Novel Biodegradable Air Filtration Material: The Combination of PLA Melt-Blown Nonwovens and Breath-Figure Technology

Academic Background

With the increasing severity of air pollution, particularly the threat of fine particulate matter (PM2.5) to human health, the demand for efficient air filtration materials is growing. Traditional air filtration materials primarily rely on petroleum-based materials such as polypropylene (PP), which are not only non-degradable but also cause long-term environmental pollution. Therefore, the development of biodegradable, efficient, and durable air filtration materials has become a research hotspot.

Polylactic acid (PLA), as a bio-based material, possesses excellent biodegradability and processability, making it an ideal alternative to petroleum-based materials. However, traditional PLA melt-blown nonwovens (Melt-Blown Nonwovens, MN) have limitations in filtration performance, especially as their filtration efficiency largely depends on electrostatic effects, which gradually diminish during long-term storage and use, leading to reduced filtration performance. To address this, researchers aim to enhance the performance of PLA-based filtration materials by introducing new technological approaches.

Source of the Paper

This paper was co-authored by Yintao Zhao, Shuai Zhang, Di Yan, Jinfa Ming, Xuefang Wang, and Xin Ning from the Industrial Research Institute of Nonwovens & Technical Textiles, College of Textile & Clothing, and Shandong Center for Engineered Nonwovens at Qingdao University, China. The paper was published on January 5, 2025, in the journal Advanced Fiber Materials.

Research Process and Experimental Design

1. Research Objective

The study aims to develop a PLA-based nonwoven (PMBP) with a hierarchical structure by combining melt-blowing technology and breath-figure (Breath-Figure, BF) technology to enhance its filtration performance, particularly maintaining high efficiency without relying on electrostatic effects.

2. Material Preparation

The research used two types of PLA materials: Revode 210 (melt flow index of 132 g/10 min at 230°C) for preparing melt-blown nonwovens and Ingeo™ 4032D (weight average molecular weight of 1.56 × 10⁵ g/mol) for constructing the breath-figure pattern. All chemicals and solvents were obtained from Sinopharm Chemical Reagent Co., Ltd., China, and used without further purification.

3. Preparation of PLA Melt-Blown Nonwovens

PLA pellets were vacuum-dried at 80°C for 24 hours to remove moisture, followed by the preparation of nonwovens using a melt-blowing machine. The melt-blowing process parameters included an extrusion speed of 22 g/min, die temperature of 230°C, hot air temperature of 240°C, hot air pressure of 0.3 MPa, and die-to-collector distance of 15 cm. The final PLA melt-blown nonwovens (MN) had a basis weight of 45 g/m².

4. Preparation of PMBP

PMBP was prepared by combining PLA melt-blown nonwovens with the breath-figure pattern. First, PLA pellets were dissolved in hexafluoroisopropanol (HFIP) to prepare PLA solutions at different concentrations (0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%). Subsequently, the PLA solution was cast onto a glass substrate, and a dynamic breath-figure process was carried out at different relative humidity levels (40%, 50%, 60%, 70%) to form a microporous structure. Finally, the wetted PLA melt-blown nonwovens were integrated with the pre-formed breath-figure pattern to complete the preparation of PMBP.

5. Characterization and Testing

The microstructure of the samples was observed using scanning electron microscopy (SEM), and fiber diameter, pore size, and cross-section thickness were measured. Solution viscosity was determined using a rotary viscometer, and water contact angle (WCA) was measured using a contact angle goniometer. Filtration performance was tested using a filter tester (AFC-131), with charge-neutralized sodium chloride aerosol particles used as PM pollutants. Pressure drop (ΔP) and filtration efficiency (E) were calculated, and the quality factor (QF) was used to comprehensively evaluate the filtration performance.

Key Research Findings

1. Filtration Performance of PLA Melt-Blown Nonwovens

The initially prepared PLA melt-blown nonwovens had larger pore sizes (average 13.2 μm), resulting in a low PM2.5 filtration efficiency (59.5%) but a small pressure drop (25.7 Pa).

2. Optimization of the Breath-Figure Pattern

Under optimized conditions (PLA concentration of 0.5 wt%, relative humidity of 50%), the breath-figure pattern formed a uniform microporous structure with an average pore size as low as 1.02 μm. The integration of large-pore PLA melt-blown nonwovens and small-pore breath-figure pattern resulted in PMBP exhibiting excellent filtration performance, with a PM2.5 filtration efficiency of 95.8% and a pressure drop of 39.3 Pa.

3. Stability of Filtration Performance

PMBP maintained stable filtration performance during long-term storage and in high-humidity environments. In actual smoke tests, PMBP removed over 99% of PM2.5 particles within 3 minutes, without relying on electrostatic effects.

4. Self-Cleaning Properties

PMBP demonstrated good self-cleaning properties, particularly maintaining efficient filtration performance in high-humidity environments.

Conclusion and Significance

This study successfully developed a PLA-based nonwoven (PMBP) with a hierarchical structure by combining melt-blowing technology and breath-figure technology, which maintained high filtration efficiency without relying on electrostatic effects. The excellent performance of PMBP is primarily attributed to its hierarchical structure, particularly the introduction of small-pore breath-figure patterns, which significantly improved filtration efficiency. Additionally, PMBP exhibited stable filtration performance during long-term storage and in high-humidity environments, along with good self-cleaning capabilities.

This research provides new insights into the development of fully bio-based, high-performance air filtration materials, with broad application prospects, especially in air pollution control and personal protection.

Research Highlights

1. Hierarchical Structure Design: By combining melt-blown nonwovens and breath-figure patterns, a multi-scale pore structure was achieved, significantly enhancing filtration efficiency.
   
2. Electrostatic-Independence: PMBP’s filtration performance does not rely on electrostatic effects, avoiding the issue of electrostatic attenuation during long-term storage.
   
3. Stability and Self-Cleaning Properties: PMBP demonstrated stable filtration performance in high-humidity environments and during long-term storage, along with good self-cleaning capabilities.
   
4. Biodegradability: The complete biodegradability of PLA materials makes this filtration material environmentally friendly, aligning with sustainable development needs.

Additional Valuable Information

This study also explored the effects of solvent selection, polymer concentration, and relative humidity on the formation of breath-figure patterns through theoretical calculations and experimental validation, providing important reference data for similar research. Additionally, the study developed a simple, low-cost, and easily scalable preparation process, offering potential for large-scale production.