Properties of Plastics
DATE：2022/12/9 8:43:08 / READ： / SOURCE：This station
1.3 Properties of plastics
(1) The density of density plastics refers to the mass per unit volume at a certain temperature.The density of plastics shall be measured as follows.
① Preparations
a. Select clean, crack free, bubble free plastic products (tubes, plates, rods) with a mass of no more than 30g.
b. Analytical balance (accuracy not less than 0.001 g).
c. Wire with diameter less than 0.13mm.
d. The impregnating solution is distilled water or kerosene (the density of the tested substance is less than 1g/cm ³ Coal and oil are used as impregnating liquid), and the temperature is (23.0 ± 0.5) ℃.
② Test method: Use a balance to test the quality of the products suspended in the impregnating solution and in the air with metal wires. The density of the tested sample can be calculated according to the actual measurement of the mass of the tested object in the air, in the impregnating solution and the density of the impregnating solution. Where, P liquid (G-g) G-G
Medium liquid -- density of impregnating solution at standard temperature, g/cm3;
③ Precautions for inspection and test
a. This test method is not suitable for film and foam plastic products.
b. Impurities and bubbles are not allowed in the impregnating solution.
c. Pay attention to prevent static electricity.
d. Pay attention to the stability of the working environment and the temperature of the impregnating solution. The standard is (23 ± 2) ℃.
e. After the test sample is immersed in liquid, the distance between the upper end and the liquid level shall not be less than 10mm.
(2) Water absorption capacity The water absorption capacity of plastic refers to the amount of water absorbed after the plastic sample is immersed in distilled water for 24h at 23 ℃. The ratio of water absorption to sample mass is water absorption.
(3) Transparency Transparency is usually expressed in terms of light transmittance. Transmittance refers to the percentage ratio (%) between the luminous flux passing through the measured object and the luminous flux transmitted to the measured object, which is measured on the photometer.
(4) The force generated by the friction coefficient to prevent the movement of two contacts is called friction. The ratio of friction force to the pressure between two contact surfaces is the friction coefficient. The friction coefficient of plastics is not only related to the surface roughness and cleanliness, but also to the pressure, moving speed, temperature, humidity and other factors on the contact surface.
(5) Tensile strength The tensile strength of plastic refers to the maximum tensile force that the specimen bears along its longitudinal (axial) tensile load until the specimen breaks under the specified standard (test temperature, humidity and tensile speed) test conditions, which is the tensile strength of the plastic. The tensile strength of plastics shall be tested according to GB/T1040-92.
(6) Tensile modulus of elasticity Tensile modulus of elasticity is a physical quantity indicating the rigidity of a material and whether it is easy to be stretched and deformed. The higher this value is, the greater its rigidity is, and the more difficult it is to deform.
(7) Elongation Elongation refers to the rate of change in the length of a material when it is broken by tension (that is, the ratio of the elongation value to the initial length value when it is broken by tension), indicating the toughness of the material. For plastic products, the greater the elongation, the softer it is.
(8) Bending strength The bending strength refers to the strength when the specimen is horizontally placed on two fulcrums and concentrated load is applied between the two fulcrums to deform the specimen until it breaks.
(9) The ratio of the bending stress to the corresponding strain of the specimen within the proportional limit is called the bending elastic modulus of the material. It is a physical quantity indicating whether plastic products are easy to bend and deform.
(10) Compressive strength and compressive elastic modulus Apply compressive load on both ends of the standard sample until the maximum compressive stress at the time of failure is the compressive strength of the material.
The ratio of the compressive stress to the corresponding strain of the specimen within the proportional limit is called the compressive elastic modulus of the material.
(11) In engineering, the impact strength is expressed by the toughness of the material. It is expressed by the energy consumed per unit fracture area, and the unit is the resistance of the material to fracture failure Tr due to plastic deformation and energy absorption under rapid load.
(12) Fatigue strength Fatigue strength refers to the ultimate strength of plastic that is destroyed under the action of alternating periodic stress.
(13) Hardness Plastic hardness refers to the resistance of the surface of plastic products to other hard objects. There are several methods for measuring and calculating hardness. The commonly used methods are Brinell hardness, Rockwell hardness and Shore hardness. Brinell hardness shall be tested according to HG 168 standard. Shore hardness shall be tested according to GB 2411. Rockwell hardness shall be tested according to GB 9342.
(14) Thermal conductivity When a material has a temperature gradient in a certain direction, it will generate heat flow, which is called heat conduction. Thermal conductivity is a measure of the thermal conductivity of a material. Thermal conductivity refers to the heat conduction rate per unit area in the direction perpendicular to the temperature gradient. Plastic has low thermal conductivity, so it is widely used as thermal insulation material, especially foam plastic, which is an excellent thermal insulation material.
(15) Linear expansion coefficient The linear expansion coefficient of plastic products refers to the ratio of the plastic elongation length (cm) per 1cm to the original length when the temperature rises by 1 ℃. The linear expansion coefficient of plastics is several times greater than that of other materials.
(16) Specific heat capacity Specific heat capacity refers to the heat required to raise the unit mass (lg) of plastic by 1 ℃, namely, the specific heat capacity of the plastic, in J/(kg · K). The specific heat capacity of plastics usually refers to the energy required to plasticize the plastics into a molten state.
(17) Glass transition temperature Glass transition temperature means that the polymer becomes a glassy solid when the temperature drops to this temperature. The glass transition temperature is the transition temperature of amorphous polymer from glass state to high elastic state, or the transition temperature of amorphous phase of semi crystalline polymer from glass state to high elastic state. Generally, the glass transition temperature is the upper limit of the temperature at which plastics can theoretically work. Beyond this temperature, the plastic loses its mechanical properties, and many other properties will decline sharply. The glass transition temperature is expressed in T.
(18) Melting temperature and flow temperature Melting temperature of plastic is the temperature at which crystalline polymer changes from crystalline state to molten state, which is indicated by T symbol.
For amorphous plastics, the temperature of transition to the molten state is the flow temperature, which is represented by the T symbol. From the point of view of molecular motion, Tm or T is the temperature at which the whole chain of polymer molecular chain can move and slip with each other. If the temperature exceeds Tm or T, the plastic becomes a fluid, which is the lower limit of the plastic molding temperature.
(19) Decomposition temperature The decomposition temperature of a plastic refers to the temperature at which the macromolecular chain breaks when it is heated, that is, the temperature at which the plastic rises after heating and suddenly accelerates its weight loss, that is, the thermal decomposition temperature. It is indicated by the symbol T.
(20) The hot deformation temperature of plastics is measured according to GB1634-79 Test Method for Hot Deformation Temperature of Plastics under Bending Load.
(21) Maximum continuous use temperature The maximum continuous use temperature of plastic products refers to the temperature at which such plastic products can work normally for a long time without serious deterioration of performance in actual application conditions.
(22) Brittleness temperature The brittleness temperature of plastics reflects the cold resistance of this kind of plastics. Generally, plastics become harder and more brittle as the temperature drops. Brittleness temperature refers to the temperature at which plastics break down due to brittleness under impact load. The embrittlement temperature is the lower limit of the plastic service temperature, which is indicated by the symbol T.
(23) Molding shrinkage The phenomenon that the size of plastic shrinks after it is formed and separated from the mold is called shrinkage. Molding shrinkage refers to the percentage of the ratio of the size reduction of plastic after molding to the size before shrinkage.
(24) Relative permittivity Relative permittivity is a macro parameter of dielectric polarization of insulating material. It refers to the ratio of capacitor capacitance to capacitor capacitance of the same size when using this material as capacitor medium ε express. The relative permittivity represents the ability of the material to store electrical energy as an insulator. Plastic products are an excellent dielectric. The smaller the relative dielectric constant is, the better the insulating property of this plastic is.
(25) The dielectric loss angle is tangent to the capacitor connected to the AC power supply. When the dielectric is an ideal insulator, it will not consume electrical energy during the storage and return of electricity. If the dielectric is not an ideal insulator, there will be leakage current through. This leakage current will be converted into heat energy to make the insulator heat, so some current is consumed. This consumed electrical energy is called dielectric loss. If there is no dielectric loss, the phase angle between the voltage applied to the insulator and the current passing through the insulator should be a right angle. However, due to the dielectric loss relationship of various insulators, the phase angle between the voltage and the current must be less than the right angle. The difference between the two is called the dielectric loss angle (8). The size of the loss angle is usually expressed by its tangent value, that is, tan δ。 The tangent value of the loss angle is called the dielectric loss factor (the smaller this value is, the better the insulation performance of the plastic is). The dielectric loss factor of common plastics shall be tested according to GB1409-1989.
(26) Surface resistivity and volume resistivity Surface resistivity refers to the ratio of the DC electric field intensity along the surface current direction of the sample to the surface conduction current per unit length, which is called the surface resistivity of the sample, and is represented by the symbol ps.
Volume resistivity refers to the ratio of the DC electric field intensity and current density along the volume current direction of the sample, which is called the volume resistivity of the sample and is represented by the symbol pv. The volume resistivity of common plastics shall be tested according to the test method specified in GB 1410-1989.
(27) Dielectric strength Dielectric strength refers to the ability of a certain insulating material to withstand voltage. It is defined as the ratio of the voltage value and the thickness of the sample when the sample is broken down in a uniform electric field under specified test conditions, expressed by the symbol Eb. The dielectric strength of common plastics and other insulating materials shall be tested according to the test method specified in GB1408-1989.
(28) Arc resistance Arc resistance refers to the ability of plastic products to withstand the action of high-voltage arc. Arc resistance is expressed by the time (s) required for the material surface to form a conductive path and the arc to extinguish under the action of the arc. The arc resistance of common plastics shall be tested according to GB1411-78 standard and the high voltage low current intermittent arc resistance test method of solid electrical insulating materials.
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