Neat polymers, mechanical properties

Covalent dynamers may also present a range of unusual properties such as crossover component recombination between neat films in dynamic polymer blends [61], soft-to-hard transformation of polymer mechanical properties through component incorporation [62], and dynamic modification of optical properties (Fig. 6) [63],... 

Injection moldings are made with the melt at or above 300 C and molds at or above 135 C for crystalline parts, or much colder for amorphous parts. Amorphous parts will begin to crystallize when heated above 90 C. Very little PPS is used as the neat polymer in molded parts because it is too brittle. As with other crystalline polymers, mechanical properties are improved by using fiber glass in the molding compounds. Minerals are used as additional fillers in some compounds. As with other highly crystalline... 

All of the monomers in Fig.46 were polymerized into neat resin castings using a thermal cure cycle with a maximum temperature of 250 °C. The polymers were then subjected to preliminary thermal and mechanical property screening and a summary of their physical properties is shown in Table 21. All of the polymers had Tgs above 200 °C (DSC) and 5% weight losses (TGA) in the range between 430 and 470 °C (air and nitrogen). Room temperature flexural moduli and strengths were 3.10-3.52 GPa and 152-207 MPa respectively. 

Poly(vinyl) alcohol (PVA) is a semi-crystalline polymer, which is already widely used for various applications, either under the form of films or fibers. Compared to other polymers, as it is water-soluble at high temperature, it is easy to process from aqueous solutions. Carbon nanotubes can also be dispersed or solubilized in water via different functionalization approaches. It was quite natural for researchers to try to mix carbon nanotubes and PVA to improve the properties of the neat polymer. In this chapter, we will first examine the different methods that have been used to process CNT/PVA composites. The structures and the particular interaction between the polymer and the nanotube surface have been characterized in several works. Then we will consider the composite mechanical properties, which have been extensively investigated in the literature. Despite the number of publications in the field, we will see that a lot of work is still to be done for achieving the most of the exceptional reinforcement potential of carbon nanotubes. 

Table 18.2 Comparison of mechanical properties of neat polymers...

This chapter deals almost exclusively with neat, or pure, diblock copolymer melts. Polymer blends are discussed in Chapter 9, micellar solutions in Chapter 12, and stabilized suspensions in Chapter 6. In the following, Section 13.2 briefly reviews the thermodynamics of block copolymers, and Section 13.3 describes the rheological properties and flow alignment of lamellae, cylinders, and sphere-forming mesophases of block copolymers. More thorough reviews of the thermodynamics and dynamics of block copolymers in the liquid state have been written by Bates and Fredrickson (1990 Fredrickson and Bates 1996). The processing of block copolymers and mechanical properties of the solid-state structures formed by them are covered in Folkes (1985). Biological applications are discussed in Alexandridis (1996). 

Short fibre polymer composites are being increasingly used as engineering materials because they provide mechanical properties superior to neat polymers and can be processed easily by the same fabrication methods, e.g. injection moulding. The mechanical properties of these materials are dependent on a complex combination of several internal variables, such as type of matrix, fibre-matrix interface, fibre content, fibre dimensions, fibre orientation, and external... 

It should be recognized that almost every thermoplastic and thermoset resin may be produced today in cellular form by means of the mechanisms and processes cited above. The physical properties of the foams reflect in many ways those of the neat polymers, taking into account the effects of density and ceU geometry. 

Mechanical Properties. To reveal the reinforcing effect of liquid crystalline polymer microfibrils on the mechanical properties of the films both their dynamic torsional moduli and dynamic tensile moduli have been studied as a function of temperature using a Rheometrics Mechanical Spectrometer (RMS 800) and a Rheometrics Solids Analyzer (RSA II), respectively. For comparison purpose the modulus of neat matrix polymers and, in some cases, the modulus of carbon fiber and Kevelar fiber reinforced composites has also been measured. 

The mechanical properties of the C3, C6, and Cl2 nanocomposites were all significantly better than those of the neat phenolic resin, even if a very small amount of the silicate was used. Among the nanocomposites prepared, the organically modified MMT-resol systems showed better mechanical properties than those of the unmodified MMT-resol system. This improvement was attributed to the formation of an end-tethered structure due to the reaction of the carboxylic acid of the organic modifier with the methylol group of the phenolic resin. Thermogravimetric analysis reported by Byun and coworkers showed that the nanocomposite systems had similar thermal stability to that of the neat polymer. 

The preparation of composite materials in general is a very important appHca-tion of the mechanical properties of nanodiamond. With many polymers like caoutchouc, polysiloxanes, fluoroelastomers polymethacrylates, epoxy resins, etc., composites with markedly improved mechanical characteristics have already been obtained from the noncovalent incorporation of nanodiamond by simple admixing during polymerization. The modulus of elasticity, the tensile strength, and the maximal elongation of the material all increase upon this modification. Depending on the basic polymer, just 0.1-0.5% (w/w) of nanodiamond are required to achieve this effect (Table 5.3). Polymer films can also be reinforced by the addition of nanodiamond. For a teflon film with ca. 2% of nanodiamond added, for example, friction is reduced at least 20%, and scratches inflicted by mechanical means are only half as deep as in neat teflon. 

Polyolefin blends are a subset of polymer blends that emerged as a result of the need to meet apphcation requirements not satisfied by synthesized neat polyolefins. In comparison to other subsets of polymer blends, polyolefin blends have distinct advantages of lower density, lower cost, processing ease, and good combination of chemical, physical, and mechanical properties. In the last several years, research and usage of polyolefin blends have increased due to new application opportunities (e.g., in medical and packaging) and the development of novel polyolefins. 

It is well known that the mechanical properties of polymer blends strongly depend on the raw materials and on their final morphologies, which are controlled by interfacial adhesion, properties of the neat materials, and processing conditions, among others [2, 37-39],... 

Whether you are working with neat polymers or blends of polymers, color and appearance must be engineered just like any other desired thermal or mechanical property. The ability to achieve the desired color can be adversely affected by the base polymer itself or the combination with other polymers, modifiers, additives or stabilizers. Even if the color can be achieved in the blended system, other performance attributes such as UV stability, flammability, or mechanical properties may be adversely affected as well. This paper looks at some of these color concerns in coloring polymers and blends. 

PROPERTIES OF SPECIAL INTEREST PPS is a semiciystalline thermoplastic. PPS reinforced with glass fiber or mineral fillers shows excellent mechanical prop>erties, high thermal stability, excellent chemical resistance, excellent flame retardance, good electrical and electronic properties, and good mold precision Recently developed linear type PPS additionally shows improved properties of elongation and toughness and opens the new route for the use of a neat polymer. 

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