Crystalline thermoplastic polymer

TABLE A.2 Thermophysical Properties of Semi-crystalline Thermoplastic Polymers... 

Mechanical properties of semi-crystalline thermoplastics polymers can be improved by incorporating various modifier particles with different physical properties [1]. Particulate mineral fillers generally enhance the stiffness but reduce the fi acture strength and toughness, while toughening rubbery inclusions reduce stiffiiess [2, 3]. However, it is possible to improve... 

Figure 6.9. Poling profile for 44 -, -dimethylaminonitrostilbene in a liquid crystalline thermoplastic polymer (27).

CAS 9003-07-0. (C3H5)n. A synthetic, crystalline, thermoplastic polymer with molecular weight of 40,000 or more. 

PET is a semi-crystalline thermoplastic polymer used in the manufacture of fibres, packaging films, bottles, electrical insulators, etc. As shown in Scheme 2.1, PET can be produced by two different routes by condensation between terephthalic acid (TPA) and ethylene glycol (EG) or through the reaction of dimethyl terephthalate (DMT) with ethylene glycol. Both alternatives lead to the monomer bis(hydroxyethyl) terephthalate (BHET), which is further polymerized into PET. 

All materials belong to the class of semi-crystalline thermoplastic polymers. Characteristic appearances of spherulitic microstructures of the polymers are shown in Figures 4 and 5 for the examples of POM and PA66. 

Quite different polymers can be obtained from butadiene by polymerisation through the 1,2 position, 1,2-PB is no longer a rubber but a semi-crystalline thermoplastic polymer rather similar to PP which has some potential as an environmentally degradable plastic (Chapter 5). 

A rapid high-temperature solid state pol5mierization of crystalline thermoplastic polymers may be done under conditions of mechanically induced surface stress and friction applied to polymer particles at the incipient melt point temperatures. ... 

Polyvinyl Fluoride Crystalline thermoplastic polymer of vinyl fluoride has good toughness, flexibility, weatherability, and low-temperature and abrasion resistance. Processed by film techniques. Used in packaging, glazing, and electrical devices. Also called PVR... 

In terms of polymer matrices for composite materials, there will be a compromise between solvent and water resistance. Thus non-polar resins are likely to be less resistant to hydrocarbon solvents, which have low polarity, but more resistant to moisture absorption. Polar resins behave in the opposite way. Strongly polar solvents, such as dimethyl sulphoxide or similar, can interact with polar structures in the resin and are difficult to resist. Crystalline thermoplastic polymers are often better for such applications. For example, polyethene will only dissolve in hydrocarbon solvents (of similar solubility parameter) at temperatures above the crystalline melting point. Polar semi-crystalline polymers such as the polyamides or nylons can be dissolved in highly polar solvents, such as cresol, because of a stronger interaction than that between molecules within the crystallites. High performance thermoplastic polymers such as polyether ether ketone (PEEK) have been promoted for their resistance to organic solvents (see Table 3.5) [12], The chemical resistance of unsaturated polyester and vinyl ester and urethane resins is indicated in Table 3.6 [15]. 

Polybutene-1, PB-1, or polybut-l-ene is another stereospecific (isotactic) polyolefin polymer, discovered by Prof. Giulio Natta in 1954. It is a linear high molecular weight crystalline thermoplastic polymer, with low density (0.91). The ethyl side groups create entanglement, which provides for the very good creep resistance of this polymer, which also has an abrasion resistance comparable to UHMWPE, and an excellent resistance to chemicals and environmental stress-cracking. 

Following are selected data for the most often used polymers. They have been divided (partly arbitrarily, because of the overlap in definitions) into four tables, numbered from 24.3 to 24.6 respectively, for general purpose polymers, engineering polymers, thermosets, and elastomers. The third colunm in each of these tables shows the values of density, the fourth of the tensile modulus, the fifth the stress at break, the sixth the elongation at break IS denotes the Izod impact strength for notched specimens. The letters A and C in the last column in Tables 24.3 and 24.4 pertain respectively to amorphous and crystalline thermoplastic polymers. 

Crystalline thermoplastic polymers made from two or more different monomers, usually ethylene and propylene. A family of polymers based on the combination of trimellitic anhydride with aromatic diamines. In the uncured form (ortho-amic acid), the polymers are soluble in polar organic solvents. The imide linkage is formed by heating, producing an infusible resin with thermal stability up to 290 °C. These resins are used for laminates, prepregs, and electrical components. 

This transformation process represents the line of demarcation separating the thermosets from the thermoplastic polymers. Crystalline thermoplastic polymers are capable of a degree of crystalline cross-linking but there is little, if any, of the chemical cross-linking that occurs during the thermosetting reaction. The important beneficial factor here lies in the inherent enhancement of thermoset resins in their physical, electrical, thermal, and chemical properties due to that chemical cross-linking polymerization reaction which, in turn, also contributes to their ability to maintain and retain these enhanced properties when exposed to severe environmental conditions. 

An example of a much-used crystalline thermoplastic polymer is polyethylene. LDPE (low density polyethylene) is considered to be semicrystalline while HDPE (high density polyethylene) or UHDPE (ultra high density polyethylene) are considered to be highly crystalline. LDPE is one of the most widely used plastics accounting for more than 20% of the total polymer market and is used extensively for milk containers and other packaging operations. HDPE and UHDPE are used extensively in water... 

Probably the best method to evaluate crystallinity is through density measurements. If, for example, specific volume (the inverse of density or vol./g) is measured as temperature is decreased, a sudden and nearly discontinuous change occurs at the melting point (due to a phase change from a semi-solid to a very viscous fluid) for a crystalline thermoplastic polymer as shown in Fig. 4.27,... 

The most important representative of polyoxiranes, poly(ethylene oxide) (PEO), is a crystalline, thermoplastic polymer. It is an tmcharged polyether with the chemical formula, -(OCHjCHj) -, which is the simplest stmcture of water-soluble polymers. Unlike most polymer systems, PEO is commercially available in an extraordinarily wide range of molecular weights (MWs) from 200 to several millions or more. The lower-MW members of this series, with MWs up to about 10000, are known as poly(ethylene glycol)s (PEG). The higher members of the series are known as PEOs or poly(oxyethylene)s. At room temperamre, PEO is completely soluble in water in all proportions for all degrees of polymerization. The water solubility of PEO is unlimited, at least up to temperatures slightly below 100 °C. In contrast to the complete water solubility of PEO, closely related polymers such as poly(oxymethylene), poly (trimethylene oxide), polyacetaldehyde, and poly(propylene oxide) (PPO) are water-insoluble under ordinary conditions. 

During the cooling of a semi-crystalline thermoplastic polymer, the macromolecules are organized around a germ of nucleation. At a particular temperature of thermodynamic balance between crystal and liquid (Tm°), the molar free enthalpies are equal in the solid and liquid phases. Crystallization is theoretically possible as soon as the solid free enthalpy... 

In this work we focus mainly on the structure and properties of semi-crystalline thermoplastic polymers. Therefore, we confine our discussion only to this class of polymers. 

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