Surface modification strengthening

Adhesion interactions at the solids/polymers interfaces are first and foremost adsorption interactions between the sofid surface and polymer molecules [1—11]. After polymerization there is a low molecular-weight fraction of coupling agents, which can decrease the cohesion and adhesion of the polymer film. If the molecules from this fraction interact with the filler particles preferentially (which can be reached due to the filler surface modification) instead of with the material surface covered, then the boundary layer of the film can be free from this fraction and adhesion increases as strengthening the boundary layer of the coating leads to stronger adhesion of the coating to the covered surfaces [46]. 

Traditionally, as a filler of rubber carbon black is used. It is an active filler able to reinforce and improve the properties of finished rubber products. For ecological and economic reasons this filler has many disadvantages i.e. on the filler surface the hydrocarbon rings are present, also the methods of carbon black production from petrochemical sources is environmental unfriendly. Nowadays the research activity is focused on looking for new methods of surface modification of inactive fillers to enhance their strengthening performance in elastomers. 

In addition to the standard sol-gel synthesis procedure, the preparation of aero-gel-hke APD materials requires a modified gel chemistry that essentially consists of either chemical surface modification and/or pore strengthening. The main issue addressed by such modification schemes is to prevent structural collapse due to the stresses formed as a consequence of high capillary pressures during drying, which normally leads to irreversible shrinkage and densification. 

It is well known that polymer chain entanglement is the primary source of a polymer s strength. It is also known that over time polymeric materials can become increasingly semi-crystalline, making their surfaces even more difficult to accept surface modification techniques. The process of axially or biaxially orienting polymer films, for example, strengthens these materials as their chains become stretched. It is therefore common practice for surface modification techniques. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

The idea of two kinds of centers on the surface of nickel in the modified MRNi catalysts was strengthened by results from the treatment of catalyst before its modification with ultrasound irradiation . Theoretically though, a more effective method might be selective poisoning of the non-enantioselective centers in chirally modified catalysts. 

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