Plastic products are ubiquitous and indispensable materials in our daily life. Compared with metal, stone and wood, plastic products have the advantages of low cost and strong plasticity. They are widely used in the national economy. Plastic industry occupies an extremely important position in the world today. Over the years, the production of plastic products has developed rapidly all over the world. Most plastics have good corrosion resistance to acid, alkali and other chemical substances. Ordinary plastics are poor conductors of electricity. Their surface resistance and volume resistance are very large, and can reach 109-1018 ohms in digital form. The tangent value of dielectric loss angle is very small when the breakdown voltage is large. Therefore, plastics are widely used in electronic and mechanical industries. Such an important material, if used in special occasions, its flame retardant properties must meet the standards. The additives that can improve the flame resistance of plastics are called flame retardants. Most plastics containing flame retardants have self-extinguishing properties or slow combustion rate. Commonly used flame retardants are antimony oxide, aluminum and boron compounds, halides and phosphate esters, tetrachlorophthalic anhydride, tetra-australian phthalic anhydride, etc. So how to test the flame retardancy of plastic products? For this reason, our country has formulated a series of relevant testing standards to determine the flame retardant properties of plastics.
GB8624-2006 "Classification of Combustion Performance of Building Materials and Products" set a strict plastic flame retardant grade for flame retardant plastic products. The V-0 grade is ******. After two 10-second combustion tests on the samples, the flame extinguishes in 30 seconds. No burning matter can fall down; V-1 is the second order. After two 10-second combustion tests on the sample, the flame extinguishes in 60 seconds. No burning material can fall; V-2 is the third stage. After two 10-second combustion tests, the flame will extinguish in 60 seconds. There can be dropping of combustibles; HB is the lowest flame retardant grade, requiring that the burning speed of samples 3 to 13 mm thick should be less than 40 mm per minute; samples less than 3 mm thick should be burned less than 70 mm per minute; or they should be extinguished before the 100 mm mark. The general testing equipment is the horizontal and vertical combustion performance tester.
GB/T 2406 Plastic Oxygen Index (POI) is used to measure the oxygen concentration required to maintain a smooth combustion of plastics in a mixture of oxygen and nitrogen under specified conditions. It is expressed by the volume percentage of oxygen, that is, the oxygen index of plastics. Oxygen index (> 27) is generally a plastic with flame retardant properties. The testing equipment used is an oxygen index measuring instrument.
GB2409 "Plastic Vertical Combustion Method" is used to test the flame retardancy of plastics in the vertical state. The testing equipment used is the vertical flame retardancy tester.
The ignition temperature measurement needs to use the ignition temperature measuring instrument. The ignition temperature testing equipment mainly includes ingot furnace and stainless steel container. The ingot furnace is made of aluminium or copper with a diameter of 100 mm and a height of 100 mm. It is equipped with thermometers, temperature control elements and jacks for containers. The ingot furnace is equipped with heating and constant temperature control system, which can make the ingot furnace constant at any temperature between 150 and 500 degrees. Stainless steel containers are used for loading specimens. The inner diameter is 9 mm, the height is 48 mm, the wall thickness is 1 mm, and a nozzle with a length of 10 mm and an inner diameter of 1.5 mm is arranged on the cover of the containers. Others are igniters, thermometers, stopwatches, scales, and crushers. The test process is to preheat the ingot furnace to the set temperature and keep it constant, then put the stainless steel container with 1g sample into the hole of the ingot furnace, start the stopwatch while quickly covering the lid (the lid is preheated on the top of the ingot furnace), shake the igniter flame on the nozzle of the lid within 5 minutes, if there is no (or) continuous flame on the nozzle within 5 minutes, then each time the stopwatch will be started. The temperature of ingot furnace increases (or decreases) by 10 degrees. The new samples were re-tested repeatedly until the ** temperature of the flame over 5 seconds continuously appeared on the nozzle, and the temperature was recorded. Three tests are carried out under each predetermined temperature condition. If two of the samples do not have a continuous flame of more than 5 seconds, the furnace temperature will be raised by 10 degrees and then three samples will be made. If two ** temperatures of more than 5 seconds occur, the ignition temperature of the material will be revised to about 10 times.
Horizontal and vertical combustion tester is needed for horizontal combustion test. Firstly, a marking line is drawn on the wide surface of the specimen at 25mm and 100mm from the ignition source, and then the specimen is placed horizontally on the long axis. The cross-section axis and the horizontal axis are fixed on the clamp of the specimen at an angle of 45 degrees. Place a water pan 300 mm below it. Light the Bunsen lamp, adjust the flame length to 25 mm and form a blue flame. Apply the tip of the flame core to the lower edge of the sample about 6 mm in length. And start the timing, apply the flame time for 30 seconds. During this period, the Bunsen lamp shall not be moved, but in the test, if the specimen has not burned to the first mark in 30 seconds, the flame shall be stopped immediately and the following observation records shall be made after the flame is stopped.
The incandescent rod method is used to test the combustion performance of plastics. The method is to use an incandescent rod with a diameter of 8 mm and a temperature of 960 C as the ignition source to contact the end face of the sample for 3 minutes, then turn the hot rod away from the sample, start when the hot rod contacts the sample, observe and record the combustion behavior of the sample, and according to its combustion condition, carry out the combustion performance of the sample. Judgement. A marking line is drawn at 25 mm and 100 mm from the wide surface of the specimen to the ignition end. Fix the specimen horizontally in the clamp. The hot rod is heated to 950 C. The hot rod is contacted with the specimen by rotating the bracket, and the time is started. Remove the hot rod from the specimen after 3 minutes. From the beginning of the timing, the visible flame of the specimen was observed in detail. If the specimen burned, the time required for the flame front from the first marking line to the second marking line was recorded, and the burning speed was calculated.
This is several important testing requirements for plastics, through which plastics can be used in daily life with confidence.
