Physical Properties of Plastics（6）
Physical Properties of Plastics（6）
Decomposition temperature refers to the temperature at which macromolecular chains break when plastics are heated, and it is also one of the indexes to identify the heat resistance of plastics; When the melt temperature exceeds the decomposition temperature, most of the melt will show a yellow color, and the strength of the product will be greatly reduced.
Melt index
The melt index (MFI) Mi refers to the weight of the melt flowing out of the thermoplastic through the small hole of the tester within 10 minutes under a certain temperature and pressure. The unit is expressed in grams / 10 minutes.
Combustion resistance
The combustion resistance of plastics is expressed by the ratio of combustion rate (the combustion length of the sample within the combustion time) to combustion weight loss rate (the percentage of the weight difference before and after combustion). The combustion time from ignition to spontaneous combustion and extinction time can also be used as a reference number for combustion resistance.
Withstand voltage
Quickly raise the voltage to a certain limit value and stay for a period of time, and the plastic sample will be broken down. The voltage value at this time is called the withstand voltage that the sample can withstand.
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 of plastics is to improve its stability and prolong its service life.
Chemical resistance
Chemical resistance of plastics refers to whether plastics are corroded in chemical medium. The evaluation is usually based on the change degree of weight, volume, strength and color of plastics after a certain time in the medium.
Molding shrinkage
Molding shrinkage refers to the shrinkage of molded products demoulded after cooling when thermoplastic is molded in the mold, that is, the molded products are smaller than the size of the mold cavity.
