Elastomer phases, interfacial bonding

Interfacial Bonding between Different Elastomer Phases... 

Evidence of Interfacial Bonding. In these experiments compounded blends were composed of two elastomer phases that were first mixed with curative ingredients before blending in various ratios. This procedure was adapted to ensure proper initial distribution of the ingredients between the two phases. Blending was accomplished, with one exception, by mill mixing on a small laboratory two-roll mill. After blending, cured specimens in the form of small 0.025-inch thick pads were swollen in a common solvent to observe the over-all state of network... 

With some elastomer systems, such as the DGEBA/CTBN/polyor propyleneamine system, there is an intermixed boundary between the elastomer and the epoxy phases which provides a graduated modulus. This type of intermixed boundary has been proven to increase interfacial bonding and reduce stress concentration between the phases (10). 

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

Reactive impact modifiers are preferred for toughening of PET since these form a stable dispersed phase by grafting to the PET matrix. Non-reactive elastomers can be dispersed into PET by intensive compounding but may coalesce downstream in the compounder. Reactive impact modifiers have functionalized end groups. Functionalization serves two purposes - first, to bond the impact modifier to the polymer matrix, and secondly to modify the interfacial energy between the polymer matrix and the impact modifier for enhanced dispersion. Some examples of commercially available reactive impact modifiers for PET are shown in Table 14.3. An example of a non-reactive elastomer that can be used in combination with reactive impact modifiers is ethylene methyl acrylate (EMA), such as the Optema EMA range of ethylene methyl acrylates manufactured by the Exxon-Mobil Chemical Company (see Section 4.2). 

Note 2 The interfacial interaction between hard and soft phase domains in a thermoplastic elastomer is often the result of covalent bonds between the phases and is sufficient to prevent the flow of the elastomeric phase domains under conditions of use. Note 3 Examples of thermoplastic elastomers include block copolymers and blends of plastics and rubbers. 

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