Xuan Li,Lili Wang,Dujin Wang,Alejandro J. Müller,Xia Dong
Successive self-nucleation and annealing (SSA) is an efficient way to thermally fractionate semicrystalline polymers. SSA thermal fractions have distinct melting points corresponding to different lamellar thicknesses. SSA was employed to investigate the in-situ evolution of lamellar thicknesses of polyamide 1012 (PA1012) during high-temperature thermal treatments. A competition between chain growth and crosslinking occurred during the thermal treatments as detected (as a function of time) by SSA, rheology, and dissolution behavior. Based on a master curve of “time–temperature superposition” at a reference temperature, the mechanism for lamellar thickness evolution was divided into three stages: initially, chemical crosslinking predominated. As the number of end groups rapidly increased, linear chain growth and crosslinking occurred simultaneously. Eventually, linear chain growth was increased by chain end-group reactions. The structural changes provoked by the thermal treatments enhanced the mechanical and heat resistance properties of PA1012. This work provides guidance for the design for high-performance polyamide materials.
Canchen Sun,Yuanyuan Wang,Bin Wang,Yanxia Cao,Jianfeng Wang,Yanyu Yang,Wanjie Wang
Here, zinc-neutralized ethylene propylene diene monomer (EPDM) ionomers with different neutralization levels are prepared through melt blending, and are then incorporated with polyamide 1012 (PA1012) to fabricate PA1012/EPDM ionomer blends. Interestingly, complex crosslinking networks are formed in the blends due to the construction of sacrificial bonds (Zn 2+ -carboxyl, Zn 2+ -amide). The as-formed network structure and sacrificial bond endow the PA/EPDM blends with largely enhanced toughness (16 times higher than that of neat PA), as well as balanced strength and stiffness. Meanwhile, the rheological behaviors of PA1012/EPDM ionomer blends indicate their relative low melting viscosity, which can avoid the processing shortcomings of plastics toughened with rubber. Moreover, PA1012/EPDM ionomer blends show obvious gelation behavior, and a maximum notched Izod impact strength exhibited at the gel point, in which unique double network structure can be observed obviously, indicating that there is a corresponding correlation between the rheological and mechanical parameters. Furthermore, the supper-toughening mechanism of PA1012/EPDM ionomer blends at gel point is explored, which origins from the large deformation and cavitation of rubber particles and the destruction of special double network morphologies. This study provides a novel and effective strategy to fabricate PA materials with outstanding toughness and excellent strength simultaneously.
Xinran Liu,Yu Wang,Yongyan Pang,Xia Dong,Dujin Wang
In this study, a fast and convenient method that can characterize the molecular weight (MW) and its distribution (PDI) of polyamide 1012 after the solid-state polymerization (SSP) was proposed with the rheological technique. Conventionally, polyamides have to be chemically modified to become soluble in an organic solvent suitable for the Gel Permeation Chromatography (GPC) measurement. Herein, to avoid the complex operation of chemical modification, the quantitative correlations between the rheological properties such as zero-shear viscosity, complex viscosity, the frequency and modulus at the crossover point between the storage and loss modulus curves, and the obtained MW and PDI were established. Thus, without chemical modifications, the characterization of PA1012 during SSP becomes convenient and time saving, which is more approach to the real “on-line” control of SSP. The lamellar thickening and SSP occur simultaneously above T g during SSP. Its influence on the final results of SSP was studied. Furthermore, the impact of crystallinity of the raw materials on the SSP behavior was also investigated. The higher crystallinity can lead to a decrease in the SSP rate and final molecular weight and molecular weight distribution.
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