Silk fibers composition

Four types of composites were manufactured. Unidirectional silk fiber composites were made using PP and MAPP matrix. By varying fiber volume fraction (30, 35, 40, and 45%), 2 mm thick composites were manufactured. 

Verpoest, 1., Van Vuure, A. W., El Asmar, N., and Vanderbeke, J. (2010). Silk Fiber Composites. Patent application number 20100040816, Washington DC, USA. 

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

Pioneering work in fibroin wet spinning can be traced back to 1930s. After that, little work has been done until the late 1980s, when more research was done to investigate the spinning dope systems, and structure and properties of the artificial fibroin silk. The composition of the dope is very important to the properties of the final fiber. Several kinds of solvents, such as LiBr—EtOH, Ca(NOo,)2—MeOH, formic acid, HFIP, hexafluoro acetone (HFA), and so on, are used to prepare the spinning dope (Table 4). Very recently, an ionic liquid was used as dope solvent (Phillips et al., 2005). 

To extend the application area of silk proteins-based materials, blending the fibroin with other natural macromolecules and synthetic polymers, or even manufacturing composites with silk fibers are a few of the possible strategies. 

The protein secondary structure of silk fibroin [60] was studied with near-lR spectroscopy, using silk fibers that had been very carefully selected from naturally generated fibers. The isolation of individual fibers allowed the trapping from Nature of a protein with a particular secondary structure. A spider is able to generate different fibers for different uses, with each fiber having its own secondary structural composition. In the case of silk, an individual fiber may well have a particular composition secondary structure, and in this case it is possible to use near-lR spectra to perform a characterization. This is quite remarkable because the use of a relatively prominent amide-1 band in the mid-lR represents a major challenge. 

Not all of the fibroin protein is in / -sheets. As the amino acid composition in Figure 6.12 shows, fibroin contains small amounts of other, bulky amino acids like valine and tyrosine, which would not fit into the structure shown. These are carried in compact folded regions that periodically interrupt the sheet segments, and they probably account for the amount of stretchiness that silk fibers have. In fact, different species of silkworms produce fibroins with different extents of such non - / -sheet structure and corresponding differences in elasticity. The overall fibroin structure is a beautiful example of a protein molecule that has evolved to perform a particular function — to provide a tough, yet flexible fiber for the silkworm s cocoon or the spider s web. 

Silkworms spin composites of two silk fibers out of two converging silk glands. These fibers are surrounded by a glue-like seridn protein coating that holds the fibers and thus the cocoons together. The individual silkworm silk fibers (brin) are 10-12 xm in diameter with a triangular cross section. 

Teuld F, Miao Y, Sohn BH, Kim YS, Hull JJ, Fraser MJ, Lewis RV and Jarvis DL. Silkworms transformed with chimeric silkworm/spider silk genes spin composite silk fibers with improved mechanical properties. Proc. Natl. Acad. Sci. USA. 109 923-928,2012. 

Silk Fibers and their Unidirectional Polymer Composites... 

In this chapter, both raw and alkali treated silk fibers are taken into consideration to characterize their properties first. The specific objective is to determine the modulus and strain to failure of the single silk fiber. Other aims of this work are to fabricate the unidirectional silk fiber reinforced polymer (MAPP and commercial grade PP) matrix composites by varying fiber volume fraction and to determine their mechanical properties such as tensile strength, flexure strength, impact strength, and hardness. 

Figure 2. Unidirectional silk fiber reinforced composite fabrication process.

The fracture surfaces of the tensile test specimens were examined by SEM. To study the surface morphology of the prepared composites, SEM photographs were taken for 30, 35, 40, and 45% fiber volume fraction, as shown in Figure 15. The SEM of fracture surface of composite indicates that fiber pullout occurs. This is due to lack of interfacial adhesion between silk and PP matrix. Due to intermolecular hydrogen bond formation between silk fibers and hydrophobic nature of PP matrix, hydrophilic silk fibers tend to agglomerate into bundles (Figure 15(d)), and become unevenly distributed throughout the matrix. It is seen that for 40% fiber volume fraction composite, less fiber pullout happens, better interfacial adhesion between silk and PP matrix occurs. 

Figure 15. SEM micrographs of fracture surface of silk fiber-reinforced composite with various fiber volume fractions (200X).

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