Preparation And Characterization Of Novel Polyamide5,6Fibers

Linear polyamides, commonly known as Nylons are very important class of materials that find their applications as such or in combination with other polymers in the field of engineering plastics, fibers, and films due to their unique properties such as high modulus, high strength and toughness, high melting temperatures, heat stability, and excellent resistance to abrasion. However, it is known that many of the commonly used polyamides like polyamide6and polyamide66are based on petrochemical building blocks. Due to the resource problems and pollution, bio-based-derived chemicals offers an enormous potential to replace the depleting fossil feedstock and are considered as an environmental friendly alternative. The use of the1,5-pentanediamine obtained through bioengineering transformation from lysine in the synthesis of polyamide5,6provides partially or entirely bio-based polyamide. And also, polyamide5,6fibers with high moisture absorption and release cool feeling, good wear resistance, good mechanical properties and can be used as a promising alternative to conventional polyamide6, and polyamide66, for the textile industry. However, there is no studies report on the preparation and characterization of this fibers.In this current studies polyamide5,6(PA56) pellets synthesized from1,5-pentanediamine obtained from L-lysine decarboxylation and adipic acid with better processing performance was selected. The structure, the kinetic parameters of the thermal degradation, rheological properties, and non-isothermal crystallization behavior were studied in order to provide a theoretical basis for the determination of the spinning process, exploring and optimizing the preparation process of PA56fibers. Polyamide5,6(PA56) has been successfully spun as fibers through the melt-spinning process. The effects of spinning conditions on the crystalline morphology, molecular orientation, mechanical properties, moisture absorption, dyeability and abrasion resistance were evaluated. Furthermore, the properties of PA56fibers were compared with PA6fibers prepared with the same conditions. According to the DSC, TGA, and MFI results, the No.2sample with moderate molecular weight of PA56was selected as raw material for the spinning process due to its outstanding processing, thermal and mechanical properties. The melting temperature, corresponds to the maximum of the melting peak and thermal degradation temperature of PA56-2are252.7℃and452.8℃, respectively.According to the TGA experiments, the thermal degradation of PA56in nitrogen atmosphere is one step reaction. As the heating rate increased, the degradation temperature and DTG peak temperature gradually increased. The kinetic parameters of the thermal degradation of PA56were investigated by using the Kissinger and Flynn-Wall-Ozawa methods. The results revealed that the activation energy (E) obtained from Kissinger and Flynn-Wall-Ozawa methods are202.79kJ/mol and207.43kJ/mol, respectively. The results from Coats-Redfern method demonstrate that the solid state process for the thermal degradation of PA56followed by the phase boundary reaction (R2) may be cylindrical symmetry, deceleration shaped curves with the integral form g(α)=1-(1-α)1/2.The rheological properties of polyamide5,6have been studied by means of a parallel-plate rheometer. The effects of temperature on the storage modulus, loss modulus, and complex viscosity were studied. The results showed that the complex viscosity, storage modulus, and loss modulus of PA5,6decrease with increasing the temperatures. It is worth noting that the complex viscosity of PA5,6remains almost constant showing a Newtonian behavior.The non-isothermal crystallization behavior of polyamide5,6was investigated by DSC under different cooling rates and the crystallization kinetics were further analyzed with the Avrami method modified by Jeziorny, the Ozawa model and the combined Avrami-Ozawa approach. The results reveal that the Avrami method modified by Jeziorny can only describe the primary stage of non-isothermal crystallization kinetics of PA56. The Ozawa model cannot adequately describe the non-isothermal crystallization kinetics due to the inaccurate assumption in Ozawa theory. However, the combined approach was able to describe the non-isothermal crystallization behavior of PA56well. The activation energy for non-isothermal crystallization was also determined and found to be189.49kJ/mol with the Kissinger method. In order to further elaborate our concept and objective of research, polyamide5,6(PA56) successfully was spun into fibers through the melt-spinning process. DSC results revealed that the melting temperature has no considerable variation, while the heat of fusion increased with increments in the draw ratio and temperature. This could be due to the existence of crystals with lower perfection and sizes. The WAXD results showed that the crystallinity and crystal size of PA5,6fibers were directly proportional to the draw ratio and temperature. This could be attributed to the molecular chain and adjacent crystals and small crystallite in the amorphous region transforming from a random state and becoming densely packed. The orientation factor was increased as expected upon drawing. The tenacity, Young’s modulus were found to be significantly increased, while the elongation at break decreased as the draw ratio and temperature increased. The maximum tenacity and Young’s modulus were obtained at draw ratio3.5with drawing temperature (70/130℃), which are2.7cN/dtex and28.4cN/dtex, respectively. The improved mechanical properties were attributed to the improvement of molecular orientation along the fiber axis, the development of more ordered crystalline structure, and the crystallinity. PA56fibers exhibit much higher moisture regain than PA6fibers at different draw ratios. This can be attributed to the amid group content in the polymer backbone, which yields higher moisture regain in PA56fibers than PA6fibers. The dyeing behavior of PA56fiber in terms of dyebath exhaustion, color strength, and wash fastness imply that the PA56behaved in a manner that was to be expected of its conventional nylon6. However, PA56showed moderate/poor washing fastness degree for wool, nylon and acetate fibers. The abrasion resistance test showed that the PA56have same abrasion resistance as PA6. Polyamide5,6spun fibers presumably a competitive fiber and the above results can help to optimize their manufacturing.