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     

Crystallization of poly(butylene adipate) in the presence of nucleating agents

The effect of nucleating agents on the polymorphic crystallization behavior of poly(butylene adipate) (PBA) was studied with four kinds of commercially available nucleating agents, such as talc and boron nitride. The crystal structures of the α and β forms were studied with wide‐angle X‐ray diffraction. The β‐to‐α‐crystal transformation of PBA in the absence and presence of the nucleating agents in isothermal crystallization and nonisothermal crystallization processes was studied with differential scanning calorimetry and polarized optical microscopy. In both isothermal and nonisothermal crystallization, the introduction of nucleating agents selectively initiated the nucleation of the α‐form crystal, which was relatively slow in the absence of nucleating agents. The nucleating activity of the four kinds of nucleating agents in the crystallization of the PBA α‐form crystal was determined by the study of the nonisothermal crystallization, spherulite morphology, and isothermal kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2340–2351, 2005     

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     

Crystallization,melting behavior,and morphology of PP/Novolac blends

The crystallization, melting behavior, and morphology of Polypropylene (PP) and PP/Novolac blends were studied by scanning electron microscopy, wide angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscope. The results showed that the crystallization of PP in PP/Novolac blends was strongly influenced by crystallization temperature, particles size of Novolac, crosslinking, and compatibilizer maleic anhydride‐grafted PP. The Novolac resin could not only affect the crystal structure, but also acted as effective nucleating agents, accelerating the crystallization of PP in the PP/Novolac blends. And the smaller the Novolac particles were, the more effective were the nucleating agent for PP crystallization. Avrami equation was used to analyze the isothermal crystallization kinetics of PP and PP/Novolac blends. The influences of curing and compatibilizer on the crystallization behavior of PP were rather complicated. The crystallization thermodynamics were estimated using the Hoffman theory. The incorporation of cured Novolac and compatibilizer evidently decreased the chain folding energy of PP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3288–3303, 2006     

Crystallization behavior of dynamically cured polypropylene/epoxy blends

Dynamically cured polypropylene (PP)/epoxy blends compatibilized with maleic anhydride grafted PP were prepared by the curing of an epoxy resin during melt mixing with molten PP. The morphology and crystallization behavior of dynamically cured PP/epoxy blends were studied with scanning electron microscopy, differential scanning calorimetry, and polarized optical microscopy. Dynamically cured PP/epoxy blends, with the structure of epoxy particles finely dispersed in the PP matrix, were obtained, and the average diameter of the particles slightly increased with increasing epoxy resin content. In a study of the nonisothermal crystallization of PP and PP/epoxy blends, crystallization parameter analysis showed that epoxy particles could act as effective nucleating agents, accelerating the crystallization of the PP component in the PP/epoxy blends. The isothermal crystallization kinetics of PP and dynamically cured PP/epoxy blends were described by the Avrami equation. The results showed that the Avrami exponent of PP in the blends was higher than that of PP, and the crystallization rate was faster than that of PP. However, the crystallization rate decreased when the epoxy resin content was greater than 20 wt %. The crystallization thermodynamics of PP and dynamically cured PP/epoxy blends were studied according to the Hoffman theory. The chain folding energy for PP crystallization in dynamically cured PP/epoxy blends decreased with increasing epoxy resin content, and the minimum of the chain folding energy was observed at a 20 wt % epoxy resin content. The size of the PP spherulites in the blends was obviously smaller than that of PP. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1181–1191, 2004     

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     

Nucleation,Crystallization, and Thermal Fractionation of Poly (ε‐Caprolactone)‐Grafted‐Lignin: Effects of Grafted Chains Length and Lignin Content

Poly(ε‐caprolactone)‐grafted‐lignin (PCL‐g‐lignin) copolymers with 2 to 37 wt % lignin are employed to study the effect of lignin on the morphology, nucleation, and crystallization kinetics of PCL. Lignin displays a nucleating action on PCL chains originating an intersecting lamellar morphology. Lignin is an excellent nucleating agent for PCL at low contents (2–5 wt %) with nucleation efficiency values that are close to or >100%. This nucleating effect increases the crystallization and melting temperature of PCL under nonisothermal conditions and accelerates the overall isothermal crystallization rate of PCL. At lignin contents >18 wt %, antinucleation effects appear, that decrease crystallization and melting temperatures, reduce crystallinity degree, hinder annealing during thermal fractionation and significantly retard isothermal crystallization kinetics. The results can be explained by a competition between nucleating effects and intermolecular interactions caused by hydrogen bonding between PCL and lignin building blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1736–1750     

Carbon nanoparticles as effective nucleating agents for polypropylene

The effect of four nucleating agents on the crystallization of isotactic polypropylene (iPP) was studied by differential scanning calorimetry (DSC) under isothermal and non-isothermal conditions. The nucleating agents are: carbon nanofibers (CNF), carbon nanotubes (CNT), lithium benzoate and dimethyl-benzylidene sorbitol. Avrami?s model is used to analyze the isothermal crystallization kinetics of iPP. Based on the increase in crystallization temperature (T _c) and the decrease in half-life time (τ_½) for crystallization, the most efficient nucleating agents are the CNF and CNT, at concentrations as low as 0.001 mass%. Sorbitol and lithium benzoate show to be less efficient, while the sorbitol needs to be present at concentrations above 0.05 mass% to even act as nucleating agent.     

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 kinetics of polypropylene/POSS composites

Polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) composites were prepared by two different processing methods: reactive blending and physical blending, and the crystallization behavior of PP and PP/POSS composites was studied by means of differential scanning calorimetry and polarized optical microscope. The results showed that the crystallization of PP in PP/POSS composites was strongly influenced by the different processing methods. POSS particles can act as effective nucleating agent, accelerating the crystallization of PP. The crystallization rate increased more dramatically for the reactive blending composite due to the stronger nucleating effect of PP grafted POSS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1762–1772, 2008     

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.     

Nonisothermal crystallization kinetics of polypropylene/montmorillonite nanocomposites

The nonisothermal crystallization kinetics of poly(propylene) (PP) and poly(propylene)/organic‐montmorillonite (PP/Mont) nanocomposite were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by previous research was used to describe the nonisothermal crystallization process of PP and PP/Mont nanocomposite very well. The values of half‐time and Z_c showed that the crystallization rate increased with increasing cooling rates for both PP and PP/Mont nanocomposite, but the crystallization rate of PP/Mont nanocomposite was faster than that of PP at a given cooling rate. The activation energies were estimated by the Kissinger method, and the values were 189.4 and 155.7 kJ/mol for PP and PP/Mont nanocomposite, respectively. PP/Mont nanocomposite could be easily fabricated as original PP, although the addition of organomontmorillonite might accelerate the overall nonisothermal crystallization process. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 408–414, 2002; DOI 10.1002/polb.10101     

Synergistic effects of PEG and MWCNTs on crystallization behavior of PLLA

This work reported the crystallization behaviors of poly(L ‐lactide) (PLLA) with the presence of polyethylene glycol (PEG) and/or functionalized multiwalled carbon nanotubes (FMWCNTs). The crystallization behaviors occurred in the different conditions, including nonisothermal, isothermal and during the annealing process, were analyzed comparatively using differential scanning calorimetry, wide angle X‐ray diffraction, and polarized optical microscope. The results show that PEG as an efficient plasticizer of PLLA enhances the mobility of PLLA chain segments, which leads to the decrease of glass transition temperature and the enhancement of crystallization ability of PLLA. FMWCNTs as a nucleating agent of PLLA crystallization promote the crystallization of PLLA apparently. With the presence of PEG and FMWCNTs, the crystallization of PLLA is well improved in all conditions, indicating the synergistic effects of PEG and FMWCNTs on PLLA crystallization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 520–528, 2010     

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.     

Enhanced crystallization rate of biodegradable poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) by cyanuric acid as an efficient nucleating agent

The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(ε-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.     

Nonisothermal crystallization behaviors of polypropylene with α/β nucleating agents

In this work, the nonisothermal crystallization and subsequent melting behaviors of polypropylene (PP) nucleated with different nucleating agents (NAs) have been studied. α‐phase NA 1,3:2,4‐bis (3,4‐dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), β‐phase NA aryl amides compound (TMB‐5), and their compounds were introduced into PP matrix, respectively. The results show that the nonisothermal crystallization behaviors and crystalline structures of PP with compounded NAs are dependent on the composition of NAs. In the sample of PP with 0.1 wt % DMDBS and 0.1 wt % TMB‐5, the nucleation efficiency (NE) of TMB‐5 is much higher than that of DMDBS and PP crystallizes mainly nucleated by TMB‐5, and in this condition, β‐phase PP is the main crystallization structure. For the sample of PP with 0.2 wt % DMDBS and 0.2 wt % TMB‐5, 0.2 wt % DMDBS has higher NE than 0.2 wt % TMB5, and α‐phase is the main crystalline structure. The cooling rate is proved to be very important in controlling the nonisothermal crystallization behavior and the final crystalline structure of nucleated PP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1853–1867, 2008     

成核剂和促进剂对聚对苯二甲酸乙二酯结晶的影响

研究了一种成核剂和结晶促进剂及其混合物对聚对苯二甲酸乙二酯（ＰＥＴ）结晶过程和熔融行为的影响．结果表明,成核剂的引入降低了ＰＥＴ的结晶成核界面自由能,起到促进ＰＥＴ结晶成核的作用,从而加快了ＰＥＴ的结晶速度．而结晶促进剂对ＰＥＴ的结晶速度影响很小,不能促进ＰＥＴ的成核结晶,但能使ＰＥＴ结晶更完善,使ＰＥＴ的结晶度提高．当两者并用时,ＰＥＴ由熔体降温的结晶行为主要由成核剂控制,而成核促进剂的作用不明显．     

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 and crystalline morphology of poly(ε-caprolactone) in blends with grafted rubber particles

The crystallization behavior of pure PCL and PCL in blends with crosslinked rubber particles was studied under (non)isothermal crystallization conditions, where the rubber particles were grafted with PCL chains via hydrogen abstraction of the aliphatic moieties in PCL. The crystal growth and the organization of crystals into spherulitic superstructures are significantly influenced by the presence of the grafted rubber particles, which act as an excellent nucleating agent for PCL. The nucleating efficiency shows an exponential dependency on the PCL grafting density and, according to an Avrami analysis, an increased PCL grafting density increases the overall crystallization rate of the PCL matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1438–1448, 2010     

Effect of carbon nanotubes on the crystallization and properties of polypropylene

The effect of different concentrations of single‐walled carbon nanotubes (SWNTs) on the nonisothermal crystallization kinetics, morphology, and mechanical properties of polypropylene (PP) matrix composites obtained by melt compounding was investigated by means of X‐ray diffraction, differential scanning calorimetry, optical and scanning electron microscopy, and dynamic mechanical thermal analysis. Microscopy showed well‐dispersed nanotube ropes together with small and large aggregates. The modulus was found to increase by about 75% at a level of 0.5 wt % nanotubes. The SWNTs displayed a clear nucleating effect on the PP crystallization, favoring the α crystalline form rather than the β form. The crystallization kinetics analysis showed a significant increase in activation energy on incorporating nanotubes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2445–2453, 2005