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Recent efforts attempting to in-situ track the polymer film formation during film blowing are summarized. The specially designed film blowing apparatus is firstly introduced, where the air ring is aligned along with the die, and it's capable of installation in the synchrotron beamline (SR-beamline). Later on, detailed structural evolution of different polymeric systems during film blowing, including polyethylene (PE) and poly(butylene adipate-co- butylene terephthalate) (PBAT), are obtained with the assistance of simultaneous acquired Small- and Wide Angle X-ray Scattering (SAXS/WAXS). The transient structure evolution information from oriented polymer melt to final crystalline tubular film clarifies the contribution of the crystallite-based network to final macroscopic performances. Also, the experimental results have shown the influence of intrinsic molecular characteristics and external processing parameters on the formation of stable tubular bubble. Additionally, the post-modification of the blown film, including stretching and surface treatment is also discussed. Current experimental efforts are expected to provide more detailed parameters for mathematical modeling of film blowing, which could help us modify or develop new numerical models. The micro-structural evolution of polymer during film blowing as in-situ characterized by synchrotron radiation X-ray scattering. Image 1 • Feature article focuses on in-situ tracking of structural evolution during Film Blowing. • A new film blowing machine which can be installed in the SR-beamline is designed. • Formation of crystal-based network is only influenced by molecular parameters. • Flow- and temperature-induced crystallization coexist during film blowing. [ABSTRACT FROM AUTHOR]

The copolymerization of ethylene and different α-olefins could result in polyethylene (PE) with different structural topologies, and lead to polyethylene products with different macroscopic performances. Herein, three different polyethylene samples, namely low-density polyethylene (l -PE), metallocene catalyzed ethylene-hexene copolymer (h -PE) and ethylene-octene copolymer (o -PE), were selected as representatives to construct the structure-process-property relationship during film blowing. The detailed crystal-based network evolution during film blowing was first characterized by in-situ synchrotron radiation X-ray scattering. The crystallization process of l -PE film is determined by the coupling effects of temperature and flow, while those of h -PE and o -PE films are dominated by the temperature. Furthermore, the hierarchical crystal structure from the molecular scale to micrometers of final films and segmental dynamics were systematically characterized by multiple ex-situ characterization techniques, i.e. Solid-State NMR, FTIR, SEM. l -PE film shows the crystalline morphology of the row-nucleated structure, whereas h -PE and o -PE show spherulite-like superstructure with better mechanical properties. The current study tentatively constructs the relation of primary chemical structure, microstructural evolution and macroscopic performances of different polyethylene copolymers during film blowing. • Three ethylene/α-olefin copolymers were selected to construct the structure-process-property relationship on the film blowing. • The structural evolution during film blowing was captured by a combination of in-situ SR-SAXS/WAXS and a custom-built film blowing device. • The multi-scale microstructure and dynamics of final films were characterized by ex-situ SAXS/WAXS, FTIR, SEM, and SS NMR. • The mechanical and optical properties of films are well correlated with their structural evolution and microstructure. [ABSTRACT FROM AUTHOR]

Abstract The structural evolution of poly (ethylene terephthalate) (PET) with distinct water absorption during uniaxial deformation slightly above glass transition temperature (T g) were investigated by in-situ synchrotron radiation wide angle X-ray scattering (WAXS). Results show that the locally ordered structures are not conducive to stretch-induced crystallization (SIC) although the corresponding entropy is more close to crystals compared to random chains, which is due to the limited chain mobility therein. The "frozen orders" should be destroyed to achieve the critical chain mobility required by SIC even with the presence of water as plasticizer. Unexpectedly, absorption of water does not enhance but suppresses SIC though it does promote the chain mobility, originating from lower stress level with higher water contents. Stress and chain mobility directly correlate with chain stretch and orientation in positive and negative manners, respectively, demonstrating that chain stretch and orientation also play important role in SIC around T g. Graphical abstract Image 10457 Highlights • The structural evolutions of PET samples with different contents of water are investigated with in-situ WAXS. • It is necessary to accumulate sufficient chain mobility for SIC by destroying the frozen orders. • The SIC in PET can be inhibited by water above glass transition temperature. [ABSTRACT FROM AUTHOR]

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. • 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. [ABSTRACT FROM AUTHOR]