Cellulosic fiber reinforced composites

It should also be mentioned that the application of wood nanocellulose prepared by the described techniques - where the cell wall is further disintegrated by mechanical treatment - leads to lower-strength cellulose fiber-reinforced composites than in the corresponding BC materials [34]. 

U.S. Pat. No. 6,743,507 [40] discloses cellulose-fiber-reinforced composites comprising a matrix polymers such as polyethylene, polypropylene, copolymers, terpoly-mers and mixture thereof in an amount ranging from about 25 to 99% by weight, and cellulose pulp having an a-cellulose purity of greater than about 80, 90, or 98% by weight. 

U.S. Pat. No. 6,743,507 (June 1, 2004). F. Barlow, Y. Khanna, D.B. Pietsch, and J. Underwood. Cellulose fiber reinforced composites having reduced discoloration and improved dispersion and associated methods of manufacture. 

Thomas S (2002) Cellulose fiber reinforced composites new challenges and opportunities. 4th International Wood and Natural Fibre Composites Symposium, Kassel Germany, April 10-11 Tu X, Young RA, Denes F (1994) Improvement of bonding between cellulose and polypropylene by plasma treatment. Cellulose 1 87-106 Urbanczyk G (1985) Nauka o Wloknie. WNT, Warszawa... 

The most recent significant development in the market place has been the very strong growth in the use of cellulose fiber reinforced composites, especially those based on wood fiber and powder. Coupling agents are often used in these formulations, especially to reduce water absorption and accompanying loss of properties. Maleic anhydride grafted polyolefins have been found to be very suitable additives for this purpose, and this has led to a marked increase in their use. 

Cellulosic fiber reinforced polymeric composites find applications in many fields ranging from the construction industry to the automotive industry. The reinforcing efficiency of natural fiber is related to the namre of cellulose and its crystallinity. The main components of natural fibers are cellulose (a-cellulose), hemicelluloses, lignin, pectins, and waxes. For example, biopolymers or synthetic polymers reinforced with natural or biofibers (termed biocomposites) are a viable alternative to glass fiber composites. The term biocomposite is now being applied to a staggering range of materials derived wholly or in part from renewable biomass resources [23]. 

U.S. Pat. No. 5,288,772 [75] discloses a cellulose-fiber-reinforced thermoplastic composition for compression molding, where thermoplastic material is polypropylene, or a mixture of polypropylene, polystyrene, and polyethylene (40-90% of plastic by weight), and the cellulosic material (10-60% by weight) was milled scrap newspaper with an initial moisture content of at least 30% by weight. The patentees suggest that lignin present in the cellulosic scrap provides a coherent mass of thermoplastic and cellulosic material. 

U.S. Pat. No. 6,780,359 [109] (by Crane Plastics Company, TimbeiTech) discloses a cellulosic fiber-polymeric composite comprising mixing a cellulosic material, such as wood fiber, with a plastic material, such as HDPE, LDPE, PVC, chlorinated PVC, polypropylene, EVA, ABS, and polystyrene, to form a cellulosic reinforced plastic composite. 

Fillers play a crucial role in the manufacture of plastics. Alone many plastics are virtually useless, but they are converted into highly useful products by combining them with fillers. For example, phenolic and amine resins are almost always used in combination with substances like wood flour, pure cellulose, powdered mica, and asbestos. Glass fiber is used as a filler for fiber-reinforced composites with epoxy or polyester resins. 

Aydin et al. reported the influence of alkali treatment on the mechanical, thermal, and morphological properties of eco-composites made by short flax fiber reinforced PLA Scanning electron microscopy (SEM) revealed that the packed structure of the fibrils was deformed by the removal non-cellulosic materials. The mechanical tests indicated that the modulus of the untreated flax fiber/PLA composites was higher than that of PLA on the other hand, the modulus of alkali treated flax/PLA was lower than that of PLA. Thermal properties of the PLA in the treated flax fiber reinforced composites were also affected. Tg values of treated flax fiber reinforced composites were lowered by nearly 10°C for 10% NaOH treatment and 15°C for 30% NaOH treatment. A bimodal melting behavior was observed for treated fiber composites different than both of neat PLA and untreated fiber composites [60]. 

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. 

Fibers have been widely used in polymeric composites to improve mechanical properties. Cellulose is the major substance obtained from vegetable fibers, and applications for cellulose fiber-reinforced polymers have again come to the forefront with the focus on renewable raw materials. Hydrophilic cellulose fibers are very compatible with most natural polymers. The reinforcement of starch with ceUulose fibers is a perfect example of a polymer from renewable recourses (PFRR). The reinforcement of polymers using rigid fillers is another common method in the production and processing of polymeric composites. The interest in new nanoscale fillers has rapidly grown in the last two decades, since it was discovered that a nanostructure could be built from a polymer and layered nanoclay. This new nanocomposite showed dramatic improvement in mechanical properties with low filler content. Various starch-based nano-composites have been developed. 

Franko, A., Seavey, K.C., Gumaer, J. and Glasser, W.G. (2001) Continuous cellulose fiber-reinforced cellulose ester composites III. Commercial matrix and fiber options. Cellulose, 8, 171-179. 

The chemical modification of a natural fiber is often performed in order to enhance the properties of the interface between fiber and matrix. A more recent method of modification, involves the deposition of a coating of nanosized cellulose onto the natural fibers or dispersing a nanosized cellulose in natural fiber reinforced composites. This method has been shown to improve the fiber-matrix interface and the overall mechanical performances. Such composites have been addressed as hierarchical, multiscale, nanoengineered, or nanostructured composites. The state-of-the-art in this field has been reviewed (46). 

Christian, S.J. and Billington, S.L. (2011) Mechanical response of PHB- and cellulose acetate natural fiber-reinforced composites for construction applications. Composites Part B, 42 (7), 1920-1928. 

Cellulosic Fiber-Reinforced Polymer Composites and Nanocomposites... 

Seung-H L, Siqun W, George M, Pharr M, Haitao X (2007) Evaluation of interphase properties in a cellulose fiber-reinforced polypropylene composite by nanoindentation and finite element analysis. Compos A 38 1517-1524... 

Figure 6.7 TGA curves of polyurethane, fibers and fiber-reinforced composites (a) cellulose (b) lignin.

It has been observed from the above discussion that mechanical, physico-chemical and fire retardancy properties of UPE matrix increases considerably on reinforcement with surface-modified natural cellulosic fibers. The benzoylated fibers-reinforced composite materials have been found to have the best mechanical and physico-chemical properties, followed by mercerized and raw Grewia optiva fibers-reinforced composites. From the above data it is also clear that polymer composites reinforced with 30% fibers loading showed the best mechanical properties. Further, benzoylated fibers-reinforced composites were also found to have better fire retardancy properties than mercerized and raw fibers-reinforced polymer composites. Fire retardancy behavior of raw and surface-modified Grewia optiva/GPE composites have been found to increase when fire retardants were used in combination with fibers. This increase in fire retardancy behavior of resulted composites was attributed to the higher thermal stability of magnesium hydroxide/zinc borate. 

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