From polypropylene to meltblown cloth, these chemicals are too critical

Affected by the new crown epidemic, the demand for masks has soared. According to the big data of Ali International Station, the demand for medical masks by global buyers has increased by 13769% from the beginning of March. China is the world's largest manufacturer and exporter of masks, with annual output accounting for about 50% of the world's output. Various companies are operating at full capacity. According to data released by the National Bureau of Statistics in March, the average daily output of Chinese masks is 116 million. With the resumption of domestic production and the increasingly serious international epidemic situation, the global demand for masks as a necessity has soared. As a major mask-producing country, the daily supply of more than 100 million masks is still very low.



As the main raw material of the mask, melt-blown cloth, the domestic prices have recently been plugged into the wings of imagination, until the cloud. The raw material of melt-blown cloth, the high melt index polypropylene (PP) market price is also rising, and the domestic petrochemical industry has set off a wave of conversion to high melt index polypropylene materials.



In addition to skyrocketing prices, exploding orders, and supply cuts, the quality of meltblown fabrics is also a hidden concern in the mask production market.



Organic peroxide degrades polypropylene in three steps


The manufacture of masks is inseparable from spunbond fabrics and meltblown fabrics, both of which are degraded high melt finger PP materials. The higher the melt index of PP used to make melt-blown cloth, the finer the melt-blown fiber, and the better the filterability of the melt-blown cloth. And PP with low molecular weight and narrow molecular weight distribution is easier to make fibers with good uniformity.



The raw material of the S layer (spunbond cloth) for the production of masks is mainly high melt index PP with a melt index of 35 to 40, while the M layer (melt blown cloth) is a melt blown with a higher melt index (1500) Grade PP. The production of PP of these two types of high-melting fingers is inseparable from a key raw material is an organic peroxide degrading agent.



Ordinary PP has a low melt index and poor fluidity in the molten state, which limits its application in certain fields. Modification of polypropylene by adding organic peroxides can improve the melt index of PP, reduce its molecular weight, and narrow the molecular weight distribution of PP, so that it has better fluidity and higher spinning rate. Therefore, PP modified by organic peroxide degradation can be widely used in the field of thin-wall injection and non-woven fabrics.



Several peroxide degradants


Organic peroxides are dangerous chemicals of Class 5.2, which have very strict requirements during production, storage, transportation and use. At present, there are only a few organic peroxides that are mainly used for PP degradation in China. Here are a few:



1. Di-tert-butyl peroxide (referred to as "DTBP")

Its main features are as follows:

● The PP has not obtained the FDA addition permission and is not recommended for the production of food-grade and sanitary-grade products.



● The flash point is only 6 ℃, which is extremely sensitive to static electricity. The energy of 0.1MJ is enough to ignite its steam, and it is easy to flash and explode under room temperature; even under nitrogen environment, it can still flash and flash even under nitrogen burst.



● The conductivity is extremely low, and it is easy to accumulate charge during the flow.



● DTBP was classified by the European Chemicals Agency (ECHA) as a Level 3 gene-inducing substance in 2010. It cannot be recommended as an additive in food contact and direct contact with human products. There is a high risk of causing biological toxicity.



2. 2,5-Dimethyl-2,5-bis (tert-butylperoxy) hexane (referred to as "101")



The degrading agent is the earliest application of peroxide in the field of degrading PP. Due to its suitable active temperature range and high active oxygen content, and it has FDA approval in the United States and BfR approval in Europe, it is still used in this field A more extensive degradation agent. Due to the high content of volatiles contained in its decomposition products, and most of them are volatiles with a heavy pungent odor, the prepared high melting finger PP has a heavy taste. Especially for the melt-blown materials used in the production of masks, the large amount of degradation agent added will cause a large odor problem for the downstream melt-blown cloth.



3. 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane (referred to as "301")



Compared with other degradation agents, 301 has excellent safety performance and degradation efficiency, and very low odor, is one of the preferred degradation PP. The advantages are as follows:



● Safer

The self-accelerating decomposition temperature is 110 ℃, and the flash point is also as high as 74 ℃, which can effectively prevent the decomposition and flashover of the degrading agent during the feeding process. It is a peroxide product with the highest safety among the known degrading agents.



● More efficient

Since there are three peroxygen bonds in one molecule, when the same proportion of active oxygen is added, more free radicals can be provided, thereby effectively improving the degradation efficiency.



● Low odor

Compared with the "Double Two Five", the decomposition products produced are only one-tenth of other products, and the types of volatiles are mainly low-odor esters, which do not contain irritating odors, so they can Greatly reduce the odor of products, help to develop high-end market with strict odor requirements, and increase the added value of products. In addition, lower volatiles can also reduce the risk of degraded PP products during storage and transportation, thereby effectively improving safety.



Although DTBP is no longer recommended as a degrading agent for modified PP, there are still some domestic manufacturers that use DTBP as a degrading agent to produce high-melt finger PP, resulting in more safety risks in the production process and subsequent use areas. The resulting products also have more serious odor problems, and there is a higher risk of rejection or failure to pass the test when exporting to the international market.



The global epidemic has produced unprecedented demand and challenges to the supply chain. The selection of suitable degradants for the production of mask materials is in line with the health interests of most manufacturers and the general public, and these important supplies to the medical and health industry and other important areas of society Chemical products are also the common social responsibility of all chemical practitioners.