Study On PEN Solid State Polymerization And Its Melt Spinning

Poly(ethylene-2,6-naphthalene dicarboxylate)is synthesized by by naphthalene-2,6-dimethyl(or 2,6-dimethynaphalene)and ethylene glycol.Compared with PET,benzene ring is replaced by the naththyl ring in PEN.Because the conjugated structure of naththyl ring is bigger than benzene ring,PEN chain is more rigid than PET chain.Its strength and modulus increase accordingly.PEN is a kind of aromatic hydrocarbon and it has a plane structure.Thus,it brings many superior properties.Such as,the meager ration of free volume,more compact supermolecular architectures,better solvent resistance,air barrier property and hydrolytic resistance.Because of its superior properties,it holds obvious attraction in industrial applications.In this thesis,the kinetics of PEN cold crystallization,solid state polymerization(SSP)and melt spinning of PEN are studied.During the process of SSP,crystallization rate of PEN chip is relatively slow and it is easy to stick to each other.Differential scanning calorimetry(DSC)is used to investigate the thermal properties of poly(ethylene-2,6-naphthalene dicarboxylate).It is appropriate to take the intersection points of baseline extension and tangent to the DSC curve as start of cold crystallization.Avrami exponent n is approximately 2.5.It reflects that amorphous chip,spun fiber and stretched fiber share the same mechanism.The mechanism of nucleation is heterogeneous nucleation and crystal grows in both 2-dimension and 3-dimension.In SSP process,the influence of different N2 flow rate and reaction temperature is studied.And a kinetic model for SSP is established in this paper.The model is solved numerically by combining finite difference method with Runge-Kutta method.With the increase of reaction temperature,intrinsic viscosity and number-average molecular weight increase correspondingly.Nitrogen flow rate have an influence on the molecular weight of SSP PEN.The molecular weight of SSP PEN increases respectively until the nitrogen flow rate rises to a critical value,which is about 15m/min.From the numerical solution of SSP kinetic model,the rate constant of esterification reaction is bigger than that of transesterification reaction.The diffusivity of water is bigger than that of EG.After SSP,the intrinsic viscosity of PEN increases and it can be used in melt spinning.In this thesis,different drawing condition and thermal finalization is used to improve the strength of PEN fiber.Beside that,the influence on the strength and degree of crystallinity is also investigated in it.The strength of PEN fiber increases to 8.5cN/dtex after drawing.If drawing ratio and temperature increase,the strength of PEN increases as well.Different method of drawing has different influence on the strength of PEN fiber.If it is drawn in water and glycerol,it can be heated homogeneously and rapidly.Moreover,micromolecule is assumed to be a kind of plasticizer.So the strength of PEN fiber which is drawn in water and glycerol is much higher.During the drawing process,super molecular structure of PEN fiber changes continuously.The orientation factor(fs)and sonic modulus increase as the drawing ratio increases.After drawing,crystalline orientation increases by 50%.Drawing conditions make no difference on grain size and it is about 10.63nm after drawing.Though the experiment,200 ℃ and 30min are the ideal condition of thermal finalization.After thermal finalization,softening temperature increases and strain decreases.