Nonisothermal crystallization and melting behavior of β‐nucleated isotactic polypropylene and polyamide 66 blends

A highly novel nano‐CaCO₃ supported β‐nucleating agent was employed to prepare β‐nucleated isotactic polypropylene (iPP) blend with polyamide (PA) 66, β‐nucleated iPP/PA66 blend, as well as its compatibilized version with maleic anhydride grafted PP (PP‐g‐MA), maleic anhydride grafted polyethylene‐octene (POE‐g‐MA), and polyethylene‐vinyl acetate (EVA‐g‐MA), respectively. Nonisothermal crystallization behavior and melting characteristics of β‐nucleated iPP and its blends were investigated by differential scanning calorimeter and wide angle X‐ray diffraction. Experimental results indicated that the crystallization temperature (T) of PP shifts to high temperature in the non‐nucleated PP/PA66 blends because of the α‐nucleating effect of PA66. T of PP and the β‐crystal content (K_β) in β‐nucleated iPP/PA66 blends not only depended on the PA66 content, but also on the compatibilizer type. Addition of PP‐g‐MA and POE‐g‐MA into β‐nucleated iPP/PA66 blends increased the β‐crystal content; however, EVA‐g‐MA is not benefit for the formation of β‐crystal in the compatibilized β‐nucleated iPP/PA66 blend. It can be relative to the different interfacial interactions between PP and compatibilizers. The nonisothermal crystallization kinetics of PP in the blends was evaluated by Mo's method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparative study on the crystallization behavior of β‐isotactic polypropylene nucleated with different β‐nucleation agents —effects of thermal conditions

In this study, the crystallization behavior of the β‐isotactic polypropylene (β‐iPP) samples nucleated by a rare earth based β‐nucleating agent (β‐NA) WBG‐II and a metal salts compound β‐NA NAB83 (denoted as WPP and NPP, respectively) under different cooling conditions were comparatively investigated. The thermal conditions such as the cooling rate, isothermal crystallization temperature, isothermal crystallization time, and the subsequent cooling to room temperature. The results of WAXD, SEM, and nonisothermal crystallization reveal that under the same processing conditions, the crystallite size of NPP is smaller, which arrange more compactly as compared with WPP. Meanwhile, NPP has shorter crystallization rate and higher β‐nucleation selectivity, but WPP can crystallization at wider temperature range. The results of isothermal crystallization showed that NPP has higher selectivity and higher β‐nucleation efficiency, which favors the formation of high proportion of β‐phase at the isothermal crystallization temperature of 110–130°C with and without subsequent cooling; WPP has lower selectivity, which can only induce high content of β‐phase under isothermal crystallization without subsequent cooling to 25°C. In tuning the crystallization behavior and the properties of β‐PP, the joint influence of the efficiency and selectivity of the β‐NA, and the thermal conditions should be taken into consideration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40115.     

Effects of melt structure on crystallization behavior of isotactic polypropylene nucleated with α/β compounded nucleating agents

In this study, the melt structure of isotactic polypropylene (iPP) nucleated with α/β compounded nucleating agents (α/β‐CNA, composed of the α‐NA of 0.15 wt % Millad 3988 and the β‐NA of 0.05 wt % WBG‐II) was tuned by changing the fusion temperature T_f. In this way, the role of melt structure on the crystallization behavior and polymorphic composition of iPP were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXD) and scanning electron microscopy (SEM). The results showed that when T_f = 200°C (iPP was fully molten), the α/β‐CNA cannot encourage β‐phase crystallization since the nucleation efficiency (NE) of the α‐NA 3988 was obviously higher than that of the β‐NA WBG‐II. Surprisingly, when T_f was in 179–167°C, an amount of ordered structures survived in the melt, resulting in significant increase of the proportion of β‐phase (achieving 74.9% at maximum), indicating that the ordered structures of iPP played determining role in β‐phase crystallization of iPP nucleated with the α/β‐CNA. Further investigation on iPP respectively nucleated with individual 3988 and WBG‐II showed that as T_f decreased from 200°C to 167°C, the crystallization peak temperature T_c of iPP/3988 stayed almost constant, while T_c of iPP/WBG‐II increased gradually when T_f < 189°C and became higher than that of iPP/3988 when T_f decreased to 179°C and lower, which can be used to explain the influence of ordered structure and α/β‐CNA on iPP crystallization. Using this method, the selection of α‐NA for α/β‐CNA can be greatly expanded even if the inherent NE of β‐NA is lower than that of the α‐NA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41355.     

A novel β‐nucleating agent for isotactic polypropylene

The nucleating ability of p‐cyclohexylamide carboxybenzene (β‐NA) towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, X‐ray diffraction, polarized optical microscopy and scanning electron microscopy. β‐NA is identified to have dual nucleating ability for α‐iPP and β‐iPP under appropriate kinetic conditions. The formation of β‐iPP is dependent on the content of β‐NA. The content of β‐phase can reach as high as 96.96% with the addition of only 0.05 wt% β‐NA. Under non‐isothermal crystallization the content of β‐iPP increases with increasing cooling rate. The maximum β‐crystal content is obtained at a cooling rate of 40 °C min^–1. The supermolecular structure of the β‐iPP is identified as a leaf‐like transcrystalline structure with an ordered lamellae arrangement perpendicular to the special surface of β‐NA. Under isothermal crystallization β‐crystals can be formed in the temperature range 80–140 °C. The content of β‐crystals reaches its maximum value at a crystallization temperature of 130 °C. © 2012 Society of Chemical Industry     

Isotactic polypropylene toughened with poly(acrylonitrile–butadiene–styrene): Compatibilizing role of maleic anhydride grafted polypropylene

The β‐nucleating activity and toughening effect of acrylonitrile–butadiene–styrene (ABS) graft copolymer on isotactic polypropylene (iPP) and the compatibilizing role of maleic anhydride grafted polypropylene (PP‐g‐MAH) on the iPP/ABS blends were investigated. The results show that ABS can induce the formation of β‐crystal in iPP, and its β‐nucleating efficiency depends on its concentration and dispersibility. The relative content of β‐crystal form is up to 36.19% with the addition of 2% ABS. The tensile and impact properties of the iPP were dramatically enhanced by introducing ABS. The incorporation of PP‐g‐MAH into the iPP/ABS blends inhibits the formation of β‐crystal. The crystallization peaks of the blends shift toward higher temperature, due to the heterogeneous nucleation effect of PP‐g‐MAH on iPP. The toughness of iPP/ABS blends improved due to favorable interfacial interaction resulting from the compatibilization of PP‐g‐MAH is significantly better than the β‐crystal toughening effect induced by ABS. POLYM. ENG. SCI., 59:E317–E326, 2019. © 2019 Society of Plastics Engineers     

Structural characterization of α‐ and β‐nucleated isotactic polypropylene

Modification of isotactic polypropylene (iPP) with two nucleation agents, namely 1,3:24‐bis(3,4‐dimethylobenzylideno) sorbitol (DMDBS) (α‐nucleator) and N, N′‐dicyclohexylo‐2,6‐naphthaleno dicarboxy amide (NJ) (β‐nucleator), leads to significant changes of the structure, morphology and properties. Both nucleating agents cause an increase in the crystallization temperature. The efficiency determined in a self‐nucleation test is 73.4 % for DMDBS and 55.9 % for NJ. The modification with NJ induces the creation of the hexagonal β‐form of iPP. The addition of DMDBS lowers the haze of iPP while the presence of NJ increases the haze. Copyright © 2004 Society of Chemical Industry     

Isothermal crystallization kinetics of anhydrous sodium acetate nucleated poly(ethylene terephthalate)

Studies on the isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nucleated with anhydrous sodium acetate were carried out. The nucleated agent had succeeded in promoting greater rates of crystallization in PET. A study of the melting behavior of the samples revealed that the nucleating agents promoted formation of thinner lamellae. The equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman Weeks procedure. The nonlinear Hoffman Week's procedure was found to be inapplicable in the current study. The Lauritzen‐Hoffman secondary nucleation theory was applied to determine the nucleation parameter (K_g), fold surface energy (σ_e), and work of chain folding (q). σ_e and q decreased on addition of nucleating agent. The approximate and exact form of the Lauritzen Z‐test was used to determine the operating regime. The operating regime was found to be primarily regime II for the range of temperatures studied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Variation of non‐isothermal crystallization behavior of isotactic polypropylene with varying β‐nucleating agent content

The non‐isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of β‐nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co‐workers could be successfully used to describe the non‐isothermal crystallization process of the nucleated iPPs. The values of n showed that the non‐isothermal crystallization of α‐ and β‐nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of β‐nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of β‐nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of β‐nucleating agent were mainly determined by the ratio of the content of α‐ and β‐phase in iPP (α‐PP and β‐PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of β‐spherulites for iPPs with small amounts of β‐nucleating agent and the small size and few intercrossing bands among the boundaries of β‐spherulites for iPPs with large amounts of β‐nucleating agent from the SEM examination. Copyright © 2010 Society of Chemical Industry     

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

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

A novel highly efficient β‐nucleating agent for polypropylene using nano‐CaCO3 as a support

In order to increase the isotactic content of β‐nucleated polypropylene (β‐iPP) and decrease the cost of its production, the investigation and development of novel highly efficient β‐nucleators are important issues. Nano‐CaCO₃ was used as a support to prepare a supported β‐nucleator, nano‐CaCO₃‐supported calcium pimelate. Fourier transform infrared spectral analysis shows that an in situ chemical reaction takes place between nano‐CaCO₃ and pimelic acid. Differential scanning calorimetry results indicate that the crystallization and melting temperatures of β‐phase in supported β‐nucleator‐nucleated iPP are higher than those of calcium pimelate‐nucleated iPP. The β‐nucleating ability of the supported β‐nucleator is little influenced by the cooling rate and crystallization temperature over a wide range. The decreased content of pimelic acid in the supported β‐nucleator slightly decreases the crystallization temperature of iPP but it has no influence on the content of β‐phase in nucleated iPP. A novel supported β‐nucleator has been successfully synthesized via pimelic acid supported on the surface of CaCO₃. The crystallization temperature of iPP and melting temperature of β‐phase in iPP nucleated using the supported β‐nucleator are higher than those of iPP nucleated using calcium pimelate. The concept of a supported nucleator will provide a new way to increase the efficiency of polymer additives and to decrease the amounts of them that need to be used by using nanoparticles as supports. Copyright © 2010 Society of Chemical Industry     

Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

A supercooled melt of isotactic polypropylene (iPP) was extruded through a capillary die. Polarized light microscopy (PLM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the effects of the relatively weak wall shear stress (σ_w), extrusion temperature (T_e), and crystallization temperature (T_c) on the structure and morphology of β‐form isotactic polypropylene (β‐iPP). β‐cylindrites crystals could be observed by PLM in the extruded specimen even at a lower σ_w's (0.020 MPa), and the β‐iPP content increased with decreasing T_e. Under a given T_e of 150°C, the increase in σ_w positively influenced the β‐iPP content. The DSC and WAXD results indicate that the total crystallinity and β‐iPP content increased when T_c was set from 105 to 125°C; the other experimental parameters were kept on the same level. Although T_c was above 125°C, the β‐iPP content obviously decreased, and the total crystallinity continued to increase. On the basis of the influences of σ_w, T_e, and T_c on the β‐iPP crystal morphology and structure, a modified model is proposed to explain the growing of shear‐induced β‐iPP nucleation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of La3+‐containing additive on crystalline characteristics of isotactic polypropylene

The influence of a mixed additive of lanthanum stearate and stearic acid on the crystalline characteristics of isotactic polypropylene (iPP) has been investigated. The results of the wide‐angle X‐ray diffraction (WAXD) measurements and the melting behaviour examination by differential scanning calorimetry (DSC) show that the additive might induce a high proportion of β‐form and act as a β‐form nucleating agent. The relative content of β‐form estimated by WAXD is 33.1% in a PP containing 2.5% (by weight) of the additive. Isothermal crystallization at 130 °C, examined by DSC, reveals that the additive considerably accelerates the overall rate of crystallization: the half crystallization period t_1/2, decreases from 11.7 min for pure PP to 7.3 min for PP containing 2.5% of the additive. However, the additive has no obvious influence on the nucleation mechanism and crystal growth mode. Polarized light microscopy (POM) examinations indicate that the addition of the additive to PP causes spherulites to become much finer. © 2003 Society of Chemical Industry     

Melting and crystallization behaviors,morphology, and mechanical properties of β‐polypropylene/polypropylene‐graft‐maleic anhydride/calcium sulfate whisker composites

The melting and crystallization behaviors, morphology, and mechanical properties of polypropylene (PP)/surface‐treated calcium sulfate (CaSO₄) whisker (T‐CSW), β‐PP/T‐CSW, and β‐PP/polypropylene‐graft‐maleic anhydride (PP‐g‐MAH)/T‐CSW composites had been investigated via differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), polarized light microscopy (PLM), scanning electron microscopy (SEM), and mechanical tests. We found that T‐CSW was an α‐nucleating agent and increased the crystallization temperatures of PP, but PP‐g‐MAH and high loadings of T‐CSW had weakly negative effects on the crystallization rates of PP. The T‐CSW restrained the formation of β‐spherulites, and the spherulitic size decreased in the composites. PP‐g‐MAH improved the compatibility and adhesion between T‐CSW and the matrix. The notched impact strength was improved, and the tensile strength was enhanced at low levels of T‐CSW, while the flexural modulus was weakened for β‐PP/T‐CSW and β‐PP/PP‐g‐MAH/T‐CSW composites versus PP/T‐CSW composites. POLYM. COMPOS., 37:2121–2132, 2016. © 2015 Society of Plastics Engineers     

Dispersion,crystallization kinetics,and parameters of Hoffman–Lauritzen theory of polypropylene and nanoscale calcium carbonate composite

Isothermal and nonisothermal crystallization of polypropylene (PP)/calcium carbonate (CaCO₃) with two particle sizes (250–300 nm and 20–25 nm) were studied by differential scanning calorimeter. Equilibrium melting temperature (T) determined from both linear and nonlinear Hoffman–Weeks relations showed that the composites had a lower T as a result of the CaCO₃ particles destroying the crystal of PP. Kinetics of the isothermal and nonisothermal crystallization was described by Avrami equation. For the first time, without the assumption of a constant U* value, Lauritzen–Hoffman parameters (U* and K_g) were evaluated directly by data‐fitting method for isothermal crystallization, and by Vyazovkin's method for nonisothermal crystallization. K_g values obtained were similar with and without the assumption of a constant U*and comparable to those in the literature. Both U* and K_g indicate the dual role the CaCO₃ particles as nucleating agents to enhance the crystallization and as obstacles to the chain movement to reduce the crystallization. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

A highly active and selective β‐nucleating agent for isotactic polypropylene and crystallization behavior of β‐nucleated isotactic polypropylene under rapid cooling

Zinc adipate (Adi‐Zn) was observed to be a highly active and selective β‐nucleating agent for isotactic polypropylene (iPP). The effects of Adi‐Zn on the mechanical properties and the β‐crystals content of nucleated iPP were investigated. The impact strength of iPP nucleated with 0.2 wt % Adi‐Zn was 1.8 times higher than that of neat iPP. In addition, wide‐angle X‐ray diffraction analysis indicated that the content of β‐crystals in nucleated iPP (k_β value) reached 0.973 with 0.1 wt % Adi‐Zn, indicating that Adi‐Zn is a highly active and selective β‐nucleating agent for iPP. Furthermore, fast scanning chip calorimetry (FSC) studies using cooling rates from 60 to 13,800 °C min^?1 revealed that the formation of β‐crystals significantly depended on the cooling rates. At cooling rates below 3000 °C min^?1, only β‐crystals existed. However, at cooling rates above 6000 °C min^?1, β‐crystals failed to form. Moreover, a lower critical crystallization temperature that corresponded to the generation of β‐crystals was investigated using cooling‐induced crystallization, and the results are in good agreement with those of a previous study. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43767.     

A novel highly efficient β‐nucleating agent for isotactic polypropylene

A novel highly efficient β‐nucleating agent for isotactic polypropylene (iPP), hexahydrophthalic barium (HHPA‐Ba), was found and its effects on the mechanical properties, the β‐phase content, and crystallization behavior of iPP were investigated, respectively. The results show that the β‐phase content of nucleated iPP (k_β value) can reach 80.2% with 0.4 wt % HHPA‐Ba. The impact strength and crystallization peak temperature of nucleated iPP are greatly increased. Compared with pure iPP, the impact strength of nucleated iPP can increase 2.4 times. Meanwhile, the spherulite size of nucleated iPP is dramatically decreased than that of pure iPP. The Caze method was used to investigate the nonisothermal crystallization kinetics of nucleated iPP and the crystallization active energy was achieved by Kissinger method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of nucleating agent addition on crystallization of isotactic polypropylene

The isothermal and nonisothermal crystallization kinetics of nonnucleated and nucleated isotactic polypropylene (iPP) were investigated by DSC and a polarized light microscope with a hot stage. Dibenzylidene sorbitol (DBS) was used as a nucleating agent. It was found that the crystallization rate increased with the addition of DBS. The influence of DBS on fold surface energy, σ_e, was examined by the Hoffman and Lauritzen nucleation theory. It showed that σ_e decreased with the addition of DBS, suggesting that DBS is an effective nucleating agent for iPP. Ozawa's theory was used to study the nonisothermal crystallization. It was found that the crystallization temperature for the nucleated iPP was higher than that for nonnucleated iPP. The addition of DBS reduced the Ozawa exponent, suggesting a change in spherulite morphology. The cooling crystallization function has a negative exponent on the crystallization temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2089–2095, 1998     

Influences of pre‐ordered melt structures on the crystallization behavior and polymorphic composition of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

As part of continuous efforts to understand the surprising synergetic effect between β‐nucleating agent and pre‐ordered structures of isotactic polypropylene (iPP) in significant enhancement of β‐crystallization (Ordered Structure Effect, OSE), two β‐nucleated iPP with different uniformities of stereo‐defect distribution (WPP‐A and WPP‐B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β‐phase can hardly form in WPP‐A (whose stereo‐defect distribution is less uniform) because of its strong tendency of α‐nucleation caused by its less uniform stereo‐defect distribution, while WPP‐B is more favorable for β‐crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β‐phase proportion can be observed from WPP‐A and WPP‐B, indicating the occurrence of OSE behavior, which provides unsurpassed β‐nucleation efficiency and induces β‐crystallization even in WPP‐A which is less favorable for β‐crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP‐A and WPP‐B are identical, suggesting the uniformity of stereo‐defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self‐nucleation behavior and equilibrium melting temperature of PP‐A and PP‐B were studied. The lower limiting temperatures of exclusive self‐nucleation domain of both PP‐A and PP‐B are identical with the lower limiting temperatures of Region II in OSE (168°C); moreover, the T_m⁰ of both PP‐A and PP‐B are close to their upper limiting temperatures of Region II in OSE behavior (189°C). The possible explanation was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42632.     

Crystallization kinetics of maleic anhydride‐modified iPP studied by POM

Melt nucleation and crystallization behavior of homo‐isotatic polypropylene (homo‐iPP), maleic anhydride (MAH)‐grafted‐iPP, and MAH‐modified iPP, produced from iPP and a small amount of MAH‐grafted‐iPP, was investigated by polarizing optical microscopy (POM), at T_c = 121–135^oC. Nucleation processes at a given T_c were faster for modified PP as compared to neat iPP. The induction time for nucleation increased nonlinearly with increasing T_c and decreased for modified PP, probably as a result of promoted heterogeneous nucleation due to the presence of carbonyl groups of MAH‐grafted‐PP. The average spherulite sizes were decreased by modification, and the growth rate was enhanced in maleated PP and modified PP. The induction time approach was applied to the results obtained by POM to compare the tendency for heterogeneous nucleation of neat and MAH‐modified PP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3107–3118, 2000