Thermally induced solid state polycondensation of nylon 66, nylon 6‐10 and polyethylene terephthalate

Abstract

The mechanism of solid state polycondensation has been subjected to a fundamental analysis. Equations were formulated for combined diffusion and chemical reaction for two separate situations. One was for solid state polycondensation in polymer flakes or chips. The other dealt with polymer powders. The resultant solutions related molecular weight changes to rote functions. A technique for deriving the rate functions from experimental data is described.Solid state polycondensations were then studied for nylon 66, nylon 6-10, and polyethylene terephthalate. These data which ranged from 120 to 200°C. were tested with various mechanisms. The most appropriate one was found to be that developed in the present work. Chemical reaction was found to be the rate controlling step in solid state polycondensation in nylon 66, polyethylene terephthalate, powders of nylon 6-10 and larger particles of nylon 6-10 at and above 160°C. Diffusion of byproduct through the solid was the rate controlling step for larger particles of nylon 6-10 a t temperatures below 160°C. Thermograms of nylon 6-10 indicated morphological changes which possibly influenced the behavior of the larger nylon 6-10 particles. The Arrhenius relation was fitted to the situations where chemical reaction controlled.The thermally induced solid state polymerization of condensation polymers is a phenomenon that is well known in industry. The process is carried out by heating (but not melting) the condensation polymers in an inert gas atmosphere. In condensation polymers an equilibrium exists (192) Pi + P 2 e P 3 + B where Pi, Pz are polymer chains which combine to form Pa which is a longer ohain, and B a byproduct which is small molecule such as water. In essence then, solid state polymerization actually involves taking off the byproduct and driving the reaction to the right. There then can be three possible rate determining steps:1. Chemical reaction 2. Diffusion of byproduct molecules in the solid polymer 3. Diffusion of byproduct molecules from the solid polymer surface to the inert gas.Most of the previous investigations ( 2 to 9 ) of solid state polymerization have generally neglected the mechanism aspect. One exception was the work of Lee and Griskey (9) who found that the rate controlling steps took place within the polymer itself. This was shown in two ways. First, varying the flow rate of nitrogen through the reactor had little effect on polymerization. This indicated that diffusion into the gas was not a rate controlling step. Furthermore, it was found that the rate of polymerization could be described by the equation A recent study has treated this combined chemical reaction and diffusion in a more fundamental manner. The study first considered two possible geometric situations, polymer flakes and polymer powders. The latter material will more closely resemble spheres while the former is closer to the geometry of plane sheets (see Figures 1 and 2 ) .In

Modeling of poly(ethylene terephthalate) reactors. IX. Solid state polycondensation process

“…The mass density of polymer is uniform through out the particle. However, the concentration of polymer end groups changes due to the polycondensation reaction and the time rate of change can be represented as and z = zo + ( e , -e ) / 2 = 1 -e / 2 (8) where A = 0 for a plane sheet, 1 for a cylinder, and 2 for a sphere. Note that in eqs.…”

“…(23) and using eq. (8), we obtain Equation (29) assumes that the diffusivity is a function of reaction time, since the polymer starts crystallizing as it builds up its molecular weight. The nonuniform profile of the molecular weight within the particle implies variation in crystallinity as a function of distance from the interface of the particle.…”

Reaction Kinetics and Simulation for the Solid-State Polycondensation of Nylon 6

“…For example, Srinivasan et al [1] found that SSP of nylon 66 fibers at and above 220 8C follows step-growth bulk polymerization kinetics. Chen et al [2] found that the SSP of nylon 66 flakes was reactioncontrolled. Tang et al [3] developed a reaction-diffusioncontrolled model for SSP of PET.…”

Broadening of molecular-weight distribution in solid-state polymerization resulting from condensate diffusion

“…An early attempt to describe SSP in single polymer particles considered only diffusion of the condensate and neglected reaction kinetics. 7 Recently, several research groups 8 -10 have developed kinetic models for the solid-state polymerization of PET and have investigated the effects of condensate (ethylene glycol) diffusion on the molecular-weight evolution. Other aspects of the SSP of PET have also been examined, such as the effect of particle size, 9,[11][12][13][14] the type of purge gas, 15 the flow rate of purge gas, [12][13][14] and the use of plasticizers to increase the rate of polycondensation.…”