Polymorphism and Thermal Behaviour of Syndiotactic Poly(propylene)/Carbon Nanotube Composites

Summary: Nanocomposite materials were obtained by blending multi‐wall carbon nanotubes (CN), obtained by acetylene catalytic chemical vapour deposition (CVD) on Co/Fe‐modified NaY zeolite, with syndiotactic poly(propylene) (sPP). The nanotubes, well dispersed in the polymer matrix, favour the crystallization of the sPP helical chains and significantly improve the sPP thermal stability either in nitrogen or in air. The morphology of the sPP affects the behaviour of the sPP degradation in air.

Thermogravimetric analysis in air of pure sPP and the nanocomposite material.     

聚(2,5-苯并(口恶)唑)/多壁碳纳米管复合材料的制备与性能

采用强氧化性酸处理多壁碳纳米管(MWNTs),形成功能化的多壁碳纳米管(MWNTs-COOH)。用傅里叶红外光谱(FT-IR)对处理前后MWNTs的表面官能团进行了分析,并利用原位聚合法成功制备了聚(2,5-苯并噁唑)(ABPBO)/MWNTs-COOH纳米复合材料。结果表明:碳纳米管经过酸处理后,表面含有较多羰基和羟基极性官能团,在ABPBO基体中分散均匀;复合材料保持了ABPBO的优异耐高温性能,其力学性能和光物理性能也得到了很大的提高。     

Isothermal and Non-Isothermal Crystallization Kinetics and Morphology of Poly(trimethylene terephthalate)/Multiwalled Carbon Nanotube Composites

Summary: Multiwalled carbon nanotubes (MWCNTs) synthesized using chemical vapor deposition method were dispersed in poly(trimethylene terephthalate) (PTT, Mv = 88,000) by melt compounding technique using DMS microcompounder. The nanocomposites consisting of varying amounts of MWCNTs were characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of carbon nanotubes on the crystallization behavior (under isothermal and non isothermal crystallization conditions) of PTT was studied using DSC. The presence of carbon nanotubes didn't show any significant effect on crystallization temperature of PTT matrix under non-isothermal conditions. Crystallization studies under isothermal conditions were carried out at different temperatures i.e 185, 190, 195 and 200 °C. Complete crystallization was observed within 60 sec at 185 °C whereas at 200 °C, longer time was required for complete crystallization. Crystal growth was also investigated using hot stage polarizing microscope (PLM). The effect of annealing time at 200 °C was investigated in the presence as well as in the absence of varying amounts of MWCNTs. Spherulitic growth was seen and the spherulite size in all the samples increased with annealing time. Morphological characterization using SEM and TEM showed a uniform dispersion of MWCNTs and poor compatibility with PTT matrix.     

Thermal and Photooxidative Degradation Behaviors of Poly(propylene)/SiO2 Nanocomposites with Various Polymer Morphologies

Photo‐ and thermal stabilities of poly(propylene) (PP)/SiO₂ nanocomposites were studied by varying the particle size of the SiO₂ nanoparticles. It was found that smaller SiO₂ nanoparticles improved the stabilities of the nanocomposites by depressing the size of spherulites. The phenomenon was successfully explained within the infectious spreading model, where the spatial spreading of oxidation was delayed at the interfacial region between the spherulites.

     

氯化聚丙撑碳酸酯增容聚丙撑碳酸酯/秸秆粉复合材料的制备及性能

聚丙撑碳酸酯(PPC)是一种新型热塑性生物降解材料,但其热性能及力学性能较差,应用受到限制。以秸秆粉这种农作物副产品作为增强体改性PPC,既可以提高PPC的力学性能同时又可开发利用秸秆资源。氯化聚丙撑碳酸酯(CPPC)是聚丙撑碳酸酯(PPC)经过氯化得到的,对天然纤维表面具有良好的浸润性和粘结性。本文以CPPC为增容剂,通过熔融共混法制备了PPC/秸秆粉复合材料。采用扫描电子显微镜(SEM)、拉伸实验、动态力学性能测试(DMA)及转矩流变仪对复合材料的结构及性能进行了表征,重点考察了CPPC的添加量对复合材料力学和流变性能的影响。结果表明,当CPPC质量分数为1.8%时,可使添加质量分数为30%秸秆粉的PPC复合材料拉伸强度提高38%,模量提高30%。同时,CPPC的引入使复合材料的粘度下降,改善了PPC/秸秆粉复合材料的加工性能。因此,作为增容剂的CPPC为制备高性能PPC/天然纤维复合材料提供了新的解决办法。     

Thermal,Mechanical and Morphological Behavior of Poly(propylene)/Wood Flour Composites

The comparative studies on the thermal, mechanical and morphological behavior of compression molded poly(propylene) (PP)/wood flour (WF) composites were performed using wood flours (WFs) of different origins. The comparison has been made on the basis of results obtained from thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile testing. It has been demonstrated that an addition of 5 wt.-% of maleic anhydride grafted polypropylene (PP-g-MA) has a significant effect on the morphological and thermomechanical behavior of the composites. Although, microscopic examinations revealed no significant differences in the morphology of the compatibilized composites, a remarkable improvement of thermal degradation behavior was observed. From the view point of mechanical properties, the composites with high amount of filler (60 wt.-%) showed similar behavior irrespective of the origin of wood flour.     

Synthesis and Dispersion Characteristics of Multi‐Walled Carbon Nanotube Composites with Poly(methyl methacrylate) Prepared by In‐Situ Bulk Polymerization

Multi‐walled carbon nanotubes (MWNT) purified by acidic solution were processed with PMMA via an in‐situ polymerization. Experimental evidences indicate the role of radical initiator (AIBN) and MWNT, showing increases of polymerization rate and MWNT diameter. Induced radicals on the MWNT by AIBN were found to trigger the grafting of PMMA. Moreover, the solvent cast film showed a better nanoscopic dispersion of MWNT and possibilities of CNT composites in engineering applications.

Fractured surface of multi‐walled carbon nanotube composite with PMMA prepared by in‐situ bulk polymerization.     

Isotactic Poly(propylene)/Monoalkylimidazolium‐Modified Montmorillonite Nanocomposites: Preparation by Intercalative Polymerization and Thermal Stability Study

Summary: Poly(propylene)/monoalkylimidazolium‐modified montmorillonite (PP/IMMT) nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/MMT catalyst. The PP synthesized possessed high isotacticity and molecular weight. Both wide‐angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposite formation with exfoliated MMT homogeneously distributed in the PP matrix. A thermal stability study revealed that the nanocomposites possess good thermal stability.

X‐ray diffraction patterns of PP/IMMT (MMT = 2.2 wt.‐%) nanocomposite before and after processing.     

Effect of Phosphorus-Nitrogen Intumescent Flame Retardant on Structure and Properties of Poly(propylene)

Summary : Phosphorus-nitrogen intumescent product (R₂₀₀₀) was filled into polypropylene (PP) as a flame retardant. The neat PP and flame-retarded PP blends were studied for their structural and mechanical properties after verification of the flame retardancy character of blends. In this paper, the influence of incorporation of different amount (5%, 10%, 15%, 20%, and 25%) of R₂₀₀₀ was studied. The flame retardancy is evaluated by limiting oxygen index (LOI) value, which is enhanced from 17.5 for pure PP to 22.7 for the blend comprising 15% intumescent product, phosphorus-nitrogen based (R₂₀₀₀). The thermal degradation behaviour of the PP/R₂₀₀₀ blends was investigated using thermogravimetric analysis (TGA) under nitrogen (N₂) and oxygen (O₂) atmospheres. The influence of the R₂₀₀₀ on the PP crystallization was examined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Further, the mechanical properties of the materials were studied by dynamic mechanical analysis (DMA). The incorporation of the flame retardant had no effect on the crystallization of the neat polymer and the mechanical properties of the materials remained unaffected.     

Homogeneously Dispersed Poly(propylene)/SiO2 Nanocomposites with Unprecedented Transparency

Summary: Physico‐chemical interactions between hydrophobic polyolefin materials and hydrophilic inorganic nanoparticles such as surface‐hydroxylated SiO₂ have not been well understood so far. In this study, the effects of particle size and content of SiO₂ nanoparticles on isothermal growth rate of PP spherulites in various PP/SiO₂ nanocomposites were investigated by polarized optical microscopy. It was unexpected to find that hydrophilic SiO₂ nanoparticles can be homogeneously dispersed in a PP matrix. Spherulite growth rates of PP in PP/SiO₂ nanocomposites decrease significantly with increasing SiO₂ content and decreasing particle size. Most interestingly, the spherulite growth rate was zero for PP/16 nm‐SiO₂ nanocomposites with SiO₂ content above 2.5 wt.‐% resulting in a highly transparent film.

Photographs of 200 µm‐thick PP and PP/16 nm‐SiO₂ (5 wt.‐%) sheets in front of a graphic pattern.     

Formation and Detection of Clay Network Structure in Poly(propylene)/Layered Silicate Nanocomposites

Summary: The study of the structure and the rheological properties of poly(propylene) (PP)/montmorillonite (MMT)/maleinated PP (MAPP) composites strongly suggests that a silicate network may form under certain conditions. Network formation could not be proven unambiguously with the usual techniques, i.e., with TEM and by plotting the frequency dependence of viscoelastic properties. Cole‐Cole plots detect the network very sensitively. A certain number of silicate layers are needed to create a house‐of‐cards structure. A threshold concentration of MAPP exists in the investigated system, which depends on the silicate content.

Cole‐Cole representation of the viscoelastic properties of PP/OMMT/MAPP nanocomposites.     

Electrorheology of Multiwalled Carbon Nanotube/Poly(methyl methacrylate) Nanocomposites

Summary: Multiwalled carbon nanotube (MWNT) nanocomposites dispersed in a poly(methyl methacrylate) (PMMA) matrix were prepared via suspension polymerization, in which radicals induced on the outer wall of the MWNTs by 2,2′‐azoisobutyronitrile initiate the grafting of PMMA. The synthesized MWNT/PMMA nanocomposite particles were found to have a spherical shape and exhibit a high electrical conductivity, mainly as a result of the carbon nanotubes. A suspension was prepared with MWNT/PMMA particles in insulating silicone oil and its electrorheological properties were investigated by controlling applied direct current (DC) electric field strengths.

Flow curve possessing a region analogous to the coexistence curve.     

A Facile Approach to Single‐Wall Carbon Nanotube/Poly(allylamine) Nanocomposites

A facile approach to polymer nanocomposites with single‐wall carbon nanotubes and cationic polymers is reported. The composite material was synthesized by producing carboxylic acid groups at the nanotube termini followed by a reaction with poly(allylamine) in water. Fourier transform infrared spectral and thermogravimetric analyses corroborate that the poly(allylamine) chains were wrapped on the surface of the carbon nanotubes. The scanning electron microscopic (SEM) image shows that the nanotubes were dispersed with little aggregation, thus, strongly suggesting that the poly(allylamine) chains have covered the single‐wall carbon nanotubes, which was further evidenced by transmission electron microscopy. The composites are soluble in water, and this solubilization process opens up new opportunities in the solution chemistry on pristine nanotubes.

     

Non-Isothermal Crystallization of Poly(vinylidene Fluoride)/Multiwalled Carbon Nanotube Composites

Poly(vinylidene fluoride)/multiwalled carbon nanotube (PVDF/MWCNT) composites were prepared by the method of solution blending. The non-isothermal crystallization of PVDF and its composites was investigated by differential scanning calorimetry (DSC). The results showed that the crystallization peaks shifted to lower temperature and the exothermic trace became wider when cooling rate increased for PVDF and its composites. The MWCNTs caused an increase in crystallization temperature and initial crystallization temperature. In addition, the Jeziorny and Mo methods were used to analyze the non-isothermal crystallization kinetics. The results showed that the crystallization rate rose with an increase in cooling rate, however, the MWCNTs decreased the crystallization rates of PVDF.     

聚3-辛基噻吩/MWNTs复合材料的导电性能研究

采用在氯仿溶液中超声共混, 制备聚3-辛基噻吩(P3OT)和多壁碳纳米管(MWNTs)复合材料. 当MWNTs掺杂量为3%时复合材料的电导率为1.43 S•m－1, 达到纯MWNTs的电导率水平. 用FTIR光谱, TG, UV-Vis光谱, XPS和FESEM进行研究分析, 认为MWNTs的离域电子与P3OT主链上的π电子之间形成π-π共轭, 增加了P3OT主链的有效共轭度, 被掺杂的P3OT具有很高的电导率, 提高了复合材料的导电性能. MWNTs与被掺杂的P3OT组成相对独立的导体单元, 对复合材料的导电网络形成起着主要作用.     

Conductive Composites Based on Metallocene Isotactic Poly(propylene): Preparation and Properties

Summary: The research deals with the preparation and the further comprehensive characterization of metallocene polypropylene-based composite materials by incorporation of carbon black nanoparticles. Composites containing up to 10 wt% of carbon black were prepared by direct melt mixing in a single screw extruder Brabender Extrusiograph type 30/25D with attached static mixer at melt temperature of 200 °C and a screw speed of 30 rpm, according to a two-step process. Some composites were treated with 3 wt% maleic anhydride grafted polypropylene (MAH-PP). The rheological behaviour of the miPP nanocomposites was determined by cone/plate rheological measurements at 180 °C. The composites were characterized by SEM for morphological details and uniaxial stress-strain measurements for determining the mechanical parameters. Electric conductivity of injection molded plates from these composites was investigated. The different miPPs studied are ranked in an ascending order according to their increasing molecular weight concerning the magnitude of their rheological parameters. The maleic anhydride compatibilizer leads to lower viscosity values even at high shear gradients and to better homogenization of the nanofiller in the polymer matrix. The processing conditions, carbon black concentration and viscosity of the virgin polymer have an impact on the final conductivity of the miPP/carbon black composites.     

Nucleating Effect and Dynamic Crystallization of a Poly(propylene)/Talc System

The addition of nucleating agents to semicrystalline polymersis largely used in the processing industry of plastic materials to improve some properties of polymers as well as for economical and technological reasons. In this work, the influence of talc concentration on the nucleation efficiency of poly(propylene) (PP), as well as on the non-isothermal kinetics of the crystallization of that system were determined by differential scanning calorimetry (DSC). The nucleating efficiency was determined by Fillon's method, and the dynamic nucleation by Ozawa's method at cooing rates of 2, 5 and 10°C min^–1. The results show that both the degree of crystallinity and the crystallization temperature increase with the filler content and decrease at higher cooling rates and that Ozawa's (n,) exponent and the nucleation efficiency increase with temperature and filler content. It was also shown that the nucleating efficiency of talc in poly(propylene) is comparable to the best heterogeneous nucleating agents available. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Degradation and Kinetics of Poly(3-hydroxybutyrate)/Organoclay Nanocomposites

Poly(3-hydroxybutyrate)/Cloisite30B (PHB/30B) nanocomposites were prepared by solution-intercalation method. The influence of 30B content on the thermal stability of PHB was investigated. With the addition of 3 wt. % of 30B the highest thermal stability of PHB was achieved. The kinetic analysis of the non-isothermal degradation was performed using the isoconversional Friedman method and invariant kinetic parameters method.