Crystal structure of polypropylene filled with rare earth oxides

The effect of a fine powder of Y₂O₃, Nd₂O₂, and Ho₂O₃, on the crystal structure of isotactic polypropylene (iPP) was studied with WAXD and DSC techniques. The results showed that the addition of the three rare earth oxides (REOs) can increase the crystallite size of the α-form crystal and the degree of crystallinity of iPP at an annealing temperature of 120°C and that both Y₂O₃ and Nd₂O₃ are the β-nucleator of iPP. REOs enhance the overall growth rate of the spherulites of iPP. All the iPP samples filled with REOs which were crystallized isothermally at 132°C from the melt exhibited their melting peaks of the β-form on the DSC heating traces, indicating that the REOs are the nucleating agents for both the α- and β-forms of iPP under isothermal conditions. © 1996 John Wiley & Sons, Inc.     

稀土改性聚丙烯纤维染色性能的研究

采用稀土化合物苯甲酸镧与聚丙烯(PP)共混纺丝,对所得的共混改性PP纤维用分散染料和染色助剂染色,探讨了改性PP纤维的染色性能。结果表明,随着苯甲酸镧含量、染料助剂含量及染色时间的增加,改性PP纤维的上染率均增加。当苯甲酸镧质量分数为3%时,选用染色助剂氯化镧含量为0.8g/L的染液,染色时间为60 min时,改性PP纤维的上染率达75%。     

Crystallization study of rare earth and molybdenum containing nuclear waste glass ceramics

A glass-ceramic waste form is being developed for immobilization of waste streams of alkali (A), alkaline-earth (AE), rare earth (RE), and transition metals generated by transuranic extraction for reprocessing of used nuclear fuel. Benefits over an alkali borosilicate waste form are realized by the partitioning of the fission product fraction insoluble in glass into a suite of chemically durable crystalline phases through controlled cooling, including (AE,A,RE)MoO₄ (powellite) and (RE,A,AE)₁₀Si₆O₂₆ (oxyapatite). In this study, a simplified 8-oxide system (SiO₂-Nd₂O₃-CaO-Na₂O-B₂O₃-Al₂O₃-MoO₃-ZrO₂) was melted, then soaked at various temperatures from 1450 to 1150°C, and subsequently quenched, in order to obtain snapshots into the phase distribution at these temperatures. For these samples, small angle X-ray and neutron scattering, quantitative X-ray diffraction, electron microscopy, ²³Na nuclear magnetic resonance, Nd³⁺ visible absorption, and temperature-dependent viscosity were characterized. In this composition, soak temperatures of 1250°C were necessary to nucleate calcium molybdate (~10-20 nm in diameter). Further cooling produced oxyapatite and total crystallization increased with lower soak temperatures. Both Na and Nd entered the crystalline phases with lower-temperature soak conditions. Slow cooling or long isothermal treatments at ~975°C produced significantly higher crystal fractions.     

Crystallization behaviors of polypropylene and functional polypropylene

The crystallization behaviors of polypropylene (PP) homopolymer and its blends with 0–15% functional polypropylene (FPP), the backbones of which were grafted with guanidine and diamide polymer chains, were investigated with differential scanning calorimetry and wide‐angle X‐ray scattering. The crystallization kinetics were studied with spectral depolarization. The results revealed that the presence of FPP reduced the crystallinity and crystallite size of PP. Meanwhile, FPP increased the crystallization rate. Compared with that of the PP homopolymer, the crystallization temperature of PP/FPP blends was increased by more than 10°C. During isothermal crystallization, the relative crystallinity, developed as a function of time, was described by the Avrami equation. The half‐time of crystallization for PP/FPP blends was much shorter than that for the PP homopolymer. The half‐time of crystallization of PP/FPP blends depended much less on the crystallization temperature than that of the PP homopolymer. Therefore, FPP accelerated the crystallization rate of PP in a manner similar to that of a nucleator. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 872–877, 2003     

聚丙烯基复合材料的结晶行为

综述了3类聚丙烯(PP)基复合材料体系包括PP/无机物体系、PP/有机物体系和PP／聚合物体系的结晶行为。阐述了PP基体的结晶结构以及结晶动力学特征,包括添加物对PP的结晶温度、结晶速率及结晶度等的影响;分析了结晶行为对复合材料力学性能的影响。复合材料界面对基体聚合物取向结晶形态及结晶行为的影响等还需进一步研究。     

Crystallization studies on fire-retardant polypropylene

A study of the effect of a series of fire retardants upon the crystallization behavior and morphology of polypropylene suggests three categories: (1) “Insolubilized nucleating additives”—these remain insolubilized at the premelting temperature of polypropylene, resulting in very high nucleation density which leads to numerous irresolveable small spherulites. (2) “Solubilized nucleating additives”—these are soluble at the premelting temperature of polypropylene but recrystallize before and/or simultaneously with the crystallization of polypropylene; the subsequent lower nucleation density results in medium-size spherulites of a fairly heterogeneous distribution. (3) “Nonnucleating additives”—these remain solubilized in the polymer matrix throughout the course of crystallization of polypropylene. The nonnucleating nature and low viscosity of these solubilized additives results in large volume-filling spherulites crystallized at a much faster growth than the unfilled polypropylene.     

Crystallization behavior of polypropylene in polypropylene/nylon 6 blend

This article describes the crystallization behavior of polypropylene (PP) in the presence of a crystallizable polymer, namely, nylon 6, in the binary blend of PP/nylon 6 in the composition range from 0 to 30 wt % of nylon 6 content in the blend. The crystallization behavior was studied through variation of the crystallinity with the blend composition and changes in the crystallization exotherms were recorded by differential scanning calorimetry (DSC) and the spherulite morphology was observed via polarized light microscopy (PLM). Comparison of the crystallization exotherms and melting endotherms revealed some differences which are attributed to the role of a sufficiently high thermal energy of the nylon 6 crystals on the melting of PP. The crystallinity of PP decreased in the presence of nylon 6, whereas the crystallinity of nylon 6 increased considerably in the presence of PP. The rate of nucleation of PP on addition of nylon 6 decreased rapidly in the region 0–10 wt % nylon 6 content, and, thereafter, at a higher nylon 6 content, decrease of the nucleation rate was relatively slow. PLM observation revealed the presence of composite spherulites with PP spherulites grown on the surface of the already‐formed nylon 6 spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1153–1161, 1999     

Crystallization features of oxidized isotactic polypropylene

The effect of the initial molecular weight parameters of polypropylene on the kinetics of isothermal polymerization is shown. It is found that the feed polymer with a wider molecular weight distribution (P-1) is characterized by lower values of the half-crystallization time as compared to the polymer with a narrower molecular weight distribution (P-2). Comparison between the crystallization parameters and the kinetics of accumulation of oxidation products showed that as the degree of oxidation of the polypropylene increases, the crystallization rate for both samples decreases and the concentration of the oxidation products increases. In this case, the degradation of tie chains accelerates the formation of crystallites. It is shown that P-1 has a higher nucleation energy as compared with P-2 and that this parameter increases during the oxidation of both polymers.     

稀土双膦酸酯配合物和稀土氯化物对Mannich反应的催化作用

研究了Dy(OTf)₃、DyCl₃和稀土双膦酸酯配合物{ ［Dy(OTf)₂L₂(H₂O)₂］(OTf)(CH₃CN)}［L=(iPrO)₂P(O)CH₂P(O)(iPrO)₂］ 等对Mannich 反应的催化作用,发现以Dy(OTf)₃为催化剂时,收率为54%,［Dy(OTf)₂L₂(H₂O)₂］(OTf)(CH₃CN)的收率仅为8%,DyCl₃收率达47%。研究了12种稀土金属氯化物对Mannich 反应的催化作用,其中,ErCl₃催化剂的收率最高,达到61%。     

High-entropy rare earth tetraborides

Six high-entropy rare earth tetraborides of the tetragonal UB₄-prototyped structure have been successfully synthesized for the first time. The specimens are prepared from elemental precursors via high-energy ball mill and in-situ reactive spark plasma sintering. The sintered specimens are >98 % in relative densities without detectable oxide impurities (albeit the presence of minor hexaborides in some compositions). No detectable secondary phase is observed in the composition (Y_0.2Nd_0.2Sm_0.2Gd_0.2Tb_0.2)B₄, which is proven homogeneous at both microscale and nanoscale. The Vickers microhardness are determined to be ～13?15 GPa at a standard indentation load of 9.8 N. A scientifically interesting observation is represented by the anisotropic lattice distortion from the rule-of-mixture averages. This work expands the family of high-entropy ceramics via fabricating a new class of high-entropy borides with a unique tetragonal quasi-layered crystal structure.     

Crystallization and chemi-crystallization of recycled photo-degraded polypropylene

Injection moulded bars have been made from virgin polypropylene and from blends containing recycled photo-degraded polypropylene, then subjected to further ultraviolet (UV) exposure. Crystallinity measurements have been made at different depths from the exposed surface using X-ray diffraction and differential scanning calorimetry. Strong evidence for chemi-crystallization is provided for the photo-degraded samples. The crystallinity results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission leads to greater crystallizability and accounts for the observed chemi-crystallization. Molecular defects inhibit crystallization and eventually limit chemi-crystallization, as observed with a blend containing 75% virgin material and 25% recycled photo-degraded polymer after further UV exposure.     

Crystallization behaviors of polypropylene/montmorillonite nanocomposites

The isothermal crystallization kinetics of polypropylene/montmorillonite (PP/MMT) nanocomposites synthesized via intercalation polymerization were investigated by using differential scanning calorimeter and polarizing optical microscope (POM). The crystallinity of the nanocomposites decreased with the increase of the montmorillonite content, indicating that the MMT layers dispersed in the PP matrices confined the PP chains and hindered the crystallization of the PP chains. The POM photographs showed that the spherulites of the PP/MMT nanocomposites were greatly decreased in size as MMT was introduced. On the other hand, the crystallization rate increased dramatically with the increasing of MMT content. The interfacial free‐energy per unit area perpendicular to PP chains in PP/MMT nanocomposites decreased with increasing MMT content, suggesting that the MMT layers acted as heterogeneous nuclei in the nucleation of crystallization. The nucleus density increased with the increasing of MMT content, leading to a positive effect on the crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1978–1985, 2002     

聚丙烯多单体接枝共聚物的结晶行为

通过固相接枝法制备聚丙烯(PP)与马来酸酐、甲基丙烯酸甲酯和丙烯酸丁酯的多单体接枝共聚物(PPTM)。采用差示扫描量热法、X射线衍射和偏光显微镜等研究接枝支链对接枝共聚物结晶行为的影响,并计算接枝共聚物的晶胞参数。接枝支链能诱导PPTM的异相成核,形成β晶型,也能阻碍结晶的进行。接枝支链诱导PPTM形成β晶型需要合适的支链长度。PPTM的微晶尺寸和晶胞参数都受到接枝支链的影响。PPTM的c轴(晶体生长方向)的晶胞参数比PP的稍大。     

Crystallization behavior of starch‐filled polypropylene

Starches of different granule sizes, including corn, rice, and amaranth starches, were used to prepare starch‐filled polypropylene (PP) and the effect of starch granule size on crystallization behavior PP was investigated. Differential scanning calorimetry and scanning electron microscopy were used to monitor the energy changes of the crystallization of the melt and to characterize the morphology of PP/starch composites, respectively. Little interaction was observed between starch and PP despite the difference in starch granule size. The crystallization temperature of PP decreased with the addition of starch and this decrease became more apparent with increasing starch granule size. During nonisothermal crystallization, the dependency of the relative degree of crystallinity on time was described by the Avrami equation. The addition of starch decreased the overall crystallization rate of PP, which was attributed to an increase in the activation energy of crystallization under nonisothermal conditions according to the Kissinger equation. An increase in starch granule size of starch would increase the crystallization activation energy of PP and consequently decrease its crystallization rate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 484–492, 2004     

Crystallization behavior of polypropylene filled with surface-modified talc

Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0–40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc. © 1996 John Wiley & Sons, Inc.     

Crystallization of running filament in melt spinning of polypropylene

The crystallization kinetics of the running filament in melt spinning have been studied for three cases: isothermal crystallization of an isotropic melt, non-isothermal crystallization of an isotropic melt, and non-isothermal crystallization of a non-isotropic melt. Both the temperature and the orientation dependences of nucleation rate and growth rate are estimated for polypropylene. Calculated curves for non-isothermal crystallization of a non-isotropic melt with partial high orientation closely approximate the experimental data. In particular, the experimental data are best explained by crystallization with two-dimensional growth. The crystallization processes in melt spinning may be governed by localized molecular orientation of the supercooled melt in the initial stage.