Polylactic acid (PLA) is currently the most widely studied and applied a new type of polymer material that is both bio-based and biodegradable. Its raw materials are made of starch raw materials proposed by renewable plant resources (such as corn). It is recognized as an environmentally friendly material with good biodegradability and biocompatibility. The research, processing, and application of PLA in melt-blown non-wovens have gradually attracted the attention of researchers and the industry.
There are still many limitations in the application of a single PLA material. Because of its shortcomings, such as toughness and poor heat resistance, scholars at home and abroad have used many methods to improve the performance of PLA raw materials and products.
1. Processing and forming of PLA-based melt-blown materials
The processing of PLA-based melt-blown non-woven materials is to dry the PLA-based masterbatch, heat and melt the screw (extrusion temperature 210~240°C), transport, filter, and measure it from the spinneret hole of the melt-blown die head (aperture 0.15~ 0.3mm) quantitative extrusion. Then after being drawn by the high temperature (230~280℃) and high speed (200~400m/s) airflow measured by the die head, it is directly cooled in an open field at room temperature or in a limited heating field. Further drawing, self-adhesion, and entanglement of the melt-blown fibers to the receiving device to form a web, and winding to obtain a non-woven material.
2. Design and modification of PLA-based melt-blown raw materials
The processing of PLA-based melt-blown non-wovens has high requirements on the physical properties of raw materials, mainly including thermal stability, relative molecular mass and distribution, melting point, viscosity/melt flow rate, viscoelasticity, and ash content. Polymer feedstocks for melt-blowing often require a relatively high melt index (MI). Different from melt-blown PP, the currently commercially available and mature melt-blown PLA grades include NatureWorks' IngeoTM6 series grades, whose MI is only about 80 g/(10 min) (temperature 190 ℃), nearly ten at home and abroad. Most of the research and application of PLA melt-blown materials carried out in the past few years are based on this raw material. The localization of PLA melt-blown raw materials is essential.
3. Modification of PLA-based melt-blown materials
Due to the inherent defects of PLA itself, such as insufficient toughness and poor heat resistance, many limitations exist in applying a single PLA melt-blown material. In addition, based on the differentiated requirements of the application field, the modification of PLA melt-blown materials is imperative. The change of PLA-based melt-blown materials mainly includes two methods: in-situ edit of masterbatch (block, copolymerization, blending, etc.) and finishing (impregnation, plasma, magnetron sputtering, etc.). Among them, the melt blending modification (grafting, strengthening, and toughening, functional modification) of PLA melt-blown masterbatch is relatively efficient in production, economical, less polluting, and easy to industrialize; the post-finishing modification of PLA melt-blown materials (electrostatic electret, antibacterial, hydrophilic, catalytic adsorption) are easier to exert the functional characteristics of the material itself, and the function is more efficient.
4. Application of PLA-based melt-blown materials
Melt-blown non-woven materials have the characteristics of fine fibers, large specific surface area, high porosity, and tiny pores. They are easy to exert high-efficiency, low-resistance, and energy-saving filtration characteristics and can effectively block harmful substances such as dust and bacteria; at the same time, Soft and skin-friendly, natural antibacterial, and highly comfortable. Based on the above characteristics, PLA-based melt-blown non-woven materials can be widely used in air filtration, medical protection, health care, cleaning and wiping, sound insulation and sound absorption, agriculture, and other fields.
5. Prospects for research directions
While PLA-based melt-blown non-wovens show advantages and characteristics in many of the above fields, problems such as flexibility, heat resistance, and durable electret must also be solved urgently. At the same time, multi-functional and high-added value improvements are also more critical. It is beneficial to broaden the application field of PLA-based melt-blown materials. In general, with the further development of textile technology and the cross-derivation of multiple disciplines, this study believes that PLA-based melt-blown non-wovens have the advantages of submicron and nanofiber fiber, multi-component, material and process compounding, and durable electret polarization. Function and intellectualization have excellent research and development prospects.
