Like tensile test, flexural test is also used to characterize strength and stiffness of the material. Flexural properties are obtained by placing a specimen horizontally on two supports. A load is applied at a specified rate in the center, normal to specimen longitudinal axis. Measured force - deformation data is used to calculate flexural modulus and flexural strength. Flexural tests can be used if material is too brittle to withstand compressive forces of fixing in tensile grips.
When handling and storing plastic packages it is important that friction between packages and pallets, shelves etc. or between packages itself is suitable. Coefficient of starting and sliding friction (static and dynamic friction) of film is measured by using a moving sled, force transducer and a static horizontal testing table. Friction can be measured either film against film or film versus metal or other material. It is determined by the material structure and the additivation, especially the addition of slip agents and antiblocking agents.
Infrared radiation induces vibrations of molecules and molecular segments. Absorption of radiation occurs only if the vibration results in the change of the molecular dipole moment. The strength of the vibrating bonds and their dipole moment affect the absorption band intensities and positions which makes FTIR spectroscopy a very useful method in qualitative polymer analysis. Also several fast quantitative FTIR methods have been developed for the structural characterisation of polyolefins.
Polymer crystallinity and orientation implies a restriction in the movement of some molecules and consequent improvement in polymer mechanical properties. This restriction in the movements reflects also to the FTIR spectrum and thus the amorphous and crystalline polymer phases can be identified.
Polymer particles having a small diameter. Those particles whose diameter is < 0.105 mm are usually classified as fines. A high amount of fines can severely reduce the operability of a plant.
Film impact testing is the very basic, simple and fast method to find out overall mechanical strength of the film product. Impact resistance of film is determined by using free-falling dart method. In this method the impact is generated by dropping a dart from constant height on clamped film sample. Mass of the dart is varied and a mass causing failure of 50 % of the specimen tested is the result.
An atom or group of atoms with an unpaired valence electron (Valence electron is an electron in the outer shell of the atom that takes part in forming chemical bonds). Free radicals are formed in High-pressure polyolefin polymerisation by decomposing organic peroxides initiating the polymerisation process and then the propagation of the ethylene monomer onto the radicals forming long chains.
Film Application tests
Mechanical properties of film are very much dependent on film blowing parameters like extrusion screw, die construction, blow-up ratio and cooling system. Customary film tests are carried out by using film samples.
Extrusion of the melt through a ring from die, blowing up, and cooling to form a thin film. Film blowing is used to produce very thin films of high mechanial strength, mostly from polyethylene.