Isothermal crystallization behaviors of isotactic polypropylene nucleated with α/β compounding nucleating agents

Sodium 2,2′‐methylene‐bis(4,6‐di‐tert‐butylphenyl) phosphate (NA40) and N,N‐dicyclohexylterephthalamide (NABW) are high effective nucleating agents for inducing the formation of α‐isotactic polypropylene (α‐iPP) and β‐iPP, respectively. The isothermal crystallization kinetics of iPP nucleated with nucleating agents NABW, NA40/NABW (weight ratio of NA40 to NABW is 1:1) and NA40 were investigated by differential scanning calorimetry (DSC) and Avrami equation was adopted to analyze the experimental data. The results show that the addition of NABW, NA40/NABW and NA40 can shorten crystallization half‐time (t_1/2) and increase crystallization rate of iPP greatly. In these three nucleating agents, the α nucleating agent NA40 can shorten t_1/2 of iPP by the largest extent, which indicates that it has the best nucleation effect. While iPP nucleated with NA40/NABW compounding nucleating agents has shorter t_1/2 than iPP nucleated with NABW. The Avrami exponents of iPP and nucleated iPP are close to 3.0, which indicates that the addition of nucleating agents doesn't change the crystallization growth patterns of iPP under isothermal conditions and the crystal growth is heterogeneous three‐dimensional spherulitic growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 590–596, 2007     

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene (iPP) were analyzed. It is found that the crystallization temperatures of nucleated iPP were increased by above 11.0°C and the relative contents of β‐crystals (K_β ) in iPP reached above 0.40 after addition of compound nucleating agents. The K_β values depend on cooling rate, crystallization temperature in isothermal crystallization, and the difference between the crystallization temperatures of iPP nucleated by two individual nucleating agents. The nonisothermal crystallization kinetics were studied by Caze method and Mo method, respectively. The effective activation energy was calculated by the Friedman's method. The results illustrate that the half crystallization time was shortened and the crystallization rate was increased obviously after addition of nucleating agents, and the effective activation energy was increased with the relative crystallinity.     

Non-isothermal crystallization behavior of polypropylene with nucleating agents and nano-calcium carbonate

The non-isothermal crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP was investigated by DSC. The crystalline morphology of iPP was observed by polarized light microscopy. It was found that the crystallization rate increased with the addition of nanometer-scale calcium carbonate (nm-CaCO₃) particles. The addition of dibenzylidene sorbitol (DBS) could greatly reduce the spherulite size of iPP. The crystallization temperature for the iPP with DBS was higher than for non-nucleated iPP. DBS was an effective nucleating agent for iPP. The results of measurements suggested that there was a coordinated action to the crystallization of iPP when the organic nucleating agents (DBS) and nm-CaCO₃ were added to iPP together. Comparison to the modified Avrami equation and Ozawa equation, another method—Mo’s method can describe the non-isothermal crystallization behavior of iPP and nucleated iPP more satisfactorily.     

Study of the crystallization behaviors of isotactic polypropylene with sodium benzoate as a specific versatile nucleating agent

Sodium benzoate (SB), a conventional nucleating agent of α‐phase isotactic polypropylene (iPP) was discovered to induce the creation of β‐phase iPP under certain crystalline conditions. Polarized optical microscopy (POM) and wide angle X‐ray diffraction (WAXD) were carried out to verify the versatile nucleating activity of SB and investigate the influences of SB's content, isothermal crystallization temperature, and crystallization time on the formation of β‐phase iPP. The current experimental results indicated that, under isothermal crystallization conditions, SB showed peculiar nucleating characteristics on inducing iPP crystallization which were different from those of the commercial β form nucleating agent (TMB‐5). The content of β crystal form of iPP nucleated with SB (PP/SB) increased initially with the increase of crystallization temperature, nucleating agent (SB) percentage or crystallization time, reached a maximum value, and then decreased as the crystallization temperature, nucleating agent percentage or crystallization time further increased. While the content of β crystal form of iPP nucleated with TMB‐5 (PP/TMB‐5) showed a completely different changing pattern with the crystallization conditions. The obvious difference of the two kinds of nucleating agents on inducing iPP crystallization can be explained by the versatile nucleating ability of SB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1183–1192, 2008     

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.     

Crystallization and melting behavior of isotactic polypropylene nucleated with individual and compound nucleating agents

In this study, α-phase nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), β-phase rare earth NA (WBG), and their compound NAs were introduced into isotactic polypropylene (iPP) matrix, respectively. Crystallization kinetics and subsequent melting behavior of the nucleated iPPs were comparatively studied by differential scanning calorimetry (DSC) under both isothermal and nonisothermal conditions. For the isothermal crystallization process, it is found that the Avrami model successfully described the crystallization kinetics. The active energy of nonisothermal crystallization of iPP was determined by the Kissinger method and showed that the addition of nucleating agents increased the activation energy. Melting behavior and crystalline structure of the nucleated iPPs are dependent on the nature of NAs and crystallization conditions. Higher proportion of β-phase can be obtained at higher content of β-nucleating agent and lower crystallization temperature or lower cooling rate.     

Specificity and versatility of nucleating agents toward isotactic polypropylene crystal phases

Nucleating agents with an ≈6.5 Å lattice parameter induced the α phase of isotactic polypropylene (iPP, α‐iPP). A 6.5 Å periodicity is also involved in the nucleating agents for the β phase of iPP (β‐iPP). The similarity in substrate periodicities suggests that some nucleating agents may induce either the α or β phase under different crystallization conditions. 4‐Fluorobenzoic acid, dicyclohexylterephthalamide, and γ‐quinacridone (the latter two are known as β‐iPP nucleators) were tested over a wide range of crystallization temperatures [up to crystallization temperature (T_c) > 145 °C]. The two former nucleating agents induce exclusively α‐iPP and β‐iPP, respectively. γ‐Quinacridone on the contrary is a versatile agent with respect to the crystal phase generated. More specifically, the same crystal face of γ‐quinacridone induces either β‐iPP or α‐iPP when T_c is below or above ≈140 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2504–2515, 2002     

Crystallization and melting behaviors of isotactic polypropylene nucleated with compound nucleating agents

Crystallization and melting behaviors of isotactic polypropylene (iPP) nucleated with compound nucleating agents of sodium 2,2′‐methylene‐bis (4,6‐di‐tert‐butylphenyl) phosphate (hereinafter called as NA40)/dicyclohexylterephthalamide (hereinafter called as NABW) (weight ratio of NA40 to NABW is 1:1) were studied by differential scanning calorimetry and wide‐angle X‐ray diffraction (WAXD), the relative β‐amount of iPP nucleated with these compound nucleating agents was also calculated in Turner‐Jones equation by using wide‐angle X‐ray diffraction data. Under isothermal crystallization, there exists a temperature range favorable for formation of β‐iPP. When the concentration of compound nucleating agents is 0.2 wt %, the temperature range is from 100 to 140 °C. While in nonisothermal crystallization, lower cooling rate is favorable for form of β‐iPP and the relative β‐amount of iPP increases with the decreasing of cooling rate in crystallization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 911–916, 2008     

Influence of CaCO<Subscript>3</Subscript> nanoparticles shape on thermal and crystallization behavior of isotactic polypropylene based nanocomposites

Summary The influence of calcium carbonate nanoparticles with different shapes (spherical and elongated) on the thermal properties and crystallization behavior of isotactic polypropylene was investigated. CaCO₃ nanoparticles were covered by an appropriate coating agent to improve the interfacial adhesion between the filler and the polyolefin matrix. The nanocomposites were prepared by melt mixing and subsequent compression molding. A remarkable effect of CaCO₃ on the thermal properties of iPP was observed. Moreover, the analysis of crystallization kinetics showed that CaCO₃ nanopowder coated with PP-MA are efficient nucleating agents for iPP, and the overall crystallization rate results higher than plain iPP.     

The influence of nucleus density on optical properties in nucleated isotactic polypropylene

The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density.     

Effects of β‐nucleating agent and crystallization conditions on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes composites

In this study, the effects of crystallization conditions (cooling rate and end temperature of cooling) on crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes (iPP/MWCNTs) composites nucleated with different concentrations of β‐nucleating agent (tradename TMB‐5) were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and scanning electronic microscopy (SEM). The results of DSC, WAXD and SEM revealed that the addition of MWCNTs and TMB‐5 evidently elevates crystallization temperatures and significantly decreases the crystal sizes of iPP. Because of the competition between α‐nucleation (provided by MWCNTs) and β‐nucleation (induced by TMB‐5), the β‐phase crystallization takes place only when 0.15 wt% and higher concentration of TMB‐5 is added. Non‐isothermal crystallization kinetics study showed that the crystallization activation energy ΔE of β‐nucleated iPP/MWCNTs composites is obviously higher than that of pure iPP, which slightly increases with the increase of TMB‐5 concentration, accompanying with the transition of its polymorphic crystallization behavior. The results of non‐isothermal crystallization and melting behavior suggested that the cooling rate and end temperature of cooling (T_end) are important factors in determining the proportion and thermal stability of β‐phase: Lower cooling rate favors the formation of less amount of β‐phase with higher thermal stability, while higher cooling rate encourages the formation of higher proportion of β‐phase with lower thermal stability. The T_end = 100°C can eliminate the β–α recrystallization during the subsequent heating and therefore enhance the thermal stability of the β‐phase. By properly selecting TMB‐5 concentration, cooling rate and T_end, high β‐phase proportion of 88.9% of the sample was obtained. Copyright © 2014 John Wiley & Sons, Ltd.     

Isothermal crystallization kinetics of polypropylene latex–based nanocomposites with organo‐modified clay

The effect of organo‐modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X‐ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X‐ray diffraction results indicated that the higher clay loading promotes the formation of the β‐phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β‐iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σ_e) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σ_e during the isothermal crystallization of the nanocomposites. The activation energy, ΔE_a, decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010     

Crystallization kinetics study of poly(L‐lactic acid)/carbon nanotubes nanocomposites

Effects of carbon nanotubes (CNT) on the isothermal crystallization kinetics of poly(L ‐lactic acid) (PLLA) were quantitatively investigated using the Avrami equation and the secondary nucleation theory of Lauritzen and Hoffman. CNT via grafting modification with PLLA could well disperse in the PLLA matrix and give significantly enhanced crystallization rate and crystallinity of PLLA as analyzed by differential scanning calorimetry and polarized optical microscopy. Analysis of isothermal crystallization kinetics using the Avrami equation demonstrated that CNT significantly enhanced the bulk crystallization of PLLA. Analysis of spherulite growth kinetics using the secondary nucleation theory of Lauritzen and Hoffman found that CNT could expand the temperature range of the crystallization regime III of PLLA. Values of the nucleation constant (K_g) in crystallization regimes III and II of PLLA both increased with increasing CNT contents. The K_g III/K_g II ratios were found to be close to the theoretical value 2 but were not clearly found to depend on the CNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 983–989, 2010     

Nucleating Agents in Polypropylene

The effects of nucleating agents such as dibenzylidene sorbitol (DBS) (a derivative of sorbitol), pine crystal 1500, sodium and potassium benzoates in commercial grade isotactic polypropylene iPP are studied using differential scanning calorimetry (DSC). Isothermal crystallization kinetics of polypropylene to the alpha phase have been analyzed using Avrami's model. Results indicate that dibenzylidene sorbitol and pine crystal are very effective in increasing the crystallization temperature of the polymer and number of nuclei formed during crystallization.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nucleation ability of multiwall carbon nanotubes in polypropylene composites

The nonisothermal crystallization of multiwall carbon nanotube (MWNT)/isotactic polypropylene (iPP) nanocomposites was investigated. The results derived from the differential scanning calorimetry curves (onset temperature, melting point, supercooling, peak temperature, half‐time of crystallization, and enthalpy of crystallization) were compared with those of neat iPP. The data were also processed according to Ozawa's theory and Dobreva's approach. These results and X‐ray diffraction data showed that the MWNTs acted as α‐nucleating agents in iPP. Accordingly, MWNT/iPP was significantly different from neat iPP: A fibrillar morphology was observed instead of the usual spherulites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 520–527, 2003     

Crystallization kinetics of isotactic polypropylene nucleated with octamethylenedicarboxylic dibenzoylhydrazide under isothermal and non-isothermal conditions

Octamethylenedicarboxylic dibenzoylhydrazide (TMC-300) was used as a nucleating agent for isotactic polypropylene (iPP) for the first time. The Avrami method and the Caze method were used to analyze the isothermal and non-isothermal crystallization kinetics of iPP incorporated with TMC-300, respectively. During isothermal crystallization, the half crystallization time at 130 °C reduces from 130 s of virgin iPP to 44 s after addition of TMC-300, which reflects that TMC-300 increased the crystallization rate of iPP obviously. The crystallization activation energy decreases from 382.5 kJ mol^?1 of virgin iPP to 275.3 kJ mol^?1 of iPP/TMC-300. During non-isothermal crystallization, the crystallization peak temperature of iPP nucleated with TMC-300 was increased by 5.1 °C when compared to that of virgin iPP at the cooling rate of 20 °C min^?1, and both the reduction of half crystallization time and the increase in peak crystallization temperature also justified that the addition of TMC-300 accelerated the crystallization of iPP.

     

Application of dsc to study crystallization kinetics of polypropylene containing fillers

The present work is concerned with the comparison of nucleating efficiency of various organic and inorganic fillers of isotactic polypropylene: talc, chalk, wood flour, nano clay particles, carbon black, chitosan in the form of powder of the same content equal to 5 mass%. The kinetics of isothermal crystallization of isotactic polypropylene in the composite systems was evaluated by using DSC. Avrami equation was applied to the results. Calculated K and n parameters depend on filler applied. The σσ_e surface free energies were also found. The best nucleating agent found here was talc and carbon black. The organic filler as a chitosan powder forms amorphous inclusions in the composites on which IPP molecules cannot be adsorbed. Their presence disturbs a macromolecular diffusion and delays crystallization process of IPP. This revised version was published online in July 2006 with corrections to the Cover Date.     

In situ Polymerization of Nanocomposites by TpTiCl2(Et) System: UHMWPE Filled with Carbon Nanotubes

Summary: Nanocomposites of ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNT) were obtained by in situ polymerization of ethylene by TpTiCl₂Et. This novel catalytic complex activated with polymethylaluminoxane (P-MAO) (Al:Ti = 200) allowed to incorporate the CNT at different compositions (0,1-1 w/w %) into the UHMWPE matrix. The filler addition produced an important enhancement of the catalytic activity when it was compared to that of homogeneous ethylene polymerization carried out under the same experimental conditions (30 min; 1bar; 25 °C). This fact was attributed to in situ support of TpTiCl₂Et onto the CNT surface, which not only could induce the stabilization of the catalytic system but also allowed the growing of polymeric chains around the CNT structures. The characterization of these nanocomposites was carried out by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Thermal analysis showed that the incorporation of CNT (at the tested concentrations) did not produce changes in the polymer thermal stability, as revealed by the initial degradation temperature values. However, the CNT produced a nucleating effect in the crystallization of UHMWPE as observed by DSC, independently of the filler content. The crystallization temperature of the obtained nanocomposites increased and the crystallinity degree slightly increased as well.     

Nucleation activity of nanosized CaCO3 on crystallization of isotactic polypropylene, in dependence on crystal modification, particle shape, and coating

A detailed analysis of the effect of calcium carbonate nanoparticles on crystallization of isotactic polypropylene (iPP) is reported in this contribution. CaCO₃ nanoparticles with different crystal modifications (calcite and aragonite) and particle shape were added in small percentages to iPP. The nanoparticles were coated with two types of compatibilizer (either polypropylene-g-maleic anhydride copolymer, or fatty acids) to improve dispersion and adhesion with the polymer matrix.It was found that the type of coating agent used largely affects the nucleating ability of calcium carbonate towards formation of polypropylene crystals. CaCO₃ nanoparticles coated with maleated polypropylene can successfully promote nucleation of iPP crystals, whereas the addition of nanosized calcium carbonate coated with fatty acids delays crystallization of iPP, the effect being mainly ascribed to the physical state of the coating in the investigated temperature range for crystallization of iPP, as well as to possible dissolution by fatty acids of heterogeneities originally present in the polypropylene matrix.     

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.