorter crystallization time and a faster overall crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak was broader and the supercooling decreased as the crystallization temperature increased. The Avrami equation was suitable to describe the primary isothermal crystallization process of iPP and blends. The addition of PcBR led to an increase of values of the Avrami exponent n, which we suggest was because the blends had a stronger trend of instantaneous three-dimensional growth than neat iPP. The equilibrium melting point depression of the blends was observed, indicating that the blends were partly miscible in the melt.     

The Role of Poly(phenylene sulfide) Microfibrils in Isothermal Crystallization of Isotactic Polypropylene under Shear

An optical polarizing microscope with a hot shear stage was used for an in‐situ investigation of the influences of poly(phenylene sulfide) (PPS) microfibrils on isothermal crystallization of isotactic polypropylene (iPP) under shear. As the nucleation sites on the PPS microfibril's surface are not able to induce a transcrystalline layer, there are only spherulites generated in a PPS/iPP in‐situ microfirbillar blend in quiescent condition. Applying shear during isothermal crystallization, the crystalline morphology greatly changes. There are fibrillar nuclei induced after steady shear with a shear rate of 5 and 10 s^–1, and these nuclei formed fibrillar crystals after crystallization completion. Two opposite effects coexist in PPS/iPP in‐situ microfibrillar blends during shear‐induced isothermal crystallization; one is the obstructive effect of PPS microfibrils on the iPP molecular chains orientation; the other is the positive effect provided by stress between fiber and matrix, generated by shear, which reduces the potential barrier of crystallization. The results of wide angle x‐ray diffraction (WAXD) show that there are β‐iPP crystals generated in neat iPP and PPS/iPP blends, but that PPS microfibrils have an inhibiting influence on the formation of β‐iPP.     

Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (K_g) – the lowest value of K_g was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be ?260 kJ/mol for pure PEO, ?538 kJ/mol for PEO/lauric acid blend, and ?387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and ?135,6 kJ/mol, ?114,5 kJ/mol, and ?92,8 kJ/mol, respectively, for nonisothermal crystallization.     

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.     

Confined Crystallization in Polymer Blends: DSC Studies of the Behavior and Kinetics of Isothermal Crystallization of Polypropylene in Poly(cis-butadiene) Rubber Blends

Thermal properties of polypropylene with poly(cis-butadiene) rubber (iPP/PcBR) blends have been measured by differential scanning calorimetry (DSC), and the melting point T_m, crystallization temperature T_c, enthalpy Δ H (melting enthalpies and crystalline enthalpies), and equilibrium melting point T⁰ _m have been measured and calculated. The variation of T_m, T_c, Δ H and T⁰ _m with composition in the blends was discussed, showing that an interaction between phases is present in iPP/PcBR blends. The degree of supercooling characterizing the interaction between two phases in the blends and the crystallizability of the blends which bears a relationship to the composition of the blends was discussed. The kinetics of isothermal crystallization of the crystalline phase in iPP/PcBR blends was studied in terms of the Avrami equation, and the Avrami exponent n and velocity constant K were obtained. The Avrami exponent n is between 3 and 2, meaning that iPP has a thermal nucleation with two dimensional growths. The variation of the Avrami exponent n, velocity constant K, and crystallization rate G bear a relation to the composition of the blends, n increases with increasing content ofPcBR. K also increased with increasing content of PcBR. All of the K for the blends are greater than for pure iPP. The crystallization rate G (t_1/2) depends on the compositions in the blends; all G of the blends are greater than for iPP.     

等规聚丙烯成核剂的结构和构型分析

成核剂在聚丙烯的结晶过程中作为晶核，参与调节晶体的晶型、大小及其分布，促使形成不同性能的聚丙烯材料．成核剂促进聚合物结晶的机制是聚合物结晶领域的研究热点，但其结构对聚合物结晶的影响尚不清晰；而成核剂通常具有同分异构体，使其结构解析更加困难，但成核剂的结构解析是进一步研究其成核机理的基础．本文综合运用核磁共振（NMR）波谱、傅里叶变换-红外（FT-IR）光谱和扫描电镜能谱分析（SEM-EDS）表征了一种二元羧酸复合物类β晶型聚丙烯成核剂的结构和构型，结果表明该成核剂cis-△4-四氢邻苯二甲酸钙为消旋体，羧酸与钙以桥式螯合方式形成有机羧酸金属盐．     

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.     

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.     

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.     

Low-temperature crystallization of the Fe−Co−B amorphous alloys

Low-temperature crystallization of the melt-spun amorphous ribbon Fe₆₄Co₂₁B₁₅ was measured by the⁵⁷Fe Mössbauerin situ scanning method in the temperature range of about 300 to 350°C. Least-squares fit of the time-dependent α-Fe?Co isothermal absorption intensity revealed up to three superimposed exponential processes. Taking into account that this method indicates the content of the crystallized metallic phase only, then the first two (nucleation and primary crystallization) processes are followed by a rather slow third one, which could only mean the decay of metastable (Fe, Co)₃B having a thermally activated character as well. Besides confirming the previously reported activation enthalpies for the two faster processes, that of the slowest one was determined as (450±10) kJ/mol.     

Isothermal crystallization in Ce70Ga6Cu24 bulk metallic glass

The isothermal crystallization behaviors in a newly developed CeGaCu bulk metallic glass have been investigated through the classic differential scanning calorimeter(DSC) method. It is found that the apparent activation energy(Ea) strongly depends on the fraction(x) of isothermal crystallization. Johnson-Mehl-Avrami(JMA) formula was used to analyze the mechanism of crystallization and the obtained Avrami exponent(n) was discovered to show an obvious correlation with the crystallization fraction x. With the help of the relation between Ea and n, the nucleation and growth activation energies, En and Eg, were estimated to be 214–304 kJ/mol and 91 kJ/mol, respectively. This result suggests that the main energy barrier against crystallization in the present glass should be the nucleation of nucleates, rather than the growth of crystals. Such a large En is also believed to be responsible for the good glass forming ability of the CeGaCu alloy.     

Nonisothermal Crystallization Kinetics of Miscible Blends of Polycaprolactone and Crosslinked Carboxylated Polyester Resin

The nonisothermal crystallization process of polycaprolactone (PCL)/crosslinked carboxylated polyester resin (CPER) blends has been investigated for different blend concentrations by differential scanning calorimetry (DSC). The DSC measurements were carried out under different cooling rates namely: 1, 3, 5, 10, and 20°C/min. Thermally induced crosslinking of CPER in the blends was accomplished using triglycidyl isocyanurate as a crosslinking agent at 200°C for 10 min. The cured PCL/CPER blends were transparent above the melting temperature of PCL and only one glass transition temperature, T_g, located in the temperature range between the two T_gs of the pure polymer components, was observed, indicating that PCL and crosslinked CPER are miscible over the entire range of concentration. The nonisothermal crystallization kinetics was analyzed based on different theoretical approaches, including modified Avrami, Ozawa, and combined Avrami–Ozawa methods. All of the different theoretical approaches successfully described the kinetic behavior of the nonisothermal crystallization process of PCL in the blends. In addition, the spherulitic growth rate was evaluated nonisothermally from the spherulitic morphologies at different temperatures using polarized optical microscope during cooling the molten sample. Only one master curve of temperature dependence of crystal growth rate could be constructed for PCL/CPER blends, regardless of different blend concentrations. Furthermore, the activation energy of nonisothermal crystallization process (ΔE_a) was calculated as a function of blend concentration based on the Kissinger equation. The value of ΔE_a was found to be concentration dependent, i.e., increasing from 83 kJ/mol for pure PCL to 115 and 119 kJ/mol for 75 and 50 wt% PCL, respectively. This finding suggested that CPER could significantly restrict the dynamics of the PCL chain segments, thereby inhibit the crystallization process and consequently elevate the ΔE_a.