Crystal morphology and crystallization kinetics of polyamide‐11/clay nanocomposites

Polyamide‐11 (PA11)/clay nanocomposites were prepared by in situ intercalative polymerization. The crystal morphology and crystallization kinetics of these nanocomposites were investigated via polarized light microscopy (PLM), small‐angle laser scattering (SALS) and differential scanning calorimetry (DSC). PA‐11 can crystallize into well‐formed spherulites, while only very tiny crystallites were observed by PLM and SALS for the nanocomposites. Both isothermal and non‐isothermal crystallization methods were employed to investigate the crystallization kinetics by DSC. Both techniques showed an increased crystallization rate with the addition of clay. However, the Avrami exponent decreased with the addition of clay in isothermal crystallization but showed a wide range of values depending on the cooling rate in the non‐isothermal crystallization. The changes in crystal morphology and crystallization kinetics can be understood as being due to the ‘supernucleating’ effect of the nanodispersed clay layers. Copyright © 2004 Society of Chemical Industry     

Investigations of the Non-Isothermal Crystallization Behavior of Polyamide 6/Polyethylene-Octene/Organomontmorillonite Nanocomposites

The crystallization behavior of polyamide 6/polyethylene-octene/organomontmoril- lonite (PA 6/POE/OMMT) nanocomposites fabricated via melting intercalation route was investigated using differential scanning calorimeter (DSC). The crystallization kinetics under non-isothermal conditions was analyzed by Jeziorny method and Mo method, and the crystallization kinetics parameters were obtained. It was found that nano-clay acted as a heterogeneous nucleation agent and the semi-crystallization time was prolonged with the OMMT loading increasing. The activation energy for non-isothermal crystallization of such nanocomposites was calculated according to the Huffman-Lauritzen theory. The average size of the composite nanocrystals was reduced with introduction of OMMT to the synthetic system.     

Isothermal and nonisothermal crystallization kinetics of syndiotactic polystyrene/clay nanocomposites

Differential scanning calorimeter (DSC) and X‐ray diffraction methods were used to investigate the isothermal and nonisothermal crystallization behavior and crystalline structure of syndiotactic polystyrene (sPS)/clay nanocomposites. The sPS/clay nanocomposites were prepared by mixing the sPS polymer solution with the organically modified montmorillonite. DSC isothermal results revealed that introducing 5 wt% of clay into the sPS structure causes strongly heterogeneous nucleation, inducing a change of the crystal growth process from mixed three‐dimensional and two‐dimensional crystal growth to two‐dimensional spherulitic growth. The activation energy of sPS drastically decreases with the presence of 0.5 wt% clay and then increases with increasing clay content. The result indicates that the addition of clay into sPS induces the heterogeneous nucleation (a lower ΔE) at lower clay content and then reduces the transportation ability of polymer chains during crystallization processes at higher clay content (a higher ΔE). We studied the non‐isothermal melt‐crystallization kinetics and melting behavior of sPS/clay nanocomposites at various cooling rates. The correlation among crystallization kinetics, melting behavior and crystalline structure of sPS/clay nanocomposites is discussed. Polym. Eng. Sci. 44:2288–2297, 2004. © 2004 Society of Plastics Engineers.     

Isothermal crystallization kinetics and melting behavior of nylon/saponite and nylon/montmorillonite nanocomposites

DSC thermal analysis and X‐ray diffraction have been used to investigate the isothermal crystallization behavior and crystalline structure of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ε‐caprolactam and then exfoliating the layered silicates by subsequent polymerization. The DSC isothermal results reveal that introducing saponite into the nylon structure causes strongly heterogeneous nucleation induced change of the crystal growth process from a two‐dimensional crystal growth to a three dimensional spherulitic growth. But the crystal growth mechanism of nylon/montmorillonite nanocomposites is a mixed two‐dimensional and three‐dimensional spherulitic growth. The activation energy drastically decreases with the presence of 2.5 wt % clay in nylon/clay nanocomposites and then slightly increases with increasing clay content. The result indicates that the addition of clay into nylon induces the heterogeneous nucleation (a lower ΔE) at lower clay content and then reduces the transportation ability of polymer chains during crystallization processes at higher clay content (a higher ΔE). The correlation among crystallization kinetics, melting behavior, and crystalline structure of nylon/clay nanocomposites is also discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2196–2204, 2004     

Ultrasonic oscillations induced morphology and property development of polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites (PPCNs) with 3% organophilic montmorillonite (OMMT) content were prepared via ultrasonic extrusion. The objective of present study was to investigate the effects of ultrasonic oscillations in processing on the morphology and property development of PPCNs. XRD and TEM results confirmed the intercalated structure of OMMT in conventional nanocomposite (without ultrasonic treatment) and ultrasonicated nanocomposite, but ultrasonic oscillations could make silicate layers finely dispersed and a little exfoliated. According to SEM, the OMMT particles were evenly and finely dispersed in the ultrasonicated nanocomposite via ultrasonic oscillations, and the aggregation size of clay particles was about 100 nm, which is less than that in conventional nanocomposite. The crystalline dimension, crystalline morphology and the growth rate of crystallization in PPCNs were investigated by DSC and PLM, it was found that the OMMT particles and ultrasonic oscillations played an important role in the nucleation rate, crystallization temperature and spherulite size of PP matrix in nanocomposites. Compared with conventional nanocomposite, the mechanical properties of the ultrasonicated nanocomposite increased due to the improved dispersion of OMMT and diminished spherulite size. The thermal stability and the rheological behavior of PP and its nanocomposites were both studied by thermogravimetry and high pressure rheometer, respectively.     

Polymer‐Clay Nanocomposites Based on Blends of Polyamide‐6 and Polyethylene

The preparation of polyamide‐6/clay, high‐density polyethylene/clay, and high‐density polyethylene/ polyamide‐6/clay nanocomposites is considered. X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier Transform Infrared (FTIR) measurements show that the clay enhances the crystallization of the γ‐form of polyamide‐6. The clay also acts as a nucleation agent and causes a reduction of spherulitte size. Scanning electron microscopy (SEM) analysis of fracture surfaces shows that the clay reduces the PA‐6 particle size in the HDPE/PA‐6/clay nanocomposites and changes the morphology. Mechanical properties and the effect of maleated polyethylene are also reported.     

Polypropylene/montmorillonite composites and their application in hybrid fiber preparation by melt‐spinning

Polypropylene (PP)/organomontmorillonite (OMMT) nanocomposites have been successfully prepared by melt intercalation by using the conventional method of twin‐screw extrusion and subsequently submitted for melt‐spinning. The structure and properties of the PP/clay nanocomposites and hybrid fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and crystallization dynamics, etc. The organoclay layers were found to disperse in the PP resin at the nanometer level. The nanoscaled OMMT layers, dispersed in the PP matrix, actually played the role of heterogeneous nuclei species in the process of PP crystallization and increased the nucleation speed of the composites, hereby leading to the increase of crystallization rate of the as‐spun fiber. Meanwhile, it was found that the crystallinity of PP/OMMT hybrid fibers is much higher than that of pure PP fiber at the same draw ratios, whereas the orientation of PP/OMMT hybrid fibers is much lower than that of pure PP fiber at the same draw ratios. Because of the effective intercalation of OMMT into PP matrix, the nanocomposites have good spinnability, and the moisture absorption of the final PP fiber is improved. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 552–558, 2004     

Structure and crystallization behavior of Nylon 66/multi-walled carbon nanotube nanocomposites at low carbon nanotube contents

Multi-walled carbon nanotubes (MWNTs) were modified with poly(hexamethylene adipamide) (also known as Nylon 66) via a controlled polymer solution crystallization method. A “nanohybrid shish kebab” (NHSK) structure was found wherein the MWNT resembled the shish while Nylon 66 lamellar crystals formed the kebabs. These Nylon 66-functionalized MWNTs were used as precursors to prepare polymer/MWNT nanocomposites. Excellent dispersion was revealed by optical and electron microscopies. Nitric acid etching of the nanocomposites showed that MWNT formed a robust network in Nylon 66. Non-isothermal DSC results showed multiple melting peaks, which can be attributed to lamellar thickness changes upon heating. The crystallite sizes L₁₀₀ and L₀₁₀ of Nylon 66, determined by WAXD, decreased with increasing MWNT contents. Isothermal DSC results showed that crystallization kinetics increased first and then decreased with increasing MWNT contents in Nylon 66. This study showed that the effect of MWNTs on Nylon 66 crystallization is twofold: MWNTs provide heterogeneous nucleation sites for Nylon 66 crystallization while the tube network structure hinders large crystal growth.     

纳米碳酸钙填充尼龙6体系结晶行为的研究

采用偏光显微镜、差示扫描量热仪和广角X射线衍射仪系统地研究了纳米碳酸钙(n-CaCO3)粒子填充聚酰胺6(PA6)体系的结晶行为。结果表明,n-CaCO3粒子的引入不仅使PA6材料变为两相结构,而且使其结晶行为发生了改变;n-CaCO3粒子对PA6等温结晶行为影响较大,球晶尺寸大小及球晶形态发生了很大变化;n-CaCO3粒子不仅具有异相成核剂的作用,而且能引发PA6产生新的晶型,且这种成核作用具有逾渗行为。     

Effect of clay addition on the morphology and thermal behavior of polyamide 6

The nanostructure, morphology, and thermal properties of polyamide 6 (PA6)/clay nanocomposites were studied with X‐ray scattering, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The wide‐angle X‐ray diffraction (WAXD) and TEM results indicate that the nanoclay platelets were exfoliated throughout the PA6 matrix. The crystallization behavior of PA6 was significantly influenced by the addition of clay to the polymer matrix. A clay‐induced crystal transformation from the α phase to the γ phase for PA6 was confirmed by WAXD and DSC; that is, the formation of γ‐form crystals was strongly enhanced by the presence of clay. With various clay concentrations, the degree of crystallinity and crystalline morphology (e.g., spherulite size, lamellar thickness, and long period) of PA6 and the nanocomposites changed dramatically, as evidenced by TEM and small‐angle X‐ray scattering results. The thermal behavior of the nanocomposites was investigated with DSC and compared with that of neat PA6. The possible origins of a new clay‐induced endothermic peak at high temperature are discussed, and a model is proposed to explain the complex melting behavior of the PA6/clay nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1191–1199, 2007     

Isothermal crystallization kinetics and melting behavior of modified high‐density polyethylene/barium sulfate nanocomposites

The melting/crystallization behavior and isothermal crystallization kinetics of high‐density polyethylene (HDPE)/barium sulfate (BaSO₄) nanocomposites were studied with differential scanning calorimetry (DSC). The isothermal crystallization kinetics of the neat HDPE and nanocomposites was described with the Avrami equation. For neat HDPE and HDPE/BaSO₄ nanocomposites, the values of n ranges from 1.7 to 2.0. Values of the Avrami exponent indicated that crystallization nucleation of the nanocomposites is two‐dimensional diffusion‐controlled crystal growth. The multiple melting behaviors were found on DSC scan after isothermal crystallization process. The multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae caused during different crystallization processes. Adding the BaSO₄ nanoparticles increased the equilibrium melting temperature of HDPE in the nanocomposites. Surface free energy of HDPE chain folding for crystallization of HDPE/BaSO₄ nanocomposites was lower than that of neat HDPE, confirming the heterogeneous nucleation effect of BaSO₄. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

PA66/可反应性纳米SiO_2复合材料的非等温结晶动力学

通过双螺杆挤出机制备出聚酰胺(PA)66/可反应性纳米SiO2(RNS)复合材料,采用Jeziorny法和Mo法对其非等温结晶行为进行了研究。结果表明,RNS具有较强的异相成核能力,能提高PA66的结晶速率,并使PA66的晶体结构和生长机制发生改变;通过对比PA66及其复合材料的结晶活化能发现RNS能够降低PA66的结晶活化能。     

Isothermal crystallization behavior of polyamide 6,6/multiwalled carbon nanotube nanocomposites

The good dispersion of functionalized multiwalled carbon nanotube (f‐MWCNT) in polyamide 6,6 (PA 6,6) matrix was prepared by solution mixing techniques. The crystalline structure and crystallization behaviors of PA 6,6 and PA 6,6/f‐MWCNT nanocomposites were studied by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM) analysis. DSC isothermal results revealed that the overall isothermal crystallization rates of PA 6,6 increased as well as the activation energy of PA 6,6 extensively decreased by adding f‐MWCNT into PA 6,6, suggesting that the addition of f‐MWCNT probably induces the heterogeneous nucleation. The effect of f‐MWCNT on the chain arrangement for the crystallization of PA 6,6/f‐MWCNT nanocomposites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Nucleation effect of polyamide on polyoxymethylene

The crystallization behavior and morphology of polyoxymethylene (POM) and POM with polyamide (PA) were studied by polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The isothermal crystallization kinetics were analyzed with the Avrami equation. Compared with the virgin POM, the addition of PA can reduce the spherulites size and improve the crystallization growth rate and crystallinity (X_c) of POM, which demonstrates that the nucleation effect of PA as the high‐molecular nucleus is favorable to the mechanical properties and dimension stability of POLYM. ENG. SCI., 45:1174–1179, 2005. © 2005 Society of Plastics Engineers     

Crystallization and melting behavior of polyester/clay nanocomposites

Polyester/clay nanocomposites were prepared by melt compounding with different clay loadings. Comparing against neat polyester resins, the crystallization and multiple melting behavior of the nanocomposites was investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Nanoclay filler is an effective heterogeneous nucleating agent, as evidenced by a decrease and an increase in the crystallization temperature for both cold and melt crystallization of polyesters, respectively. The degree of crystallinity was found to increase with increasing clay content, due to heterogeneous nucleation effects by the addition of a nanofiller. For the annealed samples, multiple melting peaks were always observed for both neat polyester and its nanocomposites. The origins of the multiple melting behavior are discussed, based on the DSC and XRD results. Interestingly, an ‘abnormal’ high‐temperature endothermic peak (T_{m, 3}) at about 260 °C was observed when the nanocomposite samples were annealed at higher temperatures (eg ≥240 °C). The constrained polyester crystals formed within intercalated clay platelets due to confinement effects were probably responsible for this melting event at these higher temperatures. Copyright © 2004 Society of Chemical Industry     

Effects of halloysite nanotubes on kinetics and activation energy of non-isothermal crystallization of polypropylene

Halloysite nanotubes (HNTs), a kind of naturally occurring silicates possessing typical fibular structure, were introduced to fabricate polypropylene (PP)/HNTs nanocomposites. The non-isothermal crystallization behaviors were investigated by differential scanning calorimetry (DSC) method according to different treatments. The results suggest, with the inclusion of HNTs in PP matrix, the nanocomposites crystallize at higher temperature regime, which are correlated with the heterogeneous nucleating effects of HNTs during the crystallization process of PP. The kinetics studies of crystallization show that PP nanocomposites possess faster crystallization process and higher activation energy due to the nucleating effect and hindrance effect of HNTs to the motion of PP chains. The polarized light microscopy (PLM) observations further show that HNTs serve as nucleation sites and accelerate the crystallization process.     

Mechanical and crystallographic properties of injection‐molded polyamide 66/sepiolite nanocomposites with different clay loading

Polyamide66 (PA66) and polyamide66/sepiolite (PA66/sepiolite) nanocomposites at 1, 3, 5, 7, and 9 wt% clay loading were prepared and injected to simulate industrial processing. Tensile tests were performed in the samples, and scanning electron microscopy was used to characterize the fracture surface. The samples were also examined by X‐ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), and vibrational spectroscopy analysis (FT‐IR and FT‐Raman). Higher tensile strength and stiffness and reduction of the strain to failure are observed in the nanocomposites with higher sepiolite content. Two‐dimensional XRD analyses show that the sepiolite also enhances the orientation of PA66 crystals. XRD and spectroscopic analyses corroborate that the nanoclay fibers are placed between the lamellar superstructure of the PA66 without affecting the polymer chains. DSC confirms that the presence of sepiolite does not influence the crystallinity nor the nucleation of PA66 as the arrangement of the fibers between the PA66 lamellae hinders the nucleation of new crystals. We propose a model for the crystallographic organization of the organic and inorganic phases in the PA66/sepiolite nanocomposites. POLYM. COMPOS., 36:2326–2333, 2015. © 2014 Society of Plastics Engineers     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/montmorillonite nanocomposites

The melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X‐ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006     

尼龙11/HGB复合材料的非等温结晶动力学

采用熔融共混法制备了尼龙(PA)11/空心玻璃微珠(HGB)(PA11/HGB)复合材料,应用差示扫描量热(DSC)仪研究了不同HGB用量下的PA11/HGB复合材料的非等温结晶过程,采用Jeziorny法和Mo法研究了复合材料的非等温结晶动力学,采用X射线衍射(XRD)仪研究了复合材料的晶型变化情况。DSC结果表明,随着降温速率的增加,复合材料的结晶温度总体上降低,结晶温度区间变宽;HGB在PA11基体中起到了异相成核作用。Jeziorny法不适用于PA11/HGB复合材料的非等温结晶动力学研究,而Mo法较为适合,其研究结果表明适量的HGB具有加速PA11基体结晶的作用,但当HGB用量达到8份后,这种作用趋于稳定。XRD结果表明,HGB可诱导PA11基体生成新的β晶。     

良好分散尼龙6/多壁碳纳米管复合材料的研究

采用柔和混合法制备纳米粒子良好分散的尼龙-6/多壁碳纳米管(PA6/MWNTs)复合材料,采用差示扫描量热仪(DSC)和广角X射线衍射法(XRD)研究了MWNTs对PA6基体结晶熔融行为的影响。DSC结果表明,MWNTs的加入大幅度地提高了PA6的结晶温度(最高提高约20℃),基体的结晶度也有所提高,说明良好分散的MWNTs在PA6结晶过程中呈现明显的异相成核作用;XRD结果证实,分散良好的MWNT促进PA6形成α晶型,抑制γ晶型的形成。同时,MWNT的加入导致复合材料出现熔融双峰现象,其形状随MWNT含量的变化而改变,双峰结构可能是由于熔融过程中伴随着重结晶而引起的。