Discussion on the quality control of raw materials of face masks
The mask is mainly a hygiene article wearing air in the mouth of the mouth and is used to filter the air entering the nose. It mainly has the effect of blocking harmful gases, odors, and foam enter and out of the wearer's mouth. The main raw materials of the mask have non-woven fabrics, nasal junction, ear hanging, filter paper, etc. In general, the two-layer disposable mask is mainly made of non-woven fabric, nose, ear hanging materials, and the three-layer disposable medical mask is made of non-woven fabric, nose, ear hanging, filter paper.
During new coronavirus pneumonia, it is preferred to select a type of medical mask that filtering 95% and above filtration efficiency. But, in areas where people are not very intensive, the general mask can also be protected.
The new crown epidemic has brought polypropylene meltblown special material (meltblown PP), a commonly used raw material in the non-woven industry, into the public eye, and its value has doubled, and even a bag is hard to find.
As the core material of filtering, protection, and isolation products, the meltblown cloth is the filter layer in the middle of Face Masks, which can filter bacteria and prevent the spread of germs. Meltblown cloth is a kind of high melt index polypropylene PP as a material, a film made of many crisscross fibers stacked in random directions. The fiber diameter ranges from 0.5 to 10 microns, which is about one-thirtieth of the hair.
Usually, the meltblown material uses an extruder to eject the melt from the spinneret and uses airflow to draw the polymer melt into fibers. The finer the fiber, the higher the filtration efficiency, and the stronger the barrier and dirt holding capacity. Therefore, to achieve the filtering effect of face masks, there is a big difference between the production process and performance of the special PP material for meltblown cloth and other non-woven materials.
The higher the melt index of PP used to make the meltblown cloth, the finer the meltblown fiber and the better the filterability of the meltblown cloth. PP with low molecular weight and narrow molecular weight distribution is easier to make fibers with good uniformity.
To obtain high melt index PP materials, PP suitable for face masks protective materials, usually use degrading agents (such as di-tert-butyl peroxide) to modify general PP raw materials and adjust the melt index (MFI) to 1000～1900 g/10 min, a narrow distribution of molecular weight distribution between 2 and 4.
In summary, process applicability and degradation agent residue are the key indicators for the selection of melt-blown materials, namely
1) Melt index;
2) Molecular weight distribution;
3) Residual amount of peroxide degradant
The above three aspects are the most critical. At the same time, attention should be paid to the particle appearance, ash content, volatile content, and other related indicators of the material (refer to GB/T2546.1-2006).
After selecting the appropriate meltblown material and selecting the appropriate melt-blown process, whether the filtration efficiency of the produced filter material can meet the requirements, further filtration efficiency testing is required.
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