Interphase crosslinking

Fig. 7. Different types of interphases. (a) Contact interphases, as produced for example by transcrystalline growth or enhanced adlayer crosslinking in the adhesive phase, (b) Diffusion interphases, as produced by interdigitation or interdiffusion of chains from either or both phases.

Restrained layers—coupling agents develop a highly crosslinked interphase region with a modulus intermediate between that of the substrate and the polymer. 

In the interphase between domains and the crosslinked continuous phase there may be regions that are immobilized by the network and are liquid crystalline at room temperature. 

The use of irradiated PTFE powder in EPDM gives enhanced mechanical properties as compared to composites containing nonirradiated PTFE. The existence of compatibility between modified PTFE powder and EPDM is indirectly revealed by , DSC, and SEM. shows that modified PTFE powder (500 kGy-irradiated) is obviously but partially enwrapped by EPDM as compared to nonirradiated PTFE powder. This leads to a characteristic compatible interphase around the modified PTFE. The resultant chemically coupled PTFE-filled EPDM demonstrates exceptionally enhanced mechanical properties. Crystallization studies by DSC also reveal the existence of a compatible interphase in the modified-PTFE-coupled EPDM. The synergistic effect of enhanced compatibility by chemical coupling and microdispersion of PTFE agglomerates results in improvement of mechanical properties of PTFE-coupled EPDM compounds. In summary, an effective procedure both for the modification of PTFE powder as well as for the crosslinking of PTFE-filled EPDM by electron treatment has been developed for the preparation of PTFE-coupled EPDM compounds with desired properties. 

It is clear that other components quite different chemically from the main constituents of the epoxy resin system may be present in the starting material. The structure of the cured epoxy may or may not incorporate these components. To the extent that these other species are not part of the crosslinked epoxy network, they can be concentrated at the interphase or they may be able to migrate to the interphase during the curing process. 

The semi-Gaussian stiffness profile indicates diffusion processes occurring before the gelation of the reactive mixture of epoxy resin and curing agent. The diffusion processes are expected to modify the local structure of chemical crosslinks. Due to its finite width of 3/c=280 nm, the gradient zone has to be considered as a volume rather than as an area and, hence, it deserves to be called interphase. 

INTERPHASE MASS TRANSFER RATES OF CHEMICAL REACTIONS WITH CROSSLINKED POLYSTYRENE Gabriella Schmuckler and Shimon Goldstein... 

Although the correlation is quite convincing, acid/base interactions are not claimed to be the only explanation for the increased adhesion since many other mechanisms and phenomena, such as formation of an interphase, co-crosslinking, interdiffiision, mechanical anchoring and interfacial shrinkage could intervene. 

The morphology can be stabilized by (i) thick interphase, (ii) partial crosslinking, or (iii) addition of an immiscible polymer with a suitable spreading coefficient [Yeung et al., 1994]. The adhesion between the phases in the solid state is improved by (i) addition of a copolymer that covalently bonds the phases, (ii) reduction of size of the crystalline domains, (iii) adequate adhesion, e.g., by the use of polyetherimine, PEIm [Bjoerkengren and Joensson, 1980], and... 

Of the various compatibilization strategies that have been devised, an increasingly common method is either to add a block, graft, or crosslinked copolymer of the two (or more) separate polymers in the blend, or to form such copolymers through covalent or ionic bond formation in situ during the Reactive Compatibilization step. The first of these processes was described in Chapter 4 of this Handbook, Interphase and Compatibilization by Addition of a Compatibilizer, while the second method is the topic of this Chapter. 

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