One of the new areas of composite study that is not sufficiently done is the addition of reinforcing nano fillers in the resin rich area of composite.  Even more important is the addition of nano fillers selectively in the  interphase between the fiber and polymer matrix.  The biofibers do not form chemical bonds as much as siliceous fibers.  Therefore, reinforcing selectively the interphase is an effective and attractive option.  However, the method to selectively adding nano fillers to interphase, effect of concentration, orientation and type of nano fillers are very poorly understood. This approach, upon better understanding, can also result in diffusion barrier of water to the hydrophilic biofibers.

As Hatuo mentioned, some studies concerning nano fillers in the matrix can be seen. CFRPs have relatively poor strength in compression due to insufficient modulus of the matrix; Nano-fillers improve the matrix properties. But achieved improvements in these studies are not so prominent. Now, I'm interested in a possibility of nano-structures in the fibres. A carbon fibre in micro-scale is actually just a bulk graphite. Contrary, nano-structures are quite common in natural fibres. This is interesting. 

Dear Prof. Ishida

Thank you very much for your helpful answer. According to your advice, I reviewed the paper you've published about toughening epoxy matrix via coating the fibers in high-performance composites. Considering the poor impact resistance of the natural fiber composites and the focus of the project on the automotive's industries, I came up with the idea of evaluating a ternary system consisting Poly Propylene, natural fibers, and a third rubber component as the impact modifier. Based on the studies conducted, EPDM rubber particles was utilized as the impact modifier. Accordingly, I assume that it would also be a good idea to survey the possibility of encapsulating short fibers with a rubber interlayer. What's your opinion?

Dear Yoshiki Fukada 

Thank you so much for your answer. Do you mean using nano-cellulose extracted from natural fibers as the reinforcement?Dou you think it would be beneficial to use nano-cellulose reinforced PP in automotive's mass production industries? 

Nano-cellulose is also one of natural fibre, but I don't consider specific materials. The interesting thing is the fundamental of composites. The most successful composite is CFRP. The diameter of the fibre is around several microns, whereas the scale of the product is meters to centimeters. So the difference of the scales between the fibre and the product is three to six of magnitudes. I believe this scale range and fracture mechanics make the composite tough and strong. 

Think about a composite with nano-fibres which is simple "fibre reinforced plastic". Is the composite strong and tough? I don't think so. FRPs are tough because the micron-scale fibrous structure prevents the micro-crack propagation. For nano-fibre reinforced structures, a "micro-crack" is already "big scale"; it can't stop the crack propagation. 

If a micron-scale fibre has nano-structure, it may have good properties. Because "cracks" in micron-scale fibre are expected to be nano-scale.