Gitterstrukturen mit räumlichen Wasserstoffbrückensystemen und Gitterumwandlungen bei Polyamiden

Abstract

8-Nylon zeigt bevorzugt eine monoklin entartete Gitterstruktur, bei der α = b und γ = 60° wird. Sie beruht darauf, daß an Stelle des bekannten Rostebenensystems ein räumliches Wasserstoffbrückensystem tritt. Dieses räumliche Netzwerk macht eine direkte höhere Orientierung unmöglich. Auch die triklinen Hochtemperaturmodifikationen von 7-, 11-, 6,6- und 8,10-Nylon stellen räumliche H-Brückensysteme dar. Die Gründe für die Entstehung und Stabilität solcher räumlicher Netzwerke werden diskutiert.

Density of heterogeneous and homogeneous crystal nuclei in poly (butylene terephthalate)

“…4, could also be caused by faster growth of the different crystal polymorph. Such situation may be evident for the specific cases of iPP, PA 6, PA 66 or PA 11, for which similar changes of the nucleation density on variation of the supercooling were detected by imaging techniques [13,21,24,25], but simultaneously show formation of different crystal structures on high and low supercooling [26][27][28]. It is worthwhile noting that due to the smallness of domains and fast kinetics of their formation measurements of the growth rate of individual domains were not performed yet.…”

“…At high supercooling of the melt, in contrast, due to the largely increased number of nuclei by several orders of magnitude, lateral growth of nuclei and formation of lamellae and spherulites was suppressed [13,[20][21][22][23][24][25]. Unfortunately, for all of these polymers, besides the drastic increase of the nucleation density on increasing the supercooling above a critical value, there is simultaneously observed formation of a different crystal polymorph [26][27][28]. In other words, it cannot be excluded that the low-temperature maximum of the gross crystallization rate is then also be caused by an increased crystal growth rate.…”

Crystal Transition of Nylon‐12,12 under Drawing and Annealing

“…Owing to the complexity of the polymer structure, the interpretation of the Brill transition has been difficult and unclear until now. Several mechanisms have been proposed to elucidate the Brill transition: Some researchers [3,8] suggested that it is the result of breaking and reorganizing of hydrogen bonds within hydrogen-bonded sheets and the formation of a three-dimensional hydrogen-bonded crosslinking network between close polymer chains present in the same and in different stacked hydrogen-bonded sheets. Others [9][10][11] believed that the hydrogen bonds did not break and the Brill transition occurred because of thermal expansion or contraction along the b axis, and that defective, unstable, and small size crystals are helpful for a Brill transition.…”

Crystallization kinetics of polyamide 11 in the presence of sepiolite and montmorillonite nanofillers

“…Regarding the crystallization behavior of unmodified PA 11 it is known that, depending on the crystallization conditions, different crystal structures may form [6][7][8][9][10][11]. Slow cooling of the melt leads to formation of triclinic -crystals which convert reversibly to -crystals at the Brill-transition temperature [12] of about 100 °C.…”

“…These crystals, which form at low supercooling of the melt, are of lamellar shape and are organized within spherulites [16]. Rapid cooling of the melt at rates between 100 and 500 K s -1 suppresses /-crystal formation at low supercooling and leads to development of a pseudohexagonal '-phase of nodular shape at temperatures lower than 80 °C [3,9]; even faster cooling prevents all ordering and causes complete vitrification of the melt at the glass transition temperature T g of around 40 °C [3].…”