Kinetics of homogeneous crystal nucleation of polyamide 11 near the glass transition temperature

Abstract

In this work, the kinetics of formation of homogeneous crystal nuclei of polyamide 11 (PA 11) near the glass transition temperature (T g), which is slightly above ambient temperature, has been analyzed using fast scanning chip calorimetry (FSC), employing Tammann's two-stage crystal nuclei development method with non-isothermal and isothermal nucleation and growth stages. The critical cooling rate above which formation of an ordered phase (crystals or mesophase) is suppressed is around 1000 K/ s. Formation of nuclei, in contrast, can only be prevented by cooling the melt faster than about 30,000 K/s to far below T g. The temperature of fastest formation of crystal nuclei is about 10-15 K higher than T g , with first detection of nuclei within less than a millisecond. As such, the onset-time of nuclei formation is about one order of magnitude shorter than the time of first observation of crystals/mesophase. Furthermore, annealing experiments performed below T g revealed glass-crystallization, with the stability of the formed ordered phase limited to temperatures near T g. Since rapid cooling and solidification of the melt of PA 11 at low temperatures often occurs in processing of this material, this work provides new insights into processingcontrolled structure formation, eventually being beneficial for tailoring the property profile.

Nucleation and crystallization kinetics of polyamide 12 investigated by fast scanning calorimetry

“…Homogeneous nucleation is entirely suppressed if cooling the sample at rates faster than 10,000 K/s. For heating rates of 5000 and 10,000 K/s, the value of Δ H cc finally cannot reach a value near zero, which will be further analyzed in the next section 18,26 …”

“…The increase of Δ H cc here refers to the suppression of crystallization during cooling. Cooling the melt at a rate higher than 300–400 K/s decreases Δ H cc due to the suppression of homogeneous nucleation, which leads to a decrease of the number of available nuclei 17,18,26,50 . Increasing the cooling rate to above 10,000 K/s, the value of ΔH cc becomes zero or constant at a certain value.…”

“…These two factors enable high‐scanning rates up to 1,000,000 K/s 8 . By using FSC, the crystallization of polyamides has been intensely investigated 9–19 . As high‐cooling rates can be applied, the polyamide melt can be quenched to both low and high supercooling 9–11,14–18,20–25 .…”

“…By using FSC, the crystallization of polyamides has been intensely investigated 9–19 . As high‐cooling rates can be applied, the polyamide melt can be quenched to both low and high supercooling 9–11,14–18,20–25 . The crystallization kinetics can be studied through non‐isothermal or isothermal experiments.…”

“…Several studies applied FSC to investigate the crystallization kinetics of different polyamides 11,15,16,18,19,24,27–29 . A bimodal temperature‐dependence of the crystallization rate was observed in most studied polyamides.…”