Polyolefins tensile testing

Coherently, as expected for immiscible blends, Tg values measured by DSC show very small variations with respect to the pure components while the mechanical properties degrade with respect to neat sPS. In particular, for minimum polyolefin contents <40 wt%, uniaxial tensile tests revealed a decrease in Young s modulus, elongation at break and energy to break. For higher contents, a phase inversion of the morphology occurs and the blend properties approach progressively those of the pure polyolefins. 

The deformation mechanisms in various polyolefins have been studied in great detail. Kravchenko and co-workers have reported on the deformation behavior of elastomeric PP, for which the orientation and deformation of lamellae during tensile testing could be followed with high resolution using intermittent contact mode SFM (175). 

ASTM D-3026 practice to determine degradation end point in degradable polyolefins using tensile testing ... 

The examples given above are, however, exceptions. In general, polymer blends are immiscible. Immiscible polymer blends usually exhibit ultimate mechanical properties such as elongation at break inferior to either of the pure components. This is notably the case in polyolefin-polystyrene blends. Another example of this inferiority of ultimate properties is found in studies of the tensile test energy to break in blends of polyethylene and polyamides [89]. 

ASTM D 5397-99 Standard Test Method for Evaluation of Stress Crack Resistance of Polyolefin Geomembranes Using Notched Constant Tensile Load Test... 

In order to minimise as far as possible the influence of processing variables, studies have been carried out using tensile creep tests on carefully prepared compression moulded specimens. It must be realised that, vv ith injection moulded articles, the creep properties will also be subject to variation with the amount and direction of residual flow orientation, while, with crystalline polymers such as the polyolefins, the creep effects will also be influenced by variations in density caused by a combination of flow orientation, compressive packing, and cooling effects. Stresses will generally be complex and will often involve compressive and flexural components. However, articles should normally be designed to limit the strains occurring to quite low levels, where a reasonable correlation can be expected between tensile, compressive, and flexural creep data. 

Hundreds of test methods referring to polyolefin properties are actually employed. They consist of both physical (hardness, stiffness, tensile properties, solubility, viscosity, etc.) and chemical (acetone extractable, carbonyl content, etc.) tests, representing the objects of international, national, or industrial standards and specifications. Some of them, elaborated by ASTM Committee D-20, Subcommittee XII, Polyolefin Plastics, are indicated in Table 1. 

GM5(a) Notched Constant Tensile Load Test for Polyolefin Resins or Geomembranes D5397... 

The specimens used were cut out of extruded rods. The polyolefines PE and PP, typical plastics used for pipe extrusion, and a PMMA has been investigated. Figure 3 shows the measured results for this material obtained from short-time tensile and compression tests at different temperatures. The tensile curves display a more pronounced curvature than the compressive curves. The same result applies for different loading velocities. The compressive stresses are thus always higher than the stresses under tension for identical compression/strains. If the material fails, fracture under tensile stress will occur at a considerably lower deformation and stress level than fracture under compressive stress. 

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