Crystallization and Component Properties of Polyamide 12 at Processing‐Relevant Cooling Conditions

Abstract

For semicrystalline thermoplastics, the temperature-time behavior during cooling of the melt can significantly affect the formation of crystalline structures (e.g., spherulite sizes, the degree of crystallization, crystal modifications, etc.) and hence, the resulting global component properties. In this paper, the crystallization of polyamide 12 at different cooling rates as well as process-based temperature-time profiles during cooling were investigated analytically with fast scanning calorimetry. Furthermore, based on analytical results, foils were extruded at different cooling conditions and tested mechanically and tribologically. The analysis reveals differences of the crystal melting behavior for different cooling conditions which is likely to originate in two different polymorphs of polyamide 12, c, and c 0 . Furthermore, mechanical investigations carried out with the extruded foils show that parts produced at high supercooling have less stiffness than parts produced at low supercooling, probably due to differences in the crystalline structures. Regarding tribological parameters, no clear differences could be measured. POLYM. ENG. SCI., 57:450-457, FIG. 5. Heat flow measured during cooling (left) and second heating (right) of PA 12 with respect to the examined cooling rates of 50-100 K/s. FIG. 6. Heat flow measured during cooling (left) and second heating (right) of PA 12 with respect to the examined cooling rates of 5-50 K/s.

Influencing hardness and wear during the dynamic tempered microinjection molding process by considering isothermal holding time

“…Furthermore, a material with relatively high crystallization kinetic has been investigated for comparison reasons since here, it is estimated that there is no significant influence of isothermal holding time, also compare Refs. . For this purpose, POM‐C (Hostaform C9021), supplied by Ticona, was used.…”

“…In Refs. it could be shown that an increase of the mold temperature leads to a decrease of the oriented skin near layer thickness of the component and also an increase of the measured degree of crystallization.…”

“…By influencing the inner component properties by using PEEK as cavity material, a significant increase of stiffness and strength of injection molded microcomponents can result, what is connected to the distinct morphology and the higher degree of crystallization due to the lower cooling velocity during the process . Regarding tribological parameters, researches showed that oriented layers with low degree of crystallization have poorer wear parameters than component layers with a spherulitic morphology and high degree of crystallization . These results were obtained by manufacturing microcomponents with different mold temperatures or cavity materials, whereas the isothermal holding time (the time after the injection begins, before the cavity temperature is being decreased to ejection temperature) has only been investigated for a material with high crystallization kinetics and, therefore, has not shown significant effects on the inner and the resulting global component properties.…”

Modeling and analysis of the process of polymeric film cooling on the drum with a liquid cooling agent

“…An analysis of publications on the production of flat polymeric films [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] showed that majority of them are devoted to numerical and experimental modeling of separate stages of their production process. The focus on the process of preparation of polymer melt in the extruder [7][8][9][10], as well as the process of orientation of semi-finished film on the section from the extrusion head to the cooling drum [11][12][13][14][15][16].…”

“…Paper [18] contains results of research in cooling a film from polyamide 12 on the drum, in this case, temperature of the drum was accepted as constant, which is justified for a thin film with thickness of 80 μm, but is unacceptable for thick films.…”