Chukwuzubelu Okenwa Ufodike

To better understand the polymer flow physics through the hot end of a material extrusion additive manufacturing process, a volume of fluid multiphase computational fluid dynamics model (CFD) was formulated to integrate the effect of interfacial forces in the air gap between the heating wall and the melting filament. The model was validated by developing a measurement system that captures the extrusion dynamics, which was quantified in terms of feeding force by using two load cells rated at 5 kg and 20 kg as force sensors and a 1 kg load cell to measure extrudate mass. The CFD experimental validation setup presents a detailed method for integrating an inline force measurement system into a commercial 3D printer, requiring minimal modifications to the printhead and gantry head arrangement. The CFD model result, validated against experimental data, follows more closely the measured feeding force of the 5 kg load cell than the 20 kg load cell. The experimental results further show that lower-rated load cells (5 kg) are more precise at low feeding rates, while higher-rated load cells (20 kg) are better for higher extrusion forces. The CFD analysis of the internal flow through the hot end revealed fascinating actionable insights for exploiting interfacial tension effects for the design of the hot end and extrusion system, enabling faster and more reliable printing. The new understanding of the interaction between thermofluid and interfacial tension can inform process parameter control and the design of desktop 3D printers.

The earth faces a pressing environmental challenge with the annual pollution of millions of tons of plastic waste. This issue is exacerbated by the inherent characteristics of plastics, including their high thermal stability and low biodegradability. In response, the scientific community has dedicated significant efforts to combat plastic pollution and develop environmentally sustainable soft materials. A promising approach is the creation of soft materials that can be efficiently recycled within a closed-loop system, thereby minimizing their chemical impact on the environment. This study introduces polyacylhydrazones as a novel class of soft materials with the potential for closed-loop recycling. Closed-loop polymers are sought after as sustainable materials of the future. Dynamic covalent polymers have the potential to act as closed-loop materials because of their reversible linkages. However, very few materials currently exist. Polyacylhydrazones have been explored as dynamic covalent polymers with multiple uses. Herein we demonstrate the first study that shows their potential as closed-loop materials. We show novel synthetic techniques that produce hydrophobic polyacylhydrazones with unique length and morphology under kinetic control. We demonstrate preliminary potential applications. Finally, we show the facile decom-position of a benzylic hydrazone bond down to monomeric units and extraction-based separation, without the need for chromatography. This work advances our understanding of these innovative materials and validates benzylic polyacylhydrazones as “closed-loop” materials for a more sustainable future.

Products made from petroleum-derived plastic materials are linked to many environmental problems, such as greenhouse gas emissions and plastic pollution. It is desirable to manufacture products from environmentally friendly materials instead of petroleum-based plastic materials. Products made from biomass–fungi composite materials are biodegradable and can be utilized for packaging, construction, and furniture. In biomass–fungi composite materials, biomass particles (derived from agricultural wastes) serve as the substrate, and the fungal hyphae network binds the biomass particles together. There are many reported studies on the 3D printing of biomass–fungi composite materials. However, there are no reported studies on the biodegradation of 3D-printed samples from biomass–fungi composite materials. In this study, two types of biomass materials were used to prepare printable mixture hemp hurd and beechwood sawdust. The fungi strain used was Trametes versicolor. Extrusion based 3D printing was used to print samples. 3D-printed samples were left for five days to allow fungi to grow. The samples were then dried in an oven for 4 h at 120 °C to kill all the fungi in the samples. The samples were buried in the soil using a mesh bag and kept in an environmental chamber at 25 °C with a relative humidity of 48%. The weight of these samples was measured every week over a period of three months. During the testing period, the hemp hurd test samples lost about 33% of their original weight, whereas the beechwood sawdust samples lost about 30% of their original weight. The SEM (scanning electron microscope) micrographs showed the presence of zygospores in the test samples, providing evidence of biodegradation of the test samples in the soils. Additionally, the difference in peak intensity between the control samples and test samples (for both hemp hurd and beechwood sawdust) showed additional evidence of biodegradation of the test samples in the soils.

Products made from petroleum-derived plastic materials are linked to many environmental problems such as greenhouse gas emissions and plastic pollution. It is desirable to manufacture products from environmentally friendly materials instead of petroleum-based plastic materials. Products made from biomass-fungi composite materials are biodegradable and can be utilized for packaging, construction, and furniture. In biomass-fungi composite materials, biomass particles (derived from agricultural wastes) serve as the substrate and the fungal hyphae network binds the biomass particles together. There are many reported studies on 3D printing of biomass-fungi composite materials. However, there are no reported studies on biodegradation of 3D printed samples from biomass-fungi composite materials. In this study, two types of biomass materials were used to prepare printable mixture hemp hurd and beechwood sawdust. The fungi strain used was Trametes versicolor. Extrusion based 3D printing was used to print samples. 3D printed samples were left for five days to allow fungi to grow. The samples were then dried in an oven for 4 hours at 120ºC to kill all the fungi in the samples. The samples were buried in the soil using a mesh bag and kept in an environmental chamber at 25℃ with a relative humidity of 48%. The weight of these samples was measured every week over the period of three months. Both types of samples (prepared from beechwood sawdust and hemp hurd, respectively) showed weight change after three months. Furthermore, the samples made from hemp hurd had more weight change than the samples made from beechwood sawdust. The SEM (scanning electron microscope) micrographs and FTIR (Fourier transform infrared) spectroscopy showed evidence of biodegradation of these samples.

Biomass–fungi composite materials primarily consist of biomass particles (sourced from agricultural residues) and a network of fungal hyphae that bind the biomass particles together. These materials have potential applications across diverse industries, such as packaging, furniture, and construction. 3D printing offers a new approach to manufacturing parts using biomass–fungi composite materials, as an alternative to traditional molding-based methods. However, there are challenges in producing parts with desired quality (for example, geometric accuracy after printing and height shrinkage several days after printing) by using 3D printing-based methods. This paper introduces an innovative approach to enhance part quality by incorporating ionic crosslinking into the 3D printing-based methods. While ionic crosslinking has been explored in hydrogel-based bioprinting, its application in biomass–fungi composite materials has not been reported. Using sodium alginate (SA) as the hydrogel and calcium chloride as the crosslinking agent, this paper investigates their effects on quality (geometric accuracy and height shrinkage) of 3D printed samples and physiochemical characteristics (rheological, chemical, and texture properties) of biomass–fungi composite materials. Results show that increasing SA concentration led to significant improvements in both geometric accuracy and height shrinkage of 3D printed samples. Moreover, crosslinking exposure significantly enhanced hardness of the biomass–fungi mixture samples prepared for texture profile analysis, while the inclusion of SA notably improved cohesiveness and springiness of the biomass–fungi mixture samples. Furthermore, Fourier transform infrared spectroscopy confirms the occurrence of ionic crosslinking within 3D printed samples. Results from this study can be used as a reference for developing new biomass–fungi mixtures for 3D printing in the future.

Agriculturally derived biowastes can be transformed into a diverse range of materials, including powders, fibers, and filaments, which can be used in additive manufacturing methods. This review study reports a study that analyzes the existing literature on the development of novel materials from agriculturally derived biowastes for additive manufacturing methods. A review was conducted of 57 selected publications since 2016 covering various agriculturally derived biowastes, different additive manufacturing methods, and potential large-scale applications of additive manufacturing using these materials. Wood, fish, and algal cultivation wastes were also included in the broader category of agriculturally derived biowastes. Further research and development are required to optimize the use of agriculturally derived biowastes for additive manufacturing, particularly with regard to material innovation, improving print quality and mechanical properties, as well as exploring large-scale industrial applications.

Limiting casting expression speed was obtained and the flow redistribution and thermal history in a horizontal direct-chill (HDC) casting was predicted using the numerical modeling approach. The governing solidification equations were non-dimensionalized to understand the relevant contribution of each term in the solidification processes in the HDC system. The effect of an increase in the casting speed on the flow characteristics and sump length was represented by the Péclet number Pe. Details of the simulation reveal that at a low Pe, the natural convective flow creates minor counter-clockwise recirculating cells in the lower half of the HDC domain. However, at a Pe above 82.75, the minor recirculating cells disappear due to the strong forced convective flow from the upstream. Additionally, an increase in the Pe increases the sump length, strength, and spread of the turbulence field within and beyond the mold region. The limiting casting conditions are computed by predicting the sump length over which the alloy temperature is above the solidus temperature. This gives a simple relation for the casting speed as a function of the geometrical data and the alloy properties. The current work is useful to casting engineers who always rely on trial and error in choosing a new casting speed whenever a new alloy is to be produced. Hence, with the new information and the casting speed relations, it is possible and easy to predict the operating window over which melt break-out can occur during HDC.

Biomass–fungi composites, an emerging class of sustainable materials, have potential applications in the construction and packaging industries. Molding-based manufacturing methods are typically employed to make products from these composites. Recently, a 3D printing-based method was developed for biomass–fungi composites to eliminate the need for making molds and to facilitate customized product design compared with manufacturing methods based on molding and hot-pressing. This method has six stages: biomass–fungi material preparation; primary colonization; mixture preparation; printing; secondary colonization; and drying. This paper reports a study about the effects of waiting time between the mixture preparation and 3D printing using biomass–fungi composites. As the waiting time increased from 0.25 to 3 h, the hardness and compressibility of the prepared mixture increased. As the waiting time increased from 0.25 to 8 h, the shear viscosity showed a decreasing trend; the yield stress of the prepared mixture increased at the beginning, then significantly decreased until the waiting time reached 3 h, and then did not significantly vary after 3 h. As the waiting time increased, the storage modulus and loss modulus decreased, the loss tangent delta increased, and the minimum required printing pressure for continuous extrusion during extrusion-based 3D printing increased. The print quality (in terms of layer-height shrinkage and filament-width uniformity) was reasonably good when the waiting time did not exceed 4.5 h.