Resistance of a (polymer) surface to deformation. The different hardness measures applied for characterising polymers are:
(a) Shore hardness (two scales, A for softer and D for harder materials)
(b) Ball indentation hardness (also useable on profiled surfaces because of bigger measuring device).
(c) Vickers hardness (normally used for steel)
type of additive, which provides surface lubrication to the polymer during and after conversion; especially important for films. Usual slip agents are amides of fatty acids.
Size Exclusion Chromatography
(SEC, also called Gel Permeation Chromatography, GPC) is used to separate dissolved polymer molecules according to their coil diameter in solution. The chromatograms can be converted to molar mass distributions, which is an important parameter because it has a significant effect on the physical, mechanical and rheological properties of a polymer. It is also possible to calculate the average molar masses, Mn, Mv, Mw and Mz, and when on-line viscometric detection is used, to study long chain branching (LCB) and its distribution.
In Solution Viscometry the rate at which a dilute polymer solution flows through a capillary is measured. Temperature and concentration of the polymer are carefully controlled. The parameter most often determined by dilute solution viscometry is intrinsic viscosity. Intrinsic viscosity is related to molar mass through a semi-empirical relationship called Mark-Houwink’s equation.
Abehaviour where the viscosity decreases when the shear stress increases. Typically broadening of the molecular weight distribution increases shear thinning.
Formation of sheet-like agglomerates in the gas phase reactor.
Single Site Catalysts
• Produces polymer having very narrow MWD
• Extremely hydrogen and comonomer sensitive
• Very uniform comonomer distribution
• Usually cocatalyst required
• Produces stereospecific polymers
Decrease of dimension, created by the introduction of internal stress to the material during processing and cooling, or by ageing and post-crystallisation processes.
Scanning Electron Microscopy
In Scanning Electron Microscopy (SEM) a focused beam of electrons scans across the surface of the sample. It is detected synchronously to the position of the scanning electron beam and recorded in an image storage device. Differencies in the topography of the sample give rise to the differencies in the intensities of the signals formed by the secondary electrons in the detector resulting in a three dimensional image. Scanning electron microscopy is suited to most types of surface morphology studies. Rough topographic features, void content and particle agglomerations are easily revealed as well as the compositional differencies within material. Energy Dispersive X-ray Spectroscopy (EDS) or Wavelength Dispersive X-Ray Spectroscopy (WDS) in conjunction with SEM allows elemental analyses to be performed directly over the surface of the sample.
A process for making polypropylene and propylene copolymers.Homopolymerization is conducted in the liquid phase in a loop tubular reactor; copolymerization is conducted in the gas phase in a fluidized-bed reactor. The catalyst is treated with a special silane.