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).

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.

Haze
Cloudiness in polymer films or thin-walled injection-moulded parts, resulting from light scattering in the material (reducing the transparency). Measured in transmission with a well-defined light source, results are given on a percentage scale.

Hydrogen sensitivity
A property of the catalyst which indicates how sensitive the molecular weight of the polymer is to hydrogen concentration, (also: hydrogen response). The property also depends on the polymerisation conditions (mode, temperature, pressure etc.).

Heat deflection temperature
Heat deflection temperature (HDT) indicates how loaded material deforms at higher temperatures. Test bars are placed in a heating bath, resting horizontally on two supports. A constant load is applied in the center of the specimen and the bath temperature is raised at a constant rate. The temperature of the bath at which the flexural deflection of the loading point has reached a predefined level is the heat deflection temperature of the material.

Homopolymers
Homopolymers (HOMO) consist only of propylene units; their properties can be regulated via molar mass distribution and the degree of isotacticity (stereoregular structure).


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).
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