Methods in Lignin Chemistry

A review is given of the structure of semi-crystalline polymers and the mechanisms of plastic deformation in them. High-density polyethylene (HDPE) is taken as the specific example because of the large number of detailed studies performed on this material. The early findings are also compared and contrasted with very recent detailed large-strain deformation studies and computer simulations of deformation-induced texture development in HDPE.

Structure and plastic deformation of polyethylene

A method and system for spectroscopic ellipsometry employing reflective optics to measure a small region of a sample by reflecting radiation (preferably broadband UV, visible, and near infrared radiation) from the region. The system preferably has an autofocus assembly and a processor programmed to determine from the measurements the thickness and/or complex refractive index of a thin film on the sample. Preferably, only reflective optics are employed along the optical path between the polarizer and analyzer, a sample beam reflects with low incidence angle from each component of the reflective optics, the beam is reflectively focused to a small, compact spot on the sample at a range of high incidence angles, and an incidence angle selection element is provided for selecting for measurement only radiation reflected from the sample at a single, selected angle (or narrow range of angles). The focusing mirror preferably has an elliptical shape to reduce off-axis aberrations in the focused beam. Some embodiments include both a spectrophotometer and an ellipsometer integrated together as a single instrument. In such instrument, the spectrophotometer and ellipsometer share a radiation source, and radiation from the source can be focused by either the spectrophotometer or the ellipsometer to the same focal point on a sample. Preferred embodiments of the ellipsometer employ a rotating, minimal-length Rochon prism as a polarizer, and include a spectrometer with an intensified photodiode array to measure reflected radiation from the sample, and a reference channel (in addition to a sample channel which detects radiation reflected from the sample).

Focused beam spectroscopic ellipsometry method and system

Plane strain compression in a channel die is kinematically very similar to drawing; however, the possibility of void formation is limited due to a compressive component of stress. In drawing, voids were detected by small-angle X-ray scattering (SAXS) and density measurements in poly(methylene oxide) (POM), polypropylene (PP), and high-density polyethylene (HDPE), but no voiding was found in polyamide 6 (PA 6), low-density polyethylenes (LDPEs), and ethylene−octene copolymer (EOC). The slope and shape of the initial elastic part of true stress−true strain curves are similar in tension and in channel die compression. When drawn samples of POM, PP, HDPE, and PA 6 already show yielding, the channel die compressed samples still undergo elastic deformation to a much larger deformation and respond with a much larger stress. Channel die compressed POM, PP, HDPE, and PA 6 exhibit strong and rapid strain hardening up to 400 MPa in contrast to their behavior in tension. The difference in strain hardening is related ...

Plastic Deformation of Crystalline Polymers: The Role of Cavitation and Crystal Plasticity

The field of mesophases is subdivided into six different phases: liquid crystals, plastic crystals, condis crystals and the corresponding LC, PC, and CD glasses. Liquid and plastic crystals are the traditional phases with positional and orientational disorder, respectively. Condis crystals are conformationally disordered. On hand of tables of thermodynamic transition parameters of small and large molecules it is shown that the orientational order in liquid crystals is only a few per cent of the total possible, while the positional order in plastic crystals is virtually complete. Condis crystals have a wide variety of different degrees of conformational disorder. The glass transitions of all mesophases are similar in type. Macromolecules in the liquid crystalline state produce high orientation on deformation. Plastic crystals consist always of small molecules. Condis crystals may under proper conditions anneal to extended chain crystals.

Thermotropic mesophases and mesophase transitions of linear, flexible macromolecules

The high density polyethylene (HDPE) sheets were drawn through a pair of heated rollers. The process, referred to as roller drawing, was found to be useful for producing high modulus and high strength HDPE sheets. The higher draw ratio could be obtained for the HDPE sheet with lower molecular weight and narrower molecular weight distribution. The Young's modulus and the breaking strength reached 43 GPa and 0.67 GPa, respectively, at the highest draw ratio. The measurements of wide-angle X-ray diffraction (WAXD) pole figures revealed that the crystallographic a-, b-, and c-axes were oriented to the normal direction (ND), the traverse direction (TD), and the drawing direction (DD), respectively. The small-angle X-ray scattering (SAXS) of the roller-drawn HDPE sheets with draw ratio higher than 7 exhibited two intensity maxima on the meridian, suggesting the presence of the two-phase structure in which crystalline and amorphous regions are stacked alternately along DD. The relationship between mechanical properties and microstructure was discussed on the basis of the concept of the formation of amorphous tie molecules in the interfibrillar and intercrystallite regions.

Preparation of high modulus polyethylene sheet by the roller-drawing method

Crystallization and melting behavior of linear polyethylene under high pressures up to 6000 kg/cm2 has been investigated with a high-pressure dilatometer. Crystallization was carried out at a cooling rate of 1°C/min from the melt at each pressure. The samples were characterized by differential scanning calorimetry, density, and electron microscopy. Folded-chain crystals are formed in the low-pressure region below 2000 kg/cm2. Crystallization in the intermediate-pressure region between 2000 and 3500 kg/cm2 gives a mixture of folded-chain and extended-chain crystals. The extendedchain crystals are the more stable and predominate at increasing pressure. At high pressures above 4700 kg/cm2, two stages of crystallization and of melting can be observed. The phenomenon suggests that the two kinds of extended-chain crystals with different thermal stability, i.e., the ordinary extended-chain crystals and “highly extended-chain” crystals form through individual crystallization processes from the melt at high pressure.

Crystallization and melting of polyethylene under high pressure. I. Crystallization by slow cooling from the melt

Thermal analysis of polymer samples by a round robin method

It is well known that the molecular chain of polyethylene becomes extended by crystallization under high pressure [1-4]. The extended-chain crystals consist of lamellae whose thickness is more than 0.2 μm. The thickness of the crystals depends largely on the conditions of crystallization and the characteristics of the sample. Most observations on the thickness of the extended-chain crystals reported values of 1 to 2 pm by electron microscopy, but, under suitable conditions, thicknesses up to 3 pm were obtained [1]. In these reports it was generally accepted that the thickness of the lamellae did not exceed the molecular length.

Large polyethylene crystals formed under high pressure

PURPOSE:To give physical properties fully satisfying with the requirements as the base material of magnetic recording tape such as strength and elastic modulus by a method wherein the film mainly consisting of polyethylene terephthalate is characterized with the specified structural and mechanical factors. CONSTITUTION:The titled film is obtained by forcibly drawing un-orientated amorphous polyester film through a pair of rolls with a narrow gap and, after that, heat-treating the drawn film. The film is characterized with: (a) A crystal face of the film is face-oriented to the surface of the film. (b) An orientation index of the film, which is obtained from the half-width of X-ray diffraction intensity in the direction of the orientation angle of a 010 crystal face, is 92% or more. (c) The images by small-angle X-ray scattering in the edgewise direction of the film show four point images in the shape of laminar lines. (d) The dynamic elastic modulus of the film measured by applying 110Hz vibration is 11 GPs or higher. (e) The shearing strength of the film is 250 MPa or more.

Hisaaki Kanetsuna

Papers

Preparation of high modulus polyethylene sheet by the roller-drawing method

Crystallization and melting of polyethylene under high pressure. I. Crystallization by slow cooling from the melt

Thermal analysis of polymer samples by a round robin method

Large polyethylene crystals formed under high pressure

Polyester film and manufacture thereof