Modification of α-ZrP nanofillers by amines of different chain length: Consequences on the morphology and mechanical properties of styrene butadiene rubber based nanocomposites

An aqueous slurry of α-ZrP lamellar nanofillers has been modified by amine type surfactants. The influence of the alkylamine chain length and of the cationic exchange rate on the nanofiller d-spacing has been analyzed. The strength of the interactions formed between the intercalating agent and the filler has been studied by Infra Red Spectroscopy (FTIR), Solid-state Nuclear Magnetic Resonance (³¹P MAS NMR) and Thermogravimetric Analysis (TGA). Different routes allowing to obtain optimized filler properties while minimizing the surfactant weight amount have been proposed from the detailed analysis of the intercalation mechanism. Styrene Butadiene Rubber nanocomposites have been prepared directly from the different slurries of modified α-ZrP. The dispersion of the organophilic α-ZrP in the SBR matrix has been characterized and the mechanical properties of the corresponding nanocomposites have been determined and discussed as a function of the filler modification, of the nanocomposite morphology and of the filler/matrix interfacial properties.     

Nucleation, structure and lamellar morphology of isotactic polypropylene filled with polypropylene-grafted multiwalled carbon nanotubes

Polypropylene-based nanocomposites filled with polypropylene-grafted multiwalled carbon nanotubes (PP-g-MWNT) were compared to PP samples filled with pristine MWNT. The effect of such additives on the structure and morphology of the polymer matrix was studied by small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD), polarized light optical microscopy (PLOM) and differential scanning calorimetry (DSC). PP-g-MWNT allowed a more efficient and unhindered crystallization at a lamellar level, while MWNT disrupted the order of lamellar stacks, probably because of their tendency to aggregate. A common trend of tensile properties and lamellar morphology as a function of filler content was noted in the series filled with functionalized carbon nanotubes.     

Poly(ε-caprolactone) filled with electrospun nylon fibres: A model for a facile composite fabrication

Electrospun fibres are very rarely used as reinforcing agents in polymer-based composites. A fabrication approach is presented that allows to easily prepare composites based on polycaprolactone (PCL) filled with nylon 6 electrospun fibres by compression moulding. At very low filler contents (3%), the obtained composites exhibited improved stiffness with a simultaneous increase in ductility, differently from what is usually found in PCL nanocomposites with a variety of fillers, in which increases in modulus happen at the expense of elongation at break. The presence of fibres with a very small diameter, typical of the products of electrospinning, favoured a good interfacial adhesion between matrix and filler. Being of a similar order of magnitude than polymer lamellae, electrospun fibres can be used to shape the morphology of lamellar stacks, and therefore the final properties of the composites.     

Thermal behaviour of compatibilised polypropylene nanocomposite: Effect of processing conditions

The thermal properties and fire behaviour of polypropylene (PP) nanocomposites were investigated using differential scanning calorimetry, dynamic-mechanical analysis, thermogravimetric analysis and glow wire test. In order to study the morphological structure of the materials obtained, TEM and XRD analyses were also carried out. The nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. Particular attention was given to studying the influence of different processing conditions (barrel temperature profile and screw rate) and compositions of PP-nanoclay blends (clay content, use of compatibiliser) on the thermal properties of the nanocomposites.The results show that all the properties analysed were strongly influenced by the nanocomposite composition; instead, the processing conditions greatly affect only the dynamic-mechanical properties. DSC curves show that the crystallinity is deeply influenced by the presence of the clay in the matrix, owing to the fact that the filler acts as nucleating agent. DMA curves show that materials processed at low temperature profile and high shear stress, i.e. when a good clay dispersion is achieved, are characterised by an enhanced modulus, thus indicating that the incorporation of clay into the PP matrix remarkably enhances its stiffness and has good reinforcing effects. TGA traces in oxidizing atmosphere show a drastic shift of the weight loss curve towards higher temperature and no variation of the onset temperature (i.e. the temperature at which degradation begins). The TGA analyses in inert atmosphere show instead marked increase of this parameter (about 200 °C) and no shift of weight loss curves. Glow wire results highlight that polymer nanocomposites are characterised by enhanced fire behaviour.     

Morphology and thermal properties relationship in poly(p-dioxanone)/layered double hydroxides nanocomposites

Nanocomposites of poly(p-dioxanone) (PPDO) with unmodified and organically modified layered double hydroxide (LDH) have been prepared by melt extrusion method. Dodecyl sulfate was used as organic modifier. The morphology of nanocomposites was analyzed by X-ray diffraction and transmission electron microscopy and their thermal properties by differential scanning calorimetry and thermogravimetric analysis. It has been found that the organic modifier decisively influences the nanocomposite morphology, resulting in a higher level of exfoliation. In addition, the glass transition temperature of nanocomposites was slightly higher than in case of unfilled PPDO. Moreover, the crystallization was delayed by LDH incorporation. The above behavior was ascribed to interactions between carbonyl groups of polymer matrix and hydroxyl groups of LDH, as supported by Fourier transformed infrared analysis. Interestingly, two different crystallization processes have been observed in the nanocomposite of PPDO and organically modified LDH. Unmodified and organo-modified LDH, practically did not alter the final melting point of PPDO. However, the thermal decomposition behavior was clearly influenced by the morphology exhibited by nanocomposites.     

Compatibilized polyethylene—thermally reduced graphene nanocomposites: Interfacial interactions and hyperspectral mapping for component distribution

Ethylene-co-acrylic acid (EAA) and ethylene-co-methacrylic acid ionomer (EMAZ) copolymers were used as compatibilizers for polyethylene-graphene nanocomposites generated by melt mixing. At 5 wt% content, the EAA compatibilizer enhanced the tensile modulus of PE by 40 % and shear modulus by >300 % (1 rad/s) due to efficient dispersion of graphene platelets which helped in effective stress transfer. These also resulted in enhanced thermal stability for PE-EAA-G nanocomposite as compared to nanocomposite with EMAZ. The properties of the nanocomposites were significantly better than the conventional nanocomposites based on layered silicate materials. Mapping of the component distribution in the nanocomposites was demonstrated by using hyperspectral imaging. The nanocomposite with EAA exhibited higher extent of spectral signal mixing due to better mixing of filler and compatibilizer in PE matrix. On the other hand, nanocomposite with EMAZ had no spectral mixing as the components did not mix optimally with each other. The DSC thermogram for this nanocomposite also exhibited a small shoulder at low temperature probably due to immiscibility of the compatibilizer with the matrix polymer. The hyperspectral imaging and mapping was thus demonstrated to be a useful method for determination of component distribution in complex nanocomposite systems.     

Decoupling the effects of screw speed and particle surface functionality on the filler suspension state in PBS/fumed silica nanocomposites

This work assessed the relative effects of processing conditions and interfacial interactions on the structure and properties of PBS/fumed silica nanocomposites. Rheology and scattering were used to investigate the dispersion state of silica particles with different surface treatments in nanocomposites produced by ultra‐high speed twin‐screw extrusion. Structural parameters of the silica, such as fractal dimension and Fisher exponent, were estimated by low‐frequency rheology responses and lower q scattering data. This study demonstrates that both decreased bulk polymer properties and improved filler suspension caused by high shear compounding determine the final properties of these PBS based nanocomposites. While the molecular weight of bulk polymer matrix was significantly reduced, the extreme shear increased the probability of forming percolated clusters, leading to remarkable reinforcement (up to 4000%) as evidenced by the low‐frequency rheological response. Further, the improvement in dispersion was enhanced when the filler was functionalized with a compatibilizing surface treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1820–1828     

Structure and dielectric properties of a thermoplastic blend containing dispersed metal

In the present work broadband dielectric relaxation spectroscopy measurements were employed to investigate the dielectric properties of polymer composites. A polyethylene/polyoxymethylene (PE/POM) thermoplastic blend was used as a matrix, while the inclusions were iron (Fe) particles. For comparison, the two pure polymers- PE and POM- were used as a matrix, too. In the PE/POM-Fe composites, the polymer matrix is two-phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. In PE-Fe and POM-Fe composites, the filler spatial distribution is random. The behaviour of all the composites studied is described in terms of the percolation theory. The PE/POM-Fe composites, based on the PE/POM blend, demonstrate different electrical behaviour compared to that of POM-Fe and PE-Fe systems. The percolation threshold value of the PE/POM-Fe composites was found much lower than that of the other two systems. The results were related to the microstructure of the composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behaviour of the PE/POM-Fe composites by taking into account the ordered distribution of the filler particles in a binary polymer matrix. Optical microscopy photographs confirm this model.     

Structural and thermal properties of polysulfone-ZnO nanocomposites

Polymer nanocomposite thin film of polysulfone with different concentration of ZnO was prepared by solution grown technique. This paper presents a study on the structural and thermal properties of ZnO filled Polysulfone (PSF) nanocomposites. The structural morphology of the resulting nanocomposites was investigated by X-ray diffraction (XRD), Scanning electron microcopy (SEM), and Atomic force microscopy (AFM). Thermal properties of PSF nanocomposites samples were investigated by Differential thermal analysis, Thermal gravimetric, and Differential thermal gravimetric. Structural result shows that the ZnO nanofiller with different mass% in polymer matrix cause the significant variation of lattice spacing, crystallite size, and percentage crystallinity. XRD result shows that the amorphous behavior of PSF (Pristine) is increasing with incorporation of ZnO nanoparticle in PSF matrix. The SEM and AFM images show the change in structural morphology of PSF due to incorporation of ZnO nanoparticles. The thermal analysis result shows that the significant thermal degradation of polysulfone nanocomposites due to catalytic behavior of ZnO nanoparticles.     

Predictive modeling of creep in polymer/layered silicate nanocomposites

A predictive creep model is developed which uses the properties of matrix and reinforcement to predict the creep of polymer/layered silicate nanocomposites. Up to this point, primarily empirical creep models such as Findley and Burgers models have been used for creep of polymer/clay nanocomposites. The proposed creep model is based on the elastic-viscoelastic correspondence principle and a stiffness model of these nanocomposites. Also, the added stiffness of polymeric matrix due to the constraining effect of layered silicates on polymer chains in the nanocomposite is considered by a parameter termed constraint factor. The results of the proposed model show good agreement with experimental creep data for different clay contents, stresses and temperatures. Comparing the model predictions with experimental data, a logical relationship between the method of processing and the constraint factor is discovered which shows that in-situ polymerization can be more efficient for improving creep resistance of polymer/layered silicate nanocomposites relative to melt processing.     

Introduction of Multiple Hydrogen Bonding for Enhanced Mechanical Performance of Polymer-Carbon Nanotube Composites

Due to their outstanding mechanical properties and high aspect ratios, carbon nanotubes (CNTs) are envisioned as attractive nanofillers in polymer composites. However, due to strong van der Waals interactions, deleterious aggregation of CNTs is typically observed in polymer nanocomposites. Moreover, due to low stress transfer between the matrix polymer and the nanotube filler, only limited reinforcement is obtained. We report here a novel functionalization strategy to obtain CNTs with pendant self-complementary hydrogen bonding groups in order to address these limitations. Multi-walled CNTs were functionalized with ureidopyrimidinone (UPy) groups, which display multiple hydrogen bonding. The functionalized CNTs were blended with acrylic copolymers containing pendant UPy moieties and significant enhancement in tensile performance of the nanocomposites was observed.     

Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites

Polyethylene (a 1:1 blend of m-LLDPE and z-LLDPE) double layer silicate clay nanocomposites were prepared by melt extrusion using a twin screw extruder. Maleic anhydride grafted polyethylene (PEgMA) was used as a compatibiliser to enhance the dispersion of two organically modified monmorilonite clays (OMMT): Closite 15A (CL15) and nanofill SE 3000 (NF), and natural montmorillonite (NaMMT). The clay dispersion and morphology obtained in the extruded nanocomposite samples were fully characterised both after processing and during photo-oxidation by a number of complementary analytical techniques. The effects of the compatibiliser, the organoclay modifier (quartenary alkyl ammonium surfactant) and the clays on the behaviour of the nanocomposites during processing and under accelerated weathering conditions were investigated. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheometry and attenuated reflectance spectroscopy (ATR-FTIR) showed that the nanocomposite structure obtained is dependent on the type of clay used, the presence or absence of a compatibiliser and the environment the samples are exposed to. The results revealed that during processing PE/clay nanocomposites are formed in the presence of the compatibiliser PEgMA giving a hybrid exfoliated and intercalated structures, while microcomposites were obtained in the absence of PEgMA; the unmodified NaMMT-containing samples showed encapsulated clay structures with limited extent of dispersion in the polymer matrix. The effect of processing on the thermal stability of the OMMT-containing polymer samples was determined by measuring the additional amount of vinyl-type unsaturation formed due to a Hoffman elimination reaction that takes place in the alkyl ammonium surfactant of the modified clay at elevated temperatures. The results indicate that OMMT is responsible for the higher levels of unsaturation found in OMMT-PE samples when compared to both the polymer control and the NaMMT-PE samples and confirms the instability of the alkyl ammonium surfactant during melt processing and its deleterious effects on the durability aspects of nanocomposite products. The photostability of the PE/clay nanocomposites under accelerated weathering conditions was monitored by following changes in their infrared signatures and mechanical properties. The rate of photo-oxidation of the compatibilised PE/PEgMA/OMMT nanocomposites was much higher than that of the PE/OMMT (in absence of PEgMA) counterparts, the polymer controls and the PE–NaMMT sample. Several factors have been observed that can explain the difference in the photo-oxidative stability of the PE/clay nanocomposites including the adverse role played by the thermal decomposition products of the alkyl ammonium surfactant, the photo-instability of PEgMA, unfavourable interactions between PEgMA and products formed in the polymer as a consequence of the degradation of the surfactant on the clay, as well as a contribution from a much higher extent of exfoliated structures, determined by TEM, formed with increasing UV-exposure times.     

An overview of boron nitride based polymer nanocomposites

Recently, boron nitride (BN) based materials have received significant attention in both academic and industrial sectors due to its interesting properties like large energy band gap, good resistance to oxidation, excellent thermal conductivity, thermal stability, chemical inertness, significant mechanical property and widespread applications. This review article deals with the preparation and properties of boron nitride and its nanocomposites with various polymers. Diverse polymers have been explored for the preparation of boron nitride filled polymer nanocomposites by adopting different mixing methods. Properties of the resulting polymer nanocomposites mainly depend up on filler size and dispersion, mixing conditions and type of interaction between polymer matrix and the filler. Herein, the structure, preparation and properties of various boron nitride based polymer nanocomposites are reviewed in detail along with a brief overview of different classes of BN nanomaterials.     

Modeling of the formation of oriented-polymer layers at filler particles in polymer nanocomposites

A theory to explain the appearance of oriented layers at the filler surface in polymer nanocomposites is proposed. The theory is based on the assumption that small oriented polymer regions have an effect on the state of neighboring regions and tend to orient polymer chains in these regions. As a result, the point-to-point transfer of this effect takes place, thereby causing the propagation of the oriented layer in the polymer nanocomposite over a considerable distance from the filler surface. The appearance of the polymer in the biaxially oriented state, which is transferred to the neighboring regions and leads to the formation of a layer with specific mechanical properties, is possible near the filler particles in this case.     

Cellulose nanomaterial reinforced polymer nanocomposites

Several forms of cellulose nanomaterials, notably cellulose nanocrystals and cellulose nanofibrils, exhibit attractive properties and are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, basis for low-density foams, additive in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic, and medical products. This entry focuses on cellulose materials as filler in polymer nanocomposites. The ensuing mechanical properties obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials that has not yet been properly resolved and remains a challenge.     

Graphite nanoplatelets/polymer nanocomposites: thermomechanical,dielectric, and functional behavior

Exfoliated graphite nanoplatelets (GNP)/epoxy resin nanocomposites were prepared and tested, varying the amount of the filler content. Systems’ morphology was investigated by means of scanning electron microscopy, while their thermal response was examined via differential scanning calorimetry (DSC). Broadband dielectric spectroscopy and dynamic mechanical thermal analysis were employed in order to characterize the produced systems. Static mechanical tests were also conducted at ambient. Reinforced systems exhibit improved performance under mechanical and electrical excitation. In particular, storage modulus increases systematically with GNP content. DSC results imply that glass transition temperature is not affected by the presence of GNP. Flexural modulus and storage modulus, as determined by static and dynamic mechanical tests, respectively, increased with filler content. Dielectric permittivity increases also systematically with GNP content. Recorded relaxation processes arise from the glass to rubber transition of the polymer matrix (α-mode), re-orientation of polar side groups of the polymer chains (β-mode), and interfacial polarization because of the accumulation of charges at the systems’ interface. Finally, the energy storing efficiency of the nanocomposites enhances with reinforcing phase in the examined frequency and temperature range. Optimum performance corresponds to the nanocomposite with maximum GNP loading.     

Polymer grafted nanoparticles: Effect of chemical and physical heterogeneity in polymer grafts on particle assembly and dispersion

Macroscopic properties of polymer nanocomposites depend on the microscopic composite morphology of the constituent nanoparticles and polymer matrix. One way to control the spatial arrangement of the nanoparticles in the polymer matrix is by grafting the nanoparticle surfaces with polymers that can tune the effective interparticle interactions in the polymer matrix. A fundamental understanding of how graft and matrix polymer chemistries and molecular weight, grafting density, and nanoparticle size, and chemistry affect interparticle interactions is needed to design the appropriate polymer ligands to achieve the target morphology. Theory and simulations have proven to be useful tools in this regard due to their ability to link molecular level interactions to the morphology. In this feature article, we present our recent theory and simulation studies of polymer grafted nanoparticles with chemical and physical heterogeneity in grafts to calculate the effective interactions and morphology as a function of chemistry, molecular weights, grafting densities, and so forth. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Characterization of kaolinite/emulsion-polymerization styrene butadiene rubber (ESBR) nanocomposite prepared by latex blending method: Dynamic mechanic properties and mechanism

The latex blending method was chosen to prepare Kaolinite/emulsion-polymerization styrene butadiene rubber (ESBR) nanocomposite to improve the interaction between filler particles and rubber matrix chains. The influences of kaolinite particles size, filler contents, and flocculants types on dynamic mechanical properties and the relative reinforcement mechanism of the prepared composite were systematic investigated and proposed. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the kaolinite particles were finely dispersed into the rubber matrix and arranged in parallel orientation. The prepared nanocomposites by latex blending exhibited improved crosslinking characteristic and dynamic mechanical parameters. The KAl (SO₄)₂ flocculant presented obvious modification in dynamic properties and crosslinking characteristic. Both the decrease in kaolinite particle size and the increase in kaolinite content can greatly improve the storage modulus and reinforcing effect of kaolinite/ESBR nanocomposites. The dynamic reinforcement mechanism of kaolinite can be explained by filler network including a certain thickness of rubber shell on the surface of kaolinite lamellar structure and the aggregations network between kaolinite particles The optimum way to balance the dynamic properties of rubber nanocomposites at different temperatures is to reduce the surface difference between kaolinite and rubber matrix and the degree of filler-filler networking on the basis of kaolinite with nanoscale (nanometer effect).     

Effect of exfoliation medium on the morphology of multi-layer graphene oxide and its importance for Poly(Ethylene terephthalate) based nanocomposites

Poly(ethylene terephthalate) (PET)/multi-layer graphene oxide (mGO) nanocomposites were produced using the melt compounding technique, with the aid of a twin-screw extruder. The main goal was to investigate the effect of different exfoliation media on the morphology of graphene oxide and its effects, mainly on the mechanical performance of PET/mGO based polymer nanocomposites. Two different exfoliation media (water and ethanol) were used for the mGO synthesis. Based on each medium, nanocomposites with three different mGO contents (0.05 wt%, 0.1 wt%, and 0.3 wt%) were produced. When exfoliated in water, mGO sheets present larger lateral dimensions, i.e., higher surface area available to interact with polymer chains. All nanocomposites presented similar crystallinity, but with a slight increase related to the neat PET, indicating the nucleating effect of mGO. A theoretical model was used to predict the nanocomposites elastic modulus, justifying the experimental results. The biggest mechanical improvement was presented by a composite with low content of water-exfoliated mGO (0.1 wt%). The polymer tensile strength, strain at break, and toughness were improved by 19%, 238% and 590%, respectively. A significant reduction in the polymer dissipation factor (tanδ) with mGO content was also verified, indicating some confinement of polymeric chains due to interactions with the mGO sheets. The different surface fracture mechanisms presented by the nanocomposite with 0.1 wt% water-exfoliated mGO were verified, in which a good interface allowed greater release of strain energy. The XR-MT data confirmed that differences in mGO morphology can sensitively affect the final composite properties, characterising it as the driving force for mechanical improvements. Therefore, a melt compounded PET/graphene derivative composite is presented, exhibiting more promising results than what is already reported by solution mixed and in-situ polymerised composites. It was possible due to the strategic processing route utilised, in which the exfoliated mGO was pre-mixed with the polymer powder using the SSD technique.     

Rheological Aspects of PP-TiO2 Micro and Nanocomposites: A Preliminary Investigation

The linear rheology of PP-TiO₂ composites was investigated as a function of the filler particle size. Small amounts (ϕ = 4.5%) of micron and nano-sized TiO₂ spherical particles were added to the polymer by melt compounding. In spite of the low particle volume fractions and the weak polymer-filler interactions, relevant changes have been observed in the linear viscoelastic behaviour of the nanostructured formulations. Microstructural analyses performed through electron microscopy have shown a good degree of dispersion of micron-sized particles. Conversely, the presence of a relevant number of TiO₂ nanoparticle clusters has been detected for the nanocomposite. The structure of these aggregates seems to be strongly responsible for the rheological behaviour of these last materials in comparison with microstructured ones. Relevant similarities between the viscoelastic properties of nanocomposite and the flow feature of many soft glassy materials have been noticed, and a simple physical picture has been proposed in order to interpret the rheological response of studied nanocomposites.