Molecular Weight Discrete Distribution-Induced Orientation of High-Strength Copolyamide Fibers: Effects of Component Proportion and Molecular Weight

Surface modification of reinforcement fibers is a potent strategy for enhancing the mechanical performance of fiber-reinfored composites. However, the strategy has rarely been applied to powder bed fusion because of the limited modification effectiveness. Here, a new surface modification method for aramid fibers (AFs) using amino-terminated hyperbranched polyamide (HBP) was proposed to improve the mechanical performance of the AF-reinforced polyamide 12 (PA12) composites printed by Multi Jet Fusion (MJF). The effect of the surface modification on the AFs was systematically examined by studying their surface morphology, chemical composition, and interfacial shear strength. The modified fibers were applied to fabricating PA12-based composite powders, which were then printed with an MJF printing testbed to reveal the effects of the fiber fraction, build orientation, and surface modification on their mechanical properties. The results showed that the surface modification of the AFs induced higher surface roughness by HBP coating and realized surface functionalization by amino groups. With the enhanced interfacial properties, the optimized AF-HBP/PA12 composite showed substantial improvement in its ultimate tensile strength and Young’s modulus by 55% (73.4 MPa) and 110% (4.2 GPa), respectively, compared with the neat PA12 part. This simple and effective surface modification method can be further applied to other manufacturing technologies. 

Improvement in the mechanical performance of Multi Jet Fusion–printed aramid fiber/polyamide 12 composites by fiber surface modification

Short wet-steaming low-carbon cleaner pad dyeing of cotton/polyamide/lyocell fabric with reactive dyes

Poly(ethylene tridecanodiate), also known as poly(ethylene brassylate) (PEB), is a short–long aliphatic polyester obtained from a renewable source. Cooled from the melt by differential scanning calorimetry or by fast scanning calorimetry, PEBs in a range of molar mass between 27000 and 188000 Da display single crystallization exotherms. On heating, PEBs exhibit two major melt-recrystallization events at ∼40 and ∼60 °C prior to their final melting at ∼70 °C. WAXD patterns collected in situ during heating rule out any polymorphic transition, but SAXS patterns collected at the isothermal crystallization temperatures below and above the highest melt-recrystallization event (∼60 °C) indicate a step increase by one repeating unit of the crystal thickness. The overall isothermal crystallization rate displays two minima at the same temperatures where melt-recrystallization was observed on heating. The minima correspond to the transition between 2–3 repeats (Tc = 40 °C) and between 3–4 (Tc = 60 °C) monomer repeats in the crystal thickness. A minimum also occurs at the same temperature in the isothermal linear growth rates and is accompanied by a minimum in nucleation density. The observed rate minima at the transition between crystals differing by a quantized thickness are equivalent to the behavior of n-alkanes and low-Mw PEO fractions and are also explained by the manifestation of self-poisoning. At Tc approaching a rate minimum from above, PEB stems with noninteger repeats attach temporarily to the integer lateral growing surface halting productive growth until they detach or expand to complete the layer. Hence, for this type of polyester, it is the length of the stem approaching the growing surface rather than stems with a different conformation that drives self-poisoning. 

Crystallization Rate Minima of Poly(ethylene brassylate) at Temperatures Transitioning between Quantized Crystal Thicknesses

Interfacial architecture of the nanofillers is the critical factor to achieve desirable dielectric properties in the polymer nanocomposites. However, a basic understanding of the role of interfacia...

Concurrently Improved Breakdown Strength and Storage Energy Capacitance in the Core–Shell-Structured Aromatic Polythiourea@BaTiO3 Polymer Nanocomposites Induced by the Nature of Interfacial Polarization and Crystallization

Effects of hydrogen-bonding density on polyamide crystallization kinetics

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Effects of hydrogen-bonding density on polyamide crystallization kinetics