Transparent optical polymer/filler systems can be produced into complex shapes for a range of applications, such as lenses, shields, and containers. This work used refractive index liquids as a model for polymer matrices to investigate the degree of refractive index match required to maintain high transmission in an inorganic-filled polymer system (cubic calcium fluoride with particle size of 1 to 5 µm) over the visible spectrum. It was determined that in order to achieve a transparent composite (>85% transmission with 10 mm pathlength) with this filler (using literature reported dispersion data), the materials must have a refractive index match within ±0.007 for 1.6 vol.% loading. With a loading of 3.1 vol.%, the matching range required was reduced to approximately ±0.002.

A ram extruder is described for high-pressure extrusion of fully compounded thermoset rubber to achieve additive manufacturing. The extruder uses a piston driven by a geared stepper motor to provide volumetric displacement of the rubber charge residing in a temperature-controlled barrel. Along with activators, accelerators, and a vulcanizing agent, the rubber compound is a formulation of 30 parts carbon black per hundred parts nitrile rubber. Sets of serpentine patterns are printed in parallel and transverse orientations relative to the load direction. From printing to post-cure, the printed specimens exhibited linear shrinkage of 65% in the print direction. Although printed samples had relatively low void content compared with typical additively manufactured parts by material extrusion, significant decreases in the tensile properties were observed relative to compression-molded specimens of the same rubber compound. The mean strain to failure was observed as 462% for compression-molded samples, compared with 347% and 183% for printed specimens with parallel and transverse orientations. To reduce the shrinkage and increase the interfacial area between extruded roads, backstitch and sinewave diddling patterns were implemented to superimpose oscillatory motions along the print path with a periodicity of 1 mm. The specimens printed with the diddling patterns were observed to provide less shrinkage and improved properties compared to the regular serpentine patterns. The mean strain to failure in the transverse orientation, respectively, increased to 218% and 265% for the backstitch and sinewave patterns. Suggested future research is discussed, and the diddling program is provided in the appendix. K E Y W O R D S material extrusion, nitrile rubber, diddling patterns, 3D printing, thermoset rubber 1 | INTRODUCTION Additive manufacturing provides a means by which complex products may be made without tooling. ASTM F2792: Standard Terminology for Additive Manufacturing Technologies defines seven families of additive manufacturing. Of

No abstract

Highly-filled polymer systems include color masterbatches, feedstocks for powder injection molding, and rigid sheets with high levels of flame retardants, but they have not been explored for flexible sheet. This work investigated the (a) selecting a polymer matrix with enough melt strength and flexibility to form a stable sheet with high filler loading, (b) the maximum achievable filler loading for the sheet, and (c) optimizing the process of extruding a highly-filled flexible polymer system. Extrusion grade low-density polyethylene (LDPE) provided sufficient flexibility and permitted a maximum filler loading of 36 vol% (~78 wt%). Good dispersion of the nanoparticle filler, however, required two passes through multiple screw extruders and a small reduction in the viscosity of the LDPE. Sheet with thickness of 415 μm, surface roughness of <1 μm, and sufficient flexibility was extruded continuously at a rate of 10 m/min., but it required a more traditional coat hanger manifold to prevent filler hang up in the sheet die. The filler particles were distributed uniformly through the core and skin of the sheet, giving the sheet good mechanical properties.

This article presents a printed tunable right/left-handed leaky wave antenna (LWA) on a new flexible, tunable low density polyethylene-barium strontium titanate composite substrate using an aerosol jet printer. The new substrate had a dielectric constant of 16 and tunability of 3.5% at f = 10 GHz. Interdigital capacitors (IDC) were utilized in the leaky wave antenna design not only to act as shunt capacitor in CRLH transmission line design but also as tunability element to implement tuning capability of the LDPE-BST substrate for antenna beam steerability for a fixed operated frequency in X-band frequency range. Up to 15 beam steering was achieved by applying DC voltage through the printed leaky wave antenna.