| Solid State Polymerization (SSP) is carried out by heating the low molecular weight polymer pellets in an inert gas atmosphere at a temperature below their melting temperature but above their glass transition temperature. SSP of nylon 6 as a powerful way to enhance its average molecular weight has been of great interest to polymer chemists and engineers. Thus, it have an important theory and industry significance to study SSP of nylon 6.In this research, experimental investigations on nylon 6 have been made to study the influence of SSP conditions on final polymer. Based on the detail analyzing of polymerization kinetics, the mechanism, and modeling studies, a kinetics mathematic model of Solid State Polymerization for nylon 6 was proposed. The model in this work can clearly describe the change of the small molecular diffusion and molecular weight between centre and surface of the pellet. Most of the effect operating such as temperature, reaction time, molecular weight regulator, initial number-average weight, original moisture, initial polydispersity index of prepolymer and the particle size were studied.In order to obtain initial values of the pellet for simulation in the solid phase polymerization, a kinetic model of the hydrolysis polymerization of ε -caprolacyam has been developed. Through simulating the isothermal liquid phase polymerization until a desiredvalue of the number-average chain length, Un0, was attained. It was availably solved the difficult problem for deciding the initial values of the pellet.SSP is carried out at the "solid" shape. Since two macromolecules have to come together for reaction in the solid phase, the new rate constants for SSP of nylon 6 was confirmed in this work.A sophisticated computer program package to simulate the hydrolysis polymerization of e -caprolacyam and SSP of nylon 6 has developed. The simulation results are found to be in reasonable agreement with the experimental data.Based on the study, the results show that the temperature is probably the most important factor due to its interrelation with other aspects of the process. An increase of the SSP temperature usually results in an increase of the overall rate of the process. Too lower temperature requires much longer reaction times, while higher temperatures, on the other hand, may favor undesired side reactions and may cause problems connected with particle stickiness; The mean value of the number-average weight, Mn, is decreased with the increasing of amount of molecular weight regulators(AMWR),such as benzoic acid. But it can also be found that the rate of polymerization in solid-state is not as sensitive to the increasing of AMWR as that in liquid phase; Small-sized nylon 6 chips have a higher SSP reaction rate for a given reaction time. The increase in particle sizemay, under certain conditions, change the reaction mechanism. If the polymer size is less than 1.5 mm, the rate-controlling factor in solid state polymerization of nylon 6 is the chemical reaction, and in the particle-size range 1.5-3.Omm SSP is controlled by both diffusion and chemical reaction. For larger particles the diffusion of by-products may become a controlling step; The molecular weight of the starting oligomers has some effect on the ultimate molecular weight of PA6 in solid-state when the PA6 pellets are extracted or unextracted; An higher value of initial molecular weight(MnO) willcause a faster reaction rate, and consequently, an higher mean number-average chain length is obtained at the end of the reaction; The increased in the spatial average value of the number-average weight is found to be very sensitive to the original moisture; The spatially averaged polydispersity index is found to rise rapidly at begining, and then increases'gently and finally decreases to an equilibrium value. Higher values of initial polydispersity index may yield a higher average molecular weight of the pellets.Finally, a 5kt/a nylon 6 SSP process is desigend on the basis of medium-size test study in the factory.
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