Natural fibers approaches

In the course of his studies of the dyeing process, he became deeply interested in the structure of natural fibers, and most of his efforts were directed toward this new field of research, with the help of able associates, among them R. Brill, M. Dunkel, G. von Susich, and E. Valkd. His investigation of various aspects of the problem utilized physical means (for example, x-ray diffraction, optical properties, and viscosity) and the purely chemical approach. A young scientist, H. Mark, who later became an authority in the field of high polymers, was appointed head of the physical chemistry laboratory. 

Raw silk was dissolved in hexafluoro-iso-propanol (HFIP) [17, 33]. A typical working concentration for spinning was 2.5% (w/v) silk fibroin in HFIP. The spinning solution was pressed through a small needle (0 80-250 pm) into a precipitation bath (methanol for Bombyx mori silk proteins and acetone for Nephila clavipes silk proteins) and the silk solution immediately precipitated as a fiber. The best performing fibers approached the maximum strength measured for native fibers of Bombyx mori, but did not achieve the mechanical properties of natural spider silk. 

Along with nylons, polyester fibers approach and exceed common natural fibers such as cotton and wool in heat stability, wash-and-wear properties, and wrinkle resistance. Blended textiles from polyester, cotton, and wool also can be made to be permanent-press and... 

Fig. 1 Approach for minimizing costs associated with the manufacture of natural fiber reinforced thermoplastic composites using unpurified PHAs...

Customer preferences for recycled products have encouraged a more efficient use of wood and natural fibers. One potential approach to preserve wood and use natural fibers is the development of commodity-engineered composites that blend wood and natural fibers with other materials, such as plastic. The idea of combining wood and plastic is to produce a product with performance characteristics that combine the positive attributes of both materials. Wood and other natural fibers have been used as fillers and/or reinforcement to improve the mechanical properties of a variety of products. The combination of wood and plastic creates the ability to develop diverse products using many different manufacturing processes. 

Recent basic research has turned up new approaches for innovative materials combining elements of, and integrating the advantages of, wood and synthetic plastics. Lignin is one of the main components of this new class of plastic-like, wood-like biocomposites. The resulting mixture of lignin, natural fibers, and additives is a compound processable as a thermoplastic. The processed materials are short fiber composites. Arboform is a trade name for this class of compounds. 

This method can be considered as an extension of the statistical approach to develop a comparative study of the behavior of different natural fibers. In this method, the density function of a quasi-stationary random process is estimated by means of an adaptive activation function neuron (FAN) endowed with a specific unsupervised learning theory with algorithms based on a neural network. The learning parameters could be chosen by carrying out several simulations. Here, one considers the values that provide a good trade-off between the convergence speed and the numerical stability of the algorithms [48]. 

The fibers taken from the same bundle showed a wide range of diameters, which is a typical drawback of natural fibers, justifying the need for the use of a more accurate statistical distribution function. In fact, all the fibers showed wide dispersion of strength with respect to diameter data, indicated by the dimensionless shape parameter of the Weibull equation. By contrast, the advanced statistical approach based on neural network algorithms (PDF estimation technique) mentioned above resulted in asymmetric curves of diameter distributions of four lignocellulosic fibers mentioned above (Fig. 8.7). 

Biagiotti J, Fioii S, Torre L, Lopez-Manchado MA, Kenny JM (2004) Mechanical properties of polypropylene matrix composites reinforced with natural fibers a statistical approach. Polym Compos 25(l) 26-36... 

As previously mentioned, the incorporation of reinforcements such as natural fibers is one of the interesting approaches to enhance the properties of polymer composites, which can address the significant requirements of most engineering applications. For this reason, the demand for natural fiber-reinforced composites has increased dramatically over the past few years for various commercial applications [6]. The increasing number of publications in recent years reflects the growing importance of this type of composite. Figure 22.1 shows the number of journals published about natural fibers and polymer composites over the past five years. Up to now, studies have established a rough indication of the increased interest of researchers on this topic. The natural fibers... 

The low impact strength is a major disadvantage of natural fiber (NF)-reinforced thermoplastic because NF provides points of stress concentrations, thus providing sites for crack initiation and potential composite failure. The impact properties of composites depend strongly on the interfacial adhesion between components. This can be maximized by improving the interaction and adhesion between the two phases in final composites. There are mainly two approaches to improve the interfacial adhesion ... 

Several studies have been made to optimize the properties of natural fiber-reinforced PLA composites from the point of view of fiber-matrix adhesion. Pretreatment of fibers, such as chemical modification, seems to be the most promising approach, in which covalent bonds are formed between the fiber and matrix. One of the most common and efficient methods is alkali treatment (for example, with 2% sodium hydroxide aqueous solution) of fibers, which has been used to... 

The most common strategy to decrease the price or improve the properties of polylactide to fulfill the requirements of different applications is blending. Polylactide has been blended with degradable and inert polymers, natural and synthetic polymers, plasticizers, natural fibers and inorganic fillers. The most common blends include blends with other polyesters such as polycaprolactone or PLA/starch blends. Usually the compatibility between the two components has to be improved by addition of compatibilizers such as polylactide grafted with starch or acrylic acid (114,115). Recently a lot of focus was concentrated on the development of polylactide biocomposites, nanocomposites and stereocomplex materials. In addition various approaches have been evaluated for toughening of polylactide. 

Although natural fibers have been used for thousands of years, synthetic fibers have only existed since the 1930s. They make up the majority of fibers used today. Raman spectroscopy has recently been used as a rapid and accurate method to separate fiber and film types for recycling. The chemical identification of these polymers is carried out in the same manner as discussed for the natural fibers in the preceding sections. Maddams [35] and Edwards et al. [36] review the use of Raman spectroscopy for the identification of polymers and studies on the kinetics of polymerization. The qualitative identification of polymers is obtained through the observation of characteristic vibrational bands, as discussed in Sections II.B and ILC. For unoriented polymers, the relative amount of comonomers can be determined quantitatively. A series of different nylons highlights this approach in the subsection on nylon. 

---