Reinforcement with cellulose-pulp

1 the fully chemical (kraft) process which has a low yield ( 45%) and results in a collapsed, ribbon-like fibre and 

2 the high temperature thermomechanical processes (TMP) which give high yield ( 90%) and an uncollapsed rod-like fibre. 

The TMP process is carried out at temperatures greater than the transition temperature of the lignin binder, and the processed fibre is lignin coated. In the kraft 

Cellulose-pulp FRC composites with flexural strengths in excess of 20 MPa can be readily produced [18,20,24-27], with about 10% fibres by mass, using processes applied in the asbestos-cement industry. From the point of view of 

Reinforcing fibre Aspect ratio Flexural strength (MPa) Impact toughness (kj/m ) Density (kglrn ) 

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Cellulose nanofibers from different sources have showed remarkable characteristics as reinforcement material for optically transparent composites [160, 161], Iwamoto et al. [160] prepared optically transparent composites of transparent acrylic resin reinforced with cellulose nanofibers extracted from wood pulp fibers by fibrillation process. They showed that cellulose nanofiber-reinforced composites are able to retain the transparency of the matrix resin even at high fiber content (up to70 % wt). The aggregation of cellulose nanofibers also contributes to a significant improvement in the thermal expansion properties of plastics. 

Cellulose cement sheets cement reinforced with cellulose fibres derived by pulping processes. These composites are produced by the Hatschek process and are applied in many instances as asbestos replacement or as the processing fibre in a hybrid composite (see Chapter 11) ... 

U.S. Pat. No. 6,270,883 [98] describes reinforced composites containing less than 50% by weight of cellulose pulp fibers dispersed in a thermoplastic matrix comprising nylons, such as Nylon 6, Nylon 12, Nylon 66, or mixtures thereof, and the cellulose pulp comprising fibers with a lignin content less than 2% by weight. 

In another study by Sdrobis et al. [57], the effect of modification on cellulose pulp fibers in LDPE was reported. They used unbleached and bleached kraft cellulose pulp fibers modified with oleic acid in cold plasma conditions as reinforcements. The melt-mixed composites contain up to 10 wt% of untreated and modified cellulose pulp fibers with LDPE. They reported that interfacial adhesion between cellulose and matrix could be improved through modification and most of the properties have been improved when the modified pulp fibers were incorporated into composite matrix. Variation of complex viscosity function of angular frequency for composites is shown in Fig. 11.11. 

Cellulose Whisker Microcrystalline cellulose (MCC) has been used as a whisker reinforcement with PLA as a matrix [61, 62]. MCC (particle size 10-15/ m) is crystalline cellulose derived from high-quality wood pulp (WP), and disintegrates into cellulose whiskers by acid... 

Yano HSJ, Nakagaito AN, Nogi M, Matsuura T, Hridta M, Handa K (2005) Optically transparent composites reinforced with networks of bacterial nanofibers. Adv Mater 17 153 Young R (1994) Comparison of the properties of chemical cellulose pulps. Cellulose 1 107-130 Zhao H-P, Feng X-Q,Gao H (2007) Ultrasonic technique for extracting nanofibers from nature materials. Appl Phys Lett 90(7) 073112... 

We already mentioned in Section 3.5 [70] the partial oxypropylation of cellulose fibres and the interest of the ensuing composite materials in which the unmodified fibre cores represent the reinforcing elements and their thermoplastic sleeves the source of a matrix. Other interesting approaches have been recently put forward to prepare composite materials in which cellulose or one of its derivatives prepared in situ are the only component. Glasser was the first to tackle this problem through the combination of cellulose esters and fibres by two distinct approaches, viz. (i) the incorporation of lyocell fibres into a cellulose acetate matrix [92] and (ii) the partial esterification of wood pulp fibres with -hexanoic anhydride in an organic medium [93] that produced thermally deformable materials in which the thermoplastic cellulose ester constituted the matrix and the unmodified fibres the reinforcing elements. 

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