Polylactic acid (PLA) is a new type of bio-based and biodegradable polymer material that is currently the most widely studied and applied. Its raw materials are made from starch raw materials proposed by renewable plant resources (such as corn). Good biodegradability and biocompatibility, it is recognized as an environmentally friendly material. The research, processing and application of PLA in meltblown nonwovens have gradually attracted the attention of researchers and the industry. Under the situation of rapid expansion, domestic enterprises have accelerated their development in pursuit of transformation.
There are still many limitations in the application of a single PLA material. Because of its own shortcomings such as toughness and poor heat resistance, domestic and foreign scholars have adopted many methods to improve the performance of PLA raw materials and products. Based on this, this paper summarizes and introduces the latest progress in the research and application of PLA-based meltblown nonwovens in processing and forming, raw material design and modification, and finishing modification, and forecasts its research and development direction and prospects.
1. Processing and forming of PLA-based meltblown materials
The processing of PLA-based melt-blown nonwoven materials is to dry the PLA-based masterbatch, heat and melt the screw (extrusion temperature 210~240 ° C), transport, filter, and measure from the spinneret of the melt-blown die head (pore size 0.15~240°C). 0.3mm) quantitative extrusion, and then subjected to the high temperature (230~280℃) and high speed (200~400m/s) airflow drafting measured by the die head, and then directly cooled in the open field of room temperature or heated in the limited field After further drafting, the meltblown fibers are self-bonded and entangled to the receiving device to form a web, and finally the non-woven material is obtained by winding. A typical PLA-based meltblown nonwoven production process is shown in Figure 1.
Fig.1 Schematic diagram of forming of PLA-based meltblown fibers and nonwovens
Meltblown process research shows that extrusion speed and temperature, hot air temperature and pressure (speed), slit distance, receiving distance, screen curtain winding rate, negative pressure suction strength, etc. Density, linear density, thickness, breathability and filtration properties have a significant effect. In addition to the conventional melt-blown open field to prepare PLA-based melt-blown materials, electrostatic, thermal, ultrasonic-thermal, thermal-magnetic coupling, and external field cooling aids have also emerged and applied to the processing of PLA-based melt-blown materials. The purpose of multi-level coupling and auxiliary melt-blown flow field is to achieve further refinement and random orientation of PLA-based melt-blown fibers by promoting drafting, random response, etc., so as to obtain higher filtration efficiency, softer, and better mechanical properties. Homogeneous PLA based meltblown material.
2. Design and modification of PLA-based meltblown raw materials
The processing of PLA-based meltblown nonwovens requires higher physical properties of raw materials, including thermal stability, relative molecular mass and distribution, melting point, viscosity/melt flow rate, viscoelasticity and ash content. Polymer feedstocks for meltblown tend to require relatively high melt index (MI). It is different from melt-blown PP. At present, the commercially available and mature melt-blown PLA grades include IngeoTM6 series grades from NatureWorks. Most of the research and application of PLA meltblown materials carried out in the past years are based on this raw material, and the localization of PLA meltblown raw materials is particularly important.
3. Modification of PLA-based meltblown materials
Due to the inherent defects of PLA itself, such as insufficient toughness and poor heat resistance, there are still many limitations in the application of a single PLA meltblown material. In addition, based on the differentiated needs of the application field, the modification of PLA meltblown materials is imperative. The modification of PLA-based meltblown materials mainly includes in-situ modification of masterbatch (block, copolymerization, blending, etc.) and post-finishing (impregnation, plasma, magnetron sputtering, etc.). Among them, PLA melt-blown masterbatch melt blending modification (grafting, strengthening and toughening, functional modification) is relatively efficient in production, economical, less polluting, and easy to industrialize; post-finishing modification of PLA melt-blown material (electrostatic electret) , antibacterial, hydrophilic, catalytic adsorption) is easier to exert the functional characteristics of the loaded material itself, and the function is more efficient.
4. Application of PLA-based meltblown materials
Meltblown non-woven materials have the characteristics of fine fibers, large specific surface area, high porosity, and small pores, which are easy to play the filtering characteristics of high efficiency, low resistance and energy saving, and can effectively block harmful substances such as dust and bacteria; at the same time, Soft and skin-friendly, natural antibacterial, and high comfort. Based on the above characteristics, PLA-based meltblown nonwovens can be widely used in air filtration, medical protection, health care, cleaning and wiping, sound insulation and sound absorption, agriculture and other fields.
