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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]

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]

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]