The structure evolution of polyamide 1212 after stretched at different temperatures and its correlation with mechanical properties

The Structural Evolution and Mechanical Properties of Semi-Aromatic Polyamide 12T after Stretching

The development of semi-aromatic polyamides with excellent mechanical properties has always been a popular research avenue. In this work, the semi-aromatic polyamide 12T (PA12T) with the maximum tensile strength of 465.5 MPa was prepared after stretching at 210 °C 4.6 times. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) were used to characterize the structural evolution of semi-aromatic polyamide 12T (PA12T) after stretching at different stretching temperatures and stretching ratios. The formation mechanism of this change in mechanical properties was investigated from different aspects of the aggregated structure such as crystal morphology, crystal orientation and crystallinity. The relevant characterization results show that the crystal structure, crystal orientation and crystallinity of PA12T were the highest when the sample was pre-stretched at 210 °C, which is crucial for improving the mechanical properties of PA12T. These findings will provide important guidance for the preparation of polymer materials with excellent mechanical properties.

Reorganization of Hydrogen Bonding in Biobased Polyamide 5,13 under the Thermo-Mechanical Field: Hierarchical Microstructure Evolution and Achieving Excellent Mechanical Performance

The hierarchical microstructure evolution of an emerging biobased odd-odd polyamide 5,13 (PA5,13) films under the thermo-mechanical field, stepping from hydrogen bond (H-bond) arrangement to the crystalline morphology, has been investigated systematically. It is found that the reorganization of H-bonds under the thermo-mechanical field plays a crucial role in the crystallization of PA5,13. Especially, it is revealed that the crystallization process under the thermo-mechanical field develops along the chain axis direction, while lamellar fragmentation occurs perpendicular to the chain axis. Consequently, a stable and well-organized H-bond arrangement and lengthened lamellae with significant orientation have been constructed. Laudably, an impressive tensile strength of about 500 MPa and modulus of about 4.7 GPa are thus achieved. The present study could provide important guidance for the industrial-scale manufacture of high-performance biobased odd-odd PAs with long polymethylene segment in the dicarboxylic unit combined with a large difference between the polymethylene segments in the dicarboxylic and diamine units.

Bio-based polyamide

Biobased polymers are sustainable polymers produced from renewable resources such as biomass feedstocks instead of the industrial fossil resources such as petroleum and natural gases. This trend helps in creating an environmentally friendly chemical processing that is characterized by low carbon footprint emission to the globe which in turn will limit the increase of the atmospheric carbon dioxide concentration even after their incineration. Synthesis of polymeric materials from biobased resources also solves the problem of polymer waste recycling. This chapter covers a basic background on the origin and importance of biobased polyamides, different synthetic routes of their starting monomeric materials obtained from biomass feedstocks, and a brief summary of the physical and chemical properties and applications of some common aliphatic, semiaromatic and fully aromatic polyamides. This chapter ends with a recent published data on the growth of the global market of biobased polyamides to emphasize on the economic importance of this manufacturing trend.

The Thermal Behavior of γ-PA1010: Evolution of Structure and Morphology in the Simultaneous Thermal Stretched Films

In this work, polyamide 1010 (PA1010) films were prepared by melt-quenching. A wide-angle X-ray diffractometer (WAXD) with a thermal stretching stage was used to investigate the structure transformation, crystallinity and degree of orientation in the course of simultaneous thermally stretched PA1010. The crystallinity increased along with the increase of draw ratio and then decreased as the draw ratio was over 2.00 times—which the maximum value reached when the draw ratio was about 2.00 times. The degree of orientation of γ-PA1010 was much greater at higher temperature than room temperature (RT); the difference gradually became weaker with the increase of draw ratio. There was a linear relationship between the draw ratios and tensile force at higher temperatures, and the tensile force increased with the increase of draw ratios. The tensile force may induce crystallization and promote orientation in the course of simultaneous thermally stretched PA1010. These phenomena are beneficial to understand the structure-processing-performance relationship and provide some theoretical basis for the processing and production.

Crystal Structure and Mechanical Properties of Uniaxially Stretched PA612/SiO2 Films

Stretching has a significant effect on the microstructure and ultimate performance of semi-crystalline polymers. To investigate the effect of stretching on structure and mechanical properties of uniaxial stretched PA612/SiO₂, PA612 and PA612/SiO2 films were prepared at four temperatures close to the glass transition temperature at various strain. The samples were characterized by a transmission electron microscope (TEM), wide-angle X-ray diffractometer (WAXD), Two-dimensional wide-angle X-ray Scattering (2D-WAXS), differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), and stretching tests. The results showed that the α phase was the dominant phase in PA612 casting film, no obvious γ phase was observed, while both stretching and the presence of SiO₂ can induce the generation of α phase and improve the crystallinity of PA612. Crystals were oriented along the stretching direction and the b axis was parallel to the equatorial direction after stretching. The interplanar spacing of (010/110) decreased with the increasing stretching temperature and expanded with the increasing strain, while stretching temperature and strain present negligible effect on the interplanar spacing of (100). The grain size increased with the stretching temperature while decreased with strain. The presence of SiO₂ led to reduce the yield stress and the stress drop beyond yielding of the composite. Uniaxial stretching gave rise to a significant improvement in the fracture stress and the glass transition temperature.

Statistical Optimization of the Sol-Gel Electrospinning Process Conditions for Preparation of Polyamide 6/66 Nanofiber Bundles

Polymeric nanofibers are widely studied in the textile industry since with them, it is possible to get a great variety of functionalities. In this paper, polyamide 6/66 (PA 6/66) solutions at different concentrations (12, 17, and 22% wt.) were made, to get nanofibers through the basic electrospinning process which were characterized by scanning electron microscope (SEM) and productivity. Afterwards, nanofiber bundles were produced using the electrospinning sol-gel process, which were characterized by SEM and tensile test. From the results of statistical optimization based on one-way analysis of variance (ANOVA) with post hoc Tukey HSD, it was found that nanofiber bundles with higher productivity (1.39 ± 0.15 mg/min), draw ratio (9.0 ± 1.2), and tensile strength (29.64 ± 7.40 MPa) were obtained with a 17% concentration. Finally, a thermal characterization through differential scanning calorimetry (DSC) was done, finding evidence of a T_g and T_m reduction in the nanofibers in relation to PA 6/66 pellets and nanofiber bundles.