Quiescent crystallization kinetics and morphology of i‐PP resins for injection molding. II. Nonisothermal crystallization as a function of molecular weight

The quiescent nonisothermal crystallization kinetics of polypropylene resins was studied as a function of their molecular weight, M_w. Differential scanning calorimetry and polarized light optical microscopy were used to follow this kinetics. It was observed that a modified Hoffman and Lauritzen equation could describe with accuracy their nonisothermal behavior. Also it was found that the polypropylene nonisothermal growth rates, G_n, were similar to their corresponding isothermal rates, G, and also decreased with the increase in M_w. The use of a prior isothermal nucleation procedure allowed to obtain data at higher temperatures and to compare these data at higher cooling rates than the ones found in the literature. The morphology of all the samples revealed a fine and radial spherulitic texture. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1733–1740, 1999     

Isothermal and nonisothermal crystallization kinetics of isotactic polypropylene nucleated with substituted aromatic heterocyclic phosphate salts

The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with substituted aromatic heterocyclic phosphate salts were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters such as the Avrami exponent n, crystallization rate constant Z_t, and crystallization half‐time t_1/2 were compared. The results showed that a remarkable decrease in t_1/2 as well as a significant increase in overall crystallization rate was observed in the presence of monovalent salts of substituted aromatic heterocyclic phosphate, while bivalent and trivalent salts have little effect on crystallization rate of iPP. The addition of monovalent metal salts could decrease the interfacial free energy per unit area perpendicular to PP chains σ_e value of iPP so that the nucleation rate of iPP was increased. During nonisothermal crystallization, Caze method was used to analyze the crystallization kinetics. It also showed that monovalent metal salts had better nucleation effects than bivalent and trivalent metal salts. From the obtained Avrami exponents of iPP and nucleated iPP it could be concluded that the addition of different nucleating agents changed the crystal growth pattern of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3307–3316, 2006     

高流动抗冲PP的结晶特性及结晶动力学

采用X射线衍射仪、差示扫描量热仪和偏光显微镜研究了5种高流动抗冲聚丙烯(PP)树脂的结晶特性和结晶动力学。结果发现：国产试样的结晶度与晶粒尺寸明显不同于进口试样;在等温结晶条件下。总结晶速率常数和总结晶速率随结晶温度的增加而下降,而结晶半值期增加;在所研究的温度范围内。所有试样的Avrami指数基本为2～3的非整数;在133℃以下,5^#试样的球晶生长速率明显高于其他试样,但在相同结晶温度时,国产试样的总结晶速率大于进口试样。5种试样在抗冲击性能上的差异归因于它们在结晶特性和结晶动力学方面的不同。     

Isothermal crystallization behavior of metallocene‐catalyzed isotactic polypropylene

Isothermal crystallization behavior of isotactic polypropylene (iPP) synthesized using metallocene catalyst was investigated in this work. The isotacticity of the polypropylene was characterized by ¹³C‐NMR spectroscopy. It was found that the melting temperature (T_m) of the iPP is 123.51°C and the crystallization temperature (T_c) is 93°C. The iPP synthesized in this work did not show a general increase of T_m with an increase of crystallization temperature T_c, due to the short crystallization time of 20 min and low molecular weight (number average molecular weight = 6,300). The iPP showed a tendency of increasing heat of fusion (ΔH_f) with decreasing crystallization temperature. All the spherulites of iPP samples showed negative birefringence. For the iPP sample crystallized at the highest T_c (= 123°C, just below T_m), the spherulite showed a pronounced Maltese Cross and a continuous sheaf‐like texture aligning radially, which suggests that R‐lamellaes are dominant in this spherulite. The crystalline structure of the iPP was also investigated by X‐ray diffraction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 231–237, 2005     

聚丙烯/聚磷酸铵复合材料的等温结晶行为

采用差示扫描量热法研究了聚丙烯(PP)聚/磷酸铵(APP)复合材料的等温结晶过程。引入APP后,PP/APP复合材料的平衡熔点升高,结晶速率大幅度提高。采用Avrami方程研究了该体系的结晶动力学,发现PP/APP复合材料呈现明显的异相成核特征,随w(APP)的增加,Avrami结晶速率常数增大,半结晶时间降低。     

聚丙烯/海泡石复合材料的等温结晶行为

采用熔融共混的方法制备聚丙烯（PP）/海泡石复合材料,通过示差扫描量热仪和偏光显微镜研究有机化改性海泡石填充PP复合材料在不同温度下的等温结晶行为,考察海泡石对PP结晶行为的影响,采用Avrami方程处理等温结晶过程,并计算结晶动力学参数。结果表明,海泡石的加入使复合材料的结晶时间缩短,结晶度增大;随着结晶温度的升高,各体系的结晶速率下降,结晶速率常数n、K降低,并且随着结晶温度（Tc）的升高,半结晶时间（t1/2）增大;在同一结晶温度（Tc）下,海泡石的加入提高了基体的结晶速率,加快了PP的异相成核过程,使得PP球晶尺寸减小。     

Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Blends of polypropylene resins with a liquid crystalline polymer. I. Isothermal crystallization

The isothermal crystallization kinetics of blends of different polypropylene (PP) resins and a liquid crystalline polymer (LCP) after two different melting conditions (200 and 290°C) were studied by DSC and polarized light optical microscopy. The resins were a homopolymer (hPP), a random copolymer with ethylene (cPP), and a maleic anhydride grafted PP (gPP). The LCP was Vectra A950, a random copolymer made of 75 mol % of 4‐hydroxybenzoic acid and 25 mol % of 2‐hydroxy,6‐naphthoic acid. It was observed that the overall crystallization rates of all the blends after melting at 200°C were higher than those after melting at 290°C. The LCP acted as a nucleating agent for all the PP resins; however, its nucleating effect was stronger for the hPP than for the cPP and gPP resins. After both melting conditions, an increase was observed in the overall crystallization rate of the hPP and gPP resins with the increase in the amount of LCP, but not in the cPP crystallization rate. The fold surface free energy σ_e of hPP and cPP in the blends decreased, but increased in the gPP blends. Finally, all the PP resins formed transcrystallites on the LCP domain surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 916–930, 2003     

管材专用PPR的等温结晶动力学

研究了管材专用无规共聚聚丙烯(PPR)的结晶温度和等温结晶行为,利用Avrami方程对等温结晶过程和动力学进行了分析。结果表明:北欧化工公司的PPR1具有更高的结晶温度、结晶度以及更快的结晶速率。同一结晶温度条件下,国产PPR3的结晶度达到一半的时间略高于其他PPR。利用Hoffman-Lauritzen结晶动力学理论计算得到了PPR的成核常数和结晶生长时大分子在垂直于分子链方向的折叠表面自由能(σ_e),与其他试样相比,PPR1的σ_e最低,PPR3的σ_e最高,结晶速率最慢。通过偏光显微镜照片可以发现,PPR1的球晶尺寸最小,PPR3和PPR4的球晶较大,球晶尺寸比较接近。     

小本体聚丙烯及其接枝丙烯酰胺的非等温结晶动力学

采用DSC方法测试了小本体聚丙烯（PP）及其接枝丙烯酰胺（PP-g-AM）非等温结晶过程的释热情况,并对两组实验数据分别运用Jeziorny法和Mo法进行了处理和比较.结果表明,两种方法均可准确地描述PP及PP-g-AM的非等温结晶过程.PP接枝前后Avrami指数n无明显改变,表明两者结晶机理基本相同;由Jeziorny法得到接枝产物的校正晶体增长速率常数Z_c略大于纯PP的Z_c;由Mo法计算得出,PP-g-AM的F(T)值略小于纯PP的F（T）,表明接枝物的相对结晶速率略大于纯PP的相对结晶速率.     

Isothermal crystallization of isotactic polypropylene blended with low molecular weight atactic polypropylene. Part I. Thermal properties and morphology development

The thermal properties and morphology development of isotactic polypropylene (iPP) homopolymer and blended with low molecules weigh atactic polypropylene (aPP) at different isothermal crystallization temperature were studied with differential scanning calorimeter and wide-angle X-ray scattering. The results of DSC show that aPP is local miscible with iPP in the amorphous region and presented a phase transition temperature at T_c=120 °C. However, below this transition temperature, imperfect α-form crystal were obtained and leading to two endotherms. While, above this transition temperature, more perfect α- and γ-form crystals were formed which only a single endotherm was observed. In addition, the results of WAXD indicate that the contents of the γ-form of iPP remarkably depend both on the aPP content and isothermal crystallization temperature. Pure iPP crystallized was characterized by the appearance of α- and γ-forms coexisting. Moreover, the highest intensity of second peak, i.e. the (0 0 8) of γ-form coexisting with (0 4 0) of α-form, and crystallinity were obtained for blended with 20% of aPP, the γ-form content almost disappeared for iPP/aPP blended with 50% aPP content. Therefore, detailed analysis of the WAXD patterns indicates that at small amount aPP lead to increasing the crystallinity of iPP blend, at larger amount aPP, while decreases crystallinity of iPP blends with increasing aPP content. On the other hand, the normalized crystallinity of iPP molecules increases with increasing aPP content. These results describe that the diluent aPP molecular promotes growth rate of iPP because the diluent aPP molecular increases the mobility of iPP and reduces the entanglement between iPP molecules during crystallization.     

Isothermal crystallization kinetics and morphology development of isotactic polypropylene blends with atactic polypropylene

The crystallization kinetics and morphology development of pure isotactic polypropylene (iPP) homopolymer and iPP blended with atactic polypropylene (aPP) at different aPP contents and the isothermal crystallization temperatures were studied with differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. The spherulitic morphologies of pure iPP and larger amounts of aPP for iPP blends showed the negative spherulite, whereas that of smaller amounts of aPP for the iPP blends showed a combination of positive and negative spherulites. This indicated that the morphology transition of the spherulite may have been due to changes the crystal forms of iPP in the iPP blends during crystallization. Therefore, with smaller amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends increased with increasing aPP and presented a lower degree of perfection of the γ form coexisting with the α form of iPP during crystallization. However, with larger amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends decreased and reduced the γ‐form crystals with increasing aPP. These results indicate that the aPP molecules hindered the nucleation rate and promoted the molecular motion and growth rate of iPP with smaller amounts of aPP and hindered both the nucleation rate and growth rate of iPP with larger amounts of aPP during isothermal crystallization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1093–1104, 2007     

聚丙烯/超支化聚酯酰胺共混物的等温结晶动力学

将超支化聚酯酰胺(HBPEA)与聚丙烯(PP)挤出共混,得到PP/HBPEA共混物。利用差示扫描量热法研究了HBPEA改性PP的结晶行为和等温结晶动力学。结果表明:Avrami方程适用于研究PP/HBPEA共混物的等温结晶动力学,Avrami指数为1.48~2.11,晶体的生长方式为二维盘状方式。加入HBPEA可加快PP的结晶速率,在不同等温结晶温度条件下,HBPEA为0.4 phr时可使半结晶速率提高到纯PP的1.3~2.0倍。使用Hoffmann-Lauritizen理论计算了端表面自由能,发现加入HBPEA可降低垂直于分子链方向的界面自由能,促进PP链折叠,提高PP的结晶能力。     

Substrate effect on the crystallization of isotactic polypropylene

The evolution of storage modulus measured by a rotational rheometer shows that the isothermal crystallization of isotactic polypropylene (iPP) melts in contact with aluminum plates (PP-Al) are considerably faster than that with stainless-steel plates (PP-SS). The difference is bigger at higher temperatures, and this behavior is opposite to that expected by our numerical simulation considering uniform bulk phase transition and substrate's ability to remove the latent heat. Polarized optical observations and surface energy evaluations via contact angle measurement indicate that surface energy of the substrates, including the effects of submicrometer morphology and roughness, should be the key factor to affect the crystallization of iPP. Transcrystallization zones, in which the nucleation density is controlled by the surface energy of substrates, were observed to grow toward the bulk with the thickness of about 0.2 mm for iPP to affect the global crystallization behavior. The critical value of surface energy of substrate to promote the interfacial crystallization of a polymer melt is derived, in terms of which the aluminum and stainless steel as well as optical glass, promote the surface nucleation with respect to the bulk nucleation of iPP. As a consequence, the conventional differential scanning calorimetry measurement mainly gives the heat fluxes of interfacial crystallization rather than the bulk crystallization due to the large surface-to-volume ratio of the specimen and the aluminum pan used which is a high surface energy substrate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Isothermal crystallization behavior and melting characteristics of injection sample of nucleated polypropylene

The isothermal crystallization behavior and melting characteristics of pure polypropylene (PP) and PPs nucleated with a phosphate nucleating agent (A) and a sorbitol derivative (D) have been studied by differential scanning calorimetry (DSC). Compared with pure PP, nucleated PPs show a shorter half‐times of crystallization. Dependence of crystallization rate of nucleated PP on the crystallization temperature is stronger than that of pure PP at the higher crystallization temperature, whereas the opposite results are obtained at the lower crystallization temperature. Addition of nucleating agent shifts the temperature at the deviation from the baseline of DSC melting curve, T, and the temperature at the completion of melting, T, to higher temperatures, indicating that nucleated PPs exhibit a higher perfection of PP crystals. A shoulder peak in the high temperature range of melting peak of nucleated PP and a wider low temperature region in the melting peak of pure PP are observed. Obviously, PP and nucleated PPs form different distribution of crystal perfection in the isothermal crystallization process. According to the half‐time of crystallization, nucleating agent A is more effective than D. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2547–2553, 2000     

Isothermal crystallization kinetics of commercially important polyalkylene terephthalates

The isothermal crystallization kinetics of virgin, melt‐mixed, and nucleated specimens of polyethylene terephthalate (PET), polypropylene terephthalate (PPT), and polybutylene terephthalate (PBT) were measured. The purpose of the study was to determine the difference in crystallization rate of PPT, which is to be commercially available in the near future, to the extensively studied, commercially important polyalkylene terephthalates PET and PBT. At equivalent supercooling, the crystallization rate of PPT was between that of PET and PBT, with PBT being the fastest crystallizing polymer. Melt‐mixing virgin materials resulted in a substantial increase in the crystallization rate for all three polyalkylene terephthalates. The addition of talc or sodium stearate as a nucleating agent resulted in a further increase in crystallization rate for all three polyesters. Although the addition of talc or sodium stearate to PPT and PET greatly enhanced crystallization rate, these nucleating agent–containing materials still did not crystallize as fast as PBT melt‐mixed in the absence of any intentionally added nucleating agents. Analysis of the crystallization kinetic data using the Avrami equation showed that melt‐mixing and the addition of sodium stearate resulted in an increase in the average Avrami exponent. This result suggested a change in the mechanism of nucleation toward more sporadic nucleation. For the sodium stearate–nucleated materials, the Avrami exponent was found to increase with increasing crystallization temperature, but a precise explanation of this behavior could not be provided without a knowledge of crystallite morphology. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1296–1307, 2000     

纳米Al_2O_3改性聚丙烯的非等温结晶动力学

采用差示扫描量热法研究了聚丙烯(PP)及PP/纳米Al_2O_3复合材料的非等温结晶动力学。结果表明:纳米Al_2O_3有异相成核的作用,使PP的结晶峰温升高;PP的半结晶时间随纳米Al_2O_3含量增大而减小;纳米粒子的填充使PP的结晶活化能(△E)增大,含纳米Al_2O_3质量分数为2%的PP的△E最大。     

聚丙烯在溶液中的等温结晶行为

采用差示扫描量热仪（DSC）分析聚丙烯（PP）在2种不同溶剂中的等温结晶过程,并使用Avrami方程研究等温结晶动力学。 结果表明,晶体生长速率随着结晶温度的升高而降低。 同时,根据Lauritzen⁃Hoffman 二次成核理论,PP在溶液中的成核常数K_g和折叠表面自由能σ_e低于PP原料,反映了其在溶液中的结晶速率较高。     

Cavitation during isothermal crystallization of isotactic polypropylene

Cavitation during isothermal crystallization of thin films of isotactic polypropylene was investigated systematically by light microscopy. Cavitation results from the negative pressure buildup due to density change during crystallization in the pockets of melts occluded by impinging spherulites. The morphology of such areas was also studied by SEM. The value of the negative pressure at the moment of cavitation was calculated from the drop of the spherulite growth rate. It was shown that the process of cavitation and the value of the negative pressure causing cavitation depend on the crystallization temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2439–2448, 2001     

Effect of isotacticity distribution on crystallization kinetics of polypropylene

The crystallization kinetics of isotactic polypropylene (iPP) depends not only on the undercooling but also on its microstructure characteristics. In this paper the effect of isotacticity distribution on the isothermal kinetics of iPPs in the crystallization regime III was examined by differential scanning calorimetry. The microstructure features of two commercial film grade iPPs were characterized with temperature rising elution fractionation and size exclusion chromatography. The results indicated that, although the overall isotacticities and molecular weights of two iPPs were similar, their isothermal crystallization kinetics displayed marked differences due to the disparity in isotacticity distributions. With increasing molecular weight of components containing crystallizable units, the isothermal crystallization rate exhibited a higher temperature dependence. When the isotactic defects in polypropylene chains increase with the molecular weight of components, both the fold surface free energy σ_e and the work of chain folding q decreases, in spite of the higher molecular weight. © 2002 Society of Chemical Industry