Natural fiber-reinforced PLA composites

Table 23.1 Mechanical properties of natural fiber-reinforced PLA composites [47]...

Improved fiber matrbc adhesion and thereby improved mechanical properties can be accomplished by engineering a superior processing condition in preparing the bio-composites, by altering the polymer architecture of the matrix or by the surface treatment on the fiber [47]. Table 23.1 showed mechanical properties of natural fiber-reinforced PLA composites. 

Bajpai, P.K., Singh, L, and Madaan, J. (2013) Tribological behavior of natural fiber reinforced PLA composites. Wear, 297 (1-2), 829-840. 

Nuthong, W., Uawongsuwan, P., Pivsa-Art, W., and Hamada, H. (2013) Impact property of flexible epoxy treated natural fiber reinforced PLA composites. Energy Procedia, 34, 839-847. 

Natural fiber-reinforced PLA composites are attractive because both the reinforcement (natural fiber) and matrix (PLA) are obtained from renewable resources. Natural fibers are considered as environment friendly alternatives to conventional reinforcing fibers such as glass, carbon, aramid, and so on. Natural fibers can be subdivided into three categories plant (cotton, jute, flax, hemp, etc.), animal (wool, silk, etc.), and mineral fibers (asbestos, inorganic whiskers, etc.). Generally, plant fibers are more popularly used as natural fiber reinforcements. Of these fibers, the most used are flax, jute, sisal, ramie, hemp, kenaf, and cotton. Plant fibers can generally be classified as nonwood (vegetable fibers) and wood fibers [20]. 

Several studies have been made to optimize the properties of natural fiber-reinforced PLA composites from the point of view of fiber-matrix adhesion. Pretreatment of fibers, such as chemical modification, seems to be the most promising approach, in which covalent bonds are formed between the fiber and matrix. One of the most common and efficient methods is alkali treatment (for example, with 2% sodium hydroxide aqueous solution) of fibers, which has been used to... 

One of the most important focus areas of research in the development of natural fiber-reinforced polymer composites is characterisation of the fiber-matrix interface, since the interface alone can have a significant impact on the mechanical performance of the resulting composite materials, in terms of the strength and toughness. The properties of all heterogeneous materials are determined by component properties, composition, structure and interfacial interactions [62]. There have been a variety of methods used to characterize interfacial properties in natural fiber-reinforced polymer composites, however, the exact mechanism of the interaction between the natural fiber and the polymeric matrix has not been clearly studied on a fundamental level and is presently the major drawback for widespread utilization of such materials. The extent of interfacial adhesion in natural fiber-reinforced polymer composites utilizing PLA as the polymer matrix has been the subject of several recent investigations, hence the focus in this section will be on PLA-based natural fiber composites. 

Due to the increasing commercial interest for natural fiber-reinforced polymer composites as well as demands for environment friendly materials, the development of fully biodegradable plant fiber-PLA composites is on the rise. Different natural plant fibers have been employed with PLA to produce composites. The most studied natural fiber reinforcements for PLA were kenaf [10, 21-23], flax [24, 25], hemp [26], bamboo [27], jute [28], abaca [29], pineapple leaf [9], and wood fibers (WF) [30, 31]. In addition to these conventional plant fibers, recently reed fibers have been used for preparation of PLA composites [31]. 

While cellulose fiber reinforced polypropylene (PP) is already used by default for example in the automobile industry for interior parts (Karas and Kaup, 2005), the conventional use of cellulose fiber reinforced PLA is still at the beginning. But there are also some products such as biodegradable urns, mobile phone shells or prototypes of spare tyre covers made from natural fiber reinforced PLA at the market (Anonymous, 2007 Iji, 2008 Grashom, 2007). Maty studies deal with the use of natural fibers as reinforcements in PLA composites. An overview about the mechanical characteristics and apphcation areas of natural fiber-reinforced PLA can be foimd for example in Bhardwaj and Mohanty (2007), Avella et al. (2009), Ganster and Fink (2006), Jo-noobi et al. (2010), and Graupner et al. (2009). For the improvement of the composite characteristics it is still necessary to carry out optimization processes for fibers, PLA matrix and the interactions of both. Moreover the processing parameters, force elongation characteristics of fibers and matrix as well as the use of additives like plasticizers or adhesion promoters have decisive influences on the mechanical characteristics of the composites. 

Yu, T., Li, Y., and Ren, J. [2009). Preparation and properties of short natural fiber reinforced poly[lactic acid)[PLA) composites. Trgn Non ferrous Metals Soc. China. 19, S651-S655. 

As an extension to the considerable amount of research undertaken on processing and properties of natural filler composites, in this last decade, a number of researchers have explored the concept of namral filler-reinforced PLA composites. An outstanding one is the project FAlR-CT-98-3919 (New ftmctional biopolymer-natural fiber composites from agriculture resources) by European Union, in which one of the key objectives was to manufacture demonstration parts on a pre-competitive level with the automotive industry as the main potential market. Within this project, Lanzillotta et al. [21] prepared biocomposites with flax fibers and PLA as the biopolymer matrix. The research focused on the idea of converting biocomposites into products for real automotive applications. 

The use of traditional composites made by glass, aramid, or carbon fiber-reinforced plastics has recently been discussed critically because of increasing environmental consciousness [8]. Thus, the recent research and development (R D) efforts have led to new products based on natural resources. Some of these are biodegradable polymers like PLA, cellulose esters, polyhydroxyalkan-otes (PHAs), and starch polymers. Furthermore, natural fiber-reinforced plastics made of natural fibers like flax, hemp, kenaf, jute, and cotton fibers are important R D achievements. Composites made of natural fibers and biopolymers... 

Three parts are covered in the chapter. First, the synthesis and properties of PLA are described. The modification and process of PLA are also discussed. Then, the composites with PLA as matrix and natural fiber or nanoparticles as reinforcement are reported in the second part. The processing and the properties of the composites are also given. The interface between PLA and the reinforcement and the surface treatment methods are discussed. Finally, the application and the development of PLA and PLA-based composites in the future are proposed. 

Thermal properties of thermoplastic starch composites reinforced with pehuen husk showed the potential of this bioliber as an excellent reinforcement for composite materials. TPS composites showed a good interaction between the fibers and the plasticized starch matrix due to the natural affinity between husk and starch in the pehuen seed. TPS/PLA/PV A blend showed partial miscibility or co-continuous phase and TPS/PLA/PV A composites presented also discontinuities at the biofiber-polymeric matrix interface. The incorporation of biofiber improved the thermal stability of the composites, increasing the initial decomposition temperature. The biofiber hinders the out-dififusion of the volatile molecules (e.g., glycerol), retarding the decomposition process of starch composites. On the other hand, the degree of crystallinity of composites decreases when pehuen husk content increases (Castano et al. 2012). 

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