Crystallization of polyamide

Gogolewski, S. and Pennings, A. J. Crystallization of polyamides under elevated pressure 5 Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-11, poly(aminoundecaneamide) under pressure, Polymer 18, 660 (1977) Stamhuis, J. E. and Pennings, A. J. Crystallization of polyamides under elevated pressure 6. Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-12, polylaurolactam under pressure. Polymer 18, 667 (1977)... 

Extensive investigations have been performed also on the crystallization of Polyamide 6. Especially the transformation of the y-phase mto the a-phase was studied. It was shown that the transformation occurs always within a time of less than 20 seconds, that means within the time in which the applied temperature change... 

Gogolewski S, Peimings AJ (1973) Crystallization of polyamides under elevated pressure. Nylon 6. Polymer 14 463 see also 18 647, 654 (1977)... 

Gogolewski S, Pennings AJ (1977) Crystallization of polyamides under elevated pressure 5. Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon 11, poly(aminoundecaneamide) under pressure. Polymer 18 660... 

Wu s explanations for this fundamental observation were couched in field theory, such as overlapping of concentrated stress fields around particles or a transition in local stress state from plane strain to plane stress, and could not furnish a specific material dimension, which, as we present below, depends on the type of the polymer and its crystalline state. The required fully consistent explanation for the discovery was provided by the studies of Muratoglu et al. (1995a), who proposed that the material-specific level of A is a consequence of a preferred form of crystallization of polyamide lamellae near particle interfaces, extending to a certain distance I away from the interface. This results in an anisotropic plastic resistance in this layer, which upon percolation through the matrix and in an... 

Full Dissolution and Crystallization of Polyamide 6 and Polyamide 4.6 in Water and Ethanol... 

M.G.M. Wevers et al. Full Dissolution and Crystallization of Polyamide 6 and Polyamide. 6 in Water and Ethanol, Lect. Notes Phys. 714, 151—168 (2007)... 

The scientific objective of the present research endeavor is the understanding of dissolution and crystallization of polyamides in water and other solvents. In this paper we report on results obtained by SEC, DSC and WAXD measurements. 

Figure 6.11 Single crystal of polyamide 6 precipitated from a glycerol solution. The lamellae are about 60 A thick. Black marks Indicate 1 um (34).

Similar investigations performed with polyamides are comparatively less telling. Indeed, the hydrogen-bonded sheets are a strong structural feature that does not leave much leeway for diverse epitaxial crystallizations. So far, the only contact plane observed in epitaxial crystallization of polyamides is indeed the hydrogen-bonded sheet [16]. This in turn implies that substrates with a periodicity close to 0.48 to 0.5 nm are most appropriate (provided of course that their compatibility with polyamides is sufficient). In this respect also, investigation of epitaxial crystallization of polyamides teaches us less than that of PE. However, further research is needed to investigate if some less standard crystal modifications of polyamides, such as the 7 form of polyamide 6, can be produced by epitaxial crystallization. 

Figure 10.26 DSC thermograms of (a) Ny6/PP-AA and (b) Ny6/PE-AA blends in the composition range 0-100 wt% Ny6, recorded on cooling from the melt at 10°C/min. The high temperature peak corresponds to the crystallization of polyamide phase, the peaks at lower temperature to the crystallization of the polyolefin phases. Reprinted from Psarski et al. [Ill], Copyright 2000, with permission from Elsevier.

Fig. 9.22. Model proposed for fracture behavior and surface morphology of chain-extended crystals of polyamide (Courtesy S. Gogolewski 12021). (Reproduced by permission of the publishers,...

For some polymers such as isotactic polystyrene (iPS), polycarbonate, and PHB, reversing heat capacity from TMDSC equals baseline heat capacity for temperatures near glass transition. For other polymers also in isothermal TMDSC experiments latent heats may contribute to the measured reversing heat capacity at the generally low frequencies available by TMDSC. Figure 11 shows the development of measirred reversing heat capacity during isothermal crystallization of polyamide 12. Similar observations were made for PE, poly(c-caprolactone) (PCL), and polyetheretherketone (PEEK) to name a few. 

Figure 11 Quasi-isothermal crystallization of polyamide 12 at 7 o=173°C, fp = 600s, ytr=0-5K. (a) Temperature profile consisting of an asymmetric sawtooth profile. The resulting heating rate and the heat flow rate show sharp spikes containing a broad spectrum of higher harmonics. (b) Specific reversing heat capacity as a function of time for different frequencies as indicated in the graph. The lines labeled Cp and Cp c indicate the data for liquid and crystalline polyamide 12 at 173 °C available from the ATHAS-DB, respectively. The used temperature time profile for sample preparation and crystallization is shown in the inset. Reproduced with permission from Schick, C. Anal. Bioanal. Chem. 2009, 395,1589-1611. ...

Fig. 3. Alignment of amide dipoles in polyamide crystals (a) for a two-dimensional array of an odd nylon, nylon-7, (b) for a one-dimensional array of an odd—odd nylon, nylon-5,7 (c) for one-dimensional arrays of polyamides containing even segments an even nylon, nylon-6 an even—even nylon, nylon-6,6 ...

The repeat length in the triclinic polymer crystals (75.3 nm) is significantly less than for PBT (86.3 nm) and PET (99.5 nm). This has been claimed to make the crystal more spring-like in the long axis resulting in enhanced resilience and wear resistance in carpet fibres to a level approaching that of polyamide fibres. 

Tab. 3.1 DNA-binding proteins that have been inhibited by polyamides. The known DNA binding motifs from NMR or crystal structure data are shown. Significant groove contacts and proposed mechanism of polyamide inhibition are also shown for each protein...

Many properties of polyamides are attributable to the formation of hydrogen bonds between the NH and CO groups of neighboring macromolecules. This is evidenced by their solubility in special solvents (sulfuric acid, formic acid, m-cresol), their high melting points (even when made from aliphatic components), and their resistance to hydrolysis. In addition, polyamides with a regular chain structure crystallize very readily. 

Applications. The polyamides have important applications. The very high degree of polymer orientation that is achieved when liquid crystalline solutions are extruded imparts exceptionally high strengths and moduli to polyamide libers and lilms. DuPont markets such polymers, e g. Kevlar, and Monsanto has a similar product, e.g.. X-500. which consists of polyamide and hydrazide-lype polymers. Liquid-crystal polymers arc also used in olccirnnpnc displays. 

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