Effect of High Molecular Weight PPTA on Liquid Crystalline Phase and Spinning Process of Aramid Fibers

Abstract

High molecular weight poly (p-phenylene-terephthalamide) (h-PPTA) was blended with the commercial PPTA in concentrated sulfuric acid to improve the spinnability of the polymer solutions and the mechanical properties of the as-spun fibers. h-PPTA in the solution has an influence on the temperature of the formation of liquid crystalline phenomenon. The temperature range with the existence of the liquid crystalline phase increases upon the contents of h-PPTA in the solution, and the extended temperature window is helpful for the preparation of PPTA fibers by the dry-jet wet-spinning technology. The long-chains of h-PPTA enhance the inter-macromolecular interactions and induce the orientation of short-chains for PPTA along the fiber axis under the shear stress in the spinneret and the stretching stress at the air gap. These effects also increase the maximum drawing ratio in the spinning process and improve the mechanical properties of the obtained fibers. The crystallinity and crystal orientation of the fibers are investigated by X-ray diffraction, and results from sonic velocity test further confirm ordering state of the macromolecular chains. The fibril morphologies of the fibers are also studied by a scanning electric microscope.

Recycling of High-Value-Added Aramid Nanofibers from Waste Aramid Resources via a Feasible and Cost-Effective Approach

“…There are many factors that affect the strength and modulus of aramid fiber, including the molecular weight of the aramid, the drawing ratio of the nozzle, the concentration of the spinning slurry, the temperature of the slurry, and other factors. However, the fundamental factor that determines the strength of the aramid fiber is the molecular weight . As a result of the extremely poor solubility of aramid fiber and it can only be dissolved in strong acid systems such as concentrated sulfuric acid (H 2 SO 4 ).…”

“…Therefore, the inherent viscosity (η inh ) is usually used to characterize the molecular weight of aramid fiber in industry. It has been reported that when the η inh increases every 1 dL·g –1 , the strength of the aramid fiber can be increased by about 3–4 cN·dtex –1 . Although the preparation of ANFs by the method of deprotonation from the macroscopic aramid fiber is widely used by researchers, people mainly focus on the applications of ANFs in nanocomposites about the compatibility, enhancement effect, and mechanism.…”

“…However, the fundamental factor that determines the strength of the aramid fiber is the molecular weight. 34 As a result of the extremely poor solubility of aramid fiber and it can only be dissolved in strong acid systems such as concentrated sulfuric acid (H 2 SO 4 ). Consequently, the molecular weight of the aramid fiber cannot be measured by conventional methods due to the high corrosiveness of H 2 SO 4 .…”

Isotropic and Anisotropic Scaffolds for Tissue Engineering: Collagen, Conventional, and Textile Fabrication Technologies and Properties

“…For the spinning of some specific polymers, spinning methods need to be adapted, further developed, and combined. Therefore, special spinning methods have been established such as matrix spinning for particularly resistant filaments made of the non-soluble or meltable polytetrafluoroethylene [130], gel spinning for high-strength filaments made of the ultra-high-molecular-weight polyethylene [131], air-gap spinning for improving polymer orientation for filaments made of aramid (e.g., Kevlar ® ) [132], or melt electrospinning for nanofilaments made of non-soluble but meltable polymers [133].…”

Composite Aramid Membranes with High Strength and pH-Response

“…However, on account of the lack of polar functional groups, high crystallinity, and the tendency of hydrogen bonds to form between molecules, aramid fibers are chemically inert and their surfaces are extremely smooth. Consequently, their interfacial bonding strength with other substrates is poor, which greatly limits the applicability of aramid fibers [ 22 , 23 , 24 ].…”