China
Africa
Explore chapters and articles related to this topic
Biomaterials for Food Packaging: An Overview
Published in Mohd Yusuf, Shafat Ahmad Khan, Biomaterials in Food Packaging, 2022
Fazilah Ariffin, Hanisah Kamilah, Kaiser Mahmood, Alias A. Karim
Cellulose microfibrils and nano-whiskers are two types of fillers that have been used in developing nanocomposites. Microfibrils have length in micrometers, while the diameter is in the range of nanometers [102]. Nano-whiskers are crystalline cellulose obtained after acid digestion of the amorphous components, and include cellulose nanocrystals and nanorods [103]. Nanocomposites are developed by three main pathways: (i) solution intercalation, (ii) melt intercalation, and (iii) in situ polymerization. In the solution intercalation method, firstly, the clay is thoroughly swelled in the solvent and then the polymer is solubilized in the solvent. Later both the components are combined, and the polymer chains intercalate the layers of clay by displacing the solvent [104]. In the melt intercalation, the polymer is heated above the melting temperature and the clay is added, and the temperature is kept higher under shear to accelerate the intercalation and exfoliation of the clay. In in situ polymerization, organoclays and monomers are combined, and the polymerization of the monomers is carried out, which precisely locks the exfoliated particles of the clays in the nanocomposites. Among these three methods, the melt intercalation is the most desirable approach, as it is compatible with the extrusion and other techniques of similar kinds. Moreover, it is benign as no solvent is used in the process [104]. On the other hand, the solution intercalation is just a type of solution casting that is considered suitable for preparation of nanocomposites of many biomaterials that degrade under high-processing temperature [105].
Structure and Properties of Polymer Matrix
Published in Noureddine Ramdani, Polymer and Ceramic Composite Materials, 2019
The most useful biopolymers in our daily life are cellulose, chitin, and chitosan [31]. Figure 1.7 shows the structures of these biopolymers. Cellulose is the most abundant renewable biopolymer representing about 40% of all organic matter. It is a skeletal polysaccharide ubiquitous in the plant kingdom and is considered the commonest naturally-occurring crystalline polymer. It is usually in a fibrous structure, and when it is used to reinforce amorphous lignin and hemicelluloses, it provides a woody composite structure. The primary structure of cellulose is mainly a regular unbranched linear sequence of 1→4-linked β-D-glucose. Microfibrils can be formed by the neighboring chains through hydrogen-bonding phenomena.
Cellulose
Published in Antonio Paesano, Handbook of Sustainable Polymers for Additive Manufacturing, 2022
Cellulose is a semi-crystalline polysaccharide, and its molecules are strongly connected through intermolecular and intramolecular hydrogen bonding and van der Waals forces, which results in the formation of small crystals called microfibrils that are embedded in a disordered, amorphous matrix, and in turn form larger fibers (Swift 1977). The length of the microfibrils is of the order of micrometers, and their species-specific diameter is 2‒25 nm (O’Sullivan 1997). Figure 7.2 is a schematic view of microstructure of plants, showing microfibrils, cellulose, and hemicellulose that is a branched polymer crosslinked to microfibrils and composed of sugars.
A review of the tensile and fatigue responses of cellulosic fibre-reinforced polymer composites
Published in Mechanics of Advanced Materials and Structures, 2020
Ng Lin Feng, Sivakumar Dhar Malingam, Ruztamreen Jenal, Zaleha Mustafa, Sivaraos Subramonian
The promising characteristics of natural fibres such as their low cost, lightweight and renewability are the leading drivers for the substitution of synthetic fibres in the market. Nevertheless, it is undeniable that the mechanical properties of natural fibre-reinforced composite materials are also influenced by several factors such as the fibre-matrix adhesion, fibre aspect ratio, fibre volume fraction, fibre orientation, etc [44]. The mechanical performance of composite materials improves when the fibre composition is increased to an optimum level. In fact, the properties of the fibres depend mainly on the microfibril angle and cellulose content of the fibres [45]. Table 1 shows the properties of several types of natural and synthetic fibres. The cellulose content determines the strength of the fibres, where high cellulose content results in high fibre strength, while the microfibril angle determines the fibre strength and stiffness. The microfibril angle, which is parallel to the fibre axis, provides high strength and stiffness to the fibre. The chemical compositions of various types of natural fibres are summarized in Table 2. Natural fibres are mainly comprised of cellulose, hemicellulose and lignin. Fibres with high lignin content have lower moisture absorption.
Proceeding toward the development of poly(ɛ-caprolactone)/cellulose microfibrils electrospun biocomposites using a novel ternary solvent system
Published in The Journal of The Textile Institute, 2020
Mohsen Zolfagharlou Kouhi, Tayebeh Behzad, Laleh Ghasemi-Mobarakeh, Alireza Allafchian, Zahra Moazzami Goudarzi, Mohammad Saeid Enayati
Figure 1(a)–(d) illustrates the morphology of cellulose microfibrils formed during different treatment stages. According to Figure 1(a), a cement-like layer from raw material, mostly composed from lignin and hemicellulose surrounding cellulose fibers, was partially removed after acidic and basic hydrolysis (Figure 1(b)) and completely omitted by bleaching (Figure 1(c)). Separation of cellulose microfibers after bleaching is clearly observed in Figure 1(c) which may be due to the removal of insoluble lignin and other impurities and weakening of hydrogen bonds between cellulose microfibers. Figure 1(d) displays the FE-SEM image of mechanically treated fibers using the super-grinder in which a classical web-like network structure of microfibrils was formed. The mechanical power disintegrated micro- and nano-fiber bundles by a combination of events including formation, growth, and collapsing of cavitation bubbles (Chen et al., 2011). The average diameter of microfibrils extracted during this study was found to be about 20 nm which approximates the diameter of cellulose fibers extracted from same source in other reports (25–30 nm) (Kalita et al., 2015).
Collection of airborne ultrafine cellulose nanocrystals by impinger with an efficiency mimicking deposition in the human respiratory system
Published in Journal of Occupational and Environmental Hygiene, 2019
Rose Roberts, Kevin Gettz, Larissa V Stebounova, Jo Anne Shatkin, Thomas Peters, E. Johan Foster
Extended and aligned cellulose macromolecules (D-glucose units, which are condensed through β(1→4) glycosidic bonds) assemble into microfibrils, in which they are stabilized through hydrogen bonds. The microfibrils are largely crystalline, but they also contain regions that are less well ordered (i.e., largely amorphous). The cross-sectional dimension of the microfibrils ranges from 2–20 nm, depending on the origin of the cellulose; in the case of wood cells[6] the smallest fibril unit, referred to as elementary fibril, has a diameter of ∼4 nm. The elementary fibrils aggregate to form microfibrils with diameters of ∼15–20 nm, which further aggregate into larger bundles and finally, with “binders” consisting of lignin and hemicelluloses, into cellulosic fibers. These hierarchical structures can be deconstructed by mechanical and chemical processes to isolate nano-cellulose (NC), collectively referred to as cellulose nanoparticles. Two main types of cellulose nanoparticles can be distinguished – cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) – although it should be noted that differences in the isolation processes and the nature of the source also cause some variation within these families.