Yuanfei Lin

A simple constrained uniaxial tensile apparatus for in situ investigation of film stretching processing

A simple constrained uniaxial tensile apparatus was designed and constructed to obtain stress-strain curve during stretching and subsequent structural evolution of polymeric films. Stretch is carried out through two motor driven clamps in the machine direction and scissor-like clamps in the transverse direction keeping the sample width constant. The force information during film stretching process is recorded by a tension sensor and structural evolution can be obtained by in situ X-ray scattering technique. All parameters related to film stretching manufacturing, such as temperature, draw ratio, and stretching speed can be set independently, making the apparatus an effective method to explore the relationship between processing parameters and structure.

A Universal Equipment for Biaxial Stretching of Polymer Films

A biaxial stretching equipment was designed and constructed to enable fundamental studies of the relationship between film processing conditions and structures of oriented film products. With programmable drive motors and scissor-like mechanism, all stretching modes, including uniaxial stretching with constant and free width, simultaneous and sequential biaxial stretching, can be applied to a square-shaped sheet. Parameters related to film stretching manufacturing, such as temperature, draw ratio and stretching speed can be set independently to meet the requirement of different polymers. The force information during stretching is recorded by two miniature tension sensors in two directions independently, which can monitor the mechanical stimulus and stress response. Using this equipment, experiments are conducted to investigate the influence of stretching parameters on the structure of polypropylene films, which provides an effective method to tailor the processing conditions to obtain the films with desired properties.

Influence of material characteristics on the structure and properties of high-density polyethylene microporous membranes

Five PE resins with different material characteristics were chosen to fabricate microporous membranes based on a melt-stretching mechanism. The lamellar morphology of the initial precursor films and stretched pore structures were characterized. It was found that the precursor films prepared using PE with an appropriate content of larger and small molecular weight species showed higher lamellar thickness and orientation degree. This kind of PE resins exhibited a weak relaxation peak on the left of the main relaxation peak in the relaxation time curves. After stretching, a porosity of around 50% could be obtained and the corresponding air permeability could meet the demands of a separator, which could be used in the field of lithium batteries. Contrary to this, a PE with too many larger molecular weight species was unfavorable for the preparation of microporous membranes, since the higher content of fibre-aligned structures limited the separation of lamellar structures during stretching. PE with too low a content of small molecular weight parts was also inapplicable for the preparation of microporous membranes. The lower lamellar thickness was easy to be deformed and could not support the scaffold of the pore structure, leading to the collapse of the pores and inferior air permeability.

Improving the Softness of BOPP Films:From Laboratory Investigation to Industrial Processing

Young’s modulus of biaxially oriented polypropylene (BOPP) films prepared with homemade film stretcher was investigated, which can be used to indicate the softness of films. It was found that the modulus of films was decreased by about 69% as the content of polyethylene (PE) added into polypropylene (PP) reached 30%. Also, increasing draw temperature can induce lower stress level during stretching, which may lead to the formation of crystals with low orientation level and thus decreased modulus of films. Based on laboratory study, BOPP films produced on commercial line were studied by differential scanning calorimetry (DSC), wide and small-angle X-ray scattering (WAXS, SAXS) with varying contents of PE. SAXS results show that the crystals are oriented in both machine direction (MD) and transverse direction (TD), and the crystals are more oriented in TD than MD according to the WAXS results for all films. Also, the orientation parameter of crystal along TD increases from 0.68 to 0.83 as the contents of PE increase from 0% to 25%. Meanwhile, the modulus of films in MD declines with increase of PE contents generally, improving the film softness. Orientation of crystals is thus an effective structure parameter to adjust the film softness. The relationship of processing-structure-property is also established.

Multiferroic properties of hexagonal Ba3Ti2MnO9

The magnetic and electrical properties of hexagonal Ba3Ti2MnO9 are investigated. The material is a noncentrosymmetric evolution from hexagonal BaTiO3 with a space group P63mc. The existence and distribution of both Mn4+ and Ti4+ are checked using an electron energy-loss spectroscopy line scan by high resolution transmission electron microscopy. Magnetic transitions are attributed to the short range ordering and magnetic frustration. The frequency independent behavior of the dielectric peak shows a ferroelectric transition at 222 K. Both Positive Up and Negative Down (PUND) techniques and the local piezoresponse confirm the ferroelectric behavior of Ba3Ti2MnO9.