Comparative study of the nucleation activity of third‐generation sorbitol‐based nucleating agents for isotactic polypropylene

The nucleation activity of the sorbitol derivatives 1,2,3,4‐bis(3,4‐dimethylbenzylidene sorbitol) and methyldibenzylidene sorbitol are compared with that of talc, a conventional nucleating agent for the monoclinic crystalline phase of isotactic polypropylene. The thermal parameters associated with the dynamic crystallization process are studied as a function of the cooling rate by differential scanning calorimetry, and the nucleating efficiency is assessed by comparison with self‐nucleation, the highest values being observed for 1,2,3,4‐bis(3,4‐dimethylbenzylidene sorbitol) over the whole concentration range. The nature of the polymer crystals formed in the nucleated polymer was studied by X‐ray diffraction, and the data show an increase in a preferred orientation of the polymer crystallites with increasing concentration of nucleating agent. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2440–2450, 2002     

Effects of additives on non-isothermal crystallization kinetics and morphology of isotactic polypropylene

In this study, effects of commercial additives such as antioxidant and stabilizer on the non-isothermal crystallization kinetics of isotactic polypropylene without nucleating agents were investigated by differential scanning calorimetry (DSC) method. Kinetic parameters by Osawa, Avrami and Liu-Mo models and apparent activation energy of the crystallization by Kissinger model were calculated. A polarized optical microscope was also used to observe crystalline morphology of the polypropylene samples crystallized at different cooling rates. On the contrary rate inducing effects of the nucleating agents on the crystallization kinetics of the polypropylene, interestingly, it was found that such types of commercial additives reduced the overall crystallization rate of the polypropylene. Based on the crystallization kinetics and morphology of the samples, it was observed that commercial additives inhibit the chain diffusion toward the growing crystal faces thus slow the crystal growth rate. Furthermore, calculated nucleation activity (ϕ) for the additives showed that they do not act as effective nucleating agents. It was found that the crystallization activation energy of additive-free sample was higher than that of the sample which has commercial additives. Activation energies were found to be 233.6 and 276.7 kJ mol⁻¹ for the PP-1 and PP-2, respectively. Kinetic results also show importance of using of nucleating agents to increase the crystallization rate of polypropylene by increasing the nucleation and thus overall crystallization rate during polypropylene processing operations (esp. for a fast processing cycle in injection molding).     

Activity of a β‐nucleating agent for isotactic polypropylene and its influence on polymorphic transitions

The influence of a nonpigmenting β‐nucleating additive in the crystallization of isotactic polypropylene (iPP) is investigated by differential scanning calorimetry and X‐ray diffraction. It is found that this additive induces the formation of a very high level of the trigonal modification of iPP. The crystallization and melting behavior of the nucleated systems are studied as a function of the cooling and heating rates and the control of the final temperature during the cooling process. The nucleating agent exerts an important effect on the crystallization temperatures and the polymorphic transitions of iPP, delaying the β–α recrystallization process through an increase in the stability of the trigonal crystals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 531–539, 2002     

Nucleating activity of the quinacridone and phthalocyanine pigments in polypropylene crystallization

The nucleating ability of two organic pigments, quinacridone and phthalocyanine, in nonisothermal polypropylene (PP) crystallization was investigated. The investigations were carried out using DSC and polarizing microscopy. The efficiency of pigments in the nucleation process was determined in a simple test comparing the crystallization temperature of the PP‐containing pigments with respect to the pure polymer. Both pigments revealed good nucleating activity. In the presence of pigments the increment of the crystallization temperature and the increase of nucleation rate were observed. The nucleating efficiency of pigments was confirmed in investigations of the obtained structure. The nucleating activity of pigments was explained by their features fulfilling several requirements for good nucleating agents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3957–3964, 2003     

Effect of nucleating agents on the crystallization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The effect of nucleating agents on the crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) was studied. A differential scanning calorimeter was used to monitor the energy of the crystallization process from the melt and melting behavior. During the crystallization process from the melt, nucleating agent led to an increase in crystallization temperature (T_c) of PHBV compared with that for plain PHBV (without nucleating agent). The melting temperature of PHBV changed little with addition of nucleating agent. However, the areas of two melting peaks changed considerably with added nucleating agent. During isothermal crystallization, dependence of the relative degree of crystallization on time was described by the Avrami equation. The addition of nucleating agent caused an increase in the overall crystallization rate of PHBV, but did not influence the mechanism of nucleation and growth of the PHB crystals. The equilibrium melting temperature of PHBV was determined as 187°C. Analysis of kinetic data according to nucleation theories showed that the increase in crystallization rate of PHBV in the composite is due to the decrease in surface energy of the extremity surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2145–2152, 2002     

α成核剂和β成核剂对高流动性聚丙烯结晶行为的影响

研究了α成核剂和β成核剂对高流动性聚丙烯(PP)结晶行为的影响,采用偏光显微镜、差示扫描量热法和广角X衍射对其微观结构和结晶形态进行了表征。结果表明:α成核剂的加入细化球晶而不改变结晶形态;β成核剂的加入改变球晶的形态,使部分α晶型向β晶型转变;两种成核剂的加入使高流动性PP的结晶速率加快结、晶过程的成核方式和生长机理发生改变,结晶活化能降低。     

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。     

Crystallization under shear in isotactic polypropylene containing nucleators

We report results from time-resolved small/wide angle X-ray scattering of well-characterized isotactic polypropylene (iPP), in its pure form as well as loaded with nucleating additives of different shapes (isotropic, elongated, platelet-like). Isothermal crystallization of these systems has been studied both under quiescent conditions and after application of a shear pulse. A quantitative analysis is presented that couples the applied shear field and the specific additive to the nucleation of iPP and the subsequent kinetics of crystallization. The effect of flow is only relevant if its contribution to the nucleation density is at least of the same order of magnitude as the nucleation density under quiescent conditions. Anisotropic additives show strong interactions with the flow field leading to extra nucleating sites.     

Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

The influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene (iPP), in their blends with poly(styrene-b-ethylene butylene-b-styrene) (SEBS), and a metallocenic ethylene-octene copolymer (EO) was investigated by DSC, optical microscopy and real-time small and wide angle X-ray scattering (SAXS and WAXS) experiments using synchrotron radiation. In non-nucleated iPP/SEBS blends, the crystallization of the iPP matrix occurred in the presence of the styrenic domains which induced a nucleating effect on the process, as observed in the synchrotron experiments. The metallocenic elastomer did not affect the crystallization behaviour of iPP in the iPP/EO blends in non-isothermal experiments, however, the development of crystallinity in the elastomer was restricted. In the nucleated isotactic polypropylene/elastomer blends a significant increase in the crystallinity and the crystallization rate of the iPP matrix was observed due to the presence of the nucleating agent. However, the nucleating efficiency of the additive was strongly affected by the nature and content of the elastomeric component. The nucleating agent efficiency was higher in the presence of the ethylene-octene component than the styrenic elastomer.     

Crystallization morphology and crystallization kinetics of poly(lactic acid): effect of <Emphasis Type="Italic">N</Emphasis>-Aminophthalimide as nucleating agent

The effect of N-Aminophthalimide compound (NA-S) as nucleating agent on crystallization behavior and morphology of poly(lactic acid) was studied. With polarized optical microscope (POM), the unique phenomena of nucleation and epitaxial crystallization of PLA/NA-S system were observed. Dynamic morphology of crystallization was also studied by POM to investigate the relationship between growth behavior of PLA and nucleating agent. Isothermal and non-isothermal crystallization behavior of PLA were studied by differential scan calorimeter (DSC). When nucleating agent was added, a new peak appeared in wide angle X-ray diffraction (WAXD) compared with pure PLA, indicating the nucleating effect of NA-S on crystallization of PLA. All the results indicate that the nucleating agent of NA-S shows obvious nucleating effect on isothermal crystallization above 120 °C and in non-isothermal crystallization after it is added in PLA, that is, the induction crystallization time is reduced, the crystallization rate and nucleation density of PLA are increased.     

Crystallization characteristics of isotactic polypropylene with and without nucleating agents

Nucleation effects of two sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). A nonisothermal crystallization kinetic equation was employed to analyze the crystallization characteristics of iPP with or without the nucleating agents from DSC crystallization thermograms. The equilibrium melting temperature of iPP necessary for the kinetic study was obtained by the extrapolation method to be 209°C. The nonisothermal crystallization kinetic analysis for the unnucleated iPP at different cooling rates was possible by assuming the spherulite growth initiated simultaneously by heterogeneous and homogeneous nucleation. On the other hand, the crystallization kinetics of the nucleated iPP could be described by the heterogeneous nucleation and growth process alone. The addition of the nucleating agents up to their saturation concentrations in iPP increased the crystallization peak temperature by 17°C, and the number of effective nuclei by three orders of magnitude. A high concentration of the nucleating agents caused agglomeration of the agents to lower the number of effective nuclei.     

Fiber reinforced polypropylene: Influence of iPP molecular weight on morphology,crystallization, and thermal and mechanical properties

The influence of molecular weight and its distribution on the nucleation density, crystallization, thermal and mechanical behavior of isotactic polypropylene based composites has been investigated. The composites were prepared by compression molding. The ability of carbon and Kevlar fibers to nucleate the polypropylene has been studied during isothermal and nonisothermal crystallization, by optical microscopy and differential scanning calorimetry (DSC), as function of crystallization temperature T_c and iPP molecular weight. Two extreme crystallization conditions were tested: quenching and slow crystallization to obtain crystals and amorphous phases of different structure. The ability of fibers to enhance mechanical properties in polypropylene based composites was examined by tensile tests at room temperature. It was found that nucleation density, crystallization parameters, and the results of tensile tests strongly depend on the molecular weight M w of iPP, molecular weight distribution, and thermal history of polypropylene. The numerical values of the nucleation density have been found to strongly depend on the nature of fiber. In fact, Kevlar fiber has shown a better nucleating ability than carbon fiber. The results of tensile tests have been related to the sample morphology. The analysis of fractured specimens also provided useful information about fiber-matrix adhesion.     

松香型成核剂成核聚丙烯的非等温结晶动力学研究

采用 DSC 法研究了聚丙烯(PP)和松香型成核剂成核 PP 在不同的降温速率下的非等温结晶动力学。采用修正的 Avrami 方程对 DSC 的测试结果进行了分析。结果表明,松香型成核透明剂和分散剂能显著提高 PP 的结晶温度,用 Jeziorny 法来处理松香型成核 PP 的非结晶等温结晶行为是较为吻合的。加入松香型成核透明剂和分散剂后,PP 的半结晶时间减少,结晶动力学常数 Z_c 增加,结晶速率增加;同一降温速率,松香型成核透明剂和分散剂成核PP 的 n 值较纯 PP 减少,说明结晶成核方式发生了改变。     

原位添加α晶成核剂对高熔体强度聚丙烯性能的影响

采用过氧化苯甲酰(BPO)为引发剂,通过一步反应挤出法将接枝单体苯乙烯(St)和端乙烯基硅油(VS)接枝到等规聚丙烯(i PP)上制备高熔体强度聚丙烯(HMSPP),同时在制备过程中原位添加α晶成核剂S20或NA11,考察了两种不同的α晶成核剂对HMSPP的制备及其结晶性能、力学性能和发泡性能的影响。熔体流动速率和分子量分布的测试结果表明,S20或NA11的原位添加没有影响i PP接枝反应的进行;差示扫描量热研究表明,成核剂的加入可以有效促进HMSPP的成核结晶,消除了HMSPP结晶过程中的双结晶峰现象,但成核剂的加入对HMSPP的力学性能并无显著影响。S20或NA11的加入可以有效调控发泡样品的泡孔尺寸,使得泡孔直径从38μm增大到50μm以上,发泡倍率也分别从25倍增大到36倍和37倍。     

β成核剂/无机填料共同作用对PP结晶行为的影响

将云母和硅美钙晶须作为无机填料,分别与稀土成核剂共同加入聚丙烯(PP)中,考察复合填充体系(填料-成核剂)对PP结晶行为的影响。结果表明,云母和晶须都能够作为聚丙烯的异相成核剂促进结晶,三元复合材料体系最终的结晶形貌、晶型含量比例等结晶性能是由无机填料与成核剂相互竞争所决定。云母的成核效率较低,加入高效的成核剂后其成核作用被抑制;而晶须的成核能力较强,与成核剂一同添加,两者能够共同促进聚丙烯结晶。     

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     

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 kinetics and nucleating agents for enhancing the crystallization of poly(p-phenylene sulfide)

An experimental study of crystallization kinetics and the influence of nucleating agents on the solidification of poly(p-phenylene sulfide) (PPS) is described. The effect of molecular weight is considered by investigating PPS samples having different viscosity levels. We studied the effect of a range of nucleating agents including aluminum oxide, calcium oxide, silicon dioxide, titanium dioxide, kaolin, and talc. All of these compounds were found to enhance the rate of crystallization; in particular, silicon dioxide, kaolin, and talc were the most effective nucleating agents. An effort to study particle size effects of the silicon dioxide showed that the nucleation was very sensitive to the source of the material. These studies did, however, show that nucleation rates tended to increase with decreasing particle size and increasing loading of silicon dioxide. Comparison of PPS crystallization rates with those of other polymers indicates that it crystallizes much more slowly than polyethylene or isotactic polypropylene and is slower than polyetherether-ketone, when comparisons are made on an equivalent basis. PPS crystallizes at similar rates to polyethylene terephthalate (PET). However, our nucleated PPS does not crystallize as rapidly as nucleated PET.     

α/β复合成核剂调控聚丙烯结晶过程的研究进展

综述了3类广泛应用的α/β复合成核剂对聚丙烯结晶动力学、结晶形态及宏观性能等方面影响的研究进展。总结了影响α/β复合成核剂调控聚丙烯结晶的主要因素在于两种成核剂的成核能力,具体表现为其成核聚丙烯结晶温度(TC)的高低:TC高的成核剂在聚丙烯结晶过程中起主导作用,TC低的成核剂基本不起成核作用,当两者的TC相接近时发生竞争成核。根据这一规律,找出了复合α、β两种成核剂的方法,并列举将其运用到调控聚丙烯的结晶过程中的实例。     

Effects of rosin‐type nucleating agent on polypropylene crystallization

In this investigation the effects of a rosin‐type nucleating agent, which was prepared from cocrystallizing of dehydroabietic acid and Na‐dehydroabietate, on polypropylene (PP) crystallization were studied. The results of differential scanning calorimetry and X‐ray diffraction proved that a cocrystal of dehydroabietic acid and Na‐dehydroabietate was formed. The lower melting point of the cocrystal caused it to be uniformly dispersed in PP. When cocrystals were added as nucleating agent, the mechanical properties, heat distortion temperature, and crystallization temperatures of PP were obviously improved, and the size of spherulites was also decreased. This proved that the cocrystals of dehydroabietic acid and Na‐dehydroabietate could act as an effective nucleating agent for PP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1069–1073, 2002