Β-nucleating Ability Research Articles

Ethylene Comonomer-Directed Epitaxial Nucleation and Growth of β-Nucleated Isotactic Polypropylene

We present a molecular-level investigation of the epitaxial crystallization of β-nucleated isotactic polypropylene associated with the minor and local topographic modification at the interface, i.e., the inclusion of an ethylene comonomer. The experimental results show that the relative fraction of β-crystal (Kβ) decreases progressively with increasing the amount of ethylene comonomer, which originates from a simultaneous reduction in the β-nucleation ability of a β-nucleating agent (N,N′-dicyclohexylterephthalamide, DCHT) toward propylene–ethylene random copolymers (PERs) and the growth rate of the β-crystal relative to the α-crystal. With the aid of molecular mechanics simulation, we demonstrate that such a topographic modification weakens the intermolecular interactions at the nucleation and growth interfaces, thereby modifying the epitaxial nucleation of the β-crystal and the growth kinetics of β- and α-crystals. The study reveals that the polymorph selection of the PERs/DCHT system is not solely determined by the lattice match but also profoundly influenced by the topography characteristics dependence of molecular interaction at the crystalline interfaces. Our fundamental insight could have important implications in the control of the polymorphism of polymers through the careful design of the topography of the nucleation and growth interfaces.

Failure mechanism of zinc adipate as a β-nucleating agent for polypropylene in the presence of calcium stearate

Although zinc dicarboxylic acids are highly effective β-nucleating agents (β-NAs), they lose their β-nucleating ability in isotactic polypropylene (iPP) upon the addition of calcium stearate (CaStr2). In this study, we investigated the failure mechanism of these β-NAs in terms of the chemical and physical interactions of zinc adipate (ZnAA) with CaStr2. No chemical reaction occurs between CaStr2 and ZnAA; rather, it is the physical interactions between this β-NA and CaStr2 that are responsible for the loss of β-nucleating ability. Based on the experimental findings and molecular dynamics (MD) simulations, we suggest a blocking effect of CaStr2 on nucleation as a possible failure mechanism. MD simulations confirmed that the aggregation of CaStr2 on the β-NA surface, observed experimentally using polarized optical microscopy and scanning electron microscopy, resulted from the binding energy for the interaction between ZnAA and CaStr2 being higher than that for iPP/CaStr2. Because the active nucleation sites on the surface of the β-NA were covered, lattice matching between ZnAA and the iPP chains was hindered. Therefore, the addition of CaStr2 weakens the β-nucleating ability of ZnAA, leading to inhibition of the epitaxial crystallization process, thereby decreasing the degree of β-crystal formation and, consequently, lowering the toughness of the resulting iPP.

Modification of illite with calcium pimelate and its influence on the crystallization and mechanical property of isotactic polypropylene

A novel illite with β-nucleation ability toward iPP has been prepared through decoration the pristine illite with CaHA, i.e. CaHA-illite. The crystallization behavior and mechanical property of the iPP/CaHA-illite composite were studied. For comparison, the composites were also made simply by adding different components simultaneously into iPP matrix during mixing in a mini-extruder. The results show that, due to the opposite nucleation ability of illite and CaHA, the illite inhibits the β crystallization whereas the CaHA promotes the β crystallization of iPP. The CaHA-illite is very efficient for inducing the β crystallization of iPP. Its efficiency is higher than any of the other samples. Due to the high crystallinity and β iPP crystal fraction, the iPP/CaHA-illite exhibits the best mechanical properties with an increase of 36% in tensile modulus, 163% in maximum strain, and 69% in non-notched impact strength. Meanwhile, the tensile strength of pure iPP has been well maintained.

The effect of structure evolution upon heat treatment on the beta-nucleating ability of calcium pimelate in isotactic polypropylene

Calcium pimelate (CaPim) is known as one of the most stable and effective β-nucleating agents for isotactic polypropylene (iPP). To establish the structure-properties relationships of CaPim, the structure and corresponding β-nucleating ability of as-synthesized CaPim and CaPim annealed at temperature (Ta) varying from 130 to 330 °C were investigated. Our results revealed that as-synthesized CaPim and CaPim annealed at a relatively lower Ta were crystalline hydrates. However, the highly ordered crystalline structure would irreversibly destroyed and transformed to a weakly ordered form when treated at about 180 °C, accompanied by the complete deprivation of crystal water. The weakly ordered CaPim still maintained relatively high ordered degree at Ta range of 180–290 °C, but a further increase of Ta leads to the conversion of CaPim to disordered amorphous form. The measurements of relative β-form content (kβ) of iPP samples containing 0.05 wt% of various annealed CaPim suggested that the β-nucleating selectivity was closely correlated to the ordered degree of CaPim. As expected, the crystalline CaPim could induce high kβ values of 0.82–0.91. Interestingly, the weakly ordered CaPim with residual ordered structure still showed a rather high β-selectivity with kβ values of 0.53–0.68, while the amorphous CaPim almost lost its β-nucleating ability. Combined with the epitaxial crystallization theory, a probable mechanism on the correlation between structure and β-nucleating selectivity of CaPim was proposed.

A novel polypropylene composite filled by kaolin particles with β-nucleation

Kaolin-filled polypropylene (PP) composites generally form α-crystal due to the effect of kaolin with α-nucleation. The transition from α- to β-nucleation of kaolin has been investigated, and a novel kaolin with β-nucleation (β-kaolin) and kaolin-filled PP composites with high β-crystal content were prepared first. The DSC and WAXD results indicated that the β-kaolin exhibits stronger β-nucleating ability than CaPA as β-nucleating agent for PP crystallization. It is found that the β-crystal content has been influenced little by filler contents in β-kaolin-filled PP composites. Mechanical properties and spherulitic morphology of filled PP composites was characterized. The synergistic effect of filler and β-crystal significantly improved impact strength of kaolin-filled PP composites.

From α- to β-crystallization in multi-walled carbon nanotubes-filled polypropylene nanocomposites

Multi-walled carbon nanotubes (MWCNTs)-filled polypropylene (PP) nanocomposites generally form α-crystal. In order to induce the transition from α-crystallization into β-crystallization of MWCNTs-filled PP nanocomposites, the calcium pimelate-supported MWCNTs were prepared. The effect of calcium pimelate-supported MWCNTs on the crystallization behavior and melting characteristics and spherulitic morphology of PP was investigated by differential scanning calorimetry, X-ray diffraction, and polarizing optical microscopy. The β-nucleating ability of calcium pimelate-supported MWCNTs prepared with different mass ratios of MWCNTs/pimelic acid and its influence on the crystallization of PP nanocomposites was discussed. It is found that the MWCNTs supported by calcium pimelate can change from α-nucleation of MWCNTs surface into β-nucleation and induce β-crystallization in the MWCNTs-filled PP nanocomposites. The MWCNTs-filled PP nanocomposites prepared with MWCNTs/pimelic acid mass ratio of 10/1 can completely form β-crystal. The β-crystal content of the PP nanocomposites filled by MWCNTs kept at high level and was little influenced by MWCNTs contents. This finding is great significant to develop MWCNTs-filled β-PP nanocomposites.

Nucleation and growth behavior of β-nucleated iPP during shear induced crystallization investigated by in-situ synchrotron WAXS and SAXS

Polymer crystallization under flow was investigated because final properties of polymers strongly depend on the crystalline structure and morphology formed during processing. In-situ synchrotron WAXS and SAXS were used to investigate the structure formation and morphological developments during quiescent and shear-induced crystallization of iPP with 3 different concentrations (0.01, 0.03 and 0.1 wt%) of β-nucleating agent. Under quiescent conditions, a high β-content was obtained at all those concentrations indicating the high β-nucleating efficiency of the nucleating agent. After application of shear, the β-nucleating ability at small concentration was retained, while at larger concentrations it was strongly retarded. Furthermore, the addition of β-nucleating agent was beneficial for the molecular alignment during processing, the anisotropic particles of β-nucleating agent were much more effective to align the molecular chains in the flow direction compared to isotropic ones. A crystallization scheme for the iPP β-nucleating agent under shear was proposed.

Influence of different β-nucleating agent on crystallization behavior, morphology, and melting characteristic of multiwalled carbon nanotube-filled isotactic polypropylene nanocomposites

To obtain isotactic polypropylene (iPP) nanocomposites with high β-crystal content, TMB5, calcium pimelate and calcium pimelate supported on the surface of nano-CaCO3 were used as β-nucleating agent and MWCNT filled β-nucleated iPP nanocomposites were prepared. The effect of different β-nucleating agent and MWCNT on the crystallization behavior and morphology, melting characteristic and β-crystal content of β-nucleated iPP nanocomposites were investigated by DSC, XRD and POM. The results indicated that addition of MWCNT increased the crystallization temperature of iPP and MWCNT filled iPP nanocomposites mainly formed α-crystal. The β-nucleating agent can induce the formation of β-crystal in MWCNT filled iPP nanocomposites. The β-nucleating ability and β-crystal content in MWCNT filled β-nucleated iPP nanocomposites decreased with increasing MWCNT content and increased with increasing β-nucleating agent content due to the nucleation competition between MWCNT and β-nucleating agents. It is found that the calcium pimelate supported on the surface of inorganic particles as β-nucleating agent has stronger heterogeneous β-nucleation than calcium pimelate and TMB5. The MWCNT filled iPP nanocomposites with high β-crystal content can be obtained by supported β-nucleating agent. POLYM. COMPOS., 36:635–643, 2015. © 2014 Society of Plastics Engineers

Crystalline morphology and mechanical properties of isotactic polypropylene composites filled by wollastonite with β-nucleating surface

Wollastonite-filled α-isotactic polypropylene (iPP) and β-iPP were prepared through introduction of wollastonite (W) and wollastonite with β-nucleating surface (Wx) in iPP matrix. The α- and β-nucleating ability of wollastonite, crystalline morphology, and mechanical properties of injected iPP filled by wollastonite with different nucleating surface were compared using differential scanning calorimetry, wide-angle X-ray diffraction, polarizing optical microscopy, mechanical testing, and scanning electron microscopy. The results indicated that iPP filled by wollastonite with different nucleating surface has different crystalline morphology, melting behavior, and mechanical properties. The W and Wx filled iPP mainly formed α- and β-phase iPP, respectively. The tensile and flexural modulus of iPP/W and iPP/Wx increased with increasing wollastonite content, and the tensile and flexural modulus of iPP/Wx were lower than that of iPP/W. The tensile property, flexural property, and impact strength of iPP/Wx were higher than that of iPP/W and β-iPP. The synergistic effect of reinforcing of wollastonite and toughening of β-phase leads to higher mechanical properties. POLYM. COMPOS., 35:1445–1452, 2014. © 2013 Society of Plastics Engineers

Nucleation effect of montmorillonite with β-nucleating surface on polymorphous of melt-crystallized isotactic polypropylene nanocomposites

Abstract Neat montmorillonite (MMT) causes strong heterogeneous nucleation of α-phase crystallites in isotactic polypropylene (iPP). By surface modification of MMT with pimelic acid (PA) MMT with tailored β-nucleation capacity (β-MMT) has been prepared and nanocomposites with β-iPP have been made. The polymorphism of the iPP in the nanocomposites, the effect of β-MMT on the morphology and its crystallization and melting behavior of iPP has been investigated by POM, DSC and XRD. β-MMT raises the crystallization temperature to a higher value than neat MMT. The β-nucleation ability of β-MMT depends both on the MMT/PA ratio and on the β-MMT content in the composite. The fraction of β-crystals with respect to the total amount of crystals increases with increasing β-MMT content and decreasing MMT/PA ratio. It can be adjusted between 0% and 98%. The accomplished surface modification of the MMT provides a simple and efficient way to prepare β-iPP nanocomposites.

Sonochemical activation calcium sulfate whisker with enhanced beta-nucleating ability for isotactic polypropylene

The crystalline morphology, structure, and the β-nucleating ability of ultrasound-activated calcium sulfate whisker (CSW)-filled isotactic polypropylene were investigated via X-ray diffraction (XRD), polar light microscopy (PLM), and differential scanning calorimetry (DSC). The XRD results revealed that ultrasound treated CSW (UCSW) could improve the β-nucleated ability, and resulted in enhancing the content of β-crystal form. The ultrasonic time was conducive to the improvement of the contents of β-crystal and reached the maximum value at ultrasonic 120 min. PLM and DSC results verified the enhanced nucleating ability of UCSW supported as β-nucleating agent. The scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy indicated the surface of CSW treated by ultrasound had been changed. The activity of the calcium ion was improved and the sulfuric acid layer appeared on the whisker surface had a significant effect on the iPP β-heterogeneous nucleation, and resulted in enhancing the content of β-crystal form.

A novel montmorillonite with β-nucleating surface for enhancing β-crystallization of isotactic polypropylene

Montmorillonite (MMT) generally has α-nucleating ability for isotactic polypropylene (iPP). A novel MMT with β-nucleating surface (β-MMT) supported by chemically calcium pimelate (CaA) was prepared through the chemical reaction between pimelic acid (HA) and calcium ion on the surface of MMT in the first time. Infrared spectrometry and thermogravimetric analysis confirmed the formation of CaA on the surface of MMT. The differential scanning calorimeter and X-ray diffraction illustrated that the iPP nanocomposites filled by MMT and β-MMT exhibit different heterogeneous nucleation. The heterogeneous nucleation of the prepared MMT surface has changed from α-nucleation into β-nucleation and a novel MMT with β-nucleating surface is obtained. Even, the heterogeneous β-nucleating ability of β-MMT is much stronger than that of CaA. Addition of MMT with β-nucleating surface into iPP matrix significantly increased the spherulite nuclei density and decreased the spherulite size, and can easily prepare the β-iPP nanocomposites with high relative β-phase content.

Preparation and β-crystallization of zeolite filled isotactic polypropylene composites

In order to prepare the zeolite filled β-iPP composites, zeolite supported by calcium pimelate as β-nucleator (β-zeolite) was prepared by the interaction between calcified zeolite and pimelic acid. The effects of Ca(Ac)2 solution concentration in the prepared calcified zeolite process and pimelic acid content on β-nucleating ability of β-zeolite were investigated and the crystallization and melting characteristic of zeolite, calcified zeolite and β-zeolite filled iPP composites were compared. DSC and WXAD analysis indicated that the zeolite and calcified zeolite have α-nucleation and the prepared β-zeolite has high β-nucleating ability for iPP crystallization. The β-nucleating ability of prepared β-zeolite is dependent of Ca(Ac)2 solution concentration and pimelic acid content. The prepared β-zeolite content has little influence on the crystallization and melting characteristic and the β-phase content of the filled iPP composites. The zeolite filled β-iPP composites with high β-phase content can be easily obtained by adding β-zeolite into the iPP matrix.

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.

Crystallization behavior and melting characteristics of wollastonite filled β-isotactic polypropylene composites

In order to obtain wollastonite filled β-iPP composites, wollastonite treated with pimelic acid (W*) were prepared with various mass ratios of wollastonite/pimelic acid (W/PA). The crystallization behavior, melting characteristics and β-nucleating ability of iPP composites filled with wollastonite (W) and W* were investigated by DSC and XRD. The results indicated that addition of wollastonite increased the crystallization temperatures of iPP, but the crystallization temperatures of iPP in iPP/W* composites were higher than those of iPP/W composites, which proved that the β-nucleation of W* is stronger than untreated wollastonite. Although iPP/wollastonite composites mainly form α-phase iPP, modification of wollastonite by PA significantly enhanced nucleation of β-phase iPP. The β-nucleating ability of W* depend on the amount of formed calcium pimelate, therefore the β-phase contents of β-iPP/W* composites increased with increasing W* content and decreasing mass ratio of W/PA. Moreover, there exist different critical mass ratios of W/PA for preparation of β-iPP composites filled with different W* contents with highest β-phase content and low cost.

Preparation and characteristics of nano-CaCO 3 supported β-nucleating agent of polypropylene

In this paper, nano-CaCO 3 supported β-nucleating agent for polypropylene (PP) was prepared by supporting pimelic acid on nano-CaCO 3 with two methods. The thermal properties of pimelic acid and nano-CaCO 3 supported β-nucleating agent were investigated by differential scanning calorimetry and thermogravimetry coupled with Fourier transform infrared spectrometry. The results indicated that the formation of β-nucleating agent supported on nano-CaCO 3 was attributed to the chemical reaction between nano-CaCO 3 and pimelic acid. The β-nucleating agent was added to PP to examine its β-nucleating ability for PP, the polymorphism of the PP was characterized by wide-angle X-ray diffractometer. The results of investigation showed that the nano-CaCO 3 supported β-nucleating agent exhibited higher nucleation ability and lower price compared to calcium pimelate β-nucleating agent.

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants. © 1996 John Wiley & Sons, Inc.

Direct evidence of row-nucleated cylindritic crystallization in glass fiber-reinforced polypropylene composites

The development and nature of the transcystalline-like superstructure produced by pulling the glass fiber (GF) from the isothermal crystallizing (Tc≈135°C) isotactic polypropylene (PP) melt was studied thermooptically. In the vicinity of the pulled GF α row-nuclei form which induce selective β-nucleation resulting in β-cylindrites. The presence of α row-nuclei was evidenced by selective melting of the β-phase having lower melting temperature than the α. Because of the above change in the crystal modification this phenomenon can not be termed by transcrystallinity. The thermal stability and β-nucleation ability of the primary α row-nuclei depend both on the applied shear stress (i.e. molecular orientation) and pulling temperature (Tpull) under the testing conditions: Tαβ T βα, where Tαβ and Tβα are the lower and upper threshold temperature of the β-formation, respectively. It was suggested that the observed αβ-bifurcation may be related with epitaxial growth.