Filler-surface modifier

Influence of the Molecular Size of the Filler Surface Modifier on the Strength of Adhesive Bonds with Solid Substrates and the Molecular Mobility of the Filled Polyurethane... 

Competitive adsorption of components of filler surface modifier systems, stabilisers and lubricants, etc., is an inevitable event that occurs in the vast majority of filled polymer formulations. Such phenomena can lead to inferior product performance in terms of reduced coupling agent efficiency and poor stabilisation. Therefore an understanding of such events is very beneficial if performance is to be optimised. 

In FMC the probe is at finite dilution and it is likely, in the case of some filler/solvent combinations, that the most active sites will always be occupied by the solvent molecules, therefore these sites may never be probed during the FMC experiment. This will almost certainly be true in cases where the solvent and filler have strong hydrogen bonding activity, i.e., alcohols with silica. However, it can be argued that in a polymer composite, particularly when additive or filler surface modifier adsorption from the matrix melt (or a liquid resin) is considered, the conditions of the FMC experiment are closer to reality. 

It should be noted that for polymerization-modified perlite the strength parameters of the composition algo go up with the increasing initial particle size. [164]. In some studies it has been shown that the filler modification effect on the mechanical properties of composites is maximum when only a portion of the filler surface is given the polymerophilic properties (cf., e.g. [166-168]). The reason lies in the specifics of the boundary layer formation in the polymer-filler systems and formation of a secondary filler network . In principle, the patchy polymerophilic behavior of the filler in relation to the matrix should also have place in the failing polymerization-modified perlite. 

As shown for the synthesis of PS [291], the monomer may be localized in the vicinity of the filler surface by previously grafting a polymer capable of swelling in the base monomer. Copolymeric latex of polychloroprenemethacrylic acid was added to the aqueous dispersion of chalk. The acid groups reacted with chalk and the latex particles became chemically grafted to chalk. When further portions of styrene were added they were completely absorbed by modified chalk. 

In order to support and meet this demand, an all-around development has taken place on the material front too, be it an elastomer new-generation nanofiller, surface-modified or plasma-treated filler reinforcing materials like aramid, polyethylene naphthenate (PEN), and carbonfiber nitrosoamine-free vulcanization and vulcanizing agents antioxidants and antiozonents series of post-vulcanization stabUizers environment-friendly process oil, etc. 

Silica used as a filler for rubbers is silicon dioxide, with particle sizes in the range of 10-40 nm. The silica has a chemically bound water content of 25% with an additional level of 4-6% of adsorbed water. The surface of silica is strongly polar in nature, centring around the hydroxyl groups bound to the surface of the silica particles. In a similar fashion, other chemical groups can be adsorbed onto the filler surface. This adsorption strongly influences silica s behaviour within rubber compounds. The groups found on the surface of silicas are principally siloxanes, silanol and reaction products of the latter with various hydrous oxides. It is possible to modify the surface of the silica to improve its compatibility with a variety of rubbers. 

In addition to the raw material cost, one also has to take into account compounding costs, the cost of any coupling agent or surface modifier that is not already present on the filler and the cost of additional stabilisers that might be re-... 

Filler surface chemistry is clearly important, although the effects vary widely according to the exact nature of the filler, polymer and surface modifier. Some of the factors that can influence toughness and are, at least in part, controlled by filler surface chemistry include the level of filler polymer interaction [40], the structure of heterophasic polymers [41], the amount of polymer degradation during compounding [42], filler dispersion [43] and polymer crystallinity arising from altered nucleation processes [44]. 

All the pre-coating methods in use rely on the addition of a fixed amoimt of surface modifier to a given amoimt of filler, thus determining the final composition. It is thus necessary to know in advance how much coating to use for a given apphcation. 

Spectroscopic techniques are extremely useful for the characterization of filler surfaces treated with surfactants or coupling agents in order to modify interactions in composites. Such an analysis makes possible the study of the chemical composition of the interlayer, the determination of surface coverage and possible coupling of the filler and the polymer. This is especially important in the case of reactive coupling, since, for example, the application of organofunctional silanes may lead to a complicated polysiloxane interlayer of chemically and physically bonded molecules [65]. The description of the principles of the techniques can be found elsewhere [15,66-68], only their application possibilities are discussed here. 

A. Roychoudhury, Chemical Interaction of Chlorosulfonated Polyethylene with Functionalised Polymers and Surface Modified Fillers, IIT Kharagpur, India,... 

H NMR transverse magnetisation relaxation experiments have been used to characterise the interactions between NR, isoprene rubber, BR, EPDM and polyethylacrylate rubbers with hydrophilic silica and silicas modified with coupling agents [124-129]. These studies showed that the physical interactions and the structures of the physical networks in rubbers filled with carbon black and rubbers filled with silicas are very similar. In both cases the principal mechanism behind the formation of the bound rubber is physical adsorption of rubber molecules onto the filler surface. 

In addition, FRs used in combination with nanoparticles differ from current FR used alone in polymers. Some FR agents are now available at the submicronic scale and, in some cases, chemically surface modified, entailing significant changes in their reactivity. For example, new varieties of metallic hydroxides are synthesized, either able to play a similar role as some lamellar nanoparticles or to act as conventional hydrated FR fillers. 

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