Anomalous molecular orientation of isotactic polypropylene sheet containing N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide

Small amount of N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide as a β-form nucleating agent is dissolved beyond 280 °C in a molten isotactic polypropylene (iPP) and appears as needle crystals around at 240 °C during cooling procedure. Further, iPP molecules crystallize on the surface of the needle crystals, in which c-axis of the β-form iPP crystals grows perpendicular to the long axis of the needle crystals. Under flow field at extrusion processing, the needle crystals orient to the flow direction prior to the crystallization of iPP. As a result, c-axis of the β-form iPP crystals orients perpendicular to the applied flow direction with a small amount of α-form iPP. Moreover, the vertical molecular orientation of the extruded sheet sample is responsible for unique mechanical anisotropy; the fracture occurs along the transversal direction.     

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 mineral additives on the β‐crystalline form of isotactic polypropylene

Nineteen kinds of minerals, alone and in bicomponent mixtures with LaC (a mixed ternary complex of trivalent lanthanum stearate and stearin), were added to isotactic polypropylene (iPP). The influences of the minerals on the crystallographic forms of iPP were investigated. A wide‐angle X‐ray diffraction examination demonstrated that no mineral or LaC acting alone could induce the occurrence of the hexagonal β‐form, whereas the bicomponent mixtures could when the mineral was a calcium compound or contained calcium compounds, whether the calcium compounds had a hexagonal crystallographic form or not. We surmise that the actual β‐iPP substrate in such a system might be some binuclear complexes of calcium and rare earth elements with some specific ligands. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1742–1748, 2002     

Effect of N,N′‐diphenyl adipamide on the formation of the β‐crystalline form in isotactic polypropylene

The polymorphic compositions and mechanical properties of isotactic polypropylene (iPP) samples nucleated by a selective β‐nucleating agent [N,N′‐diphenyl adipamide (DPA)] were investigated with wide‐angle X‐ray diffraction, polarized light microscopy, scanning electron microscopy, and mechanical tests. It was found that β‐phase crystals emerged with the addition of DPA, and the relative proportion of the β‐crystalline form reached the maximum value of 0.97 with the addition of 0.1 wt % DPA. The curved lamellae in the β spherulites were like flowers. The β spherulites were etched more easily than α spherulites because amorphous regions were distributed inside the β spherulites. The Izod notched impact strength increased sharply with the addition of DPA and attained the maximum value of 7.30 kJ/m² (the value of blank iPP was 3.13 kJ/m²) with the addition of 0.1 wt % DPA. An analysis of the misfit factors between DPA and β‐iPP showed that β‐iPP could epitaxially crystallize on the DPA crystal well. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of a novel β‐nucleating agent on the structure,morphology, and nonisothermal crystallization behavior of isotactic polypropylene

The crystalline structure, morphology, and nonisothermal crystallization behavior of isotactic polypropylene (iPP) with and without a novel rare earth‐containing β‐nucleating agent (WBG) were investigated with wide‐angle X‐ray diffraction, polar optical microscopy, and differential scanning calorimetry. WBG could induce the formation of the β form, and a higher proportion of the β form could be obtained by the combined effect of the optimum WBG concentration and a lower cooling rate. The content of the β form could reach more than 0.90 in a 0.08 wt % WBG nucleated sample at cooling rates lower than 5°C/min. Polar optical microscopy showed that WBG led to substantial changes in both the morphological development and crystallization process of iPP. At all the studied cooling rates, the temperature at which the maximum rate of crystallization occurred was increased by 8–11°C in the presence of the nucleating agent. An analysis of the nonisothermal crystallization kinetics also revealed that the introduction of WBG significantly shortened both the apparent incubation period for crystallization and the overall crystallization time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal characteristics and crystallinity of Ziegler–Natta isotactic polypropylene/metallocene isotactic polypropylene polyblended fibers

Ziegler–Natta isotactic polypropylene (ZN‐iPP) and metallocene isotactic polypropylene (m‐iPP) were extruded (in ratios of 75/25, 50/50, and 25/75) from one melt twin‐screw extruder to produce three ZN‐iPP/m‐iPP polyblended polymers and, subsequently, spin fibers. In this study, we examined the rheology of the ZN‐iPP/m‐iPP polyblended polymers and the thermal characteristics and crystallinity of the ZN‐iPP/m‐iPP polyblended fibers using gel permeation chromatography, rheometry, differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, density gradient analysis, and extension stress–strain measurement. The apparent melt viscosity of the ZN‐iPP/m‐iPP polyblended polymers revealed positive‐deviation blends. The 50/50 blend of ZN‐iPP/m‐iPP had the highest apparent melt viscosity. For five samples, the complex melt viscosity decreased with the angular frequency, which represented typical non‐Newtonian behavior. The Cole–Cole plot, which consisted of the imaginary part of the complex melt viscosity versus the real part of the complex melt viscosity plot, of the ZN‐iPP/m‐iPP polyblended polymers showed a semicircular relationship with the blend ratios. It indicated that the ZN‐iPP/m‐iPP polyblended polymers were miscible. We analyzed the shear modulus data (G′ vs G″) by plotting them on a log–log scale. The plot revealed almost the same slopes for the ZN‐iPP/m‐iPP polyblended polymers, which indicated a good miscibility between the ZN‐iPP and m‐iPP polymers. The experimental DSC results demonstrate that the ZN‐iPP and m‐iPP polymers constituted a miscible system. The crystallinity and tenacity of the ZN‐iPP/m‐iPP polyblended fibers initially increased and then fell as the m‐iPP content increased. Meanwhile, the 50/50 blend of ZN‐iPP/m‐iPP had the highest crystallinity and tenacity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of the composition ratio of pimelic acid/calcium stearate bicomponent nucleator and crystallization temperature on the production of β crystal form in isotactic polypropylene

The influence of the composition ratio of pimelic acid/calcium stearate bicomponent nucleator on the β crystal form content of isotactic polypropylene (iPP) had been studied at the crystallization temperature of 120°C and duration of 30 min. It was found that the β crystal form content increased continuously with increasing amount of calcium stearate at the constant amount of 0.15% pimelic acid. High β crystal form content polypropylene could be produced when the amount of calcium stearate was greater than 0.30% (the mass composition ratio of pimelic acid/calcium stearate was less than 1/2, the mole ratio was less than 1.89/1). It was shown that pimelic acid and calcium stearate could react to produce a high effective β nucleator (calcium pimelate) “in situ” during the melt‐mixing of iPP and the bicomponent nucleator. The influence of crystallization temperatures (100–140°C) on the β crystal form content of iPP had also been studied at the constant composition ratio of 0.15% pimelic acid/0.5% calcium stearate (the calcium pimelate produced in situ was 0.16%, which was calculated from stoichiometry). It was found that the β crystal form content increased continuously with increasing crystallization temperature and it maximized at 130°C. β Crystal form content decreased sharply at the crystallization temperature of 140°C. It was shown that β → α modification transformed between 130 and 140°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Plastic deformation behavior of β-phase isotactic polypropylene in plane-strain compression at room temperature

Isotactic polypropylene (iPP) rich in β crystal modification (constituting 92% of crystalline phase) was deformed by the plane-strain compression with constant true strain rate, at room temperature. The evolution of phase structure, morphology and orientation was studied by DSC, X-ray and SEM.

The deformation sequence and the active deformation mechanisms were found out. The most important mechanisms were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands due to localization of deformation and the crystallographic slip systems, including the (110)[001] chain slip and (110)[10] transverse slip.

Shear within deformation bands leads to β → smectic and β →  solid state phase transformations. At room temperature the β → smectic transformation appeared to be the primary transformation, yielding the oriented smectic phase with high concentration of 19 wt.% at the true strain of e = 1.49. The β →  yields only about 4 wt.% of new -phase at the same strain. As a result of the deformation and phase transformation within numerous fine deformation bands β-lamellae are locally destroyed and fragmented into smaller crystals.

Another deformation mechanism is the cooperative kinking of lamellae, leading to their reorientation and formation of a chevron-like lamellar arrangement.

At high strains, above e = 1, an advanced crystallographic slip and high stretch of amorphous material due to interlamellar shear bring further heavy fragmentation of lamellar crystals, earlier fragmented partially by deformation bands. This fragmentation is followed by fast rotation of small unconstrained crystallites with chain axis towards the direction of flow, FD. This process leads to development of the final texture of the highly deformed β-iPP with molecular axis of both crystalline and smectic phases oriented along FD.     

Influence of m‐isopropenyl‐α,α‐dimethylbenzyl isocyanate grafted polypropylene on the interfacial interaction of wood‐flour/polypropylene composites

In this article, the effects of m‐isopropenyl‐α,α‐dimethylbenzyl isocyanate grafted polypropylene (m‐TMI‐PP) on the interfacial interaction of wood‐flour/polypropylene (WF/PP) were investigated by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry, dynamic rheological analysis, and mechanical properties tests. The experimental results demonstrated that m‐TMI‐PP greatly improved the interfacial interaction between WF and PP. According to the DSC results, m‐TMI‐PP made the crystallization temperature and the crystallization degree of PP in WF/m‐TMI‐PP/PP decrease when compared with WF/PP composite without m‐TMI‐PP, but it was still higher than pure PP. These results demonstrated that WF presented the nucleate effect for the crystallization of PP and m‐TMI‐PP improved the interfacial adhesive, which restrained the mobility of PP chain. The rheological analysis indicated that the complex viscosity, storage, and loss modular of WF/PP composite increased, and the tan δ decreased with the addition of m‐TMI‐PP. This was attributed to the strong improvement effects of m‐TMI‐PP on the interfacial interaction of the composites, and was further confirmed by the mechanical properties tests and SEM analysis of the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modification of isotactic polypropylene by the free‐radical grafting of 1,1,1‐trimethylolpropane trimethacrylate

The chemical modification of isotactic polypropylene was performed by the free‐radical‐promoted grafting of 1,1,1‐trimethylolpropane trimethacrylate (TMPTMA) in the presence of dicumyl peroxide (DCP) as the initiator. The reaction was carried out both in a batch internal mixer and in a corotating twin‐screw extruder; the effects of the peroxide and monomer concentrations on the extent of modification in terms of the grafting efficiency and polymer chain structure variations were investigated. The modified samples were characterized with Fourier transform infrared to determine the structure of the grafted groups and the degree of functionalization, with gel permeation chromatography and the melt flow index to evaluate changes in the molecular weight, and with differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis to measure the final thermal properties. In addition, solvent extraction with xylene was performed to highlight the presence of gel and its extent. The structure of the grafted groups was determined, and the number of grafted groups was quantitatively evaluated. The degree of functionalization increased with an increasing TMPTMA/DCP molar ratio. Thermal analysis results hinted at the presence of grafted chains with an increased percentage of TMPTMA. Although degradation reactions predominated at high amounts of peroxide, grafting and branching processes became competitive at high levels of TMPTMA. The balance between competing β‐scission and grafting/branching reactions could be adjusted on the basis of feed conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 950–958, 2007     

A quantitative electron-microscopic investigation of α-phase lamellae in isotactic polypropylene fractions

Lamellar thicknesses and cross-hatching frequencies in α-isotactic polypropylene have been measured for two series of fractions using linear nucleation to provide large arrays of oriented lamellae in row structures for sampling. One series is of high tacticity polymers differing in molecular mass from 6 × 10⁴ to 8 × 10⁵, the other has low and high tacticity materials for 9 × 10⁴ and 2 × 10⁵ masses. These have allowed the differing influences of both molecular mass and tacticity to be evaluated. Lamellar thicknesses increase with molecular mass to 5 × 10⁵ then level off. This is consistent with the fold surface increasing its free energy by 20% for longer molecules as its structure becomes progressively more complex. Except for the lowest fraction, the thickness of cross-hatching lamellae is less than that of its radial neighbours because of differential thickening. The frequency of cross-hatching is greatest for the least tactic fraction but decreases linearly with molecular length. This dependence suggests that chain ends play a key role in initiation probably by laying down the first segment in epitaxial orientation. This suggestion could also account for the reduced thermal stability of spherulite centres and regions of high cross-hatching density where there is competition for chain ends between thickening and cross-hatching. The curvature of lamellae at the very end of a row mirrors the dependence of lamellae thickness with molecular mass and allows cilia pressure, the factor strongly involved in causing the lamellar divergence underlying spherulitic growth, to be estimated as 100 Pa.     

Electrical β-relaxation of die-drawn isotactic polypropylene

Measurements of a.c. impedance were carried out in the frequency range 1 Hz to 10⁶ Hz at room temperature on isotropic and die-drawn isotactic polypropylene. It was found that the a.c. impedance decreases with increasing draw ratio in the frequency range 1 Hz to 10⁴ Hz and then becomes independent of draw ratio with increasing frequency. A dramatic drop in the a.c. impedance was observed in the frequency range 10⁴ to 10⁶ Hz, which is associated with a β-relaxation process. The intensity of the β-relaxation peak decreases with increasing draw ratio and nearly disappears for a draw ratio of 16·8. The Cole Cole plots show good semicircles for isotropic and die-drawn samples indicating that a certain polarization mechanism is dominant in polypropylene.     

Negative effect of stretching on the development of β‐phase in β‐nucleated isotactic polypropylene

On the premise that shear in the slit die of an extruder was minimized as far as possible, β‐nucleated isotactic polypropylene (iPP) was extruded. Simultaneously, once the extrudate (in the melt state) left the die exit, it was stretched at various stretching rates (SRs). For iPP with a low content of β‐nucleating agent (β‐NA), the crystallinity of β‐phase (X_β) initially increases with increasing SR, and then decreases slightly with further increase in SR. However, for iPP containing a higher content of β‐NA, with increasing SR, X_β decreases monotonically, indicating a negative effect of SR on β‐phase formation. Small‐angle X‐ray scattering and polarized optical microscopy experiments reveal that, when SR is less than 30 cm min^?1, the increasing amount of row nuclei induced by increasing SR is mainly responsible for the increase of X_β. In contrast, when SR exceeds 30 cm min^?1, the overgrowth of shish structures unexpectedly restrains the development of β‐phase, and spatial confinement is considered as a better explanation for the suppression of β‐phase. Copyright © 2011 Society of Chemical Industry     

Recrystallization behavior of β‐isotactic polypropylene in homogeneous and heterogeneous matrix–fiber composites

β‐isotactic polypropylene (β‐iPP) cylindritic crystals were produced in homogeneous iPP fiber–matrix composites and heterogeneous polyamide (PA)–iPP fiber–matrix composites under different sample preparation conditions. The melt recrystallization behaviors of the β‐iPP crystals obtained in the homogeneous and heterogeneous composites were studied by optical microscopy. The experimental results show that, by heating the sample to 180 °C, the birefringence contributed by the iPP crystals in both α‐ and β‐forms disappears completely. During the cooling process, the β‐iPP crystals in the homogeneous composite appear again, while the iPP in the heterogeneous composite crystallizes in its α‐form. This demonstrates the different origins of the β‐iPP cylindrites in the homogeneous and heterogeneous composites. While the β‐iPP cylindrites in the heterogeneous composite are associated with the sample preparation procedure, the β‐iPP cylindrites in the homogeneous composite are produced by recrystallization of the molten but incompletely relaxed iPP fibers. In situ observation of the melt recrystallization process shows that the molten iPP oriented fibers crystallize first during the cooling process at relatively higher temperature in the α‐form. Abundant randomly dispersed β‐iPP nuclei formed at the surface of the recrystallized iPP fibers, which generate the β‐iPP cylindrites. Copyright © 2012 Society of Chemical Industry     

Calcium dicarboxylates nucleation of β‐polypropylene

Seven dicarboxylates of calcium were synthesized. The effect of dicarboxylate on the formation of β‐form polypropylene was investigated by X‐ray diffraction. Calcium pimelate, calcium suberate, calcium phthalate, and calcium terephthalate have been found to be an effective β‐nucleator. The K_x values of the isotatic propylene samples with 0.5 wt % of the nucleators above are 0.95, 0.96, 0.93, and 0.62, respectively. Calcium succinate, calcium adipate, and calcium sebacate behave invalidly on the nucleating of the β‐phase. We conducted an investigation on the affect of particle shape, crystal form, and crystallinity upon the level of the β‐form. The X‐ray diffraction of the effective nucleators reveals a common character that their first reflection locate at the d‐spacing between 10 to 13 Å, indicating structural similarity of the nucleators with β‐polypropylene. The nucleation mechanism is explained by the cooperative effect of the nonpolar and polar part of nucleating agents in the crystallization of polypropylene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 633–638, 2002     

α‐ and β‐crystalline forms of isotactic polypropylene investigated by nanoindentation

Under special crystallization conditions from the melt, both α‐ and β‐forms of isotactic polypropylene were produced simultaneously. The α‐ and β‐spherulites of polypropylene were differentiated under optical microscope, allowing the nanoindentation of individual spherulites of each crystallographic form. Elastic modulus and hardness of β‐spherulites were found to be 10 and 15% respectively lower than in α‐spherulites. The higher stiffness of α may be related to the particular interlocked structure with cross‐hatched lamellae, and to a lower molecular mobility in the crystallites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 195–200, 1999     

Nonisothermal crystallization and multiple melting behaviors of β‐nucleated impact‐resistant polypropylene copolymer

As a substitute of isotactic polypropylene in applications requiring excellent fracture resistance, impact‐resistant polypropylene copolymer (IPC) has attracted much attention in recent years. In this study, a highly effective β‐form nucleating agent (β‐NA; an aryl amide compound) was introduced into IPC, and our attention was focused on the nonisothermal crystallization and subsequent melting behaviors of the nucleated samples. The nonisothermal crystallization behaviors were investigated on the basis of the different cooling rates and different concentrations of β‐NA with differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy. The results show that both the cooling rate and concentration of β‐NA greatly determined the nonisothermal crystallization process and subsequent multiple melting behaviors. Further results show that the multiple melting behaviors were related to the transition in β crystallites and those between the β and α crystallites. The morphologies of the dispersed particles and the supermolecular structure of the matrix were characterized with scanning electron microscopy. Finally, the effect of the β‐NA concentration on the fracture resistance of IPC was evaluated by measurement of the notched Izod impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis,structure, and olefin polymerization catalysis of a novel vanadium(III) 1,1′‐bi‐2‐naphtholate complex

The reaction of VCl₃ with (S)‐(–)‐Na₂ (binol) (binol = 1,1′‐bi‐2‐naphtholate) gave a new vanadium(III) complex, [Na(OEt₂)]₃[V(binol)₃] (Fig. 1 ). The X‐ray crystallographic structure of this complex (Complex 1 ) in Figure 1 reveals its propeller‐like structure, which is similar to those of the reported rare earth analogues. The complex showed moderate catalytic activities for ethylene polymerization upon activation with modified methylaluminoxane (MMAO) and with diethylaluminum chloride (DEAC). The Complex 1 /DEAC system also catalyzed the polymerization of propylene to give atactic polypropylene with low activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1659–1662, 2003 1 Complex 1

1. Molecular structure of [Na(OEt₂)]₃[V(binol)₃] (Complex 1 ).     

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     

Charge storage behavior of isotropic and biaxially‐oriented polypropylene films containing α‐ and β‐nucleating agents

A study on the influence of the crystal modification (α and β) of isotactic polypropylene (i‐PP) films on the resulting electret properties is presented. Two commercial nucleating agents, sodium 2,2′‐methylene‐bis(4,6‐di‐tert‐butylphenyl)‐phosphate (NA11) and N,N′‐dicyclo‐hexyl‐2,6‐naphthalene‐dicarbox‐amide (NU100), were employed in this investigation. Isothermal charge decay was measured at 90°C. In hot pressed isotropic polypropylene films, no significant differences in the charge storage properties were observed for α‐ and β‐nucleated specimens. In addition, the article presents the influence of the nucleating agents at different concentrations on the PP‐film morphology of biaxially stretched films with respect to electret features. It was possible to prepare elongated cavities with the virtually insoluble NA11 additive during stretching, even at concentrations below 0.3 wt %. These films displayed slightly improved electret properties in comparison to stretched neat PP films due to generated cavities acting as barriers for the drift of charges. Various draw ratios were also studied for i‐PP films with 0.15 wt % NA11. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 650–658, 2006