Contribution to the Study of the Enthalpy Relaxation of Polyesters by DSC Experiments

Abstract

The differential scanning calorimetry (DSC) technique was used to study the enthalpy relaxation of weakly crystalline polyethylene naphatalate (PEN). The samples were examined under two different thermal histories inside the calorimeter. The first method consists in annealing samples at temperature T a below the glass transition temperature T g , for different times Dt a . The second one consists in cooling samples from a higher temperature than T g to the room temperature using following cooling ratesb. In order to highlight the effect of thermal rigidity of molecular chains on the enthalpy relaxation of polyester, a comparative study between the enthalpy relaxation of polyethylene terephtalate (PET) and PEN with very close degrees of crystallinity v c was made. This study shows that the structural relaxation (physical aging) induces a decrease in the molecular mobility of the samples, which prevents the polymer from initiating a rapid return to the equilibrium state. On the other hand, the molecular chains in PEN are stiffer than in PET and hence relax less.

Crystallinity effect on the structural relaxation of polyethylene naphtalate (PEN) by TSDC and DSC experiments

“…However, this behavior evolves in the opposite direction when the ageing temperature is close to T g (383 K <T a <T g ). The same result is reported in the literature [18][19]. When the difference between T a and T g is high, the molecular mobility is sufficiently reduced and the densification process of the system is delayed.…”

“…The activation energy of PEN 25 is about 1516 kJ / mol, while in the case of PEN a , it is 759.6 kJ / mol. Those found in previous work [19] for the PEN 5 and PEN 15, they are of the order of 1020 kJ/ mol and 1240 kJ/mol, respectively.…”

Synthesis and characterization of fully biobased polyesters with tunable branched architectures

“…This behaviour may be ascribed to the physical aging phenomenon by enthalpy relaxation owing to a non-equilibrium state (instability) of the amorphous material in the glassy state. 70 For the sake of comparison with their linear polyesters analogues, the three carboxyl-terminated branched polyesters made from BTO showed significantly higher T g values than their linear analogues prepared from the same diacids but using 1,4-butanediol (BDO). 71,72 Indeed, the linear polyesters combining SucA/ BDO, AdiA/BDO and AzeA/BDO exhibited T g values of −36 °C, −76 °C and −62 °C, respectively (vs. 19.7 °C, −23 °C, and −37.1 °C for BTO-based BPEs, respectively).…”

Physical Aging of Sustainable Polyester Materials towards High-End Consumer Products

“…The most common technique used to study physical aging in amorphous polymers, is differential scanning calorimetry (DSC) [60,[67][68][69]. DSC can be used to determine the enthalpy of the polymeric glass and thus characterizing its structural state.…”