Polycarbonate nanocomposites. Part 1. Effect of organoclay structure on morphology and properties

Polycarbonate nanocomposites were prepared by melt processing from a series of organoclays based on sodium montmorillonite exchanged with various amine surfactants. To explore the effects of matrix molecular weight on dispersion, an organoclay was melt-mixed with a medium molecular weight polycarbonate (MMW-PC) and a high molecular weight polycarbonate (HMW-PC) using a twin screw extruder. The effects of surfactant chemical structure on the morphology and physical properties were explored for nanocomposites formed from HMW-PC. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were employed to investigate the nanocomposite morphology and physical properties. The modulus enhancement is greater for nanocomposites formed from HMW-PC than MMW-PC. This trend is attributed to the higher shear stress generated during melt processing. A surfactant having both polyoxyethylene and octadecyl tails shows the most significant improvement in modulus with some of the clay platelets fully exfoliated. However, the nanocomposites formed from a range of other organoclays contained both intercalated tactoids and collapsed clay particles with few, if any, exfoliated platelets.     

Effect of organoclay structure on nylon 6 nanocomposite morphology and properties

A carefully selected series of organic amine salts were ion exchanged with sodium montmorillonite to form organoclays varying in amine structure or exchange level relative to the clay. Each organoclay was melt-mixed with a high molecular grade of nylon 6 (HMW) using a twin screw extruder; some organoclays were also mixed with a low molecular grade of nylon 6 (LMW). Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were used to evaluate the effect of amine structure on nanocomposite morphology and physical properties. Three surfactant structural issues were found to significantly affect nanocomposite morphology and properties in the case of the HMW nylon 6: decreasing the number of long alkyl tails from two to one tallows, use of methyl rather than hydroxy-ethyl groups, and use of an equivalent amount of surfactant with the montmorillonite, as opposed to adding excess, lead to greater extents of silicate platelet exfoliation, increased moduli, higher yield strengths, and lower elongation at break. LMW nanocomposites exhibited similar surfactant structure-nanocomposite behavior. Overall, nanocomposites based on HMW nylon 6 exhibited higher extents of platelet exfoliation and better mechanical properties than nanocomposites formed from the LMW polyamide, regardless of the organoclay used. This trend is attributed to the higher melt viscosity and consequently the higher shear stresses generated during melt processing.     

Morphology and properties of thermoplastic polyurethane nanocomposites incorporating hydrophilic layered silicates

Hydrophilic layered silicate/polyurethane nanocomposites were prepared via twin screw extrusion and solvent casting. Good dispersion and delamination was achieved regardless of processing route, illustrating that the need for optimised processing conditions diminishes when there is a strong driving force for intercalation between the polymer and organosilicate. Evidence for altered polyurethane microphase morphology in the nanocomposites was provided by DMTA and DSC. WAXD results suggested that the appearance of an additional high temperature melting endotherm in some melt-compounded nanocomposites was not due to the formation of a second crystal polymorph, but rather due to more well-ordered hard microdomains. Solvent casting was found to be the preferred processing route due to the avoidance of polyurethane and surfactant degradation associated with melt processing. While tensile strength and elongation were not improved on organosilicate addition, large increases in stiffness were observed. At a 7 wt% organosilicate loading, a 3.2-fold increase in Young's modulus was achieved by solvent casting. The nanocomposites also displayed higher hysteresis and permanent set.     

Elaboration and properties of novel biobased nanocomposites with halloysite nanotubes and thermoplastic polyurethane from dimerized fatty acids

Nanocomposites of biobased thermoplastic polyurethane (TPU) from dimer fatty acids and halloysite nanotubes (HNT) were elaborated by different melt processing routes such as direct mixing (1 step process) and masterbatch/dilution (2 steps process), at different temperatures (150 and 180 °C). Rheological and transmission electron microscopy (TEM) analyses indicated that the HNT distribution and dispersion were dependent on the processing conditions: the 2 steps process produced well dispersed nanocomposites and the masterbatch dilution at 180 °C improved the HNT distribution through the TPU. Consequently, a high reinforcement was achieved, with a 40% increase in the elastic modulus and 8 °C increase in the relaxation temperature related to the glass transition of the TPU soft segments. Furthermore, a percolated network was attained, even if a large extent of HNT breaking was observed during processing, suggesting that a synergistic effect between the HNT particles and the TPU's hard segments in the molten state occurred. Thus, HNT nanotubes can be seen as highly reinforcing nanofillers when good dispersion and distribution are achieved through the polymeric matrix.     

Preparation,structure and properties of comb-branched waterborne polyurethane/OMMT nanocomposites

Comb-branched waterborne polyurethane/organo-montmorillonite (CWPU/OMMT) nanocomposites were prepared by in situ intercalating polymerization process based on the main materials including IPDI, DMPA, polycaprolactone diols, comb-branched polymeric diols and OMMT. The average particle size of emulsion increases and the particle size distribution of emulsion becomes broader with the increase of OMMT content. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) show that OMMT is homogeneously dispersed into the CWPU matrix with intercalated or exfoliated structure. The properties of CWPU/OMMT nanocomposites are dependent on OMMT content. When the OMMT content is 3 wt%, CWPU/OMMT nanocomposite exhibits excellent overall properties: the particle size of emulsion 63.6 nm, tensile strength 42.0 MPa, E′ 20.3 MPa at 80 °C, water absorption 13% at 24 h and surface contact angle for water over 100°.     

Properties of bulk-polymerized thermoplastic polyurethane nanocomposites

The thermal, rheological, and mechanical properties of bulk-polymerized thermoplastic polyurethane nanocomposites of reactive and non-reactive layered silicate clay were characterized as a function of the state of dispersion of particles. True exfoliated nanocomposites were produced by mixing reactive clay particles with polymer chains carrying residual isocyanate groups. On the other hand, non-reactive clay particles yielded only intercalated composites. Most significant improvement in mechanical properties were obtained when clay particles were fully exfoliated, e.g. 110% increase in tensile modulus, 170% increase in tensile strength, 110% increase in tear strength, 120% increase in fracture toughness, and 40% increase in abrasion resistance over pristine polyurethane with 5 wt% clay. In addition, the terminal dynamic rheological data showed strong dependence on the clay content, indicating substantial hindrance to chain relaxation by tethering clay particles. The peak location and the area under the peak of hydrogen-bonded carbonyl showed two distinct zones of temperature dependence, which indicate additional hydrogen bonding between polymer chains and organic modifier of reactive clays.     

Effect of organoclay purity and degradation on nanocomposite performance, Part 2: Morphology and properties of nanocomposites

Part 1 of this series showed that the purification level and surfactant loadings of organoclays significantly affect their thermal stability; the higher rate of degradation of as-received commercial organoclay is primarily a result of excess surfactant that is intentionally or unintentionally part of the commercial organoclay. Polypropylene nanocomposites and nylon 6 nanocomposites were formed through melt processing to assess the practical consequences, in terms of nanocomposite formation and performance, of using a purified version of the organoclay with no excess surfactant and a lower rate of thermal degradation versus using the as-received organoclay. The properties and morphology of polymer-clay nanocomposites based on both as-received and purified organoclays were evaluated by TEM, WAXS, and mechanical testing. The results from the different techniques were generally consistent with each other suggesting that the differences in thermal stability of organoclays do not appear to have a significant effect on the morphology and properties of the nanocomposites formed from them.     

Effect of clay modifiers on the morphology and physical properties of thermoplastic polyurethane/clay nanocomposites

Thermoplastic polyurethanes (TPUs)/clay nanocomposites were prepared via melt processing using the ester type and the ether type TPUs and three differently modified organoclays (denoted as C30B, C25A and C15A) as well as pristine montmorillonite (PM). XRD and TEM results showed that the addition of C30B with hydroxyl group led to the nearly exfoliated structures in both TPUs. In the case of C25A and C15A clays, partially intercalated nanocomposites were obtained in both TPUs, where C25A showed better dispersion than C15A. Natural clay (PM) was not effectively dispersed in both TPUs. The tensile properties of nanocomposites with C30B were better than ones with the other clays. Higher tensile properties were obtained for ester type TPU than ether type TPU nanocomposites with all clays tested. Although the improvement in tensile properties decreased after the second extrusion of the nanocomposites, properties of the nanocomposite after first melt processing were still good enough for practical applications. Morphological changes induced by the addition of clays were analyzed using FTIR, DSC and rheological test results. Some clays were observed to cause demixing of hard and soft segments in the nanocomposites and location of clays in either soft segment or hard segment domains was also studied.     

Effect of organoclay structure on morphology and properties of nanocomposites based on an amorphous polyamide

An amorphous polyamide (a-PA) and three organoclays, M₃(HT)₁, M₂(HT)₂ and (HE)₂M₁T₁, were melt processed to explore the effect of the organoclay structure on the extent of exfoliation and properties of these nanocomposites. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were used to determine the degree of exfoliation of the nanocomposites. For quantitative assessment of the structure of the nanocomposites, a detailed particle analysis was made to provide various averages of the clay dimensions and aspect ratio. The results evaluated from different methods were generally consistent with each other. Nanocomposites based on the organoclays with one alkyl tail and hydroxyl ethyl groups gave well-exfoliated structures and high matrix reinforcement while nanocomposites from two-tailed organoclay contain a considerable concentration of intercalated stacks. Nanocomposites from the organoclays with one alkyl tail showed slightly better exfoliation and matrix reinforcement than those from the organoclays with hydroxyl ethyl groups. The organoclay structure trends for a-PA are analogous to what has been observed for nylon 6; this suggests that a-PA, like nylon 6, has good affinity for the pristine silicate surface of the clay leading to better exfoliation and enhanced mechanical properties with one-tailed organoclay than multiple-tailed organoclay. Furthermore, heat distortion temperatures were predicted from the dynamic mechanical properties of nanocomposites.     

Effect of tethering on the structure-property relationship of TPU-dual modified Laponite clay nanocomposites prepared by ex-situ and in-situ techniques

Novel Thermoplastic Polyurethane (TPU)-dual modified Laponite clay nanocomposites were prepared by ex-situ and in-situ techniques. Two types of modified clays used in this work differ from each other by the number of active functional groups (tethering). Modified nanoclays are characterized by FTIR, Solid State NMR, XRD and TGA. Structural differences in the modified clays lead to novel tubular, elliptical and spherically aggregated morphologies of clays together with the hard segments of TPU. Changes in such morphology result in the difference in segmental relaxation, mechanical and rheological properties of the nanocomposites. In-situ prepared nanocomposites register inferior properties as compared to their ex-situ counterparts. The percent improvement in tensile strength and elongation at break of the ex-situ prepared nanocomposites with the modified clay having lesser tethering are found to be 67% and 208%, respectively. Thermal stability is enhanced by 35 °C as compared to that of the neat TPU.     

Morphology and properties of polypropylene nanocomposites based on a silanized organoclay

A silanized organoclay (s-M₂(HT)₂) was prepared by reaction of trimethoxyphenyl silane with an organoclay with a M₂(HT)₂ surfactant structure. Nanocomposites were formed from polypropylene (PP) and a blend of PP and maleic anhydride-grafted polypropylene (PP-g-MA) and the M₂(HT)₂ and s-M₂(HT)₂ organoclays by melt processing to explore the extent of exfoliation and the mechanical properties. Wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) coupled with detailed particle analysis were used to determine the effect of the organoclay used and the PP-g-MA compatibilizer on exfoliation and mechanical, rheological, and thermal expansion properties. The PP/s-M₂(HT)₂ nanocomposites have higher particle densities than the PP/M₂(HT)₂ nanocomposites though the aspect ratio remains the same. Platelet dispersion is significantly improved by using PP-g-MA compatibilizer for both organoclays. The rheological properties and the relative modulus improve for the PP/s-M₂(HT)₂ nanocomposites but not to the same degree as either organoclay in a PP-g-MA compatibilized matrix. The thermal expansion properties, however, are not improved by using the s-M₂(HT)₂ organoclay. The s-M₂(HT)₂ organoclay is less prone to agglomeration during extrusion than the M₂(HT)₂ organoclay.     

Polycarbonate nanocomposites: Part 2. Degradation and color formation

Polycarbonate nanocomposites were prepared using two different twin screw extruders from a series of organoclays based on sodium montmorillonite, with somewhat high iron content, exchanged with various amine surfactants. It seems that a longer residence time and/or broader residence time distribution are more effective for dispersing the organoclay. The effects of organoclay structure on color formation during melt processing were quantified using colorimeter and UV-Vis spectroscopy techniques. Color formation in the PC nanocomposites depends on the type of organoclay and the type of pristine clay employed. Double bonds in the hydrocarbon tail of the surfactants lead to more darkly colored materials than saturated surfactants. The most severe color was observed when using a surfactant containing hydroxy-ethyl groups and a hydrocarbon tail derived from tallow. Molecular weight degradation of the PC matrix during melt processing produces phenolic end groups which were tracked by UV-Vis spectroscopy. Greater dispersion of the clay generally led to higher reduction in molecular weight due to the increased surface area of clay exposed; however, for color, the situation is far more complex. Hydroxy-ethyl groups and tallow unit on the surfactant lead to more degradation. A selected series of organoclays based on synthetic clay Laponite^® and calcium montmorillonite from Texas (TX-MMT) were also prepared to explore the effects of the clay structure. Laponite^® and TX-MMT produce less color formation in PC nanocomposites than montmorillonite probably due to lower content of iron. Dynamic rheological properties support the trends of molecular weight degradation and dispersion of clay.     

Effect of the ratio of maleated polypropylene to organoclay on the structure and properties of TPO-based nanocomposites. Part I: Morphology and mechanical properties

The structure-property relationships of thermoplastic olefin (TPO)-based nanocomposites prepared by melt processing are reported with a main focus on the ratio of maleic anhydride-grafted polypropylene (PP-g-MA) to organoclay. The morphological observations by transmission electron microscopy, atomic force microscopy, and X-ray diffraction are presented in conjunction with the mechanical and rheological properties of these nanocomposites. Detailed quantitative analyses of the dispersed clay particles revealed that the aspect ratio of clay particles decreased as clay content increased but increased as the amount of PP-g-MA increased. Analysis of the elastomer phase revealed that the aspect ratio of the elastomer phase increased in both cases. The presence of clay causes the elastomer particles to become highly elongated in shape and retards the coalescence of the elastomer particles. The modulus and yield strength are enhanced by increasing the PP-g-MA/organoclay ratios. High levels of toughness of the TPO can be maintained when moderate levels of (organoclay) MMT and PP-g-MA are used. The rheological properties suggested that the addition of clay particles and PP-g-MA has a profound influence on the long time stress relaxation of the TPO nanocomposites. Based on these analyses, it is clear that it is important to optimize the ratio of PP-g-MA and organoclay to obtain the desired balance of mechanical properties and processing characteristics for TPO nanocomposites.     

Rectorite/thermoplastic polyurethane nanocomposites: Preparation,characterization, and properties

A newly developed kind of layered clay, rectorite (REC), has been used to yield intercalated or exfoliated thermoplastic polyurethane rubber (TPUR) nanocomposites by melt‐processing intercalation. Because of the swollen layered structure of REC, similar to that of montmorillonite, organic rectorites (OREC) can also be obtained through ion‐exchange reaction with two different quaternary ammonium salts (QAS1, QAS2) and benzidine (QAS3). The microstructure and dispersibility of OREC layers in TPUR matrix were examined by X‐ray diffraction and transmission electron microscopy, which revealed not only that the composites with lower amounts of clay are intercalation or part exfoliation nanocomposites, but also that the mechanical properties of the composites were substantially enhanced. The maximum ultimate tensile strength for TPUR/OREC nanocomposites appeared at 2 wt % OREC loading. With increasing OREC contents, the tear strength of the composites increased significantly. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 608–614, 2004     

Effect of solvent on the properties of thermoplastic polyurethane/clay nanocomposites prepared by solution mixing

Effect of different solvents on the clay dispersion and the final properties of the thermoplastic polyurethanes (TPUs)/clay nanocomposites prepared via solution mixing was studied. The polyether‐ and polyester‐based TPUs were used along with organically modified clays (C30B, C25A, and C15A) and the pristine montmorillonite (PM). Dimethylacetamide (DMAc) and tetrahydrofuran (THF) were used as solvents for solution mixing. Nanocomposites containing C30B prepared from DMAc solution showed the better clay dispersion than the ones from THF solution, while THF gave the better dispersion of clays for nanocomposites containing C15A. Morphologies of the nanocomposites were observed to be determined not only by the state of clay dispersion in different solvents but also by the interaction between the polymer and the specific clay. Affinity between solvents and clays becomes important when there is no specific interaction between the clay and the polymer of interest, or when the interaction between the two is rather weak. The compatibility between clays and polymers becomes dominating if there exists a specific interaction between the two. FTIR analysis was conducted to study the interactions involved in the nanocomposites. Dynamic mechanical properties measurement was also carried out to see the effect of solvents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

硬段对热塑性聚氨酯弹性体结构及性能的影响

以实验室自制聚己二酸乙二醇酯二醇PEA为软段,二苯基甲烷-4,4’二异氰酸酯(MDI)为硬段,分别采用乙二醇(EG、1,4-丁二醇)、BOD和1,6-己二醇、HG为扩链剂,经预聚体法合成了硬段不同的聚氨酯弹性体。研究了硬段结构和硬段含量对弹性体硬度及力学性能的影响。采用旋转流变仪研究了弹性体在降温条件下的非等温结晶过程。结果表明,当硬段含量相同时,BDO-TPU结晶性能最好,拉伸强度最大;HG-TPU断裂伸长率最好。在BDO-TPU体系中,随硬段含量增加,材料硬度和强度增加,伸长率减小;结晶起始温度逐渐增大,结晶性能增强。     

Effects of organoclay Soxhlet extraction on mechanical properties, flammability properties and organoclay dispersion of polypropylene nanocomposites

The organic treatment on a layered silicate used in nanocomposite synthesis is the interface between the hydrophilic layered silicate (clay) and hydrophobic polymer in the case of polypropylene. However, the typical synthesis of an organoclay can result in excess organic treatment which can hinder mechanical and flammability benefits. This excess organic treatment may result in plasticization of the polymer matrix, possibly removing some of the mechanical and flammability property benefits provided by the nanocomposite. In this paper, the effects of using Soxhlet Extraction on the Organoclays after synthesis was investigated. Soxhlet extraction times on organoclays were found to have an effect on the mechanical and flammability properties of the resulting polypropylene nanocomposite. The removal of excess organic treatment by Soxhlet extraction resulted in improvements in flex modulus, improved clay dispersion, delayed time to ignition, and lowered heat release rate during burning.     

Pressure-sensitive polymer nanocomposites: Carbon nanofiber-reinforced MWCNT-coated PMMA microbeads

ABSTRACT

A unique, thermoplastic polyurethane (TPU)-based, pressure-sensitive nanocomposites were prepared by the solution mixing method. Poly (methyl methacrylate) (PMMA) microbeads (10µm) were coated with multiwall carbon nanotubes (MWCNT) and dispersed in TPU matrix dissolved in tetrahydrofuran. 1, 2, and 5 wt. % of carbon nanofiber (CNF) were also added to the TPU matrix. The influence of MWCNT coated PMMA-microbeads along with different CNF contents on the pressure sensing properties were studied. Electrical and thermal conductivities were measured at different external loads. The prepared nanocomposites showed repeatable and reliable electric response with increasing external load and are suitable as pressure sensors.     

The structure and physical properties of polypropylene and thermoplastic olefin nanocomposites containing nanosilica

The morphology and physical properties of thermoplastic olefin blend (TPO) based nanocomposites containing nanosilica are reported. Addition of maleated PP resulted in improved filler dispersion within the PP matrix, where the filler resided exclusively. This separated morphology resulted in selective reinforcement of the PP matrix without compromising ductility, as demonstrated by mechanical property characterization. The tensile moduli, impact and flexural properties of TPO/nanosilica composites showed improvements at low loadings of nanosilica, indicating a good balance of stiffness and toughness. The addition of nanosilica into the TPOs decreased the size of the dispersed elastomer phase, which was a factor in the observed improvements of impact strength. Silane-modified nanosilica dispersed more efficiently in the polymer matrix, giving rise to improved impact properties of the TPO composites, compared to the unmodified filler.