Nodular structure of isotactic polypropylene crystallizes from the melt

This article highlights the melt crystallization behavior of different grades of isotactic polypropylene (iPP) using a hot‐stage polarizing optical microscopy. iPP samples were heated up at a heating rate of 10°C/min passing the melting temperature and then kept for 3 min at a temperature range of 175–200°C before they cooled rapidly at 40°C/min to crystallize isothermally at a range of 130–145°C. It has been found that the temperature at which the samples were kept has a strong effect on the crystallization mode; for samples heated up and kept at temperatures below 190°C, the crystallization started with thin and long rods or nodules, which grew in the circumferential direction only while their lengths remain unchanged as the time passed. The shape of the nodules can be straight, circular, branched, or entangled, and they can grow parallel to each other or they can be crossed or in a random way. This phenomenon disappeared completely for samples melted and kept at temperatures above 195°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The spherulitic and lamellar morphology of melt-crystallized isotactic polypropylene

A study is presented concerning the basic morphology of melt-crystallized isotactic polypropylene (iPP). Involved within, is the coordinated application of optical and electronmicroscopy on a range of commercial iPP-s, crystallized in the temperature range 100°C–150°C. For electron microscopy in particular, the permanganic etching technique has been used throughout, providing the simultaneous combination of both real space microstructures with electron diffraction information. The investigation itself has centred on the five different spherulite types, as identified optically, which were then correlated with the details of their particular lamellar morphology. It was found that each spherulite type is characterized by virtue of the arrangement of its constituent lamellae, in terms of orientation, habit type and crystal structure. Thus, specific correlations were obtained between the structural entities on all scales of the structure hierarchy.     

β成核剂含量对等规聚丙烯性能的影响

研究了一种β成核剂(CHB-5)的含量对等规聚丙烯(iPP)结晶性能和力学性能的影响。用广角X射线衍射(WAXD)研究CHB-5诱导iPP晶型的变化,用差示扫描量热法(DSC)分析CHB-5对iPP熔融行为和结晶行为的影响,用偏光显微镜(POM)观察CHB-5诱导iPP结晶形态的变化。结果表明,CHB-5的加入使iPP的成核能力增强;CHB-5可降低iPP的熔融温度,提高其结晶温度和结晶起始温度,加快结晶速率;CHB-5能降低球晶尺寸;CHB-5的加入可使iPP缺口冲击强度提高。     

Self‐interference flow of an isotactic polypropylene melt in a cavity during injection molding. II. Morphology and crystallinity

This article is principally concerned with the morphology and crystallinity of isotactic polypropylene (iPP) parts molded by injection molding, during which a self‐interference flow (SIF) occurs for the melt in the cavity. Scanning electron microscopy shows that a transverse flow takes place in SIF samples. Wide‐angle X‐ray diffraction and differential scanning calorimetry show that SIF moldings exhibit a γ phase, in addition to α and β phases, and high crystallinity. Meanwhile, the results for iPP moldings made by the conventional flow process, that is, conventional injection molding, are reported for comparison. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2791–2796, 2003     

Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt

The influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF₂) has been investigated. The DSC endotherms of PVF₂ crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.     

Toughened polypropylene with balanced rigidity. IV. Morphology,crystallization behavior,and thermal properties

The morphology of toughened polypropylene with balanced rigidity (TRPP) was characterized by using transmission electron microscopy and polarizing light microscopy. The crystallization behavior and thermal properties were investigated by differential thermal analysis and thermogravimetric analysis. The PP component in the polymer blend was realized as the continuous phase and the elastomer component as the dispersed phase with a cellular structure (salami structure) containing some PP. The particles of the dispersed phase were small and regular. The cellular structure of the TRPPs resulted from the introduction of toughening master batches and was similar to the morphology of acrylonitrile‐butadiene‐styrene and high‐impact polystyrene synthesized by graft copolymerization. By gradually cooling from the melt, crystallization of TRPPs was nucleated heterogeneously and the crystallization temperature was slightly higher than that of PP whereas the crystallite size was remarkably reduced. For the samples with different compositions, the number, shape, and size of the cellular dispersed particles and the crystallite size were different. Considering the toughening theories and our experimental data, it was concluded that the samples with more regular and small cellular dispersed particles generally had better mechanical properties and the remarkably reduced crystallite size of PP was favorable for toughness improvement. The melting point, thermal oxidation temperature, and thermal oxidation onset temperature of the TRPPs were all a little lower than those of PP and the processability remained good. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1351–1358, 2001     

间规聚苯乙烯/等规聚丙烯共混物的热性能

用差示扫描量热法(DSC)、动态力学分析(DMA)和热重法(TGA)等研究了间规聚苯乙烯/等规聚丙烯(sPS/iPP)、sPS与聚-1-丁烯(B30)组成的嵌段共聚物和sPS/iPP/B30共混体系的热性能。结果表明sPS/iPP是不相容体系,B30与iPP可相容,B30可作为sPS/iPP共混物的相容剂。DSC和DMA分析结果表明,加入适量的B30时,sPS/iPP/B30共混物中iPP的玻璃化转变温度随B30加入量的增加而逐渐升高,而sPS的玻璃化转变温度则随B30加入量的增加而逐渐降低;TGA分析结果表明共混体系的热失重温度高于300℃,比iPP的高。     

Isotactic polypropylene microfiber prepared by carbon dioxide laser‐heating

An isotactic polypropylene (i‐PP) microfiber was obtained by irradiating a carbon dioxide laser to previously drawn fibers. To prepare the thinner i‐PP microfiber, it is necessary to previously draw original i‐PP fibers under an applied tension of 7.8 MPa at a drawing temperature of 140°C. The drawn fiber was heated under an applied tension of 0.3 MPa using the laser operated at a power density of 39.6 W cm^?2. The thinnest i‐PP microfiber obtained under optimum conditions had a diameter of 1.8 μm and a birefringence of 30 × 10^?3. Its draw ratio estimated from the diameter reached 51,630. It is so far impossible to achieve such a high draw ratio by any drawing. The wide‐angle X‐ray diffraction photograph of the microfiber shows the existence of the oriented crystallites. Laser‐heating allows easier fabrication of microfibers compared with the conventional technology such as the conjugate spinning. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1534–1539, 2004     

Preparation by melt mixing and characterization of isotactic polypropylene/SiO2 nanocomposites containing untreated and surface‐treated nanoparticles

In the present study two series of isotactic polypropylene (iPP)/SiO₂ nanocomposites containing 1, 2.5, 5, 7.5, and 10 wt % SiO₂ nanoparticles were prepared by melt‐mixing on a twin‐screw corotating extruder. In the first series untreated fumed silica nanoparticles were used, whereas in the second nanoparticles were surface‐treated with dimethyldichlorosilane. In both cases, the average size of the primary nanoparticles was 12 nm. Tensile and impact strength were found to increase and to be affected mainly by the type and content of silica nanoparticles. A maximum was observed, corresponding to samples containing 2.5 wt % SiO₂. These findings are discussed in light of the SEM and TEM observations. By increasing the amount of nanoparticles, large aggregates of fumed silica could be formed, which may explain the reduction of mechanical properties with higher concentrations of SiO₂. However, it was found that surface‐treated nanoparticles produced larger aggregates than did those derived from untreated nanoparticles, despite the increased adhesion of the iPP matrix, as was postulated from yield strength. This behavior negatively affected mechanical properties. In addition, an effort was made to determine if toughening theories, mainly the critical interparticle distance for rubber toughening or composites, also might be applicable in nanocomposites. From DSC measurements it was demonstrated that silica nanoparticles acted as effective nucleating agents, increasing the crystallization rate and the degree of crystallinity of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2684–2696, 2006     

Further study on double‐melting endotherms of isotactic polypropylene

The origins of the single‐ and double‐melting endotherms of isotactic polypropylene crystallized at different temperatures were studied carefully by differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering. The experimental data show that spontaneous crystallization occurs when the crystallization temperature is lower than 117°C; thus the lamellae formed are imperfect. At a lower heating rate, the recrystallization or reorganization of these imperfect lamellae leads to double endotherms. On the other hand, when the crystallization temperature is higher than 136°C, two major kinds of lamellae with different thickness are developed during the isothermal process, which also results in the double‐melting endotherms. In the intermediate temperature range the lamellae formed are perfect, and there is only a single peak in the distribution of lamellar thickness. This explains the origin of the single‐melting endotherm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 163–170, 2000     

Structure and morphology of isotactic polypropylene functionalized by electron beam irradiation

The structure and morphology of isotactic polypropylene (iPP), functionalized by electron beam irradiation at room temperature in air, are investigated by elementary analysis, FT‐infrared (FTIR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), polariscope, and static contact angle. Elementary analysis reveals that the element oxygen has been introduced onto iPP chains after electron beam irradiation. In addition, as shown from FTIR spectra, oxygen‐containing groups, such as carbonyl, carboxyl, and ether groups, are introduced onto iPP molecular chains. The dependence of oxygenation extent (as measured by O_1S/C_1S value of ESCA spectra) on electron beam dose is obtained. Under polariscope, it can be observed that the dominant alpha phase appears to become more enhanced, and there is no crystalline phase transition. The static contact angle of iPP decreases with increasing dose. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 75–82, 2000     

Effects of substituted aromatic heterocyclic phosphate salts on properties,crystallization, and melting behaviors of isotactic polypropylene

Nucleation effects of 2,2′‐methylene‐bis (4,6‐di‐tert‐butylphenyl) phosphate metal salts as a nucleating agent for isotactic polypropylene (iPP) were investigated with differential scanning calorimeter and polarized optical microscope, and their effects on mechanical, optical, and heat resistance properties of iPP were also studied. The results showed that monovalent metal salts of substituted aromatic heterocyclic phosphate such as sodium salt, lithium salt, and potassium salt had a good performance. With 0.2 wt % of sodium salt, lithium salt, or potassium salt incorporated into iPP, the crystallization peak temperature of iPP could be increased by 13.5, 13.6, and 15.0°C, respectively; the mass fraction of crystallinity of iPP could be increased by about 5%; and crystallization rate was enhanced increasingly. Meanwhile the tensile strength and flexural modulus of iPP could be increased by about 10 and 30%, respectively, and the clarity and heat distortion temperature of iPP could also be improved significantly. But bivalent and trivalent metal salts of substituted aromatic heterocyclic phosphate had little effect on properties of iPP. Meanwhile the morphology study showed that the addition of monovalent sodium salt could decrease the spherulite size of iPP significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4868–4874, 2006     

Effect of isotacticity distribution on the crystallization and melting behavior of polypropylene

The crystallization and melting behavior are closely related not only to the external conditions such as undercooling and cooling rate, but also to the chain structure characteristics such as isotacticity distribution. The isotacticity distribution of three commercial isotactic polypropylenes (iPP) used in this work was characterized using Temperature‐Rising Elution Fractionation (TREF) combining with Size‐Exclusion Chromatography (SEC). Their crystallization and melting behavior were observed by Differential Scanning Calorimetry (DSC) and Polarized Light Microscopy (PLM). The results indicated that for iPP with similar molecular weight and isotacticity, the difference in isotacticity distribution not only led to the variation in nucleation and growth rates of crystal, but also changed the perfection of crystals formed under the same condition, even causing the formation of different crystalline modification and the change in the equilibrium melting temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 333–341, 2002     

Influences of processing on the phase transition and crystallization of polypropylene cast films

Phase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41100.     

降冰片烯苄酰胺酸盐对等规聚丙烯力学性能和结晶性能的影响

采用差示扫描量热仪(DSC)和偏光显微镜(POM)考察了降冰片烯苄酰胺酸的不同金属盐在等规聚丙烯(iPP)中的成核效果,并研究了这些成核剂对iPP力学性能和光学性能的影响。结果表明,降冰片烯苄酰胺酸盐对ipp熔融峰值温度和结晶峰值温度的影响规律完全一致,降冰片烯苄酰胺酸钠盐(BHBC11)具有有较好的成核效果,添加浓度在0.2%时可使iPP的拉伸强度提高4.6%,弯曲模量提高18.6%;同时可使iPP的结晶峰值温度提高11.5℃;BHBC11的加入可以显著降低球晶的尺寸并大大缩短结晶时间;应用Caze方法对iPP和BHBC11成核iPP的非等温结晶动力学进行了研究,其Avrami指数都接近4。     

两种羧酸盐成核剂的制备及其对聚丙烯的成核效果研究

合成了两种具有相似化学结构的聚丙烯（iPP）α晶型成核剂二环［2.2.1］庚⁃5⁃烯⁃2,3⁃二羧酸钠（NA₁）和二环［2.2.1］庚烷⁃2,3⁃二羧酸钠（NA₂）,研究了其在iPP中的成核效果。首先,利用差示扫描量热仪（DSC）和偏光显微镜（PLM）分别考察了两种成核剂对iPP结晶行为的影响。结果表明,当NA₁和NA₂的含量为0.3 %（质量分数,下同）时,iPP的结晶峰值温度分别提升了14.5 ℃和16.0 ℃。同时,两种成核剂都能够明显细化iPP球晶尺寸。其次,利用广角X射线衍射仪（WXAD）对成核iPP进行了表征,两种成核剂都诱导iPP产生了α晶型,说明均为α晶型成核剂。然后,对成核iPP的力学性能进行了表征。结果表明,随着两种成核剂用量的增加,iPP的拉伸强度和弯曲模量呈现先升高后平稳的趋势。当NA₁和NA₂含量为0.05 %时,成核iPP的拉伸强度较纯iPP分别提升了4.6 %和8.6 %,弯曲模量分别提升了8.2 %和21.7 %;冲击强度基本保持不变。     

Thermal and crystallization behavior of silane‐crosslinked polypropylene

Silane‐crosslinked polypropylene (PP) has been prepared first by the grafting of silane onto the backbone of PP in a melt process and then by crosslinking in warm water. The effects of type and concentration of silane and peroxide on the silane grafting on PP were investigated. The thermal behavior of the silane‐crosslinked PP was studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) methods. TG results show that PP prepared via silane crosslinking increases its thermal stability greatly. It has been found from DSC measurements that the crystallization temperatures, ie the onset temperature and peak temperature of the exotherm of the silane‐crosslinked PP, increase compared with those of the pure PP. The silane crosslinking hardly changes the crystallinity degree of PP. The crystallization behavior of the silane‐crosslinked PP was also studied by wide‐angle X‐ray diffraction analysis. Copyright © 2004 Society of Chemical Industry     

Self‐interference flow of an isotactic polypropylene melt in a cavity during injection molding. I. Effect of the self‐interference flow on the properties

The self‐interference flow (SIF) of a melt in a cavity during injection molding is introduced. It comes from two streams of the melt being split by a patented mold gate called a twin gate. The effects of this flow on the static and dynamic mechanical properties, thickness distribution, and shrinkage in the transverse direction (TD) of injection‐molded isotactic polypropylene parts are discussed. SIF has an influence on the static mechanical properties, especially the impact strength. There are slight increases in the tensile strength and Young's modulus and an increase of approximately 70–90% in the impact strength in comparison with the properties of samples obtained by a conventional flow process with a common pin gate. Dynamic mechanical thermal analysis studies show an increase in the storage modulus for SIF samples. Results obtained from research into the effect of the mold temperature and injection pressure on the impact strength show that the impact strength of SIF specimens has a weaker dependence on the mold temperature and injection pressure. In addition, the flow brings a more uniform thickness distribution and a smaller shrinkage in the TD to SIF samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2784–2790, 2003     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/propylene‐g‐styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP‐g‐PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP‐g‐PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP‐g‐PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP‐g‐PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP‐g‐PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001     

Isothermal melt crystallization and melting behaviour of syndiotactic polypropylene

The lamellar morphological information and subsequent melting behaviour of syndiotactic polypropylene (s‐PP) samples isothermally crystallized at crystallization temperatures ranging from 30 to 95 °C have been investigated using a combination of wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. Three known methods for determining the equilibrium melting temperature T_m°, namely the Gibbs–Thomson extrapolation, the linear Hoffman–Weeks extrapolation and the non‐linear Hoffman–Weeks extrapolation, have been employed to evaluate this important thermodynamic parameter, and the results obtained are compared. Finally, an estimate of the equilibrium melting temperature for a perfect s‐PP sample (T_m°)_100% is given. © 2000 Society of Chemical Industry