The formation of crystal cross-linked network in sequential biaxial stretching of poly(ethylene terephthalate): The essential role of MD pre-stretch. (April 2021)

• Record Type: Journal Article
• Authors: Zhang, Wenwen; Chen, Jungen; Yan, Qi; Zhang, Qianlei; Zhao, Jingyun; Wu, Tong; Wang, Daoliang; Meng, Lingpu; Chen, Wei; Li, Liangbin
• Is Part Of: Polymer testing. Volume 96(2021)
• Publication Date: 2021-04
• Subjects: Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2021.107143
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: Combining a homemade uniaxial stretching device and the simultaneous in-situ synchrotron radiation WAXS measurement, the structural evolution during transverse direction (TD) stretching of machine direction (MD) pre-stretched Poly(ethylene terephthalate) (PET) film has been investigated. Current work reveals that increasing the MD pre-stretch before the occurrence of stretch induced crystallization (SIC) can enhance the crystallization and orientation in TD stretching. The concept of parallel chains structures (PCS) cross-linked network is proposed to interpret the rubber-like mechanical behavior. An appropriate stretch ratio window in stretching above the glass transition temperature ( T g ) is existed, where the PCS cross-linked network before crystallization can be induced by stretching above T g . With the help of the PCS cross-linked network, the chain orientation is retained more effectively under stretching, promoting the formation of subsequent crystallization and crystal cross-linking network. The strain hardening in different pre-stretched samples occurs accompanied by the same crystallinity and various chains orientation. This demonstrates that the strain hardening is determined by the crystal cross-linked network rather than the orientation. Current work supplies a guidance for getting the improved film products of PET with enhanced comprehensive mechanical properties, process stability and higher chain orientation. Highlights: The structural evolution in subsequent stretching of pre-stretched Poly(ethylene terephthalate) (PET) film is investigated by the in-situ synchrotron radiation WAXS measurement. The origin of the novel rubber-like mechanical behavior under the complicated stretching field is better understood by the combination of the in-situ chains orientation, crystallization behavior and mechanical behavior. The concept of parallel chains structures (PCS) cross-linked network is proposed to interpret the rubber-like mechanical behavior. The onset of strain hardening corresponds to the formation of the crystal cross-linked network.