Micro fibrils cellulosic

We have shown by our ISO brightness and Ak measurements that the lignin was attacked by the reactive species created by the y irradiation. The results indicate that the reactive species created attack indiscriminately the phenolic hydroxyl or coniferalde-hyde groups and the quinone groups. The decrease in physical properties is associated with die attack on the micro fibrils cellulose. However, at 3000 krad/h, the increase in the ISO brightness is smaller than the one observed around 300 krad/h for the TMP, while the physical properties of the pulp are affected more profoundly at 3000 krad/h than at 300 krad/h. The physical properties of the P-TMP behave similarly, while the increase in brightness is negligible at 3000 krad/h for P-TMP. 

In the last 25 years, there have been efforts to reduce wood fibers in size. As a first step, in the early 1980s Turbak et al. [18] developed a micro-fibrillated cellulose (MFC). Today, there are different ways to produce materials with controlled fiber diameters. 

Seydibeyog lu MO, Oksman K (2008) Novel nanocomposites based on polyurethane and micro fibrillated cellulose. J Compos Sci Technol 68 908-914... 

Okubo K, Fujii T, Yamashita N (2005) Improvement of interfacial adhesion in bamboo polymer composite enhanced with micro-fibrillated cellulose. JSME Int J Series A-Solid Mech Mater Eng 48 199-204... 

Schumann DA, Wippermaim J, Klemm DO et al (2009) Artificial vascular implants frran bacterial cellulose preliminary results of small arterial substitutes. Cellulose 16 877-885 Seydibeyoglu MO, Oksman K (2008) Novel nanocomposites based on polyurethane and micro-fibrillated cellulose. Compos Sci Technol 68 908-914 Shoda M, Sugano Y (2005) Recent advances in bacterial cellulose production. Biotechnol Bioprocess Eng 10 1-8... 

Vartiainen, J., Pohler, T., Sirola, K., Pylkkanen, L., Alenius, H., Hokkinen, J.,. .. Laukkanen, A. (2011). Health and environmental safety aspects of friction grinding and spray drying of micro-fibrillated cellulose. (3), 775-786. 

M. O. Seydibeyoglu, and K. Oksman, Novel nano composites based on polyurethane and micro fibrillated cellulose. Compos. Sci. Technol. 68, 908-914 (2008). 

Lopez-Rubio, A., Lagaron, J.M., Ankerfors, M., Lindstrom,T., Nordqvist, D., Mattozzi, A. and Hedenqvist, M.S. (2007). Enhanced flhn forming and film properties of amylopectin using micro-fibrillated cellulose. Carbohydrate Polymers, 68(4), 718-727. 

Iwatake et al. developed a sustainable green composite by reinforcing PLA with micro fibrillated cellulose (MFC) and needle-leaf bleached kraft pnlp (NBKP), which improved the nano fiber network to large extent (2008). At 10 wt % nano fiber dispersion of MFCs in PLA, Young modulus and tensile strength improved by 40% and 25% without any reduction in yield strain, whereas NBKP reported rednction in yield strain and strength by 30% and 50% respectively. 

Suzuki, K., Sato, A., Okumura, H., Hashimoto, T., Nakagaito, A.N., Yano, H., 2014. Novel high-strength, micro fibrillated cellulose-reinforced polypropylene composites using a cationic polymer as compatibilizer. Cellulose 21, 507—518. 

Gilberto, S., Julien, B., Allan, D. Luffa cylinderica as a lignocellulosic source of fiber, micro-fibrillated cellulose, and cellulose nanocrystals. BioResources 2010,5, T21-TAT). 

The polymer is about 0.8 nm in its maximum width and 0.33 nm2 in cross-sectional area, and can contain about 10,000 glucose residues with their rings in the same plane. In the cell wall these polymers are organized into micro-fibrils that can be 5 nm by 9 nm in cross section. These microfibrils apparently consist of an inner core of about 50 parallel chains of cellulose arranged in a crystalline array surrounded by a similar number of cellulose and other polymers in a paracrystalline array. Microfibrils are the basic unit of the cell wall and are readily observed in electron micrographs. Although great variation exists, they tend to be interwoven in the primary cell wall and parallel to each other in the secondary cell wall (Fig. 1-13). 

Cellulose is found not to be uniformly crystalline. However, the ordered regions are extensively distributed throughout the material and these regions are called crystallites [27]. Cellulose exists in the plant cell wall in the form of thin threads with an indefinite length. Such threads are cellulose micro-fibrils, playing an important role in the chemical, physical, and mechanical properties of plant fibers and wood. 

The plasma membrane of the plant cells has been considered the likely site for the synthesis and assembly of cellulosic micro-fibrils [28]. These micro-fibrils are found to be 10-30 nm wide, less than this in width, and indefinitely long containing... 

Various reports are present in the literature on the usage of cellulose fibers in the preparation of composites. Cellulose fibers like banana, sisal, oil palm, jute, pine apple leaf fiber were found to have a very good reinforcing effect on polymer matrices [38 2]. The mechanical properties and water absorption were found to be dependent on the amount of micro-fibrils. 

As will be discussed later (see p. 332), these data provide strong support for the argument that the microfibrils are produced by on-the-site synthesis and orientation (apposition) of the cellulosic microfibrils under the guiding influence of the living cell, rather than by a mechanism that proposes synthesis of the micro fibrils within the cell and subsequent translocation and crystallization (deposition) of microfibrils on the cell wall by exocellular factors. Further factors relevant to these opposing theories emerge from study of the fine structure of the cellulosic microfibrils, as discussed in the following Section. 

Hydrated cellulose (viscous) fibers, unwoven materials (e.g. felt), with different fiber interweaving and chemical reagents of high purity were used. Hydrated cellulose was chosen as a polymer precursor. Its structure is a complex system composed of micro-fibrils and micro- and macropores and also of a branched network of microscopic capillaries. Cellulose has a large inner surface that plays a determining role in absorption of aqueous or organic liquids with polymer molecules. Under the impregnation of hydrated cellulose with aqueous solutions of salts, the liquid fills the space between fibers, pores on the fiber surface and interacts with cellulose macromolecules. 

Orientation. The orientation of the cellulose chain axis in a number of different fibers has been studied in detail (21-22). Much less is known about the cellulose orientation in the plane perpendicular to the chain axis. The orientation in this plane is determined by the lateral arrangement of the microfibrils relative to each other. In algal celluloses, the evidence from x-ray and electron diffraction indicates that the microfibrils are arranged nonrandomly in the plane perpendicular to the chain axis (21-29). Preston (22) proposed the model shown in Figure 1 to explain his x-ray data. There are two different orientations of the microfibrils. The 002 planes in one set of microfibrils are approximately perpendicular to the 002 planes in the second set. In both sets of micro-fibrils, the 101 planes are oriented parallel to the cell wall surface (refer to Figure 1). Preston s model has been confirmed in more recent studies (29). In the remainder of this report, the type of orientation shown in Figure 1 will be referred to as alternating orientation. 

In this chapter we have reviewed some of the most important characteristics of cellulose and cellulose based blends, composites and nanocomposites. The intrinsic properties of cellulose such as its remarkable mechanical properties have promoted its use as a reinforcement material for different composites. It has been showed that cellulose is a material with a defined hierarchy that tends to form fibrillar elements such as elementary fibrils, micro fibrils, and macro fibers. Physical and chemical processes allow us to obtain different scale cellulose reinforcements. Macro fibers, such as lignocellulosic fibers of sisal, jute, cabuya, etc. are used for the production of composites, whereas nano-sized fibers, such as whiskers or bacterial cellulose fibers are used to produce nanocomposites. Given that cellulose can be used to obtain macro- and nano-reinforcements, it can be used as raw material for the production of several composites and nanocomposites with many different applications. The understanding of the characteristics and properties of cellulose is important for the development of novel composites and nanocomposites with new applications. 

---