Mechanical properties and crystallization behavior of polypropylene with cyclodextrin derivative as ��-nucleating agent

It was found that lanthanum complex of cyclodextrin derivative (??-CD?CMAH?CLa) was a highly active ??-nucleating agent for isotactic polypropylene (iPP) in this study. The influence of the nucleating agent on mechanical properties and isothermal and nonisothermal crystallization behavior of iPP has been investigated. Results showed that ??-CD?CMAH?CLa was efficient in inducing the crystallization of iPP into ??-modification (??-iPP), with K _?? value of 0.84, while the content of nucleating agent was 0.8?wt.%. ??-iPP could form extensively in the isothermal crystallization temperature range from 110?°C to 140?°C, and the highest amount of ??-crystal content was formed at 130?°C. Besides, it can be known that the addition of ??-CD?CMAH?CLa can obviously facilitate the overall crystallization process of iPP. Under nonisothermal condition, ??-iPP formed at the suitable cooling rates, ranging from 5?°C to 10?°C/min. Furthermore, the nucleation mechanism of ??-CD?CMAH?CLa for iPP was correlated to the special configuration of ??-CD?CMAH?CLa.     

Thermal behavior of isotactic polypropylene in different content of β-nucleating agent

The effects of non-isothermal and isothermal crystallization on the formation of α- and β-phase in isotactic polypropylene (iPP) with different content of β-nucleating agent are investigated by differential scanning calorimetry (DSC). On non-isothermal crystallization, the content of β-phase and regularity of its crystals are depended on both cooling rate and the content of β-nucleating agent. The faster cooling rate is, the lower of melting peak temperature (T_mp) and crystallization peak temperature (T_cp) of α- and β-phase are. The enthalpy of fusion (∆H) of β-phase increases with cooling rate in a certain range for the sample with 0.1 wt% β-nucleating agent (G₁) and decreases for that with 0.3 wt% β-nucleating agent (G₃). On isothermal crystallization, the enthalpy of fusion of β-phase in G₁ is higher than in G₃ which is related to the efficiency of nucleation in different concentration of nucleating center in two samples.     

Nonisothermal crystallization kinetics of isotactic polypropylene nucleated with a novel supported β-nucleating agent

The introduction of β-nucleating agent into isotactic polypropylene (iPP) is the most effective method to prepare β-iPP. In this paper, iPP nucleated with a novel highly efficient supported β-nucleating agent (NA100), calcium pimelate (CaHA) supported on the surface of nano-CaCO₃, was prepared and its nonisothermal crystallization kinetic, melting characteristic, and crystallization activation energy are investigated and compared with those of pure iPP, nano-CaCO₃ filled iPP, and β-nucleating agent CaHA nucleated iPP. The results indicate that addition of nano-CaCO₃ increases the crystallization temperature of iPP and has no influence on the crystal form of iPP. iPP and nano-CaCO₃ filled iPP mainly crystallize in the form of α-crystal. Although NA100 and CaHA induce iPP to mainly form β-crystal, NA100 nucleated iPP shows higher crystallization temperature, melting temperature, and β-phase content than that nucleated with CaHA without supports. Nonisothermal crystallization kinetic is well described by the equations of Avrami and Mo, and the crystallization activation energy was calculated from Kissinger’s method. It was found that the decreased crystallization activation energy is favorable to increase the crystallization rate and the content of β-crystal. Although the content of CaHA in 5 wt% NA100 nucleated iPP was less than that in 0.1 wt% CaHA nucleated iPP, the former formed more β-iPP than the latter, indicating that the β-nucleating agent CaHA supported on the surface of nano-CaCO₃ exhibits higher efficiency for preparation of β-iPP than pure CaHA powder.     

Synergistic nucleation effect of calcium sulfate whisker and β-nucleating agent dicyclohexyl-terephthalamide in isotactic polypropylene

Journal of Thermal Analysis and Calorimetry - The crystallization and melting behaviors and mechanical properties of isotactic polypropylene (iPP) containing a certain amount of stearic...     

Study on side-chain liquid–crystalline copolymer as a new β-nucleating agent to induce phase behavior of isotactic polypropylene

The nucleating activity of side-chain liquid–crystalline copolymer, as new β-nucleating agent (LCP-NA3), towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. The effect of LCP-NA3 content, crystallization temperature, and time on the phase behavior of the iPP has been discussed. The results indicate that the relative content of β-crystal mainly depends on LCP-NA3 content, crystallization temperature, and time. A high content of β-crystal can be obtained by the combined effect of the optimum LCP-NA3 concentration, crystallization temperature, and time. The maximum content of β-crystal reaches 0.63 when the LCP-NA3 content, crystallization temperature, and time are 0.8 wt%, 130 °C, and 1 h, respectively. In addition, LCP-NA3 is identified to have dual nucleating ability for α- and β-crystals under appropriate kinetic conditions.     

Effect of β-nucleating agent on crystallization of wollastonite-filled recycled polypropylene composites

Journal of Thermal Analysis and Calorimetry - The crystallization behavior, melting characteristics, and semicrystalline morphologies of wollastonite-filled recycled polypropylene (R-PP) composites...     

Preparation and crystallization of isotactic polypropylene composites filled by titanium dioxide-supported montmorillonite with a β-nucleating surface

To obtain multi-functional β-iPP composites, β-iPP composites are always filled by multiple fillers with α-nucleating ability. To prepare β-iPP/TiO₂/MMT composites, TiO₂-supported MMT with a β-nucleating surface was prepared through hydrolysis reaction of Tetra-n-butyl titanate and chemical reaction between pimelic acid and calcium ion. X-ray diffraction and scanning electron micrograph confirmed the formation of TiO₂ on the surface of MMT. The differential scanning calorimeter and X-ray diffraction illustrated that the β-iPP composites filled by TiO₂ and MMT had lower relative β-phase contents than β-iPP. It is observed by polarized optical microscope that addition of TiO₂-supported MMT with a β-nucleating surface into iPP can increase the spherulite nuclei density and decrease the spherulite size significantly and obtain the β-iPP/TiO₂/MMT composites with high relative β-phase content.     

The enhanced nucleating ability of carbon nanotube-supported β-nucleating agent in isotactic polypropylene

A kind of β-nucleating agent, calcium pimelate, for polypropylene (PP) was chemically supported onto the surface of multi-wall carbon nanotubes, and the effect of the multi-wall carbon nanotube-supported β-nucleating agent on the mechanical properties and morphology of isotactic polypropylene composites was investigated. The composites of isotactic polypropylene and multi-wall carbon nanotube-supported β-nucleating agent exhibited excellent impact toughness compared with pure isotactic polypropylene and β-nucleated isotactic polypropylene, being more than seven times over that of pure isotactic polypropylene and more than three times over that of β-nucleated isotactic polypropylene. The excellent impact behaviors of the composites were also evidenced by the fracture morphology based on scanning electron microscopy observations. Differential scanning calorimetry and wide-angle X-ray diffraction results verified the enhanced nucleating ability of the multi-wall carbon nanotube-supported β-nucleating agent, which greatly improved the impact toughness without significantly deteriorating the strength and stiffness of the polypropylene composites.     

Effects of stereo-defect distribution and molecular mass in the non-isothermal crystallization behavior of β-nucleated isotactic polypropylene

In this study, based on the synthesis of two Ziegler–Natta iPP with nearly same average isotacticity but different uniformities of stereo-defect distribution, we further prepared two series of β-iPP with different molecular masses by addition of different concentration of peroxide. We investigated the combination effects of stereo-defect distribution and molecular mass on the non-isothermal crystallization behavior and polymorphic composition behavior of β-iPP by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and scanning electron microscope (SEM). The results of non-isothermal crystallization kinetics revealed that the iPP molecular mass has only slight influence on the crystallization temperature of β-iPP, while the uniformity of stereo-defect distribution not only evidently influences the crystallization temperature, but also affects the dependency of crystallization temperature on cooling rate. β-iPP with less uniformity of stereo-defect distribution leads to higher dependency of crystallization temperature on the cooling rate. The calculation of crystallization activation energy ΔE showed that the lower the molecular mass, the lower the ΔE, indicating that it is easier for the occurrence of crystallization. Meanwhile, iPP with more uniform stereo-defect distribution has lower ΔE. Moreover, both stereo-defect distribution and molecular mass are important factors in determining the polymorphic composition. A more uniform stereo-defect distribution is more favorable for the β-phase crystallization; the lower the molecular mass, the harder for β-phase crystallization to take place. However, compared with iPP molecular mass, the uniformity of stereo-defect distribution is the first-order factor in determining the β-phase crystallization of iPP. Moreover, the thermal stability and the dependency of β-phase proportion on the cooling rate are also found to be highly dependent on the iPP molecular mass.     

The synergistic effects of β-nucleating agent and ethylene–octene copolymer on toughening isotactic polypropylene

The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.     

Crystallization of post-consumer polypropylene in the presence of β-nucleating agent

Journal of Thermal Analysis and Calorimetry - In this paper, the heat transfer characteristics of the nanofluid through a parallel plate soft nanochannel are investigated under the fully developed...     

Combined effect of β-nucleating agent and multi-walled carbon nanotubes on polymorphic composition and morphology of isotactic polypropylene

The effects of nucleating duality, imposed by a mixed nucleating agent (NA) system containing multi-walled carbon nanotubes (MWCNTs) and a rare earth (WBG), on the crystallization behaviors of isotactic polypropylene (iPP) including the peak temperature of crystallization (T _cp), polymorphic composition, and crystalline morphology, were probed in detail by calorimetry, X-ray diffraction, and polarized light microscopy. In such mixed nucleating agent system, MWCNTs is active filler to induce α-nucleation for iPP, while WBG serves as β-nucleating agent. When the WBG content was low (0.05%), the crystals of WBG were as a form of individual isotropic dendrite, and the enhancement of T _cp was achieved by the incorporation of MWCNTs. As the WBG content was high as 0.1%, a percolated NA network consisted of needlelike crystals of WBG yielded before nucleating the prevalent crystallization of iPP. In this case, the addition of MWCNTs has no obvious effect on T _cp. However, by varying the mass proportion of MWCNTs/WBG, the polymorphic composition was adjusted significantly, indicating a nucleation competition between MWCNTs and WBG. Although the competitive growth existed between α-crystals nucleated by MWCNTs and β-crystals nucleated by WBG, the formation of primary β-crystallite was always prior to the α-nucleated crystallization, as confirmed by crystalline morphology. These findings are useful for developing a new pathway to prepare iPP-based composite with good mechanical property via the addition of mixed nucleating system containing active inorganic filler and β-nucleating agent.     

DSC and morphological studies on the crystallization behavior of β-nucleated isotactic polypropylene composites filled with Kevlar fibers

The crystallization behavior of β-nucleated isotactic polypropylene (PP) composites filled with Kevlar fibers (KFs), as well as that of non-nucleated PP/KF composites for comparison, was investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The morphological observations revealed that the KF addition could induce thick α-transcrystalline layer around their surfaces in PP/KF composites, while no obvious transcrystalline layer could be detected in β-nucleated PP/KF composites. Detailed DSC investigations suggested that for the PP/KF composites, the dominant modification was α-form, and the crystallization process of matrix was promoted by KF addition, as illustrated by faster isothermal crystallization rate, shorter induction time, and higher crystallization temperature. However, for β-nucleated PP/KF composites, the main modification was β-form, and their crystallization characteristics were independent of KF addition, indicating that the α-nucleating effect of KFs was absent in this system. The DSC results were confirmed by further rheological and wide angle X-ray diffraction (WAXD) studies. The mechanism of the formation of transcrystalline layer was also discussed.     

Combined effect of modified zeolite 13X and β-nucleating agent on improving β-crystal content and toughening polypropylene random copolymer

Although addition of β-NUCLEATING agent directly into homo-polypropylene(PPH) is a useful method to improve β-CRYSTAL content and toughen PPH, polypropylene random copolymer(PPR) makes this method powerless due to its random structure and low crystallinity. In this study, the-nucleated PPR with high β-CRYSTAL content was prepared by a novel high effective β-NUCLEATING system which consists of-nucleation agent(TMB-5) and modified zeolite 13X(M13X). It was found that M13X and TMB-5 had a synergistic influence on improving β-CRYSTAL content and toughening PPR. The content of β-CRYSTAL in PPR/M13X/TMB-5 was significantly larger than the sum of that in PPR/M13X and PPR/TMB-5. Besides,fracture behavior, phase morphology and relaxation of matrix chain segments were also investigated. The results showed that M13X and TMB-5 improved the mobility of amorphous chain segments at low temperature and contributed to much energy dissipation. This work provides a powerful method to modify PPR.     

Effects of polyamide 6 on the crystallization and melting behavior of β-nucleated polypropylene

Non-nucleated polypropylene alloy with polyamide 6 (PP/PA6) and β-nucleated polypropylene (β-PP)/PA6 alloy, as well as its compatibilized version with maleic anhydride grafted PP (PP-g-MA) were prepared with an internal mixer. In the all alloys, PP formed a continuous phase with a dispersive PA6. Effects of PA6 on the non-isothermal crystallization behavior, melting characteristics and the β-PP content of alloys were investigated by differential scanning calorimeter (DSC) and wide angle X-ray diffraction (WAXD). The results indicated that the crystallization temperature () of PP shifts to high temperature in the non-nucleated PP/PA6 alloys due to the α-nucleating effect of PA6. However, in the β-nucleated PP/PA6 alloys, PA6 hardly has an effect on the of PP. The β-PP content in the alloys not only depends on the content of the PA6, but also on the melting temperatures. It is proved by etching the alloys with sulfuric acid that the nucleating agent mainly disperses in the PA6 phase and/or the interface between PP and PA6 when blended at high temperature. Addition of PP-g-MA promotes the formation of β-PP in the β-nucleated PP/PA6 alloys. The increase in the PA6 content has a little influence on the of PP and the β-PP content in the compatibilized β-nucleated PP/PA6 alloys. The non-isothermal crystallization kinetics of PP in the alloys was evaluated by Mo’s method.     

Improved thermal oxidation stability of polypropylene films in the presence of β-nucleating agent

Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.     

Preparation and characteristics of nano-CaCO3 supported β-nucleating agent of polypropylene

In this paper, nano-CaCO₃ supported β-nucleating agent for polypropylene (PP) was prepared by supporting pimelic acid on nano-CaCO₃ with two methods. The thermal properties of pimelic acid and nano-CaCO₃ 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-CaCO₃ was attributed to the chemical reaction between nano-CaCO₃ 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-CaCO₃ supported β-nucleating agent exhibited higher nucleation ability and lower price compared to calcium pimelate β-nucleating agent.     

In situ synchrotron X-ray scattering studies on the temperature dependence of oriented β-crystal growth in isotactic polypropylene

In this work, the growth dependence of oriented β-crystals in isotactic polypropylene (iPP) including their content, orientation and lamellar structures on the thermal treatment temperature (i.e. the final fusion temperature) is first investigated by in situ synchrotron X-ray diffraction/scattering. Interestingly, the dominance of oriented β-crystals is replaced by random α-crystals when the thermal treatment temperature in the range from 155 °C to 170 °C. This phenomenon is closely related to the nucleation efficiency of locally ordered domains of α-crystal and the template effect of residual α-crystals. Locally ordered domains of α-crystal are originated from the melting of β-crystals or (the partial melting of) α-crystals and β-α phase transformation. The orientation degree and lamellar structures of oriented β-crystals vary dramatically only when the thermal treatment temperature far exceeds the melting temperature of α-crystals. Comparably, the heat resistance of oriented β-crystals is stronger than the normal random ones.