Study on ablative properties and mechanisms of hydrogenated nitrile butadiene rubber (HNBR) composites containing different fillers

The ablative properties of hydrogenated nitrile butadiene rubber (HNBR) composites filled with fumed silica, organically modified montmorillonite (OMMT), or expanded graphite (EG) were examined. The HNBR/OMMT composite has the lowest linear ablation rate and the highest mass ablation rate and does not tend to be carbonized. On the other hand, the HNBR/EG composite has the highest linear ablation rate and the lowest mass ablation rate, and is prone to carbonization. The ablative properties of the HNBR/silica composite are between those of HNBR/OMMT and HNBR/EG. From the viewpoint of thermal shielding capability, the HNBR/OMMT has the best ablation resistance. Thermogravimetric analysis (TGA) on different HNBR composites indicated that the filler type has no significant effect on the thermal stability of the composites. To understand the ablation mechanisms, the char layers of different HNBR composites after ablation experiments were characterized by scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS), and wide-angle X-ray diffraction (WAXD). The results showed that the porosity in the char layers of the HNBR/OMMT composite was the highest and the corresponding structure was the loosest of the three composites. The montmorillonite (MMT) dispersed in HNBR experienced phase transition, melting and vaporization when exposed to the flame with the temperature over 2000 °C. Fumed silica only melted at such situation. On the other hand, the EG kept their original crystalline structures after the ablation test. Based on these results, the effect of the filler type on the ablation mechanisms of the HNBR composites was discussed.     

Microstructure,Interfacial Interactions,and Rheological Properties of PC/AES/Montmorillonite Composites

Polycarbonate (PC) and acrylonitrile–EPDM (ethylene/propylene/diene elastomer)–styrene ter‐polymer (AES) blends and PC/AES/organically modified montmorillonite (OMMT) composites were prepared at 20%, 40%, 50% by weight of AES and 3% by weight of OMMT. The microstructure, interfacial interactions, and rheological properties of the PC/AES blends and PC/AES/OMMT composites were studied systematically. X‐ray diffractometer (XRD) results reveal that the AES is easier to intercalate into OMMT than PC, and the content of AES has a little effect on the interlayer distance of OMMT. Wetting coefficient calculation indicates that OMMT distributes primarily at the interface of the polymer blend. Field emission scanning electron microscope (FE‐SEM) observation indicates that the phase morphology of PC/AES blends and PC/AES/OMMT composites is not influenced by the OMMT. However, linear rheological properties suggest that the addition of OMMT has a great effect on the linear rheological property.     

The Effect of OMMT on the Morphology and Mechanical Properties of PVC/ABS Blends

Poly(vinyl chloride) (PVC)/acrylonitrile-butadiene-styrene (ABS) blends containing organically modified montmorillonite (OMMT) were prepared using a twin-screw extruder followed by injection molding. The OMMT dispersion was evaluated by X-ray diffraction and transmission electron microscopy. The clay was preferentially situated in the PVC phase and across the interfaces of PVC/ABS. The effect of the addition of OMMT on the morphology and mechanical properties was also evaluated. Scanning electron microscopy revealed a large reduction in domain size when OMMT was used. The mechanical properties were studied through tensile and impact tests. The yield stress increased when an appropriate amount of OMMT was used without impairing the impact strength.     

Morphology,rheology property,and crystallization behavior of PLLA/OMMT nanocomposites prepared by an innovative eccentric rotor extruder

An innovative eccentric rotor extruder, which can generate continuous elongation flow, was used to fabricate the poly(L‐lactide) (PLLA)/organo‐modified montmorillonite (OMMT) nanocomposites in different OMMT concentrations. The morphology of the nanocomposites was characterized by thermal gravimetric analyzer, X‐ray diffractometer, and transmission electron microscope. The results showed that the OMMT nanoparticles were uniformly dispersed in the PLLA matrix and mainly existed in intercalation mode. The intercalation and exfoliation process of OMMT in the eccentric rotor extruder may be a double‐side exfoliation, which is more effective than the layer‐by‐layer peeling mechanism based on the shear flow. The influence of OMMT on the rheological behavior of PLLA was investigated by dynamic rheological measurements, showing greater improvement of rheological properties for the nanocomposites. The thermo‐mechanical properties analysis indicated that significant enhancement of E′ can be seen for all the nanocomposites. Presence of intercalated OMMT platelets did not lead to a significant shift of the E″ and tan δ curves compared with that of pure PLLA. The crystallization and melting behavior was studied by differential scanning calorimetry, which indicated that the incorporation of OMMT nanoparticles slightly increased the crystallinity of PLLA matrix. The polarizing microscope was further carried out and showed that the dispersed OMMT nanoparticles acted as a heterogeneous nucleating agent to promote the crystallization of PLLA.     

Studies on the migration in PA6‐OMMT nanocomposites: effect of annealing on migration as evidenced by ARXPS (angle resolved X‐ray photoelectron spectroscopy)

The present paper deals with experiments in which the angle resolved X‐ray photoelectron spectroscopy (ARXPS) technique was applied to investigate the phenomenon of migration in polyamide 6 with organically modified montmorillonite (PA6‐OMMT) nanocomposites. This is the first time ARXPS was used, to gain a more detailed insight into the migration process. Curve‐fitting analyses are reported which enable the differentiation between a manual mixture of PA6 with OMMT at room temperature from a nanocomposite structure. The ARXPS technique was applied to annealed samples at 250, 275, and 285°C, for 2 hr, and with three take of angles, α, of 90, 60, and 30°. The depth of the layer investigated is 9 nm in case the sample surface is well defined. By tilting the take‐off angle of the beam‐out electrons one can determine the intensity of the signals at various distances from the surface within the investigated layer. The concentration gradient of the Si signals is observed. The rate of migration is found to be more rapid in the layer closest to the surface. The intensity of the Si signals in the investigated layer is found to be 1.8 to 9.1 times that of the same composite sample at room temperature. This ratio determines the extent of migration. At temperatures higher than 250°C and times of annealing greater than 30 min a decrease in the extent of migration is observed. This decrease is explained by the gradual decomposition of the surfactant and the consequent removal of the polymeric matrix molecules from the migrating exfoliated units, culminating in denuded alumino‐silicate layers. These layers aggregate to noncolloidal microcomposite particles which do not migrate. The concentration of the exfoliated units decreases with consequent decrease in migration. A gradient of decreasing concentration of Si2p signals was observed after various times of annealing, where the gradient becomes more uniform with increase in time. Copyright © 2008 John Wiley & Sons, Ltd.     

SMA、OMMT对PA6/ABS共混物聚集态结构及性能影响的研究

采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)等手段研究了苯乙烯-马来酸酐共聚物(SMA)、有机蒙脱土(OMMT)对尼龙6(PA6)/丙烯腈-丁二烯-苯乙烯(ABS)共混物体系聚集态结构及性能的影响.结果表明,SMA与OMMT的加入均可提高PA6/ABS共混物体系的强度及模量,但加入OMMT后共混物的韧性有所下降,而PA6/ABS/SMA共混物的韧性随SMA含量的增加呈上升趋势.SMA、OMMT对PA6/ABS共混体系都有细化ABS分散相的作用,随SMA加入量的增加,ABS分散相尺寸逐渐减小,分布趋于均匀;当OMMT加入量在4 phr以内时,对ABS分散相粒径影响不大,超过4 phr后,随着OMMT含量的增加,ABS分散相的尺寸逐渐减小.XRD与TEM的分析结果表明,对PA6/OMMT(100/5)共混物,OMMT主要以剥离形态分布,同时也存在少量OMMT聚集体;PA6/ABS/OMMT共混物中OMMT则基本以剥离形态选择分布在PA6基体相中.     

环氧树脂／PEG／OMMT杂化体的合成及性能研究

以三乙基苄基氯化铵为催化剂,制备了环氧树脂E-44和聚乙二醇（polyglycol,PEG）的杂化体A;将接枝了马来酸酐的PEG与E-44共混,制备了杂化体B。比较杂化体A和杂化体B的性能及其对E-44的增韧效果。结果表明,杂化体A具有水溶性和较好的表面活性,且对E-44具有优异的增韧效果,加入质量分数40％的杂化体A可使E-44的冲击强度提高203％,适量的有机蒙脱土（organic montmorillonite,OMMT）可有效弥补杂化体A增韧时所引起的剪切强度下降。杂化体B中的PEG与E-44几乎没反应,但PEG会参与其固化反应,从而显著提高E-44的韧性,只是效果不如杂化体A。     

Effects of montmorillonite interlayer micro-circumstance on the PP melting intercalation

1-Octadecyl-3-methylimidazolium chloride ([C₁₈ mim]Cl) is a kind of imidazolium ionic liquid with high thermal stability. [C₁₈ mim]Cl was used to modify pristine Na-montmorillonite and a series of organo-montmorillonite (OMMT) with different loading levels of 1-octadecyl-3-methylimidazolium cation ([C₁₈ mim]⁺) were obtained. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results show that there are different loading levels and aggregative state of [C₁₈ mim]⁺ in the interlayer of OMMT. The effects of OMMT interlayer micro-circumstances on the PP melting intercalation were studied by XRD and transmission electron microscopy (TEM). Results indicate that the melting intercalation of PP into the interlayer of OMMT is not only related with d-spaces but also has something to do with the interlayer micro-circumstance of OMMT. Based on these facts, three types of interlayer absorption models of [C₁₈ mim]⁺ in the interlayer of OMMT were conceived. In addition, the aggregative state of [C₁₈ min]⁺ in the interlayer of OMMT, interlayer polarity and d-spaces of OMMT were discussed. According to these models, we try to illustrate the effect of interlayer micro-circumstance of OMMT on the PP melting intercalation.     

Properties of Poly(Lactic Acid)/ Organo-Montmorillonite Nanocomposites Prepared by Solution Intercalation

Poly(lactic acid)/organo-montmorillonite (PLA/OMMT) nanocomposite films were prepared through solution intercalation using dichloromethane as solvent. X-ray diffraction indicated that organo-montmorillonite (OMMT) was well intercalated and the interlayer spacing d increased by 0.94–1.47 nm. Transmission Electron Microscopy showed that a majority of OMMT was fully exfoliated and uniformly dispersed in the PLA matrix at low filler loading, whereas more intercalated tactoids and aggregates of OMMT existed at high loading. The crystallinity of PLA was hardly changed with the addition of OMMT. Additionally, CO₂ permeability and water vapor transmission rate of the composite films were reduced with increasing content of OMMT. At 5 wt% OMMT loading, CO₂ permeability and water vapor transmission rate were reduced by 75.8% and 23.9%, respectively. The tensile strength (TS) and Young's modulus of the PLA/OMMT nanocomposites were first enhanced, and then decreased with increasing content of OMMT. Compared with pure PLA, a 83.8% increase in the Young's modulus and a 76.0% improvement in TS were obtained with the addition of 3 wt% OMMT.