Polyamides, crystallite size

The diffraction pattern of polyamide fibers, as well as those of many other fibers, is characterized by a considerable broadening of the wide-angle diffraction maxima. This is usually explained in terms of the crystallites size responsible for the diffraction. The formal relationship between crystallite size and 6 is given by the Scherrer equation [299] D = K /A(26) cos 6, where D is the diameter of the crystallite, A(26) is the angular diffraction width of the particular crystal reflection, and K is the shape factor, which is a constant with a value close to unity. 

The melt-spinning dynamics and rheological properties of nylon 6 have been studied together with eifects of drawing and of swelling and additive incorporation,and the effects of crystallite dimensions on structure and modulus. Crystallinity and crystallite size measurement in both polyamides and polyesters has also been reviewed. ... 

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, aliphatic/aromatic polyamides, aliphatic/aromatic polyesters, poly-oxymethylene, polytetrafluoroethylene, poly(phenylene sulfide), poly(arylene ether ketone)s. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

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