Nylon Refrigerant Tubing

Air Conditioning and Refrigeration Center Project 1

Melting and Recrystallization of PA-6/PA-66 Blends

The morphology of a number of polyamides (P A) of current and potential use for mobile air conditioning and refrigerant tubing, namely PA-6, PA-66, PA-6/PA-66 blends and PA-6/PA-66 copolymers, as prepared from the melt and from HCOOH solution and the effect of annealing thereof has been examined. In tpe blends the P A -6 crystallizes within the P A -66 spherulites, the P A -66 crystallizing first in a loose lamellar framework. The copolymers also crystallize as large spherulites. When prepared from HCOOH solution at 25??C (77??F) the PA-66 containing samples show a large exothermic peak before the sample melting peak is observed by DSC. This exothermic peak, which cannot be fully explained by either previously known observations, P A recrystallization and/or the morphology changes we describe here, is not seen for PA-6 or for PA-66 prepared from HCOOH solution at 100??C (212??F).Air Conditioning and Refrigeration Center Project 1

Morphology of polypivalolactone: A polymer with a direction

The morphology of polypivalolactone crystallized from the melt in the alpha and gamma crystal forms is described. In both forms large, rather perfect lamellae form; the crystal structures require antiparallel chain packing in the lamellae in both forms and a predominantly adjacent re-entry chain folding is suggested

Poly(trimethylene teraphthalate) crystal structure and morphology in different length scales

Poly(trimethlene teraphthalate) (PTT) is one of the terephthalic polyester family members which can crystallize between its glass transition and melting temperatures. The crystal structure has been determined using both electron diffraction (ED) on single crystals and wide angle X-ray diffraction on powder and oriented fibers. The unit cell is triclinic with dimensions of a = 0.46 (3) nm, b = 0.61 (2) nm, c = 1.86 (1) nm, alpha = 97.5 degrees, beta = 92.1 degrees, and gamma = 110 degrees. The bulk PTT samples usually crystallize to form spherulites in the crystallization temperature (T-c) region studied. Between T-c = 135 and 165 degreesC, the spherulites show a banded texture, and the band spacing increases with increasing T-c. The radial direction in the spherulites has been determined to be the crystal a-axis. Observations of successive ED patterns taken along the radial direction of a spherulite within one band reveal twist of lamellar crystals along the spherulite radial direction. The chain-folding direction, determined using a polyethylene decoration method, is along the a-axis direction in the lamellar crystals and parallel to the radial direction in the spherulites. Linear growth rates of the spherulites have also been measured and the maximum growth temperature is located at 165 degreesC. This temperature is also the upper-limit temperature for PTT banded texture spherulite formation. (C) 2001 Elsevier Science Ltd. All rights reserved