Parameters Affecting SSP

In general, no two PET materials have exactly the same SSP behaviour despite the similarities in bottle grade recipes and standard pellet sizes. The reasons for this are the numerous factors that influence the SSP reaction rate, many of which are still not fully understood. The main factors and their qualitative influence are discussed briefly below  

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The advantage of direct solid-state treatment of PET bottle flakes is the faster IV increase rate when compared to pellets. This is due to the lower average thickness and therefore shorter diffusion distance (see parameters affecting SSP in Section 2.3 above). However, several aspects have to be considered, as follows ... 

A number of parameters are reported to affect the overall rate of SSP and to define the relevant rate-determining step. Reaction temperature, initial end-group concentration, particle geometry, gas flow rate, crystallinity, and catalysts are listed as the most important and their effect on the controlling mechanism is presented briefly in Table 1, assuming negligible gas-phase resistance. ... 

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