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oxygen index tester polyurethane oxygen index experiment

Author:QINSUN Released in:2023-09 Click:114

Polyurethane is the abbreviation of polyurethane. It is a thermal insulation material widely used in construction industry and industrial equipment and an important material in automobile, shipbuilding, packaging and other industries. However, due to the special structure of the polyurethane foam itself, it is very easy to burn. Its oxygen index is only about 17%. It releases a large amount of smoke and poison when burned and tends to leak. Its flammability problem has always been an important topic in the polyurethane industry. Countries around the world have formulated various flame retardant standards and regulations for testing polyurethane, gradually improved testing methods, and produced various testing instruments and equipment. Since the oxygen index is one of the indicators to determine the performance of flame retardants, the testerr of oxygen index is commonly used. Qisnun Precision Mechanical and Electrical Technology Co., Ltd. is an instrument manufacturer. Customers in need are welcome to call us in time. Additionally, the oxygen index testing experience will be affected by factors such as environmental conditions, operators, sample preparation differences, etc. In order to more accurately determine the oxygen index value of the material, qisnun technology R&D engineers studied the impact of various factors. on the oxygen index during the testing process. Discussion and analysis were conducted.

Reference standard:

The oxygen index conforms to GB/T2406-1993, and the environment standard for adjustment and testing of the condition of samples conforms to GB/T2198-1988.

Experimental principle:

The limiting oxygen index (LOI), called oxygen index, is one of the indicators allowingto determine flame retardant performance. It refers to the oxygen content of the sample under specified conditions. , the low concentration of oxygen required to maintain balanced combustion in the nitrogen-mixed gas stream, expressed as volume percent oxygen.

The principle of the test is to hold a sample of a certain size vertically in a transparent combustion tube with a sample clamp, in which there is an upward flow of oxygen and nitrogen mixed in a certain proportion. Ignite the upper end of the sample, observe the subsequent burning phenomenon, record the continuous burning time or the burnt distance, and compare it with the specified value. If it exceeds the specified value, reduce the oxygen concentration, if it is insufficient, increase the oxygen concentration. Repeat this, starting with the top and bottom sides. Approgradually increase the specified value until the concentration difference between the two is less than 0.5%.

Analysis of influencing factors:

1. The impact of status adjustment time

Depending on the country According to the requirements of GB/T2918-1988, the influence of environmental accidental effects on the test results is minimized by adjusting the condition of the test materials. It is evident from the test data that as the sample conditioning time increases, the average oxygen index obtained during the test continues to decrease. When the conditioning time reaches a certain level*, the oxygen index remains stable. The test results of samples subjected to different conditioning times are different. Therefore, samples must be strictly packaged according to standard requirements and then tested to obtain accurate values ​​ofthe oxygen index in the standard conditioning time.

2. Influence of sample ignition method

According to GB/T2406-93, two ignition methods are used to test the oxygen index of polyurethane foam samples. The ignition time is the same, for 15 seconds.

Top ignition method: make the faintly visible part of the flame touch the top of the sample and cover the entire top surface, do not let the flame touch the edges and sample side surfaces.please.

Diffusion ignition method: Fully lower and move the igniter so that the visible part of the flame is applied to the top surface of the sample and the vertical side surface at the same time on approximately 6mm long.

It was found that the same material was tested under the same conditions and that different ignition methods had little ou no effect on the oxygen index measurement data, which was not sufficient to change the oxygen rating. sample indexing results. Regardless of the ignition method, when to remove the ignition source and when to start depends on the visual assessment of the sample\'s inflammation by the naked eye. Some errors can affect inspection data. Only by increasing the number of tests can we try to reduce errors. In actual operation, it is more economical to use the top ignition method when igniting the sample.

3. The influence of the length of the sample

The length of the sample of the product tested in the standard is 70 to 150 mm, the aim is to maintain the length of the glass cylinder of the testing instrument consistent, to make the oxygen concentration in the small mixed gas environment in the cylinderuniform and constant glass. The sample length has a great influence on the test data. Within the range required by the national standard, the measured value of oxygen index increases continuously with the increase of sample length. When the sample length is short, there is still a considerable distance above the combustion zone of the tested sample from the top of the cylinder, so that the oxygen required for its flame combustion is supported only by the instrument itself and is not affected by the airflow outside the cylinder. However, as the length of the sample increases, the distance between the combustion zone of the tested sample and the top of the cylinder becomes shorter, and the oxygen flow rate required for flame combustion is gradually affected by the air flow outside the cylinder. In order to support the combustion of the flame, the instrument itselfneeds to supply more oxygen to satisfy the combustion of the flame, and therefore the measured oxygen concentration value gradually increases. Therefore, the length of the tested sample should be specified as a specific value rather than a range value in order to reduce the influence of indoor ambient air flow on the combustion conditions in the instrument cylinder.

4. The influence of flame retardants

As an expensive additive in polyurethane foam, flame retardants play a very important role. Well, we also need to consider the impact of the added amount of flame retardant on the physical and mechanical properties of the foam. Taking into account factors such as cost, safety, compliance with technical flame retardant indicators and the physical and mechanical properties of the foam, the use of appropriate flame retardants should be optimized to maximizer their effects.

The effect of adding flame retardant: Data shows that for flame retardant TDCPPt, based on polyether polyol, 10 Phr of TDCPP can make the oxygen index of PUF by 23%, and the oxygen index of PUF With the increase of the addition of flame retardant, the oxygen index of the sample increased very limitedly, but after the measurement of TDCPP was greater than 15 Phr, increasing the dose of TDCPP.

According to the flame retardant mechanism, phosphorus can interact with polymers or oxygen in the surrounding medium during the combustion process to generate phosphoric acid and metaphosphorus. A series of derivatives such as acid and polymetaphosphoric acid. These glassy liquid derivatives have high thermal stability and can form an insulating film on the surface of the polymer. Its formation can not only block the heat of the flame area to decompose the high polymer, but also prevent the gaz decomposed fuel from entering the flame zone. In addition, the decomposition of the high polymer and the combustion of the combustible gas often promote or weaken each other. Therefore, the formation of this liquid film coating layer will inevitably promote a substantial improvement in flame retardancy. The flame retardant effect of melamine is mainly due to its ability to catalyze the formation of a carbonized solid coating layer. The flame retardant effect of aluminum hydroxide is that it can form a solid protective layer of aluminum oxide on the one hand, forming a non-combustible barrier between the fire source and the foam. On the other hand, to play a flame retardant role, it contains a large amount of crystal water, which is very stable in the foam production process, but it will quickly decompose when the foam burns, absorbing heat and cooling.