A Review of Wet Compounding of Cellulose Nanocomposites

Cellulose nanomaterials (CNs) are an emerging class of materials with numerous potential applications, including as additives or reinforcements for thermoplastics. Unfortunately, the preparation of CNs typically results in dilute, aqueous suspensions, and the lack of efficient water removal methods has hindered commercialization. However, water may also present opportunities for improving overall efficiencies if its potential is better understood and if it is better managed through the various stages of CN and composite production. Wet compounding represents one such possible opportunity by leveraging water’s ability to aid in CN dispersion, act as a transport medium for metering and feeding of CNs, plasticize some polymers, or potentially facilitate the preparation of CNs during compounding. However, there are also considerable challenges and much investigation remains. Here, we review various wet compounding approaches used in the preparation of cellulose nanocomposites as well as the related concepts of wet feeding and wet extrusion fibrillation of cellulose. We also discuss potential opportunities, remaining challenges, and research and development needs with the ultimate goal of developing a more integrated approach to cellulose nanocomposite preparation and a more sophisticated understanding of water’s role in the compounding process.

Wet extrusion molding of wood powder with hydroxy-propylmethyl cellulose and with citric acid as a crosslinking agent

To mitigate global warming and the serious problems incurred by the disposal of petroleum-based plastics, it is important to develop derivatives of biomass materials that can be used as substitutes. To overcome the lack of thermoplasticity of wood, a wet extrusion molding process for wood powder using a cellulose derivative, hydroxypropylmethyl cellulose (HPMC), had been developed. However, this material quickly reabsorbed water, swelled, and disintegrated in liquid. In the present study, a natural organic acid, citric acid, was added and kneaded together with the wood powder, the HPMC, and water. The resultant clay-like material was extruded into a tube-shaped material. The tube was air-dried and heated at 180 °C for 5 min to 30 min to allow crosslinking. By heating 1% citric acid for 30 min, the material avoided disintegrating in water for 60 min. The addition of 3% citric acid with 30 min crosslinking gave the material water resistance in water for 12 h. The degradability in the water was found to be controllable by changing the amount of citric acid and the heating time. This is a novel result because wood can be molded into a practical three-dimensional (3D) biomass composite material using this technology with natural substances without relying on petroleum-based plastics.

The Potential Migrated Mechanism of Water-Soluble Components in Pellets Prepared by Wet Extrusion/Spheronization: Effect of Drying Rate

Background: At present, there were numerous researches on the migration of components in tablets and granules, the investigation in the pharmaceutical literatrue concerning the effect of drying rate on the migration of water-soluble components of pellets was limited. Temperature and relative humidity (RH) were crucial parameters during the drying process which was an essential step in the preparation of pellets via wet extrusion/spheronization. To quantify these variables, the water loss percentage of pellets per minute was defined as drying rate. Objective: The study aimed to investigate the influence of drying rate on the migration of water-soluble components in wet pellets and the potential migrated mechanism. Methods: The pellets containing tartrazine as a water-soluble model drug and microcrystalline cellulose as a matrix former were prepared by extrusion/spheronization and dried at four different drying temperature and relative humidity. Afterward, the extent of migrated tartrazine was assessed regarding appearance, in-vitro dissolution test, Differential Scanning Calorimetry, X-Ray Powder Diffraction, Attenuated total reflectance Fourier transform infrared spectroscopy and Confocal Raman Mapping. Results: Results demonstrated that red spots of tartrazine appeared on the surface of pellets and more than 40% tartrazine were burst released within 5 minutes when pellets dried at 60℃/RH 10%. While pellets dried at 40℃/RH 80%, none of these aforementioned phenomena was observed. Conclusion: In conclusion, the faster drying rate was, the more tartrazine migrated to the exterior of pellets. Adjusting drying temperature and relative humidity appropriately could inhibit the migration of water-soluble components within wet extrusion/spheronization pellets.

Modelling the Effect of Process Parameters on the Wet Extrusion and Spheronisation of High-Loaded Nicotinamide Pellets Using a Quality by Design Approach

The aim of the present study was to develop an alternative process to spray granulation in order to prepare high loaded spherical nicotinamide (NAM) pellets by wet extrusion and spheronisation. Therefore, a quality by design approach was implemented to model the effect of the process parameters of the extrusion-spheronisation process on the roundness, roughness and useable yield of the obtained pellets. The obtained results were compared to spray granulated NAM particles regarding their characteristics and their release profile in vitro after the application of an ileocolon targeted shellac coating. The wet extrusion-spheronisation process was able to form highly loaded NAM pellets (80%) with a spherical shape and a high useable yield of about 90%. However, the water content range was rather narrow between 24.7% and 21.3%. The design of experiments (DoE), showed that the spheronisation conditions speed, time and load had a greater impact on the quality attributes of the pellets than the extrusion conditions screw design, screw speed and solid feed rate (hopper speed). The best results were obtained using a low load (15 g) combined with a high rotation speed (900 m/min) and a low time (3–3.5 min). In comparison to spray granulated NAM pellets, the extruded NAM pellets resulted in a higher roughness and a higher useable yield (63% vs. 92%). Finally, the coating and dissolution test showed that the extruded and spheronised pellets are also suitable for a protective coating with an ileocolonic release profile. Due to its lower specific surface area, the required shellac concentration could be reduced while maintaining the release profile.

The effect of loading direction on the compressive behaviour of a 3D printed cement-based material

<p>Nowadays, additive manufacturing is being widely employed in several areas and is starting to be considered for the construction sector amongst the digital construction trend. The advantages that the additive manufacturing techniques can bring over the traditional construction methods are propelling multiple research projects within the field of 3D concrete printing. Technologies used for printing, material compositions and their rheological and mechanical properties are some of the research areas on 3D concrete printing. In this work, it is used a wet extrusion method for printing a cement-based mortar mixture. The compressive behaviour of printed specimens was evaluated based on the direction of loading. The results showed that with a proper printing process and rheological properties, in the case of the current mid-strength matrix, the effect of the layers interfacial behaviour on the compressive behaviour of printed specimens was reduced.</p>

Development of cement-based mortars for 3D printing through wet extrusion

<p>The construction sector is connoted as an extremely traditional business sector since long ago. However, due to the increase of the global competiveness, there is a demand on the development of new building materials and construction methods that can bring added value to the companies. The 3D concrete printing is a novel construction approach within digital construction that can offer a higher degree of optimization and flexibility for producing either structures or structural elements with complex geometries. One of the main challenges in the 3D concrete printing using wet extrusion is balancing properly the rheological and mechanical properties of the printable mixtures. In this study, several mixtures were developed and their capability for being used in 3D printing was assessed and discussed based on their rheological properties. The compressive strength of the matrices that could be properly printed are also presented.</p>