Isothermal crystallization behavior and mechanical properties of polylactide/carbon nanotube nanocomposites

Carbon nanotube (CNT)–reinforced polylactide (PLA) nanocomposites were prepared using a melt compounding process employing a twin-screw extruder. The isothermal crystallization kinetics of PLA/CNT nanocomposites according to Avrami’s theory were analyzed using differential scanning calorimetry in the temperature range 90–120 °C. There was a significant dependence of CNT on the crystallization behavior of the PLA matrix. The incorporation of CNT improved effectively the crystallization rate of PLA/CNT nanocomposites through heterogeneous nucleation. The nucleating effect of CNTs which increased the number of nucleation sites and decreased the average spherulite size was confirmed using polarized optical microscopy. The rheological properties of the PLA/CNT nanocomposites were also investigated. Changes in the microstructure of the PLA/CNT nanocomposites occurred by incorporating CNT. Furthermore, the tensile strength/modulus and thermal stability of PLA/CNT nanocomposites were enhanced when a very small quantity of CNT was added. This research accounts for the effect of CNTs, which significantly influenced the isothermal behavior, thermal stability, mechanical, and rheological properties of the PLA/CNT nanocomposites, providing a design guide for PLA/CNT nanocomposites in industrial fields.     

Biodegradable polylactide/montmorillonite nanocomposites

Our continuing research on the preparation, characterization, materials properties, and biodegradability of polylactide (PLA)/organically modified layered silicate (OMLS) nanocomposites has yielded results on PLA/montmorillonite nanocomposites. Montmorillonite (mmt) modified with dimethyldioctadecylammonium cation was used as an OMLS for nanocomposite preparation. The internal structure of nanocomposites on the nanometer scale was established with the use of wide-angle X-ray diffraction patterns and transmission electron micrographic observation. All nanocomposites exhibited significant improvement in crystallization behavior, mechanical properties, flexural properties, heat distortion temperature, and O2 gas permeability when compared with pure PLA.     

聚乳酸/有机蒙脱土纳米复合材料的结晶性能研究

采用差示扫描量热法、X射线衍射法和热台偏光显微镜研究了有机蒙脱土对聚乳酸结晶性能的影响。研究结果表明,有机蒙脱土对聚乳酸结晶过程的影响是成核效应和阻碍分子链运动的协同作用,当其含量较低时,成核作用占主导地位,聚乳酸晶体的半径生长速率随其含量的增加而增加;而当有机蒙脱土的含量较高时,它对聚乳酸分子链运动的阻碍作用逐渐增强,聚乳酸晶体缺陷增加,晶体半径生长速率则随有机蒙脱土含量的增加而降低。     

Investigation of in situ prepared polypropylene/clay nanocomposites properties and comparing to melt blending method

The morphological, physical and mechanical properties of polypropylene/clay nanocomposites (PPCNs) were prepared by in situ polymerization are investigated. Non-modified scmectite type clay (e.g. bentonite) was used to prepare bi-supported Ziegler–Natta catalyst of TiCl₄/Mg(OEt)₂/clay. Exfoliated PPCNs were obtained by in situ intercalative polymerization of propylene using produced bi-supported catalyst. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) micrograph were used to assess the clay morphology and dispersion of clay. The crystalline structures of PPCNs were characterized by differential scanning calorimetry (DSC). The mechanical properties of PPCNs were studied by tensile and impact tests. thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis DMTA were used to characterize the thermal and dynamic mechanical properties, respectively. The thermo-mechanical properties of prepared nanocomposites were considerably improved by introducing small amount of clay, which indicated that the clay most be significantly intercalated or exfoliated in the prepared nanocomposite preparation process. In addition, morphology and some of the mechanical and thermal properties of in situ PPCNs were compared with those of PPCNs prepared by melt blending method in this study and some presented reported results in literatures.     

Rubber-toughened polyamide 6/clay nanocomposites

Toughening of polyamide 6 (PA6) based nanocomposites (PN’s), with 3 wt% organically modified montmorillonite (OMMT), was investigated by blending with up to 40 wt% of maleinized styrene–ethylene/butadiene–styrene copolymer (mSEBS). The nanostructure of the PA6 matrix did not change on blending with mSEBS, nor did the nature of the two polymeric phases on addition of OMMT. The morphology of the rubber particles in the PN’s was homogeneous, with particle sizes larger than those of the corresponding blends, due to limitations imposed by the clay on the compatibilizing effect of the mSEBS. All the PN’s were ductile and, despite the incorporation of rubber, showed higher small strain tensile properties than those of the corresponding blends. Super-tough nanocomposites were obtained with 30 wt% mSEBS. The critical interparticle distance to attain super-toughness (τ_c) was slightly larger in the blends than in the PN’s, indicating that an increased modulus of the matrix on addition of OMMT leads to smaller τ_c values.     

Development and characterization of cellulose/clay nanocomposites

Cotton is the most important textile fiber for apparel use and is preferred to synthetic fibers for reasons such as comfort and feel. A major drawback of cellulosic fibers is flammability. The development of cellulose/clay nanocomposites for use as flame-retardant materials based on cotton is reported in this paper. Novel nanocomposite materials have been produced from cellulose with layered silicate clays used as the nanofiller material. Three different methods were attempted in producing these organic–inorganic hybrids. The nanocomposites show significant improvements in thermal properties when compared with cellulose control sources. The degradation temperature of the nanocomposites increased by 45 °C and the char yields for some compositions doubled those of the controls. The crystalline melt of the materials decreased by 15 °C. Tensile testing revealed an increase of approximately 80% in the ultimate stress of the cellulose/clay nanocomposites.     

Fracture behavior of polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites have been prepared via a reactive compounding approach with an epoxy based masterbatch. Compared with PP and common PP/organoclay nanocomposites, the PP/clay nanocomposites based on epoxy/clay masterbatch have higher impact strength. The phenomenon can be attributed to the epoxy phase dispersed uniformly in the PP matrix, which may act as impact energy absorber and helps to form a large damage zone, thus a higher impact strength value is achieved.     

Conducting polymer/clay nanocomposites and their applications

This review aims at reporting on interesting and potential aspects of conducting polymer/clay nanocomposites with regard to their preparation, characteristics and engineering applications. Various conducting polymers such as polyaniline, polypyrrole and copolyaniline are introduced and three different preparation methods of synthesizing conducting polymer/clay nanocomposites are being emphasized. Morphological features, structure characteristics and thermal degradation behavior are explained based on SEM/TEM images, XRD pattern analyses and TGA/DSC graphs, respectively. Attentions are also being paid on conductive/magnetic performances as well as two potential applications in anti-corrosion coating and electrorheological (ER) fluids.     

聚合物/粘土纳米复合材料研究进展

聚合物/粘土纳米复合材料(PCN)是近几年纳米材料领域中的研究热点.综述了聚合物/粘土纳米复合材料的几种制备方法及研究进展,并将纳米复合材料与普通材料的物理性能相比较,得知纳米复合材料有优良的物理性能.总结了这一领域尚待解决的问题.     

Influence of hexamethylene diamine functionalized graphene oxide on the melt crystallization and properties of polypropylene nanocomposites

Hexamethylene diamine was chemically grafted to the graphene oxide (GO) surface via two type of reactions viz. (i) amidation reaction between amine groups and carboxylic acid sites of GO and (ii) nucleophilic substitution reactions between amine and epoxy groups on surface. Successful grafting of HMDA on GO surface was confirmed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric results (TGA). These chemically modified GO (AGO) with varying loading amount were incorporated in polypropylene matrix in the presence of maleic anhydride-g-polypropylene (PP-g-MA) compatibilizer through melt processing technique. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies revealed that the loading of AGO resulted in the improvement in crystallization characteristics of polypropylene. Owing to the strong interfacial interactions between AGO and polymer, significant enhancement in mechanical and electrical properties was observed, when compared to pristine GO filled polypropylene composites.     

聚合物/蒙脱土纳米复合材料的制备与结晶性能

本文综述了制备聚合物 /蒙脱土纳米复合材料的插层方法 ,并对有代表性的结晶性聚合物 /蒙脱土纳米复合材料的结晶性能进行了讨论。蒙脱土的加入对聚合物的结晶有两种作用 ,一方面是对聚合物有异相成核的作用 ,可以提高聚合物的结晶温度和结晶速率 ,降低结晶活化能 ;另一方面是对聚合物结晶生长有阻碍作用 ,导致结晶速率下降 ,结晶活化能提高     

The kinetics of isothermal cold crystallization and tensile properties of poly(ethylene terephthalate)

The exothermic peak that is frequently observed during the heating scan of a differential scanning calorimetry (DSC) experiment of poly(ethylene terephthalate) (PET) is due to a cold crystallization process, originating from the rearrangement of amorphous regions into a crystalline phase. In this work the isothermal cold crystallization kinetics of PET was investigated by using DSC, X-ray diffraction and tensile experiments. The isothermal crystallization rate was determined as a function of temperature, and the Avrami analysis was conducted. The results showed that at low temperatures the cold crystallization is a two-regime process, whereas at high temperatures just one stage is observed. The rate constant for isothermal crystallization K increased and the half time of crystallization (t_½) decreased with increasing crystallization temperature. The Avrami exponent n was close to 2, and this corresponds to a disc-like morphology formed by heterogeneous nucleation. Cold crystallization increased the crystallinity and therefore the tensile properties of the samples were enhanced.     

Preparation and characterization of poly (styrene-acrylonitrile) (SAN)/clay nanocomposites by melt intercalation

Poly (styrene-acrylonitrile) (SAN)/clay nanocomposites have been prepared by melt intercalation method from pristine montmorillonite (MMT), using hexadecyl trimethyl ammonium bromide (C16) and hexadecyl triphenyl phosphonium bromide (P16) as the reactive compatibilizers between polymer and clay. The influence of the reactive compatibilizers proportion relative to the clay on the structure and properties of the SAN/clay nanocomposites is investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), high-resolution electron microscopy (HREM), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The effects of the two different clays (MMT and organic modified MMT) on the nanocomposites formation, morphology and property are also studied. The results indicate that the SAN cannot intercalate into the interlayers of the MMT and results in microcomposites. In the presence of the reactive compatibilizers, the dispersion of clay in SAN is rather facile and the SAN/clay nanocomposites reveal an intermediate morphology, an intercalated structure with some exfoliation and the presence of small tactoids. The appropriate proportion with 3 wt% reactive compatibilizers to 5 wt% MMT induces well-dispersed morphology and properties in the SAN matrix. The TGA analyses show that the thermal stability properties of the SAN/clay nanocomposites have been improved compared with those of the pristine SAN. The DMA results show that the storage modulus and glass transition temperature (Tg) of the SAN/clay nanocomposites have remarkably enhancements compared with the pristine SAN. At last the intercalation mechanism of the technology is discussed.     

Thermal properties of PMMA/montmorillonite clay nanocomposites

Polymer/Clay offer tremendous improvement in wide range of physical and engineering properties for polymers with low filler loading. In nanotechnology polymer/clay nanocomposites use smectitetype clays that have layered structures. In this work, Poly (methyl methacrylate) (PMMA) was synthesized by free radical addition polymerization in the presence of high power ultrasound. The Poly (methyl methacrylate) (PMMA)-Montmorillonite (MMT) clay nanocomposites were synthesized by two different techniques viz., ultrasonic mixing and magnetic stirring. An analysis of the XRD data confirms that the composites are in the nanometer scale. The FTIR spectra show that there is strong interaction between the clay and the polymer that enhances the thermal stability. The thermal stability of the experimental nanocomposite prepared by the two processes is compared. Further analysis of XRD data shows that intercalation as well as exfoliation has taken place in both the types of nanocomposites preparation. An analysis of the TG, DTG curves reveal that the thermal stability is found to increase by nearly 30% for ultrasonic mixing than that of magnetic stirring.     

尼龙6/POE/粘土纳米复合材料的研究

采用熔融方法制备出尼龙(PA)6/POE/粘土纳米复合材料,并对其力学性能及微观形态进行了研究.力学性能测试结果显示,PA6/POE/粘土纳米复合材料具有良好的力学性能,特别是其缺口冲击强度有显著提高,PA6/POE/粘土纳米复合材料有较好的韧性;广角X射线衍射分析显示,当有机粘土含量比较低时,有机粘土基本上剥离于PA6基体中;电子扫描电镜照片显示,POE相以岛状结构均匀分散于PA 6基体中.     

SiO_2-MWNTs/聚乳酸复合材料的冷结晶动力学及球晶形态

为研究多壁碳纳米管(MWNTs)对聚乳酸(PLA)冷结晶动力学和球晶形态的影响,分别以PLA和表面包覆纳米SiO2并接枝硅烷偶联剂的纳米SiO2改性MWNTs(SiO2-MWNTs)为基体和改性剂,经溶液共混法制备了SiO2-MWNTs/PLA复合材料。采用DSC、偏光显微镜、Jeziorny模型和Johnson-Mehl-Avrami模型研究了复合材料的非等温冷结晶动力学和球晶形态。结果表明:SiO2-MWNTs可作为异相成核剂,能有效降低SiO2-MWNTs/PLA复合材料的冷结晶温度,提高晶核生成速率和晶体生长活化能。SiO2-MWNTs/PLA复合材料的冷结晶过程主要由成核作用控制,加入SiO2-MWNTs可同时提高复合材料的结晶速率和结晶度。冷结晶时,PLA球晶尺寸小于熔体冷却结晶时的,且SiO2-MWNTs含量对冷结晶球晶尺寸的影响远小于其对熔体冷却结晶球晶尺寸的。所得结论对优化PLA的结晶结构和性能、制备高性能PLA复合材料具有指导意义。     

Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites

A series of gelatinized starch–clay nanocomposites which exhibit intercalated and exfoliated structures have been developed. Various nanoclay dispersions were prepared (either by standard mixing or through the use of ultrasonics) prior to their combination with a high amylose content starch using high-speed mixing and extrusion technology. Intercalated and exfoliated type structures were observed in the sheet extruded nanocomposites using X-ray diffraction and transmission electron microscopy (TEM). Due to the hydrophilic nature of the gelatinized starch nanocomposite a novel preparatory technique was developed to produce nano scale sections for TEM. A range of plasticiser levels were used in conjunction with different unmodified nanoclays (sodium montmorillonite (Na-MMT) and fluorohectorite (Na-FHT)) having different cationic exchange capacities. It was shown that an optimum level of both plasticiser and nanoclay existed to produce a gelatinized starch film with the highest levels of exfoliation, resulting in superior properties. The use of ultrasonics was only advantageous in terms of clay dispersions at medium clay concentrations in the Na-MMT nanocomposites and higher clay concentrations in the Na-FHT, most probably due to the difference in cationic exchange capacity; however when the level of clay, water and starch was optimised an exfoliated structure was produced via standard mixing which exhibited comparable improvements in mechanical properties to ultrasonically treated samples.     

Synthesis and characterization of waterborne polyurethane/organic clay nanocomposites

Stable waterborne polyurethane/organic clay latex was synthesized by ultrasonically-assisted mixing with different clay content. Fourier transform infrared (FT-IR) spectra showed that the interaction between NH and C=O was enhanced with low content organic clay loaded. X-ray diffraction (XRD) results implied that the layered organic clay was exfoliated and the crystallization of the hard domain in the waterborne polyurethane (WPU) matrix was enhanced. Transmission electron microscopy (TEM) images show that the layered clay was exfoliated by WPU molecule. The tensile test shows that the mechanical properties were improved by loading organic clay and the desired addition was 1 wt.%.     

Synthesis and characterization of waterborne polyurethane/organic clay nanocomposites

Stable waterborne polyurethane/organic clay latex was synthesized by ultrasonically-assisted mixing with different clay content. Fourier transform infrared (FT-IR) spectra showed that the interaction between NH and C=O was enhanced with low content organic clay loaded. X-ray diffraction (XRD) results implied that the layered organic clay was exfoliated and the crystallization of the hard domain in the waterborne polyurethane (WPU) matrix was enhanced. Transmission electron microscopy (TEM) images show that the layered clay was exfoliated by WPU molecule. The tensile test shows that the mechanical properties were improved by loading organic clay and the desired addition was 1 wt.%.     

Simulation of melt crystallization kinetics

Mathematical model of non-isothermal crystallization process, taking into account changes in the system composition is presented as a differential equation system. Application of the proposed model enables calculation of both general process kinetics and parameters, characterizing the forming structure (graininess) and texture of three-space systems and films. In general the presented mathematical model can be applied for the simulation of phase transition processes, such as crystallisation of melts, glasses and other vitreous solids, polymers, epitaxial growth of films, decomposition of solid solution etc.