Fiber-reinforced biodegradable plastics

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. 

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... 

This variety of polymeric building blocks can be used to tailor the properties of a polymer to the specific areas of application. They can be used for adhesives, coatings, molded goods and reinforced plastics. If the latter are made with natural fibers e.g. - flax, - hemp and - sisal as reinforcement, almost totally RR-based products are accessible (- fiber reinforced molded goods). All these products have the benefit of being based on renewable resources they are biodegradable, can be recycled and have an unlimited availabilty. 

In the recent past considerable research and development have been expanded in natural fibers as reinforcement in thermoplastic resin matrix. These reinforced plastics serve as an inexpensive, biodegradable, renewable, and nontoxic alternative to glass or carbon fibers. The various advantages of natural fibers over man-made glass and carbon fibers are low cost, low density, competitive specific mechanical properties, reduced energy consumption and biodegradability. Natural fiber reinforced composites with thermoplastic matrices have successfully proven their qualities in... 

The utilization of TPS for the production of biodegradable plastics has increased and has been the object of several studies in the last decade. However, TPS has two main drawbacks namely its water affinity and its poor mechanical properties. To overcome these problems, the addition of other materials to TPS is necessary. In order to increase its water resistance, TPS has been blended with synthetic polymers and modified by cross-linking agents such as Ca and Zr salts. Substances such as waxes and lignin have also been tested to decrease the water uptake of starch-based materials. TPS s mechanical properties have usually been improved by addition of synthetic polymers, such as ethylene-acryhc acid and ethylene-vinyl alcohol copolymers. Another approach requires the use of natural fibers and mineral fillers. The inclusion of reinforcing fillers such as fibers could, however, enhance the degradation of thermoplastic starch because of the increase in the melt viscosity [79-81]. 

Conventional plastics They are resistant to biodegradation, as the surfaces in contact with the soil in which they are disposed are characteristically smooth. Microorganisms within the soil are unable to consume a portion of the plastic, which would, in turn, cause a more rapid breakdown of the supporting matrix. This group of materials usually has an impenetrable petroleum-based matrbc, which is reinforced with carbon or glass fibers (Katarzyna et al., 2010). 

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