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Applications of nanotechnology in biomedical engineering are vast and span several interdisciplinary areas of nanomedicine, diagnostics, and nanotheranostics. Herein, we provide a brief perspective on nanotechnology as an enabling tool for the design of new functional materials and devices for medical applications. Semiconductor nanocrystals, also known as quantum dots, are commonly used in optical imaging to diagnose diseases such as cancer. Varieties of metal and metal oxide nanoparticles, and two-dimensional carbon-based nanostructures, are prospective therapeutics and may also be used in protective antiviral/antibacterial applications. Similarly, a number of nanomaterials have shown the potential to overcome the drawbacks of conventional antiviral drugs. However, assessing the adverse effects and toxicities of nanoparticles in medicine and therapeutics is becoming more critical. This article discusses the latest developments of nanomaterials in diagnosis, nanotheranostics, and nanomedicines, with particular emphasis on the importance of nanomaterials in fighting against coronavirus disease. Further, we considered the safety and toxicity of nanomaterials in the context of biomedical applications. Finally, we provided our perspective on the future of nanotechnology in emerging biomedical engineering fields.

This study examines the influence of cellulose nanocrystal (CN) particles on the morphological, thermal, and thermo-mechanical properties of polylactide (PLA)/poly [(butylene succinate)-co-adipate] (PBSA) blend foams prepared by casting and particulate leaching method using fructose as porogen particles. The morphological analysis showed an interconnected open-cell structure, with porosity above 80%. The crystallinity of the prepared foams was disrupted by the inclusion of CN particles as observed from XRD analyses, which showed a decrease in PLA crystal peak intensity. With regards to neat blend foam, the onset thermal degradation increased with the addition of CN particles, which also increased the thermal stability at 50% weight loss. Furthermore, CN acted as a reinforcing agent in improving the stiffness of the prepared blend foam. Overall, completely environmentally friendly foams were successfully prepared, as a potential material that can replace the current existing foam materials that pose many environmental concerns. However, there is a need to develop an environmentally friendly processing technique.

To obtain polyamide 6 (PA6) composites with improved flame retardancy and thermomechanical properties, highly cross-linked supramolecular poly(cyclotriphosphazene)-functionalized α-zirconium phosphate (f-ZrP) nanoplatelets were synthesized and melt-blended with PA6 in a twin-screw extruder. The performance enhancements of composites were investigated through measuring the dynamic mechanical property and observing cone calorimeter data, toxic gas evolution, and UL-94 rating. The thermomechanical performance of PA6 was increased by 37.2% after composite formation with f-ZrP. As for the fire retardancy performance, compared to neat PA6, the composite containing 10 wt % f-ZrP showed 41.7 and 30.4% decrease in the peak heat and total heat release rates, respectively, and the UL-94 rating of the composite was V-0. Moreover, the thermogravimetric analysis combined with infrared spectroscopy revealed that the addition of f-ZrP to the PA6 led to decrease in the evolution of the volatile compounds and toxic gases, with the formation of highly cross-linked P–N-containing dense char with microspheres, providing a strong barrier to the inhibition of the heat and flammable volatile components transferring between the flame zone area and substrate during the combustion test. Finally, based on the obtained results, the possible mechanisms for improved mechanical and fire retardancy properties of the composites were proposed.

In this study, polyamide 6 (PA) is blended with ethylene vinyl alcohol (EVOH) to yield packaging materials with a balance of mechanical and gas barrier properties. However, the formation of gel-like structures in both polymers because of thermal degradation at high temperatures leads to a processing challenge, particularly during thin-gauge film extrusion. To address this challenge, nanoclays are introduced either directly or via a masterbatch of maleic-anhydride-grafted polypropylene to the PA/EVOH blend and time-resolved rheometry is used to study the effect of different modes of nanoclay incorporation on the kinetics of thermo-oxidative degradation of PA/EVOH blend and its nanocomposites. Time-resolved rheometry measurements allow the acquisition of accurate frequency-dependent linear viscoelastic behavior and offer insights into the rate of degradation or gel formation kinetics and cross-link density. The thermal degradation was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy, allowing the prediction of the possible reactions that take place during the rheological property measurements. The results show that when nanoclays are incorporated directly, the oxidative reactions occur faster. In contrast, in the masterbatch method, oxidative degradation is hindered. The difference in the behaviors is shown to lie in the different nanoclay distributions in the blends; in the blends prepared by the masterbatch method, the nanoclays are dispersed at the interface. In conclusion, the masterbatch-containing blend nanocomposite would benefit processing and product development.

This work investigates the effects of modification of polylactide (PLA) using dicumyl peroxide (DCP) as a crosslinker and Joncryl as a chain extender on boehmite distribution. The PLA/boehmite (PLA/BA) composites at various concentrations were prepared via a twin-screw extruder. Transmission electron microscopy showed more agglomerations of BA particles when Joncryl and DCP were added individually to the PLA matrix, with lesser agglomeration upon simultaneous addition of DCP and Joncryl, which led to an enhancement of 10.7% of the heat distortion temperature and 8.8% of the modulus. The existence of fine dispersed BA particles in the BA3 sample improved the cold crystallization by 4 °C. Moreover, the maximum reinforcing effect in increasing the storage modulus of the prepared system was observed upon concurrent addition of DCP and Joncryl, with minimum reinforcing effect upon individual addition of DCP and Joncryl. In general, a bio-based PLA composite base BA with enhanced properties was successfully prepared for various applications.

Recently, polymer science and engineering research has shifted toward the development of environmentally benign polymers to reduce the impact of plastic leakage on the ecosystems. Stringent regulations and concerns regarding conventional polymers are the main driving forces for the development of renewable, biodegradable, sustainable, and environmentally benign materials. Although biopolymers can alleviate plastic-related pollution, several factors dictate the utilization of biopolymers. Herein, an overview of the potential and limitations of synthetic biopolymers and their composites in the context of environmentally benign materials for a sustainable future are presented. The synthetic biopolymer market, technical advancements for different applications, lifecycle analysis, and biodegradability are covered. The current trends, challenges, and opportunities for bioplastic recycling are also discussed. In summary, this review is expected to provide guidelines for future development related to synthetic biopolymer-based sustainable polymeric materials suitable for various applications.

During melt extrusion of nanocomposites, nanoparticles can be incorporated either directly or through the masterbatch, which brings up a simple question of how the mode of nanoparticle inclusion affects the morphology and hence the rheological properties of the final composite. In the study reported here, nylon6/ethyl–vinyl-alcohol (N6/EVOH) was selected to model a blend system, and the effect of the mode of organoclay inclusion on the morphology development and melt-state viscoelastic properties of ternary blend composites was investigated. The morphological study using scanning electron microscopy, transmission electron microscopy, three-dimensional tomography, and differential scanning calorimetry indicated that the intercalated silicate layers were located in the interphase region between N6 and EVOH in the N6/EVOH/masterbatch composite and core–shell particles were formed, with EVOH as the core. On the other hand, the intercalated silicate layers were well distributed in the blend matrix of the N6/EVOH/organoclay composite, and it was difficult to differentiate between two phases. Finally, the different morphological developments were correlated with the melt-state rheological properties of the composites to evaluate the processing and product performance. The results showed that the masterbatch played an important role in establishing the compatibility of N6 and EVOH, and it could impede the gel formation that would benefit processing and product development.

Polypropylene (PP) is one of the most widely used commodity polymer. However, it has a low upper service temperature. Addressing this challenge, we introduced reactive blending of PP, maleic anhydride-grafted PP (PP-g-MA) and (3-aminopropyl)triethoxysilane (3APTES) in the presence of nanoclay, which results in a highly nucleated PP composite with improved dimensional stability. At the processing temperature, the reaction between maleic anhydride, which is already grafted on the PP chain, and 3APTES forms N-substituted maleimide-grafted PP. The results indicated that the introduction of branched structures on PP chains increased the chain bulkiness and led to the formation of stable nuclei that initiate crystallization at high temperatures. By offering nucleating sites, the dispersed nanoclay particles facilitated the nucleation process to a greater extent. Compared with the neat polymer matrix, the crystallization temperature of the composite was 15.5 °C higher with moderate improvements in the heat distortion and Vicat softening temperatures. This is most likely the first report where such an improvement in crystallization temperature has been achieved for isotactic PP homopolymers. In summary, reactive processing of the PP/nanoclay composite in the presence of PP-g-MA and 3APTES has potential for the development of high-performance PP-based advanced materials.

Nucleated polypropylene (PP) masterbatch and the nanoclay-containing composite of PP are prepared by reactive processing method to improve the thermo-mechanical properties of virgin PP. PP masterbatch and the nanocomposite exhibits pronounced improvement in crystallization temperature (Tc) and the heat distortion temperature (HDT) when compared with neat PP. The melting and nonisothermal crystallization behaviors of the neat PP and the nanocomposite are studied by differential scanning calorimetry. Results indicate that half time of crystallization at a particular cooling rate remains unchanged in neat PP and the nanocomposite. However, super cooling effect is pronounced in the nanocomposite when compared with neat PP. Irrespective of cooling rate there is approximately 14% improvement in Tc in PP nanocomposite with respect the neat PP. Such an improvement in Tc with improved thermo-mechanical properties are highly desirable for rigid packaging applications.

In this study, a solvothermal method was used to synthesize Titanium dioxide (TiO2) nanoparticles in the presence of oleic acid (OA) and oleylamine (OM) as morphology-directing agents. Functional nanocomposite fibers composed of poly(ethylene terephtalate) (PET) mixed with OA-OM capped TiO2 nanoparticles were developed by electrospinning process. The different variables that affect the stability of the process were optimized to produce uniform PET/TiO2 nanofibrous mats without beads. The morphology and thermal stability of PET/TiO2 nanofibers were investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Thermo-gravimetric analysis (TGA).In this study, a solvothermal method was used to synthesize Titanium dioxide (TiO2) nanoparticles in the presence of oleic acid (OA) and oleylamine (OM) as morphology-directing agents. Functional nanocomposite fibers composed of poly(ethylene terephtalate) (PET) mixed with OA-OM capped TiO2 nanoparticles were developed by electrospinning process. The different variables that affect the stability of the process were optimized to produce uniform PET/TiO2 nanofibrous mats without beads. The morphology and thermal stability of PET/TiO2 nanofibers were investigated by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Thermo-gravimetric analysis (TGA).

Traces of quaternary ammonium salt from dispersed nanoclay in PA6/6.6 polymer nanocomposite may have some potential toxicological effects that could pose a risk to human health. Modified nanocomposite system was produced by masterbatch melt extrusion process while water-assisted nanocomposite was prepared via direct melt extrusion process. Investigations were conducted by hyphenated thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TGA-FTIR). Small traces of surfactant alkyl ammonium ions in the nanocomposite can be found in the masterbatch and nanocomposite.

Polylactide/butylated-starch/nanoclay (70/25.5/4.5 wt%) composites were prepared by melt blending with nanoclays of varying hydrophobicity. Electron microscopy studies indicated that the interphase boundary interaction was highest in the clay with intermediate hydrophobicity but decreased with clays of higher or lower hydrophobicity. Conventional and modulated differential scanning calorimetry studies showed that, in the case of composites, the change in the ratio of rigid and mobile amorphous fractions depends on the hydrophobicity of clays used for the preparation of blend composites. The mobile amorphous fraction related to the polylactide phase decreases in the case of intermediate hydrophobic clay compared with less and more hydrophobic clays or neat blend samples. Avrami bulk crystallization analysis and polarized optical microscopic observation demonstrated that hydrophobic clays hindered the crystallization of the PLA phase into the formation of disc-shaped spherulites. On the basis of obtained results, we propose a general understanding on how the morphology and thermal properties of the blend composites are related to the hydrophobicity of the nanoclays.

The performance of a heterogeneous material, such as polymer nanocomposites (PNCs) is dictated by three main factors: (i) the inherent properties of the components; (ii) interfacial interactions; and (iii) structure of the PNCs. The structure of a PNC depends on the dispersion and distribution of the nanoparticles (NPs) in the polymer matrix. However, improving the dispersion by mechanical means or via chemical bonding can influence the properties of the obtained PNCs. Therefore, elucidating the dispersion and distribution characteristics and the associated mechanisms is important and can allow prediction of the final properties. This chapter describes the different techniques used to characterize the structure and morphology of various PNCs. Primary techniques include microscopy in real space and reciprocal space, X-ray scattering analysis, as well as indirect measurements to probe the interfacial region and some physical properties. All the techniques mentioned here have certain pros and cons, but complement each other.

Processing conditions (e.g., temperature profile, feed point, screw speed, feed rate, and screw element configuration) and how nanocomposites are prepared in the extruder have a vital effect on the dispersion of nanoclay. The resultant morphology of nanocomposites is not only a question of shear stress or residence time, but also a result of the entire mechanical and thermal history of the material when extruded. Hence, this study intends to extensively investigate the aspects of processing conditions, such as temperature profile, feed point, screw speed, feed rate, and screw element configuration, and the relationship between the different parameters (optimal conditions). The clay-containing polymer nanocomposite has been selected as a model system and the effects of nanoclay and maleic anhydride grafted PP loading on the dispersion of nanoclay in the PP nanocomposite have been investigated. The aim of this study is to investigate ways of improving the dispersion of nanoclay in the PP matrix and to determine how the state of dispersion affects the morphology and properties of resultant PP nanocomposites. A co-rotating twin-screw extruder was used to produce nanocomposites owing to the flexibility of the screw profile, screw speed, feed rate, and material feeding in different areas of the machine.

The present work investigates the distribution of nanoclay particles at the interface and their influence on the microstructure development and non-linear rheological properties of reactively processed biodegradable polylactide/poly(butylene succinate) blend nanocomposites. Two types of organoclays, one is more hydrophilic (Cloisite®30B (C30B)) and another one is more hydrophobic (BetsopaTM (BET)), were used at different concentrations. Surface and transmission electron microscopies were respectively used to study the blend morphology evolution and for probing the dispersion and distribution of nanoclay platelets within the blend matrix and at the interface. The results suggested that both organoclays tended to localize at the interface between the blend’s two phases and encapsulate the dispersed poly(butylene succinate) phase, thereby suppressing coalescence. Using small angle X-ray scattering the probability of finding neighboring nanoclay particles in the blend matrix was calculated using the Generalized Indirect Fourier Transformation technique. Fourier Transform-rheology was utilized for quantifying nonlinear rheological responses and for correlating the extent of dispersion as well as the blend morphological evolution, for different organoclay loadings. The rheological responses were in good agreement with the X-ray scattering and electron microscopic results. It was revealed that C30B nanoparticles were more efficient in stabilizing the morphologies by evenly distributing at the interface. Nonlinear coefficient from FT-rheology was found to be more pronounced in case of blends filled with C30B, indicating better dispersion of C30B compare with BET which was in agreement with the SAXS results.

In this article, a combined experimental and theoretical approach has been proposed to establish a relationship between the required shear force and the degree of delamination of clay tactoids during the melt-processing of polymer nanocomposites. Polypropylene (PP) was selected as a model polymer, and nanocomposites of PP with organically modified clay were prepared by a master batch dilution technique in a twin-screw extruder. The effect of PP throughput during the dilution of the master batch on the dispersion and orientation of clay platelets were studied in detail. Powder X-ray diffraction, small and wide angle X-ray scattering and high resolution transmission electron microscopy were used to study the structure and morphology of the obtained nanocomposites. The results showed that a lower feeding rate led to the orientation of clay platelets almost in the direction of extrusion. The adhesive force and the interaction energy between the clay platelets were theoretically calculated using the Hamaker approach. The analysis showed that the peeling mechanism is a practical explanation for the delamination of clay platelets during melt extrusion and that the dimensions of the clay platelet tactoids play an important role in the peeling due to the shear stress.

Copyright: 2014 Wiley. Abstract only.The definitive version is published in Macromolecular Materials and Engineering, vol.299(8), pp 939-952

The carbon nanotubes (CNTs)-containing composites of poly(butylene succinate) (PBS) were prepared by melt-blending in a batch mixer with three concentrations by weight of CNTs: 1, 2 and 3 %. State of dispersion-distribution of the CNTs in the PBS matrix was examined by electron microscopic observations that revealed homogeneous distribution of agglomerated CNTs in PBS matrix. The dynamic mechanical studies demonstrated an increase in the storage modulus of PBS matrix with the CNTs loading. Melt-state rheological properties measurements were found to be modified with CNT loading changing from liquid-like, to gel-like and then to viscoelastic solid-like. Finally, the in-plane electrical conductivity was found to be substantially enhanced with CNT loading, whereas the through-plane conductivity was found to be only slighted increased with the CNT loading. Such changes in viscoelastic properties along with the improvements in both thermomechanical and electrical properties are expected to open opportunities for the use of PBS extending its applications from the classical field of packaging to new niches such as tissue-engineering.

Copyright: 2019 Wiley. Due to copyright restrictions, the attached PDF file contains the abstract version of the full-text item. For access to the full-text item, please consult the publisher's website. The definitive version of the work is published in the Journal of applied polymer science, vol. 137(9), pp. 1-11

The interest in designing new environmentally friendly materials has led to the development of biodegradable foams as a potential substitute to most currently used fossil fuel–derived polymer foams. Despite the possibility of developing biodegradable and environmentally friendly polymer foams, the challenge of foaming biopolymers still persists as they have very low melt strength and viscosity as well as low crystallisation kinetics. Studies have shown that the incorporation of cellulose nanostructure (CN) particles into biopolymers can enhance the foamability of these materials. In addition, the final properties and performance of the foamed products can be improved with the addition of these nanoparticles. They not only aid in foamability but also act as nucleating agents by controlling the morphological properties of the foamed material. Here, we provide a critical and accessible overview of the influence of CN particles on the properties of biodegradable foams; in particular, their rheological, thermal, mechanical, and flammability and thermal insulating properties and biodegradability.

This work evaluates the role of the surface properties and shape of clay type on the morphology, thermal, and thermo-mechanical properties of the polystyrene (PS)/clay nanocomposites prepared via free-radical emulsion polymerization. Attapulgite clay (ATT) with a needle-like morphology and montmorillonite clay (MMT) with a platelet-like structure were used in this study. The dispersed behavior of the clay particles in the PS matrix was studied using X-ray diffraction and transmission electron microscopy. Only intercalated structures were obtained with ATT at all of the clay loadings, whereas semiexfoliated structures were observed with MMT in the low clay loading. All of the composites obtained were found to be more thermally stable than neat PS. However, the composites prepared with the MMT exhibited greater thermal stability relative to those prepared using the ATT at similar clay loading. Furthermore, the composites prepared with MMT exhibited higher storage moduli than those prepared using ATT.

Silver (Ag)/montmorillonite (Mt) heterostructures were effectively synthesized utilising microwave (MW) irradiation technique in the absence of any reducing agent. Compared to conventional thermal reduction processes, this approach is simple, faster and environmentally friendly. The MW process yielded Mt surfaces with uniform distribution of Ag nanoparticles with an average size of 8–10 nm. The presence of reducing agents was found to inhibit the formation of Ag nanoparticles in MW synthesis. The method was also successfully used for the preparation of Ag/organically modified Mt. However, the transmission electron microscopy analysis showed that, on the surface of Mt which is organically modified, the Ag nanoparticles have a tendency to aggregate forming bigger Ag clusters. The nanostructures prepared by the MW assisted method showed substantially higher levels of antimicrobial properties against Gram-positive bacteria, i.e., S. aureus and B. cereus as well as Gram-negative bacteria namely E. coli , P. aeruginosa and S. enterica .

This chapter provides an overview on properties and applications of nanoclay-containing polymer nanocomposites (PNCs). Though PNCs are advantageous over traditional polymer composites, the key parameter controlling the successful commercialization of the PNCs is the cost-performance index. The future of PNCs along with the value chain from product development to the commercialization and possibility of recyclability and reusability have also been discussed.

The impact of nanoclay on the isothermal crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) (PES) is reported. A PES composite (PESNC) containing 5 wt% organically modified montmorillonite, was prepared via solvent casting method. The structural study of PESNC, using X-ray diffraction and optical microscope, showed the formation of micro-intercalated composite. The isothermal crystallization behavior of neat PES and PESNC was studied by differential scanning calorimetry, polarized optical and atomic force microscopes. Results show that the supercooling effect of neat PES reduces after composite formation. The Lauritzen–Hoffman secondary nucleation theory (the LH-model) was employed to understand the crystal growth mechanism of these systems. According to the LH-model, only one transition between regime II and regime III was found, but no transition from regime I to II was detected.

The non-isothermal crystallization behaviour and kinetics of neat poly(propylene)(PP), PP/poly[(butylene succinate)-co-adipate] (PP/PBSA) blend and its composite with nanoclay was studied by differential scanning calorimetry at six different cooling rates. Various models, namely the Avrami, the Ozawa and the combined Avrami-Ozawa, were applied to understand the kinetics of the non-isothermal crystallization. All analyses revealed that the rate dependent crystal growth mechanism of neat PP changes after preparation of blend with PBSA and in presence of nanoclay particles in blend composite. Polarized optical microscopy was used to support this conclusion. The activation energy for the non-isothermal crystallization of neat PP, PP/PBSA blend and nanoclay modified PP/PBSA blend composite samples was evaluated by using Kissinger and Augis-Bennett methods. The results showed that the absolute value of the activation energy for the PP matrix crystallization was increased in the case of PP/PBSA blend and this va...

To understand the change in dispersion and orientation of clay platelets in three-dimensional space during tensile test, neat polymer and its nanocomposite samples were studied by small- and wide-angle X-ray scattering (SWAXS). The samples after tensile tests were examined by tilting and rotating them with respect to the incident X-ray beam and also by scanning them at different positions. The tilt angle measurements provide better understanding on the dispersion and orientation of the clay platelets in nanocomposite. On the other hand, rotation and scanning measurements reveal details information on the orientation of polymer crystal planes due to the tensile stretching and percent crystallinity. Finally, the focussed ion beam electron tomography was employed to support the dispersion and orientation models of clay platelets proposed on the basis of SWAXS analyses.

The poly(ethylene terephthalate)/thermotropic liquid crystal polymer (weight ratio 80:20) blend composites with two different weight percentages of nanoclay were prepared using a twin-screw extruder. The frequency sweep experiments at a constant strain and different temperatures were carried out by a dynamic mechanical analyzer. The temperature sweep experiments of unmodified and nanoclay modified blends were conducted to find out the variation of flexural storage and tan δ values as a function of temperature. Results showed that the modulus of the blend increases after composite formation with nanoclay and the variation of frequencies during temperature sweep experiments do not affect the glass transition temperature values. The small-angle X-ray scattering studies showed that the degree of anisotropy and mean orientation angles of clay platelets in blend matrix were altered significantly after frequency and temperature sweep tests.

A poly[(butylene succinate)-co-adipate] (PBSA) nanocomposite containing 3 wt% organically modified montmorillonite exhibited an improvement in tenacity (elongation at break) as compared to the neat PBSA. The nanocomposite also showed moderate improvement in tensile modulus and strength. The small-angle X-ray scattering and transmission electron microscopy were used to investigate the exact tenacity improvement mechanism in the nanocomposite.

The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS-modified PET/LCP blends were prepared by melt-extrusion using twin-screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase-separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS-modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re-crystallisation. Finally, non-isothermal crystal-growth kinetics of pure and OMLS-modified blends were investigated.

The thermal and rheological properties of clay-containing poly[(butylene succinate)-co-adipate] (PBSA) nanocomposites are reported. The nanocomposites of PBSA with various weight percentages of organically modified montmorillonite (OMMT) loadings have been prepared by melt-mixing in a batch-mixer. The melting and crystallization behaviours of PBSA and its nanocomposites have been studied using differential scanning calorimeter (DSC). The melt-state rheological properties of pure PBSA and its nanocomposites containing different amounts of OMMT have been studied in detail. The reason for this is that the rheological responses of any nanofilled polymeric materials are strongly related by their dispersed structure and the interfacial characteristic. Results show that the structural strength of all samples remains constant in the examined time interval at an experimental temperature. The dominant viscous behaviour of pure PBSA is getting suppressed up to a certain OMMT loading (4 wt%). Nanocomposite containing 5 wt% OMMT is showing almost "at the gel point" behaviour, suggesting that the material is behaving near the borderline between liquid and solid; while nanocomposite containing 6 wt% OMMT is showing the gel character. The dispersed structure of the clay particles in the PBSA matrix was studied by scanning transmission electron microscopy (STEM). Results show that the stacked and intercalated silicate layers are nicely dispersed in the case of all nanocomposites. However, with a systematic increase in OMMT loading, the dispersed clay structure of the nanocomposites changes from a highly delaminated to a flocculated and then to a stacked-intercalated structure. In the case of all nanocomposites, melt-state rheological properties are in good agreement with the STEM observations.

The main theme of this work is to support the unusual melt-state rheological properties of the clay-containing nanocomposites of thermotropic liquid crystal polymers by small- and wide-angle X-ray scattering. The changes of dispersion of silicate particles in the LCP matrix as well as change in crystal growth of LCP were extensively studied by X-ray scattering in both small- and wide-angle regions. The generalised indirect Fourier transformation technique developed by Glatter was used to study the structural changes in nanocomposites with temperature. This is a new approach recently proposed by us for the quantitative analysis of the nanoparticles dispersion in the polymer matrix.

The main objective of this work is to propose a new approach for the quantitative analysis of the degree of dispersion of clay particles in the polymer matrix by small angle X-ray scattering (SAXS) combined with electron microscopy. Due to the low temperature processibility and good thermal stability, poly[(butylene succinate)-co-adipate] (PBSA) was chosen as a model polymer matrix for this study. The nanocomposites of PBSA with four different weight percentages of organically modified montmorillonite (OMMT) loadings were prepared via melt-blending method. The dispersed structure of the clay particles in the PBSA matrix was studied by SAXS. Results show that the clay particles are nicely dispersed in the case of all nanocomposites. However, with a systematic increase in clay loading, the dispersed clay structure of the nanocomposites changes from a highly delaminated to a flocculated and then to a stacked intercalated one. The probability of finding neighboring clay particles in the PBSA matrix as well as their thickness was calculated using the Generalized Indirect Fourier Transformation technique developed by Glatter and the modified Caille theory proposed by Zhang. The morphology of the nanocomposites was also extensively studied by scanning transmission electron microscopy (STEM). In the case of all nanocomposites, SAXS results were in good agreement with STEM observations. Finally, a correlation between the predicted morphology of nanocomposites and their melt-state rheological properties is reported.

The nanocomposites of liquid-crystal polymer (LCP) with two different weight per cents of clay were prepared via the melt extrusion method. To investigate the properties of the materials in the linear and non-linear viscoelastic regions, both oscillatory and rotational tests were carried out. The results showed that the nanocomposite with higher clay content exhibited an almost defectless partially cross-linked structure compared to the nanocomposite with lower clay content or the pure LCP. The linear stress relaxation measurements revealed that the pure LCP relaxed faster than nanocomposites after imposition of a constant strain for a specific time. During the step rate relaxation test, high shear rate modified the defects in the pure LCP very quickly and probably attained almost an equilibrium position while the nanocomposite samples showed strong shear thinning behaviour.

The influence of the degree of intercalation of polymer chains in the two dimensional silicate galleries on the crystallization behavior of poly[(butylene succinate)-co-adipate] (PBSA) is being reported on. The nanocomposites were prepared by melt-blending of PBSA and organically modified montmorillonite (OMMT) in a batch-mixer. Two different types of commercially available OMMTs, with different extents of miscibility of organic modifiers with PBSA, were used, leading to highly delaminated and stacked/intercalated nanocomposite structures as revealed by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) observations. The non-isothermal crystallization behavior of PBSA and the nanocomposite samples were studied by differential scanning calorimetry (DSC). Crystal growth kinetics studies showed that when silicate layers are highly delaminated into the PBSA matrix, nucleation behaviors decreased significantly, relative to the stacked/intercalated silicate layers. These observations indicate that the overall crystal growth kinetics retard in delaminated nanocomposites, opposed to increasing in the case of stacked/intercalated nanocomposites. Polarized optical microscopy (POM) observations and light scattering studies indicate that PBSA spherulites are fairly large and more perfectly grown in the case of delaminated nanocomposites, relative to the pure PBSA matrix. The effect of high levels of dispersion of silicate layers in the PBSA matrix on cold crystallization behavior was also studied.

This article reports the nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nanocomposites. The non-isothermal crystallization behaviors of PET and the nanocomposite samples are studied by differential scanning calorimetry (DSC). Various models, namely the Avrami method, the Ozawa method, and the combined Avrami-Ozawa method, are applied to describe the kinetics of the non-isothermal crystallization. The combined Avrami and Ozawa models proposed by Liu and Mo also fit with the experimental data. Different kinetic parameters determined from these models prove that in nanocomposite samples intercalated silicate particles are efficient to start crystallization earlier by nucleation, however, the crystal growth decrease in nanocomposites due to the intercalation of polymer chains in the silicate galleries. Polarized optical microscopy (POM) observations also support the DSCresults. The activation energies for crystallization has been estimated on the basis of three models such as Augis–Bennett, Kissinger and Takhor methods follow the trend PET/2C20A

The preparation and thermal and thermo-mechanical properties of nanocomposites based on liquid-crystalline polymers (LCP) and organically-modified layered silicate (OMLS) is described. From XRD patterns, very little smectic ordering is present in the pure LCP; in the nanocomposites, the polymer chains tended to orient in the direction of the dispersed clay layers. According to the DSC results, during first heating, the first melting peak represents the crystalline to nematic transition and, after that, a broader isotropization takes place. Although TGA of the samples showed a single-step decomposition through chain scission under an inert atmosphere, in air the nanocomposites underwent a two-step process, with onset of degradation at a higher temperature. The first step is mainly due to chain scission and the second is due to oxidative reactions.

The effect of organically modified clay on the morphology and properties of poly(propylene) (PP) and poly[(butylene succinate)-co-adipate] (PBSA) blends is studied. Virgin and organoclay modified blends were prepared by melt-mixing of PP, PBSA and organoclay in a batch-mixer at 190 °C. Scanning electron microscopy studies revealed a significant change in morphology of PP/PBSA blend in the presence of organoclay. The state of dispersion of silicate layers in the blend matrix was characterized by X-ray diffraction and transmission electron microscopic observations. Dynamic mechanical analysis showed substantial improvement in flexural storage modulus of organoclay-modified blends with respect to the neat polymer matrices or unmodified blends. Tensile properties of virgin blends also improved in the presence of organoclay. Thermal stability of virgin blends in air atmosphere dramatically improved after modification with organoclay. The effect of organoclay on the melt-state liner viscoelastic properties of virgin blends was also studied. The non-isothermal crystallization behavior of homopolymers, virgin, and organoclay-modified blends were studied by differential scanning calorimeter. The effect of incorporation of organoclay on the cold crystallization behavior of PP/PBSA blends is also reported.

In this article the thermal and thermomechanical properties of neat poly[(butylene succinate)-co-adipate] (PBSA) and its nanocomposite are reported. Nanocomposite of PBSA with organically modified synthetic fluorine mica (OSFM) has been prepared by melt-mixing in a batch mixer. The structure of nanocomposite is characterized by X-ray diffraction patterns and transmission electron microscopic (TEM) observations that reveal homogeneous dispersion of intercalated silicate layers in the PBSA matrix. The melting behavior of pure polymer and nanocomposite samples are analyzed by differential scanning calorimetry (DSC), which shows multiple melting behavior of the PBSA matrix. The multiple melting behavior of the PBSA matrix is also studied by temperature modulated DSC (TMDSC) and wide-angle XRD (WXRD) measurements. All results show that the multiple melting behavior of PBSA is due to the partial melting, re-crystallization, and re-melting phenomena. The investigation of the thermomechanical behavior is performed by dynamic mechanical thermal analysis. Results demonstrate substantial enhancement in the mechanical properties of PBS, for example, at room temperature, storage flexural modulus increased from 0.5 GPa for pure PBS to 1.2 GPa for the nanocomposite, an increase of about 120% in the value of the elastic modulus. The thermal stability of nanocomposite compared to that of neat PBSA is also examined in pyrolytic and thermo-oxidative conditions. It is then studied using kinetic analysis. It is shown that the stability of PBSA is increased moderately in the presence of OSFM. 2007 Elsevier Ltd. All rights reserved.