Thermoplastic polyurethane nanocomposites of reactive silicate clays: effects of soft segments on properties

This paper addresses the effects of soft-segment on clay particle exfoliation and resultant mechanical and thermal properties of nanocomposites of reactive layered silicate clay and thermoplastic polyurethanes (TPU). The composites were synthesized via a two-step bulk polymerization scheme from polyether- and polyesterpolyols of molecular weight 2000, diphenylmethanediisocyanate, butanediol, and up to 5 wt% reactive layered silicate clay. It was found that the extent of tethering reactions between polymer chains carrying residual -NCO groups and reactive clay particles was significant, although did not depend on the nature of polyol used. Nanocomposites were obtained only in the case of polyesterpolyol, which can be attributed to both clay-polymer reactions and higher viscosity in the clay-polymer mixing step. These nanocomposites showed 125% increase in tensile stress, 100% increase in elongation, and 78% increase in tensile modulus along with 130% increase in tear strength and a 60% reduction in volume loss in abrasion test. It was observed that hydrogen bonding did not influence the properties and the extent of hydrogen bonding was not affected by the clay particles.     

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.     

Nanoclay-tethered shape memory polyurethane nanocomposites

The study investigated shape memory properties of nanoclay-tethered polyurethane nanocomposites. Polyurethanes based on polycaprolactone (PCL) diol, methylene diisocyanate, and butane diol and their nanocomposites of reactive nanoclay were prepared by bulk polymerization in an internal mixer and the values of shape fixity and shape recovery stress were determined as function of clay content. The melting point of the crystalline soft segment was used as the transition temperature to actuate the shape memory actions. It was seen that clay particles exfoliated well in the polymer, decreased the crystallinity of the soft segment phase, and promoted phase mixing between the hard and soft segment phases. Nevertheless, the soft segment crystallinity was enough and in some cases increased due to stretching to exhibit excellent shape fixity and shape recovery ratio. A 20% increase in the magnitude of shape recovery stress was obtained with the addition of 1 wt% nanoclay. The room temperature tensile properties were seen to depend on the competing influence of reduced soft segment crystallinity and the clay content. However, the tensile modulus measured at temperatures above the melting point of the soft segment crystals showed continued increases with clay content.     

Structure,permeability, and rheology of supercritical CO2 dispersed polystyrene-clay nanocomposites

Improvement in clay dispersion and clay-polymer interfacial interactions are keys to producing superior nanocomposites. A supercritical CO₂ (scCO₂) processing method was utilized to pre-disperse commercial organic clays, for further solvent mixing with polystyrene (PS) to form nanocomposites with significant dispersion and interfacial enhancement. The effect of scCO₂ processing on clay pre-dispersion, and clay dispersion and interfacial interaction in nanocomposites were investigated. SEM and WAXD of the clays indicated that after scCO₂ processing the clays lose their long region ordered layer structure appreciably, associated with reduction in particle size. WAXD and TEM of the PS/clay nanocomposites showed that the polymer penetrated into the pre-dispersed clay, leading to a disordered intercalated/exfoliated structure with improved interfacial interaction rather than a disordered intercalated structure as seen with as-received clays. Relationships between those structures, rheological and barrier properties were investigated. The scCO₂-processed nanocomposites showed a plateau in the low-frequency storage modules and increased complex viscosity, each associated with significant clay dispersion in the nanocomposite. With only 1.09% volume fraction of clay, significant reduction (∼49%) of oxygen permeation was achieved.     

Preparation and properties of polyethylene-octene elastomer (POE)/organoclay nanocomposites

Polyethylene-octene elastomer/organoclay nanocomposites were prepared by a melt blending process. It was found that the addition of a small amount of glycidyl methacrylate and a peroxide during the melt mixing induced facile intercalation of the polymer chains into the organoclay and dispersion of the clay particles on the nanometer scale, which was confirmed by X-ray diffraction and transmission electron microscopy. Enhanced mechanical properties of the nanocomposites were observed from tensile, dynamic mechanical, and tear testing. Oscillatory shear-controlled rheology in the molten state of the nanocomposites revealed a pseudo solid-like behavior as well as an enhanced shear thinning behavior.     

Ultrasonic Preparation of Polymer/Layered Silicate Nanocomposites during Extrusion

Summary Three kinds of polymer/layered nanocomposites were prepared via ultrasonic extrusion. Experimental results showed that ultrasonic oscillations could mostly decrease the size and its distribution of clay particles in polymer matrix. Therefore, crystal size of polymer matrix decreases. For PA6-based nanocomposites with higher compatibility, the ultrasonic oscillations can also affect the microstructure of clay, causing more regions of exfoliated clay. Due to better dispersion of clay and smaller crystal size, the elongation at break of polymer/layered nanocomposites ultrasonically treated got greatly increased, meanwhile ultrasonic oscillations also improved their other mechanical properties, such as tensile and impact strength.     

Novel hybrid of clay,cellulose, and thermoplastics. I. Preparation and characterization of composites of ethylene–propylene copolymer

The present study is aimed to prepare hybrid materials by incorporating layered silicates and microcrystalline cellulose into thermoplastic polymer. Using ethylene–propylene (EP) copolymer as thermoplastic polymer matrix and maleated EP (MEP) copolymer as compatibilizer, three types of composites were prepared by (i) melt mixing of cellulose with thermoplastics [I], (ii) melt mixing of clay with thermoplastics [II], and (iii) melt mixing of cellulose with the thermoplastic clay nanocomposites [III]. They were characterized by X‐ray diffractometry (XRD), differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Instron was used to measure the mechanical properties. The composites [II] and [III] that contain layered silicates were intercalated nanocomposites as confirmed by XRD and transmission electron microscopy. The improvement in tensile properties was observed in cellulose–fiber‐reinforced composites with increasing cellulose content. In nanocomposites [II] and [III], the tensile modulus was improved. The resistance of the cellulose composites [I] for water absorption decreased with increasing content of cellulose fibers. The incorporation of layered silicates reduced the water absorption of cellulose composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2672–2682, 2007     

Polyamide nanocomposites with improved toughness

Polymer nanocomposites containing several percent of exfoliated layered silicates are materials with a unique weight/performance ratio. The only parameter that is not enhanced, but even decreased, is toughness. This work focused on the toughness enhancement of these advanced systems with polyamide matrix prepared via melt‐mixing (i.e., by a conventional method of polymer processing having an advantage of easy simultaneous addition of other components). Analogously to ternary polyamide blends with improved mechanical behavior, containing finely and separately dispersed elastomer and rigid polymer, elastomer particles with an average size of 60 nm were incorporated in the nanocomposite. The very low particle size was achieved by in situ reactive compatibilization by using suitably functionalized elastomers. The simultaneously increasing viscosity of the system enhanced exfoliation of the silicate. Melt exfoliated nanocomposites containing 3 wt % of clay and 5 wt % of elastomer particles exhibit increased toughness without significant loss of other properties. Elastomer particles increase toughness by both acting as stress concentrators (by initiating energy absorbing microdeformations) and influencing the clay‐induced matrix crystalline structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 288–293, 2005     

Effects of process conditions and mixing protocols on structure of extruded polypropylene nanocomposites

Polymer melt‐direct intercalation or exfoliation is a promising approach for the preparation of nanocomposites. The structure of nanoclay platelets in the nanocomposites depends not only on the properties of polymer matrix and nanoclay, but also on the operating conditions during processing. The objective of the present work is to investigate the effects of clay chemical modifiers, mixing protocols, and operating conditions upon the clay structure in nanocomposites prepared with a corotating twin‐screw extruder. Two mixing methods were used for the nanocomposite preparation: two‐step mixing and one‐step mixing. Experimental results obtained from melt flow index and complex viscosity measurements suggest that nanoclay C15A is more exfoliated than C30B in a polypropylene homopolymer containing a maleic anhydride grafted PP (PB) as compatibilizer. The two‐step mixing method results in better exfoliation for the nanofillers than the one‐step mixing method. A numerical simulation has been carried out to evaluate the mean residence time and shear rate in different screw configurations under various process conditions. X‐ray diffraction experiments indicate that the residence time is a dominant factor in producing satisfactory nanocomposites in extruders. However, high shear rate coupled with long residence time might result in poor exfoliation of clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1891–1899, 2004     

Mechanical and physical properties of polymer‐based nanocomposites containing different types of clay

Epoxy‐clay nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced with 2 wt% of four different types of clay were prepared by high shear mixing (HSM) technique. The resultant nanocomposites were investigated to determine the effects of clay addition and clay types on their mechanical, thermal, and physical properties. The XRD and TEM analyses revealed that good dispersions of nanoclay within the epoxy matrix have been achieved especially for the samples prepared with I.30E clay where a combination of disordered intercalated and exfoliated morphology was observed. The structure of samples synthesized with other types of clay was dominated by intercalated morphologies. The tensile results illustrated that the nanocomposite containing I.30E clay has the best mechanical properties as compared to other nanocomposites. This is mainly due to better dispersion of I.30E nanoclay in the epoxy matrix for this nanocomposite. The increase or decrease in the glass transition temperatures of nanocomposites were found to be dependent on the type of clay used. The effect of clay addition on the barrier properties was examined using water exposure test which demonstrated that the addition of 2% of I.30E and C10A clays resulted in 60% reduction in diffusivity. Noticeable reduction in maximum water uptake was also observed for all nanocomposites. The improvement in these physical properties was attributed to the tortuosity effect, where water molecules have to move around clay layers during diffusion in nanocomposites. POLYM. COMPOS., 36:1998–2007, 2015. © 2014 Society of Plastics Engineer     

Morphology evolutions of organically modified montmorillonite/polyamide 12 nanocomposites

Organically modified montmorillonites (OMMTs) by octadecylammonium chloride with two adsorption levels were dispersed in polyamide 12 (PA12) matrices with two molecular weights for different melt mixing times in order to investigate morphology evolutions and factors influencing fabrication of PA12 nanocomposites. Different adsorption levels of the modifier in the OMMTs provide different environments for diffusion of polymer chains and different attractions between MMT layers. Wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and gas permeability were used to characterize morphologies of the nanocomposites. Both OMMTs can be exfoliated in the PA12 matrix with higher molecular weight, but only OMMT with lower adsorption level can be exfoliated in the PA12 matrix with lower molecular weight. It was attributed to the differences in the levels of shear stress and molecular diffusion in the nanocomposites. The exfoliation of OMMT platelets results from a combination of molecular diffusion and shear. After intercalation of PA12 into interlayer of OMMT in the initial period of mixing, further dispersion of OMMTs in PA12 matrices is controlled by a slippage process of MMT layers during fabricating PA12 nanocomposites with exfoliated structure.     

Preparation and characterization of high performance exfoliated montmorillonite/silicone rubber nanocomposites with enhanced mechanical properties

Highly exfoliated and intercalated silicone rubber (SR) nanocomposites based on natural montmorillonite (Cloisite Na⁺) and organically modified montmorillonite (Cloisite 30B and Cloisite 20A) were successfully prepared by melt‐mixing technique. Dispersion of the nanoclays in the rubber nanocomposites was subsequently investigated. As indicated by the X‐ray diffraction (XRD) analysis, intercalation, and exfoliation of the clay particles in the nanocomposites was achieved at less than 8 parts per hundred (phr) rubber by weight, irrespective of the initial interlayer spacing of the nanoclay particles. Both Cloisite Na⁺ and Cloisite 30B were spontaneously transformed into exfoliated microstructures during the vulcanisation stage. Overall, the use of the nanoclays in silicone rubber improved the Young's modulus, tensile strength, and elongation at break by more than 50% as compared with the control rubber. In addition, this work provided a fresh insight into the way intercalated and exfoliated morphologies affect mechanical properties of silicone rubber nanocomposites. It was shown that the exfoliated Cloisite Na⁺ yielded outstanding mechanical properties with low hysteresis at the same loading of the exfoliated Cloisite 30B and intercalated Cloisite 20A organoclays. As expected, the formation of crosslinks affected the mechanical properties of the rubber vulcanizate significantly. POLYM. ENG. SCI., 53:2603–2614, 2013. © 2013 Society of Plastics Engineers     

Preparation and characterization of nylon 11/organoclay nanocomposites

Nylon 11/organoclay nanocomposites have been successfully prepared by melt-compounding. X-ray diffraction and transmission electron microscopy indicate the formation of the exfoliated nanocomposites at low clay concentrations (less than 4 wt%) and a mixture of exfoliated and intercalated nanocomposites at higher clay contents. Thermogravimetric and dynamic mechanical analyses as well as tensile tests show that the degree of dispersion of nanoclay within polymer matrix plays a vital role in property improvement. The thermal stability and mechanical properties of the exfoliated nylon 11/clay nanocomposites (containing lower clay concentrations) are superior to those of the intercalated ones (with higher clay contents), due to the finer dispersion of organoclay among the matrix.     

Thermal,mechanical, and barrier properties of polyethylene/surlyn/organoclay nanocomposites blown films prepared by different mixing methods

(Low‐density polyethylene) (LDPE)/clay nanocomposites were prepared by melt blending in a twin‐screw extruder by using different mixing methods. Zinc‐neutralized carboxylate ionomer was used as a compatibilizer. Blown films of the nanocomposites were then prepared. The effect of mixing method on the clay dispersion and properties of the nanocomposites was evaluated by wide‐angle X‐ray diffraction analysis, mechanical properties, thermal properties, and barrier properties. The structure and properties of nanocomposites containing different amounts of nanoclay prepared by selected mixing techniques were also investigated. It was found that melt compounding of Surlyn/clay masterbatch with pure LDPE and Surlyn (two‐step‐a method) results in better dispersion and intercalation of the nanofillers than melt mixing of LDPE/Surlyn/clay masterbatch with pure LDPE and surlyn (two‐step‐b method) and direct mixing of LDPE with clay. The films containing ionomer have good barrier properties. A wide‐angle X‐ray diffraction pattern indicates that intercalation of polymer chains into the clay galleries decreases by increasing the clay content. Barrier properties and tensile modulus of the films were improved by increasing the clay content. In addition, tensile strength increased in the machine direction, but it decreased in the transverse direction by increasing the clay content. DSC results showed that increasing the clay content does not show significant change in the melting and crystallization temperatures. The results of thermogravimetric analysis showed that the thermal stability of the nanocomposites decreased by increasing the clay content more than 1 wt%. J. VINYL ADDIT. TECHNOL., 21:60–69, 2015. © 2014 Society of Plastics Engineers     

Characteristics of polystyrene/polyethylene/clay nanocomposites prepared by ultrasound‐assisted mixing process

In this study, polymer‐clay nanocomposites of various concentrations were prepared by ultrasonically assisted polymerization and melt‐mixing processes. A sonication process using power ultrasonic waves was employed to enhance nano‐scale dispersion during melt‐mixing of polymer blends and organically modified clay. We expected enhanced breakup of layered silicate bundles and further reduction in the size of the dispersed phase, with better homogeneity compared to the different immiscible blend pairs. X‐ray diffraction (XRD) and Transmission Electron Microscopy (TEM) were used to characterize the structures of the nanocomposites. The rheological behaviors of the obtained nanocomposites were measured with parallel plate rheometry. It was found that the ultrasound‐assisted process successfully generated exfoliated nanocomposites and promoted in‐situ compatibilization of the matrix comprising an immiscible pair of polymers in a blend. The resulting nanocomposite exhibited superior thermal stability and elastic modulus compared to the base polymer. Polym. Eng. Sci. 44:1198–1204, 2004. © 2004 Society of Plastics Engineers.     

Structure and properties of phenolic resin/nanoclay composites synthesized by in situ polymerization

An in situ semibatch polymerization process for making phenolic resin/montmorillonite clay nanocomposites is developed. It is found that auxiliary mixing in phenol allows intercalation of the monomer and polymer between montmorillonite clay layers. At 2.7% clay by mass the montmorillonite is predominantly exfoliated (fully dispersed). At higher clay loading, a substantial amount of the clay remains in aggregate or intercalated form. When the montmorillonite is exfoliated, the material is mechanically superior. The composite has a tensile modulus that is 21% higher than the neat resin and has 87% improved fracture strength, 100% larger fracture energy, and strain to failure 13% above the pure resin. Thermogravimetric analysis shows the montmorillonite system maintains its thermal stability up to 200°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1169–1174, 2005     

Effect of water and crude oil on mechanical and thermal properties of epoxy‐clay nanocomposites

Epoxy‐clay nanocomposites were synthesized by high shear mixing (HSM) technique using diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced by Nanomer I.30E nanoclay. Disordered intercalated with some exfoliated structure were found in the resultant nanocomposites. The fabricated samples were exposed to water and crude oil to investigate the effect of nanoclay addition on diffusivity and amount of liquid uptake. The results showed good improvement in the barrier properties of epoxy as a result of clay addition. The average reduction in diffusivity and maximum water uptake for nanocomposites containing 1% nanoclay were 51% and 8%, respectively. The maximum water uptake was about double the maximum oil ingress for both neat epoxy and nanocomposites. Obvious degradations in thermal and mechanical properties of neat epoxy and nanocomposites were observed as a result of liquid uptake; with less severe impact on nanocomposites. The reduction in glass transition temperature was about 8% for each 1% of water uptake for nanocomposites as compared to 15% for neat epoxy. The tensile strength and the elastic modulus of neat epoxy and nanocomposites were adversely affected by water and oil uptake while the fracture strain was slightly improved; a behavior found to be proportional to the amount of liquid uptake. The diffusion mechanism of water in neat epoxy was well predicted by Fickian model, while that of the nanocomposites was better fitted with Langmuir model. POLYM. COMPOS., 35:318–326, 2014. © 2013 Society of Plastics Engineers     

Twin‐screw compounding of poly(methyl methacrylate)/clay nanocomposites: effects of compounding temperature and matrix molecular weight

Poly(methyl methacrylate) (PMMA)/organoclay nanocomposites prepared by melt‐compounding using a co‐rotating twin‐screw extruder were intercalated nanocomposites. Commercially available PMMA resins of various molecular weights were used for comparison. The results showed an optimum compounding temperature for maximum intercalation with balanced shear and diffusion. Higher operating temperature reduced the shear mixing effect, and might have induced early degradation of the organoclay. Lower operating temperature, in contrast, reduced the mobility of the polymer molecules, which not only hampered the intercalation attempts, but also generated high torque in the extrusion. The mechanical behavior of the nanocomposites was studied. The tensile modulus, storage modulus and glass transition temperature of the nanocomposites increased with increasing clay content; however, an associated decrease in strength and strain at break was also observed. The notched impact strength also showed a slight decrease with clay content. Nanocomposites based on the lower molecular weight PMMA yielded more significant improvement in mechanical and thermal properties at the same clay content. Copyright © 2007 Society of Chemical Industry     

Effect of processing conditions on morphology and mechanical properties of compatibilized polypropylene nanocomposites

This work focuses on the influence of processing conditions on the nanocomposites structure, i.e. intercalated or exfoliated, and on the enhancement of mechanical properties of polypropylene (PP) nanocomposites. These nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. In order to optimise processing conditions, both screw speed and barrel temperature profile were changed. The role of the compatibilizer (maleic anhydride grafted polypropylene) was also studied. The results obtained show that the barrel temperature is a very important parameter: using lower processing temperature, the apparent melt viscosity and, consequently, the shear stress are higher and, therefore, the exfoliation of the clay is promoted. Even using optimised processing conditions, exfoliation of clay can be achieved only when an high compatibility between polymer and clay exists: the PP nanocomposites containing maleic anhydride show an exfoliated structure and a sensible enhancement of mechanical properties while PP nanocomposites without compatibilizer show a structure mainly intercalated and a lower improvement of mechanical properties.     

Poly(lactic acid) and layered silicate nanocomposites prepared by melt mixing: Thermomechanical and morphological properties

Poly(lactic acid) (PLA) nanocomposites were prepared by melt mixing technique in a Haake batch mixer. The clay dispersion within the PLA matrix during melt mixing was well explained through the morphological characterization. Morphological characterizations were studied by X‐ray diffraction and transmission electron microscopy. The exfoliation/intercalation of the clay particles within the polymer matrix during melt mixing depends on the mixing torque generated during the preparation of nanocomposites. The significance of processing temperature and the mixing time in melt mixing were studied for PLA/C93A and PLA/C30B nanocomposites. The structure and properties of the nanocomposites were also characterized by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and mechanical properties by standard tensile testing. The incorporation of nanoclays into the PLA matrix enhanced the mechanical properties and thermal stability of the PLA nanocomposites. This may be due to the reinforcing effect of nanoclays within the polymer matrix. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers