Elastomer interlayers

Keywords aggregation, interfacial interaction, reversible work of adhesion, wettability, matrix-filler interaction, surface treatment, interphase, surfactant, coupling agent, elastomer interlayer... 

FIGURE 13.4 SEM micrograph of phase-separation around filler particle in PP (a) stress distributed by EPDM elastomer interlayer around a particle (b). 

The compatibilizer as such may be compatible with the clay surfaces and hence easily intercalates into the interlayer spacing of the clay platelets and separates the clay platelets, and with bulk polymer it leads to the formation of well-dispersed nanocomposites. The compatibilizer widely used for polypropylene (PP) is maleic anhydride grafted PP (PP-g-MA) [15-16], Other compatibilizers used are diethyl maleate (DEM-g-PP) and polyolefin elastomer grafted maleic anhydride (POE-g-MA),... 

The clay remains as microtactoids (dispersed in microlevels) when it is dispersed in PP without the assistance of compatibilizer. By adding maleic anhydride grafted PP (PP-g-MA) as compatibilizer, well dispersed clay platelets are observed in the PP matrix. When polyolefin elastomer grafted maleic anhydride (POE-g-MA) compatibilizer is used, even two-phase separation has been reported between PP and POE-g-PP [15]. This phase separation is not identified in TEM analysis and it confirms the compatibility of clay and POE-g-PP. POE-g-PP enters into interlayer spacing and facilitates the delamination of clay layers. 

In ternary nanocomposites, compatibilizers have been mostly used to improve the adhesion at the polymer/filler interface rather than to modify the polymer/elastomer interface. Mishra et al. [80] compounded PP/EPDM/organoclay (75/25/5 wt%) and added PP-g-MA (1 wt% MA) as a compatibilizer with a clay/PP- -MA ratio of 1/3. They characterized the interlayer spacing of the clay platelets by XRD and observed that it increased from 3.4 to 4.3 nm for systems without and with compatibilizer. This was attributed to a better diffusion of the PP-g-MA chains inside the interlayer spacing thanks to their functional groups. Numerous other authors prepared and characterized ternary composites with a compatibilizer. Examples include Lim et al. [81] and Lee et al. [5] on PP/PP- -MA/POE/ organoclay systems, Mehta et al. [23] on PP/PP-g-MA/EPR/organoclay systems, and Liu and Kontopoulou [24,45] on PP/PP-g-MA/ethylene-octene copolymer/silica composites. It should be noted that the compatibilizer itself may affect the properties of the matrix... 

A hybrid composite [121,122] can contain more than one type of reinforcement and/or more than one type of matrix, with the objective of improving or lowering the cost of the basic composite [123]. The second reinforcement may be a fiber (continuous or chopped), particles or whiskers. The fiber reinforcement can be in the same laminae and interspersed using any textile process such as weaving, or in different laminae, interspersing plies to obtain the desired mechanical/ physical properties. A sandwich composite is a special case which has an interlayer of a material such as A1 foil or a honeycomb. The matrix may be different for each type of reinforcement, or added to infiltrate the reinforced matrix (e.g. a thermoplastic resin such as PSU) to confer controlled viscosity in the matrix, or an elastomer (e.g. CTBN) for increased toughness. 

High-transparency polysiloxane elastomer used as a stress-relieving interlayer in the type of safety glass or plastic used in windshields and canopies. The photograph was provided by the Dow Corning Corporation of Midland, Ml. 

Ferroelectric Properties (Cross-linked Systems). The ferroelectric properties of the photochemically crosslinked elastomers E1-E3 differ significantly and depend on the topology of the network formed. For the systems that have interlayer cross-linking (see Fig. 7, E2 and E3), the switching time... 

The conditions for dispersing clay nanolayers into both cis-1,4-polyisoprene (IR) and epoxidized natural rubber (ENR) have been reported. The incorporation of the clays into these elastomers was achieved by mixing the components in a standard internal mixer/mixing mill (melt compounding) or by mixing their dispersions produced in toluene or methyl ethyl ketone solvents (solution Intercalation). X-ray diffraction studies indicated the intercalation of IR and ENR into the silicate interlayers, followed by exfoliation (delamination) of the silicate layers. The reinforcing effect strongly depended on the extent of dispersion of the silicate layers. 

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