Role Of Organoclay Research Articles

The role of organoclay in the diffusion of epoxy‐amine oligomers and in the cross‐linking density of the resulting network

AbstractEpoxy nanocomposites are promising for adhesive applications due to their high performance. In this work, an organoclay (PO), prepared by cationic exchanging using a quaternary phosphonium salt or a silylated PO (SPO) was added to an epoxy‐amine resin‐based adhesive to reduce its dripping. PO and SPO were dispersed in the epoxy network on a nanometric scale, mainly in an intercalated structure. A liquid‐to‐gel transition occurs at 4–6 wt% PO due to forming a continuous organoclay network throughout the epoxy volume, eliminating its dripping. The PO addition accelerates the curing reaction initially, and cured nanocomposites with over 3 wt% PO show a drastic reduction in the glass transition temperature (Tg). Moreover, a broadening of the secondary relaxation observed by DMA indicates an interaction between the epoxide‐amine oligomers with the silicate surface. This interaction, associated with forming a continuous organoclay network at 4–6 wt% PO, reduces the epoxy‐amine oligomers diffusion, resulting in their partial curing and consequent Tg decreasing. EPOXY_SPO nanocomposites show Tg values similar to or higher than that observed for the epoxy‐amine network attributed to the forming of covalent bonds between the glycidyloxypropyl end groups in the SPO surface and the hardener amine.

The role of organoclay on the properties of Polymethylsilsesquioxane: A systematic study

ABSTRACTIn this study, an attempt is made to improve the properties of PMSQ, an organosilicone polymer which possesses distinguished properties, through an easy and facile route by the inclusion of organically modified montmorillonite clay. PMSQ-clay composites were prepared by solution blending of the components initially and then heat curing under load. The effect of clay content, varied at 5–40 wt.%, on mechanical, thermal and dynamic mechanical properties was evaluated and the optimum was obtained for 20%. Morphology investigation as well as microstructure analysis revealed intercalated to exfoliated morphology of PMSQ-clay composite. An appreciable improvement in mechanical properties of PMSQ, compressive strength and impact strength in particular, was achieved by clay inclusion up to 20%. The properties declined at ≥ 30% clay loading. The composites showed increased thermal stability compared to unmodified PMSQ up to 400 °C. Also, increase in clay content accelerated conversion to ceramic SiOC. PMSQ-clay composites exhibited good visco-elastic characteristics with higher Tg probably due to enhanced polymer-clay interactions. Thus, a simple and viable method to enhance the mechanical and thermal characteristics of PMSQ by way of preparing its composite with the reinforcing filler organoclay is demonstrated here.

Morphology Control and Stabilization in Immiscible Polypropylene and Polyamide 6 Blends with Organoclay

Abstract In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.

Role of Organoclay in Controlling the Morphology and Crystal‐Growth Behavior of Biodegradable Polymer‐Blend Thin Films Studied Using Atomic Force Microscopy

This study reports the effect of organically modified nanoclay on the morphology and crystal‐growth behavior of biodegradable polylactide/poly[(butylene succinate)‐co‐adipate] (PLA/PBSA) blend thin films with the average thickness of 280 nm. The neat and organically modified blended thin films were cast on silicon (001) substrate using a spin coater. Blended composite thin films with three different types of organically modified clays were prepared, and the impact of the nature of the pristine clays, their organic modifications and their initial d001‐spacing on the morphology and crystal‐growth behavior of the PLA/PBSA blend were studied. An atomic force microscopy equipped with a hot‐stage scanner was used to examine the crystalline morphology of the thin films. The morphology and crystal‐growth behavior of the films were investigated during in situ annealing and cooling from melt. The results indicated that the initial d001‐spacing of the organoclay plays a pivotal role in controlling the morphology of the dispersed phase and hence the crystal‐growth behavior.

Resistance to fire of intumescent silicone based coating: The role of organoclay

The fire performance of a curable-silicone based coatings containing expandable graphite (EG) and an organoclay is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. It is shown that the use of organoclay allows achieving better performance. The influence of the clay as additional filler is investigated on the fire performance and on the mechanical properties of the char. It is shown that the clay increases significantly the mechanical properties of the char and hence, the fire performance of the silicone based coating. In a next part, the silicone/clay material was characterized by electron microscopy, wide-angle X-ray scattering and solid state 29Si nuclear magnetic resonance (NMR). It evidences the nanodispersion of the clay into the silicone matrix and two main interactions: (i) intercalation of some silicate layers and (ii) chemical reactions between the hydroxyl groups of the clay and the silicone matrix. Finally, X-ray fluorescence of the residue after fire testing shows the organoclay is present uniformly throughout the thickness of the char, due to the previous interaction, and hence increasing the cohesion of the char.

The Role of Organoclay on In-situ Microfibril Formation of Epoxy in Poly(butylene terephtalate) Nanocomposites

Abstract The main objective of the present work was to study the role of organoclay on the microfibrillation process of epoxy phase in Poly(butylene terephtalate), PBT, matrix both in presence and absence of epoxy curing agent. The PBT/epoxy blend samples with constant blend ratio (60/40) were prepared by melt mixing in a twin screw extruder. The elongational flow imposed by drawing the extrudate at the die exit permitted controlled generation of fibrile morphology of the dispersed epoxy phase, with a fiber diameter of 0.8 μm and an aspect ratio greater than 100. It was shown that when the curing agent was added into the extruder, its reactivity with epoxy at high temperature was high enough and selectively affected on the epoxy phase. The SEM results showed smaller epoxy droplet size for samples containing nanoclay compared to simple blends. This could be explained in terms of hindrance effect of nanoclay in reducing the coalescence as a dominating parameter due to presence of nanoclay in both phases. These results were supported by the melt linear viscoelastic results which showed enhanced low frequency viscosity and storage modulus for these samples. Addition of nanoclay was found to have little effect on extent of fibrillation epoxy droplet in stretched samples. The rheological results obtained for stretched samples showed very strong increase in low frequency solid body response whose extent was increase with increasing draw ratio. This mainly attributed to special 3-D network formed between microfibrils whose shape was stabilized by either presence of nanoclay or accelerated curing process of fibrillated epoxy. From SEM micrographs and linear viscoelastic measurements it can be deduced that curing process has small changes on the extent of fibrillation epoxy droplet in stretched samples. But it leads to improvement of interfacial interaction between two phases in the nanocomposites.

Recent Developments in PA6/PP Nanocomposites

An overview of the recent developments in PA6/PP blend nanocomposites is presented in this paper with an emphasis on their mechanical, thermal and morphological properties. The role of organoclay as a reinforcing agent and polyethylene octene (POE) as an elastomer are discussed in detail. The organoclay increases the strength and stiffness while the POE elastomer increases the impact toughness of the nanocomposites. The effects of various parameters such as PA6/PP blend ratio, organoclay loading and the concentration of elastomer on the nanocomposites properties are also examined. The exfoliated state of organoclay platelets along with the fine particle size and uniform dispersion of POE demonstrate the nanocomposite with improved properties. These materials are attracting considerable interest in polymer research community because they exhibit substantial improvement in properties at low filler contents.

The role of organoclay and matrix type in photo-oxidation of polyolefin/clay nanocomposite films

In this paper the photo-oxidation behaviour of polyolefin/clay nanocomposite films was studied; in particular, the effect of the amount of organo-modifier and the matrix polarity on the photo-oxidation was investigated. Two different organo-modified clays and compositions of LDPE/EVA blend films were used and the photo-oxidation was followed by mechanical and spectroscopic analyses. The organoclay and matrix type strongly influence the photo-oxidative behaviour of nanocomposite films. The films filled with CL15A show a faster loss of mechanical performance and higher carbonyl formation with respect to the films filled with the CL20A. Additionally, the LDPE based nanocomposite undergoes photo-oxidation more rapidly than the EVA based one.

The role of organoclay in promoting co-continuous morphology in high-density poly(ethylene)/poly(amide) 6 blends

The effect of organically modified clay on the morphology, rheology and mechanical properties of high-density polyethylene (HDPE) and polyamide 6 (PA6) blends (HDPE/PA6=75/25 parts) is studied. Virgin and filled blends were prepared by melt compounding the constituents using a twin-screw extruder. The influence of the organoclay on the morphology of the hybrid was deeply investigated by means of wide-angle X-ray diffractometry, transmission and scanning electron microscopies and quantitative extraction experiments. It has been found that the organoclay exclusively places inside the more hydrophilic polyamide phase during the melt compounding. The extrusion process promotes the formation of highly elongated and separated organoclay-rich PA6 domains. Despite its low volume fraction, the filled minor phase eventually merges once the extruded pellets are melted again, giving rise to a co-continuous microstructure. Remarkably, such a morphology persists for long time in the melt state. A possible compatibilizing action related to the organoclay has been investigated by comparing the morphology of the hybrid blend with that of a blend compatibilized using an ethylene–acrylic acid (EAA) copolymer as a compatibilizer precursor. The former remains phase separated, indicating that the filler does not promote the enhancement of the interfacial adhesion. The macroscopic properties of the hybrid blend were interpreted in the light of its morphology. The melt state dynamics of the materials were probed by means of linear viscoelastic measurements. Many peculiar rheological features of polymer-layered silicate nanocomposites based on single polymer matrix were detected for the hybrid blend. The results have been interpreted proposing the existence of two distinct populations of dynamical species: HDPE not interacting with the filler, and a slower species, constituted by the organoclay-rich polyamide phase, which slackened dynamics stabilize the morphology in the melt state. In the solid state, both the reinforcement effect of the filler and the co-continuous microstructure promote the enhancement of the tensile modulus. Our results demonstrate that adding nanoparticles to polymer blends allows tailoring the final properties of the hybrid, potentially leading to high-performance materials which combine the advantages of polymer blends and the merits of polymer nanocomposites.