A property of the catalyst which indicates how eagerly the catalyst reacts with a comonomer, defining the relation between the relation of partial concentrations (pressures) of different monomers in the polymerisation process and the relative content in the produced polymer..Comonomer sensitivity is determined in a test polymerisation in standard conditions.
Actual capillary rheometry gives information about flow properties of polymer melts. Results are given as a viscosity function, that is viscosity as a function of shear rate or shear stress. Compared to MFR measurement the shear rate range is much wider and the rates in processing applications are reached. With many products, however, flow instabilities (melt fracture) at high rates limit the useful range. A capillary rheometer consists of a barrel, piston and die. The sample is put into the barrel, heated and pushed by the piston through the die. The piston is driven by hydraulic pressure which allows more flexible choice of rates compared to MFR measurements. In addition, longer dies can be used to avoid the errors coming from the entrance and exit pressure losses.
A substance added into the reactor to initiate or accelerate a polymerisation reaction. It’s used in small quantities and is not chemically consumed during the polymerisation. Because of the catalyst’s high activity, residues in the polymer are so low that they do not need to be removed.
There are several different types of catalysts used in olefin polymerisation. The three main groups are Ziegler-Natta, chromium and single-site (metallocene).
To make a catalyst active in polymerisation, a cocatalyst is often used. Cocatalysts are highly reactive compounds, usually group I-III metal alkyls.They are used in excess compared to the catalyst, and prevent the catalyst from being poisoned by the impurities in the polymerisation reactor.
Comonomer is a monomer which is used to modify the polymer properties, e.g. to reduce the density of the polymer. Different types of copolymerisation processes are possible, leading to different structures and properties of the produced copolymer. In polyethylene, higher a-olefins like butene, hexene or octene are used as comonomers, in polypropylene, mostly ethylene and sometimes butene.
In compounding a final homogenised and stabilised product in pellet form is made. Also, this term is used for the production of compounds incorporating reinforcing fibres or fillers as well as blends with other polymers (in the case of polyolefins, frequently elastomers).
Two monomers polymerised together to form a polymer.
A support material on which the active compounds of the catalyst are deposited. Silica is commonly used as support material. Also called a carrier.
(a) Solid-state creep tests are used to measure long term behaviour of mechanically loaded material. Creep is time-dependent strain resulting from constant loading. Tensile loading is most common here but flexural loading can be used as well, testing time is typically 1000 hrs. Several loading levels are used to get an overview of creep behaviour of the material.
(b) Melt creep tests are a type of rheological measurement for the determination of the creep compliance of a polymer melt; they are carried out in the region of linear viscoelasticity.
Black pigment used in concentrations of about 2.5% in order to ensure excellent UV-resistance. In higher concentrations, 30-40%, Carbon Black is used to obtain semiconductive properties used in Cable applications. The type of CB and the particle size is very important for the end-product properties.
Most often an organometallic compound that is used to activate the catalyst.
also designated “degree of crystallinity”, it gives the relative fraction of a solid polymer having crystalline regularity. The crystallinity can be determined with various measuring techniques like DSC, density measurement or WAXS, which has the additional advantage that the relative amounts of the different crystal modifications can be determined as well. All crystallinity values are relative and the applied reference values should be quoted.
Controlled rheology PP is produced by degrading normal PP to give a product with a high melt flow index (MFI), lower molecular weight (MW), narrower molecular weight distribution (MWD) and hence easier and more consistent flow.