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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]

The evolution of poly (vinyl alcohol) PVA structure and dichromatic substance induced by uniaxial stretching PVA in the mixed solution with iodine and boric acid (BA) is systematically studied by the combination of in-situ synchrotron radiation small- and wide-angle X-ray scattering (SAXS and WAXD). The experiment is carried out under an orthogonal experimental design for the iodine concentrations of 0.01, 0.2, 1 M, and the BA concentrations of 0.3, 1, and 3 wt%, respectively. We divide the stretch process into three regions, whose boundary is the yield point and strain harden point. The PVA-I 3 - co-crystal generating at high and moderate iodine concentrations is less stable as compared with the PVA crystal, which leads to the earlier decrease of crystallinity at the end of the first region. In the second region, the broken crystal, namely the regular amorphous, is the precursor of the PVA-polyiodide complex. Further increasing the strain, the PVA-I 3 - co-crystals are generated from the one dimension polyiodide surrounded by the PVA chains through a melt-reconstruction process. The adequate BA can make it easy to form the polyiodide at the initial state. Still, the increasing rate of polyiodide is suppressed by further added BA due to the limitation of chain movement by the crosslinking agent. In the final region, the emergence of nanofibril can account for the strain hardening of the film. The evolution of polyiodide and PVA-I 3 - co-crystal revealed by this work gives a better understanding of the polarizer production process, which may guide the resolution of blue leakage of polarizer via an enhancement of the I 3 − in the crystal form during stretching. Image 1 • The structural evolution of dichromatic substance with poly (vinyl alcohol) at different concentrations of boric acid during stretch is investigated by in-situ WAXD and SAXS. • The metastable PVA-I 3 - cocrystal will be easily broken during stretching, which leads to the distinct yield point. • Polyiodide first emerges in the amorphous originated from the broken crystal and then in the highly oriented amorphous during stretching. • The one-dimension polyiodide along with the PVA chain is the precursor of PVA-I 3 - cocrystal. • Dichromatic substance emerges earlier with the increasing of boric acid concentration; however, their final content is less due to the limitation of chain mobility by the crosslinking agent. [ABSTRACT FROM AUTHOR]

Mechanical and structural evolution of poly (vinyl alcohol) (PVA) induced by uniaxial deformation at different concentrations of boric acid is systematically studied with in-situ synchrotron radiation small- and wide-angle X-ray scattering (SAXS and WAXS). The PVA films were stretched uniaxially in the aqueous solution at room temperature with concentrations of boric acid at 0.3 wt%, 1 wt% and 3 wt%, respectively. The stretching process can be divided into three stages through WAXS and SAXS results, whose boundary is the end of the crystallinity platform and the onset of the formation of nanofibrils. In the first stage, the films show elastic stretch with the crystallinity keeping constant and the d -spacing of (101) plane (d 101) decreasing. The unstable crystal breaks up and transfers into amorphous during the second stage so that the force is gradually removed from the unit cell. The connection between the crystal network breaks up in the third stage when the content of boric acid is not sufficient enough. Moreover, increasing the concentration of boric acid leads to the earlier emergence of nanofibrils due to the lower energy barrier induced by entropy decrease, which also results in a reduction of nanofibrils content by limiting the mobility of molecular chain. The results have been applied to establish relationships between the microstructure and the physical characteristics of PVA to help us tune the processing parameters during the practical production. •The structural evolution of poly (vinyl alcohol) at different concentrations of boric acid during stretch were investigated with in-suit WAXS and SAXS. •The addition of adequate boric acid can maintain the connection between the crystal. •Increasing the concentration of boric acid leads to the earlier emergence of nanofibrils. •The boric acid works as the crosslinking agent which limits the mobility of the molecular chain to form more nanofibrils. [ABSTRACT FROM AUTHOR]