1. Specific gravity (density)
The specific gravity of plastic is the ratio of the weight of the weighing sample to the weight of the same volume of water at a certain temperature, the unit is g/cm3, and the liquid buoyancy method is commonly used as the determination method.
2. Water absorption
The water absorption of plastic refers to the amount of water absorbed by a sample of a specified size after being immersed in distilled water at a certain temperature (25±2)C for 24 hours; After absorbing water, it affects its size and shape, and when the water absorption rate is expressed by weight, it is often expressed as %.
3. Breathability
Air permeability refers to the volume (cm3) value of the gas permeated by a certain thickness of plastic film in an atmospheric pressure and an area of one square meter within 24 hours, but the air permeability is related to the thickness, area, time, temperature, and air pressure difference of the thin wax.
4. Moisture permeability
Moisture permeability refers to the permeability of water vapor to plastic films, and the basic principle and definition are the same as those of air permeability.
5. Transparency
The ratio of the luminous flux passing through the object to the luminous flux hitting the object is called the light transmittance; The ratio of scattered light in the direction of incident light to all transmitted light is called haze or turbidity. Haze is usually translucent and diffuse to incoming light.
6. Tensile strength
Tensile strength refers to the maximum load when the tensile load is applied along the longitudinal axis of the specimen under the specified test temperature, humidity and tensile velocity, and the maximum load when the specimen is damaged.
7. Compressive strength
Compressive strength refers to the strength at which a compressive load is applied to a specimen to rupture (for brittle materials) or to yield (for non-brittle materials).
8. Flexural strength
Flexural strength refers to the strength of the specimen when a concentrated load is applied on two fulcrums to deform the specimen or rupture it.
9. Impact strength
Impact strength refers to the joules consumed per unit area of the specimen when it is broken by impact, and for some plastics with high impact strength, there is often a gap of specified size in the middle of the specimen, which can reduce the joules required for it to break.
Different test methods can be used for different specimens: falling ball impact test, high-speed tensile impact test.
10. Coefficient of friction
The coefficient of friction refers to the ratio of friction to positive pressure. A positive pressure is added to the specimen to determine the dynamic and static ratio of the specimen during rigid motion.
11. Abrasion
Abrasion refers to the mechanical destruction process in which the particles are continuously separated from the friction surface during the friction process of plastics, causing the size of the friction parts to change continuously, which is also called wear or abrasion.
12. Hardness
Plastic hardness refers to the performance of plastic to resist the press-in of other hard objects, and there are two kinds of general: Rockwell hardness and shore hardness.
Shore hardness refers to the depth at which the pressure pin of the indentator is injected. Shore indentators can be divided into two categories, namely: Type A and D. The applied load weight is 1.0, 5.0 kg, the pressing time is 15 seconds, type A is suitable for soft plastics, type D is suitable for semi-rigid plastics; When using type A, when measuring more than 95% of the range, the D type should be used instead, and when the D type measures more than 95% of the range, it is necessary to switch to Rockwell indentation.
13. Fatigue strength
Fatigue strength refers to the strength of plastic failure in an environment with static destructive force and a small amount of alternating cycle; The sources of fatigue load include tension and compression, bending, torsion, impact, etc.
14. Creep
Creep refers to the characteristics of plastic under a certain temperature and humidity under the continuous action of fixed external force with time, the characteristics of this deformation increase with the increase of load, decrease with the decrease of load, and its deformation is gradually recovered. The sources of creep are tensile creep, compression creep, flexural creep, etc.
15. Long-lasting strength
Endurance strength is a function of time when the ability of a plastic to withstand static load for a long time decreases from high to low. For example, the strength of a plastic before loading is 1000 hours, but after loading it may only be between 50% and 70%.
16. Linear expansion coefficient
The coefficient of linear expansion is the number of centimeters per centimeter of plastic elongation when the temperature rises by 1 degree Celsius. The coefficient of linear expansion of plastics is generally about ten times that of steel.
17. Specific heat
Specific heat refers to the unit of heat required when 1 gram of plastic is raised by 1 degree Celsius.
18. Thermal conductivity
Thermal conductivity refers to the unit of heat that a plastic can pass through per unit area and thickness. The thermal conductivity of plastic is very small, only about one percent of steel, so it is a good thermal insulation material.
19. Heat resistance
Heat resistance of plastics is a characteristic that reflects the relationship between the temperature and the deformation of plastic parts, and heat resistance is more important for temperature-related plastic parts.
20. Glass transition temperature
The temperature when the plastic is reduced from the meltable flow temperature to the solid state is called the glass transition temperature, at this time, the molecular chain segment can basically not move, and it is also difficult to rotate and fasten the chain link, only a little movement between the atoms stretches and there is ordinary elastic deformation, so the plastic at this time will have great brittleness.
21. Embrittlement temperature
When pressure is applied to a plastic at a certain low temperature, it will break under a small deformation, and this temperature is the embrittlement temperature.
22. Decomposition temperature
The decomposition temperature refers to the temperature at which the macromolecular chain of the plastic is broken when it is heated, and it is also one of the indicators to identify the heat resistance of the plastic. When the temperature of the melt exceeds the decomposition temperature, most of the melt will show a yellowish color, and the strength of the product will be greatly reduced.
23. Melt Index
Melt Flow Index (MFI) MI refers to the weight of melt flowing out of a thermoplastic through a small hole in the tester at a certain temperature and pressure in grams/10 minutes.
24. Flame resistance
The flammability of plastics is expressed by the ratio of the combustion rate (the burning length of the sample during the combustion time) and the combustion loss rate (the percentage of the difference between the weight before and after combustion).
25. Withstand voltage
Quickly raise the voltage to a certain limit value, stay for a period of time, the plastic specimen is broken down, and the voltage value at this time is called the withstand voltage that the specimen can withstand.
26. Aging resistance
The aging resistance of plastics refers to the phenomenon that the original excellent properties are reduced due to the destruction of chemical structure caused by external factors such as light, heat, oxygen, water, biology and stress in the process of use, storage and processing. The purpose of studying the aging properties of plastics is to improve its stability and extend its service life.
27. Chemical resistance
The chemical resistance of plastics refers to whether the plastic is corroded in the chemical medium, and the evaluation is usually based on the change degree of weight, volume, strength, color, etc. of the plastic after a certain period of time in the medium.
28. Molding shrinkage
Molding shrinkage refers to the shrinkage phenomenon of the molded product that is demolded after cooling when the thermoplastic is formed in the mold, that is, the molded product is smaller than the mold cavity size.
