The Preparation and Characterization of Branching Poly(ethylene terephthalate) and its Foaming Behavior

Abstract

Chain extension was an effective method for increasing the molecular weight, the melt strength and the foaming property of linear polymer. In this paper, pyromellitic dianhydride (PMDA) was used as chain extender to improve these properties of linear poly (ethylene terephthalate) (PET). The intrinsic viscosity, rheological and thermal characterizations of various PET samples was investigated. The results demonstrated that the increasement of the viscoelasticity at low frequencies was correlated to the raise of the intrinsic viscosity and the formation of long chain branching. These structural changes resulted in the decreasement of the crystallization temperature and melt temperature as well as the increase in the cold crystallization values with the increasing content of PMDA. The cellular morphology and expansion ratio of CEPET foams were also obviously improved by the introduction of PMDA. The expansion ratio of CEPET foam with the PMDA content of 1.0 phr would reach 31.78. In addition, the effect of the chain extension reaction time on the intrinsic viscosity, the rheological behavior, and foaming properties of PET were also studied. The results showed that the intrinsic viscosity, the rheological behavior, and the foamability of CEPET also decreased gradually with increasing chain extension reaction time, which should be attributed to the occurrence of more and more intense thermal degradation.

A cooling and two-step depressurization foaming approach for the preparation of modified HDPE foam with complex cellular structure

“…7 and 8 represented the storage modulus (G') and loss angle (tan δ) against shear rate for the three samples, respectively. It could be seen that the G' value of the HDPE samples (2# and 3#) was larger and their tan δ value was smaller than the corresponding values of neat HDPE sample (1#), which indicated that the melt elasticity of HDPE was enhanced by cross-linking [24].…”

Preparation of Crosslinked High-density Polyethylene Foam Using Supercritical CO2 as Blowing Agent

“…In Figure 7, tanδ of HDPE samples decreased with the DCP content, however, the HDPE samples (4#-6#) were hardly changed with the frequency, indicating the formation of the gel structure [23]. With the increasing DCP content, G' of various HDPE samples increased, while tanδ decreased, which implied that the melt elasticity of HDPE was enhanced [24]. This phenomenon suggested that HDPE with DCP had a longer relaxing process, which also testified that the branching structure improved melt elasticity of HDPE.…”

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

“…In our previous work, we found that the dynamic shear rheology behavior of PET was improved with the increased content of PMDA, and some cross-linking structures were generated in PET/PMDA samples when the content of PMDA was higher than 0.75 phr. 5 So, the concentration of PMDA was held constant at 0.75 phr in this work. Afterward, the mixtures were also thermocompressed into rectangular lamina with 1 mm thickness at 280°C to prepare for further foaming process.…”

“…The chain extension by pyromellitic dianhydride (PMDA) has been confirmed as an effective and convenient way to increase molecular weight and improve the melt strength of PET. 4,5 Surlyn which possesses good dispersion in PET 6 was used as crystal nucleating agent to form more crystal nucleus 7 and therefore acted as heterogeneous nuclei to provide more cell nucleation sites at the interface of crystal and amorphous phase. 8 Previous research also investigated PET blending with other polymers such as acrylonitrile–butadiene–styrene and polyethylene–octene copolymer or mixing with the additives such as montmorillonite nanoclay to fabricate microcellular foams.…”