Evaluation of the influence of nanoparticles' shapes on the formation of poly(lactic acid) nanocomposites obtained employing the solution method

PLA nanocomposites were prepared by adding organically modified montmorillonite clay (Viscogel B8) and a homoionic clay (NT25), as well as unmodified silica (A200) and modified organic silica (R972). All nanocomposites were obtained by the solution intercalation method using chloroform as a solvent. The materials obtained were essentially characterized by X-ray diffraction and low-field nuclear magnetic resonance relaxometry, through the measurement of proton spin-lattice relaxation time (LF-NMR). Both clays and silicas used to obtain the polymeric nanocomposites showed good dispersion in the polymeric matrix. The relaxation times were distinct for each type of nanoparticle used. The nanocomposite formed with homoionic clay, NT25, presented an increase in the relaxation data, indicating formation of intercalated nanocomposites, contrary to the action of the organoclay Viscogel B8, which preferentially formed an exfoliated nanocomposite. When unmodified and organo-modified silica were added to PLA, an increase in the relaxation time of the polymer matrix was observed. According to the relaxation data, the organosilica R972 dispersed better in the polymeric matrix and consequently interacted better than the A200.     

Morphology,rheology and mechanical properties of polypropylene/ethylene–octene copolymer/clay nanocomposites: Effects of the compatibilizer

The objective of this study was to investigate the effects of two compatibilizers, namely maleated polypropylene (PP-g-MA) and maleic anhydride grafted poly (ethylene-co-octene) (EOC-g-MA), on the morphology and thus properties of ternary nanocomposites of polypropylene (PP)/ethylene–octene copolymer (EOC)/clay nanocomposite. In this regard the nanocomposites and their neat polymer blend counterparts were processed twice using a twin screw extruder. X-ray diffraction, transmission electron microscopy, Energy dispersive X-ray spectroscopy, and scanning electron microscopy were utilized to characterize nanostructure and microstructure besides mechanical and rheological behaviors of the nanocomposites. Clay with intercalated structure was observed in EOC phase of the PP/EOC/clay nanocomposite. Better dispersion state of the intercalated clay in EOC phase was observed by adding EOC-g-MA as a compatibilizer. On the other hand, adding PP-g-MA resulted in migration of the intercalated clay from the EOC to the PP and to the interface regions. It was also demonstrated that the elastomer particles became smaller in size where clay was present. The finest and the most uniform morphology was found in the PP/EOC/clay nanocomposite. In addition, the rheological results illustrated a higher complex viscosity and storage modulus for PP/EOC/PP-g-MA/clay nanocomposite in which clay particles were present in the matrix. Mechanical assessments showed improvements in the toughness of the nanocomposites with respect to their neat blends, without significant change in stiffness and tensile strength values. These results highlight a toughening role of clay in the polymer blend nanocomposites studied.     

Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites

Owing to the improvement of properties including conductivity, toughness and permeability, polymer nanocomposites are slated for applications ranging from membranes to fuel cells. The enhancement of polymer properties by the addition of inorganic nanoparticles is a complex function of interfacial interactions, interfacial area and the distribution of inter-nanofiller distances. The latter two factors depend on nanofiller dispersion, making it difficult to develop a fundamental understanding of their effects on nanocomposite properties. Here, we design model poly(methyl methacrylate)-silica and poly(2-vinyl pyridine)-silica nanocomposites consisting of polymer films confined between silica slides. We compare the dependence of the glass-transition temperature (Tg) and physical ageing on the interlayer distance in model nanocomposites with the dependence of silica nanoparticle content in real nanocomposites. We show that model nanocomposites provide a simple way to gain insight into the effect of interparticle spacing on Tg and to predict the approximate ageing response of real nanocomposites.     

Effect of various combinations of zirconia and organoclay nanoparticles on mechanical and thermal properties of an epoxy nanocomposite coating

An epoxy based nanocomposite coating containing various combinations of treated-zirconia and clay nanoparticles were prepared. Morphology and dispersion of nanoparticles within the nanocomposites were evaluated using optical microscopy, XRD and TEM analyses. Mechanical, thermal properties and corrosion resistance of nanocomposites were studied using; tensile strength measurements, DMTA and DSC analyses and salt spray test.The results showed that simultaneous use of spherical and plate-shape nanoparticles, have a positive effect on the clay exfoliation behavior in resulting nanocomposites.Mechanical properties of nanocomposites containing nano-zirconia slightly increased compared with neat-epoxy coating. Mechanical properties of nanocomposites containing various wt.% of clay or ZrO₂/clay nanoparticles slightly decreased; formation of physical barrier clay stacks, which leads to disturbing curing procedure and decreasing polymer cross-linking density, and development of nano-sized voids in the trapped regions by clay stacks. Corrosion performance of nanocomposites increased with addition of nanoparticles, due to improving barrier properties of the coating.     

Investigation of the fracture mechanism and mechanical properties of polystyrene/silica nanocomposite in various silica contents

There is limited research on the effect of silica on the mechanical properties of polystyrene. For this lack of information, this study has focused on the fracture mechanism and mechanical properties of Polystyrene/silica nanocomposite. Transmission electron microscopy showed proper dispersion of nanoparticles in PS matrix in both low and high filler loadings. Scanning electron microscopy, TOM micrography, and non-contact surface profiler were used to study the fracture surface and fracture mechanism characteristics of the nanocomposite. It seems that the debonding mechanism is an important mechanism in toughening of Polystyrene/silica nanocomposites. In addition, mechanical behavior of the samples was investigated. Tensile, flexural, and compressive strength and also impact and plain-strain fracture toughness of nanocomposite samples showed different behaviors in low and high nanoparticle loadings and interestingly, we found an optimum value less than 2% for nanoparticle loading in which we observed the highest improvement in mechanical properties of the nanocomposite.     

Impact fracture behaviour of nylon 6-based ternary nanocomposites

This study focuses on achieving high stiffness/strength and high fracture toughness in nylon 6/organoclay nanocomposites prepared via melt compounding by incorporating a maleic anhydride grafted polyethylene–octene elastomer (POE-g-MA) as a toughening agent. Mechanical test results indicated that the ternary nanocomposites exhibited higher stiffness than nylon 6/POE-g-MA binary blends at any given POE-g-MA content. More importantly, the brittle–ductile transition of nylon 6/POE-g-MA blends was not impaired in the presence of organoclay for the compositions prepared in this study. TEM analysis shows that organoclay layers and elastomer particles were dispersed separately in nylon 6 matrix. In the binary nanocomposite, no noticeable plastic deformation was observed around the crack tip. In the ternary nanocomposites, the presence of organoclay in the matrix provided maximum reinforcement to the polymer, while their absence in the elastomer particles allowed the latter to promote high fracture toughness via particle cavitation and subsequent matrix shear yielding. The partially exfoliated clay layers also delaminated and hence, adding to the total toughness of the nanocomposites.     

Toughening of polyamide 11 with carbon nanotubes for additive manufacturing

It has been reported that the addition of nanofillers/nanoparticles into the thermoplastic polymers could enhance the toughness of the polymer matrix. In this work, the mechanical and thermal properties of a multi-walled carbon nanotubes (CNT)/polyamide 11 nanocomposite for additive manufacturing was evaluated. Well-dispersed PA11/CNT nanocomposite powders were processed successfully by laser sintering. Compared to the pristine PA11, the fracture toughness of the PA11/CNT nanocomposite was enhanced by ～54% by incorporating of only 0.2?wt% CNTs. With differential scanning calorimetry, X-ray diffraction and scanning electron microscope fractography analysis, the nanostructure and the toughening mechanism which lead to the toughness improvement was well identified and understood.     

聚合物基纳米复合材料的增强增韧机理

大量的研究数据表明,聚合物基纳米复合材料具有同时增强增韧效果。结合环氧树脂／二氧化硅和聚酰亚胺／蒙脱土纳米复合材料的研究工作和有关文献综述了聚合物基纳米复合材料的各种增强增韧机理,包括物理化学作用和微裂纹化及裂缝与银纹相互转化增强增韧机理、临界基体层厚度增韧机理、物理交联点增强增韧机理,并对不同的纳米复合材料体系的实验结果进行了合理的解释。最后展望了这些机理在聚合物基纳米复合材料设计与应用中的指导作用。     

Blends and clay nanocomposites of cellulose acetate and poly(epichlorohydrin)

The aim of this work was to investigate cellulose acetate/poly(epichlorohydrin) (CA/PEPi) blends and cellulose acetate/poly(epichlorohydrin)/organically modified montmorillonite clay nanocomposites (CA/PEPi/MMTO) prepared by melt processing in a twin-screw extruder. The combination of an elastomer and clay in the cellulose acetate matrix was an attempt made to reach a balance between toughness and strength properties. The blend and nanocomposite structure, morphology and thermal properties were investigated by small angle X-ray scattering, transmission electron microscopy and dynamical mechanical analysis. The results showed immiscibility of the polymer components for all the CA/PEPi blend composition range investigated. In the case of the nanocomposites, the results indicated a significant polymer intercalation in the clay gallery as well as the exfoliation of the silicate layers. Moreover, the organoclay was present in the CA phase, but some of the organoclay migrated to the CA/PEPi interface and tended to surround the PEPi phase. The addition of PEPi elastomer to cellulose acetate showed a significant increase in the blend impact resistance. However the combination of PEPi and MMTO did not in fact produce a good stiffness versus toughness balance.     

Hot-pressed graphene nanoplatelets or/and zirconia reinforced hybrid alumina nanocomposites with improved toughness and mechanical characteristics

This work explains the synergistic contribution of graphene nanoplatelets(GNP) and zirconia ceramic nanoparticles(ZrO_2) on the microstructure, mechanical performance and ballistic properties of the alumina(Al_2O_3) ceramic hybrid nanocomposites. Over the benchmarked monolithic alumina, the hotpressed hybrid nanocomposite microstructure demonstrated 68% lower grain size due to grain pinning phenomenon by the homogenously distributed reinforcing GNP(0.5 wt%) and zirconia(4 wt%) inclusions. Moreover, the hybrid nanocomposite manifested 155% better fracture toughness(KIC) and 17%higher microhardness as well as 88% superior ballistic trait over the monolithic alumina, respectively. The superior mechanical and ballistic performance of the hybrid nanocomposites was attributed to the combined role of zirconia nanoparticles and GNP nanomaterial in refining the microstructure and inducing idiosyncratic strengthening/toughening mechanisms. Extensive combined electron microscopy revealed complicated physical interlocking of the GNP into the microstructure as well as excellent bonding of the GNP with alumina at their interface in the hybrid nanocomposites. We also probed the efficiency of the pull-out and crack-bridging toughening mechanisms through proven quantitative methods. Based on the information extracted from the in-depth SEM/TEM investigation, we outlined schematic models for understating the reinforcing ability as well as toughening mechanisms in the hybrid nanocomposites and meticulously discussed. The hot-pressed hybrid nanocomposites owning high toughness and hardness may have applications in advanced armor technology.     

Preparation and properties of nitrile rubber/montmorillonite nanocomposites via latex blending

The nitrile rubber (NBR)/unmodified montmorillonite (Na-MMT) clay nanocomposites were prepared by latex blending method followed by melt mixing of compounding ingredients by using two-roll mill. The X-ray diffraction (XRD) studies showed an increase in the basal spacing and broadening of peak corresponding to crystal structure of Na-MMT indicating the formation of intercalated/exfoliated clay layers in the NBR matrix. Increase in clay content of nanocomposite increased the XRD peak height due to the formation of many of clay tactoids at higher loading. The transmission electron microscopy (TEM) strengthened the XRD finding by showing the presence of intercalated/exfoliated morphology of clay platelets having good dispersion. The modulus and tensile properties of the nanocomposites were improved with addition of Na-MMT which is proportional to clay concentration. The retention of tensile properties of aged nanocomposites, with all clay concentration, was superior to either pure NBR and carbon black filled NBR composite. The dynamic mechanical analysis showed proportional increase in storage modulus analogous to Na-MMT loading at all the temperature ranges due to the confinement of polymer chains between the clay layers. Nanocomposites with different proportions of clay showed a decrease in tan δ_max peak height with a shift towards higher temperature indicating the reduction in the segmental mobility of polymer chain. A linear model was proposed to correlate the influence of Na-MMT content on storage modulus of nanocomposites. Differential scanning calorimetry indicated a linear increase in glass transition of nanocomposites which is proportional to clay loading. Thermogravimetric analysis revealed a small improvement in the thermal stability of nitrile rubber/clay nanocomposites.     

Toughening mechanisms in multiphase nanocomposites

Our research is concerned with nanoreinforced structural adhesive bonds (SAB) for aerospace applications that contain dissimilar substrates and a theromoset epoxy adhesive with dispersed nanofillers. The interactions between these different phases results in unique fracture properties and mechanisms that dictate the toughness of the nanocomposite. In view of the varied length-scale, one cannot implement mere traditional approaches to evaluate the possible toughening mechanisms needed to ensure the integrity of the multiphase nanocomposite. Our current research is devoted to establishing the appropriate toughening mechanisms in multiphase nanocomposites by adopting traditional mechanisms such as crack-bridging, crack deflection, crack pinning and void nucleation, as well as investigating new nano-mechanisms such as fracture ridge creation. In this paper, the toughening mechanisms of carbon nanotube (CNT) reinforced polymer SABs are identified and their effects quantified in order to effectively estimate the fracture toughness of nanocomposite. Specific attention is devoted to examining the effect of dispersion of the nanofillers upon the strengthening mechanisms and interfacial debonding in nanocomposites, and the propensity of agglomerations-assisted crack initiation sites using atomistic based continuum modeling techniques.     

Electrical transport behaviour of silver–PMMA nanocomposite films at low temperature

In this study, the silver nanoparticles, capped with oleylamine, were embedded in polymethylmethacrylate (PMMA) using sonication to fabricate Ag–PMMA nanocomposites. The well-dispersed nanocomposite samples are analysed using UV-Vis absorption spectroscopy, atomic force microscopy and small angle X-ray scattering. The interfacial interaction of Ag nanoparticles and PMMA polymer is investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It is concluded that a ligand-exchange process occurs when capped silver nanoparticles are incorporated in PMMA polymer. Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70–300?K range. The nanocomposites showed a transition with onsets at ～230 and ～160?K. They exhibited a semiconductor-like conductivity at higher temperatures, a rapid metallic conductivity at middle range and nearly temperature independent conductivity at lower temperatures.     

The toughness of epoxy polymers and fibre composites modified with rubber microparticles and silica nanoparticles

The present paper investigates the effect of adding silica nanoparticles to an anhydride-cured epoxy polymer in bulk and when used as the matrix of carbon- and glass-fibre reinforced composites. The formation of ‘hybrid’ epoxy polymers, containing both silica nanoparticles and carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber microparticles, is also discussed. The structure/property relationships are considered, with an emphasis on the toughness and the toughening mechanisms. The fracture energy of the bulk epoxy polymer was increased from 77 to 212 J/m² by the presence of 20 wt% of silica nanoparticles. The observed toughening mechanisms that were operative were (a) plastic shear-yield bands, and (b) debonding of the matrix from the silica nanoparticles, followed by plastic void-growth of the epoxy. The largest increases in toughness observed were for the ‘hybrid’ materials. Here a maximum fracture energy of 965 J/m² was measured for a ‘hybrid’ epoxy polymer containing 9 wt% and 15 wt% of the rubber microparticles and silica nanoparticles, respectively. Most noteworthy was the observation that these increases in the toughness of the bulk polymers were found to be transferred to the fibre composites. Indeed, the interlaminar fracture energies for the fibre-composite materials were increased even further by a fibre-bridging toughening mechanism. The present work also extends an existing model to predict the toughening effect of the nanoparticles in a thermoset polymer. There was excellent agreement between the predictions and the experimental data for the epoxy containing the silica nanoparticles, and for epoxy polymers containing micrometre-sized glass particles. The latter, relatively large, glass particles were investigated to establish whether a ‘nano-effect’, with respect to increasing the toughness of the epoxy bulk polymers, did indeed exist.     

低填充SiO2/聚丙烯纳米复合材料的拉伸特性

通过对纳米SiO2辐照接枝聚合改性,结合熔融共混工艺制备了低填充SiO2/PP纳米复合材料,发现在一定拉伸速度和粒子含量下,经辐照改性的SiO2/PP纳米复合韧性得到显著提高,同时强度也有所增加,随拉伸速度的升高,纳米复合材料的模量和强度逐渐增大,而韧性则随之下降,断面扫描电镜观察表明,改性纳米粒子填充复合材料韧性提高的机理以空化和基体大面积剪切屈服为主。     

Effect of processing parameters and clay volume fraction on the mechanical properties of epoxy-clay nanocomposites

The influence of processing parameters and particle volume fraction was experimentally studied for epoxy clay nanocomposites. Nanocomposites were prepared using onium ion surface modified montmorillonite (MMT) layered clay and epoxy resin (DEGBF). Two different techniques were used for dispersing the clay particles in the epoxy matrix, viz. high-speed shear dispersion and ultrasonic disruption. The volume fraction of clay particles was systematically varied from 0.5 to 6%, and mechanical properties, viz. flexural modulus and fracture toughness, were studied as a function of clay volume fraction and the processing technique. The flexural modulus was observed to increase monotonously with increase in volume fraction of clay particles, while, the fracture toughness showed an initial increase on addition of clay particles, but a subsequent decrease at higher clay volume fractions. In general, nanocomposites processed by shear mixing exhibited better mechanical properties as compared to those processed by ultrasonication. Investigation by X-ray diffraction (XRD) revealed exfoliated clay structure in most of the nanocomposites that were fabricated. Morphologies of the fracture surfaces of nanocomposites were studied using a scanning electron microscopy (SEM). Presence of river markings at low clay volume fractions provided evidence of extrinsic toughening taking place in an otherwise brittle epoxy.     

The effect of process parameters on physical and mechanical properties of commercial low density polyethylene/ORG-MMT nanocomposites

Polyethylene/organo-montmorillonite clay (org-MMT) nanocomposites were prepared utilizing PP-g-MA as a compatibilizer by melt intercalation method. In order to increase the miscibility of polyethylene (PE) with nanoparticle surface at firs, a primary masterbatch consist of compatibilizer and org-MMT was prepared then, this compound was melt intercalated with PE to synthesis the PE/org-MMT nanocomposites. In this study, the presence of commercial low density polyethylene in Nanocomposites structure and also the effect of process parameters such as: amount of nanoparticles, mixing rate and mixing time on nanocomposite structure and properties have been investigated. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the interlayer distance of nanoparticle layers increased and a partially intercalated structure was prepared by melt intercalation method. Interaction between polyethylene chains and nanoparticle layers could be improved if the control of above parameters causes to penetrate the chains into nanoclay layers; by an optimization, this effect could improve the physical and mechanical properties. The DSC data revealed that melting temperature has slowly increased and crystalinity has lightly decreased. Consequently we can claim the thermal properties of LDPE/clay nanocomposite did not considerably change with clay content. A rise in the mechanical properties such as yield stress and modulus was observed by tension test; by addition of 5% clay content the tensile strength increased about 7%, the tensile modulus enhanced about 60% and the yield stress increased about 16% in comparison with the pure LDPE.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

Preparation of hydrophobic organic-silicanano composites

In this paper, we use silica nanoparticles modified by methacryloxy propyl trimethoxylsilane (KH570) as the core material, and employ polymers including hexafluorobutyl methacrylate (HFMA), dodecafluoroheptyl methacrylate (DFMA) and acrylic ester as the shell materials to prepare the hydrophobic inorganic–organic hybrid nanocomposites with a seed emulsion polymerization strategy. The size, morphologyandproperties of the core-shell structured nanoparticles are investigated by TEM and SEM. The results showthat the polymer nanocomposite has three concentric layers with silica nanoparticles in the center, acrylic polymer as the internal shell and fluorosilicone polymer as the outmost shell. By controlling the ratio of the silica nanoparticles and monomers, we can achieve each composite particle has the core-shell structure with silica nanoparticles as the core and the thin layer of fluorosilicone polymer as the shell. Compared with the traditional polymer film, the nanocomposite film shows a hydrophobic property with a contact angle of up to 100 degree. Therefore, it is feasible to prepare hydrophobic organic–inorganic nanocomposites using the method proposed here.     

Mechanical and dielectric properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites were prepared using two types of surface-treated montmorillonite (Closite 30B and Nanomer I28E). Wide angle X-ray scattering showed that all the nanocomposites had an intercalated structure. Improvements in tensile and fracture properties were found. The pure epoxy polymer was very brittle with a fracture energy, G _c, of 131 J m^?2. The addition of the nanoclays significantly increased the value of G _c, up to 240 J m^?2 for 5 wt% C30B. The toughening mechanisms acting in the nanocomposites were identified using scanning electron microscopy as crack deflection and plastic deformation of the epoxy matrix around the clay platelets following debonding. From electrical testing, the permittivity and loss angle of the nanocomposites decreased, and their breakdown strength increased as desired for insulation applications. The breakdown strength of the pure epoxy was found to be 11.7 kV mm^?1, while for a 2 wt% C30B nanocomposite, it increased to 14.7 kV mm^?1. It was concluded that the restriction of chain mobility inhibited electrical polarisation and thus decreased the permittivity and loss angle. The electrical damage zone was analysed using scanning electron microscopy. It was found that the higher resistance-to-surface degradation by partial discharges and the creation of a tortuous electrical path, which delayed the propagation of the electrical tree, were the main factors which improved the breakdown strengths of the nanocomposites.