Α-nucleating Agent Research Articles

Exploitation of a New Nucleating Agent by Molecular Structure Modification of Aryl Phosphate and Its Effect on Application Properties of the Polypropylene.

In this work, a novel α-nucleating agent (NA) for polypropylene (PP) termed APAl-3C-12Li was prepared and evaluated compared with the commercially available type NA-21. For the synthesis of the organophosphate-type NA (APAl-3C), the -OH group of the acid part of NA-21 was substituted by the isopropoxy group. The structure of APAl-3C was analyzed by spectroscopy and element analysis, the results of which were consistent with the theoretical molecular formula. APAl-3C's thermal stability was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG), which showed only weak mass loss below 230 °C, meaning that it would not decompose during the processing of PP. The APAl-3C-12Li was used as a novel nucleating agent, studying its effects on crystallization, microstructure, mechanical and optical properties. Tests were performed in a PP random copolymer at different contents, in comparison to the commercial NA-21. The composite with 0.5 wt% APAl-3C-12Li has a similar crystallization temperature of 118.8 °C as with the addition of 0.5 wt% NA-21. An advantage is that the composite with the APAl-3C-12Li has a lower haze value of 9.3% than the counterpart with NA-21. This is due to the weaker polarity of APAl-3C-12Li after the introduction of methyl and better uniform dispersion in the PP matrix, resulting in stronger improvement of optical and mechanical properties.

Heterogeneous mesoscopic structure modulation enhancing dielectric strength of polypropylene insulation

This paper focuses on the heterogeneous mesoscopic structure modulation enhancing dielectric strength of polypropylene insulation. α-nucleating agents are used to modulate the heterogeneous mesoscopic structure of polypropylene, and Voronoi Network models with similar structures are established to simulate the electric field distribution at the mesoscopic scale. The experimental results show that the addition of an α-nucleating agent effectively diminishes the spherocrystal size and increases its density. The high continuity and wide range electric field distortion caused by the too-large spherocrystal size and too-loose arrangement is thus suppressed. The improvement of electric field uniformity effectively inhibits the frequency and intensity of partial discharge. Compared with pure polypropylene, the partial discharge in polypropylene composite with α-nucleating agents at 0.1 wt% decreased by 2414 times, and its maximum amplitude decreased by 58.3%. The increase in the spherocrystal density also enhances its blocking effect on the electrical tree growth, and the length and width of it are reduced by 88.6% and 89.1%, respectively. The dispersive development of the electrical tree reduces the incidence of penetration channels along the electric field direction. The breakdown strength is therefore increased by approximately 20%. The simulation results demonstrate that the dielectric property difference between the crystal and amorphous regions within polypropylene at the mesoscopic scale is the main reason that triggers the electric field distortion at its interface and further leads to insulating degradation or even failure. In this study, heterogeneous mesoscopic structure modulation is proved to be an efficient means to enhance the dielectric strength of polypropylene insulation.

Effect of N,N'-Dicyclohexyl Terephthalic Dihydrazide on the Crystallization and Properties of Isotactic Polypropylene

Application of nucleating agents is a common way to manipulate the structure and properties of crystalline polymers. Our goal was to synthesize N,N'-dicyclohexyl terephthalic dihydrazide (DCTDH) and study it from the viewpoint of applicability as a nucleating agent for isotactic polypropylene (iPP). We used differential scanning calorimetry to investigate the efficiency of DCTDH in samples containing the nucleating agent in a wide concentration range. We used polarized light microscopy to study the crystalline morphology developed in the presence of this nucleating agent. To characterize the mechanical properties of the nucleated samples, we performed tensile and impact tests on injection molded specimens. DCTDH proved to be a non-soluble α-nucleating agent in iPP, with a saturation concentration around 300 ppm. The nucleating agent has a significant effect on the crystalline structure of iPP, microspherulitic structure forms in its presence. Owing to the different structure, a considerable change in the mechanical properties is observable: with increasing nucleating agent content the tensile modulus increases, while impact resistance has a maximum value around 300 ppm nucleating agent content.

Calcium Salt of L-Isoleucine-Phthalate: An α-Nucleating Agent That Enhances the Crystallization Behavior and Mechanical Properties of Isotactic Polypropylene

In this study we prepared the novel compound L-isoleucine-phthalandione (LIPTA), featuring carboxyl and amide groups, and its calcium salt, the calcium salt of L-isoleucine-phthalate (LIPTA-Ca), and characterized them using 1H nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and differential scanning calorimetry (DSC). LIPTA-Ca has a relatively high melting point and thermostability. We employed DSC and polarized optical microscopy and tests of mechanical properties to examine the effect of LIPTA-Ca on the crystallization behavior and mechanical properties of isotactic polypropylene (iPP). We found that LIPTA-Ca is a highly effective α-nucleating agent that can increase the crystallization temperature of iPP by more than 10 °C during cooling, when present as an additive at a content of 0.15 wt%, while greatly decreasing the spherulite size and accelerating the crystallization rate of iPP. In addition, LIPTA-Ca can improve the rigidity of iPP significantly without decreasing its toughness.

Enhancement of crystallization and mechanical properties in isotactic polypropylene via adding liquid-phase exfoliated graphene

In this work, liquid-phase exfoliated graphene (G) was introduced into isotactic polypropylene (iPP) via melt blending. Wide-angle X-ray diffraction measurements revealed that liquid-phase exfoliated graphene is a strong α-nucleating agent, making the iPP crystal grow preferentially on the (040) crystal plane. Differential scanning calorimetry and polarized optical microscopy results showed that the increase in both the nucleation density and crystal growth rate brings about the remarkable elevation of overall crystallization rate of iPP with the addition of liquid-phase exfoliated graphene. Moreover, remarkable enhancements in mechanical properties especially the toughness were obtained at low graphene loading. With the addition of 0.5 wt.% graphene, the impact strength and elongation at break of iPP increased by 103 % and 510 %, respectively. The significant enhancement of crystallization and mechanical properties of the composites could be attributed to favorable dispersion of liquid-phase exfoliated graphene in the iPP matrix. A possible toughening mechanism was proposed.

An effective nucleating agent for isotactic polypropylene (iPP): Zinc bis- (nadic anhydride) double-decker silsesquioxanes

The zinc bicyclo [2.2.1]-heptane-2, 3-dicarboxylate-double-decker silsesquioxanes (Zn2(DDSQ-ND)) was firstly synthesized and the crystallization behavior of isotactic polypropylene (iPP) filled with different amount of Zn2(DDSQ-ND) (0–1 wt %) was investigated in detail. With the addition of Zn2(DDSQ-ND), the crystallization temperature enhanced significantly, indicating that it acted novel and effective nucleating agent in the iPP system. The morphology of spherulites, nucleation density, and the crystal structure of the samples were characterized using POM and WAXD. Besides, ultra-fast scanning calorimetry (FSC) was employed to study the effects of Zn2(DDSQ-ND) on the non-isothermal and isothermal crystallization behaviors of the sample iPP/Zn2(DDSQ-ND) under the high cooling rates and wide crystallization temperature ranges, as well as the cold crystallization and recrystallization behavior during the heating process. The data suggested that Zn2(DDSQ-ND) accelerated the formation of α-phase iPP and acted as a novel α-nucleating agent in the iPP system.

Advantage of Preserving Bi-orientation Structure of Isotactic Polypropylene through Die Drawing

The isotactic polypropylene (iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle (80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP.

Crystallization behavior and optical properties of isotactic polypropylene filled with α-nucleating agents of multilayered distribution.

Isotactic polypropylene (iPP)-based multilayered composites containing alternating layers of pure iPP and α-nucleating agents (α-NAs)-filled iPP (αPP) were fabricated through layer-multiplying co-extrusion technology. With the manipulation of layer number, a tunable multilayered distribution of α-NAs was achieved and its effect on the crystallization behavior and optical properties of iPP was investigated. When the thickness of an individual iPP layer, which is equal to the distance between adjacent αPP layers, was large, the crystallization process of iPP was governed by homogeneous nucleation, although the crystallization of areas near the layer interfaces was induced by α-NAs. As a result, most iPP formed big spherulites thus a poor clarity. By decreasing the layer thickness via multiplying the layer number, the nucleation of iPP was gradually transformed from a homogeneous mode to a heterogeneous mode because of the more and more strong influence of αPP layers on the crystallization process of adjacent iPP layers. Consequently, iPP exhibited similar crystallization behavior compared with αPP. The polarized optical microscopy results further demonstrated that the size of spherulites in iPP was significantly reduced with the increase of layer number, which contributed to the enhancement of transmittance and decline of haze. Accordingly, this work developed a novel approach to tailor the crystallization behavior and optical properties of iPP.

Effect of chemical structure of hydrazide compounds on nucleation effect in isotactic polypropylene

A series of hydrazide compounds were synthesized and employed as nucleating agents for isotactic polypropylene (iPP). The effect of different structures of hydrazide compounds on the crystallization and melting behaviour of iPP was studied by differential scanning calorimetry (DSC). The results demonstrate that almost all nucleating agents are α-nucleating agents, some of which are highly efficient nucleating agents. In the case of the same substituent, the greater the number of hydrazide groups, the better the nucleation effect. The crystallization peak temperature (Tc) of iPP nucleated with dihydrazide is 3–4 °C higher than that of monohydrazide. When the substituent of the dihydrazide compound is hydrogen, ethyl and nonyl, their nucleating ability is relatively weak, but in the state of phenyl and cyclohexyl substitution, the Tc of iPP nucleated with dihydrazide nucleating agent is 8.5 °C than pure iPP. When the intermediate group of the dihydrazide compound is a long-chain alkyl, a phenyl, a cyclohexyl, and a naphthyl group, the phenyl group and the cyclohexyl group still exhibit an excellent effect, the Tc of nucleated iPP is raised by about 10 °C.

Nucleus density and crystallization behavior of isotactic polypropylene nucleated with different α/β compound nucleating agents

Different compound nucleating agents consisting of a highly efficient novel α-nucleating agent N,N’-bis(benzoyl) sebacic acid dihydrazide and three typical β-nucleating agents N,N-dicyclohexylterephthalamide, rare earth compound (WBG-II) and calcium pimelate were incorporated into isotactic polypropylene (iPP), and the isothermal crystallization behavior of iPP nucleated with these compound nucleating agents was investigated by differential scanning calorimetry. Based on the classical Avrami theory and the calorimetric curves under isothermal conditions, the crystallization half-time and the Avrami index can be calculated. The results demonstrate that addition of these nucleating agents reduced the crystallization half-time and speed up the crystallization process of iPP. In addition, the nucleus density of pure and nucleated iPP was further calculated from the Lamberti model and the results illustrate that the nucleus density of iPP after addition of different compound nucleating agents was increased greatly and it was several orders of magnitude higher than that of pure iPP.

Competitive growth of α- and β-transcrystallinity in isotactic polypropylene induced by the multilayered distribution of α-nucleating agents: Toward high mechanical performances

Multilayer materials containing alternating layers of isotactic polypropylene (iPP) and α-nucleating agent (NA)-filled iPP (PPN) were fabricated. Structural analysis presented that a sandwich structure of transcrystallinity (TC)/α-spherulites/TC was generated in each iPP layer and the TC structure consisted of α- and β-crystals (TCα and TCβ). Different from traditional methods, the TCβ originated from the multilayered distribution of α-NAs was reproducible and tunable, so that its competitive growth with TCα was investigated. It was demonstrated that the confined growth of TCα around layer interfaces encouraged the β-nuclei generation and the confined space of iPP layer determined the growth of TCβ. When the layer numbers reached 64 and 0.7 wt% α-NAs was introduced, the TC structure including 86.7% TCβ almost occupied each iPP layer, leading to the distinct improvement of mechanical strength and flexibility. Accordingly, this work provided a promising strategy for fabricating high-performance iPP products by controlling the distribution of α-NAs.

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

ABSTRACTThe 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 (t1/2) 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.

Optimization of tensile properties of injection molded α-nucleated polypropylene using response surface methodology

Tensile properties are among the significant properties of isotactic polypropylene (iPP). The mechanical properties including the tensile properties are fairly dependent on the overall crystallinity and crystallite size and their distribution in molded product, type of crystal structure and testing conditions. In presence of α-nucleating agents, the crystallization rate and onset temperature of isotactic PP increase. In this paper, the role of externally added commercial α-nucleating agent HPN-20E (Milliken Inc.) on tensile properties was investigated with respect to tensile properties of pure iPP. The experimental part includes the use of design of experiment (DoE) - response surface methodology (RSM) with central composite design (CCD) having three factors namely mold temperature, melt temperature and injection rate. Two levels of each factor with six centre points and five numbers of replicates were selected. The nucleating agent, HPN-20E, was added 1.0% by wt. in iPP (mfr 11.0 g/10min) using a lab scale co-rotating twin screw extruder. The compounded pellets were dried at 85 °C in a circulating hot air oven for 24 h. The tensile samples (ASTM-638D, type-I) were molded on a micro-injection molding machine (make BabyPlast, Italy). The samples were tested for tensile properties on a universal testing machine (make Lloyds, USA). The measured responses were tensile strength (MPa), Young's modulus (MPa) and work to break (N.mm). The same experimental procedure was also followed for pure iPP and same responses were measured to set the baseline of experiment. The analysis of variance (ANOVA) tests unearth that mold and melt temperatures are highly interacting in nature. That is why previous attempts based on traditional way of varying one parameter at a time were not so successful to relate tensile properties with injection molding variables. The RSM tests resulted into useful quantitative relationship between the tensile properties and injection molding process variables.

Combined effect of α-nucleating agents and glass fiber reinforcement on a polypropylene composite: a balanced approach

An approach by combining α-nucleating agents and glass fibre reinforcement for improving the comprehensive mechanical properties of polypropylene composite: a balanced approach.

Highly Efficient “Composite Barrier Wall” Consisting of Concentrated Graphene Oxide Nanosheets and Impermeable Crystalline Structure for Poly(lactic acid) Nanocomposite Films

Poly(lactic acid) (PLA), a promising sustainable packaging material, suffers from intrinsic poor gas barrier performance partly due to its innate defect of relatively low crystallization rate. In the present study, taking advantage of the excellent impermeability and heterogeneous nucleating ability of graphene oxide nanosheets (GONSs), the crystalline structure of PLA nanocomposite film was manipulated using processing techniques. We revealed that GONSs were the α-nucleating agent for PLA, inducing typical spherulite morphology. More interestingly, two-dimensional small-angle scattering characterization confirmed that GONSs were preferentially dispersed in the amorphous phase between PLA spherulites, achieving a concentrated GONS region. As a consequence, the “composite barrier wall” consisting of concentrated GONSs and impermeable PLA lamellae gave rise to O2 permeability of PLA nanocomposite film at a GONS loading of 1.0 wt % as low as 0.211 × 10–14 cm3 cm cm–2 s–1 Pa–1, reduced by ∼89.9% relative to n...

The role of nucleating agents in high-pressure-induced gamma crystallization in isotactic polypropylene.

Nucleation of the γ-form in isotactic polypropylene (PP) under high pressure was investigated. Three nucleating agents were used to nucleate crystallization of PP under atmospheric pressure: commercial Hyperform HPN-20E from Milliken Chemical, poly(tetrafluoroethylene) particles nucleating the α-form, and calcium pimelate nucleating the β-form. Crystallization of neat PP and PP with addition of 0.2 wt% of the nucleating agents was studied. Specimens were either kept at 200 °C under pressure of 200 MPa for time ranging from 2 min to 4 h or for 15 min under pressure ranging from 1.3 to 300 MPa. After cooling to ambient temperature and releasing the pressure, the specimens were analyzed by DSC, WAXD, and PLM to have an insight into the structure and to determine a crystallinity level and contents of crystallographic forms. Both α-nucleating agents strongly nucleated crystallization of PP under high pressure in the γ-form, whereas the β-nucleating agent had only a slight effect. The results show the possibility to use nucleating agents to nucleate the γ-form of PP under high pressure.

Competitive growth of α- and β-crystals in isotactic polypropylene with versatile nucleating agents under shear flow

Sorbitol derivatives, the conventional α-nucleating agents of isotactic polypropylene (iPP), are discovered to induce β-phase iPP under normal crystalline conditions. Combined effects of shear flow and sorbitol derivatives on the crystallization of iPP were investigated by using differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering. In the nucleation stage, sorbitol derivatives induce both α- and β-nuclei, while shear flow and the interactions between shear and sorbitol derivatives enhance the amount of α-nuclei. In the growth stage, the epitaxial growth of β-crystals on shear-induced α-row nuclei occurs. As the shear rate increases, more epitaxial β-crystals form due to the increase of α-row nuclei, further increasing the content of β-crystals. Under high shear rate, the presence of sorbitol derivatives and shear flow exhibit a synergistic interaction on increasing the content of β-crystals. Moreover, α-nuclei, which arise from the interaction between shear and sorbitol derivatives, emerge earlier than shear-induced α-row nuclei.

Crystallization and morphology of iPP/MWCNT prepared by compounding iPP melt with MWCNT aqueous suspension

In this work, isotactic polypropylene (iPP) composites filled with multiwalled carbon nanotubes (MWCNTs) were prepared by compounding iPP melt with MWCNT aqueous suspension using a corotating twin-screw extruder, and the morphology and crystallization behavior of the composites were investigated. Scanning electron microscopy micrographs showed that MWCNTs dispersed individually at nanoscale in the iPP matrix when the MWCNTs concentration was low, though MWCNTs aggregates were detected when the filler concentration increased. The results of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy indicated that the β-form crystal of iPP was induced by MWCNTs at the concentration of 0.1 wt.% which was dispersed individually in the iPP matrix. At higher content, however, MWCNTs acted as α-nucleating agent, and the crystals in the iPP/MWCNT composites showed higher degree of perfection than that of pure iPP though smaller in dimension. Crystallization rate of iPP increased significantly with increasing MWCNT content.

Novel polypropylene-based microporous membranes via spherulitic deformation

A novel method for creating a microporous membrane via spherulitic deformation is illustrated. The microporous structure was generated by the combination of intra-spherulitic and inter-spherulitic deformations. Polypropylene was selected due to its unique cross-hatched lamellar morphology facilitating inter-spherulitic deformation. A precursor film with a spherulitic structure was made under low-stress melt processing condition. A tangential lamellae-rich spherulite was created and identified with a positive birefringence sign. A sequential annealing process improved the crystalline structure, and in particular the thickness of the tangential lamellae. The annealing process proved to be critical for initiating the inter-spherulitic deformation. A WAXS examination provides a quick characterization method for the inter-spherulitic deformation. A highly interconnected solvent-resistant porous polypropylene membrane having a pore size in the range of 50–100 nm and a porosity of about 0.18 was thereby developed in this study. This concept can be further expanded by using an α-nucleating agent to reduce spherulite sizes. A highly methanol permeable membrane with an estimated porosity of 0.29 was produced with the nucleated polypropylene samples.

The role of specific nucleation in polypropylene photodegradation

The paper focuses on the effects of polymorphism on photodegradation of isotactic polypropylene. The starting polymer was modified by a specific α-nucleating agent, 1,3;2,4-bis(3,4-dimethylbenzylidene)sorbitol, by a specific β-nucleating agent, N, N′-dicyclohexylnaphthalene-2,6-dicarboxamide, or their combination. Samples prepared by compression moulding were then exposed to UV-irradiation in the interval from 0 to 240 h. The differences in morphology were reflected in different photooxidative behaviour. Infrared spectroscopy showed that neat polypropylene was the most sensitive to photooxidation and the sample modified solely by the β-nucleating agent was the least sensitive. The remaining two samples exhibited an intermediate sensitivity. Differential scanning calorimetry revealed that the UV-exposure led to gradual changes in crystallization mechanism specifically asserting in individual materials. This behaviour was ascribed to homogeneous nucleation of partly degraded macromolecules. Possible changes of the nucleating agent itself during UV-exposure were also discussed.