Crystallization-induced microcellular foaming behaviors of chain-extended polyethylene terephthalate

Abstract

The microcellular foaming of chain-extended polyethylene terephthalate (CPET) by crystallization induction method was reported in this article. The crystallization behaviors of various polyethylene terephthalate (PET) samples which were affected by the combined effect of pyromellitic dianhydride, Surlyn, and CO2 were investigated. After Surlyn was added to CPET, the crystal nucleation of various CPET samples was improved, and numerous but small spherulites were generated. Two kinds of CPET samples with the content of 0 phr and 1 phr Surlyn were foamed at various temperature by batch foaming method. Changing the saturation temperature could adjust the appearance of high-temperature melting crystals which would affect the final cellular structures in various CPET foams. With the decrease of saturation temperature, the cell size decreased while cell density increased. At the saturation temperature of 265°C and 250°C, the cell density of CPET foam with Surlyn was one magnitude larger than CPET foam without Surlyn. At the saturation temperature of 247°C, the microcellular PET foams with the cell density of 109 cells cm−3 and the cell size less than 10 µm had been developed successfully.

To Effectively Tune the Cell Structure of Poly(ethylene 2,5-furandicarboxylate-co-ethylene terephthalate) Copolyester Foams via Conducting a Prior Isothermal Melt Crystallization

“…This is attributed to the formation of crystals of a proper crystallinity being favorable for enhancing both the heterogeneous cell nucleation and the melt strength. 5 Third, for quenched PEFT10%, cell collapse occurred during foaming. However, for PEFT10% with isothermal crystallization, no significant improvement of the cell structure was observed.…”

“…The reason was that crystals of proper crystallinity were formed during the isothermal crystallization, and heterogeneous cell nucleation was significantly enhanced as the interface of crystalline and amorphous regions provided numerous cell nucleation sites. 5,14 With a further increase of the isothermal crystallization temperature, the cell size increased and the number of the cells decreased. This is due to the fact that the relatively lower crystallinity showed no significant effect on the improvement of the cell nucleation and the melt strength.…”

“…However, PET generally shows a low crystallization rate and low melt strength, leading to severe cell coalescence during foaming. , Therefore, an improvement of the foaming behavior and the cell structure of PET foams has been significantly required by the end uses. The cell structure of PET foams is generally improved via enhancing the melt strength via chain extension, ,− solid-state polycondensation, formation of a physical network, and so forth. In addition, crystallization has also been considered an important factor in affecting the foaming behavior and the cell structure of PET. ,,− Baldwin et al , found that the semicrystalline PET showed a smaller cell size and larger cell density than amorphous PET.…”

“…Pan et al 6 incorporated carbonaceous particulates as a heterogeneous nucleation agent to promote the melt crystallization and thus to enhance the melt strength of PET for the purpose of benefiting the cell growth. Jiang et al 5 introduced Surlyn in chain-extended PET as a heterogeneous nucleation agent to generate small and numerous crystals, and consequently, PET foams with a small cell size and large cell density were obtained. In another study, Jiang et al 11 improved the cell structure of PET foams utilizing the dual effects of in situ formed poly(tetrafluoroethylene) fibrils, enhancing both the melt strength and the heterogeneous crystallization nucleation.…”

“…Hence, cell structure control has long been an important subject in the polymer foaming field. However, PET generally shows a low crystallization rate and low melt strength, leading to severe cell coalescence during foaming. , Therefore, an improvement of the foaming behavior and the cell structure of PET foams has been significantly required by the end uses. The cell structure of PET foams is generally improved via enhancing the melt strength via chain extension, ,− solid-state polycondensation, formation of a physical network, and so forth.…”