Biofiber processing

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). 

Biofibers and wood fibers start to degrade at 2(X)°C, and, therefore only resins that are processable at temperatures less than 200°C are used as matrix polymers for WPCs. Thermoplastics used in these applications are various grades of PE, PP, PS, PVC and ABS [46,47]. About 80% of the market is dominated by polyolefins, but PVC is likely to gain an increasing market share. A significant portion of the matrix material in WPCs is post-consumer recycled... 

Before the chemical extraction process, the biofibers in their natural state have waxes and other encrusting extractions such as hemicelluloses, lignin, and pectin that form a thick outer layer to protect the cellulose inside. The presence of encrusting substances and other impurities causes the fibers to have an irregular appearance and also affects the processabiHty of the fibers. 

Successful exploitation of the use of biofibers for durable composite applications is restricted by low microbial resistance and susceptibihty to rotting. These properties pose serious problems during shipping, storage, and composite processing. 

However, it is quite evident that the advantages of the biofibers overweigh the disadvantages/limitations and most of the shortcomings have remedial measures in the form of chemical treatment. Biofibers have an advantage over the synthetic ones since they buckle rather than break during processing and fabrication. 

Diffusion and swelling studies of biofiber-reinforced rubber composites are very important as they provide information about its interface and the service performance in liquid environment. On absorption of liquid, the composite undergoes a diffusion process, which involves transfer of Hquid to its interior. Hence, the material swells as a whole, which leads to gradual deterioration in its physical and mechanical properties and subsequent premature failure. Several factors such as chemical structure and composition of the rubber compound, solvent, test piece size and shape, rubber-liquid ratio, temperature, time, presence of fillers affect the swelling behavior of elastomers. 

A surface treatment of biofibers is an important step in the processing of biocomposites. There are three main reasons for using surface treatments of biofibers before incorporating them in biopolymers. 

Alkalization is the process of subjecting a biofiber to the action of a fairly concentrated aqueous solution of a strong base (alkali] so as to produce great swelling with resultant changes in the fiber structure, dimension, morphology, and mechanical properties. It depends on the type and concentration of the alkaline solution, its temperature, time of treatment, tension of the material as well as the additives used. Most of the non-cellulosic components... 

Starch is one of the most widely used biopolymer in biocomposites because of its low cost and versatility. A plasticizer like glycol is sometimes used to make it suitable for processing. It is also blended with other polymers like aliphatic polyesters to improve its physical and mechanical properties. Biocomposites based on starch matrices show improved properties, which are comparable to E-glass/epoxy composites. Tensile, flexural, impact, and creep properties of these biocomposites are significantly better than those of neat starch. Various biofiber surface treatments have been shown to improve the properties of starch-based biocomposites. 

Recently, Flores-Hernandez et al. (2014) developed a green composite chitosan-starch as matrix and keratin biofibers as reinforcement. Keratin biofibers from feathers are non-abrasive, eco-friendly, biodegradable, renewable, and insoluble in organic solvents and also have good mechanical properties, low density, hydrophobic behavior, ability to dampen sound, warmth retention, and finally low cost (Meyers et al., 2008 Martinez-Hernandez and Velasco-Santos, 2011). Flores-Hernandez etal. (2014) developed the ecocomposites using three different kinds of keratin reinforcement short and long biofibers and rachis particles. These were added separately at different concentrations to the chitosan-starch matrix and the composites were processed by a casting/solvent evaporation method. 

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