Robust and Transparent Polyamide 1012 Membranes for Biogas Purification Controlled by the Degree of Hydrogen Bonding Order

Thepresent work aims to design thermal protocols to generate differentcrystal forms in even-even polyamides. Such structural controlcan lead to tailoring of their properties. To achieve our objective,we have chosen low molecular weight (M (n)) Polyamide 1012 (PA1012) because its crystal forms can be more easilycontrolled by changing cooling rates after erasing thermal historyin comparison with high M (n) PA1012. Whenthe chosen PA1012 was slowly cooled after erasing thermal history(e.g., 2 & DEG;C/min) to a temperature where it had crystallized untilsaturation (i.e., 150 & DEG;C), the standard & alpha; form could thenbe obtained when the sample was further cooled to room temperature(RT) at any rate. However, if the sample was first cooled at fastercooling rates (>20 & DEG;C/min) until 150 & DEG;C, two types ofdifferentcrystal forms could be obtained upon subsequent cooling to RT. Combiningself-nucleation (SN) experiments and wide-angle X-ray diffraction(WAXD) results, we found that the formation of locally ordered H-bondsat high temperatures (during crystallization from the melt) directlyaffected the final room-temperature crystal form. It was found thatthe lower crystallization degree and smaller crystal size of the lessthermodynamically stable & gamma;& PRIME; form films possess not onlygood toughness and elongation at break but also excellent transparencyas well as higher gas permeability coefficient with better gas selectionproperties. Among them, the & gamma;& PRIME; form has a broader marketprospect by endowing PA1012 films with excellent mechanical propertiesand gas transport properties to produce transparent membranes forbiogas purification.

Automated summary

The present study aims to generate different crystal forms in even-even polyamides by designing thermal protocols. The choice of low molecular weight (M (n)) Polyamide 1012 (PA1012) facilitates easy control of crystal forms. Different crystal forms can be obtained at room temperature by cooling the chosen PA1012 at different rates.