Abstract:

Objective Because of the different biological structure of virus and bacteria, traditional antibacterial polypropylene melt-blown nonwoven fabric is difficult to have good killing effect on virus. Hypochlorite or chlorine-containing disinfectant that can release active chlorine has been reported to have excellent inactivation effect on bacteria and viruses. Therefore, the design of a polypropylene melt-blown nonwoven fabric was carried out to release active chlorine in order to effectively solve the problem of poor inactivity of air filter materials on viruses.
Method Modified polypropylene (PP) grafted methyl acrylamide (MAM) resin was prepared by using reactive extrusion process to graft the halogen amine precursor onto the PP molecular chain through a free radical initiator, before the PP-g-MAM resin was added to the melt-blowing machine. The PP-g-MAM melt-blown nonwoven fabric for chlorination and re-electret was fabricated, in order to obtain polypropylene melt-blown nonwoven fabric with high efficiency filtration and sterilization and antiviral function. Scanning electron microscope was used to characterize the average diameter of PP-g-MAM melt-blown nonwoven fibers and the fiber diameter distribution.
Results The average diameter of PP-g-MAM melt-blown nonwoven fibers is 7.24 μm, and the fiber diameter distribution is concentrated in 1-3 μm (Fig. 7). Compared with the pure PP resin, two new characteristic peaks appeared in the wavelength range of 1 700-1 500 cm^-1 for the purified PP-g-MAM resin, corresponding to the C=O bond stretching vibration peak of 1 668 cm^-1 and the N—H bond bending vibration peak of 1 600 cm^-1 (Fig. 4). The grafting efficiency and grafting rate of MAM was 43.02% and 1.01% by organic element content detection. In the thermal weight loss behavior, the thermogravimetric (TG) curves of PP resin and PP-g-MAM resin almost coincided, and so did the differential thermogravimetric (DTG) curves (Fig. 5), where the initial and termination decomposition temperatures of PP-g-MAM resin were 427.9 and 469.2 ℃, respectively. In terms of mechanical properties, the tensile stress at break of PP-g-MAM melt-blown nonwoven fabric is between 1.14-1.19 MPa, and the elongation at break is about 70% (Fig. 6). The filtration effect of PP-g-MAM melt-blown nonwoven fabric on 0.3 μm particles is 98.6% (Fig. 8). After chlorination, the filtration effect decreases by 4%-14%, and the longer the chlorination time, the more the filtration performance decreases. After chlorination re-electret, the filtration performance of PP-g-MAM melt-blown nonwoven fabric is restored to more than 98%. The pore size of PP-g-MAM melt-blown nonwoven fabric has a certain increase compared with PP melt-blown nonwoven fabric(Fig. 9). In the chlorination process, PP-g-MAM melt-blown nonwoven fabrics chlorinated in acidic environment have more active chlorine content, and the longer the chlorination time, the higher the active chlorine content(Fig. 10). Under the condition of chlorinated solution pH value of 5 and chlorination time of 15 min, the content of active chlorine in chlorinated PP-g-MAM melt-blown nonwoven fabric is 0.038%. The antibacterial rate of chlorinated PP-g-MAM melt-blown nonwoven fabric against Escherichia coli and Staphylococcus aureus was more than 98% (Fig. 12), and the antibacterial rate against Escherichia coli was more than 99% under the contact time of 20 min (Fig. 13).
Conclusion MAM was successfully grafted into the polypropylene molecular chain. However, PP-g-MAM melt-blown materials and PP melt-blown materials have little difference in performance, so the grafting of MAM has little effect on the heat resistance, mechanical properties and fiber morphology of PP melt-blown materials. Due to chlorinated solution immersion reasons, PP-g-MAM electret melt-blown nonwoven fabric electrostatic charge is lost with the solution, which leads to significant decrease in the chlorination of nonwoven fabric filtration performance, and in the electret again, nonwoven fabric filtration performance restored to the level before chlorination. In the chlorination process, the acidic condition of chlorinated solution is more likely to improve the content of active chlorine in PP-g-MAM melt-blown nonwoven fabrics, which may be due to the high content of hypochlorous acid in the acidic environment solution, which is easier to transform the halo amine precursor, and the longer the chlorination time, the more the grafted halo amine precursor is transformed. Chlorinated PP-g-MAM melt-blown nonwoven fabrics can effectively kill Escherichia coli and Staphylococcus aureus.

Key words: polypropylene melt-blown material, grafted, methyl acrylamide, melt reactive extrusion, active chlorine content, medical material, antibacterial textiles