Environmental Stability of Additively Manufactured Thermoplastic Polyamide Composites.

As the adoption of additive manufacturing technologies for end-use parts continues to progress, the evaluation of environmental durability is essential for the qualification of manufactured articles in industries such as automotive, aerospace, and electrical. This study explores the effects of UV and water-spray exposure on the mechanical properties of an additively manufactured polyamide 6 blend reinforced with short carbon fiber and continuous carbon fiber. Fused-filament-fabrication-printed test samples were exposed to a Xenon-arc UV source following ASTM G155 Cycle 1 conditions for a duration of 1000 h. Tensile, flexural, and Izod impact tests were performed on exposed and unexposed test samples. While Exposed tensile and flexural samples maintained their strength (84-100% and 88-100%, of Control samples, respectively), Izod impact strength increased (104-201% of Controls). This study also examines the influence of coatings and finds that samples coated with Krylon® Fusion All-In-One® and JetFlex® Polyurethane Primer maintain similar mechanical properties and exhibit a better visual appearance as compared to uncoated, exposed samples.

Effects of Coefficient of Thermal Expansion and Moisture Absorption on the Dimensional Accuracy of Carbon-Reinforced 3D Printed Parts.

Environmental effects-temperature and moisture-on 3D printed part dimensional accuracy are explored. The coefficient of thermal expansion of four different nylon materials was determined for XY and ZX print orientations, with 0°, 45°/-45°, and 90° infill patterns. Unreinforced nylon exhibited a thermal expansion coefficient of the same order regardless of condition (from 11.4 to 17.5 × 10-5 1/°C), while nylons reinforced with discontinuous carbon fiber were highly anisotropic, for instance exhibiting 2.2 × 10-5 1/°C in the flow direction (0° infill angle) and 24.8 × 10-5 1/°C in the ZX orientation. The temperature profile of a part during printing is shown, demonstrating a build steady state temperature of ~ 35 °C. The effect of moisture uptake by the part was also explored, with dimensional changes of ~0.5-1.5% seen depending on feature, with height expanding the most. The effects of moisture were significantly reduced for large flat parts with the inclusion of continuous fiber reinforcement throughout the part.

Polypropylene crystallization at an alumina interface using single walled carbon nanotubes.

Interfaces play an important and often limiting role in the mechanical, thermal, and electrical performance of composite materials. Here we suggest a novel method to improve the interfacial interaction in polypropylene-alumina composites using single-walled carbon nanotubes (SWNTs) to nucleate lamellar crystals at the interface. Macroscopic alumina substrates are used to determine the ideal crystallization parameters and investigate the kinetics of crystal growth. SWNTs are uniformly adsorbed to the interface via Van der Waals interactions and lamellar crystals are grown on the surface using isothermal solution processing techniques. Avrami analysis of crystal surface coverage was used to confirm one-dimensional transcrystalline growth commonly seen with SWNT nucleated crystals. Scanning electron microscopy was used to confirm shish-kebab structures present at the SWNT-polypropylene interface. The determined crystallization parameters were used on colloidal solutions of alumina platelets to successfully create uniformly coated particles with an improved interface. This method shows promise for improving the interphase of semicrystalline polymer-ceramic composites to achieve excellent material properties.