Novel in situ polydimethylsiloxane-sepiolite nanocomposites: Structure-property relationship

Effect of the Welan Gum Concentration on the Rheological and Structural Behaviour of Biocomposite Hydrogels with Sepiolite as Filler

A very positive and effective approach to tuning the mechanical properties of polymers has been the development of composites. This paper deals with novel biocomposite hydrogels composed by two biocompatible materials: welan gum as biopolymer matrix and sepiolite as filler. Welan gum content was studied as a tuning parameter to control the rheological properties of the developed biocomposites. The rheological and microstructural behaviour of the composites was investigated by mean of steady-state flow curves, creep-recovery tests, small amplitude oscillatory shear tests, and electron microscopy. An increase in welan gum content provoked the progressive disappearance of the shear-thinningzero-shear-thinning behaviour with a yield point which was clearly defined, characteristic of sepiolite gels, leading to a conventional shear-thinning behaviour, typical of polymeric systems. Also, a higher content of biopolymer in the mixtures led to a more elastic and compact structure characterized by higher values of both G' and G". The fundamental novelty was based on taking the flowability provided by the biopolymer as the main objective and reinforcing the viscosity yielded by welan gum with sepiolite, which contributed to increasing the biocomposite consistency. Thus, rheological properties can be adjusted, taking into account the balance of the components to adapt them to the requirements of each application.

Preparation and characteristics of sepiolite-waterborne polyurethane composites

A kind of organic/inorganic composite material composed of waterborne polyurethane and sepiolite was prepared in this work. Sepiolite was organically modified by three kinds of silane coupling agents, and then compounded with waterborne polyurethane through layer-by-layer method in order to prepare composite materials. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) show the crystal and chemistry structure of sepiolite samples, and confirmed the preparation of organic sepiolite. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) showed the surface microstructure and elemental content of sepiolite and organic sepiolite, and was consistent with the XRD results. Transmission electron microscope (TEM) examination of waterborne polyurethane composites surfaces showed that sepiolite particles were regularly dispersed in the waterborne polyurethane matrix. Thermal resistance of waterborne polyurethane composites was determined by thermogravimetry analyzer (TG) and derivative thermogravimetry analyzer (DTG), differential scanning calorimetry (DSC), gas chromatography (GC), and mass chromatography (MS). Mechanical behavior was examined by tensile strength tester, showed higher break strength than that of the control waterborne polyurethane. Therefore, organically modified sepiolite was considered to be a kind of wonderful inorganic material that could be used to improve the thermal stability and mechanical property of polymer.

A comparative study between two novel silicone/graphene-based nanostructured surfaces for maritime antifouling

Two novel superhydrophobic nanocomposite series of polydimethylsiloxane (PDMS) enriched with reduced graphene oxide (RGO) and graphene oxide/boehmite nanorods (GO-γ-AlOOH) nanofillers were synthesized as maritime fouling-release (FR) surfaces. Controlling the nanofillers' structures and distribution in the silicone matrix influenced the self-cleaning and antifouling properties. γ-AlOOH nanorods had a single crystallinity with an average diameter of 10-20 nm and < 200 nm length. A hydrothermal method was used to prepare RGO, while the chemical deposition method was used to synthesis GO-γ-AlOOH nanocomposites for use as fouling-release coating materials. For studying the synergetic effects of graphene-based materials on the surface, mechanical, and FR features, these nanofillers were dispersed in the silicone matrix using the solution casting method. The hydrophobicity and antifouling properties of the surface were studied using water contact angle (WCA), scanning electron, and atomic force microscopes (SEM and AFM). Coatings' roughness, superhydrophobicity, and surface mechanical properties all improved for the homogeneity of the dispersion of the nanocomposite. Laboratory assessments were carried out for 30 days using selected microorganisms to determine the antifouling effects of the coating systems. PDMS/GO-γ-AlOOH nanorod composite had better antibacterial activity than PDMS/RGO nanocomposite against different bacterial strains. This is caused by the high surface area and stabilizing effects of the GO-γ-AlOOH hybrid nanofillers. The PDMS/GO-γ-AlOOH nanorod composite (3 wt%) had the lowest biodegradability percentage (1.6%) and the microbial endurability percentages for gram-positive, gram-negative, and fungi were 86.42%, 97.94%, and 85.97%, respectively. A field trial in natural seawater was conducted to confirm the coatings' FR performance based on the screening process and image analysis for 45 days in a tropical area. The most profound superhydrophobic antifouling nanostructured coating was the homogeneity of the GO-γ-AlOOH (3 wt%) dispersion, which had a WCA of 151° and a rough surface.

Controlled Methodology for Development of a Polydimethylsiloxane-Polytetrafluoroethylene-Based Composite for Enhanced Chemical Resistance: A Structure-Property Relationship Study

Polydimethylsiloxane (PDMS) polymers are highly appreciated materials that are broadly applied in several industries, from baby bottle nipples to rockets. Momentive researchers are continuously working to understand and expand the scope of PDMS-based materials. Fluorofunctional PDMS has helped the world to apply in specialty applications. Efforts are taken to develop such siloxane-fluoropolymer composite materials with good thermal, solvent, and chemical resistance performances. We leveraged inherently flexible PDMS as the model matrix, whereas polytetrafluoroethylene (PTFE) was used as the additive to impart the functional benefits, offering great value in comparison to the individual polymers. The composites were made at three different mixing temperatures, that is, 0-35 °C, and different loadings of PTFE, that is, 0.5-8% (w/w), were selected as the model condition. A strong dependency of the mixing temperature against the performance attributes of the developed composites was noted. Mechanical and thermal stability of the composites were evaluated along with optical properties. X-ray diffraction demonstrated the change in the crystallite size of the PTFE particles as a function of processing temperature. Compared to the phase II crystallite structure of the PTFE, the fibrils formed in phase IV imparted a better reinforcing capability toward the PDMS matrix. A synergistic balance between higher filler loading and mechanical properties of the composite can be achieved by doping the formulation with short-chain curable PDMS, with 238% increment of tensile strength at 8 wt % PTFE loading when compared to the control sample. The learning was extended to check the applicability of doping such PTFE powder in commercial liquid silicone rubber (LSR). In the window of study, the formulated LSR demonstrated improved mechanical properties with additional functional benefits like resistance toward engine oil and other chemical solvents.

The Influence of Melt-Mixing Conditions and State of Dispersion on Crystallisation, Rheology and Mechanical Properties of PCL/Sepiolite Nanocomposites

It is generally accepted that the benefit of anisotropic nanofiller addition is strongly dependent on the state of the dispersion of these fillers in a polymer matrix. In this paper the influence of melt-compounding conditions on the dispersion of a needle-like clay, i. e. sepiolite, in poly(∊-caprolactone) (PCL) is investigated. The crystallisation behavior as well as the rheological and mechanical properties of PCL/sepiolite nanocomposites with filler contents up to 5 wt.% are studied. By changing the screw speed during melt-mixing in a micro-compounder, the state of dispersion was varied, with the higher speed leading to better dispersion and breakdown of the sepiolite agglomerates or bundles. Rheometry showed that better dispersed nanocomposites displayed an increase in viscosity due to network formation at slightly higher filler loadings. Likewise, better dispersed composites showed a modest increase in crystallisation temperature at low filler content, accompanied by a decrease in both nucleation efficiency and degree of crystallisation at higher loadings. Better dispersed nanocomposite systems also showed superior mechanical properties, particularly at higher filler loadings. However, overall the reinforcing efficiency of sepiolite in all nanocomposites was relatively low. This was mainly a consequence of the relatively low filler aspect ratio and the simultaneous breakup of sepiolite needles together with a breakdown of bundles during compounding.

Progress in biomimetic leverages for marine antifouling using nanocomposite coatings

Because of the environmental and economic casualties of biofouling on maritime navigation, modern studies have been devoted toward formulating advanced nanoscale composites in the controlled development of effective marine antifouling self-cleaning surfaces.

Kinetic and thermodynamic properties of purified alkaline protease from Bacillus pumilus Y7 and non-covalent immobilization to poly(vinylimidazole)/clay hydrogel

The characterization of the hydrogel was performed using Fourier‐transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Purified Bacillus pumilus Y7‐derived alkaline protease was immobilized in Poly (vinylimidazole)/clay (PVI/SEP) hydrogel with 95% yield of immobilization. Immobilization decreased the pH optimum from 9 to 6 for free and immobilized enzyme, respectively. Temperature optimum 3°C decreased for immobilized enzyme. The K_m, V_m, and k_cat of immobilized enzyme were 4.4, 1.7, and 7.5‐fold increased over its free counterpart. Immobilized protease retained about 65% residual activity for 16^th reuse. The immobilized protease endured its 35% residual activity in the material after six cycle's batch applications. The results of thermodynamic analysis for casein hydrolysis showed that the ΔG^≠ (activation free energy) and ΔG^≠_E‐T (activation free energy of transition state formation) obtained for the immobilized enzyme decreased in comparison to those obtained for the free enzyme. On the other hand, the value of ΔG^≠_ES (free energy of substrate binding) was observed to have increased. These results indicate an increase in the spontaneity of the biochemical reaction post immobilization. Enthalpy value of immobilized enzyme that was 2.2‐fold increased over the free enzyme indicated lower energy for the formation of the transition state, and increased ΔS^≠ value implied that the immobilized form of the enzyme was more ordered than its free form.

Selective Orientation of Needlelike Sepiolite Nanoclay in Polymer Blend for Controlled Properties

Sepiolite nanoclay needles have been selectively localized either in the natural rubber (NR) phase or in the carboxylated nitrile rubber (XNBR) phase of the XNBR/NR (50/50) blend prepared by the solution casting method. In a systematic manner, the role of the difference value between the interaction parameter of individual blend components (NR or XNBR)/solvent and the interaction parameter of sepiolite nanoclay/solvent in selectively localizing the sepiolite nanoclay to the NR phase or the XNBR phase of the XNBR/NR (50/50) blend has been explored. A higher percentage of sepiolite nanoclay resides in the dispersed NR phase when the difference value between the interaction parameter of NR/solvent and the interaction parameter of sepiolite nanoclay/solvent is lower than the difference value between the interaction parameter of XNBR/solvent and the interaction parameter of sepiolite nanoclay/solvent. On the other hand, a higher percentage of sepiolite nanoclay resides in the continuous XNBR phase when the difference value between the interaction parameter of XNBR/solvent and the interaction parameter of sepiolite nanoclay/solvent is lower than the difference value between the interaction parameter of NR/solvent and the interaction parameter of sepiolite nanoclay/solvent. It has been shown that by judiciously choosing different solvent combinations to prepare the blend and to disperse nanoclay, it is possible to fine-tune the difference value between the interaction parameter of individual blend components (NR or XNBR)/solvent and the interaction parameter of sepiolite nanoclay/solvent and dictate the selective localization of sepiolite nanoclay to the NR phase or the XNBR phase of XNBR/NR (50/50) blend. This study shows that it is possible to generate a rubber blend with controlled properties by selectively localizing needlelike sepiolite nanoclay in the dispersed phase or the continuous phase of the rubber blend prepared by the solution casting method.

Linseed oil-based alkyd/Cu2O nanocomposite coatings for surface applications

An ecofriendly series of linseed oil based hyperbranched alkyd/Cu₂O-nanocube composites was developed as a modern stream for surface coating applications.

Silicone/Ag@SiO2core–shell nanocomposite as a self-cleaning antifouling coating material

The effects of Ag@SiO₂ core–shell nanofiller dispersion and micro-nano binary structure on the self-cleaning and fouling release (FR) in the modelled silicone nano-paints were studied. An ultrahydrophobic polydimethylsiloxane/Ag@SiO₂ core–shell nanocomposite was prepared as an antifouling coating material. Ag@SiO₂ core–shell nanospheres with 60 nm average size and a preferential {111} growth direction were prepared via a facile solvothermal and a modified Stöber methods with a controlled shell thickness. Ag@SiO₂ core–shell nanofillers were inserted in the silicone composite surface via solution casting technique. A simple hydrosilation curing mechanism was used to cure the surface coating. Different concentrations of nanofillers were incorporated in the PDMS matrix for studying the structure–property relationship. Water contact angle (WCA) and surface free energy determinations as well as atomic force microscopy and scanning electron microscope were used to investigate the surface self-cleaning properties of the nanocomposites. Mechanical and physical properties were assessed as durability parameters. A comparable study was carried out between silicone/spherical Ag@SiO₂ core–shell nanocomposites and other commercial FR coatings. Selected micro-foulants were used for biological and antifouling assessments up to 28 days. Well-distributed Ag@SiO₂ core–shell (0.5 wt%) exhibited the preferable self-cleaning with WCA of 156° and surface free energy of 11.15 mN m⁻¹.

The effects of Ag@SiO₂ core–shell nanofiller dispersion and micro-nano binary structure on the fouling release of silicone paints were studied. An ultrahydrophobic PDMS/Ag@SiO₂ core–shell nanocomposite was prepared as an antifouling coating material.

Silicone-Based Adhesives with Highly Tunable Adhesion Force for Skin-Contact Applications

A fundamental approach to fabricating silicone-based adhesives with highly tunable adhesion force for the skin-contact applications is presented. Liquid blends consisting of vinyl-multifunctional polydimethylsiloxane (V-PDMS), hydride-terminated PDMS (H-PDMS), and a tackifier composed of a silanol-terminated PDMS/MQ resin mixture and the MQ resin are used as the adhesive materials. The peel adhesion force of addition-cured adhesives on the skin is increased by increasing the H-PDMS molecular weights and the tackifier content, and decreasing the H-PDMS/V-PDMS ratio. There is an inverse relationship between the adhesion force and the Young's modulus. The low-modulus adhesives with a low H-PDMS/V-PDMS ratio exhibit enhanced adhesion properties. The low-modulus adhesives with the high MQ resin content show significantly enhanced adhesion properties. These adhesives exhibit a wide range of modulus (2-499 kPa), and their adhesion force (0.04-5.38 N) is superior to commercially available soft silicone adhesives (0.82-2.79 N). The strong adhesives (>≈2 N) provide sufficient adhesion for fixing the flexible electrocardiogram (ECG) device to the skin in most daily activity. The human ECG signals are successfully recorded in real time. These results suggest that the silicone-based adhesives should be useful as an atraumatic adhesive for the skin-contact applications.

Morphology, thermal and mechanical performances of SR composites containing sepiolite and HGMs as binary fillers

Binary fillers-filled silicone rubber (SR) matrix composites are prepared to improve the thermal and mechanical properties of SR as a lightweight thermal insulating material. Sepiolite and hollow glass microspheres (HGMs) can be evenly dispersed in SR matrix to obtain SR/sepiolite/HGM composites with superior performances at amounts of around 7.5 parts per hundreds of rubber (phr) and 20 phr, respectively, as observed from scanning electron microscopy (SEM). The density of the composites increases slightly with the addition of sepiolite in a linear trend, while the addition of HGMs results in the abrupt reduction in density lower than 0.7 g/cm3. Sepiolite exhibits a strengthening effect in the SR matrix; however, the addition of HGMs in this matrix slightly enhances the stress of the composite; its maximum elongation at break can increase up to 300%. The addition of sepiolite and HGMs improves the initial decomposition temperatures of SR composites a little; the excellent thermal insulating effect provided by HGMs is further verified by their significant decrease in thermal conductivity at 200°C, providing the facts that these SR/sepiolite/HGM composites can be used as lightweight materials for thermal insulating purposes.

EFFECT OF ORGANICALLY MODIFIED MONTMORILLONITE CLAY ON MORPHOLOGICAL, PHYSICOMECHANICAL, THERMAL STABILITY, AND WATER VAPOR TRANSMISSION RATE PROPERTIES OF BIIR-CO RUBBER NANOCOMPOSITE

Rubber nanocomposites based on bromobutyl rubber (BIIR), polyepichlorohydrin rubber (CO), carbon black (CB), and organically modified montmorillonite clay (NC) were prepared via melt compounding technique. Effects of NC dosage on various properties of the developed BIIR-CO nanocomposites were studied. Morphological characteristics of the BIIR-CO nanocomposite revealed a good level of clay dispersion. Scanning electron microscopy analyses of the tensile fractured surfaces of the nanocomposites revealed the existence of a good interaction between NC-CB. Hybrid microstructure development between NC and CB, clay exfoliation, and improved filler dispersion in the quaternary nanocomposite significantly contributed to the overall enhancement of properties. The addition of nanoclay increases the modulus up to 54%, tear strength up to 20%, and other physicomechanical properties of the rubber nanocomposite. However, higher nanoclay dose results in the agglomeration of clay particles predominantly. An increase in the volume fraction of nanoclay platelets depreciates the thermal degradation of the BIIR-CO nanocomposites. The tortuous path offered by NC is pivotal in the significant reduction in the water vapor transmission rate (up to 30% reduction). Contact angle measurements reveal the importance of nanoclay dispersion in subsiding the surface hydrophilic nature of the nanocomposite.

Tailored design of Cu2O nanocube/silicone composites as efficient foul-release coatings

Environmental concerns about the use of toxic antifoulants have increased the demand to develop novel, environmentally-friendly antifouling materials.

Elucidating and tuning the strain-induced non-linear behavior of polymer nanocomposites: a detailed molecular dynamics simulation study

By setting up a coarse-grained model of polymer nanocomposites, we monitored the change in the elastic modulus as a function of the strain, derived from the stress-strain behavior by determining uniaxial tension and simple shear of two typical spatial distribution states (aggregation and dispersion) of nanoparticles (NPs). In both these cases, we observed that the elastic modulus decreases non-linearly with the increase of strain and reaches a low plateau at larger strains. This phenomenon is similar to the so-called "Payne effect" for elastomer nanocomposites. Particularly, the modulus of the aggregation case is more sensitive to the imposed strain. By examining the structural parameters, such as the number of neighboring NPs, coordination number of NPs, root-mean-squared average force exerted on the NPs, local strain, chain conformations (bridge, dangle, loop, interface bead and connection bead), and the total interaction energy of NP-polymer and NP-NP, we inferred that the underlying mechanism of the aggregation case is the disintegration of the NP network or clusters formed through direct contact; however, for the dispersion case, the non-linear behavior is attributed to the destruction of the NP network or clusters formed through the bridging of adsorbed polymer segments among the NPs. The former physical network is influenced by NP-NP interaction and NP volume fraction, while the latter is influenced by NP-polymer interaction and NP volume fraction. Lastly, we found that for the dispersion case, further increasing the inter-particle distance or grafting NPs with polymer chains can effectively reduce the non-linear behavior due to the decrease of the physical network density. In general, this simulation work, for the first time, establishes the correlation between the micro-structural evolution and the strain-induced non-linear behavior of polymer nanocomposites, and sheds some light on how to reduce the "Payne effect".

Synthesis and characterization of a biocompatible monotyrosine-based polymer and its interaction with DNA

A monotyrosine based copolymer was synthesized, characterized and studied for its interaction with DNA for potential biological applications.

NOVEL IN SITU SILICA/POLYDIMETHYLSILOXANE NANOCOMPOSITES: FACILE ONE-POT SYNTHESIS AND CHARACTERIZATION

Synthesis of in situ silica/polydimethylsiloxane (PDMS) nanocomposites by using tetraethylorthosilicate (TEOS) as the precursor for silica and octamethylcyclotetrasiloxane for the polymer in presence of base was undertaken. Simultaneous generation of silica and polymer and dispersion of the nanofiller in the polymer have been reported for the first time. Fourier transform infrared spectroscopy was used as a tool to monitor the reaction conditions. The structure–property relationship of in situ silica/PDMS nanocomposites has been highlighted. Transmission electron microscopic studies reveal finest extent of dispersion of the in situ generated nanosilica, which is found to undergo polymorphic modification determined from wide-angle X-ray diffraction. Nanocomposites exhibit huge improvement in mechanical properties (&gt;150% improvement in tensile strength for just 2 phr TEOS-filled sample) and room temperature storage modulus (&gt;460% improvement in storage modulus for 8 phr TEOS-loaded sample). Polymer–filler interaction significantly improves oxidative thermal stability of the nanocomposites.