Composites Reinforced with Natural Fibers

The structural characteristics and mechanical properties oisisalfiberIVFK composites have been investigated by many researchers [57, 58]. Some specific cases from literature have revealed the suitability of sisal fiber reinforced polyester composites in engineering applications [44, 59, 60]. Specifically, PLA pellets can be 

The impact, tensile and flexural strengths, and stiffness of composites were found to increase, compared to sisal/PLA composites manufactured using compression molding [55]. 

Various other reinforcements, such as bamboo fibers, vetiver grass fibers, and coconut fibers [63], are used to manufacture different biodegradable composites. 

To manufacture these composites, the injection-molding method is commonly used. The brittleness of PLA requires a suitable reinforcement in order to improve its impact properties. Such an effect can be observed in composites made of bamboo fibers/PLA and coconut fibers/PLA. The reinforcement with bamboo fibers exhibited significant increase in the impact properties compared to that with grass and coconut fibers. Bamboo/PLA composites can be manufactured using the filmstacking method followed by compression molding [64]. The energy absorption capacity in the transverse direction was found to be better compared to those in the other directions. 

Composites can also be developed by PLA reinforced with chicken featherfibers (CFFs). The composite was manufactured by the compression molding technique [65]. The mechanical properties of neat PLA and CFF/PLA composites were investigated. The elastic modulus of the CFF-reinforced composites are significantly 

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Changes in the fiber and fiber/cement interfacial region due to environmental interactions can affect the long-term performance of cement-based composites reinforced with natural fibers. A significant mechanism of changes in composite properties is pulp fiber degradation... 

Polymer composites reinforced with natural fibers have received considerable attention. Polysaccharides have attracted the attention of scientists and... 

Mueller D.H. Krobjilowski A. New Discovery in the Properties of Composites Reinforced with Natural Fibers. Journal of Industrial Textiles, vol.33, No.2, (2003), pp. 111-130. 

Morvan C, Andeme-Onzighi C, Girault R, Himmelsbach D, Driouich A, Akin D (2003) Building flax fibres more than one brick in the walls. Plant Physiol Biochem 41(11) 935-944 Mueller D, Krobjilowski A (2003) New discovery in the properties of composites reinforced with natural fibers. J Ind Text 33(2) 111-130... 

Biagiotti J, Fioii S, Torre L, Lopez-Manchado MA, Kenny JM (2004) Mechanical properties of polypropylene matrix composites reinforced with natural fibers a statistical approach. Polym Compos 25(l) 26-36... 

The forming method has it that isotactic polypropylene is formed as a board on which one or more parallel layers of fibers are applied. Additionally, on one side, the ends of fibers must reach out over the edge of the board to be caught and puUed. Next, the second polypropylene board is applied. The boards are heated to 175-285°C at a constant or increased pressure, and then the set is cooled down. Below 150°C, the fibers are moved to the distance up to few millimeters at 0.01-0.1 m/s. Having obtained the desired shape, the product is cooled down to the ambient temperature [3]. The technique presented in the cited patent description ensures high content of p form in the polypropylene composite reinforced with natural fiber. 

Preparation of Thermosetting and Thermoplastic Composites Reinforced with Natural Fibers... 

The alkaline pH of cement matrix can also be reduced by reaction between carbon dioxide (CO ) and Ca(OH. This reaction is known as carbonation of cementitious matrix and occurs in three stages (i) Initially CO diffuses in matrix through pores and is dissolved (ii) subsequently CO reacts with sodium hydroxide (NaOH) of cement matrix, decreasing the pH which favors Ca(OH formation and (iii) finally a reaction occurs between COj and Ca(OH that forms Ca(HCQ ) and CaCO. Several authors have used this reaction to decrease pH of cement matrix and increase durability of cement composites reinforced with natural fibers [31, 37, 69]. To allow this reaction occurs, composite is cured in an environment rich in COj, which favors the formation of CaCQ and therefore decreases the pH in the matrix [32, 70-73]. However, cement... 

Because of waste accumulation at the end of the life cycle of traditional polymer products, the development of environmentally-ffiendly, degradable, polymeric materials has attracted extensive interest. Nevertheless, the properties of such kinds of polymers are lower than that of traditional ones. Thermoplastic polymers have been widely used as matrix of composites reinforced with natural fibers in order to achieve a final material with improved mechanical properties with respect to the pure polymer. In order to obtain competitive products, the performance of biodegradable polymers can be greatly enhanced by the incorporation of nanometer-size fillers. 

The demand for better fuel efficiency based on the strict governmental regulations on safety and emission has led to the wide application of composites and plastics in the automotive industry in the place of the traditionally used steels [32]. Thermoplastic materials reinforced with natural fibers have reported to have excellent mechanical properties, recycling properties, etc. [33-36]. Several natural and biorenewable fibers such as wheat, isora, soybean, kenaf, straw, jute, and sisal are used in the fiber/plastic composite industry, and the use of namral fibers as reinforcements for composite has attracted many industries [37, 38]. Compared to polymer resin, polymer biocomposites that are reinforced with natural fibers have many applications due to its ease of processing, comparatively lower cost, and excellent mechanical properties [39]. For more than a decade, European car manufacturers and suppliers have been using natural fiber-based composites with thermoplastic and thermoset matrices. These biocomposites and bionanocomposites... 

In case of utilization by combustion, polymeric composites reinforced with natural plant fibers emit less CO2 than chemical fibers (Bledzki 1997). The composites based on natural fibers and synthetic polymers such as PE, PS, PP, etc. are called biocomposites, and being eco-friendly can contribute to solving numerous enviroimiental problems. 

The composite materials reinforced with natural fibers will stimulate agriculture by the production of nonfood raw materials for the industry (Bledzki 1997) and by achieving high yields of raw materials derived from fibrous plants, thus leading to improvement in total yields of crops. 

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. 

The investigations mentioned above, are focused principally on the processing and mechanical response of polymers reinforced with natural fibers, without considering that their mechanical properties decrease after exposition to alkaline environmental of cement materials or weather. Natural fibers reduce their mechanical properties after exposition to alkaline environment of the cement matrix, nevertheless the use of polymeric matrix as a binder aroimd the natural fibers provides protection for them. However, if the interface of composites is not good, and/or matrix is not alkaline resistant, hydration products like calcium hydroxide will migrate to interface, and polymer composite will deteriorate. Several studies have demonstrated that the mechanical properties of natural fibers decrease after exposure to alkaline environment of the cement matrix due to three different mechanisms [30-39] ... 

On the other hand, polymer reinforced with natural fibers for construction applications could be classified according to its application as structural or nonstructural composite. A structural natural fiber composite can be defined as one that is needed to carry a load in use. Structural panels and unit beams [21], roof systems [22] and in some cases wood and engineered wood products [10, 22], are examples of structural composites. Performance of structural composites ranges broadly from high-performance to low-performance materials. As mentioned above, polymer reinforced with natural... 

Toledo Filho et al. [32] conducted a comprehensive study to determine specific modifications of cement matrix and natural fibers that were effective increasing durability. Results indicated that carbonation of the specimens for 109 days at conditions of 26.5 C is a promising alternative for increasing the durabihty of cement composites reinforced with cellulosic fibers. 

Foam composites produced from a starch matrix reinforced with natural fibers have been studied in several applications by many authors (Benezet et al., 2012 Cinelli et al., 2006 Guan and Hanna, 2006 Kaisangsri, Kerdchoechuen, and Laohakunjit, 2012 Lee et al, 2009 Mali et al, 2010 Robin et al., 2011 Salgado et al, 2008 Shogren et al 1998 Soykeabkaew, Supaphol, and Rujiravanit, 2004 Vercelheze et al, 2012). 

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