Compositions, polymer composites whiskers

Polymer/chitin whiskers nanocomposites produced by the two techniques usually showed different physical properties due to the different morphology of the composite and the fact that different interactions between whiskers can be established. 

There are organic and inorganic whiskers. Organic whiskers include fibrin whiskers, polyCbutyl acrylate-phenylethylene) whiskers, and so forth, and are usually used in polymers. Inorganic whiskers include metal whiskers and nonmetal whiskers. Metal whiskers are mainly applied in metal matrix composite material. Ceramic whiskers, a kind of nonmetal... 

Ning Liu, Youbing Fan, Dangqing He et al. The effect of rheological properties of polymer/aragonte whisker composites. Insulating Materials, 36(l) 5-8, 2003. 

Ten et al. [12] studied the mechanical and thermal properties of PHB-HV/cellulose whisker nanocomposites and found that the NCC reinforcement increases the mechanical properties due to the strong interactions between these two phases. Compared with the pure PHB-HV, the tensile modulus of composites reinforced with 5% cellulose whiskers increased 77%. According to authors, the Young modulus increase can be attributed to the creep resistance of the polymer chains due to the presence of nanocrystals. The tensile strength of the nanocomposites also ino-eased indicaling a large interfadal adhesion between the polymer and whiskers. 

Reinforcements. The high modulus, high intrinsic strength, and temperature stabiHty make SiC, in the form of whiskers, platelets, and fibers, a promising candidate reinforcement material for metal, polymer, and ceramic matrix composites (qv). 

The term s plastic, polymer, resin, elastomer, and reinforced plastic (RP) are some-what synonymous. However, polymer and resin usually denote the basic material. Whereas plastic pertains to polymers or resins containing additives, fillers, and/or reinforcements. Recognize that practically all materials worldwide contain some type of additive or ingredient. An elastomer is a rubberlike material (natural or synthetic). Reinforced plastics (also called composites although to be more accurate called plastic composites) are plastics with reinforcing additives, such as fibers and whiskers, added principally to increase the product s mechanical properties. 

Small single crystals, such as those of potassium titanatc, are being used at an annual rate of over 10,000 tons for the reinforcement of nylon and other thermoplastics. These composites are replacing die-cast metals in many applications. Another microfiber, sodium hydroxycarbonate (Dawsonite), also improves the physical properties and flame resistance of many polymers. Many other single crystals, called whiskers, such as alumina, chromia, and boron carbide, have been used for making high-performance composites. 

Testing of ceramic composites has been around since the earliest fabrication of these materials. For particulate- and whisker-reinforced composites, testing methods which are suitable for monolithic ceramics are generally used. These methods include three- and four-point flexure, uniaxial tension and compression, and many others. For fiber-reinforced ceramic composites, flexural testing was also used initially. However, as was recognized in the polymer composites area, flexural testing alone could not provide the type of... 

Ceramic reinforcing fibers are utilized both in a continuous form (endless fibers) and in a discontinuous form (e.g. whiskers, short fibers). Most of the continuous fibers are utilized in the manufacture of composites with polymer matrices (PMC), where they are in competition with other high performance fibers (boron, carbon fibers), mainly for military or aerospace applications. Discontinuous fibers are generally used for the manufacture of metal matrix (MMC) and ceramic matrix (CMC) composites. 

Whiskers can be easily mixed with powders and processed as such. Composites are formed with metal (utilization in automobile construction e.g. pi.stons of whisker-reinforced aluminum), ceramic or polymer matrices for frictional applications (e.g. brake and clutch linings). Small quantities command prices of 1500 to 2000 DM/kg. For larger quantities prices of 100 to 150 DM/kg are expected. 

Fibers having an aspect ratio of above 10, such as glass fibers, asbestos, wollastonite, cellulose fibers, carbon fibers, and whiskers, act as reinforcing agents. Composites may be classified into four groups, as shown in Table II. In modern composites, such as in the case of epoxy resins reinforced with carbon fibers (51). the polymer matrix has only a secondary function to separate the individual fibers from one another and to transfer energy to the fiber surface the fibers almost completely withstand the mechanical load. 

Classification of composites by the phase inclusion size bears a philosophical aspect how small should a component in the matrix be not to make the term composite material so universal as to include in fact all materials Interatomic distances in molecules and crystals are of 1.5 10 m dimensionality, distances between iterative elements of the crystalline structure are 10 —10 m, while the size of the smallest intermolecular voids in polymers is 10 m. Note that mean nanoparticle size (plastic pigments are 10-8-10 m in size, the diameter of monocrystalline fibers or whiskers is 10 —10 m, glass microspheres are 10 —10 m) is commensurate with parameters of monolithic simple materials. This means that in the totality of engineering materials, nanocomposites occupy a place at the boundary between composite and simple materials. 

Based on their dimensions, which are in the nanometre range, three types of fillers can be distinguished. Isodimensional nanoparticles (NP), such as spherical silica NP have three nanometric dimensions. Nanotubes or whiskers are stretched constructions in which two dimensions are in the nanometre range and the other dimension is larger. When only one dimension is in the nanometre range, the composites are termed polymer-layered crystal nanocomposites, and are obtained by the complete intercalation of the polymer inside the galleries of layered host crystals [2]. 

Helbert, W., Cavaille, J. Y., and Dufresne, A., Thermoplastic nanocomposites filled with wheat straw cellulose whiskers. Part 1 Processing and mechanical behavior, Polym. Composite, 17,604-611. 

Ceramic fibers and whiskers are used in the fabrication of composites where they are dispersed within a matrix, which may be a ceramic, a polymer, or a metal. The choice of matrix depends on the proposed applications for the composite. A primary consideration is the desired operating... 

Abstract Nature is gifted with several nanomaterials which could be obtained from different animal and plant sources. Cellulose, chitin and starch are abundant, natural, renewable and biodegradable polymers. By intelligent processing techniques they could be used as classical nano reinforcing fillers in polymers i.e., composites. They are often called whiskers. 

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