10 performance testing methods for plastic materials

Posted on :Nov 19 , 2022 By  GREFEE

10 performance testing methods for plastic materials

1. Ash test

Ash: when the polymer is burnt at high temperature, a series of physical and chemical changes occur till the volatilization of organic components and inorganic components (mainly inorganic salts and oxides)left. The left components are called ash. Generally, ash in modified products means inorganic minerals, such as silica, calcium carbonate, talc, glass fiber, titanium dioxide, etc.

Testing: forging (burn organic matter and process its residue at high temperature until constant weight). Burning the organic matter in the muffle furnace for 10mins under 600℃, and weigh the residuals.

Ash content in mass percentage: (M1-M0)×100/M

M: weight of the pattern

M1: weight of the ash and cup

M0: weight of the cup

Aim: measure the content of inorganic substances in the plastic, which works as a basis for judging the authenticity of materials and a reference for assessing the performance of materials. For instance: the plastic with fiberglass will increase the rigidity and heat resistance, but lower the hardness. Conversely, the rigidity and heat resistance decrease when the hardness increases.

2. Water testing

Moisture: water contained within an object.

Test principle: mainly include infrared rapid moisture measurement and halogen rapid moisture measurement.

Infrared moisture test: Infrared moisture test utilizes the thermal effect and strong penetration of infrared heating object. The moisture of the tested object will quickly loss the weight by evaporation. Through the data of the initial weight of object and mass of an object after evaporating water, the water content of an object can be obtained at the specific temperature.

Halogen Rapid Moisture Determination:

Formula: Suppose, G is the weight of the sample before drying, g is the weight of the sample after drying; L is the moisture content of the sample, R is the drying of the sample; LR is the moisture regain of the sample, and OR is the wet weight rate of the sample, so

L=G-g/G （1）

R=g/G （2）

0R=(G-g)/G （3）

OR=G/g （4）

Aim: moisture is an important factor which affects the processing technology, product appearance and product characteristics of resins such as polyamide (PA) and polycarbonate (PC). During the injection molding, plastic molecules with too much moisture will produce some problems during the processing, and further affect the quality of the final products. For instance, surface cracking, light reflection, and reduction in mechanical properties such as impact resistance and tensile strength, etc.

3. Melt index test

Melt Index: the value representing the fluidity of a plastic material during processing.

Test: Firstly, let the plastic pellets melt into a plastic fluid within a certain time (10 minutes) at a certain temperature and pressure (various material standards are different), and measure it with the weight or volume that flew out through a diameter round tube. method MFI: fluid mass MVR: fluid volume.

meaning: the processing fluidity of the plastic material. The larger the value, the better the fluidity, and vice versa. On the microscopic level, the larger the melting index, the smaller the viscosity and the smaller the molecular weight, and vice versa. The greater the viscosity of the plastic and the greater the molecular weight.

4. Tensile/yield test

Tensile test: used to test the basic properties of the high polymer material. After applying force on the material, the deformation volume is measured and the stress is obtained. The stress-strain curve is the most common way, which fixes the two ends of the samples with the tools. Applying a tensile load in the axial direction till it breaks when it is under stress and deformed.

Elastic modulus: E=(F/S)/(dL/L) (the stress and strain are proportional when the material is in the elastic deformation stage) Elastic modulus is a physical quantity that describes the elasticity of a material and is a general term, including “Young’s Modulus”, “Shear Modulus”, “Bulk Modulus”, etc.

Meaning of elastic modulus: elastic modulus is an important performance parameter of engineering materials. Macroscopically, it measures the ability of an object to resist elastic deformation. Microscopically, it is atoms, ions or molecules. bond strength between.

stretching graphics changes of different plastics

Strength: the maxi ability of material to against the plastically deformed or destroyed under the load.

Yield strength: the resistance of a material to significant plastic deformation.

Tensile strength: in a tensile test, the maximum tensile stress that a specimen is subjected to until it breaks.

Tensile stress: the tensile load to the unit initial cross section of a sample within the gauge length range.

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

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

Elongation at break: the ratio of the increase in the distance between the marking lines to the initial gauge length when the sample breaks.

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

Note:

The higher the E, the harder the material. Conversely, the lower the E, the softer the material.

The higher the σb or σy, the stronger the material. Conversely, the lower the σb or σy, the weaker the material.

The higher the εb or S, the tougher the material. Conversely, the lower the εb or S, the more brittle the material.

Factors affecting tensile properties

1. Forming conditions: caused by the microscopic defects and microscopic differences of the samples.

2. temperature and humidity

3. Tensile speed: plastic is the viscoelastic material, of which the stress relaxation process is closely related to the deformation rate, requiring a time process.

4. Pretreatment: during the material processing, due to the difference of time and speed of heating and cooling, the concentration of stress is likely to occur. After the heat treatment and annealing treatment under a certain temperature, the internal stress can be eliminated to increase the strength.

5. Properties of materials: Crystallinity, orientation, molecular weight and its distribution, degree of crosslinking.

6. Aging: the strength decreases significantly when it ages.

Flexural test: placing the sample on two fulcrums of a certain length and the increase the load at the middle area in a certain speed till the sample breaks or the stress reaches a certain bending amount. The test used for yielding is called the flexural test.

Flexural Strength: applying the force in a certain speed in the centre of sample. The strength is when spline breaks or reaches 5% deformation. The flexural strength refers to the test of the resistance of splines when they are bent and deformed.

Flexural modulus: refers to the ratio of the magnitude of the force applied to the upper part of the center of the spline to the deformation produced by the spline. The higher the bending amount, the tougher the rigidity, the smaller the bending amount, the softer the material.

5. Impact test

definition: the pendulum hits the middle of the supported beam sample, causing the sample to break due to impact. The impact energy consumed per unit area or unit width when the sample breaks is the impact strength.

Significance: the impact toughness is to describe the degree of toughness, or resistance to fracture that the polymer material presented under high -speed. Generally, the impact toughness include two aspects: the deformed ability and breaking capacity after impacts. The former one is usually expressed by elongation at break, while the latter is by impact strength.

Impact strength calculation formula: E=A/bd

A: work consumed by the impulse.

 b/d: width and thickness of the impacted part respectively

 E: impact strength

The work consumed by breaking the sample generally includes:

a) cracks that cause the sample to rupture

b) some of these cracks throughout the sample and cause the sample to break

c) deformation of the polymer near the crack

d) broken fragments of samples fly out

e) a small amount to overcome air resistance and friction between mechanical parts

Note: generally, the higher the absorbed impact energy before being damaged, the larger the elongation at break, the better the impact rigidity of material.

6. Thermal deformation temperature test

Heat deflection temperature: applying a certain load to the polymer material and polymer and heat them in a certain speed. The temperature shown when the sample reaches the specified deformation is the heat deflection temperature.

Testing principle: packing the plastic sample on a support with a span of 100mm, and placing them into an appropriate liquid heat transfer medium. Then, applying a specified static bending load in the middle of the two supports. Allowing the bending deformation of the sample reaches the specific value under the condition of constant temperature.

Aim: as the temperature increasing, the high polymer in the glassy or crystalline, of which the atomic and molecular motion energy increased. With the external force, the ability to deform increases due to the orienteering, which is the ability of material to against the external force —— the modulus decreases with increasing temperature. As the temperature goes up, the deformation volume raises when the plastic generation under fixed load.

Influencing factors:

1) Test instrument (reading error, sample placement position)

2) Method and size of sample preparation

3) Heat transfer medium

7. Vicat softening temperature test

Significance: Vicat softening temperature is one of the indicators that evaluates the heat resistance of the material reflects the physical and mechanical properties of the product under heated conditions. Although Vicat softening temperature of material cannot be used directly to evaluate the actual using temperature of material, but it can be used to instruct the quality control of materials. Higher Vicat softening temperature indicates greater dimension stability of material when being heated and smaller thermal deformation.The better the thermal deformation resistance, the greater the rigidity and the higher the modulus.

8. Thermal aging test

Test principle: The plastic samples are placed in a heat aging test chamber under given conditions (temperature, wind speed, ventilation rate, etc.), and they are subjected to accelerated aging by heat and oxygen.

Aim: inspect the changes in properties before and after exposure and evaluate the heat aging properties of plastics.

9. Viscosity test

The physical and chemical changes when the material is burning which include ignitability and flame spread, heat generation, smoke generation, carbonization, weight loss, and production of toxic products on the surface of materials.

Testing method: mainly include aerobic index combustion performance test, horizontal combustion performance test, vertical combustion performance test, glow wire flammability index test. The flame retardancy of the material directly related to the use of material.

Testing principle: fixing the rectangular strip spline on the horizontal or vertical fixture, and exposures another side to the specified test flame. Through the Measuring Linear Burn Rate to evaluate the horizontal burning behavior of sample. Through the measurement of the residual fireworks, afterglow time, burning range and particle drop situation to evaluate the burning properties of plastic.

Significance of testing: under the specific conditions, the properties of different kinds of materials, the usage range, manufacturing process and variation in combustion characteristics are of great significance.

10. Combustion test combustion performance

The combustion test combustion performance refers to all the physical and chemical changes when the material burning, which include ignitability and flame spread, heat generation, smoking, carbonization, weight loss, and production of toxic products on the surface of the material.

Testing method: mainly relies on the aerobic index combustion performance test, horizontal combustion performance test, vertical combustion performance test, glow wire flammability index test. The flame retardant properties of materials directly affects the usage of materials.

Testing principle: fixing one side of the rectangular strip spline on the horizontal or vertical fixture and exposure another side to the specified test flame. Through the measuring linear burn rate to evaluate the horizontal burning behavior. Through the remaining firework and afterflame time, burn range and particle drop to evaluate the flammability of plastics.

Significance of testing: under specified conditions, different material combustion performances are of great significance to the range of materials used and the manufacturing process and the changing characteristics of combustion.

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