(181bs) Effect of the Long Chain Branched Structure of Modified PET on Its Extrusion Foaming Behaviors Under Supercritical CO2
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Materials Engineering and Sciences Division
Poster Session: Materials Engineering & Sciences (08A - Polymers)
Monday, November 11, 2019 - 3:30pm to 5:00pm
Effect of the long chain branched structure of
modified PET on its extrusion foaming behaviors under supercritical CO2
Shun Yao, Tao Liu, Ling Zhao*
Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East
China University of Science and Technology, Shanghai 200237, PR China
zhaoling@ecust.edu.cn; Phone: (+86) 21 64253175; Fax: (+86) 21 64253528
ABSTRACT
Extrusionfoaming is an effective process to fabricate sheet foams continuously, which
consists of an extruding unit and die-shaping unit. It follows the same
operational principle as in plastic extrusion but the basic difference is the
introduction of blowing agents at a certain position on the extrusion line. Nowadays,
supercritical carbon dioxide (scCO2) as a green blowing agent has
attracted more attention in extrusion foaming. However, only a few commercial extrusion
foamed products of polyethylene terephthalate (PET) adopt scCO2,
which resulted from both low melt strength and slow crystallization of PET
itself as well as the complex interactions between CO2 and PET
segments. Therefore, the preparation of long chain branched PET (LCB PET) to
enhance its melt strength and crystallization behavior may be an impactful way
to accomplish PET scCO2 extrusion foaming. Three modified
PET (MPET-1, MPET-2, MPET-3) possessing different branched degree were prepared
by reactive extrusion, and two kinds of commercial PET materials were used as
received which were raw PET (RPET) with low molecular weight (Mw) and foam
grade PET (FPET) with high melt strength. Storage modulus G' was associated with melt elasticity, and G' of modified PET was always higher than RPET. Meanwhile, G' was higher than G'' as angle frequency exceeded 0.23 rad/s for MPET-1as seen in
Figure 1. The crosspoint of G' and G'' should shift to lower frequency
region when the molecular weight increases and to lower modulus region when
molecular distribution becomes broader. Therefore, MPET-1 had the broadest
molecular distribution and the highest molecular weight. Besides, MPET-1 exhibited
promoting crystallization characterizations than other four PETs, because
MPET-1 possessed most branched structures which could act as crystal precursor
nucleus sites. MPET-1 had a smaller crystal size and a higher crystal density
due to an excessively fast crystallization nucleation process. The promoting
rheological and crystallization performances of long chain branched PET improved
its cell morphology of extrusion foaming samples as seen in Figure 2.
![](https://www.aiche.org/sites/default/files/aiche-proceedings/conferences/269951/papers/566895/Paper_566895_abstract_145492_0.png)
Figure 1. Storage
modulus and loss modulus versus angle frequency of RPET, FPET and modified PETs
![](https://www.aiche.org/sites/default/files/aiche-proceedings/conferences/269951/papers/566895/Paper_566895_abstract_145493_0.png)
Figure 2. SEM
images of extrusion foamed samples: (a) MPET-1 (b) FPET