# Some important test for plastic--part 2

**Melt flow index test (Melt flow rate test)**

necessary Test equipment: Melt flow indexer/melt flow index tester/ melt flow rate tester

Melt flow index: it Is a value that represents the flowability of the plastic material during processing.

Test method: Let the plastic particles in a certain time (10 minutes), a certain temperature and pressure(weight) (depend on different standards and different materials), melt into plastic fluid, and then through a die with certain diameter(Φ2.095mm±0.005mm) out of the weight or volume. The indicated method is MFI: fluid mass; MVR: fluid volume.

Purpose of the test: It is to indicate the processing fluidity of the plastic material. Larger value means better flowability. Small value means worse flowability.

In the micro, the greater the melt flow index means that the smaller the viscosity and the smaller the weight of the molecule,On the contrary, it means that the greater the viscosity of the plastic and the greater the weight of the molecule.

**Tensile test& Bending test**

necessary Test equipment:Tensile testing machine/universal testing machine

Tensile test: Testing the basic properties of the polymer material, the stress applied to the material, the measured deformation, the stress, stress and strain curve is the most common method. The two ends of the spline with a fixed device, the application of the direction of the tensile load, until the damage to the stress and distortion.

Elastic modulus: E = (F / S) / (dL / L) (material in the elastic deformation stage, its stress and strain proportional proportion of the relationship) elastic modulus "is a physical description of material elasticity, is a general term, including "Young's modulus", "Shear modulus", "Volume modulus" and so on.

The elastic modulus is the important performance parameter of the engineering material. From the macroscopic point of view, the elastic modulus is the measure of the size of the object against the elastic deformation ability. From the microscopic point of view, it is atomic, ion or molecular Between the bonding strength of the reaction.

Different plastic stretch pattern changes

Strength: The maximum ability of a material to withstand plastic deformation or damage under load.

Yield strength: the material has obvious plastic deformation resistance.

Tensile Strength: The maximum tensile stress sustained by the specimen until it is broken during the tensile test.

Tensile stress: The tensile load on the initial cross section of the specimen in the gauge range.

Tensile fracture stress: σt-εt curve stress on the fracture.

Tensile yield stress: σt-εt stress at the yield point on the curve.

Elongation at break: The ratio of the increase in the distance between the lines and the initial gauge when the specimen breaks.

Yield point: σt-εt curve σt does not increase with εt the initial point.

Note:

The greater the E, the harder the material is, and the more soft

Σb or σy the greater, that the stronger the material, on the contrary the weaker;

The larger the εb or S, the more tough the material is, and the more brittle it is.

Factors that affect tensile properties

(1) Molding conditions: caused by the microscopic defects and microscopic differences of the sample itself;

(2) temperature and humidity;

(3) Tensile speed: plastic is a viscoelastic material, the stress relaxation process and deformation rate is closely related to the need for a time process;

(4) pretreatment: the material in the processing process, due to heating and cooling time and speed are different, easy to produce local stress concentration, after a certain temperature of the heat treatment or annealing treatment, can eliminate the internal stress and improve strength;

(5) Material properties: crystallinity, orientation, molecular weight and its distribution, cross-linking degree;

(6) aging: aging intensity decreased significantly.

Bending performance test: the spline on a certain length of the two fulcrum, at a certain speed in the middle of the application of the load when the bending, until the break or to achieve a certain amount of bending stress when the calculation method is the bending test The

Flexural Strength: The force at which the force is applied at the center of the spline, the spline is broken, or the amount of deformation is 5%. The flexural strength is a countermeasure test when the spline is deformed.

Flexural Modulus: refers to the ratio of the magnitude of the force exerted from the upper part of the center of the spline to the deformation produced by the spline. The greater the flexural modulus, the stronger the rigidity, the smaller the flexural modulus, and the softer the plastic.