Influence of thermal processing on the perfection of crystals in polyamide 66 and polyamide 66/clay nanocomposites

A study of the changes in crystal perfection of polyamide 66 (PA66) and polyamide 66/clay nanocomposites (PA66CN) due to different thermal processing was carried out. We designed three series of thermal processing including melt-quench (MQ), post-annealing MQ sample (MQA), and melt–slow cooling–annealing (MSA). The annealing temperature was set as 180 or 210 °C, which is within Brill temperature range of PA66. Fourier transform infrared (FT-IR) spectroscopy and wide angle X-ray diffraction (WAXD) were employed to characterize the perfection in short-range order and long-range order structures, respectively. The results showed that the crystal perfection of PA66 and PA66CN with different thermal processing is quite different, and the changing fashions with thermal processing for different ordered structures are not similar. In this work, MSA is optimal thermal processing for high crystallinity and crystal perfection. Exfoliated nanoclay layers exert considerable impact on the perfection of long-range ordered structures, but little on that of short-range ordered ones.     

Thermal stability and flammability of polyamide 66/montmorillonite nanocomposites

Exfoliated nanocomposites based on polyamide 66 (PA66) and montmorillonite (MMT) were prepared and their thermal stability and combustion behaviour were investigated by using thermal gravity analysis and cone calorimeter. The nanocomposites exhibit higher thermal stability and good flame retardancy. The catalytic decomposition effect of MMT and the barrier effect of layer silicates are presented directly in isothermal oxidation experiment. The initial heat release rate plots show that the addition of MMT can accelerate the ignition of PA66 matrix. A ceramic-like char forms in the surface of the nanocomposites during burning. It is characterized by attenuated total reflection infrared spectra and scanning electron microscopy.     

Processing and properties of modified polyamide 66-organoclay nanocomposites

Binary polyamide 66 nanocomposites containing 2 wt % organoclay, polyamide 66 blend containing 5 wt % impact modifier, and ternary polyamide 66 nanocomposites containing 2 wt % organoclay and 5 wt % impact modifier were prepared by melt compounding method. The effects of E-GMA and the types of the organoclays on the interaction between the organoclay and the polymer, dispersion of the organoclay, morphology, mechanical, flow, and thermal properties of the nanocomposites were investigated. Partial exfoliation and improved mechanical properties are observed for Cloisite® 15A and Cloisite® 25A nanocomposites. On the other hand, the organoclay was intercalated or in the form of tactoids in Cloisite® 30B nanocomposites. Components of the nanocomposites containing Cloisite® 15A and Cloisite® 25A were compounded in different addition orders. Mixing sequence of the components affected both the dispersion of the organoclay and the mechanical properties drastically. SEM analyses revealed that homogeneous dispersion of the organoclay results in a decrease in the domain sizes and promotes the improvements in the toughness of the materials. Melt viscosity was also found to have a profound effect on the dispersion of the organoclay according to MFI and XRD results. Crystallinity of the nanocomposites did not change significantly. It is only the type of the constituents and their addition order what dramatically influence the nanocomposite properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Morphology,thermal, and mechanical properties of polyamide 66/clay nanocomposites with epoxy‐modified organoclay

A new kind of organophilic clay, cotreated by methyl tallow bis‐2‐hydroxyethyl quaternary ammonium and epoxy resin into sodium montmorillonite (to form a strong interaction with polyamide 66 matrix), was prepared and used in preparing PA66/clay nanocomposites (PA66CN) via melt‐compounding method. Three different types of organic clays, CL30B–E00, CL30B–E12, and CL30B–E23, were used to study the effect of epoxy resin in PA66CN. The morphological, mechanical, and thermal properties have been studied using X‐ray diffraction, transmission electron microscopy (TEM), mechanical, and thermal analysis, respectively. TEM analysis of the nanocomposites shows that most of the silicate layers were exfoliated to individual layers and to some thin stacks containing a few layers. PA66CX–E00 and PA66CX–E12 had nearly exfoliated structures in agreement with the SAXS results, while PA66CX–E23 shows a coexistence of intercalated and exfoliated structures. The storage modulus of PA66 nanocomposites was higher than that of the neat PA66 in the whole range of tested temperature. On the other hand, the magnitude of the loss tangent peak in α‐ or β‐transition region decreased gradually with the increase in the clay loading. Multiple melting behavior in PA66 was also observed. Thermal stability more or less decreased with an increasing inorganic content. Young's modulus and tensile strength were enhanced by introducing organoclay. Among the three types of nanocomposites prepared, PA66CX–E12 showed the highest improvement in properties, while PA66CX–E23 showed properties inferior to that of PA66CX–E00 without epoxy resin. In conclusion, an optimum amount of epoxy resin is required to form the strong interaction with the amide group of PA66. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1711–1722, 2006     

Studies on crystallization behaviors and crystal morphology of polyamide 66/clay nanocomposites

X‐ray diffraction methods, DSC thermal analysis, and polarized light microscopy (PLM) were used to investigate the structural changes of nylon 66/clay nanocomposites. PA 66/clay nanocomposites were prepared by the method of melt intercalation. The results indicate that the addition of the intercalated organo‐montmorillonite (OMMT) can induce generation of the β‐form crystal of PA 66 and substantially affect the arrangement of molecules in the α‐form crystal, although the crystallinity scarcely changes. Also, the DSC results indicate that the addition of OMMT in the PA 66 matrix leads to increases of crystallization temperatures and the full width at half maximum (FWHM) of the exothermic peaks. Moreover, the viscosity factor is the main influence on FWHM of the exothermic peaks of PA 66/clay nanocomposites. The results of nonisothermal crystallization kinetics show that OMMT has the effect of heterogeneous nucleation and leads to the decrease of the size of the spherocrystal. The heterogeneous nucleation effects of OMMTs influence the mechanism of crystallization and the growth mode of PA 66 crystals. PLM photographs verify that the size of spherocrystal is decreased and visually confirm the theory of crystallization kinetics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 756–763, 2005     

Crystal structures and their effects on the properties of polyamide 12/clay and polyamide 6–polyamide 66/clay nanocomposites

Both polyamide 12 (PA 12)/clay and polyamide 6–polyamide 66 copolymer (PA 6/6,6)/clay nanocomposites were prepared by melt intercalation. The incorporation of 4–5 wt % modified clay largely increased the strength, modulus, heat distortion temperature (HDT), and permeation resistance to methanol of the polyamides but decreased the notched impact strength. Incorporation of the clay decreased the melt viscosities of both the PA 12 and PA 6/6,6 nanocomposites. Incorporation of the clay increased the crystallinity of PA 6/6,6 but had little effect on that of PA 12, which explained why the clay obviously increased the glass‐transition temperature of PA 6/6,6 but hardly had any effect on that of PA 12. The dispersion and orientation of both the clay and the polyamide crystals were studied with transmission electron microscopy, scanning electronic microscopy, and X‐ray diffraction. The clay was exfoliated into single layers in the nanocomposites, and the exfoliated clay layers had a preferred orientation parallel to the melt flow direction. Lamellar crystals but not spherulites were initiated on the exfoliated clay surfaces, which were much more compact and orderly than spherulites, and had the same orientation with that of the clay layers. The increase in the mechanical properties, HDT, and permeation resistance was attributed to the orientated exfoliated clay layers and the lamellar crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4782–4794, 2006     

The effect of clay on the thermal degradation of polyamide 6 in polyamide 6/clay nanocomposites

The degradation pathway of polyamide 6/clay nanocomposites was studied as a function of clay content. Well-dispersed polymer-clay nanocomposites can be easily obtained by simple melt blending between organically-modified clays and polyamide 6. Polyamide 6-clay nanocomposites exhibit a large reduction in the peak heat release rate, 60%, measured by cone calorimetry. There are no significant differences in the evolved products during thermal degradation of polyamide 6 and polyamide 6/clay nanocomposites in terms of composition and functionality. The main degradation pathway of polyamide 6 is aminolysis and/or acidolysis, primarily through an intra-chain reaction, producing ε-carprolactam, which is the monomer of polyamide 6. As the clay loading is increased, the relative quantity of ε-carprolactam in the evolved products decreases and the viscosity of the soluble solid residues increases. It is thought that inter-chain reactions become significant in the presence of clay because the degrading polymer chains are trapped in the gallery space of the clay during thermal degradation.     

Laser transmission welding of poly(lactic acid) and polyamide66/sepiolite nanocomposites

Influence of sepiolite nanoclay on the properties of the resulting join between poly(lactic acid) (PLA) and different Polyamide66 (PA66)/nanoclay nanocomposites was studied in this work. Six different polymer nanocomposites based on PA66 were manufactured through a melt compounding process by adding a fixed 1.64 wt % of a commercial IR absorber additive and the respective weight percentages of sepiolite to the polymer matrix. Several nanocomposite/PLA joints were finally performed by means of the transmission laser welding technology and the resulting weldings were characterized in terms of mechanical properties by performing peeling and shearing tests. Furthermore, both welded and mechanically tested samples were also analyzed by scanning electron microscopy in order to study the morphology of the weld seam. The results of the performed tests show that the addition of sepiolite to the PA66 improves the welding performance only in those cases in which the percentage of sepiolite of the nanocomposites is higher than 5 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46638.     

Phase transition in nylon 6/clay nanocomposites on annealing

The γ→α crystalline phase transition in nylon 6/clay nanocomposite prior to melting was investigated by X-ray diffraction. The phase transition in the nanocomposite took place at 160 °C, 40 °C higher than that of nylon 6 at 120 °C. The transition extent in the nanocomposite was lower than that in nylon 6. This could be caused by the strongly confined spaces between layers, and the favorable environment for the formation of the γ phase in the existence of clay. Besides, the less grown crystallites of the α phase transformed from the γ phase in the nanocomposite began to melt at much lower temperature than its normal melting temperature.     

橡胶／粘土插层纳米复合材料的研究进展

综述了橡胶／粘土插层纳米复合材料的制备方法及性能特征。重点介绍了溶液插层法、乳液插层法和熔体插层法及相关研究进展。评价了各种制备技术的优缺点,提出了橡胶／粘土插层纳米复合材料的发展趋势。     

The effect of clay type and of clay–masterbatch product in the preparation of polypropylene/clay nanocomposites

Clay containing polypropylene (PP) nanocomposites were prepared by direct melt mixing in a twin screw extruder using different types of organo‐modified montmorillonite (Cloisite 15 and Cloisite 20) and two masterbatch products, one based on pre‐exfoliated clays (Nanofil SE 3000) and another one based on clay–polyolefin resin (Nanomax‐PP). Maleic anhydride‐grafted polypropylene (PP‐g‐MA) was used as a coupling agent to improve the dispersability of organo‐modified clays. The effect of clay type and clay–masterbatch product on the clay exfoliation and nanocomposite properties was investigated. The effect of PP‐g‐MA concentration was also considered. Composite morphologies were characterized by X‐ray diffraction (XRD), field emission gun scanning electron microscopy (FEG‐SEM), and transmission electron microscopy (TEM). The degree of dispersion of organo‐modified clay increased with the PP‐g‐MA content. The thermal and mechanical properties were not affected by organo‐modified clay type, although the masterbatch products did have a significant influence on thermal and mechanical properties of nanocomposites. Intercalation/exfoliation was not achieved in the Nanofil SE 3000 composite. This masterbatch product has intercalants, whose initial decomposition temperature is lower than the processing temperature (T ～ 180°C), indicating that their stability decreased during the process. The Nanomax‐PP composite showed higher thermal and flexural properties than pure PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of chain-extended organifier and properties of polyurethane/clay nanocomposites

Clay organifier with hydroxyl end-group and relatively high molecular weight was synthesized. The clay treated with the organifier was suspended in DMF and the dispersibility of organoclay in polyurethane matrix was enhanced by applying the sonication to the suspension of organoclay in DMF. The d-spacing of organoclay was found to be 2.29 nm compared to 1.18 nm of pristine montmorillonite. The polyurethane/clay nanocomposites formed an intercalated structure with some disorder and their d-spacings were about 2.6-2.7 nm. The barrier property, thermal stability and tensile properties significantly increased with increasing the dispersibility of organoclay. A 2.9-fold increase in tensile strength with 1 wt% of well-dispersed organoclay, a 41% decrease in oxygen permeability and a 1.7-fold increase in Young's modulus at 5 wt% of well-dispersed organoclay were achieved.     

Flame retardant mechanism of polyamide 6-clay nanocomposites

The thermal and flammability properties of polyamide 6/clay (2 and 5% by mass fraction) nanocomposites were measured to determine their flame retardant (FR) performance. The gasification process of the nanocomposite samples at an external radiant flux of 50 kW/m² in a nitrogen atmosphere was observed, and the residues collected at various sample mass losses were analyzed by thermogravimetric analysis, transmission electron microscopy, and X-ray diffraction to determine the content of the residue and to understand the FR mechanism of the nanocomposites. The analysis of the floccules of blackened residues shows that up to 80% by mass of the residues consists of clay particles and the remainder is thermally stable organic components with possible graphitic structure. Furthermore, clay particles are stacked in the carbonaceous floccule residues and the d-spacing of the clay platelets is in the range of 1.3-1.4 nm as compared to the well exfoliated original sample. The accumulation of the initially well-dispersed clay particles in the sample on the burning/gasifying sample surface are due to two possible mechanisms. One is recession of the polymer resin from the surface by pyrolysis with the de-wetted clay particles left behind. Another mechanism is the transportation of clay particles pushed by numerous rising bubbles of degradation products and the associated convection flow in the melt from the interior of the sample toward the sample surface. Numerous rising bubbles may have another effect on the transport of clay particles. Bursting of the bubbles at the sample surface pushes the accumulated clay particles outward from the bursting area and forms the island-like floccules instead of forming a continuous net-like structure of a clay filled protective layer. Therefore, both PA6/clay nanocomposite samples did not produce sufficient amounts of protective floccules to cover the entire sample surface and vigorous bubbling was observed over the sample surface which was not covered by the protective floccules.     

Intercalation and exfoliation behaviour of clay layers in branched polyol and polyurethane/clay nanocomposites

The exfoliation of clay layers was realized in a tri‐hydroxyl branched polyether polyol by direct mixing and the corresponding exfoliated polyurethane/clay nanocomposite was prepared by further in situ curing. The effects of various surface‐modified organoclays and various polyol types on the intercalation and exfoliation behaviour of clay layers were investigated. The interaction between the polyol and clay and the mixing temperature plays an important role in the occurrence of exfoliation and intercalation. The relationship between rheological data of polyol/clay dispersion and the intercalation or exfoliation state of the clay was established. This provides a convenient and efficient way to evaluate the dispersion state of the clay. Based on the experimental results, a possible layer‐by‐layer exfoliation mechanism is proposed. Copyright © 2006 Society of Chemical Industry     

黏土/SBR纳米复合材料的加工性能

采用橡胶加工分析仪(RPA)和孟山都毛细管流变仪研究了黏土／SBR纳米复合材料的Payne效应和流变性能。并同炭黑(N330)与微米级黏土橡胶复合材料进行了对比。结果表明，黏土／SBR纳米复合材料的流变规律与传统填充体系的流变规律类似，其弹性模量均随着填料用量的增加而增大，填料之间形成拟网络结构，在加工过程中，具有Payne效应；纳米分散的黏土具有更大的宽厚比和各向异性，对橡胶分子链限制作用更强。网构化程度更高，在相同的应变和频率下，与炭黑和黏土直接混炼填充SBR体系相比，黏土／SBR纳米复合材料的弹性模量更高；纳米化程度越高，网构化程度也越高；在相同的毛细管剪切速率下，黏土／SBR纳米复合胶料的黏度略高于炭黑体系；在黏土／SBR纳米复合胶料中，加入界面剂改善界面强度和改进工艺增加增强单元数目，胶料弹性模量提高；黏土／SBR纳米复合胶料具有出口膨胀小．吃粉快。挺性好的良好加工性能。     

用橡胶乳液-黏土水悬浮液共凝法制备的橡胶/黏土纳米复合材料的结构及其复合机理

研究了利用橡胶乳液-黏土水悬浮液共凝法制备的橡胶／黏土纳米复合材料的结构和复合机理。结果表明,在加入絮凝剂使橡胶乳液-黏土水悬浮液共凝聚的过程中,由于存在胶乳粒子对黏土片层的隔离作用与在混合液中分散的黏土单片层的重新聚集作用的竞争,因此,在絮凝物中,橡胶大分子将黏土片层隔离成纳米分散单元（包括单片层和多片层的聚集体）,在多片层的黏土聚集体层间没有橡胶大分子插入。采用该共凝法制备的橡胶／黏土纳米复合材料具有“隔离型”结构。     

Lewis acid-base complexation of polyamide 66 to control hydrogen bonding, extensibility and crystallinity

Polyamide 66 (PA66) has been complexed with the Lewis acid GaCl₃ for the purpose of disrupting the interchain hydrogen bonded network. FTIR and ¹³C-NMR observations indicate that Ga metal cations form a 1:1 complex with the carbonyl oxygens of the PA66 amide groups. PA66-GaCl₃ films are amorphous and rubbery with a single relaxation, attributable to the glass transition temperature, at ∼−32 °C and a structure that appears by X-ray diffraction to be thermally stable to at least 200 °C. The complexed films could be drawn at room temperature to draw ratios (DR) up to ∼30, and could then be decomplexed, or regenerated, by soaking in water. GaCl₃ complexation and subsequent regeneration of PA66 was accomplished without changing its molecular weight, and all but ∼5 mol% of the amide groups in the regenerated PA66 were uncomplexed. The undrawn regenerated films regain levels of crystallinity much lower than possessed by the uncomplexed PA66 reference film. However, up to a DR of 8, drawing prior to regeneration increases the crystallinity, reaching crystallinity levels that are high for PA66, that has not been heat treated, and that are almost twice higher than in the uncomplexed (undrawn) reference film. It is intriguing that, in this DR regime, crystallinity increases quite sharply as the film is extended, despite the fact that molecular orientation does not appear to be increasing. For DR>8, the crystallinity decreases, but remains above that of the reference film. The level of crystallinity in PA66 can be controlled over a much wider range by the complexation-drawing-regeneration process than by conventional drawing processes.     

Toughened nylon66/nylon6 ternary nanocomposites by elastomers

The elastomer toughening of PA66/PA6 nanocomposites prepared from the organic modified montmorillonite (OMMT) was examined as a means of balancing stiffness/strength versus toughness/ductility. Several different formulations varying in OMMT content were made by mixing of PA6 and OMMT as a master‐batch and then blending it with PA66 and different elastomers in a twin screw extruder. In this sequence, the OMMT layers were well exfoliated in the nylon alloy matrix. The introduction of silicate layers with PA6 induced the appearance of the γ crystal phase in the nanocomposites, which is unstable and seldom appears in PA66 at room temperature and it further affected the morphology and dispersion of rubber phase resulting in much smaller rubber particles. The incorporation of POE‐g‐MA particles toughened the nanocomposites markedly, but the tensile modulus and strength were both reduced. Conversely, the use of OMMT increased the modulus but decreased the fracture toughness. The nanocomposites exhibited balanced stiffness and toughness. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of P(AN/VAC)/clay based nanocomposites

In this article, P(AN/VAC)/clay nanocomposites were prepared by an in situ polymerization and characterized by transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and differential scanning calorimetry. The results show that the P(AN/VAC)/clay exhibit a multilayered structure. The montmorillonite layers are totally exfoliated and distributed uniformly in the P(AN/VAC) matrix. The dimension stability and heat resistance property of P(AN/VAC)/clay are superior to those of P(AN/VAC) alone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 703–706, 2006     

Dispersion characterization in layered double hydroxide/Nylon 66 nanocomposites using FIB imaging

Layered double hydroxides (LDHs), a newly emerging 2D host material, consist of cationic brucite-like layers and exchangeable interlayer anions. In this work, the morphology and dispersion of LDH particles in LDH/Nylon 66 (salt) nanocomposites has been investigated using focused ion beam (FIB) techniques, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The FIB images show that LDHs are present in the polymer phase dispersed to different degrees, with partial intercalation, exfoliation, and aggregation all being observed. The most even dispersion was achieved in nanocomposites with the lowest loading (0.5 wt % LDH). Residual tactoids and agglomerates were most common in the samples made with the highest concentration of LDHs studied here (5 wt %). The dispersion observed using FIB was consistent with TEM and XRD analysis, yet this technique had significant benefits in terms of time and simplicity over these “conventional” technologies. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008