Kinetics of maturation phenomenon

The km values corresponding to PU sheets of different thickness were determined experimentally as the respective straight line slopes derived from equation  

The corresponding km values to the six different sheet thickness are shown in Fig. 4.71. 

For thicker PU films, the maturation proceeded slower and it was most likely that the weight of the slower reaction leading to allophanate bridges (equation 4.22(d)) should increase. The final values which could be reached, were all much lower 

With regard to computer simulation of the maturation process, if in equation (4.23) the unique value = 14.1 MPa is replaced in every case by the particular maximum values reached with time for every sheet thickness, it is possible therefore, to obtain a much better agreement between the calculated values and the cr g°p values experimentally found. 

By calculating the product (5km, we found that for PU films thicker than 6 = 2 mm, a relatively constant value of about 0.371 0.03 was obtained. This relation can be useful to estimate km values for other thickness and therefore, to approximate the length of the maturation process in other cases. 

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