Micro-silica Fillers Research Articles

Synergistic Effect of Nano-Silica and Micro-Silica Fillers on the Rheological and Thermal Properties of Epoxy Resins

This article aims to improve nanofiller dispersion in epoxy resins by using an electrostatic disperser (ED), as well as reduce costs by using a combination of microfillers and nanofillers. The ED method aids in homogenized mixing of nanofillers in epoxy resin, due to its jet elongation and shearing effect on a polymer mix. In this article, two concentrations (7.5 wt% and 5 wt%) of nanosilica are used with resin, and the rheological properties of hybrid composites are tested before and after the addition of 50 wt% microsilica. It is observed that the electrostatic dispersion method aids in the network formation of nanosilica, unlike the high shear (HS) method, wherein clusters of nanosilica are formed. Hence, the ED method aids in reducing the viscosity values with the addition of microsilica, which is helpful in the product molding process. A plausible mechanism of filler dispersion is explained for ED and HS methods. The morphological analysis showed that the composites are brittle due to the high silica content, and that the silica fillers are dispersed well within the epoxy matrix. The flexural strength lies in the same range for both composites prepared using ED and HS methods. Thermal conductivity depends both on nanosilica and epoxy matrix dispersion, while heat deflection temperature, thermal diffusivity and specific heat depend on the dispersion method.

Investigation of Hydrothermally Stressed Silicone Rubber/Silica Micro and Nanocomposite for the Coating High Voltage Insulation Applications.

Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.

Chemical interaction of different sized fumed silica with epoxy via ultrasonication for improved coating

Blank epoxy coating (EC) and fumed silica epoxy composite coatings (SECCs) reinforced with different loading levels of nano- (7 nm) and micro (0.2-0.3 μm) silica were successfully prepared using ultrasonic technique. SEM analysis revealed a uniform dispersion of nano- and micro-silica fillers in the epoxy matrix up to 3 wt.% loading. It is found that ultrasonication results in permanent chemical bonding between epoxy resin and silica particles as investigated by FT-IR spectroscopy and DSC. Quantitative FTIR generally reveals that nano-silica shows more participation in chemical bonding to epoxy than micro-silica. Coated steel panels with either EC or SECCs were evaluated with regard to surface wettability, corrosion resistance, thermal stability and mechanical properties. Micro-silica treated coatings show enhanced hydrophobicity in contrast to nano-silica samples as revealed by contact angle measurements. Results of salt spray test and thermogravimetric analysis indicate that the addition of nano-silica show improved corrosion resistance and thermal stability of the epoxy coating compared to micro-silica. The mechanical properties namely scratch hardness, adhesion, impact strength and abrasion resistance were also improved in the same manner.

On Nanoparticles Release from Polymer Nanocomposites for Applications in Lightweight Automotive Components

Nano and micro reinforced glass fibre-polymer composites have been manufactured to investigate different effect such as filler type, filler size and matrix materials on the particle emission during low velocity impact test. Nano and micro- silica, as well as nanoclay reinforced crash cones were prepared with a two step extrusion process and final injection moulding of the structures. The addition of secondary filler into the glass-fibre reinforced polymer composites had significant influence on the mechanical behaviour of the material as well as on the particle emission. In general, nano and ultrafine airborne particles were emitted from all investigated materials. However, composite filled with nanoclay emitted higher amounts of particles than those filled with nano and microsilica. One reason for the increase of particle emission of the nanoclay filled composites was the change of the failure behaviour of the matrix. However, similar results of particle emission were obtained for both nano and microsilica fillers, which in general did not vary significantly from the results obtained from traditionally reinforced glass fibres polymer composites.

Lewis acidic polypropylene for compatibilization of polypropylene/microsilica composites

Polypropylene (PP) was compounded with submicron size silica filler particles (microsilica, μSi) up to 30 wt-%. In addition, three external compatibilizers, with characteristic functionalities, were studied to examine their influence in the mechanical properties of the PP/μSi composites. As a result, the modulus of the composite increased while the other tensile values deteriorated in correlation with increased filler concentration. The addition of an external compatibilizer reduced this deterioration, but the reduction was dependent on the type of the compatibilizer used. The influence of an acid functionalized compatibilizer was unsubstantial while the fluorosilane and the Lewis acidic phenylsilane functionalized polypropylenes acted as effective compatibilizers. In addition to examining the tensile properties, the toughness of the composites was evaluated as well. The microsilica filler was found to act as toughening agent since the Brittle-to-Ductile transition point of the composite increased by 2-3 orders of magnitude at high filler concentrations. However, this increase in the toughness was rapidly lost when an effective compatibilizer was used to bind the filler with the matrix. This observation was consistent with the common understanding of the filler toughening mechanism, where particle-matrix debonding is a prerequisite for facilitating the plastic stretch of the polymer ligaments between filler particles. In our case, however, the few filler aggregates in the polymer matrix also played a crucial role. While in uncompatibilized composites the filler aggregates remained passive (could not be seen at the fracture surface), the addition of an effective compatibilizer activated these aggregates to promote crack initiation and/or propagation. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Phenylsilane; unreactive group in the metallocene/MAO catalyzed copolymerization of propylene and 7-octenyldimethylphenylsilane, reactive group in melt blending with microsilica filler

In this study, 7-octenyldimethylphenylsilane (7-SiPh) was copolymerized with propylene using Me 2Si(2-Me-4-Ph-1-indenyl) 2ZrCl 2/MAO as a catalyst. The copolymerization behaviour of the silicon-containing monomer, 7-SiPh, was compared with that of 1-dodecene, which is known to be incorporated in polypropylene (PP) using metallocenes. Both comonomers were well incorporated and randomly distributed in the main chain and had no marked influence either on the tacticity or the molar mass of the PP. In the next step, the reactivity of the synthesised polypropylene-co-octenyldimethylphenylsilane (PP-co-SiPh) was increased by post-treatment with HBF 4 to give the highly reactive fluorosilane form (PP-co-SiF). The reactivities of the post-treated form, PP-co-SiF, as well of the untreated copolymer, PP-co-SiPh, were tested by using them as modifiers (0.1–0.4 phr) in composites of commercial polypropylene and microsilica (μSi 1–4 phr). When PP-co-SiF was the modifier the influence on the morphology of the composite was negligible. However, the crystallization temperature of the PP matrix was found to increase >8 °C at most, indicating an increased adsorption of the polymer on the filler surface. Most interestingly, the untreated PP-co-SiPh showed almost the same influence on the properties of the composites, indicating an interaction/reactivity between the (hexyl)dimethylphenylsilane side group and the microsilica filler. The suspected reactivity was separately confirmed by successful coating of microsilica filler with molecular trimethylphenylsilane. The phenylsilane was found to react in a manner similar to how the halosilanes react with the hydroxyl groups at the silica surface. To our knowledge, this reaction is reported for the first time.

Silane Functionalized Ethylene/Diene Copolymer Modifiers in Composites of Heterophasic Polypropylene and Microsilica

Ethylene/1,7-octadiene copolymer was polymerised with metallocene catalyst and hydrosilylated to form silane functionalised polyethylenes (PE-co-SiX, X=Cl, OEt, Ph). The functionalised species were tested as modifiers in composites of rubber toughened polypropylene (heterophasic PP, hPP) and microsilica filler (μSi). A metallocene-based functionalised PE (PE-co-SiF) produced earlier in our laboratory and three commercial grades of functionalised polyolefins (one PE- and two PP-based) were used as reference modifiers. Major differences were seen in the toughness of the composites both above and below the glass transition temperature (Tg) of PP. In addition to increasing the stiffness, the microsilica filler enhanced the toughness of the heterophasic polypropylene by over 200% at ambient temperature. Below the Tg of PP (at −20 °C), the influence of μSi was the opposite and the impact strength of the hPP/μSi composite was below that of unfilled hPP. With the addition of just 2 wt% of functionalised polyethylene, the poor cold toughness of hPP/μSi composite was improved by nearly 100%. With the same addition, the toughness of the composites at ambient temperature was improved by 50 to 100% compared with the unfilled hPP. This behaviour was explained by significant changes in the fracture mechanism. Addition of functionalised PE increased the concentration of microsilica in the rubbery phase, allowing the crack to enter that phase. The rubbery phase was also able to absorb a large amount of impact energy below the glass transition temperature of PP.

Thermal Properties of Microsilica and Nanosilica Filled Polypropylene Composite with Epoxy as Dispersing Aid

Nanocomposite materials differ from the traditional composite materials in that they provide enhanced properties at comparatively low filler loading with respect to microsize filler. In this research work, silica filled polypropylene micro and nanocomposites were prepared and compared in terms of their thermal properties. Both composites were prepared by the melt blending method using a Thermo Haake internal mixer. Later, the epoxy resin was used as a dispersing aid to improve the adhesion between silica and polypropylene. For comparison purposes, 1% and 2% w/w of nanosilica filler is assumed to be comparable to 10% and 20% w/w of microsilica filler. Both composites at various compositions of fillers were subjected to thermal analysis including differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). From DSC analysis, the melting point of micro and nanocomposites remain almost the same as neat polypropylene. By adding the nanosize filler into the composite system, an increase in the degree of crystallinity was observed. In general, the nanocomposites exhibited comparable or better properties over the microcomposites. The employment of epoxy resins as a dispersing aid has adversely affected the properties of the composites (i.e., nano and microcomposites). However, the results were encouraging at relatively low levels of filler loading.

Approach by Nano- and Micro-filler Mixture toward Epoxy-based Nanocomposites as Industrial Insulating Materials

The main contribution of this paper is to show the realizability of epoxy-based nanocomposites as industrial insulating materials. The nano- and micro-filler mixture was invented to boost the nanocomposite in industrial insulating materials. Nano- and micro-filler mixture composites were newly made by dispersing a few weight-percentages of nano-filler and approximately 60 weight-percentages of micro-silica fillers in epoxy resin. Two kinds of nano-filler were used, such as layered silicate and silica. Experimental results demonstrated that the approach by nano- and micro-filler mixture enables the nanocomposite to have not only superior insulation properties but also the same low thermal expansion in comparison with the conventional filled epoxy (approximately 60 weight-percentages of micro-silica loading). Moreover, the nano-silica and micro-filler mixture composite has the desired properties of resin viscosity and curing reaction whereas the layered silicate and micro-filler composite has higher resin viscosity and faster curing reaction than those of the conventional filled epoxy due to modifier ions of layered silicates. Consequently, the nano-silica and micro-filler mixture composite is presently the closest to the epoxy-based nanocomposite as an industiral insulation material.

Effect of Nano-and Micro-Silica Fillers on Polyurethane Foam Properties

Two series of rigid and flexible polyurethane foams were prepared with two types of silica fillers. The density of the flexible foams was 60 kg/m 3 and that of rigid 30 kg/m3. The fillers were micro-silica of the average particle size of 1.5 mm and nano-silica of the average particle size of 12 nm. The concentration of fillers varied from 0–20%. The micro-silica filler did not show any significant effect on density of either rigid or flexible foams. Nano-silica increased the density of both types of foams only at concentration above 20%. Nano-silica lowered the compression strength of both types of foams at all concentrations while micro-silica exhibited the same effect at concentrations above 10%. The hardness and compression strength in flexible polyurethane foams with nano-silica was increased and the rebound resilience decreased. Reduced density of foams was not changed by nano-silica concentrations up to 20%. It is assumed that the nano-filler, as an additional physical crosslinker, increased modulus of the flexible segment in the polyurethane matrix, resulting in increased hardness and compression strength. The micro-filler in flexible foams lowered hardness and compression strength, but increased rebound resilience. Wide angle X-ray scattering (WAXS) showed amorphous morphology of both flexible and rigid foams filled with nano-silica. WAXS of the micro-silica filled foams showed the presence of randomly oriented crystalline quartz particles and the amorphous structure of the polymeric matrix.