Polyoxymethylene spherulites

Crystalline polymers exhibit the following basic properties They are opaque as long as the size of the crystallites or spherulites, respectively, lies above the wavelength of light. Their solubility is restricted to few organic solvents at elevated temperature. The following crystalline polymers have attained technical importance as thermoplastic materials polyethylene, polypropylene, aliphatic polyamides, ali-phatic/aromatic polyamides, aliphatic/aromatic polyesters, polyoxymethylene, polytetrafluoroethylene, poly(phenylene sulfide), poly (ary lene ether ketone)s. 

Fig. 1.2 Polarized light micrograph of this polyoxymethylene film cooled from melt shows recrystallization and formation of spherulites. The shape of the growing, birefringent spherulites is round.

Typical polymer materials studied in optical thin section include extrudates or molded parts, such as semicrystalline polyoxymethylene multiphase polymers, such as rubber toughened nylon filled polymers, such as carbon black filled nylon fibers, such as polyester and rayon and films which are too thick to transmit light. Two examples are of nylon imaged in polarized light (Fig. 4.9A), which reveals its spherulitic texture, and imaged in bright field (Fig. 4.9B), which reveals the dispersed carbon black particles. 

Figure 5.1 (a) The solution-grown polyoxymethylene single crystal, (b) spherulites of melt-cooled polyethylene sample and the hierarchical structure, (c) extended-chain crystals of polyoxymethylene (whisker), and (d) the shish-kebab structure. (See color insert.)... 

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