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Composites

Composite materials combine different properties of two or more materials to form a new material with properties unlike those of the individual components. What distinguishes composites from solid solutions and mixtures is the fact that that their individual components remain separate and distinct. Therefore, investigation and understanding of the composite materials’ properties are crucial for their application. Below you find an article about rheological investigations of biogenic nano-filler reinforced polypropylene as high-strength 3D printing material, and of pore size characterization of metal organic frameworks (MOFs) with the gas adsorption technique. With decades of experience in the fields of both rheology and gas adsorption, Anton Paar is the best possible partner when it comes to devices for rheological investigations or gas adsorption analyzers.  

Biogenic nano-filler reinforced polypropylene as high-strength 3D printing material

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Introduction

Crystalline nano cellulose (CNC) has recently been in the focus of the scientific community as a natural reinforcement material for polymers following the ubiquitous striving for green engineering and increased sustainability. CNC is typically synthesized via hydrolysis of refined cellulosic fibers taken from wood pulp. Here, this natural reinforcement material is introduced into recycled 3D printable polypropylene to improve the polymer’s mechanical characteristics for developing a high-strength material suitable for fused filament fabrication (FFF). Processing-relevant properties such as the melt viscosity are additionally monitored to ensure impeccable printability of the novel nanocomposite and thereby maintain the versatile possibilities provided by additive manufacturing.

Experimental

Material fabrication: The compatibilized CNC was compounded into the recycled polypropylene matrix at filler ratios of 5 vol%, 10 vol%, and 15 vol%. Filaments with mean outer diameters between 1.5 mm and 1.8 mm were then produced via extrusion. The filaments are shown in the figure below.

Characterization techniques: Dynamic mechanical analysis was performed on an Anton Paar MCR 702e MultiDrive equipped with a linear drive to characterize the material’s mechanical behavior represented by its storage and loss modulus as well as by its loss factor. Shear rheological measurements were performed on an Anton Paar MCR 702e MultiDrive to determine the material’s melt viscosity as a fundamental processing-relevant property.

Results and discussion

The nanocomposites show an increase in the storage modulus with increasing filler content whereas the largest increase is detected for the nanocomposite with the highest filler content. Thus, the mechanical characteristics are successfully improved by the introduction of CNC into the polypropylene matrix while only using reinforcement originating from renewable sources.

The viscosity increases with increasing filler content when determined with a capillary rheometer directly during the extrusion of the filaments. Interestingly, when performing consecutive shear rheological investigations on the extruded filaments, the viscosity decreases with increasing filler content. As the specimens darken during these measurements, this effect is attributed to a thermal degradation of the compatibilizer which highlights the material’s sensibility towards 3D printing. Nevertheless, the nanocomposites kept its printability as proved by several executed prints of the novel material.

Additional information

Instruments:

Sources:

The research was partially carried out within the framework of the FFG-funded project “Natural3D” by Dr. Joamin Gonzalez-Gutierrez and Åste Brune Tomren from the Chair of Polymer Processing, Montanuniversitaet Leoben.

  1. Gonzalez-Gutierrez, Joamin, et al. "Additive manufacturing of metallic and ceramic components by the material extrusion of highly-filled polymers: A review and future perspectives." Materials 11.5 (2018): 840.

Application Report:

Pore size characterization of metal organic frameworks (MOFs)

Introduction

Metal-organic frameworks are crystalline solids with very high pore volumes and surface area, and, as such, many are candidates for gas storage and gas separation. Theoretically, pore size can be calculated with X-ray diffraction and other scattering techniques. However, gas sorption has the unique ability to directly probe the pore space, thereby revealing additional information about the true nature of the material (is the porosity accessible?). As such it can confirm the suitability - or not - of candidate materials for such gas storage applications. In addition, information such as heat of adsorption can be calculated from isotherms measured at different temperatures.

Experimental

Characterization techniques: N2 (77 K), Ar (87 K), and hydrogen (77, 87, 97 K) gas sorption measurements on MOFs were performed using an autosorb iQ MP gas sorption (vacuum-volumetric) analyzer. Prior to the analysis, the MOF sample was outgassed at room temperature for 48 hours under a turbomolecular pump vacuum. 77 K and 87 K isotherms were obtained by cooling the samples with liquid nitrogen and liquid argon, respectively. Measurement of the hydrogen isotherm at 97 K was performed using a cryostat device.

Results and discussion

N2 (77 K) and Ar (87 K) isotherms were measured on a novel Cu MOF. The Ar (87 K) isotherm showed a structural change of the MOF upon Ar adsorption due to the hysteresis measured below p/p0 = 0.4. The pore size distribution was calculated from the Ar isotherm using the NLDFT cylindrical pore oxidic (zeolite) model, and showed pores centered around 0.5 nm. H2 isotherms were measured at 3 different temperatures, and the resulting heat of adsorption plot was calculated based on the Clausius-Clapeyron equation. The heat of adsorption was found to be around 6.5 kJ/mol. This Cu MOF had a high adsorption potential for H2, making it a potential candidate for hydrogen gas storage applications.

Additional information

Instruments:

Source:

D. Lassig et al; Angew. Chem. Int. Ed. (2011) 50: 10344-10348

Application report:

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