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.     

聚乙烯/有机蒙脱土纳米复合材料结晶动力学

采用熔融插层法制备了聚乙烯/有机蒙脱土纳米复合材料,利用示差扫描量热法(DSC)研究了复合材料的等温及非等温结晶行为,并与纯聚乙稀进行了比较.通过Avrami方程,修正Avrami方程的Jeziorny法及Ozawa法分别对等温及非等温结晶过程进行了处理.结果表明:蒙脱土片层在复合材料结晶过程中起到了异相成核作用,复合材料的成核机理与生长方式已不同于聚乙烯;在相同结晶条件下,复合材料的结晶速率明显比聚乙烯快;纯PE的表观活化能为142.14 kJ/mol,而复合材料为158.38 kJ/mol,复合材料的活化能有一定程度提高;对非等温结晶过程分析,Jeziorny方法适用,而Ozawa方法不适用.     

Step-scan DSC研究PET/纳米CaCO3复合材料的结晶和熔融行为

采用纳米碳酸钙(CaCO3)浆料直接分散于聚对苯二甲酸乙二醇酯(PET)的单体乙二醇中,原位聚合制备出分散均匀的聚对苯二甲酸乙二醇酯(PET)/CaCO3纳米复合材料。分别利用传统的差示扫描量热仪(DSC)和步进扫描DSC(Step-scan DSC)技术研究了CaCO3含量变化对PET结晶和熔融行为的影响及非等温结晶动力学过程。结果表明,纳米粒子与PET的相互作用较弱,对PET结晶主要起促进作用,使结晶更加完善,碳酸钙的含量达到3%时,相对结晶速率达到最大。结晶初期,纳米粒子异相成核作用占优势,这种优势随着纳米粒子含量的增加而有所减弱;结晶后期,纳米粒子对高分子运动的牵制作用比较明显。     

Effects of carbon black-carbon nanotube complex fillers on the properties of isotactic polypropylene nanocomposites

In this study, the reinforcing effects of carbon black (CB) and carbon nanotube (CNT) complex fillers on the properties of isotactic polypropylene (iPP) nanocomposites were investigated using various methods. The surface of the CNTs was modified using a linear alkyl chain in order to create a homogeneous CNT dispersion in the iPP matrix. When the CB content that was incorporated in the iPP matrix increased, the thermal and mechanical properties of the iPP/CB nanocomposites were enhanced. Additionally these enhancements in the properties were similarly induced by introducing a small amount of alkylated CNTs (a-CNTs). In contrast, the CB/a-CNT complex filler was more effective for the iPP nanocomposites than the CB or a-CNT single filler in terms of the thermal stability and the electrical properties. However, the mechanical properties of the CB/a-CNT complex filler incorporated iPP nanocomposites were poorer than the only a-CNT incorporated iPP nanocomposites. Additionally, the complex filler did not overcome the nucleation behavior of the a-CNTs in the re-crystallization of iPP.     

Crystallization, mechanical properties, and controlled enzymatic degradation of biodegradable poly(epsilon-caprolactone)/multi-walled carbon nanotubes nanocomposites

Biodegradable poly(epsilon-caprolactone) (PCL)/multi-walled carbon nanotubes containing carboxylic groups (f-MWNTs) nanocomposites were prepared via simple melt compounding at low f-MWNTs loading in this work. Scanning and transmission electron microscopy observations indicate a homogeneous and fine distribution of f-MWNTs throughout the PCL matrix. The effect of low f-MWNTs loading on the crystallization, mechanical properties, and controlled enzymatic degradation of PCL in the nanocomposites were studied in detail with various techniques. The experimental results indicate that the incorporation of f-MWNTs enhances both the nonisothermal crystallization peak temperature and the overall isothermal crystallization rate of PCL in the PCL/f-MWNTs nanocomposites relative to neat PCL; moreover, the incorporation of a small quantity of f-MWNTs has improved apparently the mechanical properties of the PCL/MWNTs nanocomposites compared to neat PCL. The enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites at low f-MWNTs loading was studied in detail. The variation of weight loss with enzymatic degradation time, the surface morphology change, the reduced film thickness, the appearance of f-MWNTs on the surface of the films, and the almost unchanged molecular weight after enzymatic degradation suggest that the enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites may proceed via surface erosion mechanism. The presence of f-MWNTs reduces the enzymatic degradation rate of the PCL matrix in the nanocomposites compared with that of the pure PCL film.     

Thermal and morphological characterization of poly(ethylene terephthalate)/calcium carbonate nanocomposites

Nanocomposites composed of poly(ethylene terephthalate) (PET) filled with calcium carbonate particles of nanometer scale were prepared by polymerizing the polyester in the presence of the nanosized fillers. Besides plain calcium carbonate, carbonate nanoparticles coated with stearic acid were also used, in order to improve the compatibility between the polymeric matrix and nanofillers. Morphological analysis evidenced a good dispersion of both the nanopowders into the PET matrix, especially in the case of coated calcium carbonate. The strong interfacial adhesion between the two phases is also responsible for the increase of the glass transition and melting temperatures in the nanocomposites compared to plain PET. Finally, non-isothermal crystallization studies revealed that the coated CaCO₃ is a good nucleating agent for PET. Analysis of non-isothermal crystallization data with the Ozawa theory was successful for plain PET and PET/un-CaCO₃, but this method failed to describe the dynamic solidification of the PET/c-CaCO₃ nanocomposite.     

Comparison between isothermal cold and melt crystallization of polylactide/clay nanocomposites

The isothermal cold and melt crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) were studied using differential scanning calorimetry (DSC), polarized optical microscope (POM), X-ray diffractometer (XRD) and Fourier Transform Infra-Red Spectrometer (FT-IR). The results show that the degree of crystallinity of PLA matrix decreases monotonously with increasing clay loadings for both the cold and melt crystallization. The cold crystallized sample shows a double melting behavior and lower melting temperature compared to that of melt-crystallized sample, especially in the presence of clay. The crystallization kinetics was then analyzed by the Avrami and Lauritzen-Hoffman methods for further comparison between these two crystallization behaviors. The results reveal that PLA and its nanocomposites present higher activation energy in melt crystallization than that in cold crystallization due to the reptation of entire polymer chains. The addition of clay facilitates the overall kinetics of melt crystallization, which is attributed to both the nucleation effect of clay and enhanced diffusion of PLA chains. However, for cold crystallization, only very small amounts of clay can slightly increase the kinetics, while larger amounts impede the process. The presence of clay leads to a diffusion-controlled growth of nucleation of PLA matrix in the cold crystallization process and, the hindrance effect of clay hence becomes the dominant factor gradually with increasing clay loadings in the case of high-rate nucleation.     

Preparation and properties of biodegradable poly(L-lactide)/octamethyl-polyhedral oligomeric silsesquioxanes nanocomposites with enhanced crystallization rate via simple melt compounding

Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.     

PA6/POE/OMMT纳米复合材料的非等温结晶行为

采用差示扫描量热仪(DSC)研究了熔融插层法制备的尼龙6/乙烯-辛烯共聚物/有机改性蒙脱土(PA6/POE/OMMT)纳米复合材料的结晶行为,用Jeziorny法和Mo法分析了复合材料的非等温结晶动力学,并计算得到了相关的结晶动力学参数.结果表明,纳米粘土对基体有异相成核作用,但随着其在复合材料中含量增加,半结晶时间t...     

火焰喷涂ETFE涂层的非等温结晶行为

采用火焰喷涂技术制备了乙烯-四氟乙烯共聚物(ETFE)涂层。利用红外光谱仪、接触角测定仪、差示扫描量热仪(DSC)等对涂层的结构、表面性能及非等温结晶、熔融行为进行了分析。结果表明,ETFE粉末在火焰喷涂过程中没有发生氧化降解反应,适宜采用火焰喷涂法制备涂层;涂层的结晶动力学分析表明,用Jeziorny法和Mo法处理其非等温结晶过程比较理想。     

Hybrid network structure and thermal conductive properties in poly(vinylidene fluoride) composites based on carbon nanotubes and graphene nanoplatelets

A small quantity of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were introduced into the poly(vinylidene fluoride) (PVDF)/GNP and PVDF/CNT composites, respectively, to prepare the corresponding ternary PVDF/CNT/GNP and PVDF/GNP/CNT composites. The results demonstrated that adding CNTs into the PVDF/GNP composites greatly promoted the formation of the hybrid network structure of fillers. This was much different from the scenario that adding GNPs into the PVDF/CNT composites. GNPs and CNTs exhibited excellent nucleation effects for the crystallization of PVDF matrix; however, the variation of the PVDF crystallinity was small. Adding CNTs into the PVDF/GNP composites greatly enhanced the electrical conductivity of the PVDF/CNT/GNP composites. This was also different from the scenario of the PVDF/GNP/CNT composites. Furthermore, the PVDF/CNT/GNP composites exhibit higher thermal conductivity and higher synergistic efficiency compared with the PVDF/GNP/CNT composites. The conductive mechanisms and the synergistic effects of the ternary composites were then analyzed.     

Non-isothermal Crystallization Kinetics of Polyamide 6/Diamine-modified MWNTs Nanocomposite

The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa equation and the combined Avrami/Ozawa equation were employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. It was found that the combined Avrami/Ozawa equation could successfully describe the non-isothermal crystallization process. The results showed that D-MWNTs not only acted as effective heterogeneous nucleating agents for PA6 and noticeably increased the crystallization temperature of PA6, but also influenced the mechanism of nucleation and crystal growth of PA6 and then reduced the overall crystallization rate of the neat PA6 matrix. The crystallization activation energy for the nanocomposite sample was greater than that of the neat PA6, which indicated that the addition of D-MWNTs hindered the mobility of PA6 chain segments.     

Synthesis and properties of poly(hexamethylene terephthalate)/multiwall carbon nanotubes nanocomposites

Poly(hexamethylene terephthalate) (PHT)/carbon nanotubes (CNT) nanocomposites containing 1% and 3% (w/w) of filler were prepared by two procedures: in situ ring-opening polymerization of hexamethylene terephthalate cyclic oligomers in the presence of CNT and melt blending of PHT/CNT mixtures. Arc discharge multiwalled carbon nanotubes, both pristine (MWCNT) and hydroxyl functionalized (MWCNT-OH), were used. The objective was to evaluate the effect of preparation procedure, nanotube side-wall functionalization and amount of nanotube loaded on properties of PHT. All nanocomposites showed an efficient distribution of the carbon nanotubes within the PHT matrix but interfacial adhesion and reinforcement effect was dependent on both functionalization and nanotubes loading. Significant differences in thermal stability and mechanical properties ascribable to functionalization and processing were observed among the prepared nanocomposites. All the prepared nanocomposites showed enhanced crystallizability due to CNT nucleating effects although changes in melting and glass transition temperatures were not significant.     

Electrical, thermal, and mechanical properties of polyarylene ether nitriles/graphite nanosheets nanocomposites prepared by masterbatch route

Graphite nanosheets (GN) reinforced polyarylene ether nitriles (PEN) nanocomposites were successfully fabricated through masterbatch route and investigated for morphological, thermal electrical, mechanical, and rheological properties. The SEM images showed that GN were well coated by phthalonitrile prepolymer (PNP) and dispersed in the PEN matrix. Thermal degradation and heat distortion temperature of PEN/GN nanocomposites increased substantially with the increment of GN content up to 10 wt%. Electrical conductivity of the polymer was dramatically enhanced at low loading level of GN; the electrical percolation of was around 5 wt% of GN. The mechanical properties of the nanocomposites were also investigated and showed significant increase with GN loading. For 10 wt% of GN-reinforced PEN composite, the tensile strength increased by about 18%, the tensile modulus increased by about 30%, the flexural strength increased by about 25%, and the flexural modulus increased by 90%. Rheological properties of the PEN/GN nanocomposites also showed a sudden change with the GN loading content; the percolation threshold was in the range of 3–4 wt% of GN.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

Microstructures and tensile behavior of carbon nanotube reinforced Cu matrix nanocomposites

Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to improve the mechanical performance of monolithic materials. However, the CNT/metal nanocomposites have shown lower strength than expected. In this study, the CNT reinforced Cu matrix nanocomposites were fabricated by spark plasma sintering (SPS) of high energy ball-milled nano-sized Cu powders with multi-wall CNTs, and followed by cold rolling process. The microstructure of CNT/Cu nanocomposites consists of two regions including CNT/Cu composite region, where most CNTs are distributed, and CNT free Cu matrix region. The stress–strain curves of CNT/Cu nanocomposites show a two-step yielding behavior, which is caused from the microstructural characteristics consisting of two regions and the load transfer between these regions. The CNT/Cu nanocomposites show a tensile strength of 281 MPa, which is approximately 1.6 times higher than that of monolithic Cu. It is confirmed that the key issue to enhance the strength of CNT/metal nanocomposite is homogeneous distribution of CNTs.     

Non-isothermal crystallization of polyamide 6 matrix in all-polyamide composites: crystallization kinetic, melting behavior, and crystal morphology

The difference in the melting points of polyamide 66 (PA66) fiber and polyamide 6 (PA6) film permits the preparation of all-polyamide (all-PA) composites by film-packing. Good interface performance and integrated consolidation structure in this all-PA composite are contributed to the similar chemical composition between PA66 fiber and PA6 matrix. In this paper, the non-isothermal crystallization kinetics and melting behaviors of PA6 matrix in all-PA composite are studied by differential scanning calorimetry (DSC), in which the modified Avrami equation, Ozawa model, and Mo equation combining Avrami and Ozawa equation are employed. It is found that the Mo equation exhibits great advantages in treating the non-isothermal crystallization kinetics for both neat PA6 and PA6 matrix in all-PA composite. The crystal morphologies of single PA66 fiber–PA6 composite by polarizing microscope (POM) clearly show a transcrystallinity layer of PA6 around PA66 fiber that proves a remarkable nucleation effect of PA66 fiber surface on the crystallization of PA6 matrix.     

Preparation and dielectric properties of poly(arylene ether nitrile) containing carboxyl groups/carbon nanotubes composites

Poly(arylene ether nitrile) (PEN)/carbon nanotubes (CNTs) hybrid films were prepared with different CNTs content (0–2.5 wt%) by solution blending method. The dispersion of CNTs can be improved by the functional groups, which is attributed to the pendent carboxyl groups on the PEN matrix itself. Namely, the carboxyl groups on the side-chain of PEN react with the hydroxyl groups of CNTs. Scanning electron microscope showed that the dispersion of the CNTs was enhanced by the carboxyl groups on the PEN. Differential scanning calorimetry and thermal gravimetric analyses experiments showed that the hybrid films exhibit a good thermal stability. The dielectric constant of the hybrid film with 2.5 wt% CNT content reaches 27 compared to 4 at pure PEN at 1 kHz. From room temperature to 150 °C, temperature variation over the range has a slight effect on the dielectric properties of the hybrid films. The dielectric constant of the hybrid film with 2.5 wt% CNT content reaches 30 compared to 5 at pure PEN at 150 °C. The results illustrate that the PEN/CNTs hybrid films are good dielectric materials, which is favorable for many industrial applications.     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate) nanocomposites

This article reports the nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nanocomposites. The non-isothermal crystallization behaviors of PET and the nanocomposite samples are studied by differential scanning calorimetry (DSC). Various models, namely the Avrami method, the Ozawa method, and the combined Avrami-Ozawa method, are applied to describe the kinetics of the non-isothermal crystallization. The combined Avrami and Ozawa models proposed by Liu and Mo also fit with the experimental data. Different kinetic parameters determined from these models prove that in nanocomposite samples intercalated silicate particles are efficient to start crystallization earlier by nucleation, however, the crystal growth decrease in nanocomposites due to the intercalation of polymer chains in the silicate galleries. Polarized optical microscopy (POM) observations also support the DSC results. The activation energies for crystallization has been estimated on the basis of three models such as Augis-Bennett, Kissinger and Takhor methods follow the trend PET/2C20A < PET/1.3C20A < PET, indicating incorporation of organoclay enhance the crystallization by offering large surface area.     

PP/PA6/OMMT纳米复合材料的非等温结晶动力学

采用熔融插层法制备了聚丙烯(PP)/尼龙6(PA6)/蒙脱土(OMMT)纳米复合物材料,并用差示扫描量热法(DSC)对体系的非等温结晶动力学进行了研究.结果表明,PA6和OMMT的加入,对PP有异相成核的作用,能提高PP的结晶速率和结晶度;运用莫志深方法处理纯PP和PP/PA6/OMMT复合材料的非等温结晶动力学,结果...