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     

端胺基聚氨酯/环氧树脂胶粘剂的固化反应特征及其反应动力学研究

采用差示扫描量热法(DSC)研究了含有柔性链和刚性结构单元的端胺基聚氨酯(ATPU)对环氧树脂E-44固化反应过程特点和反应过程动力学的影响。结果表明,固化剂(ATPU)的掺加量对环氧树脂E-44固化反应过程有显著的影响,随着ATPU的增加,固化放热量增加。当ATPU的掺加量为1.6时,固化反应放热量达到最大值。固化温度研究表明,ATPU/E-44固化体系的等温固化起始温度和最高温度分别为121℃和177℃。固化反应的动力学研究表明,ATPU/E-44胶粘剂固化反应的表观活化能为81.8kJ/mol;固化反应的级数为1.3。     

Effect of Clay Dispersion on the Nonisothermal and Isothermal Crystallization Behaviors of Polyethylene Composites

The presence of nanosized clay fillers can greatly influence the crystallization behaviors and crystalline morphologies of polymer composites. In this study, the modified montmorillonite polyethylene nanocomposites have been prepared by melt mixing, followed by injection molding. The morphology and microstructure of the composites were characterized by scanning electron microscopy and Fourier transform infrared spectrometry. The nanosized clay particles act as a nucleating agent in the solidification process of the matrix. The relative crystallinity ratio decreases with the decrement of polymer loading. Nonisothermal and isothermal crystallizations were conducted to characterize the crystallization kinetics of nanocomposites. The effects of clay dispersion on the crystallization of polymer were quantified by Avrami and Hoffman models. The addition of 1?wt% clay into polymer matrix has significantly increased the activation energy. The crystallization rate constants (G) have been determined which are higher for the composites than that for the polymer matrix.     

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 temperature investigation of Cu2ZnSnS4 by using Differential scanning calorimetry (DSC)

The Cu₂ZnSnS₄ (CZTS) powder was systematically investigated by energy dispersive X-Ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ramam spectrometer, and further studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA). The Ramam and XRD results showed that the sample is a structure of Kesterite type under a condition of Cu-rich and Zn-poor with few impurity phases. The DSC results show that incubation time, peak time and end time of crystallization are all reduced with the increasing temperature; and the temperature of 550 ℃ will be more suitable for annealing treatment of CZTS. A CZTS film is also fabricated and annealed at 550 ℃ to confirm the result of the research. The systematic investigation of CZTS by using differential scanning calorimetry provided a fundamentally dynamic reference for the temperature selection of anneal during the fabrication of CZTS.     

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。     

PP/木粉复合材料的热性能

以聚丙烯(PP)/木粉(WF)复合材料(WPC)为对象,研究了WF及马来酸酐接枝聚丙烯(PP-g-MAH)含量对WPC热性能的影响。PP和WF的熔融热焓分别为75.84 J/g和189.50 J/g,而w(WF)为10%,20%,30%,40%,50%的WPC的熔融热焓分别为54.99,40.37,38.66,27.34,22.09 J/g,加入PP-g-MAH后,WPC熔融热焓值有所提高。所有WPC在200～750℃的热分解都是分两步完成的,WF含量越高,两步分解现象越明显,第一步失重率越大;WPC每步分解的起始分解温度及峰值温度均有所提高,WPC对热更稳定。     

Surface functionalization of polypropylene by entrapment of polypropylene‐grafted‐poly(ethylene glycol)

A surface functionalization polypropylene was prepared by entrapment a copolymer of polypropylene‐grafted‐poly(ethylene glycol) into polypropylene. The effects of structure of copolymer, contact dies, and content of modifiers were studied. The results of attenuated total reflection infrared spectroscopy(ATR‐FTIR) and contact angle measurements indicated that PP‐g‐PEG could preferably diffuse onto the surface and effectively increase the hydrophilicity of PP. PPw‐g‐PEG with lower PEG contents, lower molecular weight of PPw and PEG had better selective enrichment on the surface of PP blend film. By grafting of PEG‐OH onto the MPP, PP macromolecular surface modifier with better solvent‐resistance than that of PEG can be achieved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comparison of carboxylated and maleated polypropylene as reactive compatibilizers in polypropylene/polyamide‐6,6 blends

Using reactive extrusion, polypropylene is functionalized with maleic anhydride and compared on an equimolar basis to polypropylene that is functionalized with an asymmetric, carboxylic acid containing peroxide. The grafting efficiency for the asymmetric peroxide is double that obtained for the maleic anhydride system. Moreover, the asymmetric peroxide yields a functionalized material with minimal molecular weight degradation and desirable mechanical properties, relative to maleic anhydride‐grafted polypropylene. In compatibilized blends of polypropylene and nylon 6,6, the polypropylene that was functionalized with the asymmetric peroxide is found to be an improved compatibilizer compared to that of maleic anhydride‐grafted polypropylene. The differences in mechanical properties of the two different functionalized polypropylene materials and their respective blends are rationalized on the basis of the grafting efficiency, molecular weight degradation during reactive extrusion, and effect of free functional species on the ability to form graft copolymers in compatibilized blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2398–2407, 2001     

Crystallization of hydroxybutyrate oligomers. Part 2. Growth and thickening of solution grown crystals observed in situ using synchrotron radiation

Synchrotron X-ray radiation has been used in situ to follow the crystallization of a hydroxybutyrate oligomer containing 32 repeat units from dilute solution in propylene carbonate, and to study chain unfolding during heating in oligomers with 24 and 32 repeat units. A discontinuity in growth rate occurs at 36–37 °C for the 32-mer: crystals grown below this temperature contain folded chains, which transform during heating through a process of partial dissolution and re-crystallization to form extended chain crystals. Crystals grown above the transition temperature contain extended chains that do not rearrange during heating. A similar change happens in the 24-mer between 35 and 40 °C. Thermal expansion in the (110) lattice direction (the fold direction) was in the range 5.3+/−0.3×10⁻⁵ nm °C⁻¹, with an additional discontinuous increase in 0.001 nm accompanying chain unfolding.     

N-羟甲基丙烯酰胺熔融接枝PP的流变性能

采用熔融接枝法在双螺杆挤出机上制得接枝率为0．20％～0．85％的N-羟甲基丙烯酰胺接枝聚丙烯(PP-g-NHA),讨论了接枝物的组成、剪切应力和剪切速率以及温度对PP-g-NHA熔体流变行为、熔体黏度的影响,测定了接枝物的非牛顿指数。在相同剪切应力时,PP-g-NHA的剪切黏度比PP低,但黏流活化能比PP高。     

Effect of silane‐grafted polypropylene on the mechanical properties and crystallization behavior of talc/polypropylene composites

Talc‐filled polypropylene (PP) composites coupled with silane‐grafted polypropylene (PP‐g‐Si) were prepared. Effect of PP‐g‐Si on the mechanical properties, crystallization, and melting behavior of PP composites was investigated. Compared with the uncoupled composites, the mechanical properties of Talc/PP composites coupled with a small amount of PP‐g‐Si were increased to some extent. Meanwhile, PP‐g‐Si can promote crystallization rate and increase crystallization temperature of PP in the composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2974–2977, 2000     

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     

Effect of chain disentanglement on melt crystallization behavior of isotactic polypropylene

Isotactic polypropylene (iPP) with “disentangled” chains was generated through crystallization of iPP from its mineral oil solution. TGA test assured complete removal of mineral oil from iPP precipitates. Time sweep rheological measurements showed the modulus build-up with time indicating the formation of “disentangled” chains in iPP after the sample disentanglement treatment. The “disentangled” chains could preserve for a certain time before completely re-entangled during melting. Crystallization kinetics of iPP with “disentangled” chains was studied by using polarized optical microscope. The growth rate of spherulites in “disentangled” iPP was faster than that in the entangled one.     

Phase behaviors of poly(oxyethylene)-grafted polypropylene copolymers

A family of amphiphilic graft copolymers were prepared from a maleated polypropylene (PP-g-MA) and various crystalline poly(oxyethylene)-segmented amines of 1000 to 3000 molecular weight. Structurally, these copolymers consist of polypropylene (PP) backbone and several crystalline poly(oxyethylene) (POE) pendants in the structure. In the observation of their phase behaviors by using a differential scanning calorimeter (DSC), the interference between the POE segments and PP backbone was found. In a particular case (PP-g-MA/ED-2001), the heat of POE crystallization did not show off in the cooling curve of the DSC, but appeared during the consecutive heating process. Generally, heating and cooling patterns of the DSC analyses showed the shifts of melting and crystallizing temperatures, depending on the length and the termini of POE, from those of the starting materials— PP-g-MA and POE amines. The TGA and optical microscopy observation further supported the DSC analyses.     

Influence of pre-shearing on the crystallization of an impact-resistant polypropylene copolymer

Impact-resistant polypropylene copolymer (IPC) samples with various pre-shear histories were prepared by a Brabender Rheometer. The influence of pre-shearing on crystallization of IPC, including isothermal and nonisothermal crystallization behaviors was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results of nonisothermal crystallization showed that compared with as-received IPC, the temperatures referred to the peak of crystallization exotherm, T_p, were prominently elevated for pre-sheared IPC. In isothermal crystallization experiment, combining Avrami Method and Hoffman-Lauritzen Model, it was found that the half-time of crystallization (t_1/2) of pre-sheared IPC was greatly shortened and the calculated fold surface free energy (σ_e) within the isothermal temperatures investigated showed a large reduction. Morphological development during isothermal crystallization observed by POM clearly confirmed that the enhancement in crystallization is mainly due to the fast formation of nuclei during crystallization. Besides, using successive self-nucleation and annealing (SSA) thermal fractionation technique, changes in chain structures induced by pre-shearing were obtained. The relaxation behavior of pre-sheared IPC was also evaluated and it was found that the shear-induced enhancement in crystallization could be relaxed to various extents under annealing conditions.     

Influence of thermal treatments,molecular weight,and molecular weight distribution on the crystallization of β‐isotactic polypropylene

Six samples of isotactic polypropylene were examined to study the influence of the thermal treatments and the molecular weights and their distribution on the β‐crystallization of the polymer. The highest amount of the β‐phase was obtained by isothermal crystallization and in correspondence of high average molecular weights and wide molecular weight distributions. Small‐angle X‐ray scattering pointed out that a partial β‐crystallization seems not to influence the lamellar morphology parameters. Differential scanning calorimetry measurements, at different heating rates, allowed us to confirm that the multiple melting endotherms behavior of the β‐phase is to be correlated to a melting–recrystallization–melting mechanism. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1008–1012, 2004     

Morphology, reorganization and stability of mesomorphic nanocrystals in isotactic polypropylene

The morphology and thermodynamic stability of crystals of isotactic polypropylene (iPP) were analyzed as a function of the path of crystallization by atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Samples were melt-crystallized at different rates of cooling using a “controlled rapid cooling technique”, and subsequently annealed at elevated temperature. Mesomorphic equi-axed domains with a size less than 20 nm were obtained by fast cooling from the melt at a rate larger about 100 K s⁻¹. These domains stabilize on heating by growing in chain direction and cross-chain direction, to reach a maximum size of about 40-50 nm at a temperature of 433 K, with the quasi-globular shape preserved. Annealing at 433 K additionally triggers formation of different types of lamellae. It is suggested that these lamellae either develop by coalescence of nodules, or by recrystallization from the melt. The transition from the disordered mesomorphic structure, evident at ambient temperature after fast crystallization, to monoclinic structure on heating at about 340 K occurs at local scale within existing crystals, and cannot be linked to complete melting of mesomorphic domains and recrystallization of the melt. The temperature of melting of initial mesomorphic domains, after reorganization at elevated temperature, is identical to the temperature of melting of rather perfect lamellae, obtained by initial slow melt-crystallization, followed by annealing. The close-to-identical temperatures of melting of these crystals of largely different shapes are confirmed by model calculations, using the Gibbs-Thomson equation. Modeling of the melting temperature reveals that nodular crystals, stabilized by annealing at high temperature, exhibit a similar fold-surface as lamellar crystals.     

等规聚丙烯/顺丁橡胶合金的结晶和抗冲击性能

研究了熔融共混法制备的不同共混比的等规聚丙烯(iPP)／顺丁橡胶(PcBR)合金的结晶特性及抗冲击性能。结果显示,随着(?)(PcBR)从0增至40％,iPP球晶的完整程度逐渐下降,球晶间的边界模糊化,球晶不断细化; PcBR的加入诱导了iPP的β晶型生成,其含量的增加导致合金中的微晶尺寸减小,晶面间距值基本不变,而长周期则明显增加;同时,合金的结晶峰所对应的温度有所升高,结晶速率明显增大,而相对结晶度减小,PcBR对iPP的结晶起到异相成核剂的作用;PcBR对iPP有显著的增韧效果。