Polymer Dictionary

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	Metal deactivators Some metal ions may contribute to accelerated degradation. For polyolefins in contact with metals, such as cable insulation of copper wires, metal deactivators are added to passivate the degradation reactions.
	Shore Hardness 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)
	Heterophasic copolymers Heterophasic copolymers (HECO) also contain ethylene (and possibly higher a-olefins) as comonomer. The production is however carried out in a two-stage process, resulting in a multiphase structure with a homopolymer matrix and inclusions consisting of amorphous EP-copolymer (rubber) and crystalline PE. Variations of molar mass and composition of the elastomeric phase in relation to the matrix allow a wide variation of properties (stiffness, toughness and transparency).
	BorAPC Borealis tailor-made Advanced Process Control (APC) for polyolefin polymerisation processes. APC is process control utilising detailed knowledge, compared with traditional process control where the method is standard and not specifically adapted to the process. The basis for APC is knowledge of a process expressed as mathematical models. Model predictive control (MPC) ensures that control actions also compensate for the future behaviour of the process, leading to optimal grade changes. BorAPC includes non-linear MPC, making it well-suited for polymerisation processes and ahead of what "normal" control vendors offer.
	Comonomer sensitivity 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.
	Heterogeneous Something relating to two ore more phases, i.e. not mixed so as to be homogeneous.
	Homogeneous Something relating to only one phase, i.e. so well mixed that the mixture have the same composition throughout.
	Vicat softening temperature Vicat softening temperature shows heat softening characteristics of thermoplastics. Flat specimen are placed in a temperature regulated heating bath, a needle type, loaded penetrator is set on the specimen surface and bath temperature is raised at a constant rate. The temperature of the bath at which the penetration of the needle has reached a predefined level is the Vicat softening temperature of the material.
	Acid scavengers Neutralise acidic residues to protect processing equipment from corrosion.
	VLDPE Very low density polyethylene Based on the same technology as HDPE, but the density is reduced through the incorporation of longer a-olefins as comonomers. With this, another way of adapting the products to the final applications turns up. Single-site catalysts allow an expansion of the application range, mainly by allowing higher comonomer contents and a more even distribution of these.
	ULDPE Ultra low density polyethylene Based on the same technology as HDPE, but the density is reduced through the incorporation of longer a-olefins as comonomers. With this, another way of adapting the products to the final applications turns up. Single-site catalysts allow an expansion of the application range, mainly by allowing higher comonomer contents and a more even distribution of these.
	Melt strength A property of the polymer melt which indicates its ability to withstand drawing without breaking. Melt strength is improved by the presence of high molecular weight tail or long chain branches.
	Pelletising A process where the polymer powder is homogenised, addiviated and made to pellets. The polymer melt coming from the extruder is pressed through dies in a die plate and cut to pellets by knives under water (underwater pelletising) or cooled to solid strands and then cut to pellets (strand pelletising).
	Permeability Material constant characterising gas penetration, like water vapour, oxygen or carbondioxide.
	Capillary rheometry 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.