The Structure,Dynamic Thermo-mechanical And Rheological Properties Of Bio-based Nylon 56

Nylon?polyamide?plays an significant role in the field of clothing,home textile and industry due to its excellent properties.As it is well known,petroleum resource,which is the origin of traditional nylon raw materials,is not renewable.There is a contradiction between the limited oil resources and increasing demand for nylon,restricting the development of conventional nylon.As a result,bio-based nylon derived from biological materials is growing in popularity in polymer material field.In this paper,the novel nylon 56 is synthesized by adipic acid and pentamethylene diamine obtained by biological fermentation,with a content of 41% biomass.It has been reported that nylon 56 exhibits great superiority on elastic recovery,moisture absorption,mechanical property,good dyeing property and wear resistance.Therefore,nylon 56 has a great potential and competition advantage to become the world's third largest nylon variety.It is well-known that properties of polymer materials are determined by their inner structure.Unfortunately,studies on nylon 56 are insufficient and seldom.Based on this,research on the crystal structure and the related properties of bio-based nylon 56 has been carried out in this paper.The main contents and results studied in this paper are as follows:The crystallization process and kinetics of bio-based nylon 56 were investigated by differential scanning calorimeter?DSC?.The results showed that the crystallization of bio-based nylon 56 was greatly affected by the cooling rates and crystallization temperatures.A rare phenomenon,that crystallization peaks during cooling were double under 30?/min cooling rates and higher,was discovered in nylon 56.The value of the Avrami exponent was determined to be approximately 3 and 3.5 to 4 during isothermal and non-isothermal crystallization process,respectively.This indicated that the crystallization was probably three-dimensional growth.The non-isothermal crystallization behavior of nylon 56 could be well described by Mo method.The activation energies for isothermal and non-isothermal crystallization of bio-based nylon 56 were-99.04 k J/mol and-191.05 k J/mol,which were determined through the Arrhenius and Kissinger method,respectively.In addition,the equilibrium melting point of bio-based nylon 56 was determined to be 256?.The hot-stage polarized optical microscope?POM?was used to study the crystal morphology of bio-based nylon 56.It was showed that 3-dimensional radial spherulite structure was formed during both isothermal and non-isothermal crystallization processes.Compared with nylon 66 and nylon 6,nylon 56 exhibited higher crystallization rate,higher symmetry and regularity and larger spherulites size,which was an evidence to the favorable crystalline properties of bio-based nylon56.The crystal nucleation mechanism of nylon 56 was heterogeneous nucleation at the temperature above 200? and tended to be homogeneous nucleation at low temperatures.A linear relationship between the spherulite radius and crystallization time was found and the growing rate of spherulite increased with the decrease of isothermal crystallization temperatures.The synchrotron radiation wide angle X ray diffraction?WAXD?was used to explore the crystalline structure and crystalline transition under different external conditions.The results showed that only a strong diffraction peak appeared at 2? =16.77°?d=0.425nm?at room temperature.The crystalline phase in nylon 56 is ?,belonging to hexagonal packing.Brill transition,which resulted in pseudohexagonal packing,was found at 220? during heating process and the Brill transition was reversible.Similarly,the crystalline transition could happen during cooling process.A special structure with two directional hydrogen bonds,which is similar to the ? structure in the conventional nylon,was formed during the cooling process.And the final crystalline phase underwent different cooling rates was ? crystal form.As a result,the transition during cooling was from pseudohexagonal packing to a special structure with two directional hydrogen bonds and to hexagonal packing ? successively.Loss transition peak and corresponding molecular motion mechanism during temperature variation of nylon 56 were investigated by dynamic thermomechanical analysis?DMA?.As for nylon 56,T_?=60?,T_?=-30?,T_?=-114?.? transition was the result of molecular chain segment movement,mainly hydrogen bonded acylamino.? transition could be attributed to the movement of the carbonyl group.And ? transition was related to crank motion of-CH₂-segment in amide chains.The capillary rheometer was used to study rheological properties of bio-based nylon 56.The study showed that nylon 56 was provided with good rheological property.Like other polymer fluids,nylon 56 was pseudoplastic fluid and its viscosity decreased at the shear rate range of 3000¹0000s^-1.In addition,the high temperature would lead to small apparent viscosity and the viscous flow activation energy increased with the decrease of shear rate.