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.     

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.     

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.     

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.     

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.     

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 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.     

MWCNTs Supported N,N′-Dicyclohexyl-1,5-diamino-2,6-naphthalenedicarboxamide: A Novel β-Nucleating Agent for Polypropylene

N,N′-Dicyclohexyl-1,5-diamino-2,6-naphthalenedicarboxamide (NA), a highly efficient and selective β-nucleating agent for isotactic polypropylene (iPP), was synthesized and chemically supported on the surface of multiwall carbon nanotubes (MWCNTs) via an amidation reaction. The β-nucleation ability of NA, itself, is superior to the commonly used, highly efficient, and selective β-nucleating agents, e.g., commercial rare earth WBG-and aryl amide derivative TMB-5, as proved by the results of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The effect of MWCNTs supported NA (MWCNT-NA) on the crystallization and melting behavior of iPP was investigated by means of WAXD and DSC. The results show that the MWCNTs supported NA can effectively induce the formation of β-crystals in iPP/MWCNT-NA, although the grafting degree of NA onto the surface of MWCNTs could still to be improved.     

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.     

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．     

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.     

Effect of Interfacial Structure on Crystallization Behavior of Polypropylene/Polyolefin Elastomer/Barium Sulfate Ternary Composites

In this paper, interfacial structure induced development of crystallization behavior of polypropylene (PP)/polyolefin elastomer (POE)/barium sulfate (BaSO₄) ternary composites was studied by DSC. Two kinds of PP (copolymer and homopolymer) were used. The compatibility between PP and POE had a distinct influence on nucleation and crystal growth of PP in PP/POE binary composites. The crystallization rate of PP homopolymer increased because of the heterogeneous nucleation by POE, while the crystallinity of PP homopolymer decreased because of an inhibition effect of the hexane side chains in POE. BaSO₄ particles acted as heterogeneous nucleating agents of PP in ternary composites. The dispersion of BaSO₄, controlled by interfacial design, had a distinct influence on the nucleation activity of BaSO₄ in ternary composites. Interfacial structure had the same effect on nucleation activity of BaSO₄ particles and crystallization rate of PP matrix in PP copolymer ternary composites as those in PP homopolymer ternary composites.     

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.     

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 Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C₆₀) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (T_c), half-time for the crystallization (t_1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C₆₀ accelerates the crystallization of PP, implying a nucleating role of C₆₀. Furthermore, due to the reduced viscosity of PP by adding 5% C₆₀, the parameters of crystallization kinetics for the PP-5%C₆₀ nanocomposites changed remarkably relative to that of neat PP and when lower contents of C₆₀ were added to PP.     

Structure and Properties of Polypropylene/Polyolefin Elastomer/Organic Montmorillonite Nanocomposites

The crystallinity, mechanical properties, and thermal stability of polypropylene (PP)/organic montmorillonite (OMMT) and PP/polyolefin elastomer (POE)/OMMT composites, with polypropylene-g-maleic anhydride/styrene (PPMS) as a compatibilizer for both, were compared. The results showed that the strong interaction between the clay platelets and compatibilizer, which were generated by the maleic anhydride (MAH), improved the compatibility of the polymer matrices with the OMMT. A unique lamellar, flocculated structure of OMMT was formed after introduction of the POE. The highly dispersed clay layers could act as nucleating agents, resulting in smaller spherulites and higher crystallization temperatures. Compared with pure PP, the PP/OMMT nanocomposite showed enhanced mechanical properties and thermal stability; however, the PP/POE/OMMT had the best impact toughness.     

Nucleation of Polypropylene Crystallization with Gold Nanoparticles. Part 2: Relation between Particle Morphology and Nucleation Activity

The influence of gold nanoparticle morphology on nucleation of isotactic polypropylene (PP) crystallization was investigated. Previous experiments indicated certain nucleation activity of gold nanoparticles, varying with their size. In this work, eight types of gold micro/nanoparticles were used: vacuum-sputtered nanostructures (nanoparticles, nanoislands, and nanolayers), chemically prepared isometric gold nanocrystals (5, 20, and 100 nm diameters), and two types of gold microcrystals with well-developed crystal facets [with (100) and (111) facets, respectively]. To minimize the effect of particle agglomeration, we used our recently introduced sandwich method, in which the nucleating agent was deposited between thin PP films and the nucleation was evaluated by polarized light microscopy (PLM), X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The nucleation activity of Au particles in PP was lower than it might be expected from the previous studies and depended on their morphology. The nucleation activity of Au microcrystals with well-developed facets was higher than the activity of non-faceted Au nanocrystals.     

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.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Effect of Metallic Salts of Malonic Acid on the Formation of β Crystalline Form in Isotactic Polypropylene

The effects of malonic acid and the lithium, sodium, potassium, zinc, magnesium, calcium, strontium, and barium salts of malonic acid on the formation of β crystalline form in isotactic polypropylene at the crystallization temperatures 120 and 130°C have been investigated. It was found that malonic acid and the lithium, sodium, and potassium salts of malonic acid inhibit the formation of β crystalline form in polypropylene. Zinc malonate has a limited positive effect on the formation of β crystalline form, while magnesium, calcium, strontium, and barium salts are β nucleating agents, in descending order. The decreased β nucleation abilities of the alkaline earth metallic salts of malonic acid are attributed to the increasing atomic radii of the combined metals and decreasing crystallization temperatures.