1. Project Objective
The purpose of this study is to evaluate the anti-mold performance of polypropylene (PP) wastewater tanks used in floor-cleaning robots. By applying anti-mold additives to PP materials, we aim to verify their effectiveness in preventing mold and fungal growth under simulated real-life wastewater conditions.
2. Verification Methodology
Unlike antibacterial testing, there are currently no established national or international standards specifically designed for mold prevention in wastewater tanks. Therefore, a customized non-standard methodology was developed with the following steps:
- Establish a domestic floor-cleaning wastewater model.
- Adapt elements from international anti-mildew and antifungal testing standards to design a practical and reliable verification method.
3. Development of the Floor-Cleaning Wastewater Model
3.1 Definition of Floor-Cleaning Wastewater
Floor-cleaning wastewater is generated during household cleaning, such as with mops or automated floor-cleaning robots. While it does not usually contain toxic substances, it provides an ideal environment for microbial growth.
Key pollutants in such wastewater include:
- Microorganisms: especially molds and fungi.
- Organic matter: carbohydrates, proteins, and oils, which serve as nutrients for mold and bacteria.
3.2 Selection of Indicator Molds
Using references from international mold resistance standards, several indicator fungi commonly found in daily environments were selected and cultured.
| Species | Code | Colony Color | Morphology | Growth Period |
|---|---|---|---|---|
| Aspergillus niger | ATCC6275 | Black-brown | Dense velvet | ≥ 3 days |
| Chaetomium globosum | ATCC6205 | Black | Hair-like dense | ≥ 3 days |
| Penicillium funiculosum | ATCC9644 | White | Flocculent | ≥ 3 days |
| Paecilomyces variotii | ATCC628.66 | Yellow-brown | Cottony | ≥ 3 days |
| Trichoderma viride | ATCC13631 | White/Green | Ring-shaped | ≥ 3 days |
From these, three molds were selected due to ease of growth, strong visibility through PP walls, and practical relevance:
- Aspergillus niger
- Chaetomium globosum
- Penicillium funiculosum
3.3 Preparation of Mold-Contaminated Wastewater
To simulate realistic conditions, the wastewater mixture contained:
- Spore suspension of indicator fungi (5×10⁶ spores/mL)
- Nutrient salts and minerals
- Nutrient agar providing proteins and carbohydrates
- Pure water
This composition provided both the nutrients required for mold proliferation and the representativeness of household wastewater.
4. Mold Growth Validation in PP Samples
4.1 Single-Fungus Trials
PP sheet samples (5×5 cm) were inoculated with individual fungi and incubated at 24 ± 1 °C with ≥85% humidity for up to two weeks. Colonies of Aspergillus niger, Chaetomium globosumdan Penicillium funiculosum were clearly visible even through PP walls, confirming their suitability as test fungi.
4.2 Mixed-Fungus Wastewater Model
A composite wastewater inoculated with the three fungi was tested. The model successfully produced distinct mold growth visible through PP tank walls, validating its use as an effective contamination model for anti-mold evaluation.
5. Anti-Mold Verification of PP Wastewater Tanks
5.1 Experimental Setup
Three groups of PP wastewater tanks (with lids) were tested:
| Group | Description |
|---|---|
| Control | Untreated PP wastewater tank |
| Sample 1 | PP tank with 0.2% anti-mold additive |
| Sample 2 | PP tank with 0.6% anti-mold additive |
Each tank was sterilized, inoculated with the mixed-fungus spore suspension, and incubated at 24 ± 1 °C with ≥85% humidity for two weeks. Mold growth was then visually evaluated.
6. Conclusion: Next-Generation Mold Prevention for Plastics
This preliminary study demonstrates that:
- A reliable floor-cleaning wastewater mold model was successfully developed using three representative fungi.
- Untreated PP wastewater tanks showed visible mold growth, confirming the high risk of contamination in real-world use.
- Tanks containing anti-mold additives (antifungal masterbatch formulations) exhibited improved resistance, with 0.6% loading showing stronger mold prevention than 0.2%.
7. Industry Relevance
The findings are highly relevant for industries producing plastic wastewater tanks, robot vacuum cleaner components, and antifungal solutions for household appliances.
By applying anti-mold additives, antifungal agents, and plastic anti-fungus masterbatches, manufacturers can significantly enhance hygiene, extend product lifespan, and reduce microbial contamination.
This research also lays the foundation for future standardized anti-mildew testing protocols in plastics, particularly in PP, PVC, and EVA-based components used in smart appliances.
