TiO2 nanoparticle-Coated 3D-Printed porous monoliths enabling highly sensitive speciation of inorganic Cr, As, and Se

Post-printing functionalization can enhance the functionality and applicability of analytical devices manufactured using three-dimensional printing (3DP) technologies. In this study we developed a post-printing foaming-assisted coating scheme-through respective treatments with a formic acid (30%, v/v) solution and a sodium bicarbonate (0.5%, w/v) solution incorporating titanium dioxide nanoparticles (TiO2 NPs; 1.0%, w/v)-for in situ fabrication of TiO2 NP-coated porous polyamide monoliths in 3D-printed solid phase extraction columns, thereby enhancing the extraction efficiencies of Cr(III), Cr(VI), As(III), As(V), Se(IV), and Se(VI) for speciation of inorganic Cr, As, and Se species in high-salt-content samples when using inductively coupled plasma mass spectrometry. After optimizing the experimental conditions, the 3D-printed solid phase extraction columns with the TiO2 NP-coated porous monoliths extracted these species with 5.0- to 21.9-fold enhancements, relative to those obtained with the uncoated monolith, with absolute extraction efficiencies ranging from 84.5 to 98.3% and method detection limits ranging from 0.7 to 32.3 ng L-1. We validated the reliability of this multi-elemental speciation method through determination of these species in four reference materials [CASS-4 (nearshore seawater), SLRS-5 (river water), 1643f (fresh water), and Seronorm Trace Elements Urine L-2 (human urine); relative errors between certified and measured concentrations: 5.6 to +4.0%] and spike analyses of seawater, river water, agriculture waste, and human urine samples (spike recoveries: 96-104%; relative standard deviations of these measured concentrations all below 4.3%). Our results demonstrate that post-printing functionalization has great potential for future applicability in 3DP-enabling analytical methods.

Improved Rotational Foam Molding Properties of Tailored Polyethylene Blends with Higher Crystallization Temperature and Viscosity-Temperature Sensitivity

Rotational foam molding has attracted more and more attention due to the inexpensive machines required, low residual stresses, and flexible design for special and high-value-added applications. However, it is a great challenge to control cell sizes and morphology because of its coalesce and collapse during prolonged heating or at different temperatures. A novel tailored polyethylene blend with a unique chain structure for rotational foam molding was creatively proposed and demonstrated, and the effects of crystallization temperature and viscosity–temperature sensitivity on foaming were also investigated. The polyethylene blends with few chain branches in the low-molecular-weight part and many chain branches in the high-molecular-weight part effectively improved the crystallization temperature and the viscosity–temperature sensitivity for better prevention of coalesce and collapse during the foam-shaping stage.

Morphological, thermal and mechanical properties of recycled HDPE foams via rotational molding

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

Morphological and Mechanical Properties of Bilayers Wood-Plastic Composites and Foams Obtained by Rotational Molding

In this work, the suitability for the production of sustainable and lightweight materials with specific mechanical properties and potentially lower costs was studied. Agave fiber (AF), an agro-industrial waste, was used as a reinforcement and azodicarbonamide (ACA) as a chemical blowing agent (CBA) in the production of bilayer materials via rotational molding. The external layer was a composite of linear medium density polyethylene (LMDPE) with different AF contents (0–15 wt %), while the internal layer was foamed LMDPE (using 0–0.75 wt % ACA). The samples were characterized in terms of thermal, morphological and mechanical properties to obtain a complete understanding of the structure-properties relationships. Increases in the thicknesses of the parts (up to 127%) and a bulk density reduction were obtained by using ACA (0.75 wt %) and AF (15 wt %). Further, the addition of AF increased the tensile (23%) and flexural (29%) moduli compared to the neat LMDPE, but when ACA was used, lower values (75% and 56% for the tensile and flexural moduli, respectively) were obtained. Based on these results, a balance between mechanical properties and lightweight can be achieved by selecting the AF and ACA contents, as well as the performance and aesthetics properties of the rotomolded parts.

Rotomolding of Foamed and Unfoamed GTR-LLDPE Blends: Mechanical, Morphological and Physical Properties

In this work, a simple method is presented to produce ground tire rubber (GTR) -linear low density polyethylene (LLDPE) compounds and foams via rotational molding. In particular, different GTR concentrations (0 to 50% wt.) were dry-blended with different chemical blowing agent (CBA) content (0 to 1% wt.). From the samples produced, a complete set of characterization was performed in terms of mechanical properties (tensile, flexural and impact), density and morphological properties. The results show that increasing GTR content or CBA content not only decreased both tensile and flexural moduli, but decreased ultimate strength and strain at break. As expected, increasing blowing agent content decreased density. Besides, with respect to impact strength, the value of all samples decreased with the addition of GTR or CBA except for 0.2% wt. CBA of GTR-LLDPE composite foams, which nearly remain at the same level.

Foams and Wood Composite Foams Produced by Rotomolding

In this work, a simple method is presented to produce foams and wood composite foams by rotational molding. As a special case, wood flour (maple) / linear low density polyethylene (LLDPE) was used to study the effect of chemical blowing agent (CBA) concentration (0-0.6%wt.) and wood content (0-20%wt.). From the samples produced, a complete characterization was performed including density, morphology, and mechanical properties in tension and flexion. The results show that tensile and flexural moduli increased with wood content, while tensile strength and elongation at break decreased. The optimum wood content was found to be around 20%wt. for the composites and around 0.4% wt. CBA for the range of conditions studied.