Treated silica fillers

The moisture resistance properties of filled molding compounds are enhanced by the treatment of the fillers with silane adhesion promoters prior to compounding. Silane promoters on wollastonite fillers in thermoplastic polyester molding compounds (50 percent filled) will improve the flexural strength after 16 h in 50°C water by as much as 40 percent. Silane-treated silica fillers have been found to significantly increase the moisture resistance of epoxy adhesives used in the electronics industry for chip, surface-mounted, and printed-circuit processes.8... 

Aziz et al. [55] advocated that the water absorption of the PDMS elastomers might depend on the surface-treated filler component. Presence of hydrophilic, non-surface-treated silica fillers in the polymer matrix, increase the water uptake of the material (Cosmesil St, Prestige). The presence of -OH groups on the surface of the silica fillers helps to absorb water into the polymer matrix [57]. In the same manner, surface-treated hydrophobic silica filler containing polymer matrixes (Cosmesil HC, A-2186, MED-4920) had negUgible water absorption. The surface groups on these silica particles repel water molecules, and hence prevent water absorption into the material [55]. 

Organofunctional silanes are used to promote polymer-to-filler bonding with clay or silica fillers. Vinyl silanes are used in peroxide-cured wire insulation to promote stronger bonding with calcined clay fillers. Mercapto silanes are used to treat kaolin clay in sulfur-cured compounds. 

Figure 18 shows the bound rubber content of samples filled with untreated silica, plasma-treated silicas, and silane-modified silica, as representative of the filler-polymer interactions. Samples SPTh and SPA show the highest bound rubber contents, and the ST the lowest value. The SPPy sample shows a bound rubber content slightly lower than that of SU. 

Compounds containing PA-silica, PTh-silica, or silane-treated silica show the lowest reinforcement parameters in this series. This indicates a good dispersion of the polymer and a low degree of filler-filler interaction, as also shown by the Payne effect values. 

The higher amounts of bound rubber for all samples filled with plasma-treated silica demonstrate an improved filler-polymer interaction between the plasma-treated silica and the polymers in the blend compared to untreated and silane-treated silica. The highest filler-polymer interaction for the PPy-silica can be due to the best compatibilization effect of PPy-silica with both polymers in the blend, as... 

White (silica) fillers, often surface treated, are sometimes used to improve flow, moisture resistance, and tensile properties.25 27... 

Dutta and Ryan (1979) examined the effects of fillers (carbon black and silane-surface-treated silica) on the cure of DGEBA/MPDA epoxy-amine systems. They found that the rate constants of the cure reaction are affected by the presence of the fillers in an unusual fashion (a function of temperature and concentration) with respect to concentrations up to 10%. This was postulated to be due to the reactive surface groups on the fillers. The reaction order, however, is not affected. 

Similar techniques have been used to incorporate silica into various polymers. (Mineral fillers are often given hydrophobic coatings to help in their dispersion in polymers such as polyolefins.60) Methacrylatopropyltrimethoxysi-lane has been used to add the methacrylate group on to silica. The treated silica was used in the emulsion polymerization of ethyl acrylate.61 Transparent films could be formed from the product. Living polystyrene was end-capped with a triethoxysilane (5.20), after which it was used to treat silica and alumina.62... 

Thus, silica or fumed silica is truly the work-horse filler of the silicone industry. One attribute of silica fillers, when of the proper particle size and properly dispersed, is their transparency in the polymer. This allows the preparation of the clear silicone sealants commonly used. The silicas can either be untreated or treated by any of several methods.This treat-... 

Silica Treating Unit Filler Loading (phr) Polymer % Trans. % Haze (100 mil)... 

Surface treatments for Cab-O-Sil influence the viscosity and thixotropic properties of an adhesive as shown in Figure 3.19 where MS-5 is untreated Cab-O-Sil , TS-720 is treated with polydimethylsiloxane, and TS-610 and TS-530 are treated with dimethyldichlorosilanes. The silica filler treated with polydimethylsiloxane (TS-720) produces greater van der Waals forces of attraction and thus higher viscosity compared to TS-610 and TS-530. ... 

The amount of polysiloxane-based plasticizer depends on a combination of factors including the required modulus of rubber, the amount of silica filler, and the type of silica filler (treated or untreated with silane). 

Another approach of chemical modification of silica for rubber nanocomposite for the same aim, i.e. to reduce the filler-filler interaction, is differential microemulsion polymerization. In general, the process involves two main continuous steps (i) pre-treatment/chemical bonding of silica particles with coupling agent, and (ii) polymerization of the monomer in a reaction medium containing the pre-treated silica. The resultant product is a core-shell structure where nano-silica is the core encapsulated by a nanopolymer shell. 

The influence of MCA-treated silica as a filler of PVA films differs from that of initial A-300 (Figures 1.194 and 1.195) because of more compacted secondary particles in the treated silica powder. The activation energy of water evaporation from the films (Figure 1.194g and h) depends... 

Figure 1. Plots of T p vs. filler content for treated and untreated silica fillers. O — iPPO + untreated silica. = iPPO MeSiCl treated silica. 3 = overlapping point.

In the following section, preparation of silicone composites and films thereof is discussed. A highly homogenous solution of PDMS precursor and cross-linker is first formed. To adjust the viscosity of the mixture, solvents such as toluene, heptane, or cyclohexane can be used. Fillers including surface-treated silica can also be added. When particles are used, it is recommended that they be dispersed using a tip sonicator or a SpeedMixer. After a homogenous dispersion is formed, the catalyst is added. To remove the air bubbles (if a SpeedMixer is not used), further sonication... 

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