Filler surface functional groups

Further insight into the nature of the interaction between irreversibly adsorbed species and the filler surface can be gained from DRIFTS analysis of the filler sample taken from the FMC cell after completion of the adsorption - desorption cycle. DRIFTS is described in more detail in Section 3.5.4, but in summary, it is an infrared spectroscopic technique, that by virtue of a significant proportion of glancing angle reflections, affords enhanced resolution of filler surface functional groups. The authors have found this technique particularly useful when studying competitive adsorption of polymer stabilisers and carboxylic acids onto silica and metal hydroxides, respectively. 

In the last part of the paper, filler-elastomer chemical interactions which are able to take place through surface functional groups or surface reactive hydrogens are studied. The effect exerted by the created filler-elastomer bonds in the reinforcement process is then discussed. 

The filler-elastomer chemical interactions take place through its surface functional groups and hydrogen atoms. Coupling agents improve polymer-filler adhesion. From the point of view of dynamic-mechanical properties for low strains, the filler-elastomer bonds have a positive effect in the reinforcement process. 

This study is devoted to the investigation of porous methacrylate polymeric systems filled with chemically modified fumed silicas. IR and 13C NMR spectroscopies combined with AFM was applied to characterize changes in the material structure, and also the effect of surface functional groups of inorganic particles on the polymer-filler interaction. 

Chemically modified silica fillers with grafted methyl groups or methyl and silicon hydride groups, influenced the micro- and macrostructures of various copolymers. Changes in cross-linking, orderliness, crystallinity, microtacticity and conformation of macromolecules have been detected in the presence of fillers. Surface functionality of the silica filler determines the disposition of macromolecular chains at the interface. 

Figure 10.1 shows the effect of the addition of fillers to polypropylene on its crystallinity. This study was conducted under the same conditions for all specimens tested. There is a difference in the effect of CaCO-, and talc. Calcium carbonate lacks surface functional groups so it tends to have a very small influence on crystallinity and the crystallization behavior. Talc has interacting functional groups on its surface which cause the increase in crystallinity along with the concentration increase. 

A similar mechanism acts in the case of reactive adhesion promoters such as polyurethanes. Here water is a factor, as well as surface functional groups of fillers. The adhesion promoter is exhausted within the bulk of organic material (coating, adhesive, etc.) and unable to perform the task. 

For semicrystalline polymers, fillers may affect crystallinity, size of crystallites, and direction of crystal growth. Filler surface may provide a large number of nucleation sites, although this also depends on surface functional groups and surface treatments. In certain polymers, fillers may promote transcrystallinity, which can improve adhesion and other properties [10]. 

It can be seen that modification of filler snrfaces both to aid processing and improve composite properties is an important and active area of research. While there are a considerable number of treatments proposed, they all follow the principle of a filler surface reactive group linked to an organic backbone, which may carry further functionality. The main variation is in the group used to achieve surface reaction. As we have seen this may be an acid or acid precursor, an aluminate, borate, phosphate, silane, titanate or zirconate. 

A rational analysis of filler effects on structural, proton transport properties and electrochemical characteristics of composite perfluorosulfonic membranes for Direct Methanol Fuel Cells (DMFCs) was reported [7]. It has been observed that a proper tailoring of the surface acid-base properties of the inorganic filler for application in composite Nafion membranes allows appropriate DMFC operation at high temperatures and with reduced pressures [7]. An increase in both strength and amount of acidic surface functional groups in the fillers would enhance the water retention inside the composite membranes through an electrostatic interaction, in the presence of humidification constraints, in the same way as for the adsorption of hydroxyl ions in solution [7]. 

Early reports and patent applications of Stonehart and Watanabe [22], Antonucci et al. [23], and Antonucci and Arico [24] claim the advantage of the introduction of small amounts of sihca particles to Nafion to ino-ease the retention of water and improve the membrane performance above 100°C. The effect is believed to be a result of water adsorption on the oxide surface. As a consequence the back-diffusion of the cathode-produced water is enhanced and the water electro-osmotic drag from anode to cathode is reduced [3]. A recent report of the group of Arico et al. [25] confirms the effect of water retention with the inclusion of oxide particles in Nafion and the importance of the acidity of the particle surface. An increase in both strength and amount of add surface functional groups in the fillers enhances the water retention in the membrane SiO -PWA (modified with phosphotungstic acid) > SiOj > neutral-AljOj > basic-AI2O3 > ZrO. ... 

Thus, UDD can be used in polymer composites as active filler and potent structure former increasing their strength, wear resistance, and heat resistance. This is due to record values of specific surface and, therefore, surface energy the presence of surface functional groups and high heat conduction. Also, owing to the sphericity of its particles UDD plays the role of dry lubricant decreasing the friction coefficient. 

For the second method the threshold concentration of the filler in a composite material amounts to about 5 volume %, i.e. below the percolation threshold for statistical mixtures. It is bound up with the fact that carbon black particles are capable (in terms of energy) of being used to form conducting chain structures, because of the availability of functional groups on their surfaces. This relatively sparing method of composite material manufacture like film moulding by solvent evaporation facilitates the forming of chain structures. 

In the following section, a new technique of surface modification of fillers and curing agents will be discussed plasma polymerization. This technique allows for surface coating of powders, whereby the chemical structure of the coating is determined by the monomer used for the process. The morphology of the substrate is preserved, which is an important precondition for filler treatment. The polarity of the functional groups can be chosen to fit the matrix of the polymer wherein it will be applied. 

It appears from the evolution of the adhesion index that a distinction has to be made between the interactions carbon blacks are able to have with unsaturated or with saturated (or near-to-saturated) elastomers. Thus, the adhesion index of butyl rubber is enhanced upon oxidation of the black, while the reverse is observed with polybutadiene 38). The improvement of the reinforcing ability of carbon black upon oxidation, in the former case, has been interpreted by Gessler 401 as due to chemical interactions of butyl rubber with active functional groups on the solid surface. Gessler, relating the reinforcing characteristics of the oxidized carbon black for butyl rubber to the presence of carboxyl groups on the surface of the filler, postulated a cationic... 

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