Crystallization behavior and morphological development of isotactic polypropylene with an aryl amide derivative as β‐form nucleating agent

This article reports crystallization behaviors of isotactic polypropylene (iPP) with an aryl amide derivative (TMB‐5) as β‐form nucleating agent. The effects of nucleating agent concentration, thermal history and assemble morphology of nucleating agent on the crystallization behaviors of iPP were studied by differential scanning calorimetry, X‐ray diffraction, and polarized optical microscopy. The results indicated that the TMB‐5 concentration should surpass a threshold value to get products rich in β‐iPP. The diverse morphologies of TMB‐5 are determined by nucleating agent concentration and crystallization condition. At higher concentrations, the recrystallized TMB‐5 aggregates into needle‐like structure, which induces mixed polymorphic phases on the lateral surface and large amount of β modification around the tip. High β nucleation efficiency was obtained at the lowest studied crystallization temperature, which is desirable for real molding process. TMB‐5 prefers to recrystallize from the melt at higher concentration and lower crystallization temperature. The difference in solubility, pertinent to concentration and crystallization temperature, determined the distinct crystallization behaviors of iPP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1725–1733, 2008     

Crystallization behavior of polypropylene with or without sodium benzoate as a nucleating agent

The crystallization kinetics of polypropylene (PP) with or without sodium benzoate as a nucleating agent were investigated by means of DSC and polarized optical microscopy in isothermal and nonisothermal modes. A modified Avrami equation was applied to the kinetic analysis of isothermal crystallization. The addition of the nucleating agent up to its saturation concentration increased the crystallization temperature by 15 °C and shortened both the isothermal and nonisothermal crystallization half‐times. It was concluded that the sodium benzoate acted as a good nucleating agent for α‐form PP. By adding the nuclefier to PP, adequately controlled spherulites increased the mechanical properties including especially the Izod impact strength and shortened cycle time of PP. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1001–1016, 2001     

Effect of a sorbitol nucleating agent on fractionated crystallization of polypropylene droplets

The effect of a sorbitol nucleating agent on crystallization of polypropylene (PP) in droplets was studied. Layer‐multiplying coextrusion was used to fabricate assemblies of 257 layers, in which PP nanolayers alternated with thicker polystyrene (PS) layers. The concentration of a commercial nucleating agent, Millad 3988 (MD) in the layers was varied up to 2 wt %. When the assembly was heated into the melt, interfacial driven breakup of the 12 nm PP layers produced a dispersion of submicron PP particles in a PS matrix. Analysis of optical microscope images and atomic force microscope images indicated that the particle size was not affected by the presence of MD. The crystallization behavior of the particle dispersion was characterized by thermal analysis. In the absence of a nucleating agent, the submicron particles crystallized almost exclusively by homogeneous nucleation at about 40 °C. Addition of a nucleating agent to the PP layers offered a unique opportunity to study the nature of heterogeneous nucleation. Nucleation by MD resulted in fractionated crystallization of the submicron PP particles. The concentration dependence of the multiple crystallization exotherms was interpreted in terms of the binary polypropylene‐sorbitol phase diagram. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1788–1797, 2007     

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     

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     

Effect of nucleating agent supported on zeolite via the impregnation on the crystallization ability of isotactic polypropylene and its mechanism

Addition of an α‐nucleating agent is the simple and effective method to increase nucleation efficiency of isotactic polypropylene (iPP). However, severe agglomeration and poor dispersibility of sodium 2,2′‐methylene‐bis(4,6‐di‐tertbutylphenyl) phosphate (NA11) decrease the nucleation efficiency in the iPP, and much more nucleating agent is needed to maintain the nucleating property. As a result, it becomes the key how to decrease the size of NA11 and increase the nucleating property. In this paper, zeolite 4A (Z4A) was firstly supported by NA11 through solution impregnation, and NA11 was dispersed by Z4A depending on the dispersion of zeolite as carrier for the second component. Then, the dispersed NA11 system (NA11‐Z4A) exhibited a superior nucleation behavior during the crystallization of the iPP matrix when it was used with iPP together. The isothermal and nonisothermal crystallization kinetics indicated that the NA11‐Z4A/iPP system had the best crystallization effect. Polarized optical microscopy (POM) and scanning electron microscopy (SEM) analyses showed that the size of NA11 decreased obviously when it was adsorbed on the surface of Z4A, which leads a better dispersibility of the nucleating agent and thus an accelerated nucleation process in the iPP matrix. In the end, the mechanism for the excellent dispersibility of NA11‐Z4A, which was based on hydrogen bonding between NA11 and Z4A, was confirmed by Fourier‐transform infrared spectroscopy (FTIR). Based on the research work, the solution impregnation strategy can potentially be applied to other systems to inhibit the agglomeration and improve the dispersibility of additives in iPP.     

Morphology, crystallization behavior and properties of impact-modified polypropylene copolymer with or without sodium benzoate as a nucleating agent

 The morphology, crystallization behavior, and properties of an impact-modified polypropylene (PP) copolymer with or without sodium benzoate were investigated. The contents of ethylene–propylene rubber (EPR) in the reactor-made PP copolymer is about 15 wt%. For comparison, blends of PP and EPR containing the same EPR composition were prepared by melt-mixing. Morphological studies by scanning probe microscopy indicated that the impact-modified copolymer consists of three different phases, i.e., polyethylene, PP, and EPR phases, which is considerably different from the morphology of the conventional PP/EPR blend of the corresponding composition. The impact-modified PP copolymer exhibited a higher crystallization rate in terms of the lower crystallization half-time and thus higher thermal and mechanical properties, such as impact strength and hardness, than the PP/EPR blend did. The addition of sodium benzoate as a nucleating agent to the copolymer increased the crystallization rate and the mechanical properties. Received: 4 June 2001 Accepted: 31 October 2001     

Study of the assembled morphology of aryl amide derivative and its influence on the nonisothermal crystallizations of isotactic polypropylene

The nonisothermal crystallization behaviors of isotactic polypropylene (iPP) with an aryl amide derivative TMB‐5 as β‐form nucleating agent has been investigated by differential scanning calorimetry, X‐ray diffraction, and polarized optical microscopy. The feature of crystallite morphology depends on concentration and thermal conditions. At low concentrations, TMB‐5 molecules aggregate into fibril structures and presented blunt exothermic peak with a shoulder at high temperature. The surface of these fibrils host active sites tailored for the nucleation of β‐iPP, represented by clusters of microcrystallites. With increasing concentration, αβ‐transcrystalline layer develops on the lateral surface of needle‐shaped TMB‐5. Enhanced multiple endotherms indicate the ensuing crystals are less perfect and easily transformed into more stable forms. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 314–325, 2009     

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.     

Crystallization and melting of isotactic polypropylene crystallized from quiescent melt and stress‐induced localized melt

Temperature dependency of crystalline lamellar thickness during crystallization and subsequent melting in isotactic polypropylene crystallized from both quiescent molten state and stress‐induced localized melt was investigated using small angle X‐ray scattering technique. Both cases yield well‐defined crystallization lines where inverse lamellar thickness is linearly dependent on crystallization temperature with the stretching‐induced crystallization line shifted slightly to smaller thickness direction than the isothermal crystallization one indicating both crystallization processes being mediated a mesomorphic phase. However, crystallites obtained via different routes (quiescent melt or stress‐induced localized melt) show different melting behaviors. The one from isothermal crystallization melted directly without significant changing in lamellar thickness yielding well‐defined melting line whereas stress‐induced crystallites followed a recrystallization line. Such results can be associated with the different extent of stabilization of crystallites obtained through different crystallization routes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 957–963     

Effect of poly(vinyl alcohol) fine particles as a novel biodegradable nucleating agent on the crystallization of poly(3‐hydroxybutyrate)

The effect of poly(vinyl alcohol)(PVA) fine particles as the nucleating agent on the crystallization behavior of bacterial poly(3‐hydroxybutyrate)(PHB) was studied using differential scanning calorimetry measurements and polarized light microscope observation. The results were compared with the effect of PVA conventionally blended with PHB. The PVA fine particles were found to be able to greatly enhance the crystallization of PHB, while the conventionally blended PVA extremely retarded the crystallization of PHB. The nucleating effect of PVA fine particles is almost comparable to that of the talc powder. Considering the biodegradability and biocompatibility of PVA, the usage of PVA particle as a nucleating agent provides marked benefits over the currently employed nonbiodegradable nucleating agents, such as talc and boron nitride. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:1813–1820, 2006     

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

In this study, memory effect of mesomorphic isotactic polypropylene (iPP) was investigated using polarized optical microscope and small‐angle X‐ray scattering. Differing from classical memory effect, mesomorphic iPP melt had a higher growth rate and a higher memory temperature. The relative growth rate increased with increasing crystallization temperature. Lauritzen–Hoffman plots indicated that the increased growth rate arose from reduced surface nucleation barrier. The highest memory temperature was estimated to be 185 °C, which was close to the equilibrium melting point of iPP crystal. Additionally, Small‐angle X‐ray scattering measurements showed that a liquid crystal layer might exist between lamellar and amorphous layers. Based on above results, a crystallization model was proposed. In the mesomorphic iPP melt, there exist aggregates structurally similar to β phase except α‐phase crystal residuals, which cannot act as nucleation sites or transform to β crystal through surface nucleation. The only way for the aggregate is to transform to α crystal during crystal growth. The aggregate decreases the surface nucleation barrier and promotes the helical growth, leading to higher growth rate. Only when the aggregate relaxes to polymer coils through thickening at a higher temperature, can the memory effect be erased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1573–1580     

Simultaneous wide‐angle X‐ray diffraction and differential scanning calorimetry analysis of the melting and recrystallization behavior of polyethylene and isotactic polypropylene containing cyclopentane units in the main chain

The melting and crystallization behavior of polyethylene and isotactic polypropylene containing 1,2‐ or 1,3‐disubstituted cyclopentane units in the main chain has been studied with simultaneous wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. For the ethylene‐based copolymers, the position of a reflection peak in the WAXD patterns shifts to a low angle with the increasing acquired temperature. The temperature dependence on the axial length of the crystal lattice is more marked in the copolymers forming orthorhombic crystals (containing 1,2‐cyclopentane or 5.6 mol % 1,3‐cyclopentane units) than in those forming hexagonal crystals (containing 8.1 mol % 1,3‐cyclopentane units). For the isotactic propylene‐based copolymers, the position of the reflection peaks in the WAXD patterns is independent of the acquired temperature. The proportion of the γ form in the copolymer containing the 1,2‐cyclopentane units is higher than that in the copolymers containing the 1,3‐cyclopentane units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1457–1465, 2004     

Changes in the melting behavior with the radial distance in isotactic polypropylene spherulites

The melting of highly tactic i‐polypropylene occurs in two stages even for crystallization at 145 °C, a temperature at which reorganization during scanning is negligible. A comparison of two such polypropylenes, one nucleated and the other not nucleated, together with fractions from the latter, has been made with electron microscopy following permanganic etching, in addition to differential scanning calorimetry. This has allowed the two melting stages to be assigned to two components of the lamellar morphology, with progressive changes in both occurring with increasing radial distance within a spherulite. The highest melting temperature is for dominant radial lamellae far from a spherulite center. The lowest melting regions are the evenly crosshatched spherulite centers and a narrow peripheral band. Lower melting is attributed to the suppression of isothermal lamellar thickening paralleling recent direct demonstrations in polyethylene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2342–2354, 2003     

Structure and morphology development in syndiotactic polypropylene during isothermal crystallization and subsequent melting

Structure and morphology development during the isothermal crystallization and subsequent melting of syndiotactic polypropylene (sPP) was studied with differential scanning calorimetry (DSC), time‐resolved simultaneous small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray diffraction (WAXD) methods with synchrotron radiation. The morphology of sPP isothermally crystallized at 100 °C for 3 h was also characterized with transmission electron microscopy (TEM). Time‐ and temperature‐dependent parameters such as the long period (L), crystal lamellar thickness (l_c), amorphous layer thickness (l_a), scattering invariant (Q), crystallinity (X_c), lateral crystal sizes (L₂₀₀ and L₀₁₀), and unit cell dimensions (a and b) were extracted from the SAXS and WAXD data. Results indicate that the decreases in L and l_c with time are probably due to the formation of thinner crystal lamellae, and the decreases in a and b are due to crystal perfection. The changes in the morphological parameters (Q, X_c, L, and l_c) during subsequent melting exhibited a two‐stage process that was consistent with the multiple melting peaks observed in DSC. The two high‐temperature peaks can be attributed to the melting of primary lamellae (at lower temperatures) and recrystallized lamellae (at higher temperatures). An additional minor peak, located at the lowest temperature, was also visible and was related to the melting of thin and defective secondary lamellae. TEM results are consistent with the SAXS data, which supports the assignment of the larger value (l₁) from the correlation function analysis as l_c. WAXD showed that the thermal expansion was greater along the b axis than the a axis during melting. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2982–2995, 2001     

Rheooptical Fourier transform infrared spectroscopy of the deformation behavior in quenched and slow‐cooled isotactic polypropylene films

Emerging technological applications for complex polymers require insight into the dynamics of these materials from a molecular and nanostructural viewpoint. To characterize the orientational response at these length scales, we developed a versatile rheooptical Fourier transform infrared (FTIR) spectrometer by combining rheometry, polarimetry, and FTIR spectroscopy. This instrument is capable of measuring linear infrared dichroism spectra during both small‐strain dynamic deformation and large‐strain irreversible deformation over a wide temperature range. The deformation response of quenched and slow‐cooled isotactic polypropylene (iPP) is investigated. In quenched iPP, under dynamic oscillatory strain at an amplitude of ～0.1%, the dichroism from the orientation of the amorphous chains is appreciably less than that from the crystalline region. At large irreversible strains, we measured the dichroic response for 12 different peaks simultaneously and quantitatively. The dichroism from the crystalline peaks is strong as compared to amorphous peaks. In the quenched sample, the dichroism from the crystalline region saturates at 50% strain, followed by a significant increase in the amorphous region dichroism. This is consistent with the notion that the crystalline regions respond strongly before the yield point, whereas the majority of postyielding orientation occurs in the amorphous region. Our results also suggest that the 841 cm^?1 peak may be especially sensitive to the ‘smectic’ region orientation in the quenched sample. The response of the slow‐cooled sample at 70 °C is qualitatively similar but characterized by a stronger crystalline region dichroism and a weaker amorphous region dichroism, consistent with the higher crystallinity of this sample, and faster chain relaxation at 70 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2539–2551, 2002     

Phenomenological approach to compare the crystallization kinetics of isotactic polypropylene and polyamide‐6 under pressure

Reliable experimental data for semicrystalline polymers crystallized under pressure are supplied on the basis of a model experiment in which drastic solidification conditions are applied. The influence of the pressure and cooling rate on some properties, such as the density and microhardness, and on the product morphology, as investigated with wide‐angle X‐ray scattering (WAXS), is stressed. Results for isotactic polypropylene (iPP) samples display a lower density and a lower microhardness with increasing pressure over a wide range of cooling rates (from 0.01 to 20 °C/s). Polyamide‐6 (PA6) samples exhibit the opposite behavior, with the density and microhardness increasing at higher pressures over the entire range of cooling rates investigated (from 1 to 200 °C/s). A deconvolution technique applied to iPP and PA6 WAXS patterns has allowed us to evaluate the final phase content and to assess the crystallization kinetics. A negative influence of pressure on the α‐crystalline phase crystallization kinetics can be observed for iPP, whereas a slightly positive influence of pressure on the crystallization kinetics of PA6 can be noted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 153–175, 2002     

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Isotactic polypropylene reversible crystallization investigated by modulated temperature and quasi‐isothermal FTIR

Modulated temperature techniques allow to separate the reversing and non‐reversing contributions of material transitions. To investigate reversible crystallization and melting of isotactic polypropylene (iPP) at microstructural level, in this research, modulated temperature Fourier transform infrared (MTFTIR) and quasi‐isothermal FTIR (QIFTIR) analyses are used. By following the intensity variation of iPP regularity bands, associated with 3₁ helix structures of different lengths (n repeating units), MTFTIR evidences that, independently from helix length, a reversing coil–helix transition takes place few degrees below the non‐reversing crystallization onset. By comparing spectroscopic and differential scanning calorimetry experiments performed in quasi‐isothermal conditions, the reversing transition was found to be associated with the reversible melting‐crystallization phenomenon. Moreover, QIFTIR evidences that helices of different lengths contribute differently to the reversible transition: the helices composed of n = 10 and n = 12 are active into all the explored temperature range (30–130 °C) whereas the shortest (n = 6) and the longest (n > 15) helices contribute to reversibility at T > 100 °C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 922–931     

Influence of the graphite type on the synthesis of polypropylene/graphene nanocomposites

In this work, the synthesis of polypropylene (PP)/graphene nanosheet (GNS) nanocomposites by in situ polymerization using metallocene catalysts was studied. Initial reactions were performed using rac‐Et(Ind)₂ZrCl₂ and rac‐Me₂Si(Ind)₂ZrCl₂ catalysts to select the best one to obtain good molecular weight, thermal properties, and tacticity. Subsequently, PP nanocomposites with different loadings of GNS were obtained. GNS from two different sources [Graphite Nacional (GN) and Graphite Aldrich (GA)] have been used, and the differences between the obtained nanocomposites were evaluated. The GNS and nanocomposites were studied by scanning electronic microcopy, transmission electronic microcopy, and X‐ray diffraction. They showed that the GN nanosheets had lower crystal size and diameter than the GA nanosheets and dispersed better in the PP matrix. Differential scanning calorimetry analyses of both types of nanocomposites showed an increase in the crystallization temperature with increasing graphite loading. The polymeric materials were also characterized by GPC, thermogravimetric analysis, and ¹³C NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012