Hybrid composites and silk fibers

This is relatively a recent development whereby two or more different kinds of fibers are used as reinforcements in a ‘hybrid’ composite. The advantage of incorporating hybrid fibers is basically what composites are all about: achieve better overall properties. Consider using carbon fibers with glass fibers as reinforcement inside a single matrix. Carbon fibers are stiffer and stronger and lighter than glass fibers but glass fibers are a lot cheaper and tougher than the carbon fibers. This enables the composite formed with a polymer resin to be cheaper, tougher and lighter than using all carbon fiber reinforcement or stronger and stiffer than using only glass fibers as reinforcements.
How would this arrangement work? Naturally carbon fibers will bear the brunt of the load and as they are stiff they will fracture first as the intact glass fibers serve to provide toughness until the fail and the matrix has to come in to play to sustain the load. These better overall properties can be achieved in other ways as well because hybrids offer a chance to manipulate the ‘structure’ of the composite as well. For instance, fibers could be laid out as laminates with each layer composed of a single fiber and these laminates could be alternated to make up the composite.
Presently at least, from a commercial stand point probably the greatest advantage of using hybrid fiber is the potential reduction in the cost of the composite other than that, hybrid composites are mainly being used as structural components in transport vehicles and some orthopedic components.
Integrating fibers such as capture silk with other fibers have similar applications to those mentioned above, namely to increase toughness and strength of the composite and decrease the overall weight. Because, as of now, some kinds of silk such as dragline silk have strength and toughness much greater than even high-tensile steel. According to research, dragline silk has a strength-to-weight ratio five times greater than high tensile steel.
While the arrangement between other fibers to construct hybrid reinforcement is useful, using the amazing silk fibers in a composite is not a feasible proposition and combining them with other fibers to achieve a hybrid may be even harder. Firstly, extracting silk naturally or through artificial methods is extremely expensive. For use, a large scale manufacture will be required but the costs are too damning to make this possible. Second, as the nature of these natural fibers and man-made fibers are so different, finding a material which can work for both these fibers is difficult. Silk may ‘wet’ a particular matrix much better than the man-made fiber reinforcement which will be used in conjunction with it, so while the silk is a good fit with the matrix, the man-made fiber may not be. Wetting broadly refers to how good an interface is formed between the reinforcement and the matrix. Better wetting means a good interface which allows the matrix to transfer load effectively to the reinforcement fibers.