PLA composites: From production to properties

Recent developments on nanocellulose reinforced polymer nanocomposites: A review

Recent developments in nanocellulose-based biodegradable polymers, thermoplastic polymers, and porous nanocomposites

Research on nanocellulose has significantly increased over the past few decades, owing to the various attractive characteristics of this material, such as renewability, widespread availability, low density, excellent mechanical properties, economic value, biocompatibility, and biodegradability. Nanocellulose categorized into two main types, namely cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). In this review, we present the recent advances made in the production of CNFs and CNCs. In addition to the conventional mechanical and chemical treatments used to prepare CNFs and CNCs, respectively, other promising techniques as well as pretreatment processes have been also proposed in recent times, in an effort to design an economically efficient and eco-friendly production route for nanocellulose. Further, while the hydrophilic nature of nanocellulose limits its use in polymeric matrices and in some industrial applications, the large number of hydroxyl groups on the surface of nanocellulose provides a suitable platform for various kinds of modification treatments. The various chemical and physical surface treatment procedures reported for nanocellulose have been reviewed in this paper. Finally, in this review, we summarize the life cycle assessment studies conducted so far on nanocellulose, which quantify the environmental impact of nanocellulose products. The current paper is a comprehensive review of the recent literature on nanostructured cellulose.

Advances in cellulose nanomaterials

How do trees support their upright massive bodies? The support comes from the incredibly strong and stiff, and highly crystalline nanoscale fibrils of extended cellulose chains, called cellulose nanofibers. Cellulose nanofibers and their crystalline parts-cellulose nanocrystals, collectively nanocelluloses, are therefore the recent hot materials to incorporate in man-made sustainable, environmentally sound, and mechanically strong materials. Nanocelluloses are generally obtained through a top-down process, during or after which the original surface chemistry and interface interactions can be dramatically changed. Therefore, surface and interface engineering are extremely important when nanocellulosic materials with a bottom-up process are fabricated. Herein, the main focus is on promising chemical modification and nonmodification approaches, aiming to prospect this hot topic from novel aspects, including nanocellulose-, chemistry-, and process-oriented surface and interface engineering for advanced nanocellulosic materials. The reinforcement of nanocelluloses in some functional materials, such as structural materials, films, filaments, aerogels, and foams, is discussed, relating to tailored surface and/or interface engineering. Although some of the nanocellulosic products have already reached the industrial arena, it is hoped that more and more nanocellulose-based products will become available in everyday life in the next few years.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.202002264

Surface and Interface Engineering for Nanocellulosic Advanced Materials.

Cellulose nanocrystals (CNCs) using different polymorphs of cellulose were fabricated from raw bamboo pulp through alkali treatment followed by acid hydrolysis. The effect of CNC polymorphs, namely CNC I, CNC II and CNC:I → II (CNC II from cellulose I), on morphology, crystal structure, degree of hydrogen bonding and thermal stability were studied. These polymorphs were dispersed in polylactic acid (PLA) films using a casting evaporation approach and their effect on the structural, thermal, mechanical and barrier properties of the PLA were investigated. The CNC polymorphs differ significantly in their reinforcement capability and ability to form percolated networks. Incorporation of CNC II and CNC:I → II significantly improved the Young's modulus of composites (by ∼72%). However, their elongation at break significantly decreased compared to CNC I, due to high hydroxyl functionality, which forms an entangled hydrogen bonded network within the polymer matrix, leading to improvement in mechanical as well as barrier properties. The theoretically calculated moduli of composites using Halpin–Kardos, Cox–Krenchel and Ouali models showed good agreement for CNC I, CNC II and CNC:I → II, albeit at higher aspect ratio. All three CNCs showed the ability to form percolated networks, the occurrence and stability of which varied with the type of polymorph. Therefore, the current study provides an insight towards selection of appropriate polymorphs for fabrication of CNC reinforced high performance poly (lactic acid) based bionanocomposites.

Effect of cellulose nanocrystal polymorphs on mechanical, barrier and thermal properties of poly(lactic acid) based bionanocomposites

Thermally recyclable polylactic acid/cellulose nanocrystal films through reactive extrusion process

Steady and unsteady solutions of the thermal flows through a curved duct with various aspect ratios are numerically studied by using the spectral method over a wide range of the Dean number, Dn. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, 500 and 1000, where the outer wall is heated and the inner wall is cooled. Firstly, steady solutions are obtained by the Newton-Raphson iteration method. As a result, we obtain multiple branches of steady solutions with multi-vortex solutions on various branches. Then, we perform time evolution calculations with a view to study the non-linear behavior of the unsteady solutions. It is found that time periodic solutions appear when Dn or Gr is increased. If they are increased further, the chaotic solution is obtained. For large aspect ratios, however, chaotic solutions occur for small Dn or for small Gr.

Debashis Tarafder

Papers

Effect of cellulose nanocrystal polymorphs on mechanical, barrier and thermal properties of poly(lactic acid) based bionanocomposites

Thermally recyclable polylactic acid/cellulose nanocrystal films through reactive extrusion process

Steady and unsteady solutions of the thermal flows through a curved duct