| Melt-blown is one of the most cost-effective and multifunctional commercial processes for producing micro/nanofiber products.The melt-blown micro/nanofibers prepared provide microscale voids through entanglement between fibers,resulting in high porosity,high specific surface area,and excellent barrier properties of the prepared melt-blown nonwoven material.These characteristics make them suitable for manufacturing high-quality filters,protective clothing,wound dressings,tissue scaffolds,and drug delivery materials.At present,the commonly used polymer chips for melt blowing include polyamide,polyethylene,polypropylene（PP）,polytetrafluoroethylene,polybutylene terephthalate（PBT）,ethylene-vinyl acetate copolymer,etc.PP is widely used in the melt-blowing field because of its high mechanical strength,low price,and good corrosion resistance.However,PP is a petroleum-based non-degradable plastic.At the same time,it is difficult to classify and recycle PP melt-blown nonwovens,which makes PP melt-blown nonwovens a new pollution source in the ocean.Poly（lactic acid）（PLA）,one of the most promising biodegradable materials in the21st century,has attracted wide attention due to its complete biodegradability,good processability,and mature production technology.At the same time,the development of PLA melt-blown nonwoven materials and their commercial applications and large-scale production have also become hot spots in the industry in recent years.Despite the rapid development of PLA melt-blown nonwovens in recent years,the poor fluidity and a low melt index of PLA itself limit the application and large-scale production of PLA in the melt-blown field.In order to obtain PLA melt-blown nonwovens with high melt index and biodegradability,and expand their application fields.In this paper,Sn（Oct）2,PEG,Mg O,Ca O,antioxidant 168,and Na OH were selected to modify the melt index of PLA melt-blown nonwovens.PLA-modified materials with different melt indexes were prepared by the most commonly used melt blending method in the industry,and the melt index,infrared spectrum,molecular weight,section morphology,thermal stability,and thermo-crystallization properties of PLA for melt blowing and PLA chips modified with high melt index were analyzed,and the effects of different catalysts and processing conditions on the melt index of PLA were explored,and the spinnability of PLA chips modified with high melt index was also explored,It provides a theoretical basis for the successful preparation of high melt finger PLA melt blown nonwoven materials.On this basis,PLA and high melt index PLA melt-blown nonwovens were prepared by melt-blown mechanism,and their apparent morphology,fiber diameter and diameter distribution,surface density,hydrophilic and hydrophobic properties,oil absorption properties,oil-water separation,filtration properties,degradation properties were tested and analyzed in turn.Finally,the actual effects of high melt index PLA melt-blown nonwovens in different application scenarios were summarized,The degradability of PLA melt-blown nonwovens with high melt index was evaluated,and its application potential in different fields was explored and the recycling treatment after actual use was provided as a reference.Finally,the superhydrophobic modification was carried out on high melt index PLA melt-blown nonwoven materials,providing a new way to prepare biodegradable oil-water separation materials.The main conclusions of each part are as follows:（1）PLA can not achieve the effect of a high melt index only by mechanical degradation and thermo-oxidation degradation.Different catalysts have different effects not only on the melt index of PLA,but also on the color of modified PLA;Sn（Oct）2 has a good catalytic effect on the thermal degradation of PLA,which can effectively reduce the molecular weight of PLA,thus achieving the effect of improving the melt index of PLA;There is basically no lactide monomer in the PLA modified by the melt index,and the lactide produced by the thermal degradation of PLA catalyzed by Sn2+at high temperature is basically discharged from the reaction system in the form of gas;With the increase of the content of Sn（Oct）2 added,the effect of increasing the melt index of PLA is more obvious.The melt index of PLA with 0.3%Sn（Oct）2 added can reach 835 g/10min.（2）The introduction of PEG has significantly improved the catalytic effect of Sn（Oct）2 on PLA.The hydroxyl group in PEG and Sn2+form a new non-volatile Sn alkoxide to prevent Sn（Oct）2 from volatilizing at high temperatures,thus ensuring the catalytic effect of Sn2+on PLA;The added antioxidant 168 has the effect of stabilizing the melt index and preventing the excessive degradation of PLA to a certain extent;The introduction of TMC-300 and PEG improved the crystalline properties of PLA to a certain extent,and increased the crystallization rate of PLA;The melt index of PLA with 0.3%Sn（Oct）2,5%PEG,0.3%antioxidant 168 and 0.5%nucleating agent TMC-300 reached1054 g/10 min.However,due to the catalytic effect of Sn（Oct）2 on the thermal degradation of PLA,the molecular weight of PLA with a high melt index becomes wider and its thermal stability decreases,but it still meets the processing requirements of melt blowing process in general.（3）Compared with PLA melt-blown nonwovens,PLA melt-blown nonwovens with high melt index have a large number of submicron microfibers,accounting for more than15%,and most of the microfibers are distributed at 300-400 nm.The average diameter of the microfibers is 541.6 nm,and the smallest fiber even reaches about 200 nm.However,due to the broadening of molecular weight,the differences between the fibers become greater.（4）In terms of application,PLA melt-blown nonwovens with high melt index show great application potential.In terms of oil absorption,it has a certain absorption capacity for common vegetable oil,silicone oil,and organic solvent,and can achieve rapid and selective absorption for both n-hexane floating on the water surface and silicone oil sinking on the bottom in a short time;In terms of oil-water separation,PLA melt-blown nonwovens with high melt index show excellent separation performance.For the n-hexane/water mixture,the initial separation flux is 14365 L/（m2·h）,and the flux for 11times of separation is still above 10000 L/（m2·h）,which has a certain recycling performance;In terms of filtration,the untreated single-layer high melt index PLA melt-blown nonwoven material has a geometric diameter of 0.3μm.The oily particle efficiency of m reaches 41%,and the filtration efficiency of three-layer high melt index PLA melt-blown nonwovens reaches 72.3%.（5）In terms of degradation,PLA melt-blown nonwovens with high melt index have certain hydrolysis with time in acidic,neutral,and alkaline solutions at 55±1℃,and the degradation rate is alkaline>acidic>neutral.In the alkaline solution with p H 12,the degradation rate of PLA melt-blown nonwovens with a high melt index reached about 95%within 60 hours,showing excellent degradation performance.（6）A PDA with a specific viscosity is formed by in-situ polymerization of DPA on the surface of high melt index PLA melt-blown nonwoven materials.Furthermore,Si O2is used to enhance the surface roughness of the fibers.Finally,HDTMS is used to modify the surface roughness of the enhanced PLA melt-blown nonwoven material with low surface energy,thereby obtaining a superhydrophobic PLA melt-blown nonwoven material that exhibits high separation efficiency and excellent recycling ability in oil-water separation,it has great potential in oil spill accidents and industrial wastewater discharge. |
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