Crystalline bridge model

In POM a careful examination of WAXS and SAXS measurements on a wide range of drawn samples, showed that the average crystal length, even for the highest modulus material was only comparable with the long period Again it must be concluded that the crystalline bridge model is not applicable. 

Deformation Mechanism. The deformation mechanism has been studied in more detail for the case of semicrystalline polymers, polyethylene, in particular (1,2). There exist a number of models explaining the evolution of polymer structure at high draws. The models can be subdivided into two categories (2), namely, the microfiber plus the tie molecule model, as proposed by Peterlin and co-workers and the extended chain model, which is similar to Ward s crystalline bridge model. 

As a first stage, the contribution of the crystalline bridges can be considered as one element of a Takayanagi model (in Figure 8.9(b) this is the continuous phase) that is in parallel with the series combination of the remaining lamellar material and the amorphous component. Young s modulus would then be... 

It was realised by Takayanagi [50] that oriented highly crystalline polymers with a clear lamellar texture might be modelled in terms of a two-component composite in which the alternating layers corresponded to the crystalline and amorphous phases [51]. The model was later extended to include a parallel component in addition to that in series, and was applied first to describe the relaxation behaviour of amorphous polymers with two distinct phases, and later to crystalline polymers in which the parallel component represented either interlamellar crystalline bridges or amorphous tie molecules threading through the amorphous phase. 

The structure of high modulus polyethylene fibres obtained by optimized drawing of linear polyethylene is viewed as crystalline lamellae linked by intercrystalline bridges.Accordingly, the component B is then viewed as crystalline, and its content (1 — >1) corresponds to the volume fraction of the material incorporated in the crystalline bridges. A more complex model consisting of four components has been proposed for these fibres by Grubb. 

Another model assumes that gel zones are formed by hydrated lead dioxide (PbO(OH)2) and act as bridging elements between the crystallite particles. Electrons can move along the polymer chains of this gel and so cause electronic conductivity between the crystalline zones 137],... 

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