Natural fiber composites moisture

As the performance of the composite is profoxmdly dominated by the micromechanical deformation process, its knowledge and control are critical for the improvement of composite properties. The effect of particle characteristics and interfacial adhesion on the micromechanical deformation processes in PP-wood composites was investigated by Renner et al. [7]. They proposed a failure map as well as the practical results and considered the influence of matrix characteristics on deformation and failure in PP-natural fiber composites in other research [24]. Hietala et al. [78] studied the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio during the processing and mechanical properties of WPCs. The use of pretreated wood chips enhanced the flexural properties of the wood chip-PP composites. Moreover, the use of undried wood chips compared to dried one can improve and reduce the flexural strength and flexural modulus, respectively. On the other hand, they concluded that the use of pretreated and undried wood chips lead to the highest aspect ratio after compounding. The effect of composition and the incorporation... 

Keywords compatibilizer, flax, natural fibers, natural fiber composites, processing, recycling, moisture content. 

Various researchers had found that stalk fibers have better properties than that of the other parts of plant fiber and indicated that they can be used for composite and other industrial applications (Reddy and Yang, 2009). Natural fiber composite laminates with distributed areca and maize stalk fibers using phenol formaldehyde were investigated (Kumar, 2008). Composite laminates were prepared with different proportions of phenol formaldehyde and fibers. Mechanical test such as tensile test, adhesion test, moisture... 

Table 7.10 somewhat positions typical natural fibers such as jute and kenaf vs. glass fiber, when used at equal level in polypropylene. Tensile, flexural, and impact properties, along with water absorption and specific gravities were measured on injection molded samples. As can be seen, natural fibers composites are quite challenging the glass fibers-filled composite with however a significant difference in moisture sensitivity. 

Additionally, the dependence of the mechanical properties on humidity is clearly reduced because of the moisture repellency of glass fibers [69]. The moisture absorption of composites is clearly smaller when natural fibers are replaced by glass fibers [65]. 

The mechanical properties of composites are mainly influenced by the adhesion between matrix and fibers of the composite. As it is known from glass fibers, the adhesion properties could be changed by pretreatments of fibers. So special process, chemical and physical modification methods were developed. Moisture repel-lency, resistance to environmental effects, and, not at least, the mechanical properties are improved by these treatments. Various applications for natural fibers as reinforcement in plastics are encouraged. 

A.K. Bledzki, V.E. Sperber, K. Specht, M.A. Letman and A. Viksne. Effect of defined waxes and coupling agents on moisture behavior of injection molded wood fiber-rein-forced PP composites. In Eighth International Conference on Woodfiber-Plastic Composites (and Other Natural Fibers), Madison, WI, May 23-25, 2005. 

The properties of thermoplastic composites containing fibers as fillers are dependent on a number of parameters, which include the properties of the matrix material, the size and aspect ratio of the fibers, dispersion of the fibers and the interface. In development of these composites, two important issues need to be addressed, namely, the incompatibility between the natural fibers and polymer matrix, and the tendency of the fibers to form aggregates [67]. Additionally, the composites exhibit poor dimensional stability due to moisture absorption. The orientation of the fibers is also important. In short-fiber reinforced composites, the orientation of the fibers is usually random and therefore the properties of such composites are not as superior as those containing continuous fibers. Optimization of processing conditions and use of coupling agents/compatibilizers and treatment of fibers can enhance the properties of these composites. 

Presently there is a huge potential market for recyclable, energy efficient, and more environmentally friendly composite materials. The utilization of natural fiber can thus lead to the reduction of waste disposal problems and environmental pollution. These NFC find applications in various engineering, electronic and automotive fields once the issues such as moisture sensitivity, compatibility, dispersion are addressed in a proper way. Green, environmentally friendly, sustainable, renewable, biodegradable, composites from natural fibers are most desired materials for future. 

In both studies shown above, the authors dried the hybrid fiber mat prior to molding. The importance of the drying stage lies in the fact that the high content of moisture of natural fibers is detrimental for the properties of the composite [2], since, in combination with the hydrophobic character of the polymer matrix, is responsible for void formation and weak adhesion [59]. 

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